Environ Monit Assess (2014) 186:2121–2133 DOI 10.1007/s10661-013-3522-7 Water and sediment quality in Qinghai Lake, China: a revisit after half a century Hongyi Ao & Chenxi Wu & Xiong Xiong & Liandong Jing & Xiaolong Huang & Kai Zhang & Jiantong Liu Received: 27 June 2013 /Accepted: 28 October 2013 /Published online: 9 November 2013 # Springer Science+Business Media Dordrecht 2013 Abstract Qinghai Lake, situated on the Qinghai–Tibet of C/N suggest that the organic matter in the sediments plateau, is the largest lake in China. In this study, the are primarily from autochthonous sources. TN and total water and sediment quality were investigated in Qinghai organic carbon in the sediment cores increased slowly Lake, three sublakes, and five major tributaries. Both up the core while TP and total inorganic carbon have Na+ and Cl− were found to be the major ions present in been fairly constant. Qinghai Lake and the three sublakes, while Ca2+ and HCO3− dominated the tributaries. Compared with his- Keywords Water and sediment quality. Qinghai Lake . + torical data from the 1960s, the concentrations of NH4 , Ion composition − NO3 , and soluble reactive silica have increased consid- erably, likely caused by increased human activities in the area. Compared to the historical data, chemical Introduction oxygen demand has increased and lake water transpar- ency has decreased, likely related to an increase in Qinghai Lake (36°32′−37°15′N and 99°36′–100°47′E) nutrient levels. Relatively high concentrations of total isaremoteclosedsemisalineinlandlakesituatedonthe nitrogen (TN) and total phosphorus (TP) were observed Qinghai–Tibet plateau at an altitude of about 3,200 m. It in Qinghai Lake sediments, although P fraction types is the largest lake in China, with a surface area of and low water concentrations of these two indicate low roughly 4,500 km2 and a catchment area of over possibility of transfer into the water column. The ratios 30,000 km2. The average and maximum water depths of the lake are 19 and 29 m, respectively. Forty rivers flow into the lake, most of which are seasonal. Seven Electronic supplementary material The online version of this major rivers account for about 95 % of the total dis- article (doi:10.1007/s10661-013-3522-7) contains supplementary charge into the lake. Decreases in the main lake water material, which is available to authorized users. : : : : : levels over recent decades have created three sublakes H. Ao C. Wu (*) X. Xiong L. Jing X. Huang (Li et al. 2007;Colmanetal.2007). Currently, Gahai : * K. Zhang J. Liu ( ) and Erhai are hydrologically independent while Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, People’sRepublicofChina Jinshawan is still partially connected to the main lake e-mail: [email protected] through a narrow channel. The Qinghai Lake area is e-mail: [email protected] located at the crossroads of several bird migration routes in Asia, and many species, including several endangered X. Xiong : L. Jing : X. Huang : K. Zhang University of Chinese Academy of Sciences, ones, use the lake as an intermediate stop during their Beijing 100039, People’s Republic of China migration. For the protection of wildlife and the lake 2122 Environ Monit Assess (2014) 186:2121–2133 ecosystem, Qinghai Lake Natural Reserve was five major tributary rivers (Heima, Caiji, Buha, established in 1975. Now the lake is considered one of Quanji, and Shaliu). Most of the sampling sites the most scenic places in China and attracts tourists from were referred to the survey in 1960s with few all over the world every year. more sampling sites added at the estuarine areas In 1961, the Chinese Academy of Sciences organized of the major tributaries. Sampling locations and an the first comprehensive field survey of Qinghai Lake overall map of the area are provided in Fig. 1. with a purpose to understand the lake geology, water Water samples were collected using an acrylic physicochemical properties, hydrodynamics, hydrobiol- water sampler (5 L). Surface sediment samples ogy, sedimentology, geochemistry, and diagenesis. The (0–10 cm) were collected in June using a collected data was primarily used to target petroleum Peterson sampler (25 L) from sites 01–03, 05–12, geology-related questions and was published in 1979 and 15–17. Three short sediment cores from sites (CAS 1979). Further studies have been conducted since 01, 08, and 09 (lengths of 9, 15, and 15 cm, the original survey, although the focus has been on respectively) were collected in August using a paleoclimate. Qinghai Lake is located in a transitional gravity sediment core sampler and were sliced at zone affected by East Asian and Indian monsoons and 1-cm intervals on-site. Water samples were stored westerly atmospheric flow (Jin et al. 2010). As a result, in polyethylene bottles and analyzed within 24 h the lake has been an ideal place for studying past global of collection. Sediment samples were stored in climate changes (Colman et al. 2007; Liu et al. 2011; polyethylene plastic bags and kept frozen (−20 °C) until Shen et al. 