Analysis of phosphorus concentration in a subtropical river basin in southeast China: Implications for management

Ocean & Coastal Management 81 (2013) 29e37

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Analysis of phosphorus concentration in a subtropical river basin in southeast China: Implications for management Jinliang Huang a, b, *, Jie Lin b, Yuzhen Zhang c, Qingsheng Li b, Huasheng Hong a, b a

Coastal and Ocean Management Institute, Xiamen University, Xiamen 361005, China Environmental Science Research Center, Xiamen University, Xiamen 361005, China c Fujian Research Academy of Environmental Sciences, Fuzhou 350003, China b

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 16 October 2012

The study analyzed the factors that led to high total phosphorus (TP) concentrations in the Jiulong River Basin, a subtropical basin with intensive agricultural activities. The results showed that the TP in the river basin originated mainly from non-point sources. Livestock (including poultry) breeding was the main contributor, accounting for 35% of the total load in 2003 and 43% in 2007. The close correlation between TP load and environmental capacity explained the spatial variability of TP concentration in the entire watershed. There was also significant correlation between flow and water quality from 2003 to 2007. Key areas with high concentrations of TP were further identified and evaluated. The results suggest that livestock breeding should be controlled to reduce the TP load. The water requirement for sustaining ecosystem functions should also be addressed. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction As one of the essential plant nutrients, phosphorus (P) in the natural environment is generally stable. However, urbanization and agricultural intensification have led to widespread P enrichment in surface waters, causing a wide range of environmental, social and economic problems at the regional and local levels (Withers and Jarvie, 2008). In the United States, freshwater eutrophication, which is caused by biological enrichment of surface waters and accelerated by anthropogenic inputs of P, remains one of the most pervasive surface water quality problems (Kleinman et al., 2009). The Nordic Algal Experiment Program showed that P is the only limiting factor in 80% of water bodies (OECD, 1989). In China, the use of large amounts of inorganic fertilizer to facilitate higher crop production is still common (Li and Zhang,1999). Nitrogen (N) and P, from excessive N and P fertilizer use, are discharged into the receiving water from the effect of rainfall and irrigation practices, causing eutrophication in the receiving water and an eventual loss of biodiversity in the aquatic ecosystem. In recent years, the occurrence of harmful algal blooms (HABs) and contamination of drinking water sources have been reported in many places in China (Huang et al., 2008). Riverine systems and associated watersheds are particularly vulnerable to pollution due to their proximity to population centers * Corresponding author. Coastal and Ocean Management Institute, Xiamen University, Xiamen 361005, China. Tel.: þ86 592 2182175. E-mail address: [email protected] (J. Huang). 0964-5691/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ocecoaman.2012.09.016

and sensitivity to land use changes, which are hastened by urbanization (Malmqvist and Rundle, 2002; Walsh et al., 2005). Although P input enriches aquatic biodiversity (Odum et al., 1979; Niyogi et al., 2007), excessive concentrations of P have been reported to pose threats to the normal functioning of the river ecosystems (Smith, 2003; Hilton et al., 2006). The Jiulong River Basin plays a vital role in the human and ecological health of the region (Huang et al., 2012). Annual flow from the Jiulong River, which discharges into the Jiulong River estuary and Xiamen-Kinmen coastal waters is about 12 billion m3. The total phosphorus (TP) concentration in the Jiulong River, however, has exceeded the national surface water environmental quality standard (GB3838-2002) in recent years (SEPA, 2002). Sixteen HABs have been reported in the Jiulong River estuary and the Xiamen-Kinmen coastal waters during the period 1997e2003 (Office of Water Source of Fujian, 2004). The average TP concentration in the Jiulong River is higher than in the Taihu Lake, which is extremely polluted, and most rivers in Fujian Province (Environmental Monitoring Bureau of China, 2008). Unfortunately, recent observations have shown an increasing trend in TP concentrations in specific areas in the Jiulong River Basin. The relationships between P supply, ambient P concentration in the water column and ecological responses are complex. In addition, residence times of P can fluctuate widely, and the capacity of riverine ecosystems to assimilate P varies both spatially and temporally (Fisher et al., 1998; Edwards et al., 2008). In view of this, the delivery and cycling mechanisms of P were not

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J. Huang et al. / Ocean & Coastal Management 81 (2013) 29e37

considered in this study. Instead, the main focus was directed in identifying and analyzing the factors that led to high concentrations of TP using a GIS-based model and the empirical export coefficient. The objectives of this study were three-fold: (1) to identify the pollution sources of TP for the main counties (districts) within the watershed; (2) to locate areas with high concentrations of TP; and (3) to put forward suggestions for sustainable watershed management.

