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Article

Analysis of Water Chemistry Characteristics and Main Ion Controlling Factors of Lakes in the Nagqu Area of the Qinghai–Tibet Plateau in Summer

by
Yifan Jin
1,
Boshan Zhu
1,
Fang Wang
1,*,
Shichun Sun
2,
Pengfei Wang
2 and
Xiaoshou Liu
3
1
The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China
2
Institute of Evolution and Marine Biodiversity, Ocean University of China, Qingdao 266003, China
3
College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China
*
Author to whom correspondence should be addressed.
Water 2023, 15(16), 2900; https://doi.org/10.3390/w15162900
Submission received: 5 July 2023 / Revised: 3 August 2023 / Accepted: 8 August 2023 / Published: 11 August 2023
Browse Figures
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Abstract

:
The Nagqu area is in the northern part of the Qinghai–Tibet Plateau, and its average altitude is above 4000 m. Due to the area’s high altitude, there is relatively little information about its lakes. Therefore, to supplement the basic information of lakes in the area, this study collected surface water samples from 12 lakes, including Gangtang Co, Pusaier Co, Guojialin Co, Dagze Co, Yangnapeng Co, Bankog Co, Dangqung Co, Chaxiabu Co, Angdar Co, Bengze Co, Guogen Co, and Yibug Caka from July to August 2020. Furthermore, the factors controlling the lake water chemistry characteristics and the main ion sources were explored using the Piper, Gibbs, and ion ratio methods. The results were as follows: (1) The lakes had high levels of salt, alkalinity, and mineralization, and all the lakes except Bengze Co were salt lakes. The 12 lakes met the Class V water standard. (2) Dangqung Co, Bankog Co, Guojialin Co, Daze Co, and Yangnapeng Co were in the initial stage of lake succession, while the others were in the later stages of lake succession. (3) Evaporation–crystallization was the most important factor controlling the water chemistry of the 12 lakes, and most of the ions in the lakes come from the dissolution of evaporite.

1. Introduction

Lakes are an important component of the terrestrial hydrosphere, the natural water cycle, water regulation, and material and energy exchange. Furthermore, in addition to playing an important role at the ecosystem level, lakes are valuable repositories of information that can help understand climate, environmental, and hydrological changes [1,2,3,4]. Lake ecosystems are highly vulnerable, and due to the heavy reliance of human beings on their resources, lake acidification and eutrophication have become increasingly prominent problems [5,6,7]. Plateau lakes are especially vulnerable and have particularly unique geographical features, developmental drivers, and biological species, all of which elevate their ecological value [8].
The average altitude of the Qinghai–Tibet Plateau exceeds 4500 m [9]. Known as the “Asian Water Tower”, it is the source of major rivers in China [10]. It is also home to the highest, most numerous, and largest group of lakes on Earth [11], making it one of the most densely distributed lake areas in the world [12]. The Qinghai–Tibet Plateau is divided into internal and external water systems by the Qilian Mountains, Bayan Har Mountains, Nyainqentanglha Mountains, and Gangdise Mountains. Most of the internal water system is located in the northwest part of the Qinghai–Tibet Plateau and includes the Qiangtang Plateau, Chaidamu Basin, and some small closed lake basins; this water system is mainly supplied by precipitation, surface runoff, snow, and glacier melt [13]. This internal water system includes a large number of lakes and glaciers, with most of the lakes in the system being saline and salt lakes [14]. Overall, due to the high altitude and low intensity of human activities, the actual surface water environment and water quality of the Qinghai–Tibet Plateau have been well preserved. Moreover, due to its unique geographical location, the lakes of the plateau contain a large number of unique biological resources, such as Artemia and Dunaliella salina [15], which contribute rich economic, ecological and cultural values to the local area.
However, due to global warming, the distribution of lake water bodies has undergone significant changes. Between 1984 and 2015, approximately 9.00 × 104 km2 of all global permanent surface water bodies disappeared, while new water bodies making up an area of 1.84 × 105 km2 were formed [16]. As the world’s third pole, the Qinghai–Tibet Plateau has been particularly heavily affected [17]. According to research, the temperatures of most lakes on the Qinghai–Tibet Plateau have risen at a rate of 0.08 degrees per year [18], which is twice the global average [19]. This temperature increase has led to the melting of glaciers and frozen soil on the Qinghai–Tibet Plateau and increased rainfall, which has caused varying degrees of increase in lake area and depth [18,19,20,21] and affected the ion composition of lakes. Ion composition is an important indicator for evaluating the water environment [22], and it reflects the strength of lake water environmental processes, surface weathering, and erosion, as well as climate change, rock and mineral characteristics, and human activities [23,24,25,26]. Ion composition is highly valuable for determining the geochemical sources of water ions, regional chemical weathering, and the relationship between water temperature and geochemistry [27]. Due to environmental, transportation, and social historical developmental constraints, the water environment of the Qinghai–Tibet Plateau remains in a relatively pristine state [28]. Therefore, conducting investigations on the water chemistry of lakes on the Qinghai–Tibet Plateau is of great urgency [29]. To date, most research has focused on Selin Co [30,31,32], Qinghai Lake [33,34,35], and Yarlung Zangbo River [36,37], while relatively little work has focused on the water chemistry of lakes in the Nagqu area. Nagqu City is located between the Tanggula Mountains, Nyenchenthanglha Mountains, and Kailas Range in northern Tibet. It has abundant salt resources such as rock salt and saltpeter. The Gangtang Co, Pusaier Co, Guojialin Co, Dagze Co, Yangnapeng Co, Bankog Co, Dangqung Co, Chaxiabu Co, Angdar Co, Bengze Co, Guogen Co, and Yibug Caka investigated in this study are recorded in the China Lakes Record [38] and China Salt Lake Chronicle [39], but the investigation time of these sources is relatively old, and data for some lakes are scarce. In order to enrich the basic data of lakes in Nagqu region and provide a baseline data reference for the future impacts of global warming on plateau lakes, we conducted a survey on the 12 lakes mentioned above. This investigation collected surface water samples from the 12 lakes from July to August 2020 to analyze their water chemistry characteristics and main factors controlling their ion concentrations.

