Changhu Lake, a large, shallow, eutrophic lake in central China, experienced an extremely low water level event from November 2015 to January 2016 followed by an extremely high water level event in July 2016. In this study, we examined the effects of two extreme water levels on the nutrient dynamics of Changhu Lake over five years. The nutrient parameters in Changhu Lake showed significant interannual variations, and the nutrient concentrations at the sites in the western part of Changhu Lake were 2–41% higher than those at the outlet of the lake. In late 2015, the effects of low water levels led to a 17–74% increase in nutrient concentrations. After July 2016, however, a high water level event occurred, leading to a 34–48% decrease in nutrient concentrations. These changes in nutrient parameters were strongly related to water level fluctuations (p < 0.05). As extreme water levels are likely to become more frequent during the twenty-first century, this work may provide some insights into the conservation and management of lake ecosystems in the face of climate change and human activity.

Climate change is expected to drive significant alterations in rainfall patterns, which will pose considerable threats and pressures on aquatic ecosystems. Phytoplankton, as a critical component of these ecosystems and a reliable biological indicator of environmental health, may respond variably to such climatic changes. However, our understanding of how phytoplankton communities respond to climate change remains limited. In this study, we investigated the response of phytoplankton functional groups to rainfall patterns and their relationships with environment factors in a subtropical eutrophic lake (Changhu Lake, China) from May 2020 to April 2022. Our findings indicate that changes in phytoplankton functional structure over time were influenced by rainfall patterns. A total of 119 genera, 21 functional groups, and 15 dominant functional groups were identified, with the dominant functional groups exhibiting strong seasonal variations. Notably, shifts in rainfall patterns led to a transition in dominant phytoplankton functional groups: from taxa tolerant of mixing and low nitrogen levels (e.g., H1, J, and S1) during the rainy season to taxa that thrive under eutrophic and stratified conditions (e.g., X2, C, N, and W1) during the dry season. The use of phytoplankton functional approaches simplifies identification and reflects environmental conditions effectively. Redundancy analysis (RDA) revealed strong correlations between changes in phytoplankton functional groups and environmental factors such as water temperature, precipitation, water level, and nutrient availability. The insights from this study improve our understanding of how aquatic ecosystems shift under climate change and demonstrate the potential of phytoplankton functional responses as a valuable tool for water management and conservation.

Agricultural drainage from catchments significantly impacts aquatic ecosystems due to high nitrogen and phosphorus concentrations in runoff. While original ecological ditches and wetlands have demonstrated effectiveness in nutrient load removal, the overall impact of an ecological ditch-wetland system (EDWS) on agricultural nutrient removal has received limited attention. This study conducted a field experiment to investigate the physicochemical conditions and nutrient removal efficiency of an EDWS for purifying nutrient discharge from rice-crayfish paddy fields. Variations in water temperature (WT), dissolved oxygen (DO), pH, and total suspended solids (TSS) within the EDWS were assessed. Nutrient concentrations—including total nitrogen (TN), ammonium nitrogen (NH₄-N), nitrate nitrogen (NO₃-N), total phosphorus (TP), and soluble reactive phosphorus (SRP)—were monitored from the tillering to the ripening stage of the rice growth cycle. The evaluation of nutrient removal efficiencies in the EDWS revealed that ecological ditches exhibited higher removal efficiencies compared to wetlands. The average total removal efficiencies for TN, NH₄-N, NO₃-N, TP, and SRP were 37.50 %, 39.38 %, 38.62 %, 37.94 %, and 39.51 %, respectively, with peak removal efficiencies observed at specific growth stages of the rice crop. Furthermore, the study explored the influence of hydraulic retention time on nutrient removal efficiency in the EDWS, indicating higher nutrient discharge removal efficiencies under low water discharge rates. Linear regression analysis identified water discharge, influent nutrient loads, and TSS as significant factors affecting nutrient removal efficiency in the EDWS. This study provides valuable insights into the effectiveness of EDWS in purifying nutrient discharge from rice-crayfish paddy fields, highlighting their potential as sustainable solutions for nutrient management in agricultural landscapes.

