Phosphorus Fractions and Phosphate Sorption Characteristics in Relation To

Journal of Colloid and Interface Science 289 (2005) 339–346 www.elsevier.com/locate/jcis

Phosphorus fractions and phosphate sorption characteristics in relation to the sediment compositions of shallow lakes in the middle and lower reaches of Yangtze River region, China

Shengrui Wang a, Xiangcan Jin a,∗,YanPanga, Haichao Zhao b, Xiaoning Zhou a, Fengchang Wu c

a Research Center of Lake Environment, Chinese Research Academy of Environment Sciences, Chaoyang District, Beijing 100012, China b Inner Mongolia Agriculture University, Huhhot 010018, China c State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China Received 18 December 2004; accepted 29 March 2005 Available online 6 May 2005

Abstract Phosphorus is recognized as the most critical nutrient limiting lake productivity. The trophic status and development of lake systems are also influenced by the phosphorus content and fractions and phosphate sorption characteristics of the lake sediments. The phosphorus fractions and phosphate sorption characteristics of sediments in shallow lakes from the middle and lower reaches of Yangtze River region − in China were investigated. The results show that the phosphorus contents in the sediments ranged from 217.8 to 1640 mg kg 1; inorganic phosphorus (IP) was the major fraction of total phosphorus (TP); phosphorus bound to Al, Fe, Mn oxides, and hydroxides (Fe/Al–P), and calcium bound phosphorus (Ca–P) were the main fractions of IP. Phosphate sorption on the sediments mainly occurred within 2 h and then reached equilibrium in 10 h. The phosphate sorption rate was closely related to the concentration of fine particles. The phosphate sorption − capacity ranged from 128.21 to 833.33 mg kg 1, showing a significant correlation with the contents of Fe, Fe + Al, total organic carbon (TOC), cationic exchange capacity, total nitrogen, TP, Ca, IP, and the ratio of P/(Al + Fe), and it was higher in the sediments of eutrophic lakes than in mesotrophic lakes. Phosphate was mainly sorbed onto Fe and Al particles. The phosphate sorption efficiency ranged from − 26.74 to 312.50 L kg 1, and had a strong positive correlation with Fe content. For the eutrophic lake sediments, there were no significant relationships between the phosphate sorption efficiency and the selected physical and chemical parameters. But for the mesotrophic lake sediments, the phosphate sorption efficiency was found to be positively related to the contents of Al and Fe + Al.  2005 Elsevier Inc. All rights reserved.

Keywords: Phosphorus fractions; Phosphate sorption; Sediment; Middle and lower reaches of Yangtze River region; Lake

1. Introduction lake system [4,5]. Not all of the phosphorus fractions can be released from sediments into the overlying water and lead to The phosphorus content and fractions and phosphate lake eutrophication [1,6]. Therefore, the phosphorus behav- sorption characteristics of the lake sediments affect the ior in lake sediments for promoting lake eutrophication can trophic status and development of the lake system [1,2].Usu- be more efﬁciently evaluated based on the phosphorus frac- ally lake sediments act as a sink for phosphorus [3].How- tions, instead of the total phosphorus content [3]. Phospho- ever, under certain conditions, the sediment may become a rus fractions in lake sediments can be divided into different phosphorus source that can support the trophic status of the fractions such as labile phosphorus, reductant phosphorus, metal-bound phosphorus, occluded phosphorus, and organic * Corresponding author. Fax: +86 010 84915190. phosphorus using various chemical extractants [7–9].Ac- E-mail address: [email protected] (X. Jin). cording to the SMT protocol [10], the phosphorus fractions

