Estimates of early-industrial inputs of nutrients to river systems: implication for coastal eutrophication

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The Science of the Total Environment 243/244 (1999) 43-52

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Estimates of early-industrial inputs of nutrients to river systems: implication for coastal eutrophication Gilles Billena3b3*, Josette Garnier a, Chlo6 Deligneb, Claire Billenb "UMR-CNRS7619 Sisyphe, University of Puns m,4pluce Jussieu, 75005 Puns, Frunce bIGEAT,University of Brussels, 50 uv. F.D. Roosevelt, 1000 Brussels, Belgium Received 16 April 1999; accepted 15 July 1999

Abstract

Although coastal eutrophication is generally recognised as a recent phenomenon related to the well-documented increase in riverine nutrient delivery during the last 30 or 40 years, a few historical records paradoxically show that, in some places like the Southern Bight of the North Sea, or the Northern Adriatic, algal proliferation as intense as presently observed was already regularly occurring at the end of the 19th century. Estimated riverine nutrient loads from diffuse sources or from domestic point sources of waste water at that time are too low to account for these observations. We attempted a retrospective evaluation of the possible contribution of industrial activity to nutrient river loading. The figures indicate that, by the end of the last century, large scale use of traditional processes in textile and paper industries, in tanneries, candles factories and others was responsible for a dominant part of the nutrient load carried by rivers in Western Europe and could have caused nutrient inputs to coastal zones similar to the present ones. 0 1999 Elsevier Science B.V. All rights reserved. Keywords: Eutrophication; History; Industrial pollution load; Nutrients

1. Introduction

Nitrogen and phosphorus riverine delivery to coastal zones in Western and Southern Europe, when expressed per unit watershed area, are typically in the range 750-1500 kg N/km2/year and

* Corresponding author, UMR-CNRS 7619 Sisyphe, University of Paris VI, case 123, 4 place Jussieu, 75005 Paris, France. Tel.: + 33-144-27-50-19;fax: + 33-144-27-51-25. E-mail address: [email protected] (G. Billen)

50-150 kg P/km2/year, respectively, representing a 10-20-fold increase with respect to nearpristine exportation from remote temperate forested areas (75 kg N/km2/year and 5 kg P/km2/year for North Canadian rivers) (Howarth et al., 1996). The amount of nutrients leaving the watershed often represents as much as twice these figures, because very effective retention processes within the drainage network of large river systems, including their riparian zones and stagnant annexes, eliminate or immobilise a sig-

0048-9697/99/$ - see front matter 0 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 ( 9 9 ) 0 0 3 2 7 - 7

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depends on the urban population density of the watershed (presently between 50 and 400 inhabitants/km2 in most of Western Europe). Available data on per capita release rate of nutrient since the last century (Fig. 1) show that the specific nitrogen load did not deviate a lot from the value of 10-15 g N/inhab/day, close to the physiological excretion rate cited by Verbanck et al. (1994). For phosphorus, data close to the physiological emission (1-1.5 g P/inhab/day) are found until the 1960s, when the introduction of polyphosphate containing washing powders resulted in a threefold increase of the per capita load (Fig. 1). A progressive reduction is observed during recent years following the substitution of polyphosphates by other sequestering agents in washing powders. The example of Switzerland, where polyphosphate was banned in 1986, is spectacular from this respect (Rapin et al., 1995). As for industrial nutrient release, current values of specific pollution loads (expressed by unit

nificant fraction of the nitrogen and phosphorus load discharged into surface waters before it reaches the sea (Billen et al., 1991; Howarth et al., 1996). Nutrients are brought into rivers from both non-point sources (mainly soil leaching) and point sources (domestic and industrial waste water discharge). Soil leaching in areas of modern intensive agriculture under temperate climate, can lead to nitrogen export fluxes as high as 5000 kg N/km2/year, while phosphorus exportation generally stays below 50 kg P/km2/year (Howarth et al., 1996). Before the relatively recent general use of chemical fertilisers (around 19501, nitrogen leaching should not have been higher than approximately 500 kg N/km2/year. Thus, data on nitrate concentration in the river Seine upstream from Paris at the end of the 19th century (Naves et al., 1991) show a diffuse nitrogen load of approximately 400 kg N/km2/year. Domestic contributions to the nutrient budget of river systems 2o