Background: The Yellow River irrigation area in Ningxia faces spring drought, resalting, severe water resource shortage, and significant water wastage in saline–alkali soils. Objective: To explore the effects of two different improvement measures on maize fresh biomass and the basic physical and chemical properties of saline soil under four irrigation gradients, aiming to provide a theoretical basis for water-saving irrigation in the Yellow River irrigation area of Ningxia while ensuring maize yield. Methods: The experiment designed four irrigation gradients, W1: local conventional water volume (240 mm), W2: 10% water-saving (216 mm), W3: 20% water-saving (192 mm), W4: 30% water-saving (168 mm), and two different soil improvement treatments, a combination treatment of desulfurization gypsum, ETS microbial agent, and biochar (JC), and a combination treatment of desulfurization gypsum, humic acid, and mulching (FS), with a blank control (CK), resulting in 12 treatments in total. Results: The results showed that compared with CK, both JC and FS treatments reduced soil pH, with JC treatment showing a more significant reduction in soil alkalinity than FS treatment. Both JC and FS treatments inhibited the rise in soil electrical conductivity (EC), with JC showing a significantly higher ability to suppress the rise in EC than FS treatment. Both FS and JC treatments improved soil water retention, but in May 2023 during the maize seedling stage, FS treatment had a stronger water retention ability than JC treatment; however, in July at the maize big jointing stage and in September at the maize maturity stage, JC treatment exhibited better water retention ability than FS treatment. Both JC and FS treatments increased maize fresh biomass under four water conditions, but under WI and W2 conditions, there was no significant difference in the ability of JC and FS treatments to increase maize fresh biomass. Under any irrigation condition, the ability of JC treatment to improve WUE is higher than that of FS treatment. Under W3 and W4 conditions, JC treatment significantly outperformed FS treatment in increasing maize fresh biomass yield. Additionally, under W3 irrigation conditions, using JC treatment not only achieved greater water-saving goals but also prevented crop yield reduction due to water-saving measures. This article can provide a theoretical basis for agricultural irrigation management, especially in the Ningxia Yellow River irrigation area of China. It can help ensure crop yields while protecting the ecological environment and promoting sustainable agricultural development.

The impact of global climate change has led to an increase in extreme rainfall events, causing fluctuations in terrigenic inputs that significantly affect aquatic communities. Lake Changhu, the third-largest freshwater lake in Hubei Province, plays a crucial role as a reservoir of aquatic germplasm resources in the middle reaches of the Yangtze River. In recent years, the lake has experienced a series of extreme rainfall events. In response to recent extreme rainfall events, a 42-day mesocosm experiment was conducted to understand the effect of terrigenic inputs on various aspects of phytoplankton in Lake Changhu, such as species composition, abundance, biomass, diversity, community turnover rates, resource use efficiency, and stability. The experiment involved the application of different terrigenic treatments, including a control group (CK, using lake water), low terrigenic input (LT), medium terrigenic input (MT), and high terrigenic input (HT). The results showed a noticeable shift in phytoplankton composition from a co-dominated state of Chlorophyta and Cyanobacteria in the CK treatment to a Cyanobacteria-dominated state in the other terrigenic treatments. Furthermore, the terrigenic inputs increased phytoplankton abundance, community turnover rates, diversity, and resistance. Comparatively, the diversity index of phytoplankton increased by 82.61%, 73.83%, and 70.41% in the LT, MT, and HT treatments, respectively, in contrast to the CK treatment. However, phytoplankton abundance decreased by 6.99%, 15.55%, and 14.76% in the LT, MT, and HT treatments. Additionally, the resource use efficiency decreased by 1.94%, 5.16%, and 14.19% in the LT, MT, and HT treatments, respectively, compared to the CK treatment. These findings provide valuable insights into monitoring and managing the water ecology in Lake Changhu, offering a scientific basis for implementing effective management strategies.

In the context of global climate change, frequent summer heavy rainfall events act as significant disturbances to the ecosystem functions of shallow lakes. This study examined the response of phytoplankton community structure and dynamics to heavy rainfall in Lake Changhu, a shallow eutrophic lake, through monthly monitoring during the summer months (June–August) of 2020–2022. The results revealed that heavy rainfall induced substantial water level fluctuations and shifts in key environmental parameters. Marked interannual variations were observed in the phytoplankton community, with the highest species richness in summer 2021 and lowest in 2022. While Chlorophyta dominated in species composition, Cyanobacteria overwhelmingly dominated in abundance, with key taxa including Dolichospermum flos-aquae L., Pseudanabaena limnetica L., Oscillatoria princeps V., Microcystis wesenbergii K., and Merismopedia minima B. Both phytoplankton abundance and biomass peaked in summer 2021. Community diversity indices were consistently lower in June compared to July–August, indicating higher environmental stress and a more simplified community structure during the initial rainfall period. A comprehensive water quality evaluation suggested that Lake Changhu was in a lightly to moderately polluted state. Correlation and redundancy analyses (RDA) identified rainfall, water temperature, and nutrient concentrations as the primary environmental drivers shaping phytoplankton community succession. These findings systematically elucidate the mechanistic responses of phytoplankton to heavy rainfall disturbances, offering a scientific foundation for ecological resilience assessment and adaptive management of shallow lakes under climate change.