ABSTRACT Climatic conditions strongly influence tropical karst lake limnology, but more information is required to understand how human impacts can modify their ecological patterns. The Lagunas de Montebello lake district, a tropical, high-altitude karst landscape, comprises 139 solution lakes surrounded by tropical rainforests. To investigate the limnological changes in the Lagunas de Montebello in the past 20 years, we selected 14 lakes for a comparative study: 4 impacted and 10 pristine. The impacted lakes are on the northwest (NW) plateau area fed by surface and underground waters, whereas the pristine lakes are on the southeast (SE) intermontane zone fed by underground waters. Impacted lakes receive nutrients and organic matter from agricultural and urban/domestic wastewater from point and nonpoint surface sources. Heavy tropical storms flood the plateau zone, interconnecting the lakes and facilitating pollutant dispersion among lakes. Pristine lakes remain isolated, and groundwater pollution is limited because most anthropogenic activities occur in the NW plateau zone. Most of the limnological variables measured differed between pristine and impacted lakes. Nutrients, chlorophyll a, total suspended solids, and particulate organic carbon concentrations were higher in the impacted lakes. The hydraulic connection between the Montebello Lakes facilitates the rapid dispersion of pollutants from one lake to another, threatening lakes that are still pristine. Although natural aquatic karst environments promote phosphorus precipitation, which leads to phosphorus limitation of primary production, anthropogenic additions of phosphorus, as well as nitrogen and organic matter, are leading to eutrophication and ecosystem degradation of lakes ecosystems in the Lagunas de Montebello lake district.

The cold temperate helocrenes are usually attributed to high biodiversity because of environmental heterogeneity. Their temporal stability of environmental conditions reduces seasonal changes in assemblage composition. However, the within-site patterns and processes have been only rarely studied in springs, thus our knowledge remains limited. In this study, we investigated a microcrustacean assemblage of a helocrenic calcareous spring at a high spatial resolution. We tested differences among visually distinct mesohabitats, and related the assemblage composition variation to environmental variables and seasonal changes by a repeated sampling in spring, summer and autumn. At this single site, we recorded 26 species of ostracods and harpacticoids, accounting for almost 50% of the whole known regional species pool. Species richness and composition varied significantly between the mesohabitats, the latter mainly due to differences in environmental variables (mainly water depth and temperature). The occurrence of cold-adapted species was restricted to the spring source, but species inhabiting other mesohabitats had clearly broader ecological niches. Despite significant temporal changes in water temperature, microcrustaceans showed almost negligible seasonal changes in species composition, suggesting that their microdistribution remains stable throughout the year. Our findings have important implications for sampling design of large-scale ecological studies and spring conservation.

Pesticides used in food production contaminate freshwater ecosystems. We present a critical analysis of pesticide use in Latin America and the Caribbean (LAC) from 1990 to 2020 and a systematic review of scientific literature about the presence of pesticides in freshwater, encompassing studies published from 1990 to 2023. Data were collected from FAOStat, PubMed, ScienceDirect, Scopus, and Google Scholar. Brazil was the primary pesticide user, with an annual consumption of 231,621 t, followed by Argentina (132,255 t) and Colombia (52,553 t). In 2020, LAC had the highest rate of pesticide application globally, with Ecuador leading at 13.74 kg/ha. South America dominates the total amount with 90.9% of pesticide use, primarily herbicides (51.5%), while pesticide usage in North and Central America, as well as the Caribbean, varied due to differing agricultural practices. The study examined 221 records for 26 out of 51 countries in the literature, highlighting the significant lack of information from numerous countries. Argentina, Mexico, and Brazil had the highest publication rates. Rivers, streams, and lakes (37%, 20%, and 12%, respectively) were the most commonly studied systems, and research focused mainly on pesticide concentration in water (46%), sediments (27%), and aquatic biota (15%). The imbalance between pesticide usage and monitoring in freshwaters leads to concerns about the awareness of ecological risk. Therefore, there is an urgent need for increased research on environmental monitoring in LAC to better understand pesticide impacts on these vital ecosystems.

