Pedosphere 18(3): 394–400, 2008 ISSN 1002-0160/CN 32-1315/P c 2008 Soil Science Society of China Published by Elsevier Limited and Science Press
Organic Phosphorus in Shallow Lake Sediments in Middle and Lower Reaches of the Yangtze River Area in China∗1 JIN Xiang-Can1 , WANG Sheng-Rui1 , CHU Jian-Zhou1,2 and WU Feng-Chang3 1 State
Environmental Protection Key Laboratory for Lake Pollution Control, Research Center of Lake Eco-Environment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China). E-mail: [email protected]
2 Colleges of Resource and Environment, Hebei Agriculture University, Baoding 071001 (China) 3 State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002 (China) (Received June 20, 2007; revised January 18, 2008)
ABSTRACT Thirteen sediment core samples (0–10 cm) were taken from the seven lakes in the middle and lower reaches of the Yangtze River to determine the contents and distributions of organic phosphorus (P) fractions in the sediments of the shallow lakes in the area. The organic P fractions in the sediments were in the order of moderately labile organic P (MLOP) > moderately resistant organic P (MROP) > highly resistant organic P (HROP) > labile organic P (LOP), with average proportional ratios of 13.2:2.8:1.3:1.0. LOP, MLOP, and MROP were signiﬁcantly related to the contents of total organic carbon (TOC), water-soluble P (WSP), algal-available P (AAP), NaHCO3 -extractable P (Olsen-P), total P (TP), organic P (OP), and inorganic P (IP). However, HROP was signiﬁcantly related to OP and weakly correlated with TOC, WSP, AAP, Olsen-P, TP or IP. This suggested that organic P, especially LOP and MLOP in sediments, deserved even greater attention than IP in regards to lake eutrophication. In terms of organic P, sediments were more hazardous than soils in lake eutrophication. Although OP concentrations were higher in moderately polluted sediment than those in heavily polluted sediment, LOP and MLOP were higher in the heavily polluted sediment, which indicated that heavily polluted sediment was more hazardous than moderately polluted sediment in lake eutrophication. Key Words: bioavailability, chemical extracted phosphorus, lake sediment, middle and lower reaches of the Yangtze River area, organic phosphorus fractions Citation: Jin, X. C., Wang, S. R., Chu, J. Z. and Wu, F. C. 2008. Organic phosphorus in shallow lake sediments in middle and lower reaches of the Yangtze River area in China. Pedosphere. 18(3): 394–400.
INTRODUCTION Phosphorus (P) has been recognized as the most critical nutrient limiting lake productivity (Kaiserli et al., 2002). P transformation, bioavailability, and exchange between sediments and the overlying water in lake systems has already been intensively investigated (Abrams and Jarrell, 1995; Bostrom, 1988; Gonsiorczyk et al., 1998; Xie et al., 2003; Linge and Oldham, 2004). Most previous studies mainly focused on the role of inorganic P in lake eutrophication (Ramm and Scheps, 1997; Zhou et al., 2001; Kaiserli et al., 2002). However, organically bound P represents a signiﬁcant portion of total P in most Chinese lake sediments (Jin et al., 1990; L¨ u et al., 2005), but little information is available on the role of organic P in lake eutrophication. Previous studies have demonstrated that organic P plays a vital role in P cycling and plant nutrition in both temperate (Sharpley, 1985; Clarke and Wharton, 2001) and tropical soils (Adepetu and Corey, 1976). The fractionation scheme developed by Bowman and Cole (1978) facilitates the separation of soil organic P into four distinct fractions: labile organic P (LOP), moderately labile organic P (MLOP), moderately resistant organic P (MROP), and highly resistant organic P (HROP). According to Makarov ∗1 Project
supported by the China’s National Basic Research Program: “Studies on the Process of Eutrophication of Lakes and the Mechanism of the Blooming of Blue Green Alga” (No. 2002CB412304).
