Producción, nutrientes, eutrofización y cianobacterias en Uruguay : armando el rompecabezas

Si bien las causas y consecuencias de la eutrofización son múltiples, este artículo analiza aspectos fundamentales en el contexto actual en Uruguay, con especial énfasis en las floraciones cianobacterianas como una de las consecuencias más frecuentes y notorias. El agravamiento de la eutrofización y sus síntomas, que se predicen con el cambio climático; las claves para la reducción de las pérdidas difusas de fósforo hacia el agua superficial en suelos bajo uso agropecuario; y los cambios actuales y futuros en la gobernanza del agua y la gestión ambiental, son algunos de los temas más importantes considerados. En el análisis se identifican también múltiples desafíos, tanto en la generación de conocimiento como en la gestión ambiental asociada

Produção, nutrientes, eutrofização e cianobactérias no Uruguai: montando o quebra-cabeça

Despite there are multiple causes and consequences of eutrophication, this article analyses key aspects in the current context of Uruguay, emphasizing on cyanobacterial blooms as one of the most frequent and noticeable consequences. The worsening of eutrophication and its symptoms predicted with climate change, the keys for the reduction of diffuse losses of phosphorus with surface runoff on agricultural lands and the ongoing and future changes of water governance and management of the problem are some of the most important issues considered here. In this analysis, we also identify several challenges, both to fill knowledge gaps and in the arena of environmental management.Si bien las causas y consecuencias de la eutrofización son múltiples, este artículo analiza aspectos fundamentales en el contexto actual en Uruguay, con especial énfasis en las floraciones cianobacterianas como una de las consecuencias más frecuentes y notorias. El agravamiento de la eutrofización y sus síntomas, que se predicen con el cambio climático; las claves para la reducción de las pérdidas difusas de fósforo hacia el agua superficial en suelos bajo uso agropecuario; y los cambios actuales y futuros en la gobernanza del agua y la gestión ambiental, son algunos de los temas más importantes considerados. En el análisis se identifican también múltiples desafíos, tanto en la generación de conocimiento como en la gestión ambiental asociada.  Embora as causas e consequências da eutrofização sejam múltiplas, este artigo analisa aspectos fundamentais no contexto atual no Uruguai, com ênfase especial nas florações de cianobactérias como uma das consequências mais frequentes e notórias. O agravamento da eutrofização e seus sintomas previstos pelas mudanças climáticas, as chaves para reduzir as perdas difusas de fósforo para as águas superficiais em solos sob uso agrícola e as mudanças atuais e futuras na governança da água e gestão ambiental, são algumas das questões mais importantes consideradas. A análise também identifica múltiplos desafios, tanto na geração de conhecimento como na gestão ambiental associada

Climate change impacts on lakes: an integrated ecological perspective based on a multi-faceted approach, with special focus on shallow lakes

Freshwater ecosystems and their biodiversity are presently seriously threatened by global development and population growth, leading to increases in nutrient inputs and intensification of eutrophication-induced problems in receiving fresh waters, particularly in lakes. Climate change constitutes another threat exacerbating the symptoms of eutrophication and species migration and loss. Unequivocal evidence of climate change impacts is still highly fragmented despite the intensive research, in part due to the variety and uncertainty of climate models and underlying emission scenarios but also due to the different approaches applied to study its effects. We first describe the strengths and weaknesses of the multi-faceted approaches that are presently available for elucidating the effects of climate change in lakes, including space-for-time substitution, time series, experiments, palaeoecology and modelling. Reviewing combined results from studies based on the various approaches, we describe the likely effects of climate changes on biological communities, trophic dynamics and the ecological state of lakes. We further discuss potential mitigation and adaptation measures to counteract the effects of climate change on lakes and, finally, we highlight some of the future challenges that we face to improve our capacity for successful prediction

Diets and trophic structure of fish assemblages in a large and unexplored subtropical river: The Uruguay river