2. Materials and Methods

2.1. Study Area Overview

The Nagqu area is in the northern part of the Qinghai–Tibet Plateau at an average altitude of about 4500 m. Due to the plateau terrain, the climate is dry, cold, hypoxic, and experiences little rainfall. The annual average temperature ranges from −3.30 to −0.90 °C, reaching the highest temperatures in July and temperatures as low as −40 °C in December. The oxygen content is half that at sea level and the relative humidity is 48.00–51.00%. The annual average precipitation ranges from 247.30 to 513.60 mm, mainly concentrated from June to September [40,41] when as much as 80% of the annual total rainfall can occur. The lakes surveyed in this study were mainly located in Shuanghu County, Nyima County, and Bangor County (Figure 1).

2.2. Sample Collection, Testing, and Analysis

2.2.1. Sample Collection

Surface water samples were collected from the 12 lakes (Table 1) from July to August 2020. Sampling was conducted 5 m from the shore and at a surface water depth of 0–5 cm. Three samples were collected and mixed and they were frozen at −20 °C before being brought back to the laboratory for analysis.

2.2.2. Sample Testing

A YSI portable water quality analyzer was used to monitor the conductivity, pH, dissolved oxygen, and salinity of lake water on-site. The alkalinity, CO32−, and HCO3− of the water were determined by acid–base titration, and the hardness, Ca2+, and Mg2+ were determined by EDTA complexometric titration. The contents of Cl−, SO42−, and K+ were determined using the CleverChem380 nutrient analyzer (DeChem-Tech GmbH, Hamburg, Germany), with Cl− determined using the mercury thiocyanate method, SO42− determined using the barium sulfate turbidity method, K+ determined using the tetraphenylborate method, and the Na+ content was calculated using the anion–cation charge balance method. The alkaline potassium persulfate-UV spectrophotometric method was used to measure the total nitrogen (TN) content, the potassium persulfate oxidation method was used to measure the total phosphorus (TP) content, and the zinc-cadmium reduction method was used to measure the nitrate nitrogen (NO3-N) content. The CleverChem380 nutrient analyzer was used to measure the nitrite nitrogen (NO2-N), ammonia nitrogen (NH4-N), and orthophosphate (PO4-P) content, with the nitrite nitrogen determined using the diazo coupling method, ammonia nitrogen determined using the indophenol blue method, and orthophosphate determined using the phospho-molybdenum blue method [42].

2.2.3. Classification of Lake Water Chemistry

The Piper diagram was used to determine the water chemistry type and succession stage of the lake [11]; and the surface water environmental quality standards were used to determine the trophic level of the lake. The Gibbs diagram was used to identify the controlling units of the lake’s water chemistry composition. Pearson correlation coefficients were used to analyze the relationship between ions and if the data did not conform to the normal distribution, they were logarithmically treated. Ion concentration ratios were used to determine the sources of ions in the lake.