Since 1985, 17 gage stations had been set up to regularly monitor variations in water quality. Eleven stations are located in the North River and six stations are located in the West River. Eleven hydrological stations had also been set up to monitor changes in water quantity in the Jiulong River Basin. 3. Materials and methods The methods used for the comprehensive analysis of P concentrations in the Jiulong River Basin in terms of variations in water quantity and quality, as well as environmental capacity are described below.

2. Description of the study watershed The Jiulong River Basin, situated in southeast China, is the second largest watershed in Fujian Province, covering 1.47  104 km2 (116 460 5500 w118 0201700 E, 24 230 5300 w25 530 3800 N) (Fig. 1). It has a subtropical monsoon climate. The North River and West River are the two biggest branches of the Jiulong River. The annual stream flow of the North River, as measured at its outlet at the Jiulong River estuary at Punan station is 8.2 billion m3, while for the West River, the annual stream flow measured at its outlet at Xiamen-Kinmen coastal water at Zhengdian station is 3.7 billion m3. More than 5 million residents of Xiamen, Zhangzhou and Longyan use the Jiulong River as their water source for drinking, as well as industrial and agricultural use (Huang and Hong, 2010). Administratively, it comprises six counties (districts), namely, Zhangzhou (district), Xinluo (district), Zhangping, Changtai, Pinghe, and Nanjing, and a large part of Hua’an and Longhai (these eight counties/districts were involved in this study), and a small part of nine counties including Shanghang, Liancheng, Yongding, Datian, Yongchun, Anxi, Zhangpu, Haicang and Tong’an.

3.1. Overall evaluation of water quality A single factor index method, expressed by Equation (1), was used to assess TP concentration for each segment and gage station of the Jiulong River Basin based on the national surface water environmental quality standard (GB3838-2002) (SEPA, 2002).

Pi ¼

Ci Si

(1)

where Pi is the environmental quality index; Ci is the concentration of index i in the environment; and Si is the environmental quality standard. Water quality data for the 17 gage stations in the Jiulong River Basin were taken from Water Quality Monitoring Reports (Zhangzhou Environmental Protection, 2000e2008; Longyan Environmental Protection, 2000e2008).

Fig. 1. Location of the study watershed.

J. Huang et al. / Ocean & Coastal Management 81 (2013) 29e37

3.2. TP sources

31

sources and the sources of the required data are summarized in Table 1.

Six sources of TP load in the Jiulong River Basin were estimated and analyzed, namely: industrial wastewater (IW), soil erosion (SE), domestic wastewater (DW), domestic solid waste (DSW), livestock (including poultry) breeding (LPB) and farmland runoff (FR). The method of calculating TP load from these six

3.3. Environmental capacity for TP The data for estimating the environmental capacity of TP was obtained from Zhang (2009). It should be noted that the

Table 1 Methods and data sources used to quantify the TP load from six sources. TP sources

Definitions of the TP sources

Industrial wastewater (IW)

Here, IW is defined as the wastewater produced by industrial productive activities.

Soil erosion (SE)

Here, SE is defined as the wearing away of the land surface mainly driven by rainfall that detach and remove soil (as well as nutrients in soil, such as P). Here, DSW is defined as all types of solid waste generated by households.

Domestic solid waste (DSW)

Farmland runoff (FR)

Here, FR is defined as the runoff caused by rainfall occurred in farmland which carries the fertilizer and pesticide accumulated in farmland and then discharge into the receiving waters.

Livestock & poultry breeding (LPB)

Here, LPB is defined as the waste from livestock & poultry breeding production, mainly including the excrements.

Domestic wastewater (DW)

DW is defined as the wastewater from residential settlements and services which originates predominantly from the human metabolism and from household activities.

