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Accounting for nitrogen in Denmark—a structural decomposition analysis
Ecological Economics 30 (1999) 317 – 331 www.elsevier.com/locate/ecolecon
ANALYSIS
Accounting for nitrogen in Denmark—a structural decomposition analysis Mette Wier a,*, Berit Hasler b b
a AKF, Danish Institute of Local Go6ernment Studies, DK-L602 Copenhagen, Denmark National En6ironmental Research Institute, Department of Policy Analysis, P.O. Box 358, DK-4000 Roskilde, Denmark
Received 18 March 1998; received in revised form 20 August 1998; accepted 6 January 1999
Abstract This paper examines the environmental-economic cycle for nitrogen in Denmark based on nitrogen input and output from different economic sectors. An input-output model is employed together with a nitrogen mass balance to apportion total nitrogen loading by final demand and estimate export and import of nitrogen from foreign trade. The changes in agricultural and industrial nitrogen loading from the mid 1960s to the late 1980s are broken down into changes related to different technological and economic factors. The analysis reveals that technological change (intensified agricultural production) and economic growth (especially rising exports) are the key factors, structural shifts (changes in commodity mix in the household and production sectors) generally being of less importance. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Marine nitrogen loading; Nitrogen mass balance; Decomposition analysis; Input-output modelling
1. Introduction Nitrogen loading of the Danish aquatic environment has increased in recent decades, giving rise to serious problems with eutrophication of inland and marine waters throughout the 1980s. In the Øresund, the Kattegat and the Belt Seas, increases in the winter concentration of nitrogen were observed from the mid 1970s to the mid * Corresponding author. Tel.: +45-33-11-03-00; fax +4533-15-28-75. E-mail address: [email protected] (M. Wier)
1980s, in many cases leading to oxygen deficit1 (Danish Environmental Protection Agency, 1984; Christensen et al., 1994). In 1984, the Danish Environmental Protection Agency reported an oxygen deficiency in areas where it had not previously been detected, including in the North Sea 1 In Denmark, the term ‘oxygen deficit’ is used when the water oxygen concentration falls below 4 mg/l. If the concentration falls below 2 mg/l, the term ‘severe oxygen deficit’ is used. Many fish species flee from areas affected by oxygen deficiencies. In the case of a prolonged severe oxygen deficit, benthic invertebrates that are unable to flee eventually die.
0921-8009/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 8 0 0 9 ( 9 9 ) 0 0 0 0 4 - X
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and other open marine waters (Danish Environmental Protection Agency, 1984). The frequency of the recorded episodes of oxygen deficit was also found to have increased. Both the extent and frequency of oxygen deficit have increased even more during the late 1980s, this being attributable to the increase in nitrogen loading of the aquatic environment (National Environmental Research Institute, 1990–1997). The increase in nitrogen loading is attributable to increased production in the agricultural sector and growth in the amount of sewage effluent. The latter is the result of enhanced population growth and increased industrial production. The major part of the increase is attributable to increased agricultural production resulting from general intensification of production and to a lesser extent to the incorporation of marginal land in production (Christensen et al., 1994). The negative environmental consequences of enhanced nutrient loading of the Danish aquatic environment led Parliament to adopt the Action Plan on the Aquatic environment in 1987 (Dubgaard, 1990; Rude and Frederiksen, 1994). Among other things, this stipulated that nitrogen discharge from agricultural sources was to be reduced by 50% while discharges from other sources (industry, sewage works) were to be reduced by 60%. The present article quantifies the change in marine nitrogen loading due to intensification of agricultural production, general economic growth and general structural shifts in the economy over two decades from 1965 to 1989. The purpose of this paper is to analyse the background for the serious situation at the end of the 1980s and place it in a historic perspective with a view to identifying the main shifts in the agricultural sector and economy that have been responsible for this change in loading. The intention is to identify the factors responsible for the development and quantify their respective contributions. The analysis follows a top-down approach, focusing on the main tendencies on both the environmental and economy sides. The analysis is made at the national level because the political goals are set at this level. Nitrogen loading is generally too high in the majority of the inner Danish marine waters and the adjoining marine waters2 (Christensen et al., 1994), and the
political goal of halving nitrogen loss applies uniformly to the whole country. An analysis at the national level is therefore meaningful. The analysis was carried out by combining an input-output model with a nitrogen budget for agriculture and emission factors for sewage effluent. This comprehensive integrated model system enables behavioural and technological shifts in the household and production sectors to be related to changes in nitrogen loading, thereby revealing the economic reasons for the development. This study distinguishes itself by relating nitrogen loading to the whole economy, i.e. to production as well as consumption activities, and by applying input-output structural decomposition analysis on a new area. Furthermore, it covers a very long period, analysing input-output tables from 1966 to 1988, whereby it is possible to examine changes during three separate decades. A final distinguishing feature is that the study includes an assessment of the importance to nitrogen loading of foreign trade.
2. Model and data The model consists of two parts, an economic input-output model and a nitrogen sub-model. The latter describes nitrogen loading from the different economic sectors, while the former describes intersectoral commodity flows within whole economy. The nitrogen flows from the nitrogen sub-model are linked to the input-output model by estimating emission coefficients, i.e. nitrogen discharges per unit of production per year from all sectors in the economy.
2.1. The input-output model The model framework is the extended inputoutput system, as introduced by Leontief and Ford (1972). The strength of the model is that it 2 While nitrogen is the primary factor causing eutrophication of marine waters, phosphorus is the main cause of eutrophication in inland waters. Consequently, only marine nitrogen loading will be considered in this paper.
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covers all sectors of the economy, operates on a very disaggregated level, and handles both direct and indirect use of goods. Structural decomposition analysis has been widely applied to changes in output, use of primary factors, etc. (Fujimagari (1989), Forssell (1989), Skolka (1989)). With regard to environmental performance, energy consumption has been decomposed in Denmark by Pløger (1984), in the USA by Rose and Chen (1991), Boyd et al. (1987), in Taiwan by Chen and Rose (1990), Li et al. (1990), in Singapore by Liu et al. (1992), and in five OECD countries by Howarth et al. (1993). In addition, Lin and Polenske (1995) have decomposed energy-demand changes in China, while Lin (1996) has examined the technological and energy-demand implications. With regard to decompositional analysis of emissions, CO2 emissions have been decomposed in Australia by Common and Salma (1992), in nine OECD countries by Halvorsen et al. (1991) in Taiwan by Chang and Lin (1997), in China, Taiwan and South Korea by Ang and Pandiyan (1997), in nine OECD countries by Torvanger (1991) and in Denmark by Wier (1998). The latter author also decomposed Danish SO2 and NOx emissions. This paper further expands the environmental use of decomposition analysis to nitrogen loading, presenting a decomposition of the changes in nitrogen loading in Denmark over the period 1966 –1988. The analytical framework is the static activity x activity input-output model with endogenous import. At a given point in time, nitrogen loading is given by, 1 Nt = wt (I−A − t )Dtdt,
(1)
where Nt, is a scalar3 of total nitrogen loading, wt, is a 1× 117 vector of nitrogen discharges from all sectors (i.e. the output of the nitrogen sub-model) per unit of production (i.e. wt, is a vector of emission factors), (I − A)t− 7 is the 117 × 117 Leon-
tief inverse matrix, Dt is a 117×9 matrix for the composition of final demand (final demand apportioned by economic activity) and dt, is a 9× 1 vector for the absolute level of final demand for all categories. The nine final demand categories are private consumption, public consumption, exports, stock building, agricultural breeding stock building, imputed bank service charges and investments (gross fixed capital formation) in machinery, in transport equipment and in construction. The structural decomposition analysis is employed to clarify how the different factors in Eq. (1) have affected nitrogen loading. Total change in loading is decomposed into the effects due to the four components; loading per unit produced (emission factor effect), input mix in production sectors, commodity mix of final demand and level of final demand. The analysis was performed by changing the components one by one in order to quantify the contribution of each effect to the total change in loading. This contribution may be weighted using either the base year values for the other three components or by the current year values. The interaction effect is quite large, and will therefore cause considerable bias. The effect of a change in each component has therefore been determined using an average of the two approaches, as proposed by Fujimagari (1989) and Sawyer (1992). The change in emissions from sectors given by Eq. (1) from time t−1 until time t is Nt − Nt − 1 = Dw +D(I −A) − 1 + DD + Dd where the emission factor effect is Dw = ([(wt − wt − 1)(I − A)t−−11Dt − 1dt − 1] + [(wt − wt − 1)(I− A)t− 1Dtdt ])/2 The input mix effect is D(I−A)−1=([wt (I−A)t− 1 − (I− A)t−−11) Dt − 1dt − 1] + [wt − 1((I − A)t− 1(I−A)t− 1)Dtdt ])/2 the composition of final demand effect is
3
Applying element-wise multiplication to the total loading rather than matrix multiplication yields an activity x final demand matrix. This has been done to provide full information on changes in all sectors and demands, and will be referred to, but not presented in this paper.
319
DD= ([wt (I−A)t− 1(Dt − Dt − 1)dt − 1] + [wt − 1(I−A)t−−11(Dt − Dt − 1)dt ])/2 and the level of final demand effect is
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Dd = ([wt (I−A)t− 1Dt (dt −dt − 1)] +[wt − 1(I−A)
−1 t−1
Dt − 1(dt −dt − 1)])/2
The economic data used for the study are the Danish input-output tables (Statistics Denmark) from 1966 to 1988 expressed in constant (1980) prices. The tables encompass 117 sectors and nine categories of final demand. Data on nitrogen inputs and outputs are from the Ministry of Agriculture, Statistics Denmark, the Ministry of Environment and Energy, and the Danish Environmental Protection Agency. The data used in the nitrogen budget is documented in Section 2.2.2.