ABSTRACT Lakes are widely distributed across Costa Rica, from coasts to the highest elevation regions, and located in the main terrestrial biomes. However, updated biogeochemical information about the main types of lakes is still lacking. We present comparative biogeochemistry (water chemistry, stable isotopes, and picoplankton) for a coastal lake (Lake Madre de Dios, LMD), a volcanic lake (Lake Barva, LB), and a glacial lake (Lake Ditkevi, LD). Sampling was conducted between February-November 2022 including dry and rainy seasonal conditions. Hydrological and chemical conditions were evaluated using water and carbon stable isotopes, dissolved organic matter (DOM), major ions, and microbiota analysis. Isotopic data (δ18O, δ13CDIC) confirmed lower evaporative losses for the maar and tarn lakes and productivity response to precipitation inputs. Excitation/Emission matrices confirmed the prevalence of fulvic and humic acids in the coastal and glacial lakes, mainly aromatic proteins and soluble microbial by-products in the volcanic lake. Picophytoplankton (PPP, ∼0.2 to 10 μm) was mainly represented by phycocyanin-rich picocyanobacteria (PC-Pcy) events in the three lakes, but maar and tarn lakes had more representation of phycoerythrin (PE-Pcy) events. We confirmed fluctuations in PPP cell abundance in the lakes lower than in temperate lakes. Like in other eutrophic lakes, Pcy also dominated over picoeukaryotes (Peuk) algae abundance. This work seeks to promote adopting an ecosystem approach to study the biogeochemical functioning of tropical lakes using the combination of chemical, hydrological, and biological data and to provide baseline information for future studies (e.g., climate change and pollution impacts) on tropical lakes of Costa Rica.

As global flow intermittency increases, understanding how macroinvertebrates respond at a functional level in streams becomes crucial for effective water management. This study investigates the functional response of macroinvertebrates to flow intermittency in Hungarian lowland streams over a 10-month period, comparing intermittent and perennial streams across the entire community, trait groups, and trait states. We aimed to demonstrate differences in functional diversity using metrics such as functional richness, evenness, divergence, dispersion, and Rao's quadratic entropy. For trait groups, we focused on both response and stable traits, anticipating greater differences in response traits. Additionally, we identified which trait states, as indicated by community-weighted means, contribute significantly to variations between streams. Our findings indicate that functional diversity in intermittent streams is generally lower or equivalent to that in perennial streams, suggesting disparities in functional trait composition. Significant differences were observed within trait groups, indicating specific responses of trait groups to intermittency. We identified resilience trait states—including current velocity, reproduction, respiration, female length, locomotion, substrate relation, aquatic stages, and resistance forms—that contributed to these differences. The three-level analysis revealed a hidden relationship: differences at the state level do not consistently manifest at the trait group or whole community levels. Investigating functional changes at the trait group or trait state level can serve as an early indicator of community shifts. Incorporating trait groups as indices into assessment frameworks could facilitate early detection of functional changes during bioassessment. We recommend considering trait groups when evaluating functional responses to flow intermittency in future studies.

ABSTRACT Rising bubbles play a fundamental role in emitting greenhouse gases from shallow waters. Their size is crucial for bubble dissolution, gas exchange with the surrounding water, and the release of gases into the atmosphere. However, little is known about bubble sizes in shallow waters. To address this, we investigated bubble diameters in a 1.2 m deep fish pond, employing 2 methods: first, we measured the bubble size distributions by optical bubble sensors; second, we used an existing single bubble dissolution model to determine diameters representative for the respective bubble size distributions at the water surface based on measured bubble oxygen contents and dissolved oxygen concentrations. Results from optical bubble sensors were relatively similar at all sites; however, subsequent analysis revealed problems, particularly in detecting small bubbles under turbid, shallow water conditions. Model-derived bubble diameters ranged from 0.5 to 10.5 mm, varied spatially within the pond, and displayed diurnal fluctuations. With increasing bubble flux, bubble diameters increased; bubbles at feeding sites were larger than in the open water area. A detailed sensitivity analysis revealed that, depending on the bubble size distribution, the uncertainty of the model increases with increasing water depth. For a typical bubble diameter of 5 mm, the simple method can provide robust estimates of representative bubble size in waters shallower than 50 m.