-

1

specific nitrogen load

I

1880

1

04 1880

1900

1920

1940

1960

1980

0

specific phosphorus load

1900

1920

2000

I

I

1940

1960

I

1980

2000

years

Fig. 1. Records of daily per capita load of nitrogen (a) and phosphorus (b) in domestic raw wastewater since the end of the 19th century. (1) Wien, 1895 (Petermann, 1895); (2) Frankfurt, 1949 (Imhoff, 1963); (3) OCDE, 1970; (4,5) Germany (NUT-Task Team Paris convention, 1991); (6) Brussels, 1986 (Verbanck et al., 1994); (7) Belgium, (AR 23 jan 1974) and (DETIC-TRACGRAS for the 1990s); (8) France (Journal Officiel, 1991); (9) Paris, 1994 (Servais et al., in press).

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52

45

cal literature of the 19th century (Anon., 1765; Figuier, 1872; Laboulaye, 1891; Privat-Deschanel and Focillon, 1908; Briavoinne, 1939; Daumas, 1968). These descriptions allowed us to establish complete input-output budgets of the processes, or at least to estimate the loss of organic matter during washing or rinsing phases. A few examples are provided in Table 2. Our analysis has been restricted to those industrial sectors assumed to have represented the major sources of organic matter and nutrient pollution of surface waters in Western Europe: tannery, hat-trade and felt industry, cotton and wool bleaching and dyeing industry, clothes washing, glue and gelatine production, candle and soap production, paper industry, sugar refinery and brewery. For many of these sectors, the fabrication processes used at an already industrial scale in the second half of the 19th century, were still nearly identical to those in use several centuries before, on a cottage industry scale. These data on specific pollution loads may be combined with productivity figures (e.g. the amount of products handled by one artisan in a

products delivered) are legally stated for taxation purposes. Values defined by the French Law (Journal Officiel, 1975) and used by the Water Authorities are given in Table 1 below. Much more difficult to evaluate is the pollution load caused by industrial activities during historical times. In this paper we report estimates of the amount of organic matter and associated nutrients released by some major industrial processes in use during the second half of the 19th century in Western Europe. On the basis of these estimates, we try to make use of available production and employment statistics to evaluate the significance of the industrial load discharged into some river systems compared with the nutrient contamination caused by other sources one century ago. 2. Methods

The approach presented here is based on a careful examination of the available description provided in full quantitative details by the techni-

Table 1 Estimated specific raw pollution loads and productivity figures for some industrial processes as in use in the second half of the 19th century and in the 1980s Industrial sector

Tannery Felt industry Textile bleaching Textile dyeing Laundry Grease and oil ind. Soap industry Glue and gelatine Paper industry Sugar industry Brewery Dairy industry Other food ind.

Production unit

kg Skin kg Skin kg Textile kg Textile kg Linen kg Product kg Product kg Product kg Pulp kg Beets hl Beer hl Milk Worker-day

Spec. poll. load" (inheq/unit)

Productivityb (unit/worker-day)

Pollution index (inheq/worker-day)

1880

1980

1880

1980

1880

1980

2.5 1.2 4 35 0.5 5 0.9 140 15 0.1 35

0.9

40

125 25 20 175 5 300 110 4200 450 20 105

34

0.25 0.1 0.05 140 1 0.1 30 7.5 150

50 22 5 5 10 60 130 30 30 200 3

10 340 265

430 6000 3 12 1

2.5 34 13 430 600 90 90 150

"Original data, expressed either as 'oxidisable matter' (for modern specific pollution load, Journal Officiel, 1975) or as organic matter (for our estimates of 19th century ancient pollution load, see Table 2), were converted into inhabitant equivalents, defined as a daily release of 54 g oxidisable matter, 20 g organic carbon, 12.5 g total N, 1.25 g total P. bDerived from national economical statistics (INS, Belgium) providing total industrial production and employment by sectors, assuming 300 working days per year.