0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.03.081 340 S. Wang et al. / Journal of Colloid and Interface Science 289 (2005) 339–346 can be characterized as inorganic phosphorus (IP), phos- of the nutrient external loading and in several cases also phorus bound to Al, Fe, and Mn oxides and hydroxides from the ﬂux of the nutrient released from sediments [23]. (Fe/Al–P), calcium-associated phosphorus (Ca–P), organic The aims of this study were to investigate the character- phosphorus (OP), and total phosphorus (TP). istics of the phosphorus fractions in the surface sediments The phosphate sorption at the sediment–water interface of lakes from the middle and lower reaches of the Yangtze of lakes is an important process that affects the phosphorus River region, to calculate the phosphate sorption capacity, to transport, the bioavailability, and the concentrations in the describe the kinetics and isotherms of the phosphate sorp- overlying water, so this process had been widely investigated tion on the sediments, and also to analyze the relationship [11,12]. When phosphorus was sorbed onto the particle sur- between the phosphate sorption characteristics and the sedi- face, the equilibrium process was usually described by the ment compositions. Langmuir sorption isotherm [13]. The phosphate sorption capacity of lake sediments was related to their compositions [14]. Although the phosphate sorption mechanism is 2. Materials and methods not well understood, a large phosphate sorption capacity was reported to be related to the contents of Fe/Al (hydr)oxides 2.1. Study area in oxic estuarine and oceanic sediments [15–18]. One of the more important factors affecting the phosphorus exchange The studied lakes are located in the middle and lower between the lake sediment and its overlying water was the reaches of Yangtze River region (Fig. 1). There are 651 lakes particle-size distribution in the sediments [19]. Thus, sedi- with areas are larger than 1 km2 and there are 18 lakes with ments with different characteristics may have different phos- areas larger than 100 km2 in this region [24]. Most of the phate sorption characteristics [20]. lakes are shallow with large surface areas. The total lake sur- The phosphate sorption of the sediments from coastal es- face area in this region is more than 21,000 km2, accounting tuaries, oceans, and deep lakes has been extensively studied for 25% of all water surface area of lakes in China. Poyang over the past 30 years [21]. However, studies on the sedi- Lake, Dongting Lake, and Taihu Lake have surface areas of ments from shallow lakes were not often reported, and little 3960, 2470, and 2440 km2, respectively, and they are the is known about the phosphorus fractions of the sediments largest surface area lakes in China [25]. Most of the lakes from those Chinese shallow lakes. are under mesotrophic or eutrophic conditions due to agro- The middle and lower reaches of the Yangtze River re- chemical and chemical fertilizer overusage, discharge of the gion are central areas of freshwater shallow lakes in China. municipal sewage, large-scale cultivation, and high-density Most of the lakes in this region have been under mesotrophic population in the watershed. Those lakes are the main eu- or eutrophic conditions, and the eutrophication is especially trophic region in China [22], and are a restriction factor that common [22]. The source of the nutrient enrichment in the affects the economic development of this region [26]. Taihu lake sediment is the nutrient loaded from the watershed, and Lake is eutrophic [27], Yue Lake and Xuanwu Lake are ur- the high primary production of the lake is the consequence ban lakes and have been hypereutrophic [28], Chao Lake,

Fig. 1. The geographic location of the sampling sites. S. Wang et al. / Journal of Colloid and Interface Science 289 (2005) 339–346 341

Table 1 Geographic and limnological features of the chosen lakes Lakes Feature parameters Positions Surface area Mean depth Trophic status References (km2) (m) ◦ ◦ 30 55 –31 58 N Taihu Lake ◦ ◦ 2338 0.89 Eutrophication [27] 119 53 –120 36 E ◦ 29 58 N Yue Lake ◦ 0.7 1.5 Hypereutrophication This study 113 41 E ◦ 32 03 N Xuanwu Lake ◦ 3.7 1.14 Hypereutrophication [28] 118 47 E ◦ ◦ 30 25 –31 43 N Chao Lake ◦ ◦ 760 3 Mesotrophication [29] 117 16 –117 51 E ◦ ◦ 33 06 –33 40 N Hongze Lake ◦ ◦ 2069 1.5 Mesotrophication [30] 1185 10 –118 52 E ◦ ◦ 28 24 –29 46 N Poyang Lake ◦ ◦ 3210 8.4 Mesotrophication [31] 115 49 –116 46 E

