Aquatic Sciences最新文献

Eucalyptus afforestation negatively affects the ecological condition of streams by impacting macroinvertebrates, whose responses to habitat deterioration and changes in basal resources are not well understood. This study examines the effects of Eucalyptus afforestation on macroinvertebrate functional diversity and trait structure, driven by variations in local habitat and basal resources. The study was conducted once in summer and winter across 27 subtropical lowland streams along an Eucalyptus spp. afforestation gradient. We measured physicochemical water parameters, habitat variables (substrates, depth and current velocity) and biomass of basal resources (macrophytes, periphyton and detritus) simultaneously with macroinvertebrate sampling. We used co-inertia multivariate RLQ and four-corner analyses to explore relationships between physicochemical water parameters, local habitat and basal resources, with trait structure. Structural equation modelling-SEM was used to understand the direct and indirect effects of Eucalyptus afforestation on macroinvertebrate functional diversity. SEM revealed that Eucalyptus afforestation indirectly reduced macroinvertebrate functional diversity by reducing macrophyte biomass in both seasons. The RQL analysis revealed a positive correlation among the biomass of macrophytes, density of predators and number of small- and medium-sized animals. This suggests that the decrease in macrophyte biomass may affect the available refuges and biological interactions by affecting predators and small and medium body sizes. These findings emphasise the importance of macrophytes in sustaining a unique functional trait composition of macroinvertebrates in stream ecosystems. Although afforestation did not influence substrate types, they positively affect functional diversity. Macroinvertebrate functional traits are effective indicators of ecological degradation in streams affected by Eucalyptus afforestation.

Graphical abstract

Rivers are globally important sources of carbon emissions, but the diurnal pattern of greenhouse gas (GHG) emissions from rivers colonized with submerged macrophytes has rarely been explored. We determined the dissolved concentrations and diffusive fluxes of CO₂, CH₄, and N₂O from a river covered with submerged macrophytes under different meteorological conditions (i.e., nighttime, cloudy, and sunny daytime) over a continuous 36-h period. Overall, the river functioned as a CO₂ sink during the daytime, while it transitioned to a CO₂ source at nighttime, primarily because of diurnal variations in plant metabolisms. No similar diurnal fluctuations in CH₄ or N₂O emissions were detected, and the highest fluxes of CH₄ or N₂O were measured during sunny daytime. In total, the river emitted more carbon at nighttime, with CH₄ contributing most to the total emissions on the basis of a CO₂ equivalent. Dissolved organic matter (DOM) in the river, whose properties were potentially modulated by submerged macrophytes, considerably influenced GHG emissions. Distinct dissimilarities were observed in the microbial communities inhabiting the river sediment and biofilms on plant leaves. Microbial communities in the sediment played more important roles in biogeochemical cycles, while the regulatory effects of epiphytic microbiota on GHG emissions should not be ignored. Multiple regression and structural equation modeling analyses revealed that the dissolved oxygen concentration, temperature, humification index (HIX) of DOM, and NH₄⁺–N concentration significantly influenced CO₂ diffusive fluxes, while CH₄ dynamics were predominantly influenced by DOM properties. Salinity, HIX, NH₄⁺-N concentration, and microbial consortia were the predominant factors influencing N₂O emissions.

Biological invasions threaten biodiversity and cause severe ecological and socioeconomic impacts. Freshwater snails are very diverse and many became invasive or have the potential to do so. Studies on the relationship between bioecological traits and invasiveness are needed to prevent new invasions. The tolerance to environmental stressors of the neonate, one of the most vulnerable ontogenetic phases, may be an important component of invasiveness in freshwater snails. We hypothesize that tolerance of neonates to environmental stressors increases the chances of population establishment and persistence and hence of becoming an invader. We predict that the neonates of invasive freshwater snails will show higher survival under starvation and desiccation than those of non-invasive ones and tested this experimentally for three species of each type. We also estimated neonate volume as a proxy of tolerance. We found that the desiccation stress was more severe than the starvation one. The tolerance to starvation of two of the invasive species (Melanoides tuberculata and Pomacea canaliculata) was much higher than that of remaining species but the pattern was less clear for desiccation, which was more directly related to neonate volume. None of the non-invasive species showed high tolerance to these stressors and the invasive Physella acuta groups with them in this regard. On the whole our prediction about the relationship between neonate tolerance and invasiveness stands for five out of the six species tested, indicating that the tolerance of neonates of freshwater snails merits more research effort on other stressors to gain a sounder comprehension of their invasiveness.