2.2. The nitrogen sub-model 2.2.1. The nitrogen budget at the close of the 1980s The nitrogen budget for Denmark in the late 1980s is summarized in Fig. 1. The main tendencies are described here. This is the first time such a detailed national scale budget has been drawn up. The greatest uncertainty is related to the agricultural data, the loading data for sewage and atmospheric deposition being quite robust. The flows should be interpreted as an average for the period 1986–1989. In reality, large climate-dependent variation will occur every year. The sectors of the economy mainly responsible for nitrogen loading are agriculture, industry and households, with the former accounting for the major part. Nitrogen balances for the agricultural sector can be calculated as farm-gate balances or soil-surface balances4 (Schleef and Kleinhanss, 1997). The soil-surface approach was selected for 4 With a farm-gate balance, the interface for the balance is the farm as a whole, all nitrogen inputs to the farm being calculated, i.e. fodder, livestock and commercial fertilizer, as well as nitrogen fixed from the atmosphere, atmospheric deposition of nitrogen and nitrogen applied in sewage sludge. The outputs are calculated as the nitrogen in all sold products (crops as well as animals) and the loss to the environment. When using the farm-gate approach, the internal nitrogen streams in the farm are not explicitly calculated, i.e. the nitrogen in animal fertilizer and fodder crops. With the soilsurface approach, in contrast, the interface in the balance is the soil surface. In this case, the nitrogen inputs are commercial fertilizer and animal fertilizer, as well as nitrogen fixed
the estimations in the present study because this is the most appropriate balance when calculating the losses relating to nitrate leaching to the aquatic environment. As is apparent from Fig. 1, the main nitrogen inputs are animal and commercial fertilizers. Other sources of nitrogen include nitrogen fixation, sewage sludge and atmospheric deposition. Approximately one-third of the deposition takes place as NOx (nitrogen oxides) and two-thirds as NHx (ammonia and ammonium). The major sources of the NOx are the transport sector and power plants, while the NHx is mainly derived from volatilization from agriculture. (Asman, 1990; Asman and Runge, 1991). According to the estimated nitrogen budget (see Section 2.3.2), 46% of the nitrogen input to the fields is removed with harvested crops. This uptake is in good agreement with other studies of Danish agriculture based on the soil-surface approach, where estimates of uptake range from 41–44% (Nielsen, 1990) to 45% (Ministry of Agriculture, 1991) to 48% (Schleef and Kleinhanss, 1997). Using the farm-gate approach, Andersen (1996) estimated a utilization rate of 49% (nitrogen removed in the sold products expressed as a percentage of nitrogen input). Nitrogen balances have also been determined for the EU member states (EU 12) by Brouwer et al. (1995) using the farm-gate approach. From that study it can be estimated that 49% of the nitrogen input was removed in the sold products in Denmark in 1990/1991. The estimated utilization rate for the Netherlands was 31%, the difference between the rates in the two countries mainly being explicable by differences in livestock production and density. The average utilization rate for the EU member states was 50%. The nitrogen utilization rate in Danish agricultural production is therefore average in a European context, and the estimated value for Danish agriculture reported by Brouwer et al. is in good agreement with the utilization rate estimated in the present study. from the atmosphere, atmospheric deposition of nitrogen and nitrogen applied in sewage sludge. The outputs are calculated as harvested crops for both internal and external use, and loss to the environment.
M. Wier, B. Hasler / Ecological Economics 30 (1999) 317–331 Fig. 1. Nitrogen budget for Denmark, late 1980s (metric tonnes N). * It is assumed that nitrogen in animal fertiliser is equal to nitrogen in fodder consumed less the nitrogen in livestock products. ** Includes a background load (i.e. loading that cannot be attributed to a specific source) of 23 000 tonnes N. Approximately 175 000 tonnes are retained in inland waters. Sources: Asman (1990), Asman and Runge (1991), Runge et al. (1991), Ministry of Agriculture (1991), Danish Environmental Protection Agency (1991a,b, 1992a,b), Nielsen (1990).
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As is apparent from Fig. 1, losses to the atmosphere take place through denitrification in soil water and water bodies, soil erosion and ammonia volatilization from livestock housing and the storage and spreading of animal fertilizer. Loss to the aquatic environment takes place as leaching from the root zone, whereafter the nitrogen is transported to lakes and watercourses and further on to the sea. As shown in Fig. 1, this amounted to 250 000 tonnes in the late 1980s. However, much of the nitrogen is retained during transport and, on average, only 75 000 tonnes of the nitrogen leaching from rural land actually reaches the sea annually, 70%, of the total being retained in inland waters (Danish Environmental Protection Agency, 1991a). Total input to the sea amounts to 110 000 tonnes (Danish Environmental Protection Agency, 1991a), including loading from agriculture, industry, household sewage, deposition to inland waters, etc. Atmospheric deposition and inflow from foreign seas are sizeable, while direct nitrogen loading of marine waters by sewage effluent is minor. For inland water bodies, however, sewage effluent from households, industry and fish farming may constitute an important source of nitrogen input.
2.2.2. Historical de6elopment in the agricultural nitrogen budget In this section, leaching from the root zone of agricultural land every fifth year from the mid 1960s until the present is estimated according to the nitrogen mass balance principle as the residual of estimates of all nitrogen inputs and outputs. These estimated levels of leaching are not the actual leaching in the different years, but an approximation of the expected leaching level given the actual harvest size, atmospheric deposition, input of animal and commercial fertilizers, etc., and assuming that climatic conditions in the entire period from 1960 – 1989 were the same as the average conditions during the late 1980s. The elements of the nitrogen budget are shown in Table 1 below, inputs being listed in the upper half and outputs in the lower half. Note that the balance is based on the soil-surface approach. A considerable number of statistics were needed to calculate the figures, and some assumptions
have been made in order to estimate the development in input and output flows. Biological fixation at the end of the 1980s is estimated at 30 000 tonnes N/year (Ministry of Agriculture, 1991). The amount of nitrogen fixed depends on crop composition, in particular the area planted with pulses and clover grass, and is calculated on the basis of a constant fixation coefficient per hectare for each crop type multiplied by the total area of pulses and clover grass. The fixation coefficient is estimated on the basis of data from the end of the 1980s (Ministry of Agriculture, 1991). In other words, it is assumed that fixation by each crop type is constant per hectare over time, which implies that the percentage of clover in grass fields is also assumed to be constant. It is difficult to determine whether the percentage of clover in grass has changed during the early part of the study period, however. Thus based on the findings of Kyllingsbæk (1995), the percentage of clover in grass is assumed to have remained constant during the period 1965–1980. In the period from 1980 to the end of the 1980s, the clover content increased (Kyllingsbæk, 1995), but insufficient data is available to enable the increase to be quantified. Kyllingsbæk’s findings indicate that nitrogen fixation in the 1980s is underestimated in our study. The figure for nitrogen input in sewage sludge is derived from Kyllingsbæk (1995), who calculates this to be 3 million kg N/year in 1970, increasing to 5 million kg N/year in 1989. Based on these figures, we assume a constant input of 3 million kg N/year from the mid 1960s to the beginning of the 1980s, 4 million kg N/year in the mid 1980s, and 5 million kg N/year at the end of the 1980s. The estimates are subject to a considerable degree of uncertainty, albeit that this is of little importance for the budget as a whole due to the small magnitude of these inputs. Input from commercial fertilizers was taken directly from the agriculture statistics (Statistics Denmark, various years). Nitrogen input from animal fertilizers has been estimated to be 292 000 tonnes N/year in 1985/1986 (Laursen, 1989), 330– 340 000 tonnes N/year in the late 1980s (Sibbesen, 1990), 330 000 tonnes N/year in the late 1980s (Ministry of Agriculture, 1991), and 337 000 ton-
Input flows
Biological fixation
1965/1966 1970/1971 1975/1976 1980/1981 1985/1986 1988/1989
36 34 31 28 30 30
Output flows
Volatilization from comm. Fertilizers
1965/1966 1970/1971 1975/1976 1980/1981 1985/1986 1988/1989
13 19 21 24 24 25
a
Sewage sludge
NHx-deposition
Commercial fertilizers
Animal fertilizer
30 34 34 38 39 39
206 290 330 375 380 390
270 285 285 315 320 320
Volatization from Removed with harvested manure crops
Dentrification
Leaching from the root zone
84 80 90 98 100 100
40 50 50 60 60 60
70 160 175 220 240 250
3 3 3 3 4 5
NOx-deposition 13 14 15 20 22 20
350 345 365 380 375 370
M. Wier, B. Hasler / Ecological Economics 30 (1999) 317–331
Table 1 Nitrogen budget for Danish agriculture (1000 metric tonnes N/year)a
Sources: See Fig. 1.
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nes N/year in 1987/1988 (Nielsen, 1990). As a compromise, input from this source is assumed to be 320 000 tonnes N/year in the present study. For the period 1965 – 1985, production of nitrogen in animal fertilizer was determined from the trend in consumption of animal fertilizer as estimated in Jensen and Reenberg (1986). It should be mentioned that these estimates are subject to some degree of uncertainty. To validate the results, we have also calculated the input of nitrogen in animal fertilizer based on the composition of the livestock and the current norms for the nitrogen content of manure per animal (Laursen, 1987), which are available for 1975 onwards. The findings with this method only deviate slightly (1 – 7%) from the estimates of Laursen (1987) except for 1965/1966, where the norm-based method yields an estimate that differs from ours by 14%. However, the use of the norm-based estimation method in 1965/1966 poses considerable problems. The protein content of the fodder is of decisive importance for the nitrogen content of the animal fertilizer. Since the protein content increased from the 1960s to the 1970s, figures for the nitrogen content of animal fertilizer in 1965/ 1966 based on 1975 norms will be overestimated. We have therefore chosen not to correct our estimates. It can be concluded, though, that the uncertainty in the estimates of the nitrogen content of animal fertilizer is greatest in the first part of the period studied. Atmospheric deposition of NOx and NHx in the late 1980s was estimated from emission data for agriculture, transport and power stations using the TREND model for atmospheric transport and deposition (Asman and Runge, 1991; Asman and van Jaarsveld, 1992). Atmospheric deposition of NOx back through time was estimated on the basis of information on NOx emissions (CORINAIR database, National Environmental Research Institute), deposition being assumed to be proportional to emissions. While this approach does not take into account regional shifts in the geographic location of emission sources at home and abroad, only a small part of NOx emissions are deposited locally (Asman and Runge, 1991) and this weakness is therefore of minor significance.