Hongze Lake, and Poyang Lake are mesotrophic [29–31]. by HCl and the residual was treated at 450 ◦C to analyze These 6 lakes represent major lake types in this region and organic phosphorus. Total phosphorus in the sediments was were chosen in this study. Their morphometric features and determined by treating the sample at 450 ◦C, followed by chemical characteristics are shown in Table 1 [27–31]. HCl extraction. Phosphate concentrations in the supernatant of the extraction were analyzed using the molybdenum blue 2.2. Sediment sampling and analyses method [37]. For all samples, triplicates were analyzed and the data were reported as the average in this study. Eleven sediment core samples were collected from the 6 lakes in the region. A core sampler with a 30 cm length, 5 cm 2.4. Phosphate sorption kinetic experiments i.d. Plexiglas cylinder tube was used. The sediment samples were taken to the laboratory in sealed plastic bags that were Dried sediment samples (0.5 g) were added in a series of put in iceboxes, and the samples were then freeze-dried and 100-ml acid-washed screw-cap centrifuge tubes with 50 ml −1 ground. They were analyzed for cationic exchange capac- phosphate solution (KH2PO4, containing 1 mg L P). The ity (CEC), total nitrogen (TN) [32], and total phosphorus centrifuge tubes were capped and incubated at 25 ± 1 ◦C (TP) [33]. Water content and loss on ignition measurements in an orbital shaker at 250 rpm for different time intervals, were based on the weight loss after drying and combustion varying within 72 h (0.5, 1, 1.5, 3, 5, 7, 12, 24, 48, 60, and of the sediments at 105 and 550 ◦C, respectively. Total or- 72 h). The sample solution was immediately centrifuged at ganic carbon (TOC) in the sediments was analyzed with an 5000 rpm for 10 min and then filtered through 0.45-µm GF/C Appollo 9000 TOC Analyzer (Tekmar Dohrman Co.) after filter membrane. The filtrate was taken for phosphate analy- pretreatment in warm HCl 50% (v/v) to eliminate inorganic ses [37]. The phosphate sorption capacity of sediments was carbon [34]. The grain-size distribution was determined us- obtained from the difference between the initial phosphate ing a Mastersizer 2000 Laser Size Analyzer (Malvern Co., concentration and the equilibrium phosphate concentration UK), and was classified into clay (<0.002 mm), silt (0.002– [38,39]. For all samples, triplicates were analyzed and the 0.05 mm), and sand fractions (0.05–2 mm) [35]. The con- data were expressed as the average. tents of main elements in sediments were measured by ICP- AES (ICP/6500, PE, USA). 2.5. Phosphate sorption isotherm experiments

2.3. Phosphorus fractionation Sorption isotherm experiments were performed on the top 10 cm sediments of the cores, following the previous stud- The sediment samples were sieved with a standard 100- ies by Carman et al. [40] and Gachter et al. [41]. Approxi- mesh sieve, and the sequential phosphorus fraction was car- mately 0.5 g sediment samples were put into the screw-cap ried out using the SMT procedure [33]. The SMT protocol centrifuge tubes (100 ml), and 50 ml phosphate standard so- based on the William method is a common approach for lutions (anhydrous KH2PO4) of various concentrations from studying the phosphorus fractions of the lake sediment [36]. 0to15mgL−1 were added. Although the phosphate con- The operationally deﬁned scheme separates phosphorus into centrations in the experiments were considerably higher than ﬁve fractions. Phosphorus bound to Al, Fe, and Mn oxides those naturally occurring, phosphate sorption sites were al- and oxyhydrates was extracted by NaOH (Fe/Al–P). Phos- lowed to reach saturation and the maximum phosphate sorp- phorus bound to calcium was extracted by HCl (Ca–P). In tion capacity can be calculated. Those centrifuge tubes were a separated extraction, inorganic phosphorus was extracted incubated at 25 ± 1 ◦C in an orbital shaker at 250 rpm. After 342 S. Wang et al. / Journal of Colloid and Interface Science 289 (2005) 339–346