ORGANIC P IN LAKE SEDIMENTS
et al. (2004), LOP and MLOP contents determined using Bowman and Cole’s method are useful indexes for determining whether a particular soil is rich in P and organic matter or not. A highly fertile soil was characterized by larger organic P fractions. The objective of the study was to determine the contents and distributions of organic P fractions in the sediments of the shallow lakes in the middle and lower reaches of the Yangtze River area, and then to compare them in the sediments and soils in the same area. With these data the role of organic P fractions in sediments for lake eutrophication was discussed. MATERIALS AND METHODS Study area For this study, seven lakes (Table I) were chosen in the middle and lower reaches of the Yangtze River (Fig. 1). The Yangtze River area has the highest density of lakes in China, and most of the lakes TABLE I Geographic and limnological features of the lakes in the middle and lower reaches of the Yangtze River Lake
Feature parameter Position
Meiliang Lake Gonghu Lake Dongting Lake Yuehu Lake Xuanwu Lake Hongze Lake Poyang Lake
31◦ 25 N 120◦ 10 E 31◦ 24 N 120◦ 15 E 28◦ 30 –30◦ 20 N 113◦ 10 –14◦ 40 E 29◦ 58 –31◦ 22 N 113◦ 41 –115◦ 05 E 32◦ 03 N 118◦ 47 E 33◦ 06 –33◦ 40 N 118◦ 10 –118◦ 52 E 28◦ 24 –29◦ 46 N 115◦ 49 –116◦ 46 E
Natural trophic status
Li et al., 2007
Wang et al., 2006
Wang et al., 2006
Wang et al., 2006
Wang et al., 2006
Jin et al., 2006
Hu et al., 2007
Fig. 1 Geographic locations of the sampling sites. B1, B2, and B3 are the sampling sites in Poyang Lake, D1 and D2 in Dongting Lake, H1 and H2 in Hongze Lake, T1 in Gonghu Lake, T2 in Meiliang Lake, X1 and X2 in Xuanwu Lake, and Y1 and Y2 in Yuehu Lake.
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are shallow with a large surface area. Total lake surface area in this area is more than 21 000 km2 , accounting for 25% of all lake surface area in China. In this region the number of lakes with surface area above 1 km2 is 651, and the number of those above 100 km2 is 18 (Jin et al., 1990). Most lakes in this area are under mesotrophic or eutrophic conditions because of rapidly expanding township enterprises, large population densities, the general over-use of agrochemical and chemical fertilizers, the discharge of municipal sewage, and large-scale cultivation (Qin, 2002). The eutrophication problem has already become one of the main factors restricting the economic development of this area (Qin, 2002; Wang et al., 2006). The morphometric features and selected chemical characteristics of the lakes studied are shown in Table I. Sediment sampling and analysis The lakes studied (Fig. 1) cover a wide range of sediment types and characteristics, from mesotrophication to hypereutrophication (Table I). Thirteen sediment core samples (0–10 cm) were taken from the seven lakes in September 2003 with a core sampler having a plexiglas tube of 30 cm in length and 5 cm in diameter. The samples were taken to the laboratory in sealed plastic bags placed inside iceboxes and then freeze-dried and ground for analysis. For total phosphorus (TP) analysis samples were digested with potassium persulphate and 300 mL L−1 sulphuric acid. P was determined using the method previously developed by Murphy and Riley (1962). Total organic carbon (TOC) was analyzed with an Appollo 9000 TOC analyzer (Tekmar Dohrman Co., USA) after pre-treatment in warm HCl (500 mL L−1 ) to eliminate inorganic carbon (Zanini et al., 1998). Organic P was operationally deﬁned into four fractions, i.e., LOP, MLOP, MROP, and HROP, using the previously reported scheme (Bowman and Cole, 1978). LOP was extracted with 0.5 mol L−1 NaHCO3 (pH = 8.5) and determined after perchloric acid digestion. MLOP was extracted with 1.0 mol L−1 H2 SO4 and determined in the same way as LOP. MROP stands for fulvic acid P and HROP for humic acid P, both of them extracted with 0.5 mol L−1 NaOH and determined together after perchloric acid digestion (fraction