46

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52

day) to provide a measure of the pollution generated by worker-day. Productivity estimates for a given period were obtained from general (whole country) industrial statistics, by dividing the total production of a given industrial sector by the number of workers employed in that sector.

3. Results and discussion

Table 1 compares the estimated specific raw pollution loads in the mid-19th century, with the current values for the corresponding industrial

sectors. For some activities (like brewery) for which no basic technological changes occurred, 19th century and modern values (expressed as raw pollution, i.e. before waste-water treatment process) are found to be rather similar, which provides some confidence in the method used. For others (like dyeing, bleaching or tannery), ancient specific pollution was much higher, sometimes by more than one order of magnitude, owing to the traditional technology used, which often- involved long maceration in- plant decoctions, animal excrement, blood, etc., followed by ample rinsing in running water. The estimations of late-19th century and pre-

Table 2

Input-output analysis of selected ancient industrial processes from 19th century technical literature Operations

Reagent added

(a) Wool bleaching Washing-rinsing cycles successively with soap, soda, and sulphur dioxide + sunlight exposition

(For 1kg raw wool) 30 g soap (loss of raw material amounts to 3 6 ~ 4 5 % )

(b) Cotton bleaching Washing-rinsing cycles successively with lime or soda, sulphuric or chlorhydric acid, hypochlorite

(For 1kg raw wool) (loss of raw material amounts to 5 ~ 1 5 % )

(c) Andrinople Red dyeing Washing with lime Sheep excrement bath, then drying Oil bath, then drying Degreasing by washing-rinsing Gall impregnation Alum application Madder dying Reviving: boiling with soda, oil and soap Brightening: boiling with tin salts, soap and Nitric acid; rinsing

(For 1kg cotton stuff) 300 g excrement + lime 100 g vegetal oil + lime Soda lime 250 g gallnut Madder-root + animal blood, 500 g Soda, 50 g oil and 100 g soap 150 g soap, tin salts, nitric acid Total

(d) Tannery Soak Depilation Manual scraping in flowing water Maceration in acid baths for 6 months Maceration with tan for 1year Rinsing

(For 1kg raw fresh skins) Immersion for 1-2 days in flowing water Maceration in lime water for 2-3 months ( 1 0 ~ 2 0 %weight loss) Fermented barley and excrement decoction 800 g tanner’s bark (mostly recycled)

Loss as organic matter in waste water (g)

400

100

300 100

500 150 150 1450

?

?

Total

> 50

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52

sent productivity values we could obtain from national statistics are gathered in Table 1, as well as the corresponding values of the pollution caused by worker-day. These figures represent raw pollution rate, as they do not take into account the effect of any purification treatment applied to industrial effluents before their discharge into surface water. Today, this reduction is considerable and often exceeds the abatement obtained for domestic waste-water treatment. Even by the mid-19th century, some reduction of organic and nutrient pollution should have occurred through settlement in wastewater stabilisation ponds allowing an easier management of waste discharge into the rivers. These ponds were of common use and often became compulsory

47

during the second half of the 19th century (Onclincx, 1991). The load abatement realised by such stabilisation ponds is generally excellent ( > 70%) for suspended and organic matter, but rather limited (20-30%) for total nitrogen and phosphorus (Racault et al., 1993). In our estimation of pre-industrial loadings, we used the conservative assumption of a maximum of 50% abatement of the nutrient loads. The sector-specific pollution indexes of Table 2 can be directly used to evaluate the order of magnitude of the industrial pollution load from a worker census by industrial sectors when the latter is available for a given watershed. We applied this approach to two contrasting situations: the Zenne river system (a fifth-order tributary of the

Table 3 Estimated effective industrial, domestic and total loading to the Zenne river basin (1225 km2) in 1897 and 1986

