Spatial Variation of P and N in Water and Sediments of Dianchi Lake, China

Pedosphere 15(1): 78-83, 2005ISSN 1002-0160/CN 32-1315/PG 2005 SCIENCE PREss, BEIJINGSpatial Variation of P and N in Water and Sedimentsof Dianchi Lake, China*1LU Jun-Jie, YANG Hao, GAO Li and YU Tian-YingState Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing210008 (China). E-mail: jjlw@issas.ac.cn(Received August 9, 2004; revised October 10, 2004)ABSTRACTDianchi Lake is one of the most eutrophic lakes in China. In order to understand this eutrophication and to help.control the pollution, this research investigated the spatial distribution of Kjeldahl nitrogen (K-N) and total phosphorus(TP) through analysis of bottom water and sediment (3 depths) samples collected at 118 sites around Dianchi Lake. Theconcentrations of K-N and TP for the lake bottom water in the Caohai part of the lake were much higher than those inthe Waihai part, generally decreasing from north to south. In the sediments, the K-N concentration was higher in theCaohai part and the middle of the Waihai part. On the other hand, TP in the sediments was greater in the southernand western parts. Both K-N and TP had similar spatial distributions for the sediment samples of three diferent depths.Vertically, the K-N and TP concentration in the sediments decreased with an increase in depth. This was evidence thateutrophication and pollution of Dianchi Lake was becoming gradually more severe. Exterior factors including uncontrolledinput of domestic and industrial effuents as well as non- point pollution around the lake were the main reasons for seriouseutrophication; therefore, controlling these was the first step in reducing eutrophication of Dianchi Lake.Key Words: nitrogen, phosphorus, sediments, spatial distribution, waterINTRODUCTIONEutrophication of inland water has been a topic of widespread interest since the 1960's (Vezjak et al,1998; Koelmans et al, 2001). The effects of eutrophication could be catastrophic with blue-green algalblooms resulting in livestock deaths, human sickness, and interference with water supplies (Bowlingand Baker, 1996). With the development of its economy, lake eutrophication has also become a seriousenvironmental problem in China (Jin, 2001; Dokulil et al, 2000; Chen et. al, 2002; Pei and Wang,2003).Presence of phosphorus in water and sediments is often related to eutrophication (Flanner et al,1982; Zhang et al, 2003; Lu et al, 2004) or to the trophic development of lakes (Gonsiorczyk et al,1998). The increase of phosphorus concentration is a crucial factor causing the eutrophication of waterbody, while land use has an important impact on agricultural non-point sources phosphorus discharge(Yang et al, 2003). In addition, nitrogen is also a major contributor to lake eutrophication (Andreadakisand Katsara, 1996). Murphy et al. (2001) also found that the release of phosphorus from sedimentswas at least partially responsible for the appearance of blue-green algal blooms.In Dianchi Lake, located in the southwest of Kunming City, Yunnan Province, Southwest China, theserious deterioration of water quality from eutrophication was quantified in terms of increased nutrients(Gray and Wang, 1999). Nevertheless, the first step in estimating the level of eutrophication in lakes wasto determine the level of nitrogen and phosphorus in the water and sediments. In order to understandthe eutrophic circumstances, the spatial distribution of eu中国煤化工nd sediments couldbe estimated (Kitsiou and Karydis, 2000; Denis -KarafistanYHC N M H Ghe objective of thispaper was to investigate the spatial distribution of KjeldahI nitrogen and total phosphorus in water andsediments in the severely eutrophic Dianchi Lake in order to understand the anthropogenic and physicalfactors afecting eutrophication, thereby assisting in water quality restoration.Proje万势数据ed by the State Key Laboratory of Soil and Sustainable Agriculture, China (No 5022505).SPATIAL VARIATION OF P AND N IN WATER AND SEDIMENT79MATERIALS AND METHODSAn artificial dam located near Haigeng divided Dianchi Lake into two parts, i.e, Caohai and Waihai(Fig. 1). The lake has the following characteristics: elevation, 1885 m; length, 32 km (from north tosouth); mean width, 7.6 km; maximum depth, 8 m; average depth, 5.0 m; and surface area, 310 km2(with the Caohai part being about 10 km2). .