Martín C. M. Blettler

Influence of hydrological changes on the fish community in two lotic environments of the Middle Paraná Floodplain, Argentina

Temporal variations of fish abundance and species richness in two sites of a secondary channel of the Middle Paraná Floodplain (Argentina) have been analyzed from 2010 to 2012. Relationships of these ecological attributes with alternations of floods and dry periods were appraised. Permutational analyses of variance were applied to determine significance in temporal changes of the fish community, taking into account catch per unit effort and species richness of the whole community, by groups of distinct reproductive strategy and considering fish sizes. The results reveal significant differences in structure and composition of fish assemblages at distinct stages of the hydrological regime. Those temporal differences are associated with changes in timing, duration, and magnitude of floods since the three groups have shown distinct responses to the hydrological variations. Long-distance migrants depend on major inundations for a successful reproduction, short-distance migrants seem to have distinct responses to floods according to the kind of species, and sedentary fish-developing parental care essentially needs high floodplain connectivity for juvenile development.

Sandy rivers: a review on general ecohydrological patterns of benthic invertebrate assemblages across continents

ABSTRACT The middle and lower sections of most large rivers have fine-grained bed sediments, which may have a strong influence on the functional and taxonomical structure of benthic invertebrates. Based on results from several studies by the authors on the faunal assemblages and habitat structures of the Paraguay–Paraná River system (Brazil, Paraguay, Argentina), from European (Rhine, Loire) River systems, and data from the literature, this review identifies general patterns which appear to have a global character. On one hand, the invertebrate assemblages largely differed between the main channel (MC) and the corresponding floodplain habitats in different sections, and also the floodplain habitats along the river channel revealed great differences in their biodiversity. On the other hand, there was a remarkable homogeneity among the main-channel sections within and even between river systems. We consider physical habitat features as the crucial variables responsible for these patterns. In cross-sections from the MC towards the floodplain habitats, grain size, organic matter content and oxygen supply change dramatically, and different floodplain habitats along the same river system may have different successional stages even at small geographical distances. The sandy structure of potamal habitats (including underwater dunes), however, provides a set of habitat features characterized by continuously changing sediment structures with well-defined grain sizes, low organic matter contents and good oxygenation, which force a set of adaptations by the invertebrates that limits but stabilizes the diversity of invertebrates in these large river sections. A better understanding of the ecohydrological interactions between habitat dynamics and benthic invertebrates is needed to improve sustainable river ecosystem management. We discuss the non-recovery of large benthic invertebrate species in the lower section of large rivers after improvement of the water quality in the context of these ecohydrological features. Conclusions are drawn for river restoration.

Plastic pollution in freshwater ecosystems: macro-, meso-, and microplastic debris in a floodplain lake

Plastic pollution is considered an important environmental problem by the United Nations Environment Programme, and it is identified, alongside climate change, as an emerging issue that might affect biological diversity and human health. However, despite research efforts investigating plastics in oceans, relatively little studies have focused on freshwater systems. The aim of this study was to estimate the spatial distribution, types, and characteristics of macro-, meso-, and microplastic fragments in shoreline sediments of a freshwater lake. Food wrappers (mainly polypropylene and polystyrene), bags (high- and low-density polyethylene), bottles (polyethylene terephthalate), and disposable Styrofoam food containers (expanded polystyrene) were the dominant macroplastics recorded in this study. Contrary to other studies, herein macroplastic item surveys would not serve as surrogates for microplastic items. This is disadvantageous since macroplastic surveys are relatively easier to conduct. Otherwise, an average of 25 mesoplastics (mainly expanded polystyrene) and 704 microplastic particles (diverse resins) were recorded per square meter in sandy sediments. Comparisons with other studies from freshwater and marine beaches indicated similar relevance of plastic contamination, demonstrating for the first time that plastic pollution is a serious problem in the Paraná floodplain lakes. This study is also valuable from a social/educational point of view, since plastic waste has been ignored in the Paraná catchment as a pollutant problem, and therefore, the outcome of the current study is a relevant contribution for decision makers.

Freshwater plastic pollution: Recognizing research biases and identifying knowledge gaps

The overwhelming majority of research conducted to date on plastic pollution (all size fractions) has focused on marine ecosystems. In comparison, only a few studies provide evidence for the presence of plastic debris in freshwater environments. However, owing to the numerous differences between freshwater studies (including studied species and habitats, geographical locations, social and economic contexts, the type of data obtained and also the broad range of purposes), they show only fragments of the overall picture of freshwater plastic pollution. This highlights the lack of a holistic vision and evidences several knowledge gaps and data biases. Through a bibliometric analysis we identified such knowledge gaps, inconsistencies and survey trends of plastic pollution research within freshwater ecosystems. We conclude that there is a continued need to increase the field-data bases about plastics (all size fractions) in freshwater environments. This is particularly important to estimate river plastic emissions to the worlds oceans. Accordingly, data about macroplastics from most polluted and larger rivers are very scarce, although macroplastics represent a huge input in terms of plastics weight. In addition, submerged macroplastics may play an important role in transporting mismanaged plastic waste, however almost no studies exist. Although many of the most plastic polluted rivers are in Asia, only 14% of the reviewed studies were carried out in this continent (even though the major inland fisheries of the world are located in Asias rivers). The potential damage caused by macroplastics on a wide range of freshwater fauna is as yet undetermined, even though negative impacts have been well documented in similar marine species. We also noted a clear supremacy of microplastic studies over macroplastic ones, even though there is no reason to assume that freshwater ecosystems remain unaffected by macro-debris. Finally, we recommend focusing monitoring efforts in most polluted rivers worldwide, but particularly in countries with rapid economic development and poor waste management.

Linking hydro‐morphology with invertebrate ecology in diverse morphological units of a large river‐floodplain system

Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto Nacional de Limnologia. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina

Influence of hydrology on the fish body condition in a large subtropical floodplain

With the objective of finding fluctuations on fish body condition in the Middle Parana River floodplain in different hydrological scenarios, this attribute was analyzed in several trophic groups of a secondary floodplain channel and its associated lakes between 2010 and 2012. Standardized residuals generated by length-weight regressions were calculated for each species and the relative weight (Wr) of the most abundant species per group was examined. A two-way factorial ANOVA was carried out (factors: hydrology and habitats) to evaluate the existence of significant spatial-temporal differences by groups and species. Results showed that body condition in detritivorous, herbivorous and omnivorous species fluctuated significantly depending on hydrology and the environment. Optimal body condition was recorded after the largest flood pulse in most species. Body condition decreased during the low-water period and after two disconnection periods, whereas during the second flood pulse it increased in detritivores, herbivores and omnivores. No floods occurred thereafter, but two flow pulses were registered, and body condition increased under these hydrologic scenarios, with similar or higher values to those recorded after the largest pulse. These results indicate that flow pulses, which are supplementary to flood pulses, may have a positive effect on fish body condition.