Calculation methods LIW ¼

n P

Fi  Qi  r, where LIW is the pollutant losses

i

from point source pollution; F is the flow rate for sewage outlet I (m3/s); Q is the concentration of pollutants monitored at the sewage outlet I (mg/L); and r is a loss coefficient for physical, chemical and biological removal of nutrients during the transportation process. LSE ¼ a$CSkt $Xkt $ER$SDR, where LSE in kg/km2 is the particulate P load in the river; a is a unit conversion constant; CSkt in & is the particulate P concentration in the soil; Xkt in t/km2 a is the average annual soil loss amount; ER is the enrichment ratio; and SDR is the sediment delivery ratio. LDSW ¼ ½ðPt  ft  DDW Þ  Ct þ ðPc  fc Þ  Cc   R=1000, where LDSW in t is the TP load discharged from domestic solid waste; Pt and Pc in 10 thousands are the population in the town and in the countryside; ft and fc in kg/cap a are annual solid wastes produced per person in the town and the countryside, namely 440 and 180; DDW in t is the amount of solid waste disposal; Ct and Cc in mg/g are the TP concentration of domestic waste in the town and in the countryside; and R is loss rate of TP.

Pm LFR ¼ j ¼ 1 Ej Aj Sj Tj Oj Lj Fj Rj , where LFR is the loss of P discharged into the receiving water; j represents the jth type of farmland; m is the total number of farmland types; Ej is the P concentration from type j farmland; Aj is the area of farmland occupied by type j; Sj is the slope correction factor of type j farmland; Tj represents the farmland correction factor of type j farmland; Oj is the soil correction factor of type j farmland; Lj is the rainfall correction factor of type j farmland; Fj is the fertilization correction factor of farmland occupied by type j; and Rj represents the rate of loss of jth farmland. Pn LLPB ¼ i ¼ 1 Ni  fi  R=1000, where LLPB in t is the TP load discharged into the river as a result of livestock breeding, and livestock includes poultry, pigs and cattle; Ni is the amount of the ith livestock; fi in kg/cap a is the annual TP emission factor of the ith livestock; and R is the loss rate of TP.

LDW ¼ f½ðPt  Wt  DÞ  Ft þ Ds  Ftt   Rt þ Pc  Wc  Fc  Rc g  365  105 , where LDW in t is the TP load discharged from domestic wastewater; Pt and Pc in 10 thousands are the population in the town and in the countryside respectively; Wt and Wc in L/cap d are daily composite water per capita in the town and in the countryside; Ds in 10 thousands of tons is the amount of sewage which goes to a sewage treatment plant; Ft, Fc, Ftt, in mg/L are the TP concentration in composite water in the town, in the countryside and in the town after treatment; and Rt and Rc are the loss rates of TP from sewage in the town and in the countryside.

Methods reference

Data sources

(Chinese Academy on Environmental Planning, 2003; Xiamen University, 2005)

China Pollution Source Census of 2007 (SEPA, 2007)

(Wischmeier and Smith, 1978)

Annual precipitation, soil properties, land use and Digital Elevation Model (DEM) of study watershed

(Chinese Academy on Environmental Planning, 2003; Xiamen University, 2005)

Pt and Pc came from the Committee for Compiling Zhangzhou County Annals (2004 e2008) and the Committee for Compiling Longyan Annals (2004e2008); DDW in 2003 was from Xiamen University (2005); and DDW in 2007 was from China Pollution Source Census of 2007 (SEPA, 2007) A in 2003 was from Xiamen University (2005) and the 2007 data was from China Pollution Source Census of 2007 (SEPA, 2007)

(Chinese Academy on Environmental Planning, 2003; Xiamen University, 2005)

(Chinese Academy on Environmental Planning, 2003; Xiamen University, 2005)

(Chinese Academy on Environmental Planning, 2003; Xiamen University, 2005; Jiangsu Environmental Science Research Institute, 2008)

Ni came from the Committee for Compiling Zhangzhou County Annals (2004 e2008) and the Committee for Compiling Longyan Annals (2004e2008), together with some data from the survey Wt and Wc came from the Water Resource Report in Zhangzhou and Longyan, Fujian Province (Office of Water Source of Fujian, 2007); Rt and Rc were from Jiangsu Environmental Science Research Institute (2008); D in 2003 was from Xiamen University (2005) and that in 2007 was from the China Pollution Source Census of 2007 (SEPA, 2007)

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environmental capacity was calculated using the Qual2k model (Brown and Barnwell, 1987). Twenty segments and six segments were established in the North River and West River, respectively, and the environmental capacity for each segment was calculated based on the Qual2k model. 3.4. Water quantity The data on water quantity for each hydrological station in the Jiulong River Basin from 2003 to 2007 were obtained from the Office of Water Source of Fujian (2007). Based on the data, a hydrographic analysis was conducted to determine the seasonal correlation between TP concentration and water quantity. 4. Results and analysis Fig. 2. Annual average of TP concentrations in gage stations of the Jiulong River Basin from 2003 to 2008.

