International Review of Hydrobiology最新文献

Freshwater ecosystems are highly susceptible to degradation, underscoring the importance of assessing their health using ecological indicators. In this study, we developed an Ecopath mass-balance model for Lake Tinshu Abaya, Ethiopia, and analyzed its trophic structure and energy flows. The model integrated seven functional groups using data on fish catch, diet composition, and plankton biomass collected from March to August 2022. The seven functional groups were detritus, phytoplankton, herbivorous zooplankton, carnivorous zooplankton, zoobenthos, Nile Tilapia (Oreochromis niloticus), and birds. Four trophic levels were determined, ranging from 1.00 for primary producers and detritus to 3.56 for birds of prey. The calculated values for the EE of the primary producers (phytoplankton: 0.87; detritus: 0.75) indicated that they were highly exploited compared to the secondary producers, the herbivorous zooplankton (0.40), the carnivorous zooplankton (0.065), and the zoobenthos (0.60). The computed primary production to total respiration (P/R) ratio of 1.19 suggested that the ecosystem is in a developing, net autotrophic state. The ecosystem exhibited a high degree of internal recycling (Finn's Cycling Index = 15.2%), reflecting efficient energy and nutrient utilization. The trophic connectivity index of 0.56 suggested a moderately interconnected food web. Collectively, these metrics indicate that Lake Tinshu Abaya is a developing ecosystem in a transitional stage, not yet having reached full ecological maturity.

Lake Nakuru, historically a hypersaline lake in Kenya's Rift Valley, has undergone a significant ecological transformation due to a sustained saline–freshwater inversion driven by increased rainfall, catchment degradation, and anthropogenic inputs. This study provides a spatially resolved assessment of the lake's current physico-chemical status, biological structure, and socioeconomic dynamics. Results show a dramatic decline in salinity from historical levels of 20–40 to 2.58–2.6 g/kg, weakening the lake's buffering capacity and altering nutrient stoichiometry. Molar TN/TP ratios across all sites were exceptionally low (0.09–0.19), indicating persistent nitrogen limitation and conditions conducive to cyanobacterial dominance. Microcystis comprised 27.58% ± 3.78% of the mean dietary contribution of Oreochromis niloticus, whose proliferation reflects a major shift in the lake's food web. Flamingo populations have declined, likely due to the collapse of their specialized food base. Microbial contamination was highest at river inflow sites. Further, we found elevated concentrations of arsenic and lead in fish tissue, raising critical public health concerns. The emergence of an informal tilapia fishery, driven by ecological changes and declining tourism, has introduced new economic opportunities but also sparked conflict due to its illegality within the protected national park. Vulnerable groups, particularly women, face heightened exposure to both economic instability and health risks. The findings indicate that Lake Nakuru has moved beyond early pollution symptoms into a phase of advanced ecological disruption, underscoring the need for urgent, multisectoral interventions.

In coastal areas, salinity is an important variable structuring diatom composition. The Caspian Sea is the world's largest enclosed water body. Variations in benthic diatom composition along salinity gradients were investigated in two important rivers flowing into the southeast Caspian Sea, Gorganroud and Atrak. Epipelic diatom samples were collected from 11 sites from November 2020 to April 2021, along with water samples. One hundred three taxa belonging to 34 genera were identified, of which 47 taxa (≥ 1% relative abundance in ≥ 5 samples were used to model optima and tolerance). The results revealed a shift from freshwater to brackish taxa in dominant and subdominant diatoms with increasing salinity (from 0.02 to 6.64 g.L⁻¹). Taxa such as Amphora inariensis and Cymbella excisa dominated low-salinity sites, while Navicula salinarum, Nitzschia cf. thermaloides, and Haslea spicula increased downstream. Salinity significantly affected the diatom distribution and separated brackish taxa from freshwater ones. However, ammonium and temperature were equally important in Atrak, and phosphate and dissolved oxygen also contributed. However, salinity was not the only factor determining diatom distribution, as nutrients and thermal regime modulated assemblages where salinization was less extreme. Shannon diversity and evenness declined at intermediate salinities (5–7 g.L⁻¹), reflecting Remane's species-poor zone. These findings underscore diatom's value for monitoring salinization and nutrient impacts in Caspian tributaries and support their use in catchment management and long-term ecological assessments.

