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.

The Konya Closed Basin (KCB) in Turkey has a cold semiarid to warm Mediterranean climate and hosts the largest Turkish freshwater lake, Lake Beyşehir, and the iconic saline Lake Tuz. Using published as well as our own ground-truth and remote sensing data, we provide (1) a brief description of the paleoenvironmental changes in the KCB; followed by (2) a detailed description of the changes in land use, crop farming, groundwater and surface water levels, and climate; and (3) associated changes in lake water surface area and salinity as well as in waterbird and fish communities during the past 40 years. The KCB is intensively farmed, and the farming of mainly water intensive crops has increased substantially, especially since 2000. This, combined with climate warming, has led to a substantial rate of reduction of the groundwater level (up to 1 m/yr) and the surface area of the lakes and wetlands, followed by an increase in salinisation, and even complete loss of several wetlands. Three globally threatened waterbird species face extinction in the basin, and 18 of the 62 previous breeding species have already been lost. The KCB has 38 fish species, of which 74% are endemic and 61% are considered threatened or near threatened. Modelling projections using various climate and land use scenarios predict serious additional reductions of the water level in the future due to climate change, leading to deterioration (or complete loss) of lake ecosystems and the services they provide.

Climate change is affecting freshwater ecosystems globally, particularly those in semi-arid and arid regions. The Central Anatolian Ecoregion (CAE) in Türkiye has a semi-arid climate and is home to numerous endemic fish species. We used species distribution modelling to elucidate the distribution of sixteen endemic fish species in CAE and predicted their potential distributions for 2041–2060 and 2081–2100 based on the CMIP6 climate model. Half of the species are predicted to experience a significant loss of climatically suitable areas. Anatolichthys fontinalis, Gobio gymnostethus, Gobio hettitorum, and Pseudophoxinus burduricus will face a complete loss of suitable areas by 2081–2100 under a high emissions climate scenario, whereas Cobitis bilseli, Egirdira nigra, Gobio intermedius, and Squalius anatolicus will experience a significant loss. The other eight species can potentially benefit from climate warming if all other stressors remain equal. Anthropogenic stressors, such as water abstraction for irrigation, pollution, invasive species introductions, and dam construction, are already putting endemic fish populations in CAE under extreme pressure. Climate change is expected to exacerbate these threats. Regular monitoring of freshwater ecosystems and fish fauna in the CAE and protecting the region from key anthropogenic stressors are recommended to successfully conserve these endemic freshwater fishes under climate change.

Freshwater fishes are at the center of the freshwater biodiversity crisis

Salinization of freshwater ecosystems is one of the major challenges imposed largely by climate change and excessive water abstraction for irrigated crop farming. Understanding how aquatic ecosystems respond to salinization is essential for mitigation and adaptation to the changing climate, especially in arid landscapes. Field observations provide invaluable data for this purpose, but they rarely include sufficient spatial and temporal domains; however, experimental approaches are the key to elucidating complex ecosystem responses to salinization. We established similar experimental mesocosm facilities in two different climate zones in Turkey, specifically designed to simulate the effects of salinization and climate change on shallow lake ecosystems. These facilities were used for two case-study experiments: (1) a salinity gradient experiment consisting of 16 salinity levels (range: 0–50 g/L); and (2) a heatwave experiment where two different temperature regimes (no heatwave and +6 °C for two weeks) were crossed with two salinity levels (4 and 40 g/L) with four replicates in each treatment. The experiments lasted 8 and 2 months, respectively, and the experimental mesocosms were monitored frequently. Both experiments demonstrated a significant role of salinization modulated by climate on the structure and function of lake ecosystems. Here, we present the design of the mesocosm facilities, show the basic results for both experiments and provide recommendations for the best practices for mesocosm experiments conducted under saline/hypersaline conditions.

Lakes face anthropogenic stressors such as climate change, salinization, and eutrophication, and microplastics (MPs) now emerge as a new concern since they act as vectors for pathogenic bacteria, giving rise to concern about environmental health. This study explores cultivable viable bacterial (CVB) biofilm communities on MPs along a salinity gradient (0.25 to 192.69‰) in 11 lakes in Türkiye. The MPs consisted mainly of fibers and 50-µm to 5-mm-sized fragments. The dominant cultivable bacterial phyla in both MP-associated biofilms and lake water were Proteobacteria and Firmicutes. On MPs, Pseudomonadaceae was the dominant family (94.7%), followed by Enterobacteriaceae (1.2%). Various halolerant pathogens occurred as well, e.g., Proteus spp. strains on MP surfaces in Lake Bolluk (95.7‰) and Alcaligenes spp. in Lake Tuz, the two lakes with the highest salinity, while the halophilic Shewanella putrefaciens was prevalent in highly alkaline Lake Salda. Staphylococcus, Commomonas, and Enterobacter were found in all lakes regardless of salinity level, and CVB strains were more common on MPs surfaces than in lake water. Our findings suggest that MPs promote the development, dispersion, and bioavailability of bacteria, including pathogens, thus increasing ecological and health-related impacts in lakes under different salinity conditions.