ABSTRACT Global climate change, particularly altered precipitation patterns, has significantly impacted tropical ecosystems like floodplain lakes that are highly sensitive to fluctuations in riverine discharge. Here, we investigate the effects of interannual hydrological changes in the Upper Paraguay River on floodplain lake ecosystems in the Pantanal, the largest tropical wetland on Earth. Our analysis includes a time series of river levels (1985–2023), Landsat imagery, and lake sediment geochemistry datasets that untangle connections among river hydrology, lake basin morphology, and the proliferation of aquatic vegetation. Our results found that Lakes Cáceres, Vermelha, Uberaba, and Negra have significant temporal variations in open water habitats. They are particularly vulnerable to hydroclimatic changes because of their flat lake beds and shallow bathymetry, which promote rapid replacement of open water habitats with dense aquatic macrophyte cover during droughts. Lakes Gaíva and Mandioré are more resistant to changes in the Upper Paraguay River level, with a dominance of open water habitats even during severe drought events. Our time series analysis shows the severe drought of 2019–2020 as a tipping point in the Pantanal’s floodplain lake ecosystems, with the analyzed lakes experiencing marked reductions in open water habitat and expansion of aquatic vegetation. Predictive climate models indicate that more frequent, extended drought may result in floodplain lake ecosystem transformations in the coming decades. Low river levels drive transitions in tropical floodplain lakes, leading to macrophyte and terrestrial vegetation expansion and increased fuel accumulation. These changes elevate wildfire risk, reduce aquatic biodiversity, and threaten local livelihoods that depend on fisheries and other ecosystem services.

Abstract Essential biomolecules, such as physiologically essential fatty acids, can critically influence consumers' performance and the ecosystem's functioning. Eicosapentaenoic (EPA; 20:5ω3) and docosahexaenoic (DHA; 22:6ω3) fatty acids are physiologically crucial for consumers, and they must be either obtained from the diet or bioconverted from precursors. We monitored the synthesis of EPA and DHA by primary producers in the largest man‐made ecosystem (Lake Kariba) and in situ fatty acid production, trophic transfer, and endogenous production of EPA and DHA in the tropical lake food web using 13C‐labeling, compound‐specific isotopes, and gene expression of fads2 and elovl5 genes in most abundant fish species. Seston pigment analysis and 23S rRNA sequencing revealed that cyanobacteria dominated primary producers throughout three seasons, and the biosynthesis rate of EPA and DHA was under the detection limit. Moreover, due to the low zooplankton densities and EPA and DHA content in zooplankton, the transfer of EPA and DHA from phytoplankton–zooplankton to upper trophic levels is low. The low production of EPA and DHA by primary producers is mitigated by bioconversion of α‐linolenic acid to EPA and DHA in two tilapia species, especially by Nile tilapia (Oreochromis niloticus) known to feed on cyanobacteria. Compound‐specific isotope analysis revealed that tigerfish (Hydrocynus vittatus), the main predatory fish on the lake, was more closely related to Nile tilapia than to lake planktivorous fish (Limnothrissa miodon). Therefore, trophic interaction between cyanobacteria and algivorous fish has replaced traditional phytoplankton and zooplankton trophic interaction in the synthesis and transfer of EPA and DHA to upper trophic levels.

Lake Sentani is a tropical lake in Indonesia, consisting of four interconnected sub-basins of different water depths. While previous work has highlighted the impact of catchment composition on biogeochemical processes in Lake Sentani, little is currently known about the microbiological characteristics across this unique ecosystem. With recent population growth in this historically rural area, the anthropogenic impact on Lake Sentani and hence its microbial life is also increasing. Therefore, we aimed to explore the influence of environmental and anthropogenic factors on the microbial diversity of Lake Sentani. Here, we present a detailed microbiological evaluation of Lake Sentani, analyzing 49 different sites across the lake, its tributary rivers and their river mouths to assess diversity and community structure using 16S rRNA gene sequencing. Our results reveal distinct communities in lake and river sediments, supporting the observed geochemical differences. Taxonomic assessment showed the potential impact of anthropogenic pressure along the northern, urbanized shore, as river and river mouth samples revealed high abundances of Bacteroidota, Firmicutes, and Cyanobacteria, which could be attributed to pollution and eutrophication. In contrast, lake sediment communities were dominated by Thermodesulfovibrionia, Methanomethylicia, Bathyarchaeia, and Thermoplasmata, suggesting sulfate reducing, thermophilic, acidophilic bacteria and methanogenic archaea to play an important role in tropical lake systems. This study provides novel insights into ecological functions of tropical lakes and contributes to the optimization of management strategies of Lake Sentani, ensuring its holistic preservation in the future.