3. Results and Discussion

3.1. Lake Water Chemistry Characteristics

3.1.1. Physicochemical Analysis of Lakes

The basic water characteristics of the 12 lakes in July–August are shown in Table 2. During the investigation period, the average temperature of the lakes was 16.09 °C, the pH range was 8.19–9.24, the dissolved oxygen range was 3.58–12.82 mg·L−1, the salinity range was 0.64–106.90 g·L−1, the conductivity range was 1.27–138.20 mS·m−1, the alkalinity range was 12.38–351.04 mmol·L−1, and the hardness range was 8.20–121.35 mmol·L−1.
The total dissolved solids (TDS) values were calculated as the sum of the eight major ions in the lake water [11] and ranged from 3.53 to 47.27 g·L−1. According to the classification standards of the main ion contents in lake water [43], Bengze Co was a saline lake (3.50–5.00 g·L−1) and the other lakes were salt lakes (>5.00 g·L−1). The TDS of the 12 lakes in the Nagqu area were higher than those of the rivers and lakes in plain areas. For example, the TDS of Taihu Lake ranged from 276.08 to 681.54 mg·L−1 [25], and that of Songhua River was less than 270.00 mg·L−1 [44]. The TDS of lakes is affected by factors such as lake precipitation, evaporation, and basin rock composition [45]. Strong evaporation may have been the driving factor underlying the high TDS of the 12 lakes in the Nagqu area [45]. However, the TDS of most lakes surveyed in this study were significantly lower compared with the records of lake salinity in the China Salt Lake Chronicle [39], which is likely related to global warming and the melting of glaciers and snow.

3.1.2. Nutrient Levels of Lake Water

Lake eutrophication is the phenomenon in which lake productivity is increased due to the influx of large amounts of nutrients from either natural or anthropogenic sources. Nitrogen and phosphorus inputs are considered the main factors that drive lake eutrophication [46].
The total nitrogen content in the 12 surveyed lakes ranged from 4.47 to 16.22 mg·L−1, and the total phosphorus content ranged from 0.89 to 3.40 mg·L−1. Among them, the highest total nitrogen (16.22 mg·L−1) and total phosphorus (3.40 mg·L−1) contents were found in Dangquang Co, and the lowest total nitrogen (4.47 mg·L−1) and total phosphorus (0.89 mg·L−1) contents were found in Yibug Caka (Figure 2a). The lake water samples had ammonia nitrogen contents ranging from 0.03 to 0.18 mg·L−1, nitrate contents from 0.07 to 0.12 mg·L−1, nitrite contents from 0.01 to 0.02 mg·L−1, and orthophosphate contents from 0.75 to 2.63 mg·L−1. The concentrations of ammonia nitrogen, nitrate, nitrite, and orthophosphate did not vary much among the 12 lakes. The nitrate concentration in Bengze Co was higher than in the other 11 lakes. This may have been because ammonia nitrogen and nitrite were converted into nitrate through nitrification in this lake. Nitrification is influenced by temperature and dissolved oxygen, both of which were highest in Bengze Co in this study, possibly enhancing nitrification rates and resulting in higher nitrate levels [47]. The phosphorus content was highest in Dangqung Co and lowest in Bengze Co. This may have been due to differences in salinity (106.90 g·L−1 in Dangqung Co and 0.64 g·L−1 in Bengze Lake), which can affect the concentrations and species of phytoplankton in lakes and subsequently affect the phosphorus content in the water.
Using the single-factor evaluation method [48], the water quality of the 12 surveyed lakes was evaluated based on their nitrogen and phosphorus contents [43,49]. The total nitrogen content in the lakes ranged from 4.47 to 16.22 mg·L−1, and the total phosphorus content ranged from 0.89 to 3.40 mg·L−1. According to the classification criteria in Table 3, the surveyed lakes had Class V water.
The nitrogen-to-phosphorus ratio is the primary indicator used to examine the nutrient structure of lakes [50]. N/P ratios less than 16 indicate that nitrogen is the limiting factor and phosphorus is relatively abundant, while N/P ratios greater than 16 indicate that phosphorus is the limiting factor and nitrogen is relatively abundant [51,52]. The nitrogen-to-phosphorus ratios of the 12 lakes surveyed in this study ranged from 2.97 to 10.98, indicating that nitrogen was the limiting factor.
Due to the high altitude of the surveyed lakes (above 4500 m), there was relatively little anthropogenic influence. The low correlation coefficients (<0.5) between NO3− and other ions indicated that agricultural activities made relatively small contributions to the nitrogen and phosphorus in the lake water [26]. Therefore, the high nitrogen and phosphorus contents in the surveyed lakes might have been related to the high pH, salinity, alkalinity, and hardness of the lake water, which can limit the biomass of phytoplankton and result in a low nutrient utilization rate. In addition, any nutrients generated from the decomposition of dead planktonic organisms in the lakes are retained because the water exchange between the lakes and external rivers is limited, and strong evaporation can also lead to higher concentrations of nutrients resulting in the accumulation of nutrients in the lakes over time and ultimately leading to eutrophication.