Table 2 Physical and chemical characteristics of the sediments Items Sampling sites T-1 T-2 B-1 B-2 B-3 C-1 C-2 Y H X T-3 TOC (%) 0.75 0.90 0.50 0.73 0.36 0.18 0.29 5.53 1.27 2.97 1.67 − CEC (meq (100 g) 1)11.30 13.33 9.01 8.88 8.56 9.06 10.80 30.12 13.45 19.60 22.15 C/N ratio (atoms) 9.75 9.94 7.93 7.70 6.19 5.11 11.66 10.70 22.78 8.02 8.85 TN (%) 0.08 0.09 0.06 0.09 0.06 0.03 0.03 0.52 0.06 0.37 0.19 − TP (mg kg 1) 420.20 420.50 323.70 486.10 291.20 217.80 221.10 1640.00 631.70 1062.40 809.20 − IP (mg kg 1) 241.10 365.98 200.50 314.37 171.17 144.76 197.12 1155.66 413.15 726.76 594.28 Al (%) 5.58 6.16 8.96 8.04 8.01 4.84 6.29 8.51 9.49 7.33 6.55 Fe (%) 2.98 3.61 3.69 3.21 2.70 1.77 2.47 6.02 5.15 3.59 3.44 Ca (%) 0.78 0.98 0.74 0.29 0.16 0.53 0.74 3.71 3.36 1.96 0.69 − P/(Al + Fe) (µmol mM 1)4.91 4.62 2.56 4.32 2.72 3.30 2.52 13.09 4.31 9.73 8.09 Clay (%) 5.43 6.35 4.63 4.72 4.21 4.96 9.53 6.28 7.02 3.72 7.95 Silt (%) 68.50 74.60 64.30 64.80 59.60 70.40 86.40 81.81 68.50 78.00 71.00 Sand (%) 26.07 19.05 31.07 30.48 36.19 24.64 4.07 11.91 24.48 18.28 21.05 C-1 and C-2, sampling sites in Chao Lake; B-1, B-2 and B3, sampling sites in Poyang Lake; T-1, T-2, and T3, sampling sites in Taihu Lake; H, sampling sites in Hongze Lake; X, sampling sites in Xuanwu Lake; Y, sampling sites in Yue Lake.

24 h, the samples were centrifuged at 5000 rpm for 10 min, and the equilibrium phosphate concentrations were analyzed [37]. In the experiments, triplicates were carried out and the data were expressed as the average.

3. Results and discussion

3.1. Sediment characteristics

The general features and the chemical component contents of sediments of various lakes are presented in Table 2. The silt fraction was the major fraction in the lake sediments, accounting for 59.6–86.4% of the total. The clay fraction was the minor fraction, accounting for 3.7–7.9% Fig. 2. Contents of different phosphorus fractions of the sediments of vari- of the total. TOC contents ranged from 0.2 to 5.5%, CEC ous lakes. from 8.56 to 30.12 meq (100 g)−1, C/N ratio (atoms) from 5.1 to 22.8, TN from 0.06 to 0.5%, TP from 217.80 to Table 3 1640 mg kg−1, and IP from 144.76 to 1155.66 mg kg−1.Fe Pearson correlation coefﬁcients between the phosphorus fractions and the sediment properties (n = 11) contents ranged from 1.77 to 5.15%, Al from 4.84 to 9.49%, Ca from 0.16 to 3.36%, and the ratio of P/(Al+Fe) from 2.52 TP Fe/Al–P Ca–P IP OP to 13.09 µmol mM−1. This suggests that the selected phys- TOC 0.96** 0.81* 0.83* 0.97** 0.91** TN 0.93** 0.80* 0.78* 0.93** 0.87* ical and chemical characteristics of the 11 lake sediments ** * * ** * varied greatly. CEC 0.90 0.78 0.80 0.93 0.77 Al 0.12 0.10 0.07 0.10 0.18 Fe 0.27 0.09 0.36 0.25 0.28 3.2. Phosphorus fractionation Ca 0.59 0.30 0.66 0.57 0.59