Atmospheric deposition of ammonia and ammonium back through time was estimated by assuming that these were proportional to the N content of animal manure and the N content of commercial fertilizer. The data used was from the end of the 1980s (Asman and Runge, 1991; Statistics Denmark (various years); Danish Environmental Protection Agency, 1991a). Denitrification was estimated as a constant fraction of total fertilizer consumption (8%). Ammonia volatilization was estimated as constant fractions of animal and commercial fertilizer consumption (31 and 6%, respectively). The estimates are based on information from the end of the 1980s (Ministry of Agriculture, 1991; Danish Environmental Protection Agency, 1991a; Asman and Runge, 1991). Note that changes in the handling of animal fertilizer are not taken into account. Depending on storage conditions and the time and method of application, between 3 and 40% of the nitrogen in animal fertilizer volatilizes in the form of ammonia (Danish Agricultural Advisory Centre, various years). Until the end of the 1980s, there was no decisive change in the utilization of animal fertilizer, and this problem is therefore of limited significance. It should be mentioned, though, that there has been a general shift from solid to liquid manure which has not been taken into account. As a consequence, ammonia volatilization at the beginning of the study period has probably been overestimated to some extent. Nitrogen removal in crops was assumed to be constant over time per kilogram of different crops. Information on nitrogen uptake by the various crops derives from Danish Agricultural Advisory Centre (various years), while the information on harvested crops derives from Statistics Denmark (various years). The uptake coefficients are from 1970, and are assumed to apply to the whole study period. An uncertainty factor in the calculation of nitrogen removal is that there has been a general increase in nitrogen uptake per kilogram crop (Kyllingsbæk, 1995). There is insufficient data to quantify this increase, however. Therefore, it can be assumed that our figures for nitrogen removal in the crops are underestimated in 1980 since the
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Fig. 2. Marine nitrogen loading from industry and agriculture apportioned by demand (1988; metric tonnes N).
uptake coefficients used are from 1970. It should be mentioned, though, that our estimates are in full agreement with those of the Ministry of Agriculture (1991). It should also be noted that nitrogen removal has not increased much during the study period (6%), which is in poor agreement with the far greater simultaneous increase in crop yield. This is attributable to changes in crop composition, primarily due to the decrease in areas planted with clover grass since the latter takes up three times as much nitrogen per hectare as cereals. Thus, clover grass fields accounted for 29% of the total area of arable land in 1965 but only 7.5% in 1988. Finally, leaching was calculated as the residual (rounded up). As such, leaching also included the non-quantifiable loss in connection with silage and changes in the soil nitrogen pool. As there is a considerable time lag in the transport of nitrogen in soil and water bodies due to chemical and biological processes, 70% of the nitrogen leaching from the root zone was assumed to be retained in inland waters, with only 30% eventually reaching the sea (Danish Environmental Protection Agency, 1991a). As is apparent from Table 1, leaching from the root zone has increased considerably since the mid 1960s especially in the first half of the period. This is due to the increase in nitrogen input from animal and commercial fertilizers, together with almost unchanged nitrogen removal in crops. The nitrogen input surplus has more than tripled during the period.
2.2.3. Nitrogen loading from sewage effluents The sewage part of the nitrogen sub-model is quite simple, concerning only loading from industrial sectors. Nitrogen loading from sewage works is measured in a nationwide monitoring programme, which was initiated in 1988 as part of the Action Plan on the Aquatic Environment. The estimates back through time were made by correcting 1988/1989 discharges with data on the development in sewage treatment technology (Tonni Christensen, Danish EPA, personal communication).
3. Nitrogen loading and the economy—results and discussion
3.1. Allocation of final demand As already stated, agriculture is the main sector contributing to nitrogen loading. With regard to sewage effluent inputs to inland and marine waters, the sectors which pollute most include the food industry (abattoirs in particular), the chemicals industry, fish farming and fish processing. Production activities reflect the composition of the final demand, changing with changes in export, consumption and investments. In Fig. 2, total nitrogen loading of marine waters in 1988 is shown apportioned by final demand, i.e. the direct and indirect loading due to each demand category. Total nitrogen loading of the sea by agriculture and industry amounted to 87 000 tonnes in the late 1980s, of which the industry accounted for 13%.
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Table 2 Decomposition analysis of changes in marine nitrogen loading from agriculture (1000 metric tonnes N)a Technology
Final demand
Total
Emission factor
Input mix
Composition
Level
1966–1976 1976–1986 1986–1988
30 520 3330 830
60 −7130 −1480
−13 940 2410 −2840
14 360 20 400 6490
31 000 19 000 3000
1966–1988
40 690
−6740
−14 920
33 970
53 000
a
Source: The authors.
As is apparent from Fig. 2, export and private consumption are by far the most important categories of final demand with regard to nitrogen loading. Thus, export is responsible for 65% of the agricultural loading and 74% of the industrial loading, while the corresponding figures for private consumption are 32 and 17%, respectively. In contrast, public consumption and investments demand commodities from less polluting production sectors, accounting for only 3 – 4% of nitrogen loading.
3.2. Decomposition analysis The calculations indicate that since the mid 1960s, nitrogen loading from the economy has undergone major change. According to the estimated nitrogen budget (Table 1) and the input – output calculations, nitrogen leaching from agriculture has risen by 240%, while loading from sewage effluent has fallen by 16%. Production technology, abatement technology, shifts in commodity mix in the production and household sectors and economic growth are all of importance for this development. In the following, structural decomposition analysis is employed to clarify how these different factors have affected nitrogen loading. Total change in loading is decomposed into the effects due to the four components; loading per unit produced (emission factor effect), input mix in production sectors, commodity mix of final demand and level of final demand.
The emission factor effect incorporates technical, chemical and legislative factors. For agriculture, the effect depends on production behaviour and other factors influencing nitrogen input to agricultural land. For industry, the emission factor effect depends on production technology and legislation on sewage treatment. The results of the decomposition analysis are presented in Tables 2 and 3 grouped in intervals of 10 years except from the third period, which is shorter because the data only runs to 1988. Please note that the total change cannot be derived by simple addition of the changes during the three intervals studied as all changes in a component are multiplied with the values which the other components initially have in the period (i.e. at time t−1). Nitrogen loading from agriculture increased by 53 million tonnes from 1966 to 1988, due to increased nitrogen loading per unit of production and increased level of final demand (i.e. export, consumption and investment). Intensified nitrogen loading per unit of agricultural production was the most important factor in the first decade, whereafter growth in the level of final demand led to increased loading. More detailed decomposition shows that it is export in particular that has grown markedly. As is apparent from the agricultural nitrogen budget (Table 1), fertilizer inputs have been increasing without a corresponding increase in nitrogen removal with harvested crops. This trend is attributable to the enhanced input of commercial fertilizer and the resulting poorer utilization
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Table 3 Decomposition analysis of changes in marine nitrogen loading from sewage (1000 metric tonnes N)a Technology
Final demand
Total
Emission factor
Input mix
Composition
1966–1976 1976–1986 1986–1988
−11 370 −10 500 −1890
460 420 −20
2750 1980 −1210
7260 6420 1870
−900 −1680 −1250
1966–1988
−27 150
880
6290
17 170
−2810
a
Level
Source: The authors.
of animal fertilizer (Dubgaard, 1994; Hasler, 1998)5. The tendency is especially clear up to 1980, whereafter fertilizer inputs stagnated. This is supported by the fact that the input – output analysis (Table 2) shows that it is the first half of the period in particular that is characterized by increasing nitrogen intensity; in contrast, the second half of the period is characterized by an increase in the demand for agricultural products, and hence increased nitrogen loading. Thus, nitrogen loss during this second half of the study period cannot be chiefly explained by increased nitrogen input per unit of production, but rather by an increase in the production of both vegetable and animal agricultural products. The analysis thus indicates that even if the nitrogen input flows per unit of production had remained unchanged during the period, the growth in production would per se have led to an increase in nitrogen loading in the environment. The environmental impact can thus be viewed as a resultant from a few dominant trends. The 5 There are several explanations for this development. According to Hasler (1998), it is partly due to changes in crop mix, as different crops have different nitrogen requirements and nitrogen leaching per hectare differs. An example is clover grass which was substituted for grass during the period 1965– 1975. Clover grass fixes nitrogen from the air, while grass requires nitrogen to be supplied in the form of fertilizer. This means that nitrogen input increased without a similar increase in nitrogen removal in the crops. Moreover, as commercial fertilizers are relatively cheap compared to other inputs, farmers are encouraged to apply surplus nitrogen. Finally, according to most functions of crop response to nitrogen, both yield and nitrogen uptake exhibit diminishing returns (Hasler, 1998).
economic driving force during the study period has been a high level of growth in agricultural exports. Due to Denmark’s small geographic size, this has necessitated particularly intensive agriculture with a high environmental impact per unit area. The agricultural production has been intensified through increasing the use of production inputs, including markedly growing use of nitrogen, especially during the first half of the study period. Thus, in order to reduce future nitrogen loading, policy measures should aim at controlling production by, e.g. approval schemes for or limits on livestock production. Also, levies on nitrogen loss would encourage more efficient use of nitrogen input, i.e. by better utilization of animal fertilizers or by optimization of fodder mix. Structural shifts, i.e. commodity composition in the household and production sectors have had minor effects, an exception being during the first decade, when a shift in the composition of final demand (commodity mix of export, consumption and investments) reduced loading by almost 14 000 tonnes. Further decomposition revealed this to be mainly due to a decrease in the agricultural exports during that period. From 1976– 1986, changes in input mix also reduced nitrogen loading by 7130 tonnes as the production sectors reduced demand for inputs from agriculture per unit of production. Table 3 summarizes the decomposition analysis of total change in nitrogen loading from sewage. This has fallen by 2.8 million tonnes and this again is mainly due to changes in emission intensity and level of final demand (particularly exports
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from abattoirs and the fish processing industry). In this case, however, emission technology lowers nitrogen loading, sewage treatment having intensified considerably during the whole period. In addition to the rising level of final demand, structural shifts also increase nitrogen loading. However, treatment technology is able to compensate for the effects of economic growth and structural shifts, ensuring a total decline in nitrogen loading of 2.8 million tonnes.
