Natural recovery and restoration of acidified shallow soft-water lakes: Successes and bottlenecks revealed by assessing life-history strategies of chironomid larvae

Unravelling the influence of cattle stocking rate on the macroinvertebrate community of freshwater wetlands subjected to hydrological modifications in three hydroclimatic periods

The Paraná River Delta in South America, a large wetlands macromosaic, faces threats from climate change, human activities like livestock intensification, and hydrological modifications driven by the construction of water management infrastructure to prevent flooding in productive lands. Macroinvertebrates, essential for wetland health, are affected by cattle-induced changes in water quality, nutrient enrichment, and trampling, posing challenges to the ecosystem's ecological balance and long-term survival of these organisms. In this study, we analyzed the impact of two categories of cattle stocking rates (low and high) on the taxonomic and functional structure of the aquatic macroinvertebrate community in freshwater marshes. In addition, we compare the influence of cattle stocking rate on macroinvertebrates in natural and modified freshwater marshes, and, finally, the effect of cattle stocking rate in three contrasting hydrometeorological periods: a drier, a humid, and an extreme drought period. Samplings were conducted in 16 freshwater habitats of the Lower Paraná River Delta, examining variables such as temperature, pH, dissolved oxygen, coliforms, and nutrient concentrations. Macroinvertebrates were collected and functional and taxonomic metrics were estimated. Statistical analyses, including ANOVA and Kruskal-Wallis tests, were conducted to evaluate the effects of cattle stocking rates, hydrological modifications, and hydrometeorological periods on macroinvertebrate metrics and environmental variables. RDA, PERMANOVA, and SIMPER analyses explored the relationships between assemblage composition and environmental factors. High stocking rate altered the community structure, modifying its composition and decreasing the density, taxonomic and functional richness. Moreover, hydrological alterations exacerbated these negative impacts of cattle overstocking in macroinvertebrates. Under severe drought conditions, only tolerant species can survive cattle overstocking conditions. Our findings provide relevant insight into the ecological risks associated with cattle overstocking in natural and modified freshwater marshes and underscore the need to control cattle stocking rates in extreme drought to avoid loss of ecological functions.

Response of Chironomids to Key Environmental Factors: Perspective for Biomonitoring

Chironomids are the species-richest family among macroinvertebrates and are often used as indicators of ecological conditions in inland waters. High taxonomic expertise is needed for identification and new species are still being described even in the well-known West Palearctic region. Our Microsoft Access relational database comprises data on Chironomid species collected in rivers and lakes in Italy and some other European countries over a period of about 50 years, often associated with physical-chemical data, but in some cases, only data on Chironomids are available with no associated environmental data. The aim of the present paper was to propose the calculation of ecological traits of Chironomid species as a tool to derive information on water quality, when only data on Chironomid species composition are present, while environmental data are lacking. Traits summarizing the species' response to environmental variables were evaluated, with emphasis on natural and man-influenced factors: current velocity, water temperature, conductivity, dissolved oxygen, and nutrients. Traits calculations were carried out in the R environment using a subset of our data, including both environmental data and Chironomid abundances. The relations between sites, Chironomid, species and traits were evaluated using correspondence analysis and other multivariate methods. The response of species showed an interaction among different factors, with the possibility of ordering species along a single environmental gradient, extending from cold running waters to warm standing waters, with few exceptions.

Chironomidae traits and life history strategies as indicators of anthropogenic disturbance

In freshwater ecosystems, Chironomidae are currently considered indicators of poor water quality because the family is often abundant in degraded sites. However, it incorporates taxa with a large ecological and physiological diversity and different sensitivity to impairment. Yet, the usual identification of Chironomidae at coarse taxonomic levels (family or subfamily) masks genus and species sensitivities. In this study, we investigate the potential of taxonomic and functional (traits) composition of Chironomidae to detect anthropogenic disturbance. In this context, we tested some a priori hypotheses regarding the ability of Chironomidae taxonomic and trait compositions to discriminate Mediterranean streams affected by multiple stressors from least-disturbed streams. Both taxonomic and Eltonian trait composition discriminated sites according to their disturbance level. Disturbance resulted in the predicted increase of Chironomidae with higher number of stages with hibernation/diapause and of taxa with resistance forms and unpredicted increase of the proportion of taxa with longer life cycles and few generations per year. Life history strategies (LHS), corresponding to multivoltine Chironomidae that do not invest in hemoglobin and lack strong spring synchronization, were well adapted to all our Mediterranean sites with highly changeable environmental conditions. Medium-size animals favored in disturbed sites where the Mediterranean hydrological regime is altered, but the reduced number of larger-size/carnivore Chironomids suggests a limitation to secondary production. Results indicate that Chironomidae genus and respective traits could be a useful tool in the structural and functional assessment of Mediterranean streams. The ubiquitous nature of Chironomidae should be also especially relevant in the assessment of water bodies naturally poor in other groups such as the Ephemeroptera, Plecoptera, and Trichoptera, such as the lowland rivers with sandy substrates, lakes, or reservoirs.