* ** TP contents in the sediments ranged from 217.8 to P<0.05, P<0.01. 1,640 mg kg−1 (Table 2), whereas OP contents from 26.17 to 413.32 mg kg−1, IP contents from 144.76 to 1155.66 Table 4 mg kg−1, Ca–P contents from 57.31 to 565.62 mg kg−1, and The intercorrelations between various phosphorus fractions in the sediments (n = 11) Fe/Al–P contents from 59.28 to 591.2 mg kg−1 (Fig. 2). The relationships between phosphorus fractions and sedi- TP (Fe–Al)–P Ca–P IP OP ment compositions are shown in Table 3. TP, Fe/Al–P, Ca–P, TP 1.00 0.91** 0.93** 0.99** 0.97** * ** * IP, and OP contents were all significantly correlated with (Fe/AL)–P 1.00 0.71 0.91 0.89 ** * TOC, TN, and CEC contents, but there were no significant Ca–P 1.00 0.93 0.86 IP 1.00 0.94** relationships for Al, Fe, and Ca contents. OP 1.00 There were intercorrelations among various phosphorus fractions (Table 4). TP and IP contents had the most sig- * P<0.05, ** P<0.01. S. Wang et al. / Journal of Colloid and Interface Science 289 (2005) 339–346 343 nificant relationship. The relationships between IP content This suggests that the quick phosphate sorption of the sedi- and Fe/Al–P, Ca–P contents were also significant. Thus, IP ments was mainly the physical sorption process. The higher was caused together by Fe/Al–P and Ca–P contents. Simi- the volume percentage of the fine particles of the sediments, lar results were also reported in the river delta and reservoir the bigger their phosphate sorption rate. sediments [42,43]. IP was the major phosphorus fraction in the sediments. This fraction was reported as an important source of bioavail- able phosphorus in eutrophic sediments [10]. With the observed relationships among the various phosphorus fractions (Table 4), Fe/Al–P and Ca–P contributed substantially to the supply of IP in these sediments. Significant correlation between phosphorus fraction contents and Fe and Al contents indicates the major role of Fe and Al in removing phosphorus from the overlying water through a sorption mechanism (Table 3). Although no significant relationship was observed between Fe and Al contents and phosphorus sorption capacity, Fe and Al may contribute significantly to phosphorus bioavailability in sediments by enhancing the cation-exchange capacity and reducing phosphorus fixa- tion [6]. In this study, different phosphorus fraction contents were all significantly correlated with TOC and TN contents. Fig. 3. The phosphate sorption kinetics of the sediments of various lakes. 3.3. The sorption kinetics of phosphate on sediments

The phosphate sorption kinetic results are shown in Fig. 3. The phosphate sorption capacity increased rapidly with time increasing within 10 h. After 10 h, the sorption process reached equilibrium. The sorption kinetics was similar among the studied sediment samples. The results are consistent with previous reports [21,44]. The sorption rate was used to describe the phosphate sorption by the sediments. The sorption rates of the sediment samples with time are shown in Table 5. The average sorption rates of 0–0.5 h were the highest within 72 h, rang- ing from 59.17 to 116.04 mg (kg h)−1. This indicates that a quick sorption process mainly occurred within 0.5 h. Phos- phate sorption on sediment mainly depends on its physical and chemical properties such as grain-size distribution [45]. In this study, the sorption rates within 0.5 h had a strong positive correlation with the volume percentage of ﬁne par- Fig. 4. The relationship between phosphate sorption rate and the less than ticle less than 50 µm (r = 0.94, P 0.01, n = 11) (Fig. 4). 50 µm ﬁne particle content.

