Soil enzyme activities are potentially valuable indicators of soil health in cases of heavy metal and metalloid (HM) pollution. However, the extent to which HM pollution affects specific enzyme activities remains unclear. In this study we assessed the level of HM pollution and its effects on soil enzyme activities to select the most reliable biochemical indicators of soil health under HM stress. The initial hypothesis was that enzyme responses would be site-specific, depending not only on the level of pollution but also on soil abiotic and biotic properties. The Nemerow pollution index (NPI) and the enzyme activity index (EAI) were calculated. EAIs were based on the activities of dehydrogenase (Dha), β-glucosidase (BGl), acid (AcP) and alkaline (AlP) phosphatases, arylsulphatase (Ars) and urease (Ur). NPI indicated slight (1.0) to serious (67.46) soil pollution. The EAI varied from 4.50 to 11.54. The overall functional dissimilarity between soils was around 26%. Cluster and SIMPER analyses both indicated that the activities of Dha, BGl and AlP grouped together with Cu, Zn and Pb, and accounted for 85% of the between-soil functional dissimilarity. The results indicated that there was enzyme functional redundancy between soils. Soil enzymes showed a relatively high capacity to tolerate long-term HM pollution. Dha, BGl and AlP were highly sensitive to environmental fluctuations, including HM concentrations. The long-term HM stress on soil enzyme activities calls for further studies of the soil properties and the time scale involved in the evolution of metal tolerant enzyme producers in HM-impacted soils.

Remote-sensing satellite images provided rapid and continuous spectral and spatial information of the land surface in the Sougia River catchment by identifying the major changes that have taken place over 20 years (1995–2015). Vegetation indices (VIs) of normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and leaf area index were derived for monitoring and mapping variations in vegetation cover. The quantified decrease in NDVI was found to be 4% between 1995 and 2005, and further decreased by 77.1% between 2005 and 2015; it declined back to almost the initial status of 1995. EVI results were inconsistent suggesting that seasonal crops influence the temporal distribution of vegetation cover. The temporal variations in the VIs were important input parameters for the modelling and management of the catchment’s hydrological behaviour. Image classification found that the 4- and the 6-class classifications between 1995 and 2005 were unstable and produced, respectively, a 13.8% and 16.2% total change between classes. Meanwhile, the 8-, 10- and the 12-class showed an almost horizontal line with a minor fluctuation of less than 0.05%. The results of the post-classification change detection analysis indicated a land degradation in terms of natural vegetation losses with sparser or even with no natural vegetation cover.

Global warming poses a significant threat to lake ecosystems, with high-mountain lakes being among the earliest and most severely impacted. However, the processes affecting water ecology under climate change remain poorly understood. This study investigates, for the first time, the effects of regional warming on three high-mountain lakes, Sulzata, Okoto and Bubreka, located in the Rila Mountains, Bulgaria, by examining shifts in bacterial metabolic capacity in relation to the rate and range of utilizable carbon sources using the Biolog EcoPlate™ assay. Over the last decade, ice-free water temperatures in the lakes have risen by an average of 2.6 °C, leading to increased nutrient concentrations and enhanced primary productivity, particularly in the shallowest lake. Bacterial communities responded to these changes by increasing their metabolic rates and shifting substrate preferences from carbohydrates to carboxylic acids. While the utilization rates of some carbon sources remained stable, others showed significant changes—some increased (e.g., D-galactonic acid γ-lactone and itaconic acid), while others decreased (e.g., α-D-lactose and D-xylose). The most pronounced effects of warming were observed in June, coinciding with the onset of the growing season. These findings suggest that rising temperatures may substantially alter bacterial metabolic potential, contributing to a long-term positive feedback loop between lake nutrient cycling and climate change.

High-altitude lakes are sensitive sentinels of climate change, and yet the microbial processes driving biogeochemical cycles under warming remain poorly understood. Seasonal dynamics of sediment microbial communities in four glacial lakes within the cirques of the Seven Rila Lakes (Rila Mountains, Bulgaria) were investigated during June, August, and October 2024. Environmental monitoring showed pronounced seasonal variability with summer peaks in temperature, dissolved organic carbon and nitrogen, and increased inputs of labile organic matter. Multivariate analyses revealed strong seasonal structuring of microbial assemblages, with the largest shifts occurring between the early ice-free season and summer. Archaeal communities were dominated by Halobacteriota over time, whereas lake warming corresponded to a shift from early-season dominance of Actinomycetota and Bacillota to the summer prevalence of Pseudomonadota and Cyanobacteriota, as well as a proliferation of minor phyla Gemmatimonadota. At the genus level, summer enrichment of archaeal methanogen Methanosaeta and bacterial genera Paucibacter, Ca. Accumulibacter, Methylibium, Crenothrix, and Pseudanabaena was observed. Canonical correspondence analysis identified temperature and nutrient availability as the primary drivers of microbial community restructuring. Our results provide empirical evidence that warming and associated changes in organic matter inputs drive shifts in sediment microbial communities, with direct implications for carbon cycling and methane production. Additionally, the results highlight the sensitivity of high-altitude lakes to global warming and emphasize the critical role of microbial communities in modulating ecosystem responses to climate change.