3.2. Lake Water Chemical Types

All lakes contained all eight major ions with the exception of Yibug Caka where CO32− was not detected (see Table 4). Na+ had the highest equivalent concentration in all surveyed lakes and was the dominant cation, accounting for 73.14–95.14% of the cations. All the points in Figure 3 fell at one end of the cation triangle (Na+ + K+), reflecting the dominance of Na+. Mg2+ was the second most abundant cation, accounting for 4.51–22.12%. The dominant anions varied among the lakes, as illustrated by the distribution of the 12 points in the anion triangle in Figure 3. Most lakes were dominated by CO32− + HCO3−, with the highest proportion found in Yangnapeng Co (81.62%) and the lowest in Yibug Caka (1.98%). Chaxiabu Co and Angdar Co were dominated by SO42−, where it accounted for 45.68% and 52.26%, respectively. Bengze Co, Guogen Co, and Yibug Caka were dominated by Cl−, where it accounted for 39.68%, 41.68%, and 58.28%, respectively.
The hydro-chemical characterization of lakes samples is shown in the Piper trilinear diagram [53]. The results show that the water chemistry profiles of Gangtang Co, Pusaier Co, Guojialin Co, Dagze Co, Yangnapeng Co, Bankog Co, and Dangqung Co were of the carbonate sodium type, Chaxiabu Co and Angdar Co were the sulfate sodium type, Bengze Co was the chloride sulfate sodium type, and Guogen Co and Yibug Caka were the chloride sodium type.
Due to its unique geographical location and climate, the lakes on the Qinghai–Tibet Plateau follow the following evolutionary pattern: freshwater lake → saline lake → salt lake → dry salt lake [54], and their water chemistry evolves along the following pattern: carbonate type → sulfate-sodium type → magnesium sulfate type → chloride type [29]. Based on the Piper diagram (Figure 3), the lake water could be divided into Ca(Mg)-SO4 (Zone A), Ca-HCO3 (Zone B), Na(K)-Cl(SO4) (Zone C), and Na-HCO3 (Zone D) types. The figure shows that the lakes located in Zone C, including Gangtang Co, Angdar Co, Yibug Caka, Pusaier Co, Bengze Co, Chaxiabu Co, and Guogen Co, had the Na(K)-Cl(SO4) water chemistry type, indicating that they are in a later stage of lake succession. The lakes located in Zone D, including Dangqung Co, Bankog Co, Guojialin Co, Daze Co, and Yangnapeng Co, had the Na-HCO3 water chemistry type, indicating that they are in an earlier stage of lake succession.

3.3. Lake Water Chemistry Characteristics and Types

3.3.1. Gibbs Diagram

In 1970, Gibbs [55] conducted a global analysis of the chemical compositions of different surface water types, such as rainwater, river water and lake water, and then proposed the Gibbs model which includes three natural factors controlling the elements in surface water: atmospheric precipitation, rock weathering, and evaporation–crystallization. In this study, since the concentration of Ca2+ in the 12 lakes was low, the concentration of Na+/(Na+ + Ca2+) in the lakes was high, with values above 0.99. Due to the different dominant anions in different lakes, the value of Cl−/(Cl− + HCO3−) varied greatly, ranging from 0.18 to 0.95. The points representing the 12 lakes in Figure 4a,b all fell in the upper right area of the Gibbs diagram, indicating that the lakes experienced strong evaporation and that the chemical composition of lake water was mainly controlled by evaporation–crystallization. Similar conclusions have been drawn in studies of other lakes, such as Namtso Lake [23] and Qinghai Lake in Tibet [56], and Hulun Lake, Dali Lake, and Wuliangsuhai Lake in inner Mongolia [45]. However, some lakes, such as Bengze Co in Figure 4a and Yangnapeng Co, Dangqung Co, and Chaxiabu Co in Figure 4b, fell outside the dashed line, similar to Chencuo Lake [22] and Qinghai Lake [56] in Tibet. This may have been because the Gibbs model is mainly based on large lakes and rivers and may not be applicable to small water bodies and small lakes in arid and semi-arid areas [57]. In addition, the lakes surveyed in this study fell in the upper right area of the Gibbs diagram, indicating a tendency for continued evaporation. Strong evaporation can lead to high TDS and high EC values in lakes and cause Ca2+ to form low-solubility mineral components, such as calcium carbonate, resulting in a reduced proportion of Ca2+ in the total cations.

3.3.2. Correlation Analysis Studies

Berner [58] and others have shown that ions in water are mainly soluble components released from terrestrial rocks, sea salt components carried by atmospheric circulation, and salts introduced by human activities. A correlation analysis can reveal the relationships between cations and anions in lake water. Ions with strong correlations are likely to have common sources or be subject to similar geochemical processes. Larger correlation coefficients (absolute value closer to 1) indicate stronger correlations between two variables, in this case ions, and smaller correlation coefficients (absolute value close to 0) indicate weaker correlations.
According to Table 5, CO32−, HCO3−, Na+ and Mg2+ were positively correlated with TDS, and the correlations were relatively strong. This indicated that increases in their contents could increase the mineralization of lake water during the lake evolution. This was especially true for Na+, which had a correlation coefficient with TDS as high as 0.99, indicating that Na+ concentration was closely linked to TDS. Ca2+ and Mg2+ usually come from the dissolution of carbonate or silicate minerals. The strong correlations between CO32−, HCO3−, and Mg2+ indicated that the dissolution of carbonates affects the source of ions in lakes. The lack of a significant correlation between nitrate and other ions suggested that anthropogenic inputs were not an important source; rather, nitrate might come from algae and bacteria in the water that fix nitrogen from the air into biologically available compound forms and accumulate in the lake water.