This article belongs to the Special Issue Trophic Interactions in Warm Freshwater EcosystemsThe Neotropics represent a hotspot for freshwater biodiversity with vast number of fish species of scarce ecological knowledge. This holds true for the Uruguay River, where fish assemblages and their diets remain unexplored. Fish assemblages were surveyed in 14 sites along the river main course, from headwaters to mouth (approximately 1800 km), with the aim to identify the trophic roles of fishes and to describe trophic structure of these assemblages, following standardized sampling campaigns and laboratory procedures. One hundred species (2309 gut contents) were analysed and classified into four trophic groups subdivided into eight lower-level groups: Piscivore, piscivore-invertivore, detritivore, omnivore-detritivore, omnivore-invertivore, omnivore-planktivore and omnivore-herbivore. The trophic structure of the assemblages varied along the river, with the relative species richness of fish consuming terrestrial invertebrates increasing towards the middle river section, probably driven by the large floodplains in that areas, supporting global theories such as the flood pulse concept. This study describes the feeding habits of fish along the Uruguay River, being the first dietary description for 29 species. This knowledge is essential for management and conservation, serving as baseline in the context of future environmental changes while generating novel evidence on the functioning of ecosystems in this scarcely studied climatic region

Fish but not macroinvertebrates promote trophic cascading effects in high density submersed plant experimental lake food webs in two contrasting climate regions

Predators play a key role in the functioning of shallow lakes. Differences between the response of temperate and subtropical systems to fish predation have been proposed, but experimental evidence is scarce. To elucidate cascading effects produced by predators in contrasting climatic zones, we conducted a mesocosm experiment in three pairs of lakes in Uruguay and Denmark. We used two typical planktivorous-omnivorous fish species (Jenynsia multidentata + Cnesterodon decemmaculatus and Gasterosteus aculeatus + Perca fluviatilis) and one littoral omnivorous-predatory macroinvertebrate (Palaemonetes argentinus and Gammarus lacustris), alone and combined, in numbers resembling natural densities. Fish predation on zooplankton increased phytoplankton biomass in both climate zones, whereas the effects of predatory macroinvertebrates on zooplankton and phytoplankton were not significant in either climate zone. Macroinvertebrates (that freely colonized the sampling devices) were diminished by fish in both climate areas; however, periphyton biomass did not vary among treatments. Our experiments demonstrated that fish affected the structure of both planktonic and littoral herbivorous communities in both climate regions, with a visible positive cascading effect on phytoplankton biomass, but no effects on periphyton. Altogether, fish impacts appeared to be a strong driver of turbid water conditions in shallow lakes regardless of climatic zone by indirectly contributing to increasing phytoplankton biomass

Effects of Temperature, Salinity and Fish in Structuring the Macroinvertebrate Community in Shallow Lakes: Implications for Effects of Climate Change

Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lakes

Importancia de las plantas flotantes libres de gran porte en la conservación y rehabilitación de lagos someros de Sudamérica

Las plantas acuáticas presentan un papel muy importante en la estructura y funcionamiento de los lagos someros, y constituyen, por tanto, un elemento clave en el diseño de estrategias de conservación y rehabilitación de estos ambientes. Para algunas formas de vida, como las plantas sumergidas, se conoce ampliamente su influencia en las propiedades fisico-químicas del agua o en la estructura de otras comunidades bióticas, particularmente en regiones templadas. En cambio, aún se desconocen aspectos importantes del papel en los ecosistemas acuáticos de las plantas flotantes libres de gran porte, características de las zonas tropicales y subtropicales. Esta revisión presenta aquellos aspectos conocidos y desconocidos en Sudamérica, de donde son nativas las especies más representativas, y cuáles son las perspectivas futuras en el área básica y aplicada del conocimiento.Facultad de Ciencias- Universidad de la República, CSIC, DINACYT, IMM y PEDECIBA (Uruguay); Foreign and Commnonwealth Office y BES (Reino Unido), y Danish Research Agency (Dinamarca)

Habitat complexity in shallow lakes and ponds: importance, threats, and potential for restoration