I). Then, an aliquot of the 0.5 mol L−1 NaOH extract was acidiﬁed with concentrated HCl to pH = 1–1.8 and MROP was determined after perchloric acid digestion (fraction II). HROP was obtained by subtracting fraction II from fraction I. All the P concentrations were determined colorimetrically using the method developed by Murphy and Riley (1962). Chemical extractable P was analyzed as follows: 0.5 g of dried sediment was placed into 100 mL acid washed screw cap centrifuge tubes and 50 mL deionized water was added for water-soluble P (WSP) extract (Friend and Birch, 1960; Psenner et al., 1988; Andrieux and Aminot, 1997), 50 mL 0.01 mol L−1 CaCl2 solution for readily desorbable P (RDP) extract (Reddy et al., 1980), 50 mL 0.1 mol L−1 NaOH solution for algal-available P (AAP) extract (Dorich et al., 1984, 1985), and 50 mL 0.5 mol L−1 NaHCO3 (pH = 8.5) solution for Olsen-P extract (Olsen et al., 1954; Gonsiorczyk et al., 1998), respectively. The samples were then incubated at 25 ± 1 ◦ C in an orbital shaker set at 250 r min−1 for 2.0 h for WSP, 1.0 h for RDP, 4.0 h for AAP, and 0.5 h for Olsen-P, respectively, and immediately centrifuged at 5 000 r min−1 for 10 min. The suspensions were ﬁltered through 0.45 µm GF/C ﬁlter membranes and analyzed for PO3− 4 using the molybdenum blue method (Wang et al., 2005). Experimental data were subjected to standard analysis of variance technique appropriate to a factorial randomized block design. When appropriate, the treatment means were compared at a 5% level of signiﬁcance using the least signiﬁcant diﬀerence. RESULTS AND DISCUSSION Fractional composition of sedimentary organic P The contents of organic P fractions in the sediments are illustrated in Fig. 2a. The contents of organic P fractions varied; LOP, MLOP, MROP, and HROP ranged from 1.44 to 17.58, 34.12 to 274.89,
ORGANIC P IN LAKE SEDIMENTS
2.40 to 85.54, and 2.40 to 29.80 mg kg−1 , respectively. The order of organic P fractions was MLOP > MROP > HROP > LOP, with mean relative contribution ratios of 13.2:2.8:1.3:1.0.
Fig. 2 Concentrations of organic P fractions (a) and bioavailable P fractions (b) in lake sediments in the middle and lower reaches of the Yangtze River. LOP = labile organic P; MLOP = moderately labile organic P; MROP = moderately resistant organic P; HROP = highly resistant organic P; WSP = water-soluble P; AAP = algal-available P; Olsen-P = NaHCO3 -extractable P. Bars denote standard deviations (n = 13).
Relationships between organic P fractions and other factors The correlations between TP, inorganic P (IP), organic P (OP), TOC, WSP, AAP, Olsen-P, and organic P fractions in the sediments were analyzed. Their correlation coeﬃcients are shown in Table II. TOC had a strong positive correlation with LOP, MLOP, and MROP (P < 0.01, n = 13), but it did not have a signiﬁcant correlation with HROP. Similar results have also been reported in lake sediments (Anshumali and Ramanathan, 2007). LOP, MLOP, and MROP were signiﬁcantly related to WSP, AAP, Olsen-P, TP, OP, and IP. However, HROP was signiﬁcantly related to OP and weakly correlated with WSP, AAP, Olsen-P, TP, or IP. Again, similar results have been reported in soils (Reddy et al., 2000; Feng et al., 2001). TABLE II Correlation coeﬃcients between total organic carbon (TOC), water-soluble P (WSP), algal-available P (AAP), NaHCO 3 extractable P (Olsen-P), total P (TP), organic P (OP), inorganic P (IP), and organic P fractions in the lake sediments in the middle and lower reaches of the Yangtze River Organic P fractiona)
LOP MLOP MROP HROP
0.862** 0.912** 0.925** 0.437
0.868** 0.923** 0.955** 0.483
0.637* 0.813** 0.805** 0.360
0.732** 0.889** 0.862** 0.314
0.907** 0.963** 0.969** 0.442
0.937** 0.979** 0.965** 0.626*
0.878** 0.943** 0.955** 0.501
*, **Signiﬁcant at P < 0.05 and P < 0.01, respectively (2-tailed, n = 13). a) LOP = labile organic P; MLOP = moderately labile organic P; MROP = moderately resistant organic P; HROP = highly resistant organic P.