4.1. Overall observation of TP concentration

was exceptionally high, far beyond the Class V surface water standard (SEPA, 2002). Also in 2003, the TP concentrations for B4 in January, together with X1 and X5 in May, were quite high, which is close to the Class III surface water standard. The highest TP concentrations in B4, B7, B8 and X3 appeared during the dry period, whereas B2, B3, B10, X1, X2, X4, X5 and X6 during the wet period, but all other gage stations were in the level period. Compared with TP concentrations in 2003, there was an increase in all gage stations in 2007, especially during the wet period. TP concentrations increased in B2, B4, B8, B9, X3, X4, and X5 during all periods, whereas in B5, B6 and B11, TP concentrations decreased during all periods, meeting or close to the Class II surface water standard. TP concentrations in X1, X2 and X6 decreased during the dry period but increased in the level and wet periods. The highest TP concentration in B6 and X1 appeared in the level period and in B3, B5, B11, and X6 in the wet period, while in the dry period, the highest TP concentrations occurred in the remaining 12 gage stations.

Table 2 shows the overall situation concerning annual average TP concentration exceeding the water quality standards for each gage station of the Jiulong River Basin from 2003 to 2008. As shown in Table 2, TP concentration exceeded the standard 21 times in the 17 gage stations during the period 2000e2008. The water quality in gage station B2 exceeded the standard in 100% of the samples. Slightly better was B4 with 44% of the samples exceeding the standard. The gage stations B9, B10, X5 and X6 exceeded the standard twice, during 2000e2008. When comparing among the years, it was observed that in 2004, five gage stations exceeded the standard; 2003 had four, while 2007 and 2008 had three each. From 2003 to 2008, annual TP concentration in the Jiulong River Basin met the national Class III surface water standard (TP < 0.2 mg/L). From Fig. 2, the largest contributor of TP in the Jiulong River Basin was B2. The TP concentration in the Jiulong River Basin increased from 2006 to 2008, although TP concentration fluctuated from 2003 to 2006. It should be noted that TP concentration of B4, B5, B6, X1 and X5 increased largely from 2003 to 2004 and all gage stations increased slightly from 2004 to 2006. For B2, the greatest increment of TP concentration occurred from 2007 to 2008, whereas for B4, it was from 2006 to 2007. Fig. 3 presents the TP concentrations in the North and West Rivers during the dry period (January and March), the level period (September and November, stream flow is in its normal condition), and the wet period (May and July) in 2003 and 2007. It can be seen that TP concentration in B2 during all periods and X6 in May 2003

4.2. Analysis of TP sources In this study, analysis of the sources and the proportions contributed by soil erosion, farmland runoff, livestock breeding, domestic wastewater and solid waste was made. In addition, point source (PS) TP pollution from industrial wastewater and sewage discharged into the river through a sewage treatment plant was

Table 2 Overall situation concerning annual average TP concentration exceeds the water quality standard for each gage station of the Jiulong River Basin from 2003 to 2008. Gage stations

Water quality standards

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 X1 X2 X3 X4 X5 X6

Class Class Class Class Class Class Class Class Class Class Class Class Class Class Class Class Class

Ⅱ Ⅳ Ⅲ Ⅲ Ⅲ Ⅲ Ⅲ Ⅲ Ⅱ Ⅲ Ⅱ Ⅲ Ⅲ Ⅲ Ⅲ Ⅱ Ⅲ

2000

2001

2002

2003

2004

2005

2006

2007

2008

C

C

C

C

C

C

C

C

C

C

C

C

C

C C

C C

C

C C

Note: The water quality standard (SEPA, 2002) for each gage station is based on the water environmental function zoning results in the Jiulong River Basin.