Table 4 Import and export of nitrogen loading due to foreign trade (metric tonnes N)a 1966
1988
Loading due to export of goods, i.e. import of nitrogen loading Loading due to import of goods, i.e. export of nitrogen loading
25 720
61 260
7460
6760
Residual
18 260
54 500
a
3.3. The global aspect The above analysis is based exclusively on nitrogen loading within Denmark. However, the import of commodities gives rise to loading in the countries from which they are imported. Analogously, foreign demand for Danish commodities leads to loading in Denmark through Danish production of goods for export. To obtain a full picture of the effects of Danish economic activities, nitrogen loading caused abroad as a result of Danish imports has to be included. Such estimates are based on two important assumptions. Firstly, foreign technology is identical to Danish technology, i.e. foreign producers use the same inputs per unit of production as the corresponding Danish producers. Secondly, foreign production activities generate the same nitrogen loading per unit of production as the Danish activities, i.e. the activities are assumed to have the same abatement technology. It is important to note that while these assumptions are critical and entail considerable uncertainty, they are nevertheless widely applied in input-output analysis. The nitrogen-intensive imported goods primarily derive from the chemicals industry and the production of commercial fertilizer and pesticides (Danish Environmental Protection Agency). Differences in the production of these goods between countries are not taken into account as the technologies used at home and abroad are assumed to be equivalent. However, as our imports of agricultural goods are relatively small compared with production for export (Statistics Denmark), any major difference in agricultural practice between Denmark and the
Source: The authors.
countries we import from will be of limited significance in the present context. However, an exception would include fodder, where imports are considerable. In this case, the assumption of equivalent technology at home and abroad is more problematic as agricultural conditions in the countries from which Denmark imports fodder deviate somewhat from those in Denmark. The estimated nitrogen loading in Denmark and abroad resulting from foreign trade is shown in Table 4. The first row shows loading occurring in Denmark as a result of the export of goods (excluding the import content of the exports). This can be considered as ‘imported’ nitrogen loading as it would otherwise have occurred in the importing country had the goods instead been produced there. The next row shows nitrogen loading occurring abroad as a result of Danish imports of goods (exclusive of imports for export purposes). This corresponds to ‘exported’ nitrogen loading as it would otherwise have occurred in Denmark. Finally, the third row shows the residual of loading due to exports minus loading due to imports. If the residual is negative, Denmark is a net exporter of nitrogen loading (through the import of goods) whereas if the residual is positive, Denmark is a net importer of nitrogen loading (through the export of goods). As is apparent from Table 4, Denmark is a net importer of nitrogen loading, loading due to exports being much greater than imports. The main reason for this is the sizeable Danish exports from agriculture and the food industry relative to total production, Denmark being the seventh largest exporter of agricultural products in the world (Statistics Denmark). International trade, in
M. Wier, B. Hasler / Ecological Economics 30 (1999) 317–331
which Denmark has specialized in the export of a number of agricultural products, thus entails enhanced pressure on the environment. The nitrogen loading ‘deficit’ was much smaller in 1966, however. While loading due to exports increased by 140% during the period, loading due to imports fell by 10%, thereby increasing the deficit. This development was partly a result of the growing agricultural exports, partly a result of difference in commodity mix in exports and imports. This is because nitrogen loading imports are mainly due to the export of agricultural products, while loading exports are mainly due to imports from the pulp and paper, fertilizer and chemical sectors. As agricultural production has become more nitrogen-intensive, leaching from agricultural land has increased throughout the period and ‘imported’ nitrogen loading has therefore increased. Conversely, improved abatement technology abroad has reduced ‘exported’ nitrogen loading. Thus, the environmental impact of Danish exports has increased while that of imports has declined.
4. Conclusions The model system described in this paper is an input-output model incorporating a nitrogen budget for the agricultural sector and emission factors for industry. The approach provides new information on major trends and development in nitrogen loading during the last decades and relates environmental impact to the responsible demand categories in the economy. The analysis points out driving forces behind the development and hence which factors the policy measures should be directed towards. The main findings are as follows: Nitrogen loading in Denmark from the production sector is now chiefly attributable to leaching from agricultural land and sewage effluent from the food industry production mainly intended for export. The agricultural sector has been responsible for the major part of nitrogen loading since the 1960s, but increased leaching throughout the period has made the sector even more dominant. The main factors behind this development include
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an increase in leaching per unit production due to excessive nitrogen input, together with a growing level of final demand, especially exports. Structural changes (i.e. changes in commodity mix in Danish production sectors and households) are generally less important. The effect of increasing leaching per unit of production was most apparent in the period 1966–1976, while the effect of increasing demand dominated in the period 1976–1986. Thus, in contrast to what is often presumed, increasing nitrogen input is a characteristic of the 1960s and 1970s, excessive nitrogen input actually having stagnated in the 1980s, when eutrophication was mainly due to growth in agricultural production. Hence, in order to reduce future nitrogen loading, policy measures should aim at controlling livestock production by, e.g. approval schemes or limits on livestock production. In addition, levies on nitrogen loss would encourage a more efficient use of nitrogen input, i.e. by better utilization of animal fertilizers or by optimization of fodder mix. The period was also characterized by an overall decrease in nitrogen loading from sewage effluent due to the widespread application of treatment technology. This effect compensates the effect of economic growth and structural change, thereby providing evidence for the ability of cleaner technology to offset economic growth. As a result of foreign trade, Denmark is a net importer of nitrogen loading, domestic production of export goods being much more polluting than the production of imported goods abroad. Since the 1960s, nitrogen loading has increased due to increasing agricultural exports and increasing leaching per unit of production from agricultural land. In conclusion, the problems affecting the Danish aquatic environment are closely associated with our role in international trade. Denmark has specialized in the export of agricultural products, the extent of which is considerable relative to the country’s size. This entails highly intensive production, high nitrogen consumption and high nitrogen loading per unit area, thus leading to oxygen deficit in the marine environment.
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Acknowledgements The authors would like to thank three anonymous referees for helpful comments.
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Danish Environmental Protection Agency, 1991b. Renseanlæg i Danmark i 1989 (Sewage works in Denmark in 1989, in Danish), Danish EPA, Copenhagen. Danish Environmental Protection Agency, 1992a. Vandmiljø92 (Aquatic Environment-92, in Danish), Danish EPA, Copenhagen. Danish Environmental Protection Agency, 1992b. Industrielle punktkilder 1989 (Industrial point sources, in Danish), Danish EPA, Copenhagen. Dubgaard, A., 1990. Danish Policy Measurements to Control Agricultural Impacts on the Environment. Report No. 52. Danish Institute of Agricultural Economics, Copenhagen. Dubgaard, A., 1994. The Danish Aquatic Environmental Programmes: An Assessment of Policy Instruments and Results. In: Napier, T.L., Camboni, S.M., Elswaify, S. (Eds.), Adopting Conservation on the Farm — An International Perspective on the Socioeconomics of Soil and Water conservation. Soil and Water Conservation Society. Forssell, O., 1989. The input-output framework for analysing transmission of technical progress between industries. Econ. Syst. Res. 1, 429 – 445. Fujimagari, D., 1989. The sources of change in Canadian industry output. Econ. Syst. Res. 1, 187 – 202. Hasler, B., 1998. Analysis of environmental policy measures aimed at reducing nitrogen leaking at the farm level. Env. Poll. 102, 749 – 754. Halvorsen, B., Mæchle, N., Nyborg, K., 1991. Dekomponering af utslipp til luft energibruk og produksjon i Norge 1985 – 1987 (Decomposition of emissions to air, energy consumption and production in Norway, in Norwegian), Statistics Norway, Oslo. Howarth, R., Schipper, L., Andersson, B., 1993. The structure and intensity of energy use: trends in five OECD nations. Energy J. 14, 27 – 45. Jensen, K.M., Reenberg, A., 1986. Landbrugsatlas Danmark (Agricultural mapping of Denmark; in Danish, with English summary). Det Kgl. Danske Geografiske Selskab, Copenhagen. Kyllingsbæk, A., 1995. Kvælstofoverskud i dansk landbrug 1950 – 1959 og 1979 – 1994 (Nitrogen Surplus in Danish Agriculture 1950 – 1959 and 1979 – 1994; in Danish). Danish Institute of Soil Science, Report No. 23, Denmark. Laursen, B., 1987. Normal for husdyrgødning (Norms for nitrogen in manure; in Danish). Danish Institute of Agricultural Economics, Copenhagen. Laursen, B., 1989. Notat om landbrugets kvælstofbalance (Note on nitrogen budget of the agricultural sector; in Danish). Danish Institute of Agricultural Economics, Copenhagen. Leontief, W., Ford, D., 1972. Air Pollution and the Economic Structure: Empirical Resets of Input-Output Computations, In: Brody, A., Carter, A. (Eds), Input-Output Techniques, North-Holland, Amsterdam. Li, J.-W., Shrestha, R.M., Foell, W.K., 1990. Structural change and energy use — the case of the manufacturing sector in Taiwan. Energy Econ. 12, 109 – 115.