Table 5 − The phosphate sorption rates on the sediments at different sampling intervals (mg (kg h) 1) Sampling intervals Sample 0–0.5 0.5–1.5 1.5–3 3–5 5–7 7–2 12–24 24–48 48–60 60–72 T-1 80.18 17.28 4.57 0.44 0.63 1.41 0.23 0.04 0.20 0.01 T-2 77.18 10.50 3.52 0.41 0.50 0.83 0.44 0.00 0.25 0.03 B-1 59.17 12.46 2.94 2.20 2.69 1.72 0.82 0.16 0.28 0.03 B-2 66.44 15.66 10.71 4.33 3.06 1.24 0.41 0.12 0.17 0.02 B-3 46.17 12.74 10.39 6.44 1.77 1.60 0.29 0.02 0.09 0.01 C-1 64.05 0.11 0.33 0.47 1.47 0.41 0.47 0.12 0.39 0.03 C-2 116.06 6.50 0.33 0.25 0.88 0.27 0.07 0.07 0.05 0.02 Y 114.18 0.94 0.46 0.44 0.28 0.04 0.06 0.45 0.30 0.04 H61.17 2.50 0.74 0.81 0.02 0.15 0.07 0.35 0.08 0.02 X-1 106.18 1.42 1.00 0.04 1.46 0.69 0.72 0.47 0.14 0.02 T-3 75.18 11.00 1.33 1.59 0.36 1.72 0.17 0.21 0.10 0.01 344 S. Wang et al. / Journal of Colloid and Interface Science 289 (2005) 339–346

Table 7 Coefﬁcients of correlation between the sediment composition and the maximum phosphate sorption capacity (Qmax), and the phosphate sorption ef- ﬁciency (slope) Items Whole sediments Heavily polluted Slightly polluted (n = 11) sediments (n = 6) sediments (n = 5)

Qmax Slope Qmax Slope Qmax Slope Fe 0.86** 0.80** 0.64 0.35 0.91* 0.70 Fe + Al 0.74** 0.24 0.61 0.05 0.67 0.88* Al 0.59 0.41 0.54 0.12 0.51 0.89* TOC 0.77** 0.45 0.82* 0.58 0.92* 0.34 CEC 0.71* 0.59 0.72 0.77 0.32 0.42 C/N 0.51 0.24 0.44 0.19 0.41 0.10 TN 0.70* 0.41 0.68 0.53 0.83 0.56 TP 0.80** 0.44 0.80 0.59 0.89* 0.39 IP 0.78** 0.49 0.79 0.63 0.86 0.19 P/(Al + Fe) 0.71* 0.53 0.68 0.62 0.36 0.28 Ca 0.80** 0.50 0.96** 0.57 0.36 0.45

* ** Fig. 5. Sorption isotherms of phosphate on the sediments of various lakes. P<0.05, P<0.01.

