Study on Environmental Factors of Fluorine in Chagan Lake Catchment, Northeast China

Optimizing fertilizer usage for source reduction of salt and fluoride ion runoff discharge from a soda saline-alkali paddy field

Planting rice is a beneficial strategy for improving soda saline-alkali soil, but it comes with the challenge of increased runoff discharge of salt and fluoride (F-) ions. The use of different nitrogen (N) fertilizers can impact this ion discharge, yet the specific characteristics of ion runoff under different N-fertilizer applications remain unclear. A field experiment was conducted in this study, applying five commonly used N-fertilizer types to monitor the ion runoff throughout an entire rice growing season. Salt ions and F- runoff discharge was significantly affected by N-fertilizer type, runoff event, and their interaction (p < 0.001). Regardless of N-fertilizer types, sodium (Na+) and bicarbonate (HCO3-) ions were consistently discharged from runoff in soda saline-alkali fields, constituting 20.55-25.06 % and 47.57-50.49 % of total ion discharges, respectively. Compared to no N-fertilizer (CK) and other N-fertilizer treatments, the organic-inorganic compound fertilizer (OCF) application significantly reduced Na+ and HCO3- runoff discharge, causing a decrease in the competitive adsorption capacity between HCO3- and F- (p < 0.05). The use of OCF and inorganic compound fertilizer (ICF) lowered pH in runoff water, resulting in reduced dissolution capacity of calcium fluoride in the soil and thereby decreasing total F- runoff discharge. In conclusion, OCF proves to be an effective N-fertilizer in mitigating salt ions and F- runoff discharge in soda saline-alkali paddy fields. Additionally, ICF demonstrates the ability to control F- runoff discharge.

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.

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.

Chemical characteristics, evolution, and quality of groundwater and processes controlling its fluoride concentration features: case study of a typical high-fluoride areas in the Southwestern Shandong Plain, China

In this study, the groundwater (GW) in the high-fluorine area of the Southwestern Shandong Plain was divided according to the characteristics of high Na% (> 75%), and its water chemistry characteristics and causes were discussed separately, and the hydrochemical process of the formation of high-fluorine GW was determined. Finally, the GW quality of the study area was evaluated. The results proved that silicate hydrolysis can significantly promote the release of F^- in fluorine-containing minerals; high %Na can be used as one of the early-warning conditions for judging high-fluoride areas. To this end, 132 GW samples were collected from 66 wells during the dry and wet seasons. The study area was found to have weakly alkaline GW (pH 7.1-8.9) and could be divided into high %Na areas (HNA) and non-HNA. GW exhibited different hydrochemical characteristics between HNA and non-HNA. In non-HNA, total hardness (TH) exceeded 200 mg/L, and total dissolved solids (TDS) ranged from 514.1 to 5246.1 mg/L; in HNA, TH was less than 200 mg/L, TDS ranged from 552.8 to 1298.3 mg/L, and Na⁺ increased with TDS, whereas Ca²⁺ and Mg²⁺ contents were low. The main water type in HNA was HCO₃-Na and in non-HNA was SO₄·Cl-Ca·Mg and SO₄·Cl-Na. The study area is experiencing serious fluoride pollution. GW in HNA is mostly controlled by carbonate and silicate hydrolysis and evaporation, whereas GW in non-HNA is controlled by dolomite dissolution and cation exchange in the main. Moreover, GW in HNA has significantly been altered by albite hydrolysis, which produces Na⁺ and HCO₃^- and triggers various reactions promoting the release of F^- from fluorine-containing minerals (FCM). Regarding the water quality for irrigation, GW in HNA was found to be less suitable than that in non-HNA. Nevertheless, in terms of the water quality index (WQI), GW is moderate for drinking and poor for irrigation. Therefore, extensive attention should be paid to the exploitation and management of high-sodium GW in the plain area.