In this review we describe patterns and mechanisms by which habitat complexity is crucial for the functioning of shallow lakes and ponds, and for the abundance and diversity of biological communities in these ecosystems. Habitat complexity is affected by processes acting at different spatial scales, from the landscape to the ecosystem level (i.e., morphometric attributes) that generate different complexities, determining the potential for organisms to succeed and processes to occur, such as energy and nutrient transfer, and fluxes of greenhouse gases, among others. At the local scale, the three major habitats, pelagic, littoral, and benthic, are characterised by different degrees of structural complexity and a particular set of organisms and processes. Direct and indirect effects of changes in within-lake habitat complexity can either hinder or promote regime shifts in these systems. We also review several anthropogenic pressures (eutrophication, urbanisation, introduction of exotic species, and climate change) that decrease lake resilience through changes in habitat complexity and strategies for habitat complexity restoration. Overall, we emphasize the need to preserve and/or restore habitat complexity as key challenges to account for ecosystem integrity, maintenance of local/regional biodiversity, and for the provision of crucial ecosystem services (e.g., biodiversity, self-purification, and carbon sequestration).Fil: Meerhoff, Mariana. Universidad de la Republica; UruguayFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Habitat complexity in shallow lakes and ponds: importance, threats, and potential for restoration

In this review we describe patterns and mechanisms by which habitat complexity is crucial for the functioning of 10 shallow lakes and ponds, and for the abundance and diversity of biological communities in these ecosystems. Habitat 11 complexity is affected by processes acting at different spatial scales, from the landscape scale to the ecosystem level 12 (i.e., morphometric attributes) generate different complexities, determining the potential for organisms to succeed and 13 processes to occur such as energy and nutrient transfer, fluxes of greenhouse gases, among others. At the local scale, the 14 three major habitats, pelagic, littoral, and benthic, are characterised by different degrees of structural complexity and a 15 particular set of organisms and processes. Direct and indirect effects of changes in within-lake habitat complexity can 16 either hinder or promote regime shifts in these systems. We also review several anthropogenic pressures 17 (eutrophication, urbanisation, introduction of exotic species, and climate change) that decrease lake resilience through 18 changes in habitat complexity and strategists for habitat complexity restoration. Overall, we emphasize the need to 19 preserve and restore habitat complexity as key challenges to account for ecosystem integrity, maintenance of 20 local/regional biodiversity, and provision of crucial ecosystem services (e.g., biodiversity, self-purification, and carbon 21 sequestration).European Union’s Horizon 2020- grant agreement No 869296The PONDERFUL Projec

Community Structure and Diel Migration of Zooplankton in Shallow Brackish Lakes: Role of Salinity and Predators

Diel horizontal migration (DHM), where zooplankton moves towards macrophytes during daytime to avoid planktivorous fish, has been reported as a common migration pattern of zooplankton in shallow temperate freshwater lakes. However, in shallow eutrophic brackish lakes, macrophytes seem not to have the same refuge effect, as these lakes may remain turbid even at relatively high macrophyte abundances. To investigate the extent to which macrophytes serve as a refuge for zooplankton at different salinities, we introduced artificial plants mimicking submerged macrophytes in the littoral zone of four shallow lakes, with salinities ranging from almost freshwater (0.3) to oligohaline waters (3.8). Furthermore, we examined the effects of different salinities on the community structure. Diel samples of zooplankton were taken from artificial plants, from areas where macrophytes had been removed (intermediate areas) and, in two of the lakes, also in open water. Fish and macroinvertebrates were sampled amongst the artificial plants and in intermediate areas to investigate their influence on zooplankton migration. Our results indicated that diel vertical migration (DVM) was the most frequent migration pattern of zooplankton groups, suggesting that submerged macrophytes were a poor refuge against predation at all salinities under study. Presumably, this pattern was the result of the relatively high densities of small planktivorous fish and macroinvertebrate predators within the submerged plants. In addition, we found major differences in the composition of zooplankton, fish and macroinvertebrate communities at the different salinities and species richness and diversity of zooplankton decreased with increasing salinity. At low salinities both planktonic/free-swimming and benthic/plant-associated cladocerans occurred, whilst only benthic ones occurred at the highest salinity. The low zooplankton biomass and overall smallerbodied zooplankton specimens may result in a lower grazing capacity on phytoplankton, and enhance the turbid state in nutrient rich shallow brackish lakes.JRC.H.1-Water Resource