1897

1986

(a) Industrial and domestic organic loading (lo3 inhab-equivalent) Industrial load (lo3 inhab-equ) Dairy industry Other food industries Brewery Sugar industry Chemistry Paper industry Soap industry Grease, candle and oil factories Linen washing Textile industry Felt and hat factories Tannery Total industrial load ( l o 3 inhab-equ) Domestic load (lo3 inhab) Total point load (lo3 inhab-equ)

18 266 25 3 77 238 14 1

0 200 15 49 293 21 156 11 130 20 65

0 0 1

1460 880 2340

660 1540 2200

Nitrogen (kg N/km2 year) 1897 1986

Phosphorus (kg P/km2 year) 1897

1986

540 330 10 880

250 1380 30 1660

(b) Nitrogen and phosphorus loading (kg/km2 year) Industrial waste Domestic waste Diffuse from soil leaching Total

5440 3280 400 9760

2460 5740 1660 9860

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52

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river Scheldt, draining the city of Brussels, Belgium) and the Seine river at its crossing of Paris agglomeration (France). For the Zenne catchment, we used the detailed worker census of 1897 (Statistiques Gkn6rales de la Belgique. ‘Expos6 de la Situation du Royaume’, 1876-1900, INS, Belgium) to estimate the overall industrial load. For the purpose of comparison and check of the method, the same calculations were performed with the labour census of 1986 (Statistiques de I’Emploi et du Travail 1986, ONSS, Belgium). The results are presented in Table 3, together with estimations of the domestic load, based on population figures for urban centres larger than 2000 inhabitants. The figures we arrive at for the present period are quite similar to those derived from the detailed direct estimations by Wollast and Van Haute (cited by Verbanck, 19891, based on actual measurements of waste water release. On the other hand, domestic contribution is certainly overestimated in the 19th century figures, because application of domestic sewage as fertiliser onto cropland was still significant at that time. Our analysis thus strongly suggests that industrial pollution in the middlc of thc 19th ccntury should havc rcprcsented the largest part in the organic pollution of River Zenne. Note that the reverse is true today, with the domestic load representing about 70% of the total point pollution generated in the basin. Assuming a diffuse nitrogen and phosphorus load associated with soil leaching of approximately 400 kg N/km2/year and 10 kg P/km2/year in the 19th century, and considering the total area of the Zenne river catchment (1225 km2), industrial

discharges can be calculated to amount to more than 60% of the total nitrogen and phosphorus load to the river system. Corresponding figures for the 1986 situation indicate that industry contributes less than 25% for nitrogen and 3% for phosphorus, while domestic effluents represents 58 and 95% of the total nitrogen and phosphorus loading, respectively. These conclusions about the significance of industrial pollution in the 19th century in the Zenne basin is supported by independent data concerning the main sewer of Brussels (Van Ermengem, 1898; Petermann, 1899) (Table 41, showing that the nitrogen load carried in 1875 was higher than it is presently, and exceeded by at least a factor of four the domestic pollution generated by the population at that time. Clearly, industrial discharge should have represented the major share in the nitrogen pollution at the end of the 19th century. As a second case study, similar estimations were carried out for Paris agglomeration. From the census of workers by industrial sector (Archives du D6partement de la Seine, 1896) and the above mentioned specific pollution loads by workers-day, the pollution resulting from industrial activity in Paris agglomeration at the end of the 19th century was estimated (Table 5a). Grease and candle factories, paper industries and tanneries (Fig. 2) together represent the most important part of the industrial load from Paris agglomeration. The total figure represents at least three times the pollution load generated by the domestic sector as estimated from the population census for the same period [approx. 3.35 million inhabitants by 1900 with only 30% connected to a

Table 4 Nitrogen concentration and load in the Main Sewer of Brussels city by dry weather conditionsa Date

1875 1897 1898 1989

Population drained (inhabitants)

Total N conc. (mg N/1)

225000 310000 325000 355000

112 69 52 43

Flow

N loading

(m3/day)

t N/day

100000 100000 100000 98 000

11.2 6.9 5.2 4.2

Authors inhab-equ

% domestic

1120000 690 000 520 000 420 000

20 45 62 85

Petermann, 1899 Van Ermengem, 1898 Petermann, 1899 Verbanck, 1989

“Because this sewer collects many small streams forming the primitive waste-water disposal system of the city from the Middle Ages on, its flow is rather independent on the pollution load and has remained nearly unchanged. Nitrogen concentration and loading, however, increased regularly.