3.3.3. Main Sources of Ions in the Lakes

When studying the main components of natural water bodies, the contents and proportions of major ions can be used to identify the possible sources of dissolved substances in terrestrial water bodies, such as atmospheric precipitation, weathering of evaporite, carbonate and silicate rocks, deep high-mineralization fluid sources, and human-generated pollutants [59]. Under natural processes, Ca2+ and Mg2+ can come from the dissolution of carbonate, silicate, or evaporite rocks, while Na+ and K+ ions can come from the weathering of evaporite and silicate rocks. HCO3− and CO32− mainly come from the dissolution of carbonate rocks, while Cl− and SO42− mainly come from eroding evaporite [60,61]. As all 12 lakes were located at altitudes over 4000 m and not affected by human activities, the impact of human activities as sources can be ignored. Therefore, given the arid climate conditions in the region, it was concluded that rock weathering and leaching were the main sources of ions in the lakes.
The equivalent ratios of (Na+ + K+)/(Ca2+ + Mg2+) and (HCO3− + CO32−)/(Cl− + SO42−) are usually used to determine the contributions of different types of rock weathering to lake water ions [28]. According to Figure 5a, the equivalent concentration ratio of (Na+ + K+)/(Ca2+ + Mg2+) was greater than 1 in all 12 lakes, while the equivalent concentration ratio of (HCO3− + CO32−)/(Cl− + SO42−) was less than 1 in most lakes (Figure 5d). Furthermore, (HCO3− + CO32−) was significantly greater than (Cl− + SO42−) in Dangqung Co, Daze Co, Bankog Co, and Yangnapeng Co, indicating that carbonate weathering had a high impact on these lakes.
When all Ca2+, Mg2+, HCO3−, CO32−, and SO42− in lake water come from carbonate and sulfate rocks, the equivalent concentration ratio of (Ca2+ + Mg2+)/(HCO3− + CO32+ SO42−) should be close to 1 [62]. However, as shown in Figure 5b, all 12 lakes fell below the y = x line, indicating that the Ca2+ and Mg2+ in the lakes came from the weathering of evaporite rocks, in addition to carbonate. When Ca2+ and Mg2+ in the water come from calcite (CaCO3) and dolomite [CaMg(CO3)2], the ratio of 2 (Ca2+ + Mg2+)/HCO3− should be close to 1 [27]. According to Figure 5c, most lakes were close to this ratio, indicating that Ca2+ and Mg2+ mainly came from carbonate dissolution and that the dissolution of dolomite exceeded that of calcite.
Na+ and K+ usually come from the dissolution of evaporite. When all Na+ and K+ in a lake come from evaporite, the ratio of Cl−/(Na+ + K+) should be 1. When the ratio of Cl−/(Na+ + K+) is less than 1, it indicates that the weathering of silicate also contributed to the Na+ and K+ [59]. According to Figure 5e, all of the 12 lakes fell below the y = x line, indicating that the Na+ and K+ in the lakes come from silicate weathering in addition to evaporite weathering.
Na* = Na+ − Cl−, TZ = Na+ + K+ + 2 (Ca2+ + Mg2+), (Na* + K+)/TZ, or (Ca2+ + Mg2+)/TZ are commonly used to indicate the contribution of silicate dissolution to cations in lake water [27]. According to Figure 5a,d, the ions in Lake Gongtang, Co, Angdar Co, Yibug Caka, Chaxiabu Co, Pusaier Co, Guojialin Co, Guogen Co, and Bengze Co mainly come from evaporite or silicate weathering. The (Na* + K+)/TZ ratios of Angdar Co, Chaxiabu Co, Pusaier Co, and Guojialin Co were all slightly greater than 0.5 (Figure 5g), with an average value of 0.57, indicating that the ions in these lakes mainly come from silicate weathering, while the ions in the other four lakes mainly come from evaporite dissolution. The (Ca2+ + Mg2+)/TZ ratios of Dangqung Co, Daze Co, Bankog Co, and Yangnapeng Co were all less than 0.1 (Figure 5h), with an average value of 0.07, indicating that silicate weathering had a smaller impact on these four lakes, which is consistent with the conclusion in Figure 5d.