好KunmlnpRNVOSSHaigengeiCaohai1 BaONi)NAHuiwanDounanGuanyinshanTaqyu RiverTanglangRiverLegendRiVer●City, town orP fertizer faqto'yfactorySampling siteKunyangFertiizer jactory8kmFig. 1 Dianchi Lake with sampling sites.A total of 118 sediment and water sampling sites (5 sites were located in the Caohai part) aroundthe lake (Fig. 1) were fixed with Global Positioning System (GPS). At each site, sediment samples werecollected from 0-5, 5- 10, and 10- -20 cm layers, respectively, with a Uwitec Core sampler (Made inAustria) and air-dried from May 7 to July 30, 2002. Water samples at each site were collected from thebottom layer of water (the interface of the water and sediment, with the distance to the sediment surfaceof about 10 cm) using an exhaust sampler (made in the Institute of Hydrobiology, Chinese Academy ofSciences). At the time of water sampling, the sampling barrel (2.5 L, polyethylene) was rinsed 3 timeswith the water sample, filled, immediately sealed, and the中国煤化工4- -8 hours. Standardmethods for water and wastewater examination (State|YHCNMH G Administration ofChina, 1998) were utilized for the water and sediment sample analysls. The parameters chosen formeasurement included Kjeldahl nitrogen (K-N) and total phosphorus (TP). .Descriptive statistics tables were obtained through the statistical software SPSS (Version 11.5). Mapswere drawn based on the geographic information system (GIS) software ArcView and ArcMap. Carto-80J.J. LU et al.graphic techniques employed the IDW (inverse distance weighted) interpolation method.RESULTSKjeldahl nitrogen and total phosphorus in water at the water- sediment interfaceResults of Caohai and Waihai water samples for Kjeldahl nitrogen are given in Table I. It could beseen obviously from the table that the water K-N concentration was much higher in the Caohai partthan in the Waihai part. In the bottom water samples the spatial distribution of Kjeldahl nitrogenconcentration around the lake was uneven (Fig. 2a). Higher concentrations were mainly found at thenorthern part of the lake with low concentrations at the southern part.TABLE IResults of water and sediment samples for Kjeldah! nitrogen (K-N) and total phosphorus (TP) from the two parts, Caohaiand Waihai, of Dianchi LakeLakeItemSedimentWater of lakepart ,bottomK-NTP0 -5cm 5-10 cm10-20 cm0-5cm 5-10 cm10- -20 cmgkg1mg L-1CaohaiSample No.55Minimum3.251.521.480.570.450.443.200.83Maximum13.7920.3614.442.231.8513.961.24Mean10.5412.048.741.931.301.066.74Stanc4.436.84.861.260.680.714.300.19deviationWaihai Sample No.113112101031020.410.380.400.250.810.260.069.957.57.956.666.156.4118.130.735.644.372.502.301.991.861.540.20Stand1.901.140.880.931.770.11 .bNAK.N (mgL")TP (mgL')曾8:9:8:382.85-5.01中国煤化工48km9.76-18.13YHCNMHGFig. 2 Spatial distribution of Kjeldahl nitrogen (K-N) (a) and total phosphorus (TP) (b) in the lake bottom water ofDianchi Lake..SPATIAL VARIATION OF P AND N IN WATER AND SEDIMENTResults of Caohai and Waihai lake bottom water samples for total phosphorus are also shown inTable I. As with Kjeldahl nitrogen, total phosphorus in Caohai was also much higher than in Waihai.In Fig. 2b the spatial distribution of TP for lake bottom water showed higher concentrations in thenorthern and western parts of Dianchi Lake, while much lower concentrations in the eastern part.K-N and TP in the sedimentsTable I shows Kjeldahl nitrogen in the sediments for the Caohai and Waihai samples. For eachlayer, the mean value of K-N in the Caohai sediment samples was much higher than that in the Waihaisediment samples. The middle part of Waihai had high sediment nitrogen concentrations (Fig. 3) whilemost parts along the shoreline had low concentrations. Similar distribution patterns were found in the5- -10 and 10- 20 cm sediment layers for the two parts of the lake. Also, the mean Waihai sediment K-Nconcentrations decreased from the surface to lower depths.abN▲mA(A ehinK-N (g kg')K-N{g kg") .K-N{gkg")040-375? 