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52

sewer system (Mouchel et al., 199811. Even if the urban pollution from cities located upstream in the Seine catchment is neglected, industrial activity should have represented at least 35% of total N and 60% of total P delivered by the river Seine, while the present day figures (Billen et al., 1998) show the predominant share of diffuse agricultural sources for nitrogen, and of domestic sources for phosphorus (Table 5b). 4. Conclusion

The results of the above investigations, carried

49

out in close collaboration between historians and hydrobiologists, reveal the importance of organic matter and nutrient contamination of surface water by industrial activities during the middle of the 19th century. Sectors like candle factories, paper production, leather manufacture, which make use of highly polluting processes, were growing rapidly at that time, owing to an increasing demand, not only for domestic consumption, but mostly for other sectors of the industry. Contrarily to the common view expressed, e.g. by Meybeck et al. (19891, industrial pollution thus preceded, rather than followed, domestic pollution in West European countries. Owing to this

Table 5 Estimated effective industrial, domestic and total loading to the Seine river basin (65 730 km2) in 1896 and 1991-1994

1896

1991-1994

(a) Industrial and domestic organic loading (lo3 inhab-equivalent) from Paris agglomeration Industrial load (lo3 inhab-equ) Brewery Sugar industry Other food industries Chemistry Paper industry Soap industry Grease, candle and oil factories Linen washing Textile industry Felt and hat factories Tannery Total industrial load (lo3 inhab-equ) Domestic load (lo3 inhab) Total point load (lo3 inhab-equ)

70 50 850 50 1960 70

3780 1005a 5120

195b 7540b 7735

Nitrogen (kg N/km2 year) 1896

Phosphorus (kg P/km2 year) 1991~1994~

(b) Nitrogen and phosphorus loading (kg/km2 year) for the whole Seine catchment 265" 73 Industrial waste 95" 672 Domestic waste Diffuse from soil leaching 400 1150 Total 760 1895

1896

1991~1994~

27" 10" 10

29 140 11 180

47

"Maximum estimate, corresponding to 30% of total population in the Seine department (3 350000 inhab.), taking into account the known rate of connection to the sewer system (Mouchel et al., 1998). bAESN census of direct discharges by industries and by municipal waste water treatment plants. Paris agglomeration only. dAfter the budget calculated by Billen et al. (1998).

50

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52

Fig. 2. The tanneries along the river Bievre, South of Paris, by the middle of the 19th century. This picture, reproduced from ‘Les Merveilles de l’Industrie’, 2nd volume (Figuier, 1872), is illustrative of the severe impact of proto-industrial activities on river ecosystems at the onset of the industrial revolution.

important and early pollution by the industrial sector, point discharge of nutrients into surface water may have been maximum at the turn of the 19th century, and have levelled off or decreased since then. These considerations allow new insights into past trends of coastal eutrophication. Evidence for tracing back long-term variations of coastal

eutrophication is obviously scarce. For the continental coastal zone of the North Sea, however, some indications exist, showing on the one hand a clear increasing trend of winter nitrate concentration and flagellates blooms since 1970 (Radach et al., 1990; Cad6e and Hegeman, 1991; Lancelot et al., 19971, but also the occurrence by the end of the 19th century of blooms of Phaeocystis of the