Bioavailable organic P and chemical extractable P WSP, AAP, and Olsen-P are chemical extractable P and they are closely related to potential bioavailability of P in lake sediments (Zhou et al., 2001). According to the previous study in soils (Turner et al., 2005), the bioavailability of LOP and MLOP is higher than that of MROP and HROP. LOP and MLOP represent the main source and sink for plant available P in soils (Lindo et al., 1995), so they are useful indexes to decide whether a particular soil is rich in P and organic matter or not (Makarov et al., 2004). This indicates that the bioavailability of soil organic P can be evaluated by LOP and MLOP. The bioavailable organic P (LOP + MLOP) and chemical extractable P (WSP, AAP, and Olsen-P) are shown in Fig. 2b. The bioavailable organic P was about 139.20 mg kg−1 . This was 12.42, 1.70, and 1.61 times WSP, AAP, and Olsen-P, respectively. Thus, organic P (especially LOP and MLOP) should be
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paid even greater attention than inorganic P in lake eutrophication studies. Comparison between organic P fractions in soils and sediments Most sediments were from the soils in the lake watersheds. There may be a strong correlation between soils and sediments in the same area for organic P compositions. Organic P fractions in soils from the middle and lower reaches of Yangtze River area have been widely reported (Sun and Zhang, 1992; Feng et al., 2001; Xu et al., 2003; Yu, 2003). The comparison between the reported organic P fractions in soils and those in the sediments is illustrated in Fig. 3. Total organic P (TOP), LOP, and MLOP concentrations in sediments were higher than those in soils, while MROP and HROP concentrations were contrary. LOP, MLOP, MROP, and HROP fractions in soils accounted for, on average, 4.83%, 54.50%, 29.52%, and 11.15% of TOP and those in sediments accounted for 5.47%, 72.08%, 15.25%, and 7.21% of TOP, respectively. The relative contribution of LOP and MLOP to TOP was higher in sediments than in soils. Therefore, in terms of organic P, sediments are more hazardous than soils in lake eutrophication. Although few studies have been carried out in this aspect, there may be more organic matter in sediments than soils according to the environmental characteristics of soils and sediments (Clarke and Wharton, 2001), and TOP concentrations are higher in sediments than in soils. In addition, microorganism activity is stronger in sediments than in soils (Sorrell et al., 2002), resulting in higher concentrations of LOP and MLOP, and higher relative contributions of LOP and MLOP to TOP in sediments. This aspect needs further investigation.
Fig. 3 Contents of the organic P fractions and total organic P (TOP) in soils and sediments. LOP = labile organic P; MLOP = moderately labile organic P; MROP = moderately resistant organic P; HROP = highly resistant organic P. Bars denote standard deviations (n = 13). Fig. 4 Contents of the organic P fractions and total organic P (TOP) in diﬀerent polluted sediments. See Fig. 3 for description of the abbreviations.
Eﬀect of pollution on organic P fractions in sediments Most lakes in China are P limited. According to common Chinese environmental dredging standards, when TP concentrations in lake sediment are over 500 mg kg−1 , the sediment is considered to be heavily polluted and should be dredged (Liu et al., 1999). The 13 sediment samples studied can mainly be divided into two types: heavily polluted sediment (those lakes were hypereutrophic) and moderately polluted sediment (those lakes were mesotrophic). The order of TOP concentrations and OP fractions in the sediments was as follows: heavily polluted sediment > moderately polluted sediment (Fig. 4). However, the relative contribution of OP fractions to TOP was diﬀerent (Fig. 4). For the heavily polluted sediment the relative contribution of MLOP to TOP was lower than that for moderately polluted sediment. However, the relative contributions of MROP, LOP, and HROP were contrary. The relative contribution of bioavailable OP (MLOP + LOP)
ORGANIC P IN LAKE SEDIMENTS