2005). analysis. Since the original survey in 1961, water quality research has been limited at Qinghai Lake due to Analysis the remote location. However, the rapid develop- ment of the local economy near the lake, as well Water transparency (Secchi depth, SD) was mea- as climate change, has begun to raise concerns sured using a Secchi dish. Water pH and temper- over water quality issues in the area. Between ature (T) were measured using a YSI pH60 pH 1959 and 2000, lake water levels have decreased meter. Dissolved oxygen (DO) and conductivity 3.35 m (Li et al. 2007) and overgrazing has (EC) were measured with a Mettler SevenGo caused the degradation of the surrounding grass- Duo meter. Major ions (K+,Na+,Ca2+,Mg2+, − 2− land (Zhang et al. 2006). The tourism industry is Cl ,andSO4 ) were analyzed using an ion chro- increasing rapidly in the area, with tourist arrivals matograph (883 Basic IC plus, Metrohm). Total increasing from roughly 400,000 in 2007 to over phosphorus (TP) was determined by ammonium one million in 2012. The stark changes since metamolybdate spectrophotometry after a potassi- 1960s to this once remote area are possibly putting um persulfate digestion. Chemical oxygen demand negative pressure on the local ecosystem. Therefore, the (CODMn) was determined using the potassium per- objective of this study was to generate updated water manganate alkaline method. Soluble reactive silica and sediment quality data for Qinghai Lake, several (SRSi) was determined using the yellow tributaries, and the sublakes. The results will provide a silicomolybdate method. Total dissolved solids (TDS) + current dataset to be used as a management tool for were measured gravimetrically. NH4 -N was deter- − assessing change to the lake area. mined by Nessler's reagent spectrophotometry. NO3 - N was determined by ultraviolet spectrophotometry. − NO2 -N was determined by naphthylethylenediamine − 2− Materials and methods spectrophotometry. HCO3 and CO3 were determined by titration. Chlorophyll a (Chl.a) was determined using Sampling a spectrophotometric method after extraction with ace- tone. All the analysis was performed following standard Field sampling campaigns were carried out in 2012, protocols (SEPA 2002). The method detection limits −1 −1 + June 15–18 and August 25–28. Surface water sam- were 0.01 mg L for TP, 0.02 mg L for NH4 -N, −1 − −1 − ples were collected from 27 sites at Qinghai Lake, 0.08 mg L for NO3 -N, 0.001 mg L for NO2 -N, three sublakes (Gahai, Erhai, and Jinshawan), and and 0.04 mg L−1 for SRSi. Environ Monit Assess (2014) 186:2121–2133 2123 Fig. 1 Geographic location of Qinghai Lake and sampling sites in Qinghai Lake, three sublakes (Gahai, Jinshawan, and Erhai), and five major tributary rivers (Heima, Caiji, Buha, Quanji, and Shaliu) Sediment samples were lyophilized, sieved to analyte was detected in blank samples, with the varia- <2 mm, digested at 450 °C in a muffle furnace for 3 h, tion of duplicate samples being less than 12 %. Analysis and analyzed for TP following the methods described in of standards showed analytical accuracy to be over Paludan and Jensen (1995). Phosphorus fractions in the 90 %. surface sediment samples were extracted according to the sequential fractionation methods described in Hupfer et al. (1995) and Pettersson et al. (1988). These Results and discussion methods allow phosphorus to be fractionated into loose- ly sorbed phosphorus (NH4Cl-P), reductant soluble Physicochemical parameters and major ion composition phosphorus (BD-P), metal oxide-bound phosphorus in water (NaOH-SRP), organic phosphorus (NaOH-NRP), calcium-bound phosphorus (HCl-P), and residual phos- The physicochemical parameters and major ion compo- phorus (RP). Total nitrogen (TN) was determined using sition of the surface water samples from Qinghai Lake, a Kjeldahl analysis system (S5, Behr Labor Technik). three sublakes, and five major tributary rivers are sum- Total carbon (TC) and total organic carbon (TOC) were marized in Table 1 and provided in full in the analyzed using a TOC analyzer (Vario TOC cube, Supplementary material. All water samples were weakly Elementar), and total inorganic carbon (TIC) was calcu- basic with pH values of 8–9. The pH was slightly higher lated as the difference between TC and TOC. in August than in June and can be attributed to the For both water and sediment quality test, blank sam- growth of phytoplankton consuming more CO2 in sum- ples, duplicates, and standards were routinely checked mer (August) compared to the spring (June). The pH of during the sample analysis for data quality assurance tributary water samples was about half a unit lower than and quality control purposes. Generally, no target that of Qinghai Lake and sublakes, presumably related 2124 Ta b l e 1 Physicochemical parameters and major ion composition of the surface water samples from Qinghai Lake, sublakes, and tributary rivers − Site Month pH DO SD EC TDS Chl.a Major ions (mg L 1) −1 −1 −1 −1 + + 2+ 2+ − 2− 2− − (mg L )(m)(mScm)(gL)(μgL )K Na Ca Mg Cl SO4 CO3 HCO3 Qinghai Lake Jun.