4. Conclusions

(1)
The pH values of all 12 lakes were above 8.00, indicating they were alkaline environments. The lakes had high levels of hardness, alkalinity, and mineralization, and most were salt lakes. According to the surface water environmental quality standards, all 12 lakes had class V water.
(2)
The cations in the 12 lakes were mainly Na+, and the anions were mainly HCO3− + CO32−. Gangtang Co, Angdar Co, Yibug Caka, Pusaier Co, Bengze Co, Chaxibu Co, and Guogen Co were in the later stages of lake succession, while Bankog Co, Dangqung Co, Guojialin Co, Dagze Co, and Yangnapeng Co were in the initial stage of lake succession.
(3)
The hydrochemical composition of the 12 lakes was controlled by evaporation–crystallization. The ions in the lakes may have similar sources, with most coming from the erosion of evaporite and carbonate rocks.

Author Contributions

Data curation: Y.J., B.Z. Investigation: Y.J., S.S., B.Z., P.W., X.L. Methodology: Y.J. Resources: F.W., S.S. Writing—original draft: Y.J. Writing—review and editing: F.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science and Technology Project of the Tibet Autonomous Region, grant number XZ202102YD0022C.

Data Availability Statement

The data presented in this study are available in the article.

Acknowledgments

We are appreciative to the reviewers for their guidance on this paper. And we are grateful to the local authorities for their support of this experiment. Thanks to all the authors for their contributions to this study.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Distribution of surveyed lakes. Chaxiabu Co, Gangtang Co, and Yibug Caka are located in Shuanghu County. Bengze Co, Guojialin Co, Dagze Co, and Dangqung Co, are located in Nyima County. Guogen Co, Pusaier Co, Yangnapeng Co, Angdar Co, and Bankog Co are located in Bangor County.
Figure 1. Distribution of surveyed lakes. Chaxiabu Co, Gangtang Co, and Yibug Caka are located in Shuanghu County. Bengze Co, Guojialin Co, Dagze Co, and Dangqung Co, are located in Nyima County. Guogen Co, Pusaier Co, Yangnapeng Co, Angdar Co, and Bankog Co are located in Bangor County.
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Figure 2. Nutrient content of surveyed lakes. (a) represents the total nitrogen and total phosphorus content. (b) represents the content of nitrate, nitrite, and ammonia nitrogen. (c) represents the content of orthophosphate.
Figure 2. Nutrient content of surveyed lakes. (a) represents the total nitrogen and total phosphorus content. (b) represents the content of nitrate, nitrite, and ammonia nitrogen. (c) represents the content of orthophosphate.
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Figure 3. Piper diagram of lake samples. The diamond in the diagram can be divided into four zones, representing the different types of water chemistry in the water body. The lower-left triangle is a cation triangle and the lower-right triangle is the anion triangle.
Figure 3. Piper diagram of lake samples. The diamond in the diagram can be divided into four zones, representing the different types of water chemistry in the water body. The lower-left triangle is a cation triangle and the lower-right triangle is the anion triangle.
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Figure 4. Gibbs chart. The Gibbs chart is divided into three parts which are evaporation–crystallization, rock weathering and atmospheric precipitation. (a) represents the relationship between Na+/(Na+ + K+) and TDS for 12 lakes. (b) represents the relationship between Cl−/(Cl− + HCO3−) and TDS for 12 lakes.
Figure 4. Gibbs chart. The Gibbs chart is divided into three parts which are evaporation–crystallization, rock weathering and atmospheric precipitation. (a) represents the relationship between Na+/(Na+ + K+) and TDS for 12 lakes. (b) represents the relationship between Cl−/(Cl− + HCO3−) and TDS for 12 lakes.