M. Wier, B. Hasler / Ecological Economics 30 (1999) 317–331 Lin, X., Polenske, K., 1995. Input-output anatomy of China’s energy-demand change, 1981–1987. Econ. Syst. Res. 7, 6784. Lin, X., 1996. China’s Energy Strategy: Economic Structure. Technological Choices, and Energy Consumption. Westport, CT: Praeger. Liu, X.Q., Ang, B.W., Ong, H.L., 1992. The application of the divisia indeks to the decomposition of changes in industrial energy consumption. Energy J. 13, 161–177. Ministry of Agriculture, 1991. Bæredygtigt landbrug (Sustainable Agriculture; in Danish), Copenhagen. National Environmental Research Institute, Various years. Technical Reports on the Danish Nationwide Water Quality Monitoring Programme, Denmark. Nielsen, H., 1990. Nitrogen circulation in Danish Agriculture, 1980 – 88 (in Danish, with English summary), National Environmental Research Institute, Denmark. Pløger, E., 1984. The Effects of Structural Changes on Danish Energy Consumption. In: Smyshlyaev, A. (Ed.), Input– Output Modelling, Springer, Berlin. Rose, A., Chen, C.Y., 1991. Sources of change in energy use in the U.S. economy 1972–82. Res. Energy 13, 1–21. Rude, S., Frederiksen, B.S., 1994. National and EC Nitrate Policies — Agricultural Aspects for 7 EC Countries. Report No. 52. Danish Institute of Agricultural Economics, Copenhagen.
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Runge, E.H., Asman, W., Kilde, N., 1991. A detailed emission inventory of nitrogen oxides for Denmark. Report RISØM-2929, Risø National Laboratory, Roskilde, Denmark, p. 68. Sawyer, J., 1992. Forecasting with input-output matrices: are the coefficients stationary? Econ. Syst. Res. 4, 325 – 348. Schleef, K.H., Kleinhanss, W., 1997. Nitrogen balances at regional level in the European Union. In: Brouwer, F., Kleinhanss, W. (Eds.), The implementing of nitrate policies in Europe: Processes of change in environmental policy and agriculture. Wissenschaftsverlag Vauk Kiel KG, Kiel. Sibbesen, E., 1990. Kvælstof, fosfor og kalium i foder, animalsk produktion og husdyrgødning i dansk landbrug i 1980’erne (in Danish). Tidsskrift for Planheavls Specialserie. Skolka, J., 1989. Input-output structural decomposition analysis for Austria. J. Policy Modelling 11, 45 – 66. Statistics Denmark, Various years. Landbrugsshanistik (Agricultural Statistics, in Danish). Torvanger, A., 1991. Manufacturing sector carbon dioxide emissions in nine OECD countries, 1973 – 87. Energy Econ. 12, 168 – 186. Wier, M., 1998. Sources of changes in emissions from energy. Econ. Syst. Res. 10, 99 – 112.
. .
ANALYSIS
Accounting for nitrogen in Denmark—a structural decomposition analysis Mette Wier a,*, Berit Hasler b b
a AKF, Danish Institute of Local Go6ernment Studies, DK-L602 Copenhagen, Denmark National En6ironmental Research Institute, Department of Policy Analysis, P.O. Box 358, DK-4000 Roskilde, Denmark
Received 18 March 1998; received in revised form 20 August 1998; accepted 6 January 1999
Abstract This paper examines the environmental-economic cycle for nitrogen in Denmark based on nitrogen input and output from different economic sectors. An input-output model is employed together with a nitrogen mass balance to apportion total nitrogen loading by final demand and estimate export and import of nitrogen from foreign trade. The changes in agricultural and industrial nitrogen loading from the mid 1960s to the late 1980s are broken down into changes related to different technological and economic factors. The analysis reveals that technological change (intensified agricultural production) and economic growth (especially rising exports) are the key factors, structural shifts (changes in commodity mix in the household and production sectors) generally being of less importance. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Marine nitrogen loading; Nitrogen mass balance; Decomposition analysis; Input-output modelling
1. Introduction Nitrogen loading of the Danish aquatic environment has increased in recent decades, giving rise to serious problems with eutrophication of inland and marine waters throughout the 1980s. In the Øresund, the Kattegat and the Belt Seas, increases in the winter concentration of nitrogen were observed from the mid 1970s to the mid * Corresponding author. Tel.: +45-33-11-03-00; fax +4533-15-28-75. E-mail address: [email protected] (M. Wier)
1980s, in many cases leading to oxygen deficit1 (Danish Environmental Protection Agency, 1984; Christensen et al., 1994). In 1984, the Danish Environmental Protection Agency reported an oxygen deficiency in areas where it had not previously been detected, including in the North Sea 1 In Denmark, the term ‘oxygen deficit’ is used when the water oxygen concentration falls below 4 mg/l. If the concentration falls below 2 mg/l, the term ‘severe oxygen deficit’ is used. Many fish species flee from areas affected by oxygen deficiencies. In the case of a prolonged severe oxygen deficit, benthic invertebrates that are unable to flee eventually die.
0921-8009/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 8 0 0 9 ( 9 9 ) 0 0 0 0 4 - X
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and other open marine waters (Danish Environmental Protection Agency, 1984). The frequency of the recorded episodes of oxygen deficit was also found to have increased. Both the extent and frequency of oxygen deficit have increased even more during the late 1980s, this being attributable to the increase in nitrogen loading of the aquatic environment (National Environmental Research Institute, 1990–1997). The increase in nitrogen loading is attributable to increased production in the agricultural sector and growth in the amount of sewage effluent. The latter is the result of enhanced population growth and increased industrial production. The major part of the increase is attributable to increased agricultural production resulting from general intensification of production and to a lesser extent to the incorporation of marginal land in production (Christensen et al., 1994). The negative environmental consequences of enhanced nutrient loading of the Danish aquatic environment led Parliament to adopt the Action Plan on the Aquatic environment in 1987 (Dubgaard, 1990; Rude and Frederiksen, 1994). Among other things, this stipulated that nitrogen discharge from agricultural sources was to be reduced by 50% while discharges from other sources (industry, sewage works) were to be reduced by 60%. The present article quantifies the change in marine nitrogen loading due to intensification of agricultural production, general economic growth and general structural shifts in the economy over two decades from 1965 to 1989. The purpose of this paper is to analyse the background for the serious situation at the end of the 1980s and place it in a historic perspective with a view to identifying the main shifts in the agricultural sector and economy that have been responsible for this change in loading. The intention is to identify the factors responsible for the development and quantify their respective contributions. The analysis follows a top-down approach, focusing on the main tendencies on both the environmental and economy sides. The analysis is made at the national level because the political goals are set at this level. Nitrogen loading is generally too high in the majority of the inner Danish marine waters and the adjoining marine waters2 (Christensen et al., 1994), and the
political goal of halving nitrogen loss applies uniformly to the whole country. An analysis at the national level is therefore meaningful. The analysis was carried out by combining an input-output model with a nitrogen budget for agriculture and emission factors for sewage effluent. This comprehensive integrated model system enables behavioural and technological shifts in the household and production sectors to be related to changes in nitrogen loading, thereby revealing the economic reasons for the development. This study distinguishes itself by relating nitrogen loading to the whole economy, i.e. to production as well as consumption activities, and by applying input-output structural decomposition analysis on a new area. Furthermore, it covers a very long period, analysing input-output tables from 1966 to 1988, whereby it is possible to examine changes during three separate decades. A final distinguishing feature is that the study includes an assessment of the importance to nitrogen loading of foreign trade.
2. Model and data The model consists of two parts, an economic input-output model and a nitrogen sub-model. The latter describes nitrogen loading from the different economic sectors, while the former describes intersectoral commodity flows within whole economy. The nitrogen flows from the nitrogen sub-model are linked to the input-output model by estimating emission coefficients, i.e. nitrogen discharges per unit of production per year from all sectors in the economy.
2.1. The input-output model The model framework is the extended inputoutput system, as introduced by Leontief and Ford (1972). The strength of the model is that it 2 While nitrogen is the primary factor causing eutrophication of marine waters, phosphorus is the main cause of eutrophication in inland waters. Consequently, only marine nitrogen loading will be considered in this paper.