Forestry plantations occur across the globe, and they are important in many tropical countries for timber supply. Plantations of non-native species, such as those of Eucalyptus species, may greatly affect the functioning of detritus-based ecosystems. However, despite eucalyptus plantations covering about 20 million hectares in tropical and subtropical regions (from a total of about 25 million hectares globally), there is scarce information about their effects on forest stream functioning. Our aim was to assess the effects of catchment-scale eucalyptus plantations (with native riparian buffers) on the functioning of tropical streams in the Cerrado biome. For that, three streams in catchments with eucalyptus plantations (eucalyptus streams) and three streams in catchments with native vegetation (native streams) were compared regarding water characteristics, litter inputs (vertical and lateral), decomposition of leaf litter (from a common native species, an eucalyptus species used in plantations, and a palatable exotic species) and litter-associated aquatic communities. We hypothesized that catchment-scale Eucalyptus plantations negatively affect stream characteristics (reduced water flow, heightened water acidity), litter inputs, aquatic communities, and litter decomposition in streams because dense, even-aged monocultures of eucalyptus trees have higher water consumption rates and produce recalcitrant litter. We also hypothesized that the effects of plantations would be stronger on shredders, as they are directly influenced by changes in litter input compared to other functional feeding groups. Finally, we hypothesized that plantation impacts on leaf litter decomposition would be stronger for palatable leaf litter, where invertebrate shredders play a major role, than for more recalcitrant and less palatable leaf litter. We found lower dissolved oxygen concentrations, lateral litter inputs, and litter decomposition in eucalyptus streams than in native streams. Conversely, fungal biomass on decomposing litter did not differ between eucalyptus streams and native streams. Eucalyptus plantations reduced overall invertebrate densities but did not affect shredder densities. Our study shows that catchment-scale eucalyptus plantations can change water characteristics and litter inputs to streams, thus slowing down litter decomposition in tropical streams, even when a native buffer is present. Increasing the width of the native buffer vegetation may contribute to increasing its protective role.

Using a subset of the aquatic insect assemblage (e.g., Trichoptera, Odonata, and Diptera) and less refined identifications can reduce identification time and costs in aquatic biomonitoring. Using data collected from urban Amazonian streams, we evaluated the congruence between the macroinvertebrate fauna and the Trichoptera, Odonata, and Diptera subsets at the family and genus level. In addition, we evaluated the congruence between the abiotic and macroinvertebrate data sets. Data were collected during the dry and rainy seasons of 2004/2005 and the dry season of 2010. Our results indicate high intra-annual congruence for both abiotic and biotic (occurrence and abundance) variables. However, low interannual congruence was observed. Interannual congruence for biotic variables was slightly above 70%. Macroinvertebrate occurrence and abundance of all taxa showed a moderate correlation with abiotic data. The highest level of congruence with abiotic data was observed for the abundance of Odonata genera in 2010, while the lowest was found for the abundance of Diptera family in 2010. The concordance values between biotic and abiotic data were generally similar when considering both abundance and occurrence data. In all seasons, congruence between genera and families was greater than 90% for abundance and occurrence data. Our results suggest that assessments based on macroinvertebrate family abundance and occurrence may be sufficient for biomonitoring and that the families of Trichoptera, Odonata, and Diptera represent most of the total invertebrate assemblage in the streams studied.

Rotifera are found in nearly all terrestrial and freshwater habitats, however, the knowledge about rotifers in groundwater is scarce. To enhance our understanding of Rotifera distribution in groundwater in the lowland regions of Central Europe, we investigated 101 wells throughout the Biebrza Valley—one of Europe's largest wetland complexes. Rotifers were found in most of the studied wells (97%); however, only 22 Monogononta species were identified. The majority of these were littoral species commonly associated with surface water macrophytes, suggesting passive transport from the river network rather than active colonization or specialization for subterranean life. No strictly stygobiontic (obligate groundwater) or stygophilic (preferring groundwater) Rotifera species were found. Instead, our results indicate a high prevalence of stygoxenic species—organisms that occur in groundwater environments only incidentally. Species richness was low compared to surface or transitional habitats such as springs and the hyporheic zone, which showed much greater rotifer diversity. These findings suggest that while rotifers can occur in groundwater, their ecological traits favor opportunistic colonization over groundwater specialization.