Abstract Wetlands are important to continental evolution, providing both arenas and refugia for emerging and declining biotas. This significance and the high preservation potential make the resulting fossiliferous deposits essential for our understanding of past and future biodiversity. We reconstruct the trophic structure and age of the early Permian Manebach Lake ecosystem, Germany, a thriving wetland at a time when the tropical biosphere faced profound upheaval in the peaking Late Palaeozoic Icehouse. Nine excavations, high‐resolution spatiotemporal documentation of fossils and strata, and U–Pb radioisotopic dating of tuffs allow us to distinguish autogenic and allogenic factors shaping the limnic biocoenosis. The Manebach Lake was an exorheic, oxygen‐stratified, perennial water body on the 101–102 km2 scale, integrated into the catchment draining much of the European Variscides. Lake formation paralleled an Asselian regional wet climatic interval and benefited from rising base level due to post‐Variscan half‐graben tectonics. Stromatolite‐forming cyanobacteria, bivalves, several crustaceans, amblypterids and xenacanthid sharks formed a differentiated biocoenosis in the lake. Fossil stomach remains and teeth prove the rare presence of acanthodians, branchiosaurs and large amphibians. The results indicate woody‐debris‐bearing lake littorals devoid of semi‐aquatic and aquatic plants as places suitable for stromatolites to grow, underpin the model of declining freshwater‐shark diversity in most Permian Variscan basins, demonstrate fish/amphibian ratios in limnic assemblages to measure lake perenniality and reveal taphonomic biases in lake taphocoenoses. Our outcomes call for more knowledge about the diversity, ecology and fossilization pathways of past limnic biotas, particularly microorganisms and actinopterygian fishes, to reconstruct deep‐time continental ecosystems.

ABSTRACT The 7 maar lakes of San Pablo are a cluster of small volcanic lakes on Luzon Island, Philippines. These lakes, which are heavily utilized for aquaculture and ecotourism, usually experience fish kills that coincide with the northeast monsoon (NEM). This study explores limnophysical processes, particularly mixing regimes, in the lakes in relation to prevailing monsoons. We monitored monthly vertical and seasonal profiles of water temperature, salinity, conductivity, and dissolved oxygen from October 2016 to December 2018. Three types of mixing regimes were observed among the lakes, which have similar surface areas but different depths: polymixis in the shallowest; warm monomixis in lakes with intermediate depth; and meromixis in the deepest. A boundary between monomixis and meromixis was identified between 36 and 62 m depth. Monthly monitoring showed seasonal mixing occurred exclusively during the NEM (Nov–Apr). We also incorporated meteorological data into the model and performed multiple regression analysis for each lake to determine the best predictor: lake stability, as indicated by the Schmidt stability (ST ). A between-lake comparison showed lake stability was strongly correlated with both air temperature and wind speed, suggesting these 2 meteorological variables are involved in establishing thermal stratification in the lakes during the southwest monsoon. This study provides insights for adaptive lake management and projections of climate impacts on these understudied tropical lake ecosystems in Southeast Asia.

Ecohydrological costs and benefits of common carp, the dominant species in a `novel' tropical lake ecosystem

A Bayesian Belief Network, validated using past observational data, is applied to conceptualize the ecological response of Lake Maninjau, a tropical lake ecosystem in Indonesia, to tilapia cage farms operating on the lake and to quantify its impacts to assist decision making. The model captures ecosystem services trade-offs between cage farming and native fish loss. It is used to appraise options for lake management related to the minimization of the impacts of the cage farms. The constructed model overcomes difficulties with limited data availability to illustrate the complex physical and biogeochemical interactions contributing to triggering mass fish kills due to upwelling and the loss in the production of native fish related to the operation of cage farming. The model highlights existing information gaps in the research related to the management of the farms in the study area, which is applicable to other tropical lakes in general. Model results suggest that internal phosphorous loading (IPL) should be recognized as one of the primary targets of the deep eutrophic tropical lake restoration efforts. Theoretical and practical contributions of the model and model expansions are discussed. Short- and longer-term actions to contribute to a more sustainable management are recommended and include epilimnion aeration and sediment capping.