C

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Fig. 3. Monthly average of TP concentration in 17 gage stations of the Jiulong River Basin; (a) and (c) represent the North River in 2003 and 2007; (b) and (d) represent the West River in 2003 and 2007.

investigated. Six sources of the TP load were identified and the contribution of each to the Jiulong River Basin was calculated and presented in Tables 3 and 4. Table 3 shows the order of the amount of the TP load in the whole watershed for 2003, namely, livestock breeding > soil erosion > domestic wastewater > farmland runoff > industrial wastewater > domestic solid waste. The livestock breeding source brought about 1091 t TP to the river, accounting for 35% of all TP sources, and was the main pollution source. Xinluo discharged 798.5 t TP into the river, accounting for 26% of the whole watershed, which made Xinluo the largest contributor of the TP load in 2003. Table 4 reveals that the order of the amount of the TP load in the whole watershed in 2007 was livestock breeding > domestic wastewater > soil erosion > farmland runoff > industrial wastewater > domestic solid waste. The contribution of livestock breeding had increased from 35% in 2003 to 42% in 2007 (1555.4 t TP). Xinluo was still the largest contributor in 2007, discharging 1033.2 t TP into the river, and accounting for 28% of the whole watershed load. The study showed that non-point source (NPS) and PS pollution accounted for 91% and 9% of the TP load in 2003, and 94% and 6% in 2007, respectively. The main sources of NPS for TP in the Jiulong River Basin were livestock breeding, domestic wastewater and soil erosion. Further analysis was carried out to identify the causes of high concentrations of these three sources.

4.2.1. Livestock breeding In the process of cattle, pig and poultry breeding, the animal wastes are normally returned to the field. Improper treatment and management of these wastes, however, can lead to substantial loss of P into the watershed. While studying the impact of livestock breeding on water quality of the Jiulong River Basin, Zeng et al. (2005) found that the fodder for hoggery was the main source of TP, accounting for 92.98e99.96%. Our field surveys also showed that local fodder could not support the entire animal husbandry in the area, and hence 80% of the fodder was being imported from outside. TP was thus imported at the same time with the fodder. It is important to note that the input of TP in the Jiulong River Basin exceeded its output, and consequently, a large amount of P remains in the field. Obviously, the animal wastes reused in the field posed TP stress to the farmlands. On the one hand, the unfavorable N:P ratio in most animal wastes often resulted in over-application of P for the crop (Sharpley et al., 1996). Moreover, the animal waste loads in the field in the Jiulong River Basin was larger than the average value for Fujian Province and the highest areas in the Jiulong River Basin was Xinluo and Zhangzhou (Xiamen University, 2005). The number of pig increased from 2003 to 2007, especially during the period 2006e2007, with an increase of 29%. As the number of cattle and poultry decreased and the number of pig

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J. Huang et al. / Ocean & Coastal Management 81 (2013) 29e37

Table 3 Sources and contributions of TP in the Jiulong River Basin in 2003. Area

Hua’an Nanjing Pinghe Zhangzhou Changtai Longhai Xinluo Zhangping Total

TP load (t)

Contribution (%)

IW

SE

DW

FR

LPB

DSW

Total

IW

SE

DW

FR

LPB

DSW

0.9 34.2 5.4 37.8 81.9 15.3 72.9 16.2 264.6

115.9 95.2 66.4 0.2 42.6 7.5 196 204.4 728.2

31.1 64.4 102.2 91.3 34.6 141.5 84.2 52.6 601.9

19.8 46.2 55.8 13.7 27.4 45.9 40.1 30.7 279.6

59.3 76.9 127.2 157.7 88.6 115.5 373 92.8 1091

8.7 17.4 27 17.4 9.1 36.6 32.3 14.7 163.2

235.7 334.3 383.9 318 284.1 362.3 798.5 411.4 3128.2

0.4 10.2 1.4 11.9 28.8 4.2 9.1 3.9 8.5

49.2 28.5 17.3 0.1 15 2.1 24.6 49.7 23.3

13.2 19.3 26.6 28.7 12.2 39.1 10.6 12.8 19.2

8.4 13.8 14.5 4.3 9.6 12.7 5 7.5 8.9

25.2 23 33.1 49.6 31.2 31.9 46.7 22.6 34.9

3.7 5.2 7 5.5 3.2 10.1 4.1 3.6 5.2

Note: Abbreviations as in Table 1; Zhangzhou refers to Zhangzhou district.

