Dramatic changes in lake water conditions may induce sensitive feedback in sediments, such as the release of phosphate and ammonia. There is a lack of the understanding of sediment nutrient release fluxes and their responses to various environmental factors in plateau lakes. In this study, nutrient contents in the water and sediment, sediment nutrient release rates, and their responses to various influential factors in a steppe shallow plateau lake, Lake Hulun, China, were investigated. Sediment is a large store of nutrients, with bioavailable phosphorus of 555 mg kg⁻¹ in surface lake sediments. If water became anoxic, sediments will release appreciable amounts of phosphate (2.1 mg P m⁻² d⁻¹) and ammonia (40.0 mg N m⁻² d⁻¹), three times greater than those in oxic conditions. Raised temperatures greatly increased sediment phosphate release rates, while the highest temperature (23 °C) slightly decreased ammonia release rates due to strong nitrification. Assuming a whole year of internal loading, ammonia and dissolved reactive phosphorus concentrations in water column would increase by an estimated 0.22 mg N L⁻¹ and 0.01 mg P L⁻¹, respectively, which is equal to 2 and 0.5 times of their ambient concentrations. A pH increase from 8.4 to 9.4 significantly decreased internal nitrogen and phosphorus release rates by around three times. Overall, dissolved oxygen (DO) and pH had a greater impact on sediment nutrient release from lake sediments compared to temperature, and further increased the eutrophic status in the overlying water when these three parameters varied within the normal seasonal range (temperature: 1.9–23.1 °C, DO: oxic and anoxic; pH: 7.5–9.4). With the periodic low DO and frequency of drought in the future, lake management strategies that mitigate water eutrophication, such as water diversion, may need to be considered.

The number of surface water pollution accidents (abbreviated as SWPAs) has increased substantially in China in recent years. Estimation of economic losses due to SWPAs has been one of the focuses in China and is mentioned many times in the Environmental Protection Law of China promulgated in 2014. From the perspective of water bodies’ functions, pollution accident damages can be divided into eight types: damage to human health, water supply suspension, fishery, recreational functions, biological diversity, environmental property loss, the accident’s origin and other indirect losses. In the valuation of damage to people’s life, the procedure for compensation of traffic accidents in China was used. The functional replacement cost method was used in economic estimation of the losses due to water supply suspension and loss of water’s recreational functions. Damage to biological diversity was estimated by recovery cost analysis and damage to environmental property losses were calculated using pollutant removal costs. As a case study, using the proposed calculation procedure the economic losses caused by the major Songhuajiang River pollution accident that happened in China in 2005 have been estimated at 2263 billion CNY. The estimated economic losses for real accidents can sometimes be influenced by social and political factors, such as data authenticity and accuracy. Besides, one or more aspects in the method might be overestimated, underrated or even ignored. The proposed procedure may be used by decision makers for the economic estimation of losses in SWPAs. Estimates of the economic losses of pollution accidents could help quantify potential costs associated with increased risk sources along lakes/rivers but more importantly, highlight the value of clean water to society as a whole.

Tidal flats in eastern China have undergone various transformations into other land-use types. Understanding the impact of land-use conversion on soil properties and microbial communities is crucial for effective ecological conservation efforts. In this study, we compared soil chemical properties and the diversity, composition, and ecological functions of soil bacterial and fungal communities across four land-use types: natural bare land (BL), unused reclaimed tidal land (Phragmites, PL), agricultural land (maize, ML), and shelterbelt land (SL), utilizing next-generation sequencing technology. The results indicated that soil electrical conductivity decreased, while soil organic carbon (SOC) and nutrient contents increased in ML and SL compared to BL and PL. The bacterial Chao1 and fungal Chao1 and Shannon values vary across different land-use types. A higher relative abundance of Acidobacteriota, specifically RB41, was found in ML compared to BL. Principal coordinate and PerMANOVA analysis showed that the composition of bacterial and fungal communities differed significantly across the four land-use types. SOC explained the most variance in both bacterial and fungal communities. Carbon-related functional genes and fungal guilds exhibit greater diversity across the four land-use types compared to nitrogen-related functional genes. In conclusion, the transformation of natural land-use types to managed one greatly altered soil chemical and microbial properties. Our study offers foundational insights into the microbial communities in the typical land-use types of Eastern China’s coastal area. Future studies should emphasize the quantification of human interventions and their impact on soil microbial communities and ecological functions.

Dissolved organic matter (DOM) is generally the dominant carbon pool in freshwater lakes and plays a vital role in the regional or even global carbon cycle. In recent years, steppe lakes have been subject to two stressors: eutrophication and abnormally high concentrations of organic matter. However, little is known about the sources and composition of the organic matter. In this study, carbon/nitrogen (C/N) ratios and three-dimensional excitation–emission matrix (3DEEM) fluorescence spectroscopy were adopted to identify the sources and composition of DOM in Hulun Lake, a large shallow steppe lake. The physicochemical and water quality parameters of Hulun Lake and three inflow rivers, Crulen River, Orshen River and Hailar River, were also investigated. The results showed that visible fulvic-like fluorescence (peak C) and tryptophan-like substances (peak T) were the main components of the DOM. The C/N atomic ratios and spectral characteristics of the DOM suggested that approximately 82% of the DOM in Lake Hulun is derived from terrigenous material. The results underscore that it is necessary to devote more research attention to terrestrial inputs into steppe lakes.