to TOP in the heavily polluted sediment was 10% lower than that in the moderately polluted sediment. This indicates that OP may be released into the overlying water by mineralization and the proportion of OP was higher in the moderately polluted sediment than that in the heavily polluted sediment. However, LOP and MLOP were higher in the heavily polluted sediment than those in the moderately polluted sediment because they can be mineralized and transformed into the bioavailable P. Thus, in terms of the organic P, the heavily polluted sediment was more hazardous for lake eutrophication than the moderately polluted sediment. Therefore, the role of OP in lake eutrophication should not be neglected, especially in regards to heavily polluted sediment. This study suggests that more studies should be carried out to understand the mechanism and control measurement of lake eutrophication. CONCLUSIONS The organic P fractions in the sediments studied were in the order of MLOP > MROP > HROP > LOP, with average proportional ratios of 13.2:2.8:1.3:1.0. LOP, MLOP, and MROP were signiﬁcantly related to TOC, WSP, AAP, Olsen-P, TP, OP, and IP. However, HROP was signiﬁcantly related to OP, and weakly correlated with TOC, WSP, AAP, Olsen-P, TP or IP. Compared with IP in lake eutrophication, more attention should be taken to OP, especially LOP and MLOP in sediments from the studied area. In terms of OP, sediments were more hazardous than soils for lake eutrophication. OP may be released into the overlying water by mineralization, and the proportion of OP was higher in the moderately polluted sediment than that in the heavily polluted sediment. However, LOP and MLOP concentrations were higher in the heavily polluted sediment. Therefore, heavily polluted sediments were more hazardous in lake eutrophication than moderately polluted sediments. REFERENCES Abrams, M. M. and Jarrell, W. M. 1995. Soil-phosphorus as a potential non-point source for elevated stream phosphorus levels. Journal of Environmental Quality. 24: 132–138. Adepetu, J. A. and Corey, R. B. 1976. Organic phosphorus as a predictor of plant available phosphorus in soils of southern Nigeria. Soil Science. 122: 159–164. Andrieux, F. and Aminot, A. 1997. A two-year survey of phosphorus speciation in sediments of the Bay of Seine (France). Continental Shelf Research. 17: 1 229–1 245. Anshumali and Ramanathan, A. L. 2007. Phosphorus fractionation in surﬁcial sediments of Pandoh Lake, Lesser Himalaya, Himachal Pradesh, India. Applied Geochemistry. 22(9): 1 860–1 871. Bostrom, B. 1988. Relations between chemistry, microbial biomass and activity in sediments of a sewage-polluted vs. a nonpolluted eutrophic lake. Verh. Int. Ver. Limnol. 23: 451–459. Bowman, R. A. and Cole, C. V. 1978. An exploratory method for fractionation of organic phosphorus from grassland soils. Soil Science. 125: 95–101. Clarke, S. J. and Wharton, G. 2001. Sediment nutrient characteristics and aquatic macrophytes in lowland English rivers. Science of the Total Environment. 266: 103–112. Dorich, R. A., Nelson, D. W. and Sommers, L. E. 1984. Availability of phosphorus to algae from eroded soil fractions. Agriculture, Ecosystems and Environment. 11: 253–264. Dorich, R. A., Nelson, D. W. and Sommers, L. E. 1985. Estimating algae available phosphorus in suspended sediments by chemical extraction. Journal of Environmental Quality. 14: 400–405. Feng, Y. H., Zhang, Y. Z., Huang, Y. X. and Zhou, Q. 2001. Fractionation of organic phosphorus forms in major types of paddy soils in Hunan Province. Journal of Hunan Agricultural University (Natural Sciences) (in Chinese). 27(1): 24–28. Friend, M. T. and Birch, H. F. 1960. Phosphate responses in relation to soil tests and organic phosphorus. Journal of Agricultural Science. 54: 341–346. Gonsiorczyk, T., Casper, P. and Koschel, R. 1998. Phosphorus binding forms in the sediment of an oligotrophic and an eutrophic hardwater lake of the Baltic Lake district (Germany). Water Science and Technology. 37: 51–58. Hu, Q., Feng, S., Guo, H., Chen, G. Y. and Jiang, T. 2007. Interactions of the Yangtze River ﬂow and hydrologic processes of the Poyang Lake, China. Journal of Hydrology. 347(1–2): 90–100. Jin, X. C., Liu, H. L. and Tu, Q. Y. 1990. Eutrophication of Lakes in China (in Chinese). China Environmental Science Press, Beijing. 121pp. Jin, X. C., Wang, S. R., Bu, Q. Y. and Wu, F. C. 2006. Laboratory experiments on phosphorous release from the sediments of 9 lakes in the middle and lower reaches of Yangtze River region, China. Water, Air, and Soil Pollution. 176(1–4): 233–251.
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