increased, pig raising formed an increasingly larger proportion of animal husbandry in the Jiulong River Basin, from 69% in 2003 to 87% in 2007 [using one pig as the base unit (SEPA and AQSIQ, 2001)]. Meanwhile, the TP in the river caused by livestock breeding in 2007 was 42% more than that of 2003. Tables 3 and 4 show that wastes from animal husbandry is the dominant source of TP load in the Jiulong River Basin. The TP load in the Jiulong River produced by animals increased from 1091 t in 2003, accounting for 35%, to 1555.4 t in 2007, accounting for 42.3%, which was consistent with the trend of animal husbandry development. The order in the amount of the TP load coming from livestock breeding in each county or district was Xinluo > Zhangzhou > Pinghe > Longhai > Zhangping > Changtai > Nanjing > Hua’an in 2003 and Xinluo > Zhangzhou > Zhangping > Longhai > Changtai > Nanjing > Pinghe > Hua’an in 2007. With the rapid development of livestock breeding, Xinluo became one of largest bases for pig breeding in the Jiulong River Basin, and thus was directly related to the water quality degradation of the river. Moreover, large-scale pig breeding in the Jiulong River downstream in Zhangzhou and Longhai caused the X5 gage station to slightly exceed the standard.

only two out of eight counties or districts, namely, Zhangzhou and Xinluo, have constructed wastewater treatment plants. However, even in Zhangzhou and Xinluo, the treatment rates were merely 24% and 54%, respectively. It is apparent that domestic wastewater had a significant impact on the water quality of the Jiulong River Basin. 4.2.3. Soil erosion At the county (district) level, the TP load from soil erosion in Longhai, Nanjing, Pinghe and Zhangzhou increased from 2003 to 2007, mainly due to higher rainfall in 2007. On the other hand, the TP load caused by soil erosion in Xinluo, Hua’an, Zhangping, Pinghe and Changtai has decreased. The spatialetemporal changes of soil erosion in the Jiulong River Basin from 2003 to 2007 were significantly related to variations in precipitation. Changes in land use/ cover were proposed as another cause. The high TP load in Hua’an, Nanjing and Pinghe is due to the intensive agricultural activities and the steep slopes and mountainous relief, which hastens soil erosion to occur. With regard to the TP load per unit area, the order was Xinluo > Hua’an > Zhangping > Pinghe > Nanjing > Changtai > in 2003 and Pinghe > Longhai > Zhangzhou Nanjing > Xinluo > Hua’an > Zhangping > Changtai > Longhai in 2007. It is noted that the TP load per unit area in Hua’an, Changtai and Xinluo was reduced from 2003 to 2007.

4.2.2. Domestic wastewater Domestic wastewater was the second largest source of TP in the Jiulong River Basin in 2007. The TP load produced by domestic wastewater and discharged into the river increased from 602 t in 2003 to 712 t in 2007. The TP in domestic wastewater comes from washing powder, cleaner and other detergents. It was reported that the TP concentration in washing powder was 5.03% twice that in pig fodder (Zhang, 2000). TP load in the Jiulong River introduced by domestic wastewater increased from 2003 to 2007. Specifically, the TP load produced by domestic wastewater increased in the town but decreased in the countryside, partly due to urbanization. In the Jiulong River Basin,

4.3. Environmental capacity for TP in the Jiulong River Basin The TP load and the environmental absorption capacity for TP at the county (district) level are illustrated in Fig. 4. The TP loads discharged into the river in 2003 and 2007 exceeded the environmental capacity for TP in the dry period (441.7 t) and the average environmental carrying capacity (519.5 t) in Xinluo. The TP loads in Nanjing and Zhangping were less than their average environmental capacity for TP, but more than that in the dry period. The TP loads in

Table 4 Sources and contributions of TP in the Jiulong River Basin in 2007. Area

Hua’an Nanjing Pinghe Zhangzhou Changtai Longhai Xinluo Zhangping Total

TP load (t)

Contribution (%)