M. Wier, B. Hasler / Ecological Economics 30 (1999) 317–331
covers all sectors of the economy, operates on a very disaggregated level, and handles both direct and indirect use of goods. Structural decomposition analysis has been widely applied to changes in output, use of primary factors, etc. (Fujimagari (1989), Forssell (1989), Skolka (1989)). With regard to environmental performance, energy consumption has been decomposed in Denmark by Pløger (1984), in the USA by Rose and Chen (1991), Boyd et al. (1987), in Taiwan by Chen and Rose (1990), Li et al. (1990), in Singapore by Liu et al. (1992), and in five OECD countries by Howarth et al. (1993). In addition, Lin and Polenske (1995) have decomposed energy-demand changes in China, while Lin (1996) has examined the technological and energy-demand implications. With regard to decompositional analysis of emissions, CO2 emissions have been decomposed in Australia by Common and Salma (1992), in nine OECD countries by Halvorsen et al. (1991) in Taiwan by Chang and Lin (1997), in China, Taiwan and South Korea by Ang and Pandiyan (1997), in nine OECD countries by Torvanger (1991) and in Denmark by Wier (1998). The latter author also decomposed Danish SO2 and NOx emissions. This paper further expands the environmental use of decomposition analysis to nitrogen loading, presenting a decomposition of the changes in nitrogen loading in Denmark over the period 1966 –1988. The analytical framework is the static activity x activity input-output model with endogenous import. At a given point in time, nitrogen loading is given by, 1 Nt = wt (I−A − t )Dtdt,
(1)
where Nt, is a scalar3 of total nitrogen loading, wt, is a 1× 117 vector of nitrogen discharges from all sectors (i.e. the output of the nitrogen sub-model) per unit of production (i.e. wt, is a vector of emission factors), (I − A)t− 7 is the 117 × 117 Leon-
tief inverse matrix, Dt is a 117×9 matrix for the composition of final demand (final demand apportioned by economic activity) and dt, is a 9× 1 vector for the absolute level of final demand for all categories. The nine final demand categories are private consumption, public consumption, exports, stock building, agricultural breeding stock building, imputed bank service charges and investments (gross fixed capital formation) in machinery, in transport equipment and in construction. The structural decomposition analysis is employed to clarify how the different factors in Eq. (1) have affected nitrogen loading. Total change in loading is decomposed into the effects due to the four components; loading per unit produced (emission factor effect), input mix in production sectors, commodity mix of final demand and level of final demand. The analysis was performed by changing the components one by one in order to quantify the contribution of each effect to the total change in loading. This contribution may be weighted using either the base year values for the other three components or by the current year values. The interaction effect is quite large, and will therefore cause considerable bias. The effect of a change in each component has therefore been determined using an average of the two approaches, as proposed by Fujimagari (1989) and Sawyer (1992). The change in emissions from sectors given by Eq. (1) from time t−1 until time t is Nt − Nt − 1 = Dw +D(I −A) − 1 + DD + Dd where the emission factor effect is Dw = ([(wt − wt − 1)(I − A)t−−11Dt − 1dt − 1] + [(wt − wt − 1)(I− A)t− 1Dtdt ])/2 The input mix effect is D(I−A)−1=([wt (I−A)t− 1 − (I− A)t−−11) Dt − 1dt − 1] + [wt − 1((I − A)t− 1(I−A)t− 1)Dtdt ])/2 the composition of final demand effect is
3
Applying element-wise multiplication to the total loading rather than matrix multiplication yields an activity x final demand matrix. This has been done to provide full information on changes in all sectors and demands, and will be referred to, but not presented in this paper.
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DD= ([wt (I−A)t− 1(Dt − Dt − 1)dt − 1] + [wt − 1(I−A)t−−11(Dt − Dt − 1)dt ])/2 and the level of final demand effect is
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Dd = ([wt (I−A)t− 1Dt (dt −dt − 1)] +[wt − 1(I−A)
−1 t−1
Dt − 1(dt −dt − 1)])/2
The economic data used for the study are the Danish input-output tables (Statistics Denmark) from 1966 to 1988 expressed in constant (1980) prices. The tables encompass 117 sectors and nine categories of final demand. Data on nitrogen inputs and outputs are from the Ministry of Agriculture, Statistics Denmark, the Ministry of Environment and Energy, and the Danish Environmental Protection Agency. The data used in the nitrogen budget is documented in Section 2.2.2.
2.2. The nitrogen sub-model 2.2.1. The nitrogen budget at the close of the 1980s The nitrogen budget for Denmark in the late 1980s is summarized in Fig. 1. The main tendencies are described here. This is the first time such a detailed national scale budget has been drawn up. The greatest uncertainty is related to the agricultural data, the loading data for sewage and atmospheric deposition being quite robust. The flows should be interpreted as an average for the period 1986–1989. In reality, large climate-dependent variation will occur every year. The sectors of the economy mainly responsible for nitrogen loading are agriculture, industry and households, with the former accounting for the major part. Nitrogen balances for the agricultural sector can be calculated as farm-gate balances or soil-surface balances4 (Schleef and Kleinhanss, 1997). The soil-surface approach was selected for 4 With a farm-gate balance, the interface for the balance is the farm as a whole, all nitrogen inputs to the farm being calculated, i.e. fodder, livestock and commercial fertilizer, as well as nitrogen fixed from the atmosphere, atmospheric deposition of nitrogen and nitrogen applied in sewage sludge. The outputs are calculated as the nitrogen in all sold products (crops as well as animals) and the loss to the environment. When using the farm-gate approach, the internal nitrogen streams in the farm are not explicitly calculated, i.e. the nitrogen in animal fertilizer and fodder crops. With the soilsurface approach, in contrast, the interface in the balance is the soil surface. In this case, the nitrogen inputs are commercial fertilizer and animal fertilizer, as well as nitrogen fixed
the estimations in the present study because this is the most appropriate balance when calculating the losses relating to nitrate leaching to the aquatic environment. As is apparent from Fig. 1, the main nitrogen inputs are animal and commercial fertilizers. Other sources of nitrogen include nitrogen fixation, sewage sludge and atmospheric deposition. Approximately one-third of the deposition takes place as NOx (nitrogen oxides) and two-thirds as NHx (ammonia and ammonium). The major sources of the NOx are the transport sector and power plants, while the NHx is mainly derived from volatilization from agriculture. (Asman, 1990; Asman and Runge, 1991). According to the estimated nitrogen budget (see Section 2.3.2), 46% of the nitrogen input to the fields is removed with harvested crops. This uptake is in good agreement with other studies of Danish agriculture based on the soil-surface approach, where estimates of uptake range from 41–44% (Nielsen, 1990) to 45% (Ministry of Agriculture, 1991) to 48% (Schleef and Kleinhanss, 1997). Using the farm-gate approach, Andersen (1996) estimated a utilization rate of 49% (nitrogen removed in the sold products expressed as a percentage of nitrogen input). Nitrogen balances have also been determined for the EU member states (EU 12) by Brouwer et al. (1995) using the farm-gate approach. From that study it can be estimated that 49% of the nitrogen input was removed in the sold products in Denmark in 1990/1991. The estimated utilization rate for the Netherlands was 31%, the difference between the rates in the two countries mainly being explicable by differences in livestock production and density. The average utilization rate for the EU member states was 50%. The nitrogen utilization rate in Danish agricultural production is therefore average in a European context, and the estimated value for Danish agriculture reported by Brouwer et al. is in good agreement with the utilization rate estimated in the present study. from the atmosphere, atmospheric deposition of nitrogen and nitrogen applied in sewage sludge. The outputs are calculated as harvested crops for both internal and external use, and loss to the environment.
M. Wier, B. Hasler / Ecological Economics 30 (1999) 317–331 Fig. 1. Nitrogen budget for Denmark, late 1980s (metric tonnes N). * It is assumed that nitrogen in animal fertiliser is equal to nitrogen in fodder consumed less the nitrogen in livestock products. ** Includes a background load (i.e. loading that cannot be attributed to a specific source) of 23 000 tonnes N. Approximately 175 000 tonnes are retained in inland waters. Sources: Asman (1990), Asman and Runge (1991), Runge et al. (1991), Ministry of Agriculture (1991), Danish Environmental Protection Agency (1991a,b, 1992a,b), Nielsen (1990).
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As is apparent from Fig. 1, losses to the atmosphere take place through denitrification in soil water and water bodies, soil erosion and ammonia volatilization from livestock housing and the storage and spreading of animal fertilizer. Loss to the aquatic environment takes place as leaching from the root zone, whereafter the nitrogen is transported to lakes and watercourses and further on to the sea. As shown in Fig. 1, this amounted to 250 000 tonnes in the late 1980s. However, much of the nitrogen is retained during transport and, on average, only 75 000 tonnes of the nitrogen leaching from rural land actually reaches the sea annually, 70%, of the total being retained in inland waters (Danish Environmental Protection Agency, 1991a). Total input to the sea amounts to 110 000 tonnes (Danish Environmental Protection Agency, 1991a), including loading from agriculture, industry, household sewage, deposition to inland waters, etc. Atmospheric deposition and inflow from foreign seas are sizeable, while direct nitrogen loading of marine waters by sewage effluent is minor. For inland water bodies, however, sewage effluent from households, industry and fish farming may constitute an important source of nitrogen input.
2.2.2. Historical de6elopment in the agricultural nitrogen budget In this section, leaching from the root zone of agricultural land every fifth year from the mid 1960s until the present is estimated according to the nitrogen mass balance principle as the residual of estimates of all nitrogen inputs and outputs. These estimated levels of leaching are not the actual leaching in the different years, but an approximation of the expected leaching level given the actual harvest size, atmospheric deposition, input of animal and commercial fertilizers, etc., and assuming that climatic conditions in the entire period from 1960 – 1989 were the same as the average conditions during the late 1980s. The elements of the nitrogen budget are shown in Table 1 below, inputs being listed in the upper half and outputs in the lower half. Note that the balance is based on the soil-surface approach. A considerable number of statistics were needed to calculate the figures, and some assumptions
have been made in order to estimate the development in input and output flows. Biological fixation at the end of the 1980s is estimated at 30 000 tonnes N/year (Ministry of Agriculture, 1991). The amount of nitrogen fixed depends on crop composition, in particular the area planted with pulses and clover grass, and is calculated on the basis of a constant fixation coefficient per hectare for each crop type multiplied by the total area of pulses and clover grass. The fixation coefficient is estimated on the basis of data from the end of the 1980s (Ministry of Agriculture, 1991). In other words, it is assumed that fixation by each crop type is constant per hectare over time, which implies that the percentage of clover in grass fields is also assumed to be constant. It is difficult to determine whether the percentage of clover in grass has changed during the early part of the study period, however. Thus based on the findings of Kyllingsbæk (1995), the percentage of clover in grass is assumed to have remained constant during the period 1965–1980. In the period from 1980 to the end of the 1980s, the clover content increased (Kyllingsbæk, 1995), but insufficient data is available to enable the increase to be quantified. Kyllingsbæk’s findings indicate that nitrogen fixation in the 1980s is underestimated in our study. The figure for nitrogen input in sewage sludge is derived from Kyllingsbæk (1995), who calculates this to be 3 million kg N/year in 1970, increasing to 5 million kg N/year in 1989. Based on these figures, we assume a constant input of 3 million kg N/year from the mid 1960s to the beginning of the 1980s, 4 million kg N/year in the mid 1980s, and 5 million kg N/year at the end of the 1980s. The estimates are subject to a considerable degree of uncertainty, albeit that this is of little importance for the budget as a whole due to the small magnitude of these inputs. Input from commercial fertilizers was taken directly from the agriculture statistics (Statistics Denmark, various years). Nitrogen input from animal fertilizers has been estimated to be 292 000 tonnes N/year in 1985/1986 (Laursen, 1989), 330– 340 000 tonnes N/year in the late 1980s (Sibbesen, 1990), 330 000 tonnes N/year in the late 1980s (Ministry of Agriculture, 1991), and 337 000 ton-
Input flows
Biological fixation
1965/1966 1970/1971 1975/1976 1980/1981 1985/1986 1988/1989
36 34 31 28 30 30
Output flows
Volatilization from comm. Fertilizers
1965/1966 1970/1971 1975/1976 1980/1981 1985/1986 1988/1989
13 19 21 24 24 25
a
Sewage sludge
NHx-deposition
Commercial fertilizers
Animal fertilizer
30 34 34 38 39 39
206 290 330 375 380 390
270 285 285 315 320 320
Volatization from Removed with harvested manure crops
Dentrification
Leaching from the root zone
84 80 90 98 100 100
40 50 50 60 60 60
70 160 175 220 240 250
3 3 3 3 4 5
NOx-deposition 13 14 15 20 22 20
350 345 365 380 375 370
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Table 1 Nitrogen budget for Danish agriculture (1000 metric tonnes N/year)a
Sources: See Fig. 1.