+ Table 6 Ca, TOC, TP, IP, TN, CEC contents, and the ratio of P/(Al The calculated Qmax, Kd, slopes, and standard errors and coefficients Fe) provide an estimation of the free sorption sites in sedi- 2 ment particles. Ratios of total C/N may indicate the amount Samples Qmax SE Kd SE Slope R − − − (mg kg 1) (mg L 1) (L kg 1) and type of organic matter present in the sediments. The cor- Y 833.33 32.45 8.58 2.34 48.54 0.97 relation efficients among sediment compositions, the maxi- X 666.67 26.89 3.93 0.67 84.75 0.94 mum phosphate sorption capacity, and phosphate sorption T-3 526.32 12.45 3.63 0.59 72.46 0.95 efficiency are shown in Table 7. The maximum phosphate H 714.29 25.83 3.21 0.65 111.11 0.99 sorption capacity was positively related to Fe, Fe + Al, B-1 409.09 27.87 2.27 0.72 90.00 0.95 TOC, CEC, TN, TP, Ca, and IP contents, and the ratio of T-2 512.50 17.23 2.28 0.47 112.33 0.94 + T-1 555.56 25.64 1.56 0.23 178.57 0.98 P/(Al Fe) and the phosphate sorption efficiency were pos- B-2 526.32 45.17 0.84 0.34 312.50 0.97 itively related to Fe content. B-3 359.09 25.31 2.09 0.32 85.87 0.92 However, for maximum phosphate sorption capacity and C-2 294.12 36.52 1.15 0.88 128.21 0.96 phosphate efficiency, significant differences were observed C-1 128.21 25.23 2.40 0.94 26.74 0.95 between the eutrophic and the mesotrophic sediments. For the eutrophic sediments, the maximum phosphate sorption 3.4. The sorption isotherm of phosphate on sediments capacity was positively related to the TOC and Ca contents, while for the mesotrophic sediments, the maximum phos- The sorption isotherms of phosphate on the sediments are phate sorption capacity was positively correlated with Fe, shown in Fig. 5. The phosphate sorption capacity was fitted TOC, and TP contents. For phosphate sorption efficiency, by [45]. a significant relationship between the phosphate sorption efficiency and the physical and chemical parameters of = × + Q Qmax C/(Kd C), (1) the eutrophic sediments was not observed. While for the where C is the phosphate sorption equilibrium concentration mesotrophic sediments, the phosphate sorption efficiency (mg L−1), Q is the phosphate sorption capacity (mg kg−1 was positively related to the contents of Al and Fe + Al. dry weight) and is the sorbed phosphate when the equilib- The phosphate sorption capacity and phosphate efficiency rium is reached, Qmax is the maximum phosphate sorption of sediments can be related to many factors. In oxic sedi- −1 −1 capacity (mg kg dry weight), Kd is the half-saturation ments, the phosphate sorption efficiency was 20–40 ml g concentration (mg L−1), i.e., the phosphate concentration in UK lakes [46], and can reach nearly 4000 ml g−1 in iron- that must be added to obtain an sorption equal to half Qmax, rich oceanic sediments [15]. The metal content was the main and the slope is a measure of the phosphate sorption effi- factor affecting the phosphate sorption capacity due to the ciency of sediments [45]. The calculated data of Qmax, Kd, high specific surface of the Fe/Al (hydr)oxides [16,18,47].In and slope are shown in Table 6. The maximum phosphate some cases, the phosphate sorption sites can be occupied by sorption capacity ranged from 128.21 to 833.33 mg kg−1, Fe and Al, and the sorption efficiency was lower. Thus, the −1 Kd from 0.84 to 8.58 mg L , and slope from 26.74 to ratio P/(Fe + Al) was used to estimate the free sorption sites 312.5 L kg−1. for phosphate in sediments [48]. In calcareous areas a large The sorption capacity and efficiency were compared with fraction of the sedimentary phosphate can be associated with some sediment physical and chemical parameters. Fe, Al, calcium minerals [49]. This may hold true as a strong corre- S. Wang et al. / Journal of Colloid and Interface Science 289 (2005) 339–346 345 lation between Qmax and Ca content was observed in this Acknowledgments study. Based on the above discussion, the phosphate sorption capacity of sediments with the highest contents of car- The authors thank the financial support from China’s na- bon, nitrogen, and phosphorus should be high, so the highest tional basic research program: Studies on the Process of value should be observed in the Yue Lake sediments. The Eutrophication of Lakes and the Mechanism of the Bloom- obtained results (Table 7) agree with this hypothesis. There- ing of Blue Green Alga (2002CB412304). We also thank the fore, the eutrophic lake sediments with higher contents of assistance from colleagues of Research Center of Lake En- TOC, N, P, Fe, and Ca had a lower phosphate sorption effi- vironment, the Chinese Research Academy of Environment ciency. Sciences. Mesotrophic lake sediments had a higher phosphate sorption efficiency than those from the eutrophic lakes based on the lower TOC, TP, TN, Al, Fe, and Ca contents. 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