Freshwater Biology最新文献

1. Both abundant and rare microorganisms are critical in regulating soil biogeochemical processes such as nitrification and denitrification. However, the community assembly mechanisms of abundant and rare microorganisms involved in nitrification and denitrification remain unclear, especially at large scales.
2. Here, using high-throughput sequencing of archaeal amoA, bacterial amoA, nirK, and nirS genes, we investigated the biogeographic patterns and assembly mechanisms of nitrifying and denitrifying communities in multiple habitats (riparian rhizosphere soils, riparian bulk soils, and channel sediments) of 30 rivers along a latitudinal gradient in China.
3. The results showed that the α- and β-diversity of nitrifying and denitrifying communities usually decreased with increasing latitude. Nitrifying and denitrifying communities presented a significant distance-decay relationship (DDR), and the DDR slopes were steeper for abundant subcommunities than for rare subcommunities. Latitude, climate, vegetation, and soil properties (e.g., pH and carbon content) were important in explaining community composition variation.
4. Our results indicate that community assemblies of nitrifiers and denitrifiers were mainly affected by stochastic processes, with those of denitrifiers and abundant nitrifiers being governed by dispersal limitation and those of rare nitrifiers by undominated processes (also known as ecological drift).
5. To our knowledge, this is one of the few studies showing that stochastic rather than deterministic processes dominate the community assembly of abundant and rare microorganisms involved in nitrification and denitrification across China, comprising 25% of the Asian continent. Our findings have potential implications for predicting soil microorganism responses to environmental change.

1. Knowledge of how aquatic insects use riparian zones can inform the conservation and management of both rivers and riparian zones. This study reports the habitat use and spatial segregation of winged EPT (Ephemeroptera, Plecoptera, Trichoptera) adults in the river channel and riparian zone of the gravel-bed Satsunai River in Hokkaido, northern Japan.
2. Adult insects were caught using sticky and Malaise traps in the summer of 2019 and 2020. The relative use of forest-covered and gravel-covered riparian zones and their edge habitats was examined in relation to above-water space. Furthermore, the habitat use of the natural forest-covered riparian zone in two dimensions (i.e., lateral and vertical over 104 and 18 m, respectively) was measured.
3. Ephemeroptera were largely captured above the river channel and showed no preference for forest-covered or gravel-covered riparian habitats. In contrast, Plecoptera were caught primarily in the forest-covered riparian zone. Capture of Trichoptera was moderately higher along the edge of the forest-covered riparian zone, representing an intermediate response.
4. We identified clear spatial segregation of EPT taxa in lateral and vertical dimensions. Most individuals were caught > 5 m above the ground in forest strata and < 30 m from the channel laterally. At the family level, Plecoptera taxa (Nemouridae and Chloroperlidae) occurred at the medium and lowest height in the vertical dimension. In particular, the numerically dominant Plecoptera family, Chloroperlidae, was most frequently found near the ground (< 5 m height), and was also distributed furthest from the stream (40 m). Other Trichoptera families such as Philopotamidae were found within relatively short distances from the channel.
5. Riparian zones can provide preferable habitat for some EPT adults, with their structural and microclimatic diversity influencing taxon-specific two-dimensional distributions. Identification of taxa with high abundance, ease of observation, and laterally extensive use of riparian zones as a useful candidate indicator, in our case Chloroperlidae, could enable the assessment of ecosystem status in the river–riparian continuum and its responses to landscape changes in gravel-bed river corridors.

Braided rivers are dynamic ecosystems characterised by frequent flows that rework the braidplain, forming a shifting mosaic of habitats of varying successional age. This dynamic habitat mosaic facilitates movement of resources between aquatic and terrestrial environments, fostering biodiversity and ecological resilience. Anthropogenic impacts such as impoundments, water and gravel extraction and weed encroachment can reduce the ability for the river to rework the riverbed, stabilising and homogenising the braidplain, impacting ecosystem functioning as well as geomorphology. We examined how the availability and consumption of adult aquatic insects by terrestrial invertebrate consumers varied among different-aged habitat patches within a New Zealand braided river reach with minimal anthropogenic alteration. Terrestrial and adult aquatic insect availability was quantified at ground level and aerially using pitfall and sticky traps, respectively, in five sites of three different-aged braidplain habitat types (recently formed bare gravel, intermediate and older vegetated habitats). Stable (δ¹³C and δ¹⁵N) isotope analyses were used to quantify the use of aquatic insect prey by predatory terrestrial invertebrates (ground-hunting spiders and predatory beetles) in each habitat type. Aquatic prey availability and consumption by terrestrial predators varied between habitat types, and different-aged habitats better supported ground- and aerial-active terrestrial predators. At ground-level, more adult aquatic insects were available and consumed by predatory beetles in bare gravel habitat types. In contrast, older vegetated habitats had higher aerial aquatic insect availability, potentially better supporting aerial-active consumers. Our results show that a relatively natural braided river reach with minimal geomorphological alteration had spatial heterogeneity in aquatic prey availability, the locations of which differed for aerial- and ground-active consumers during the austral summer. These height-dependent locations of variable aquatic prey abundance will move at varying timescales within the naturally dynamic habitat mosaic. The observed spatial heterogeneity of resource availability is likely to enhance braidplain-scale biodiversity and resilience by supporting diverse consumer groups and providing stability during high-flow events. Understanding the structure of relatively unimpacted braided river systems can support their geomorphological conservation and restoration, thus enhancing their ecological resilience in the face of environmental change. Our results provide evidence that habitat patches of varying successional age, which require frequent bed-mobilising floods to maintain, can support diverse braided river ecosystems.