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nes N/year in 1987/1988 (Nielsen, 1990). As a compromise, input from this source is assumed to be 320 000 tonnes N/year in the present study. For the period 1965 – 1985, production of nitrogen in animal fertilizer was determined from the trend in consumption of animal fertilizer as estimated in Jensen and Reenberg (1986). It should be mentioned that these estimates are subject to some degree of uncertainty. To validate the results, we have also calculated the input of nitrogen in animal fertilizer based on the composition of the livestock and the current norms for the nitrogen content of manure per animal (Laursen, 1987), which are available for 1975 onwards. The findings with this method only deviate slightly (1 – 7%) from the estimates of Laursen (1987) except for 1965/1966, where the norm-based method yields an estimate that differs from ours by 14%. However, the use of the norm-based estimation method in 1965/1966 poses considerable problems. The protein content of the fodder is of decisive importance for the nitrogen content of the animal fertilizer. Since the protein content increased from the 1960s to the 1970s, figures for the nitrogen content of animal fertilizer in 1965/ 1966 based on 1975 norms will be overestimated. We have therefore chosen not to correct our estimates. It can be concluded, though, that the uncertainty in the estimates of the nitrogen content of animal fertilizer is greatest in the first part of the period studied. Atmospheric deposition of NOx and NHx in the late 1980s was estimated from emission data for agriculture, transport and power stations using the TREND model for atmospheric transport and deposition (Asman and Runge, 1991; Asman and van Jaarsveld, 1992). Atmospheric deposition of NOx back through time was estimated on the basis of information on NOx emissions (CORINAIR database, National Environmental Research Institute), deposition being assumed to be proportional to emissions. While this approach does not take into account regional shifts in the geographic location of emission sources at home and abroad, only a small part of NOx emissions are deposited locally (Asman and Runge, 1991) and this weakness is therefore of minor significance.
Atmospheric deposition of ammonia and ammonium back through time was estimated by assuming that these were proportional to the N content of animal manure and the N content of commercial fertilizer. The data used was from the end of the 1980s (Asman and Runge, 1991; Statistics Denmark (various years); Danish Environmental Protection Agency, 1991a). Denitrification was estimated as a constant fraction of total fertilizer consumption (8%). Ammonia volatilization was estimated as constant fractions of animal and commercial fertilizer consumption (31 and 6%, respectively). The estimates are based on information from the end of the 1980s (Ministry of Agriculture, 1991; Danish Environmental Protection Agency, 1991a; Asman and Runge, 1991). Note that changes in the handling of animal fertilizer are not taken into account. Depending on storage conditions and the time and method of application, between 3 and 40% of the nitrogen in animal fertilizer volatilizes in the form of ammonia (Danish Agricultural Advisory Centre, various years). Until the end of the 1980s, there was no decisive change in the utilization of animal fertilizer, and this problem is therefore of limited significance. It should be mentioned, though, that there has been a general shift from solid to liquid manure which has not been taken into account. As a consequence, ammonia volatilization at the beginning of the study period has probably been overestimated to some extent. Nitrogen removal in crops was assumed to be constant over time per kilogram of different crops. Information on nitrogen uptake by the various crops derives from Danish Agricultural Advisory Centre (various years), while the information on harvested crops derives from Statistics Denmark (various years). The uptake coefficients are from 1970, and are assumed to apply to the whole study period. An uncertainty factor in the calculation of nitrogen removal is that there has been a general increase in nitrogen uptake per kilogram crop (Kyllingsbæk, 1995). There is insufficient data to quantify this increase, however. Therefore, it can be assumed that our figures for nitrogen removal in the crops are underestimated in 1980 since the
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Fig. 2. Marine nitrogen loading from industry and agriculture apportioned by demand (1988; metric tonnes N).
uptake coefficients used are from 1970. It should be mentioned, though, that our estimates are in full agreement with those of the Ministry of Agriculture (1991). It should also be noted that nitrogen removal has not increased much during the study period (6%), which is in poor agreement with the far greater simultaneous increase in crop yield. This is attributable to changes in crop composition, primarily due to the decrease in areas planted with clover grass since the latter takes up three times as much nitrogen per hectare as cereals. Thus, clover grass fields accounted for 29% of the total area of arable land in 1965 but only 7.5% in 1988. Finally, leaching was calculated as the residual (rounded up). As such, leaching also included the non-quantifiable loss in connection with silage and changes in the soil nitrogen pool. As there is a considerable time lag in the transport of nitrogen in soil and water bodies due to chemical and biological processes, 70% of the nitrogen leaching from the root zone was assumed to be retained in inland waters, with only 30% eventually reaching the sea (Danish Environmental Protection Agency, 1991a). As is apparent from Table 1, leaching from the root zone has increased considerably since the mid 1960s especially in the first half of the period. This is due to the increase in nitrogen input from animal and commercial fertilizers, together with almost unchanged nitrogen removal in crops. The nitrogen input surplus has more than tripled during the period.
2.2.3. Nitrogen loading from sewage effluents The sewage part of the nitrogen sub-model is quite simple, concerning only loading from industrial sectors. Nitrogen loading from sewage works is measured in a nationwide monitoring programme, which was initiated in 1988 as part of the Action Plan on the Aquatic Environment. The estimates back through time were made by correcting 1988/1989 discharges with data on the development in sewage treatment technology (Tonni Christensen, Danish EPA, personal communication).
3. Nitrogen loading and the economy—results and discussion
3.1. Allocation of final demand As already stated, agriculture is the main sector contributing to nitrogen loading. With regard to sewage effluent inputs to inland and marine waters, the sectors which pollute most include the food industry (abattoirs in particular), the chemicals industry, fish farming and fish processing. Production activities reflect the composition of the final demand, changing with changes in export, consumption and investments. In Fig. 2, total nitrogen loading of marine waters in 1988 is shown apportioned by final demand, i.e. the direct and indirect loading due to each demand category. Total nitrogen loading of the sea by agriculture and industry amounted to 87 000 tonnes in the late 1980s, of which the industry accounted for 13%.
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Table 2 Decomposition analysis of changes in marine nitrogen loading from agriculture (1000 metric tonnes N)a Technology
Final demand
Total
Emission factor
Input mix
Composition
Level
1966–1976 1976–1986 1986–1988
30 520 3330 830
60 −7130 −1480
−13 940 2410 −2840
14 360 20 400 6490
31 000 19 000 3000
1966–1988
40 690
−6740
−14 920
33 970
53 000
a
Source: The authors.
As is apparent from Fig. 2, export and private consumption are by far the most important categories of final demand with regard to nitrogen loading. Thus, export is responsible for 65% of the agricultural loading and 74% of the industrial loading, while the corresponding figures for private consumption are 32 and 17%, respectively. In contrast, public consumption and investments demand commodities from less polluting production sectors, accounting for only 3 – 4% of nitrogen loading.
3.2. Decomposition analysis The calculations indicate that since the mid 1960s, nitrogen loading from the economy has undergone major change. According to the estimated nitrogen budget (Table 1) and the input – output calculations, nitrogen leaching from agriculture has risen by 240%, while loading from sewage effluent has fallen by 16%. Production technology, abatement technology, shifts in commodity mix in the production and household sectors and economic growth are all of importance for this development. In the following, structural decomposition analysis is employed to clarify how these different factors have affected nitrogen loading. Total change in loading is decomposed into the effects due to the four components; loading per unit produced (emission factor effect), input mix in production sectors, commodity mix of final demand and level of final demand.
