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 composi- tions [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.