Effects of Irrigation Discharge on Salinity of a Large Freshwater Lake: A Case Study in Chagan Lake, Northeast China

Attribution of lake eutrophication risk to anthropogenic forcing adjacent to the agriculture areas: a case study of Chagan Lake

Lake eutrophication, exacerbated by high-intensity anthropogenic forcing, threatens water ecological security and the sustainable development of fisheries. Accurately evaluating lake eutrophication is the basis for effective management of the water environment. This study aimed to study eutrophication and its anthropogenic forcing in Chagan Lake, which is surrounded by agricultural areas with irrigation discharge as the primary water source. The spatiotemporal evolution characteristics of lake eutrophication and the anthropogenic forcing factors were analyzed based on the long-series multi-source data and modified eutrophication index. The results showed that (1) the average trophic state of Chagan Lake was eutrophic according to the modified eutrophication index (TLI = 58.31) and the nutrient level was higher in summer, reaching hypertrophy (TLI 61.49); (2) the maximum pollution footprint affecting the lake reached 34.7 km2, with a maximum buffer zone radius of 1 km; (3) the gross domestic product of primary industry, total sown area, and rice field area were the main anthropogenic factors leading to the lake eutrophication, with contribution rates of 64.43%, 13.09%, and 10.23%, respectively. Multidimensional management strategies for maximum pollution footprint, buffer zone radius, and contribution of anthropogenic factors were used to improve the water quality of the lake. The findings provided scientific support for the management of water environment of Chagan Lake and guided the formulation of "one lake, one policy."

A modeling approach to the efficient evaluation and analysis of water quality risks in cold zone lakes: a case study of Chagan Lake in Northeast China

Due to the influence of complex regional climate, water quality perturbation factors of lakes in cold regions are complicated, and the uncertainty of each factor needs further study. This study coupled two algorithms (clustering and EM) to establish a water quality uncertainty model of Chagan Lake, a typical cold region lake in China. A BN model containing nine influencing factors (including water temperature (WT), total phosphorus (TP), total nitrogen (TN), etc.) was established and optimized, and sensitivity analysis was also performed. The results indicate that the water quality status of the lake is class III and 27.47% risk of exceeding the standard. The water quality of the lake is more susceptible to disturbance during the freezing period (WT < 1 °C). TP is the most sensitive factor for water quality disturbance in the lake followed by chemical oxygen demand (COD), TN, and fluoride (F). Parameter control result displays, and the multifactor synergistic control scheme could reduce the water quality risk of the lake by 36.47%. This study demonstrates that our proposed method can be used to predict both sudden water quality events and the overall trend of water quality fluctuation, which is important for rapid water quality evaluation and management decisions.

Characteristics of fluoride migration and enrichment in groundwater under the influence of natural background and anthropogenic activities

Excessive enrichment of fluoride threatens ecological stability and human health. The high-fluoride groundwater in the Chagan Lake area has existed for a long time. With the land consolidation and irrigation area construction, the distribution and migration process of fluoride have changed. It is urgent to explore the evolution of fluoride under the dual effects of nature and human. Based on 107 groundwater samples collected in different land use periods, hydrogeochemistry and isotope methods were combined to explore the evolution characteristics and hydrogeochemical processes of fluoride in typical high-fluoride background area and elucidate the impact of anthropogenic activities on fluoride migration. The results indicate that large areas of paddy fields are developed from saline-alkali land, and its area has increased by nearly 30%. The proportion of high-fluoride groundwater (>2 mg/L) has increased by nearly 10%, mainly distributed in the new irrigation area. Hydrogeochemical processes such as dissolution of fluorine-containing minerals, precipitation of carbonate minerals and exchange of Na⁺, Ca²⁺ on the water-soil interface control the enrichment of fluoride. The groundwater d-excess has no obvious change with the increase of TDS, and human activities are one of the reasons for the increase of fluoride. The concentration of fluoride is diluted due to years of diversion irrigation in old irrigation area, whereas the enrichment of δ²H, δ¹⁸O and Cl^- in new irrigation area indicates that the vertical infiltration of washing alkali and irrigation water brought fluoride and other salts to groundwater. Fertilizer and wastewater discharges also contribute to the accumulation of fluoride, manifesting as co-increasing nitrate and chloride salts. The results of this study provide a new insight into fluoride migration under anthropogenic disturbance in high-fluoride background areas.

Urbanization drives geographically heterogeneous freshwater salinization in the northeastern United States

Rising trends in freshwater salinity, collectively termed the Freshwater Salinization Syndrome (FSS), constitute a global environmental concern. Given that the FSS has been observed in diverse settings, key questions regarding the causes, trend magnitudes, and consequences remain. Prior work hypothesized that FSS is driven by state factors, such as human-centered land use change, geology, and climate. Here, we identify the fundamental overriding factors driving FSS within the northeastern United States and quantify the diversity of FSS severity within the region. Specifically, we analyzed decadal-scale trends in specific conductance (a salinity proxy) for 333 lotic sites over four decades. Next, we quantified potential variables driving the rising or falling trends, including impervious surface cover (ISC), winter temperature and precipitation, watershed size, and ambient conductance. Temperature and ISC were considered the most likely candidates for predicting FSS severity because road salts have previously emerged as the fundamental regional driver. Most (62.5%) sites exhibited patterns of significantly increasing conductance; thus, the overall regional state reflects advancing FSS. However, others exhibited an absence of change (28.8%) or decreasing values (8.7%), and slope magnitude did change with latitude. Linear modeling demonstrated that two variables-ISC and watershed size-constitute the best predictors of long-term conductance trends and that an intercept not significantly different than zero suggests that the FSS does not reign in the absence of urbanization. We also detected areas with consistently decreasing trends despite moderate ISC. Therefore, within the region, advancing urbanization causes the typical condition of advancing FSS, but heterogeneity also exists.

