Humid highland forest enclaves form critical water sources and wet refugia within the surrounding semi-arid landscapes of northeastern Brazil. However, maintaining water quality in these systems is increasingly challenging because of anthropogenic pressure and climate change. Reynolds phytoplankton functional groups (RFGs), which cluster species based on shared ecological traits and sensitivities, are valuable bioindicators of environmental change. In this study, we examined temporal variations in RFGs in three reservoirs located in humid upland enclaves subjected to varying levels of environmental variability. Physical and chemical variables, along with phytoplankton composition, were monitored monthly over one year. Results showed significant differences in the composition of RFGs among the reservoirs. Water transparency and pH were identified as the primary environmental drivers shaping community structure. The strongest associations were found with flagellated unicellular and colonial cyanobacteria (Lo), filamentous cyanobacteria (S1), and elongated diatoms (MP). These findings highlight light availability and pH as key factors influencing the dynamics of phytoplankton in tropical reservoir ecosystems. The conservation of reservoirs in highland enclaves requires greater attention considering the increasing effects of global warming and anthropogenic pressure. Measures are needed to avoid water over-enrichment, cyanobacterial blooms, and reduced water availability.
Functional Group V (FG V), which comprises anoxygenic phototrophic purple and green sulfur bacteria, has traditionally been associated with stratified lakes, where pronounced vertical redox gradients are typically described. Here, we report the repeated occurrence of anoxygenic phototrophic sulfur bacteria in two shallow riparian wetlands, suggesting that the ecological context of this functional group may extend beyond classical stratified systems. Environmental variables and phytoplankton functional structure were analysed in a lowland and a semi-mountain wetland characterized by dense macrophyte cover, high summer temperatures, elevated organic matter content, and low dissolved oxygen conditions. FG V, represented by Chromatium okenii and Thiospirillum jenense, was detected in all samples and episodically reached high relative abundance. It co-occurred within a functionally coherent assemblage of motile flagellates (W1, X2, Y), filamentous cyanobacteria (TC), and metaphytic diatoms (MP), typical of shallow, weakly mixed systems. Although direct redox measurements were not performed, the combination of low dissolved oxygen, high organic loading, and restricted mixing indicates the potential for reduced conditions and localized redox discontinuities. Our results are consistent with the interpretation that macrophyte-dominated shallow wetlands may locally provide environmental conditions functionally analogous to those of deeper stratified systems, allowing FG V to persist within phytoplankton communities. These findings support a process-based view of FG V ecology, emphasizing the role of redox-related conditions over water depth, and highlight shallow wetlands as potentially important but underexplored habitats for redox-dependent phototrophic communities.
Amphibians are one of the most endangered groups of vertebrates, and they have key ecological roles in freshwater ecosystems and linking the aquatic and terrestrial environments. Still, studies on how amphibian species loss can alter freshwater ecosystem structure and functioning are scarce. This review summarizes the results of 129 studies exploring the effects of amphibians on freshwater communities (algae, zooplankton and macroinvertebrates) and food webs, as well as key ecosystem processes (leaf litter decomposition, phytoplankton and periphyton accrual, nutrient cycling, and ecosystem metabolism). Most studies (71%) focused on anuran species and less so on urodeles (21%) or both groups (8%). While we found some general patterns, species-specific characteristics often induced different outcomes. The high variety of results suggests that amphibians should be prioritized in future experimental studies if we are to understand the ecological consequences of species loss in this vulnerable group.
In tropical lakes, thermal stratification is essential for oxygen dynamics and ecosystem function, and it responds sensitively to short-term weather variation. Using high-resolution temperature profiles and weather data in 2016–2017, this study examines the effects of meteorological variability on water column stratification and oxygen levels in Lake Maninjau, a eutrophic tropical lake in West Sumatra, Indonesia. The results show that seasonal drops in air temperature were the primary factor influencing stratification in 2016, while, wind speed and sunshine duration had a greater impact on its occurrence in 2017. Furthermore, in 2016, stratification breakdown triggered full-depth mixing and a sharp drop in dissolved oxygen (DO) from >3 mg/L to <2 mg/L at 5 m depth. Generally, stratification occurs at the minimum air temperature (Tmin) of above 20.25°C. At lower Tmin, the water column can either be stratified or mixed, notably when the average wind speed (Vave) exceeds ~2.75 m/s, in which stratification tends to break down. These findings highlight how thermal and mechanical forces contribute to weakening stratification and increasing the risk of hypoxia which are detrimental to aquaculture in floating net cages, and are linked to fish kills. Recognizing these thresholds can guide risk forecasting and adaptive management of tropical lakes.
Human-induced climate change is accelerating and is profoundly impacting remote aquatic ecosystems. In the Sierra Nevada, these climatic shifts exacerbated by increased Saharan dust inputs are likely driving major transformations in lake environments. This study presents paleolimnological research reconstructing ecological and environmental trends in Sierra Nevada lakes and their catchments over the past two centuries. We analyzed multiple independent paleoindicators from high-resolution, chronologically, dated sediment cores, including spectrally inferred chlorophyll-a, sedimentary ancient prokaryotic DNA, and subfossil remains of diatoms, cladocerans, and chironomids. A compilation of the paleolimnological research conducted in Sierra Nevada lakes was made, examining the effects of environmental variables on indicators of the lake structure and function, which were grouped accordingly. Results reveal that ecological changes began subtly over a century ago, intensifying in the 1960s-1970s, coinciding with re-gional warming, reduced precipitation, and intensified Saharan dust deposition. Generalized linear models (GLM) and Redun-dancy Detrended Analyses (RDA) were applied to analyze the effects of climate variables on community assemblages. Results indicate major shifts in aquatic community composition and recent algal biomass increases, with temperature emerging as the dominant driver, and Saharan dust and precipitation as secondary factors. Species shifts indicate rising water temperature and alkalinity and greater eutrophication. Microbial communities show significant restructuring, with increased archaeal and bac-terial diversity and abundance, suggesting heightened microbial activity and functional changes in biogeochemical processes. The synchrony among proxies and climate variables across sites suggests a region-wide phenomenon. These changes are linked to prolonged ice-free seasons, elevated lake water temperatures, and reduced hydrological input, factors that influenced lake volume and water residence time, and reflect the increasing severity of summer droughts in the Sierra Nevada highlands over the past five to six decades. Continued global warming, reduced precipitation, and increased Saharan dust transport are expected to intensify these ecolo-gical shifts in the future.