G. Billen et al. /The Science of the Total Environment 243/244 (1999) 43-52 200

P m

‘El

51

1

I

Marsdiep (

0

T

e

x

e

l

F

1 1890

1900

1970

1980

1990

2000

years

Fig. 3. Observed duration of Phaeocystir blooms (periods with more than 1000 cells/ml) along the Belgian (open symbols) and Dutch (closed symbols) coastal zones since 1880. Data from CadCe and Hegeman (1991) and Lancelot et al. (1997).

same duration and intensities as observed recently (Grossel, 1985; Cad6e and Hegeman, 1991) (Fig. 3). Similarly, in the Northern Adriatic Sea, although the eutrophication related ‘Mare Sporco’ events have been obviously increasing in frequency and intensity since the 1970s (Justic et al., 19871, a large number of records of similar events have been found in the literature between 1872 and 1931 (Marchetti, 1991). Collectively, the available information suggests that there might have been a wave of coastal eutrophication before the one recently observed. Some authors have concluded that other factors than nutrient enrichment, e.g. long-term climatic variations, are primarily responsible for the observed trends (Owens et al., 1989). Our work presents an alternative explanation by showing that nitrogen and phosphorus delivery from densely industrialised catchments might have been at a maximum in the second half of the 19th century, and contributed to the first wave of coastal eutrophication suggested by retrospective data. Variations of the retention capacity of the drainage network, particularly with respect to non-point sources of nitrogen, may also have contributed to the complexity of the response of coastal systems to the changes in land use and human practices in West-

ern European watersheds over the last two centuries. Acknowledgements

This work has been funded in the scope of the Belgian Global Change Programme (SSTC, Federal Ministry of Science Policy), the EC-Environment Programme (‘BINOCULARS’ Project) and the French CNRS PIREN-Seine programme. References Anon. Encycloptdie ou Dictionnaire RaisonnC des Sciences, des Arts et des MCtiers. Neuchgtel, 1765 Billen G, Lancelot C, Meybeck M. N, P and Si retention along the aquatic continuum from land to ocean. In: Mantoura RFC, Martin JM, Wollast R, editors. Ocean margin processes in global change. John Wiley and Sons, 1991: 19-44. Billen G, Garnier J, Meybeck M. Les sels nutritifs: l’ouverture des cycles. In: Meybeck M, de Marsily G, Fustec E, editors. La Seine en son bassin: fonctionnement Ccologique d’un syst2me fluvial anthropisC, ch. 12. Paris: Elsevier, 1998: 531-566. Briavoinne N. L’industrie en Belgique. Causes de dtcadence et de prospCritC. Sa situation actuelle. Bruxelles, 1939. CadCe GC, Hegeman J. Historical phytoplankton data of the Marsdiep. Hydrobiol Bull 1991;24:111-188. Daumas A. Histoire GCnCrale des Techniques. Paris, 1968.

