Long-Term Limnological Assessment of Freshwater Ecosystems Under Climate Variability and Anthropogenic Environmental Changes

This study intended to examine long-term changes in the status of freshwater ecosystems due to climate variability and anthropogenic pressures on the environment through the use of physico-chemical, hydrological, nutrient, biological, and microbiological parameters. Freshwater ecosystems that have varying degrees of anthropogenic pressure were used for the assessment. Water temperature, dissolved oxygen, electrical conductivity, turbidity, nutrients, biochemical oxygen demand, chlorophyll-a, microbial indicators, and biodiversity were evaluated. Descriptive, trend, correlation, regression, and multivariate analyses were performed for climatic variables and anthropogenic pressure indices. Spatial and temporal differences were evident along the gradient of disturbance. Dissolved oxygen concentration ranged from 3.2 to 5.5 mg/L and from 6.2 to 8.1 mg/L; total nitrogen content rose from 0.32–0.86 to 1.28- 3.15 mg/L; and total phosphorus content increased from 0.02 to 0.08 and from 0.13 to 0.39 mg/L. Chlorophyll-a increased from 3.5 and 10.8 to 18.6 and 46.2 μg/L, suggesting higher levels of eutrophication. Biodiversity index decreased from 3.82 to 1.76, and microbial contamination increased from 45 to 1,850 CFU/100 mL. Total ecological state index changed from 91 at the reference sites to 42 at wastewater sites. These results show that climate variability and anthropogenic pressure are involved in the degradation of freshwaters together. This means that long-term monitoring of ecological condition, including environmental and biological indicators, is required for climate-resilient freshwater management and conservation.