IW

SE

DW

FR

LPB

DSW

Total

IW

SE

DW

FR

LPB

DSW

2.1 3.8 9.5 10.0 27.4 19.4 80.8 11.6 164.6

72.3 130.1 164.7 1.8 33.9 26.6 128.4 115.8 673.6

31.9 70.0 106.2 134.7 40.1 169.1 106.5 53.9 712.4

60.8 81.8 13.7 24.9 55.0 88.6 65.5 68.0 458.3

53.2 111.2 104.2 240.2 117.9 137.5 636.3 154.9 1555.4

6.8 11.0 19.0 5.1 9.6 37.9 15.7 7.3 112.4

227.2 407.9 417.2 416.6 283.9 479.0 1033.2 411.6 3676.6

0.9 0.9 2.3 2.4 9.7 4.1 7.8 2.8 4.5

31.8 31.9 39.5 0.4 11.9 5.6 12.4 28.1 18.3

14.1 17.2 25.5 32.3 14.1 35.3 10.3 13.1 19.4

26.8 20.0 3.3 6.0 19.4 18.5 6.3 16.5 12.5

23.4 27.3 25.0 57.7 41.5 28.7 61.6 37.7 42.3

3.0 2.7 4.6 1.2 3.4 7.9 1.5 1.8 3.1

Note: Abbreviations as in Table 1; Zhangzhou refers to Zhangzhou district.

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TP concentration was at the highest in the Jiulong River. The correlation might explain the cause of the HAB in February to March 2009, as precipitation for this period was only 75% of the normal, which might slow down the flow rate in the main river.

Fig. 4. Comparison of TP load and environmental capacity in the main counties or districts of the Jiulong River Basin.

Hua’an and Zhangzhou were less than the respective environmental capacity in the dry period. This result was in line with the monitoring result obtained from the gage stations for these years. For example, the TP concentration in Xinluo B2 exceeded the standard in all years. 4.4. The correlation between flow and TP concentration 4.4.1. Annual mean flow variation for key hydrological stations during 2003e2007 The correlations of the annual mean flow variation in the Punan station of the North River and the Zhengdian station in the West River with the annual average distribution of the TP concentration (the average value from the 17 gage stations during 2003e2007) were analyzed (Fig. 5). The annual mean flow in the North River and West River of the Jiulong River Basin dropped from 2003 to 2004, especially in the North River. The flow from both the North River and West River sharply increased from 2004 to 2006, and then decreased in 2007. As the flow decreased from 2003 to 2004, the TP concentrations increased. Five out of the 17 gage stations were found to exceed the standards in 2004, as shown in Table 1. It can be inferred that there is a strong correlation between river flow and TP concentration. For example, the TP concentration in the Jiulong River decreased as annual mean flow increased from 2003 to 2004, and then increased as annual mean flow decreased from 2006 to 2007. The lowest annual mean flow in both the North River and West River was observed in 2004, and this occurred when the

4.4.2. Monthly mean flow for key hydrological stations in 2003 and 2007 Monthly mean flow was further analyzed to determine the relationship between water quantity and TP concentration. Fig. 6 shows the monthly flow in Zhengdian, Punan, Zhangping, Longshan, Longmen, Maiyuan and Chuanchang stations in 2003 and 2007. The monthly flow in the seven hydrographic stations was greater in 2007 than in 2003. The increase in the rate of flow in the dry period and the level period was slight, whereas it was markedly high in the wet period. The TP concentrations in most gage stations during the three periods showed an increasing trend from 2003 to 2007. Take B8 for example, TP concentration increased in this station during all periods. However, the TP concentrations in different periods were not so significantly correlated with water quantity. The main reason is that NPS accounted for a large proportion of TP both in 2003 and 2007. Bowes et al. (2005) showed that in a catchment with high proportions of PS, the P input has an increased seasonal pattern, which is in agreement with this study; there was low proportion of PS and no seasonal pattern. 5. Implications to watershed management 5.1. Controlling TP pollution from sources Based on source contribution, livestock breeding was the largest source of TP load for five counties or districts, namely, Xinluo, Zhangping, Zhouzhou, Changtai and Longhai. On the other hand, soil erosion was the largest source of TP load for three counties, namely, Hua’an, Nanjing and Pinghe. The results suggest that livestock breeding requires greater management attention in order to reduce the TP load in Zhangzhou, Changtai, Longhai Xinluo and Zhangping, while soil erosion should be controlled in Hua’an, Nanjing and Pinghe. In addition, farmland runoff should be controlled in Hua’an and Changtai. It is also noted that in all eight counties/districts, the largest TP loads from domestic wastewater, agricultural land runoff and solid waste occurred in Longhai. Xinluo, on the other hand, was the largest contributor from two sources: livestock breeding and industrial wastewater. The largest TP load caused by soil erosion was in Pinghe. Therefore, in order to control the TP pollution caused by soil erosion, management measures should be put in place in Pinghe and Nanjing. Measures to reduce TP from livestock breeding should focus on Xinluo and Zhangzhou. In order to control TP pollution from domestic wastewater, agricultural land runoff and solid waste, management measures should also be put in place in Longhai, Zhangzhou, Nanjing and Pinghe. 5.2. Controlling TP pollution from livestock breeding

Fig. 5. Annual average of TP concentration versus annual mean flow in the Jiulong River Basin.