40-1936:38-9.994.18-6.258 00-10.0810.33-13.456.26-8.8810.09-13 8013. 46-20.408.89-14.40 !4 8km048 kmFig. 3 Spatial distribution of Kjeldahl nitrogen (K-N) in the sediments of Dianchi Lake: 0 5 (a), 5-10 (b) and 10-20 (c)cm.Table I also exhibits means of total phosphorus in the sediment samples at three depths for the Caohaiand Waihai samples. Obviously, TP in the southern part of Waihai was higher than TP in the northernpart of Waihai and TP in Caohai. The spatial distribution of TP in Fig. 4 revealed high concentrationsof TP in the southern and western parts of Dianchi Lake. The spatial distribution patterns of the threelayers were similar, having no obvious differences, with the mean TP in the sediment samples decreasingwith depth.DISCUSSIONThe K-N and TP concentrations in the water were fo中国煤化工aohai part than theWaihai part of Dianchi Lake. This was because Caohai,chi Lake, was closeto Kunming City and directly received most of the city's:.HCNMHGwage which had notbeen treated prior to discharges into the lake. Thus, the large volume of sewage discharged into theCaohai part resulted in severe pollution.The spatial distributions of K-N and TP for the three layers in the sediments showed differentB2J.J.LUetal.abCN▲ATP(gkg).TP(g kg)TP(gkg )0.40-1.7994βkm4.30-6.66948km '3.86-6.15948kmFig. 4 Spatial distribution of total phosphorus (TP) in the sediments of Dianchi Lake: 0-5 (a), 5- 10 (b) and 10 -20 (c)cm.patterns, with high K-N concentrations for Caohai and the middle part of Waihai. Vegetable and flowerproductions were important near the northwestern part of Kunming City. This meant high fertilizerapplication that would result in high nitrate loss from the land and high nitrogen input to the lake.Additionally, there was difficulty in controlling agriculture non- point pollution sources, which could haveaccounted for a greater percentage of pollution.On the contrary, the TP concentration appeared highest in the southern and western parts ofDianchi lake. This was due to accumulation of nitrogen and phosphorus in sediments caused by bothpoint and non- point pollution. In addition to domestic sewage and agricultural non-point pollution,industrial pollutants were a primary reason for spatial variation in TP. Much higher TP was recordedin the southwestern and southeastern parts of Dianchi lake, which neighbored the Kunyang PhosphorusFertilizer Factory and the Kunming Fertilizer Factory. Meanwhile, for the northern part of the lake,some of the sediments consisted of residual aquatic vegetation, which possibly caused the high nitrogenconcentration (Fig. 3). Although TP in the sediments of Caohai was low (Fig. 4) especially at lowerdepths due to a 4-km2 area being dredged in 1999, the TP concentration of the water was still high(Fig. 2b).Vertically the K-N and TP concentrations in the sediments decreased with an increase of depth(Table I). This was evidence that eutrophication and pollution of Dianchi was gradually becoming moresevere. Control measures to reduce the sewage flow to the lake have been in place for many years,however, the lake maintained its severe eutrophic state. This suggested that lake eutrophication wasa complex matter. The first step in controlling Dianchi Lake eutrophication should be decreasing thedischarge of domestic and industrial efuents from Kunming City and the surrounding areas.中国煤化工REFERENCESAndreadakis, A. D. and Katsara, A. 1996. 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