A study was conducted on the stable isotope variation of muscle tissues from selected freshwater fish species from Temenggor Lake and Chenderoh Lake, Perak, Malaysia from December 2014 to March 2015. The objective is to assess the stable isotopes of δ13C to identify the carbon sources and δ15N of fish species from Temenggor and Chenderoh Lake, Perak, Malaysia to infer the trophic position of these fishes. Four types of fish species were analyzed by using stable isotope approach which were Hampala barb (Hampala macrolepidota), Oxygaster cyprinus (Oxygaster anomalura), Peacock Bass (Cichla ocellaris) and Nile Tilapia (Oreochromis niloticus). Stable isotopes of δ13C and δ15N were analysed using an elemental analyser Thermo Finnigan Flash EA 2000 connected to Finningan delta v avantage plus isotope ratio mass spectrometry by a ConFlo II interface. The δ13C values from both lakes implies a C3 phytoplankton as reported from the literature. Based on δ15N values of fish species, O. anomalura occupies the highest trophic level in Temenggor Lake, reflecting its carnivorous feeding habit despite its small size while C. ocellaris was the highest in Chenderoh Lake, implying its predatory behaviour. Further analysis should be carried out to incorporate primary producers and consumers to elucidate the food web in the tropical lake ecosystem. This study provides a reference record for conducting stable isotopes in the food web of tropical lake ecosystem for better management and deeper understanding of the ecosystem functioning.

The colonization process and successional patterns of a periphytic algal community were evaluated in a Amazonian Viveiro Lake (Rio Branco, Acre, Brazil). Sampling was performed over a period of 35 days; at four-day intervals for 20 days, and then at five-day intervals. Water sampling for physical, chemical and biological analyses was done during the dry and rainy season. Glass slides were used as artificial substrates for periphyton colonization. The structural community was evaluated through population density, algae class, diversity indices and descriptive species. Species richness, diversity and evenness increased as succession progressed. While density of Bacillariophyceae, Euglenophyceae and Zygnemaphyceae increased with succession, Cyanobacteria remained dominant. Synechocystis aquatilis, Synechocystis diplococcus and Navicula pseudolanceolata were the main descriptive species in both the dry and rainy season. Cymbela tumida, Frustulia rhomboides, Trachelomonas lacustris and Closterium acicularis was correlated with an increase in hydrologic level during the rainy season. Conversely, the density of Chlamydomonas sp., Chroomonas nordstedtii, Trachelomonas volvocinopsis, Trachelomonas volvocina and Synechococcus linearis was correlated with an increase in water transparency during the dry season. In general, the periphytic algal community showed high diversity and species richness independent of season. Season also had little influence on representation of algae class and main descriptive species. However, successional patterns varied by season, and changes in hydrologic levels acted directly on the succession path of periphytic algae. More research on periphyton dynamics is needed to improve our understanding of tropical lake ecosystems, especially in Amazonian.

Lake of flies, or lake of fish? A trophic model of Lake Malawi

We use a new approach to characterize the absorption characteristics of chromophoric dissolved organic matter (CDOM) in standard solutions and in several tropical lake ecosystems (Lake Victoria, Lake Tanganyika, Laguna Ibera). Compared with the common methods where a single slope of CDOM absorption spectrum is determined over a broad spectral region, we estimate the variations in spectral slope as a function of wavelength from 200 to 700 nm. Hence, our results show a distribution of spectral slope, referred to as the spectral slope curve, Sλ, which was used to identify similarities between lakes and standard solutions as well as to show the wavelength intervals in which photodegradation modifies spectral slope. In contrast to the plethora of wavelength intervals and ratios presented in the CDOM literature, a comparison of spectral slope curves between ecosystems provides a potentially important tool to examine the characteristics of CDOM in a consistent manner.

We report on exquisitely preserved specimens of freshwater siliceous algae belonging to the classes Synurophyceae (scaled chrysophytes) and Bacillariophyceae (diatoms) from middle Eocene lake sediments in Northern Canada. When considered in the context of closest extant relatives, these microfossils present unequivocal biogeographic and ecological affinities with warm-water ochrophyte assemblages. We have identified scales that are unambiguously assigned to Mallomonas bangladeshica, a chrysophyte now restricted to tropical lake ecosystems. The diatom genus Actinella is also well represented in these sediments, again with the most comparable extant congeners found in tropical to subtropical localities, particularly in the Southern Hemisphere. We surmise that fundamental biogeographic reorganizations among lacustrine algae took place during Eocene hothouse paleoclimates. In this light, future climate warming should be viewed as a potent vector for similar community shifts, with attendant limnological implications.