The Andes mountains extend North-South in a latitudinal gradient of 8,500 km. Due to the great climatic variety and the peculiar north-south orographic distribution, lakes are very diverse, including different lake origins and very contrasting morphometries. Here, we reviewed more than 700 ecological studies on Andean lakes to identify the main threats to these freshwater systems. The most important threats are UV radiation, changes in water balance, eutrophication, all three interacting with climate change, alien species introduction, and mining. Ultraviolet radiation is an important factor in Andean lakes not only because of the altitude but also because many lakes are included in the Antarctic ozone hole. The introduction of alien species, particularly exotic salmonids, also had detrimental effects, affecting native fish populations and behaviour, and endemic species by disrupting the indigenous food web. Eutrophication and browning caused by human activities, including land use interacting with climate change, are increasing in Andean lakes causing a decrease in water quality. Finally, mining can cause water contamination (both groundwater and surface water) by chemicals emitted from mining processes thus, producing a loss of biodiversity. Although an important number of Andean lakes have been declared as RAMSAR sites because of their uniqueness and their extreme conditions, they are subject to significant human impacts. Here, for the first time, we identify these impacts all along the Andes, however, further studies at different scales are mandatory if we pretend to understand, conserve, and manage Andean lakes.

ABSTRACT The Galapagos Archipelago - due to its remoteness, isolation, recent volcanic origin, and endemic fauna and flora - is iconic for inspiring Darwin's evolutionary theory. Since Darwin’s day researchers have focused on the Archipelago’s terrestrial and marine species. Its location in an important climate regulating body of water, coupled with a low level of human activity for most of its history, attracted several paleolimnologists to the inland waters of the Archipelago. Studies of the many lagoons, crater lakes, and other inland waters were mainly in support of paleolimnological research and are therefore limited in scope. Because of the presence of permanent human settlements on four of the Archipelago’s islands, plus increased tourism, the limited number of permanent freshwater bodies are under unprecedented environmental stress. This bibliometric analysis assembles what is known about Galapagos lentic inland water bodies. It shows that studies on biodiversity, water quality, and threats to these ecosystems are few and fragmented across time and space.

Indigenous people and local communities play a vital role in conserving inland water ecosystems and their resources through their cultural and spiritual values embedded in the geographic, socio-political, and economic contexts. The Central Mexico lakes along the Trans-Mexican Volcanic Belt harbored important prehispanic cultures that hybridized during the Spanish conquest, evolving into modern Mexico and changing how lakes were valued. The terrestrial Spanish ways of life were inimical to the prehispanic indigenous lacustrine culture. After the conquest, various actions were carried out to drain the lakes for urban growth and to provide agricultural land. The result has been a decline (e.g., Lake Cuitzeo, Michoacán) and, in some extreme cases, the near disappearance (e.g., Lake Texcoco, Mexico City) of what were once extensive water bodies. Unsustainable use of resources, unsympathetic spatial planning (anthropic impacts), and climate change to warmer/drier conditions have all placed additional pressure on the inland ecosystems. Nonetheless, as herein presented, the prehispanic lacustrine cultural knowledge and traditions persist locally in some locations, having been perpetuated by indigenous people's traditions and habits.

Interpreting long-term variability in mountain stream ecosystems is challenging where potential causes such as climate change and altered land-use act simultaneously. The scarcity of historical data also limits research opportunity, especially at low latitudes. Here we assess the macroinvertebrate fauna of 12 Himalayan streams in Nepal covering an altitudinal gradient from 1500 to 3900 m asl using data from 1992, 2022 and 2023. We aimed to: 1) compare long-term change in richness and community composition over three decades to short-term seasonal variation, and 2) analyse long-term changes in relation to catchment properties. Rarefied richness decreased equally with altitude in 1992 and 2022, but was greater at most sites in 2022, with several new families detected. In contrast, no clear seasonal pattern was found. The 2022:1992 ratio in rarefied richness was positively correlated with catchment area and weakly with maximum catchment altitude, while the two highest and glaciated sites gained relatively more taxa than other sites. NMDS ordinations from rarefied Bray-Curtis dissimilarities showed considerable overlap in communities among the three datasets. Pairwise rarefied dissimilarities among all sites increased significantly with altitudinal distance between sites in 1992 while there was no such relationship in 2022. Dissimilarities between 1992 and 2022 samples showed a near-significant correlation with increased catchment vegetation cover as shown by NDVI. Our study is the first to document long-term variations in stream macroinvertebrate communities in Himalayan mountain streams, illustrating how some altitudinal patterns have remained stable through time while others appear to have weakened with links to global change.