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Figure 5. Proportion of ions in surveyed lakes. The figures are based on the lake equivalent ion concentrations. (a) represents the relationship between (Na+ + K+) and (Ca2+ + Mg2+) for 12 lakes. (b) represents the relationship between (Ca2+ + Mg2+) and (HCO3− + CO32+ SO42−) for 12 lakes. (c) represents the relationship between 2(Ca2+ + Mg2+) and HCO3− for 12 lakes. (d) represents the relationship between (Cl− + SO42−) and (HCO3− + CO32+) for 12 lakes. (e) represents the relationship between Cl− and (Na+ + K+) for 12 lakes. (f) represents the relationship between Cl− and Na+ for 12 lakes. (g) represents the relationship between (Na*+ K+) and TZ for 12 lakes. (h) represents the relationship between (Ca2+ + Mg2+) and TZ for 12 lakes.
Figure 5. Proportion of ions in surveyed lakes. The figures are based on the lake equivalent ion concentrations. (a) represents the relationship between (Na+ + K+) and (Ca2+ + Mg2+) for 12 lakes. (b) represents the relationship between (Ca2+ + Mg2+) and (HCO3− + CO32+ SO42−) for 12 lakes. (c) represents the relationship between 2(Ca2+ + Mg2+) and HCO3− for 12 lakes. (d) represents the relationship between (Cl− + SO42−) and (HCO3− + CO32+) for 12 lakes. (e) represents the relationship between Cl− and (Na+ + K+) for 12 lakes. (f) represents the relationship between Cl− and Na+ for 12 lakes. (g) represents the relationship between (Na*+ K+) and TZ for 12 lakes. (h) represents the relationship between (Ca2+ + Mg2+) and TZ for 12 lakes.
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Table 1. Basic information on surveyed lakes. The latitude, longitude and altitude of the lakes were obtained by GPS.
Table 1. Basic information on surveyed lakes. The latitude, longitude and altitude of the lakes were obtained by GPS.
Lake Latitude (N)Longitude (E)Altitude (m)DateWeather
Bengze Co32°04′57.88″88°38′42.50″453631 July 2020Sunny
Chaxiabu Co31°55′45.66″87°52′21.06″468031 July 2020Sunny
Guogen Co32°21′23.87″89°10′30.44″465931 July 2020Sunny
Pusaier Co32°22′29.93″89°29′58.92″458631 July 2020Sunny
Guojialin Co32°01′40.35″88°31′18.15″452431 July 2020Sunny
Dagze Co31°49′40.52″87°23′02.71″445931 July 2020Cloudy
Yangnapeng Co32°19′46.64″89°47′49″462030 July 2020Rainy
Angdar Co32°40′00″89°31′36″490030 July 2020Cloudy
Bankog Co31°44′21.86″89°25′49.61″451526 July 2020Sunny
Gangtang Co33°10′17.90″86°39′51.08″48661 August 2020Sunny
Yibug Caka32°59′31.10″86°40′06.09″45571 August 2020Rainy
Dangqung Co31°35′26.16″86°47′30.24″44752 August 2020Sunny
Table 2. Water quality parameters of the surveyed lakes (mean values). The temperature, conductivity, pH, dissolved oxygen (DO), salinity and oxidation–reduction potential were measured by a YSI portable water quality analyzer. The alkalinity and hardness were measured by titration. TDS was calculated as the sum of the main eight ions.
Table 2. Water quality parameters of the surveyed lakes (mean values). The temperature, conductivity, pH, dissolved oxygen (DO), salinity and oxidation–reduction potential were measured by a YSI portable water quality analyzer. The alkalinity and hardness were measured by titration. TDS was calculated as the sum of the main eight ions.
LakePhysicochemical Analysis
Temperature
(°C)		Conductivity
(mS·m−1)		pHDO
(mg·L−1)		Salinity
(‰)		Oxidation/Reduction
(mV)		Alkalinity
(mmol·L−1)		Hardness
(mmol·L−1)		TDS
(g·L−1)
Bengze Co20.601.278.906.810.64−52.6012.38 ± 0.7613.71 ± 0.033.53 ± 0.02
Chaxiabu Co19.185.348.966.422.89−100.3031.96 ± 0.4118.27 ± 0.1211.06 ± 0.02
Guogen Co12.748.368.987.264.67−85.1036.41 ± 0.358.2 ± 0.198.49 ± 0.03
Pusaier Co13.538.299.006.624.70−105.7067.75 ± 0.914.49 ± 0.1410.85 ± 0.03
Guojialin Co16.1417.208.945.3810.20−105.5070.7 ± 0.5718.35 ± 0.038.63 ± 0.02
Dagze Co18.8619.758.196.6211.82−113.50162.12 ± 1.1518.84 ± 0.0815.11 ± 0.03
Yangnapeng Co18.5549.329.033.5832.31−94.00271.67 ± 0.7825.42 ± 0.1420.68 ± 0.02
Angdar Co13.2851.558.875.3333.88−79.2057.42 ± 0.3322.17 ± 0.810.06 ± 0.02
Bankog Co14.4065.399.247.2044.25−65.10125.84 ± 0.2919.13 ± 0.5611.52 ± 0.03
Gangtang Co13.7867.018.853.7345.52−90.9037.64 ± 0.2315.15 ± 0.076.27 ± 0.02
Yibug Caka16.3272.478.765.3649.85−93.0015 ± 0.4121.35 ± 0.0747.27 ± 0.02