Livestock breeding was found to be the largest TP contributor in the Jiulong River Basin. At present, livestock breeding in the Jiulong River Basin includes both intensive animal production and “dispersed raising”; but the latter plays a dominant role. However, “dispersed raising” has a number of environmental disadvantages. For example, it produces greater pollutants in a larger area and it is almost impossible to build treatment facilities to reduce the discharge load. Therefore, “dispersed raising” should be discouraged in the future development of animal husbandry. On the contrary, intensive animal production is expected to expand (Zhang

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Fig. 6. Monthly mean flow in 2003 and 2007 in the main hydrologic stations of the Jiulong River Basin.

et al., 2003), but the scale should be carefully managed, so that the TP load is within the absorption capacity of the environment. At the same time, the scale of corresponding waste treatment ideally should match the scale of animal production. Seasonal differences of runoff and rainfall should also be taken into account. In order to facilitate P absorption by plants, the ratio of N:P in the wastes should be increased according to the requirements of different plants (Sharpley et al., 1996). To reduce further pollution and allowing further expansion of animal husbandry, efforts should be made to convert animal wastes into fertilizers (Zeng et al., 2005).

5.3. Addressing the water quantity issue As discussed in Section 4.4, the distribution of TP concentration is significantly correlated with the level of water quantity. From 2004 to 2007, the correlation coefficient between annual TP concentration and annual water quantity in the Jiulong River (namely the sum of that at Punan and Zhengdian station) was 0.98. The amount of water is under the influence of both climatic changes and human activities (Zhang and Schilling, 2006). While mitigating or adapting to climate change requires a holistic, strategic and long-term action programs at the national and local levels, controlling TP levels at source in the Jiulong River Basin can be easily done through adequate control of the animal husbandry activities and waste management, as well as regulating other related human activities such as changes in irrigation, drainage and the hydraulic structure of rivers (including hydropower stations and dams), which also affects water quality both temporally and spatially (Hao et al., 2008). Since 1995, more than 100 hydropower stations and dams have been built along the main streams and tributaries of the Jiulong River Basin (Xiamen University, 2006). As a result, water quantity along the river course is controlled by the operation of the dams instead of allowing natural hydrological responses. Usually, water quantity in the river course is low and the flow rate is very slow during dry periods, and this condition has harmful effects on the riverine ecosystem (Ni et al., 2003). In view of the importance of

maintaining water quantity, it is recommended that the relevant management departments should develop a minimum flow rate for each hydropower station or dam.

6. Conclusions Non-point source pollution is the main source of total phosphorus (TP) in the Jiulong River Basin, accounting for approximately 91% of the total load in 2003 and 94% in 2007. Livestock breeding, soil erosion and domestic wastewater were the main contributors. The close correlation between TP load and environmental capacity explains the spatial variability of TP concentration in the entire watershed. There was also significant correlation between flow and water quality from 2003 to 2007. Therefore, NPS pollution, especially from livestock breeding, should be controlled for TP load management in the Jiulong River Basin. “Dispersed raising” should be discouraged in the future development of animal husbandry. When expanding intensive animal production, the scale should be carefully managed so that the TP load is within the absorption capacity of the environment and efforts should also be made to convert animal wastes into fertilizers. It is also important to regulate the quantity of water flow from the tributaries of watersheds to meet basic downstream ecological requirements. The relevant management departments are recommended to develop a minimum flow rate for each hydropower station or dam. Several critical source areas for TP were identified where management measures to reduce TP should be directed. Hopefully, this research will be meaningful for watershed-scale water quality management for many coastal watersheds of China that face similar situations of land use patterns and water resource exploitation.

Acknowledgments This study was supported by the National Natural Science Foundation of China (grant no. 40901100, grant no. 40810069004) and the Fujian Provincial Department of Environmental Protection.

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