The emission factor effect incorporates technical, chemical and legislative factors. For agriculture, the effect depends on production behaviour and other factors influencing nitrogen input to agricultural land. For industry, the emission factor effect depends on production technology and legislation on sewage treatment. The results of the decomposition analysis are presented in Tables 2 and 3 grouped in intervals of 10 years except from the third period, which is shorter because the data only runs to 1988. Please note that the total change cannot be derived by simple addition of the changes during the three intervals studied as all changes in a component are multiplied with the values which the other components initially have in the period (i.e. at time t−1). Nitrogen loading from agriculture increased by 53 million tonnes from 1966 to 1988, due to increased nitrogen loading per unit of production and increased level of final demand (i.e. export, consumption and investment). Intensified nitrogen loading per unit of agricultural production was the most important factor in the first decade, whereafter growth in the level of final demand led to increased loading. More detailed decomposition shows that it is export in particular that has grown markedly. As is apparent from the agricultural nitrogen budget (Table 1), fertilizer inputs have been increasing without a corresponding increase in nitrogen removal with harvested crops. This trend is attributable to the enhanced input of commercial fertilizer and the resulting poorer utilization
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Table 3 Decomposition analysis of changes in marine nitrogen loading from sewage (1000 metric tonnes N)a Technology
Final demand
Total
Emission factor
Input mix
Composition
1966–1976 1976–1986 1986–1988
−11 370 −10 500 −1890
460 420 −20
2750 1980 −1210
7260 6420 1870
−900 −1680 −1250
1966–1988
−27 150
880
6290
17 170
−2810
a
Level
Source: The authors.
of animal fertilizer (Dubgaard, 1994; Hasler, 1998)5. The tendency is especially clear up to 1980, whereafter fertilizer inputs stagnated. This is supported by the fact that the input – output analysis (Table 2) shows that it is the first half of the period in particular that is characterized by increasing nitrogen intensity; in contrast, the second half of the period is characterized by an increase in the demand for agricultural products, and hence increased nitrogen loading. Thus, nitrogen loss during this second half of the study period cannot be chiefly explained by increased nitrogen input per unit of production, but rather by an increase in the production of both vegetable and animal agricultural products. The analysis thus indicates that even if the nitrogen input flows per unit of production had remained unchanged during the period, the growth in production would per se have led to an increase in nitrogen loading in the environment. The environmental impact can thus be viewed as a resultant from a few dominant trends. The 5 There are several explanations for this development. According to Hasler (1998), it is partly due to changes in crop mix, as different crops have different nitrogen requirements and nitrogen leaching per hectare differs. An example is clover grass which was substituted for grass during the period 1965– 1975. Clover grass fixes nitrogen from the air, while grass requires nitrogen to be supplied in the form of fertilizer. This means that nitrogen input increased without a similar increase in nitrogen removal in the crops. Moreover, as commercial fertilizers are relatively cheap compared to other inputs, farmers are encouraged to apply surplus nitrogen. Finally, according to most functions of crop response to nitrogen, both yield and nitrogen uptake exhibit diminishing returns (Hasler, 1998).
economic driving force during the study period has been a high level of growth in agricultural exports. Due to Denmark’s small geographic size, this has necessitated particularly intensive agriculture with a high environmental impact per unit area. The agricultural production has been intensified through increasing the use of production inputs, including markedly growing use of nitrogen, especially during the first half of the study period. Thus, in order to reduce future nitrogen loading, policy measures should aim at controlling production by, e.g. approval schemes for or limits on livestock production. Also, levies on nitrogen loss would encourage more efficient use of nitrogen input, i.e. by better utilization of animal fertilizers or by optimization of fodder mix. Structural shifts, i.e. commodity composition in the household and production sectors have had minor effects, an exception being during the first decade, when a shift in the composition of final demand (commodity mix of export, consumption and investments) reduced loading by almost 14 000 tonnes. Further decomposition revealed this to be mainly due to a decrease in the agricultural exports during that period. From 1976– 1986, changes in input mix also reduced nitrogen loading by 7130 tonnes as the production sectors reduced demand for inputs from agriculture per unit of production. Table 3 summarizes the decomposition analysis of total change in nitrogen loading from sewage. This has fallen by 2.8 million tonnes and this again is mainly due to changes in emission intensity and level of final demand (particularly exports
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from abattoirs and the fish processing industry). In this case, however, emission technology lowers nitrogen loading, sewage treatment having intensified considerably during the whole period. In addition to the rising level of final demand, structural shifts also increase nitrogen loading. However, treatment technology is able to compensate for the effects of economic growth and structural shifts, ensuring a total decline in nitrogen loading of 2.8 million tonnes.
Table 4 Import and export of nitrogen loading due to foreign trade (metric tonnes N)a 1966
1988
Loading due to export of goods, i.e. import of nitrogen loading Loading due to import of goods, i.e. export of nitrogen loading
25 720
61 260
7460
6760
Residual
18 260
54 500
a
3.3. The global aspect The above analysis is based exclusively on nitrogen loading within Denmark. However, the import of commodities gives rise to loading in the countries from which they are imported. Analogously, foreign demand for Danish commodities leads to loading in Denmark through Danish production of goods for export. To obtain a full picture of the effects of Danish economic activities, nitrogen loading caused abroad as a result of Danish imports has to be included. Such estimates are based on two important assumptions. Firstly, foreign technology is identical to Danish technology, i.e. foreign producers use the same inputs per unit of production as the corresponding Danish producers. Secondly, foreign production activities generate the same nitrogen loading per unit of production as the Danish activities, i.e. the activities are assumed to have the same abatement technology. It is important to note that while these assumptions are critical and entail considerable uncertainty, they are nevertheless widely applied in input-output analysis. The nitrogen-intensive imported goods primarily derive from the chemicals industry and the production of commercial fertilizer and pesticides (Danish Environmental Protection Agency). Differences in the production of these goods between countries are not taken into account as the technologies used at home and abroad are assumed to be equivalent. However, as our imports of agricultural goods are relatively small compared with production for export (Statistics Denmark), any major difference in agricultural practice between Denmark and the
Source: The authors.
countries we import from will be of limited significance in the present context. However, an exception would include fodder, where imports are considerable. In this case, the assumption of equivalent technology at home and abroad is more problematic as agricultural conditions in the countries from which Denmark imports fodder deviate somewhat from those in Denmark. The estimated nitrogen loading in Denmark and abroad resulting from foreign trade is shown in Table 4. The first row shows loading occurring in Denmark as a result of the export of goods (excluding the import content of the exports). This can be considered as ‘imported’ nitrogen loading as it would otherwise have occurred in the importing country had the goods instead been produced there. The next row shows nitrogen loading occurring abroad as a result of Danish imports of goods (exclusive of imports for export purposes). This corresponds to ‘exported’ nitrogen loading as it would otherwise have occurred in Denmark. Finally, the third row shows the residual of loading due to exports minus loading due to imports. If the residual is negative, Denmark is a net exporter of nitrogen loading (through the import of goods) whereas if the residual is positive, Denmark is a net importer of nitrogen loading (through the export of goods). As is apparent from Table 4, Denmark is a net importer of nitrogen loading, loading due to exports being much greater than imports. The main reason for this is the sizeable Danish exports from agriculture and the food industry relative to total production, Denmark being the seventh largest exporter of agricultural products in the world (Statistics Denmark). International trade, in
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which Denmark has specialized in the export of a number of agricultural products, thus entails enhanced pressure on the environment. The nitrogen loading ‘deficit’ was much smaller in 1966, however. While loading due to exports increased by 140% during the period, loading due to imports fell by 10%, thereby increasing the deficit. This development was partly a result of the growing agricultural exports, partly a result of difference in commodity mix in exports and imports. This is because nitrogen loading imports are mainly due to the export of agricultural products, while loading exports are mainly due to imports from the pulp and paper, fertilizer and chemical sectors. As agricultural production has become more nitrogen-intensive, leaching from agricultural land has increased throughout the period and ‘imported’ nitrogen loading has therefore increased. Conversely, improved abatement technology abroad has reduced ‘exported’ nitrogen loading. Thus, the environmental impact of Danish exports has increased while that of imports has declined.
4. Conclusions The model system described in this paper is an input-output model incorporating a nitrogen budget for the agricultural sector and emission factors for industry. The approach provides new information on major trends and development in nitrogen loading during the last decades and relates environmental impact to the responsible demand categories in the economy. The analysis points out driving forces behind the development and hence which factors the policy measures should be directed towards. The main findings are as follows: Nitrogen loading in Denmark from the production sector is now chiefly attributable to leaching from agricultural land and sewage effluent from the food industry production mainly intended for export. The agricultural sector has been responsible for the major part of nitrogen loading since the 1960s, but increased leaching throughout the period has made the sector even more dominant. The main factors behind this development include
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an increase in leaching per unit production due to excessive nitrogen input, together with a growing level of final demand, especially exports. Structural changes (i.e. changes in commodity mix in Danish production sectors and households) are generally less important. The effect of increasing leaching per unit of production was most apparent in the period 1966–1976, while the effect of increasing demand dominated in the period 1976–1986. Thus, in contrast to what is often presumed, increasing nitrogen input is a characteristic of the 1960s and 1970s, excessive nitrogen input actually having stagnated in the 1980s, when eutrophication was mainly due to growth in agricultural production. Hence, in order to reduce future nitrogen loading, policy measures should aim at controlling livestock production by, e.g. approval schemes or limits on livestock production. In addition, levies on nitrogen loss would encourage a more efficient use of nitrogen input, i.e. by better utilization of animal fertilizers or by optimization of fodder mix. The period was also characterized by an overall decrease in nitrogen loading from sewage effluent due to the widespread application of treatment technology. This effect compensates the effect of economic growth and structural change, thereby providing evidence for the ability of cleaner technology to offset economic growth. As a result of foreign trade, Denmark is a net importer of nitrogen loading, domestic production of export goods being much more polluting than the production of imported goods abroad. Since the 1960s, nitrogen loading has increased due to increasing agricultural exports and increasing leaching per unit of production from agricultural land. In conclusion, the problems affecting the Danish aquatic environment are closely associated with our role in international trade. Denmark has specialized in the export of agricultural products, the extent of which is considerable relative to the country’s size. This entails highly intensive production, high nitrogen consumption and high nitrogen loading per unit area, thus leading to oxygen deficit in the marine environment.
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Acknowledgements The authors would like to thank three anonymous referees for helpful comments.
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