Combined effect of freshwater salinization and harmful algae on the benthic invertebrate Chironomus pallidivittatus

Global climate change as well as human activities have been reported to increase the frequency and severity of both salinization and harmful algal blooms (HABs) in many freshwater systems, but their co-effect on benthic invertebrates has rarely been studied. This study simultaneously examined the joint toxicity of salinity and different cyanobacterial diets on the behavior, development, select biomarkers, and partial life cycle of Chironomus pallidivittatus (Diptera). High concentrations of salts (e.g., 1 g/L Ca2+ and Mg2+) and toxic Microcystis had synergistic toxicity, inhibiting development, burrowing ability and causing high mortality of C. pallidivittatus, especially for the Mg2+ treatment, which caused around 90% death. Low Ca2+ concentration (e.g., 0.01 g/L) promoted larval burrowing ability and inhibited toxin accumulation, which increased the tolerance of Chironomus to toxic Microcystis. However, low Mg2+ concentration (e.g., 0.01 g/L) was shown to inhibit the behavior, development and increase algal toxicity to Chironomus. Toxic Microcystis resulted in microcystin (MC) accumulation, inhibited the burrowing ability of larvae, and increased the proportion of male adults (>50%). The combined toxicity level from low to high was verified by the weight of evidence and the grey TOPSIS model, which integrated five lines of evidence to increase the risk assessment accuracy and efficiency. This is the first study that provided insights into ecological risk arising from the joint effect of salinity and harmful algae on benthic organisms. We suggest that freshwater salinization and HABs should be considered together when assessing ecological threats that arise from external stress.

Increased Water Abstraction and Climate Change Have Substantial Effect on Morphometry, Salinity, and Biotic Communities in Lakes: Examples from the Semi-Arid Burdur Basin (Turkey)

Global warming and altered precipitation patterns are predicted to intensify the water loss in semi-arid and arid regions, and such regions in Turkey will be particularly affected. Moreover, water abstraction, not least for irrigation purposes, is expected to increase markedly, posing major threats to the water balance of the lakes and thus their biodiversity. Among the closed basins in Turkey, the Burdur Closed Basin (BCB), located in the southwest of Turkey, is expected to be most affected. The BCB includes several types of aquatic ecosystems which support high biodiversity, including one Ramsar site, six Important Bird Areas, and a considerable richness of native and endemic fish species. Therefore, it is essential to analyze the potential environmental impacts of climate change and increased water abstraction on BCB lakes and their biotic communities. Here, we combined historical data on ecosystems as well as meteorological, remote sensing, and ground-truth data to analyze the changes in the temperature and precipitation of the BCB, water surface areas, and land use, as well as the potential effects on waterbird and fish communities. We calculated the water budget to elucidate water availability in the basin over the last few decades and predicted future conditions based on rainfall and temperature forecasts using climate models. The Standardized Precipitation–Evapotranspiration Index (SPEI) was used to relate the water surface area to precipitation and temperature change in the basin. Crop-farming irrigation in the BCB has increased notably since 2004, leading to intensive water abstraction from the lakes and their inflows, as well as from ground water, to meet the increased demand for irrigation. The water abstraction from the lakes, inflows to the lakes, and the groundwater in the basin has increased the water loss in the catchment substantially. Remotely sensed data on lake surface areas showed a major shrinkage of shallow lakes in the last 40 years. Moreover, the largest lake in the basin, Lake Burdur, lost nearly half of its surface area, which is worrisome since the shallower areas are the most suitable for supporting high biodiversity. Climate models (CNRM-ESM2-1GCM for temperature and GFDL-ESM4-GCM for precipitation) suggest that from 2070, the BCB will face long-term, moderate-to-severe dry periods. This, and the increased demand for water for irrigation, along with climate change, may accelerate the drying of these lakes in the near future with devastating effects on the lake ecosystems and their biodiversity.