Dangqung Co15.78138.208.8012.82106.90−61.40351.04 ± 0.2120.36 ± 0.226.43 ± 0.02
Table 3. Partial table of environmental quality standards for surface water (GB3838−2002).
Table 3. Partial table of environmental quality standards for surface water (GB3838−2002).
Hydration IndexClassification Standards
IIIIIIIVV
TP (mg·L−1)0.010.0250.050.100.20
TN (mg·L−1)0.200.501.001.502.00
Table 4. Concentrations of major ions in sampled lakes. The Cl−, SO42−, K+ concentrations were determined using the CleverChem380 nutrient analyzer (DeChem-Tech GmbH, Hamburg, Germany). The CO32−, HCO3−, Ca2+ and Mg2+ were determined by titration. ”-” represents a non-detection. The units in the table are mg·L−1.
Table 4. Concentrations of major ions in sampled lakes. The Cl−, SO42−, K+ concentrations were determined using the CleverChem380 nutrient analyzer (DeChem-Tech GmbH, Hamburg, Germany). The CO32−, HCO3−, Ca2+ and Mg2+ were determined by titration. ”-” represents a non-detection. The units in the table are mg·L−1.
LakeNa+K+Ca2+Mg2+CO32−HCO3−Cl−SO42−
Bengze Co937 ± 9.3843 ± 0.3631 ± 0.80148 ± 1.09179 ± 3.38391 ± 4.80785 ± 1.731019 ± 1.72
Chaxiabu Co3406 ± 6.9142 ± 0.1516 ± 0.40213 ± 4.01461 ± 2.941013 ± 3.131707 ± 1.724206 ± 3.68
Guogen Co2824 ± 7.7642 ± 0.3111 ± 0.2093 ± 5.23592 ± 0.841017 ± 4.371956 ± 0.51953 ± 7.79
Pusaier Co3424 ± 9.1440 ± 0.2413 ± 0.22168 ± 5.23943 ± 5.482216 ± 5.741714 ± 0.562331 ± 2.05
Guojialin Co2670 ± 9.2739 ± 0.2915 ± 1.6214 ± 0.611303 ± 2.281663 ± 6.121110 ± 1.551617 ± 1.82
Dagze Co5073 ± 9.4943 ± 0.127 ± 2.20225 ± 2.683515 ± 4.082742 ± 6.93777 ± 1.192726 ± 2.29
Yangnapeng Co7040 ± 2.8739 ± 0.1514 ± 2.14301 ± 5.475656 ± 5.645070 ± 1.041078 ± 0.791480 ± 3.16
Angdar Co3049 ± 2.2434 ± 1.0326 ± 1.80254 ± 5.841151 ± 3.91164 ± 2.43967 ± 0.813419 ± 3.77
Bankog Co3920 ± 6.0234 ± 0.4322 ± 2.20219 ± 4.52824 ± 4.561637 ± 1.591375 ± 3.691488 ± 3.31
Gangtang Co1978 ± 4.1943 ± 0.4312 ± 1.60177 ± 2.31911 ± 2.28444 ± 1.131141 ± 2.341568 ± 2.78
Yibug Caka14072 ± 4.0741 ± 0.3482 ± 2.611426 ± 1.95-913 ± 4.69834 ± 2.321741 ± 1.96
Dangqung Co9731 ± 4.0238 ± 0.5012 ± 1.60241 ± 5.118912 ± 2.103292 ± 2.08836 ± 3.123364 ± 3.93
Table 5. Matrix of correlation coefficients for water chemistry parameters in lakes. Correlation between ions can be analyzed by SPSS25. An asterisk (*) indicates significant differences (p < 0.05) and two asterisks (**) indicate significant differences (p < 0.01).
Table 5. Matrix of correlation coefficients for water chemistry parameters in lakes. Correlation between ions can be analyzed by SPSS25. An asterisk (*) indicates significant differences (p < 0.05) and two asterisks (**) indicate significant differences (p < 0.01).
CO32−HCO3−Cl−SO42−Na+K+Ca2+Mg2+NO3−TDS
CO32−1
HCO3−0.844 **1
Cl−−0.304−0.0731
SO42−0.2290.2990.1321
Na+0.906 **0.899 **−0.0420.5141
K+−0.401−0.3080.021−0.111−0.3121
Ca2+−0.438−0.421−0.115−0.293−0.506−0.4881
Mg2+0.695 *0.637 *−0.440.2580.627 *−0.4760.0621
NO3−−0.0510.099−0.0610.142−0.0260.452−0.54−0.2471
TDS0.896 **0.909 **−0.0620.5330.998 **−0.315−0.4780.659 *−0.0251
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Jin, Y.; Zhu, B.; Wang, F.; Sun, S.; Wang, P.; Liu, X. Analysis of Water Chemistry Characteristics and Main Ion Controlling Factors of Lakes in the Nagqu Area of the Qinghai–Tibet Plateau in Summer. Water 2023, 15, 2900. https://doi.org/10.3390/w15162900

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Jin Y, Zhu B, Wang F, Sun S, Wang P, Liu X. Analysis of Water Chemistry Characteristics and Main Ion Controlling Factors of Lakes in the Nagqu Area of the Qinghai–Tibet Plateau in Summer. Water. 2023; 15(16):2900. https://doi.org/10.3390/w15162900

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Jin, Yifan, Boshan Zhu, Fang Wang, Shichun Sun, Pengfei Wang, and Xiaoshou Liu. 2023. "Analysis of Water Chemistry Characteristics and Main Ion Controlling Factors of Lakes in the Nagqu Area of the Qinghai–Tibet Plateau in Summer" Water 15, no. 16: 2900. https://doi.org/10.3390/w15162900

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