Abstract: The introduction of the Nile perch in the 1960s enhanced the economic value of the local fishery and encouraged women to become involved in fish processing and marketing. Over time, however, the predatory perch has severely reduced stocks of popular indigenous fishes. Currently, competition created by high foreign demand for the perch is forcing small-scale traders out of business and depriving local consumers of fish protein. Case studies reveal that the increased competition also has elicited various forms of production relations among men and women processors and traders. The complexities associated with the socio-ecology of this ecosystem hinder attempts to develop effective management policies.IntroductionThe introduction of the Nile perch (Lates niloticus) into Lake Victoria in the middle of this century has had far-reaching repercussions. To examine this phenomenon adequately requires a powerful analytical framework that combines both historical and processual ecological methods. Historical ecology as outlined by Schmidt (1994) seeks to identify ecological transformations induced by human cultural systems over time by analyzing the interplay of cultural systems with the physical environment. Processual ecological methods also serve to identify various mechanisms that link environment and behaviour by employing small and large units of analysis, dropping assumptions of equilibrium and balance and addressing processes of conflict and co-operation (Orlove 1980). Processual ecological anthropology examines the interactions between the choices which actors make, behaviours on an individual or group level, and the biological and social systems which influence the distribution of resources, constrain the possible adaptive strategies and provide some of the goals which the actors attempt to meet (Orlove 1980:257).This article investigates a few of the complex relationships between the Lake Victoria ecosystem and the human populations that depend on its resources. It suggests that the development of useful resource management policies becomes problematic when the very patterns and dynamics of resource production and distribution are constantly undergoing changes that are incompletely understood and relatively unpredictable.The Setting: Lake Victoria and Its Western ShoreLocated mostly in the Kagera Region of Tanzania, the western shore of Lake Victoria consists of three main agro-ecological zones: a well-watered area stretching along the shore from Muleba and Biharamulo Districts north to the border with Uganda; a drier, flatter area located in Biharamulo District to the south; and a high plateau that stretches west toward the Ruwenzori mountains (see Figure 1). Seasonally heavy rainfall in the northwestern portion of the region has leached the soils of their nutrients over the millennia. Local farmers responded by painstakingly building up the land, using mulching techniques to nourish their plantations of plantains and coffee. The poor quality of the soil has also obliged many local women to look to off-farm activities for personal income generation.The western shore is inhabited by Haya peoples in the north and Zinza -- mixed with other groups -- in the south. In pre-colonial and colonial times, the highly stratified, patriarchal Haya and Zinza societies were ruled by kings who maintained their control through a feudal, agropastoral system based on plantains and cattle. European colonization of East Africa at the turn of this century greatly diminished the power of these kings. The introduction of animal and human diseases, Western religions, new fish species and the cultivation of coffee for export during the German and British rule strongly influenced the social and physical environments of the west lake region.Figure 1 The Western Shore of Lake Victoria [Map Not Transcribed]Perched on a plateau about 1128 metres above the Indian Ocean, Lake Victoria is the largest tropical lake in the world, approximately the same size as Ireland [between 26 200 and 26 828 square kilometres (EAHC 1953; Ford 1955)]. …

Parakrama Samudra (Sri Lanka) Project, a study of a tropical lake ecosystem I. An interim review

(1981). Parakrama Samudra (Sri Lanka) Project, a study of a tropical lake ecosystem III. Composition, density and distribution of the zooplankton in 1979. SIL Proceedings, 1922-2010: Vol. 21, No. 2, pp. 1001-1008.

(1981). Parakrama Samudra (Sri Lanka) Project, a study of a tropical lake ecosystem II. Chemical environment with special reference to nutrients. SIL Proceedings, 1922-2010: Vol. 21, No. 2, pp. 994-1000.

SummaryLake Chilwa (Malawi) is a shallow tropical lake surrounded by an extensive zone of littoral swamp mainly composed ofTypha domingensis. The data produced show that the physical and chemical conditions are different and more varied in the littoral region when compared with the open lake. Primary production in the littoral is confined almost entirely toTypha domingensis, which also acts as a nutrient pump by absorbing nutrients from the soils and eventually releasing them into the lake waters. Long term and short term exchanges in organic and inorganic materials between the littoral swamps and the open lake are described. These, as well as available evidence on the distribution, reproductive habits and diet of certain faunal groups, indicate that the littoral region of Lake Chilwa has an important regulating influence on the functioning of the whole lake.