Analysis of Landscape Change and Its Driving Mechanism in Chagan Lake National Nature Reserve

Lake ecosystems play an important role in regional ecological security and the sustainable development of the economy and society. In order to study the evolution of landscape patterns and the main driving forces in the Chagan Lake Nature Reserve in recent years, we used landscape type data from 2005, 2010, 2015, and 2019 to study the characteristics of the regional landscape’s structural changes. At the same time, the spatial heterogeneity of the driving factors of landscape change was analyzed using the spatial analysis method, and the driving mechanism of landscape change was quantitatively analyzed. The results showed that: (1) from 2005 to 2019, the area of cultivated land, marshland, and water bodies increased, while the area of grassland and the area of bare land decreased. (2) The dominant patch types in the study area formed good connectivity, and the degree of landscape fragmentation increased. (3) In the past 15 years, there has been spatial heterogeneity in the regression coefficients of different driving factors of landscape change: the area with a greater influence of the elevation factor was in the south; the regression coefficient of precipitation showed the spatial distribution characteristics of highs in the west and lows in the east; the gross domestic product had a greater impact on the east and the south; the spatial variation of grain yield was mainly reflected in the southeast and northwest regions; the fishery yield gradually changed from high in the southeast and low in the northwest to the distribution characteristic of decreasing from the east to the southwest; the lake fluorine content showed a distribution pattern that gradually changed from high in the southeast and low in the northwest to high in the middle and low in the north and south; the distribution pattern of the distance to oil production changed from north to southeast to south to north; the distance to the road changed from high in the east and low in the west to the opposite spatial distribution pattern. (4) The interaction of precipitation and lake fluoride content with other factors showed a strong driving effect, which had a significant impact on the landscape change of Chagan Lake Nature Reserve. Since the study area is located in a typical fluorine-rich geochemical environment, human activities, such as the expansion of irrigation areas around Chagan Lake and groundwater exploitation, have accelerated the dissolution of fluorine-containing minerals, promoted the enrichment process of fluorine in Chagan Lake, and enhanced the explanatory power of lake fluorine content in terms of landscape changes. At the same time, the increase in precipitation during the study period is beneficial to the growth of vegetation and the storage of water in lakes, which promotes changes in landscape types such as grasslands and areas of water.

Anion-type modulates the effect of salt stress on saline lake bacteria

Beside sodium chloride, inland saline aquatic systems often contain other anions than chloride such as hydrogen carbonate and sulfate. Our understanding of the biological effects of salt composition diversity is limited; therefore, the aim of this study was to examine the effect of different anions on the growth of halophilic bacteria. Accordingly, the salt composition and concentration preference of 172 strains isolated from saline and soda lakes that differed in ionic composition was tested using media containing either carbonate, chloride or sulfate as anion in concentration values ranging from 0 to 0.40 mol/L. Differences in salt-type preference among bacterial strains were observed in relationship to the salt composition of the natural habitat they were isolated from indicating specific salt-type adaptation. Sodium carbonate represented the strongest selective force, while majority of strains was well-adapted to growth even at high concentrations of sodium sulfate. Salt preference was to some extent associated with taxonomy, although variations even within the same bacterial species were also identified. Our results suggest that the extent of the effect of dissolved salts in saline lakes is not limited to their concentration but the type of anion also substantially impacts the growth and survival of individual microorganisms.

Ecological Risk Assessment and Contamination History of Heavy Metals in the Sediments of Chagan Lake, Northeast China

The study deals with the spatio-temporal distribution of heavy metals in the sediments of Chagan lake, Northeast China. The pollution history of heavy metals is studied simultaneously through the 210Pb dating method by analyzing the characteristic of As, Hg, Cd, Cr, Ni, Cu, Pb, and Zn concentration-depth profiles. The potential ecological risk index (RI) and geo-accumulation index (Igeo) were used to evaluate the contamination degree. Principal component analysis (PCA), based on the logarithmic transformation and isometric log-ratio (ilr) transformed data, was applied with the aim of identifying the sources of heavy metals. The element concentrations show that the heavy metals are enriched in the surface sediment and sediment core with a varying degree, which is higher in the surficial residue. The results of Igeo indicate that the Cd and Hg in the surface sediment have reached a slightly contaminated level while other elements, uncontaminated. The results of RI show that the study area can be classified as an area with moderate ecological risk in which Cd and Hg mostly contribute to the overall risk. For the sediment core, the 210Pb dating results accurately reflect the sedimentary history over 153 years. From two evaluation indices (RI and Igeo) calculated by element concentration, there is no contamination, and the potential ecological risk is low during this period. The comparative study between raw and ilr transformed data shows that the closure effect of the raw data can be eliminated by ilr transformation. After that, the components obtained by robust principal component analysis (RPCA) are more representative than those obtained by PCA, both based on ilr transformed dataset, after eliminating the influence of outliers. Based on ilr transformed data with RPCA, three primary sources could be inferred: Cr, Ni, As, Zn, and Cu are mainly derived from natural sources; the main source of Cd and Hg are associated with agricultural activities and energy development; as for Pb, it originated from traffic and coal-burning activities, which is consistent with the fact that the development of tourism, fishery, and agriculture industries has led to the continuous increasing levels of anthropogenic Pb in Chagan Lake. The summarized results and conclusions will undoubtedly enhance the governmental awareness of heavy metal pollution and facilitate appropriate pollution control measures in Chagan Lake.