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Figuier L. Les Merveilles de 1’Industrie ou description des principales industries modernes. Paris: Furne, Jouvet et Cie, 1872. Grossel H. Le milieu marin: Un milieu vivant et fluctuant: Perception par les populations littorales du Nord de la France d’un phCnomkne planctonique caractCrisC. Cah Centre Ethno-Techno1 Milieu Aquatique 1985;2:93-97. Howarth RW, Billen G, Swaney D et al. Regional nitrogen budgets and riverine N and P fluxes for the drainages to the North Atlantic ocean: natural and human influences. Biogeochemistry 1996;35:75-139. Imhoff K. Taschenbuch der Stadtentwasserung. Miinchen: Oldenbourg Verlag, 1963. Journal Officiel. ArretC du 28 octobre 1975. Annexe 1:Tableau des coefficients sptcifiques de pollution pour l’estimation forfaitaire. Paris: Journal Officiel de la RCpublique Frangaise, 7 nov 1975. Justic D, Legovic T, Rottini-Sandrini L. Trends in oxygen content 1911-1984 and occurrence of benthic mortality in the northern Adriatic Sea. Estuarine Coastal Shelf Sci 198725x435-445. Laboulaye C. Dictionnaire des arts et manufactures et de l’agriculture. Paris, 1891. Lancelot C, Rousseau V, Billen G, Van Eeckhout D. Coastal eutrophication of the Southern Bight of the North Sea: assesment and modelling. Sensitivity of North Sea, Baltic Sea and Black Sea to anthropogenic and climatic changes. NATO-AS1 Series, 2 Environment, Vol. 27. Berlin: Springer Verlag, 1997:439-453. Marchetti R. Algal blooms and gel production in the Adriatic Sea. In: Barth H, Fegan L, editors. Eutrophication-related phenomena in the Adriatic Sea and in other Mediterranean coastal zones. Brussels: CEC, DG. XII, 1991. Meybeck M, Chapman DV, Helmer R. Global freshwater quality: a first assessment. Global environmental monitoring system. WHO & UNEP, Blackwell Reference, 1989. Mouchel J-M, Boet P, Hubert G, Guerrini M-C. Un bassin et des hommes: une histoire tourmentCe. In: Meybeck M, de Marsily G, Fustec E, editors. La Seine en son bassin: fonctionnement Ccologique d’un systkme fluvial anthropisC, ch. 2. Paris: Elsevier, 199877-126. Naves J, Bousquet G, Leroy P, Hubert P, Vilagines R. Evolution de la qualit6 de l’eau de la Seine B Ivry-sur-Seine (France) de 1887 B 1986. Comptes Rendus de 1’Atelier

International UNESCO/AISM/ENIT: Application des modkles mathkmatiques B 1’Cvaluation des modifications de la qualit6 de l’eau. Tunis: ENIT, 1991:35-44. Onclincx F. Les entreprises de blanchiment, de teinture et d’impression sur Ctoffes B Anderlecht, Forest et Uccle entre 1830 et 1870. Approche du problkme de la pollution industrielle de la Senne et de ses affluents. Thesis. Belgium: University of Brussels, 1991. Owens NJP, Cook D, Calebrook M, Hunt H, Reid PC. Long term trends in the occurrence of Phaeocystis sp. in the north-east Atlantic. J Mar Biol Assoc UK 1989;69:813-821. Petermann A. Le sewage de la ville de Vienne. Bruxelles: Ministkre de 1’Agriculture et des Travaux Publics, 1895. Petermann A. Analyse du sewage de Bruxelles. J SOCAgricole Brabant 1899:733. Privat-Deschanel and Focillon. Dictionnaire GCnCral des Sciences ThCoriques et Appliqutes. Paris, 1908. Racault Y, Boutin C, Seguin A. Waste stabilization ponds in France: a report of fifteen years experience. International Conference on Waste Stabilization Ponds. Oakland: IAWQ, 1993. Radach G, Berg J, Hagmeier E. Long-term changes of the annual cycles of meteorological, hydrographic, nutrient, and phytoplankton time series at Heligoland and at LV Elbe 1 in the German Bight. Cont Shelf Res 1990; 10:305-328. Rapin F, Blanc P, Pelletier JP, Balvay G, Gerdeaux D, Corvi C, Perfetta J, Lang C. Impacts humains sur les Ccosystkmes lacustres: exemple du LCman. In: Pourriot R, Meybeck M, editors. Limnologie GtnCrale, ch. 28. Masson, 1995: 806-840. Servais P, Garnier J, Demarteau N, Brion N, Billen G. Supply of organic matter and bacteria to aquatic ecosystems through waste water effluents. Water Res 1999 (in press). Van Ermengem L. Assainissement des villes d’Ostende, Mariakerke et Middelkerke. Rapport prCsentC le 19.10.1897 B la Commission nommCe par le Gouvernement, Gand, 1898. Verbanck M. L’Cpuration des eaux B Bruxelles: caractCrisation des charges polluantes. Belgium: Forum, University of Brussels, 1989. Verbanck M, Vanderborght J-P, Wollast R. Major ion content of urban wastewater: assessment of per capita loading. J Water Pollut Cont Fed 1994;61:1722-1728.