1. Freshwater springs often have high rates of endemism with species displaying restricted distributions, low genetic diversity and increased risk to anthropogenic influences. Several models such as the Theory of Island Biogeography, the Stream Hierarchy Model or the Death Valley Model have been invoked to explain diversity patterns in springs, especially in arid systems. However, little information exists about whether previously developed models can predict population genetic and species-level diversity of temperate spring-obligate invertebrates. As a case study, we examined the biodiversity and genetic diversity of spring-obligate gastropods at six sites in the southeastern United States to examine gastropod diversity and test how well previously developed biogeographic models characterise an understudied and imperilled system.
2. We examined two species of Pleuroceridae snails, Princess Elimia (Elimia bellacrenata) and Cockle Elimia (Elimia cochliaris), endemic to springs in central Alabama. We sampled specimens of both species from across their current ranges and generated genome-scale data using a 2b-RAD sequencing approach. To assess species diversity and ranges, we used maximum likelihood, species tree inference and phylogenetic network approaches. We also inferred genetic diversity, population genetic structure and historical demography of each species.
3. Phylogenetic analyses recovered four species-level lineages, including two undescribed species. Each species was found in a single spring system, resulting in an extremely small distribution. Additionally, all four of these spring-obligate lineages had higher genetic diversity than most riverine pleurocerid species. Furthermore, demographic analyses suggested that each lineage has maintained a stable population size since the Pleistocene.
4. Our findings indicate that diversity patterns of temperate, spring-endemic gastropods do not conform to previously developed biogeographic models. Moreover, differences among species studied here and other spring-obligate groups suggest that applying broad biogeographic models to any given spring system has the potential to obscure unique characteristics of regional spring ecosystems. Empirical data should be more widely generated for understudied spring systems, and such data should inform biodiversity assessments, conservation planning and, potentially, the development of additional biogeographic models.

1. Myanmar is a biodiversity hotspot and holds at least 570 different freshwater fish species with a high amount of endemism. Nevertheless, freshwater systems in Myanmar are highly threatened by anthropogenic perturbation such as pollution.
2. We examined impacts on streams from nutrient enrichment and catchment degradation on the fish community composition and trophic structure. We studied 12 stream sites, and treated these as two groups (six impacted vs. six less impacted), as well as covering a gradient in degradation. We did quantitative electrofishing, collected potential food resources, invertebrates and fish for stable isotope analysis of δ¹³C and δ¹⁵N, and measured a number of environmental site variables. To determine fish diversity, we extracted DNA from tissue samples of 193 specimens, thereby identifying a total of 44 different species from 20 families.
3. The most impacted sites had higher nitrogen concentrations and lower minimum O₂ saturation. Fish biomass m⁻² increased with degradation as it correlated positively with total nitrogen concentration and negatively with minimum O₂ saturation. Fish communities did not differ significantly between the two groups nor across the environmental gradient, except that pairwise similarities were negatively related to differences in catchment forest cover.
4. Likewise, trophic niches of the fish did not differ significantly between the two groups nor across the environmental gradient, but fish at the more impacted sites had significantly lower minimum δ¹⁵N signal and higher δ¹⁵N range compared to the least impacted.
5. The tropical fish assemblages studied were diverse and showed overall weak response to human impact. Likewise, there was little indication of differences in tolerance to environmental stress among taxa. Thus, in contrast to previous studies on macroinvertebrates in the same region, our results suggest that fish communities are less suitable as bio-indicators of environmental degradation and biodiversity loss in these tropical lowland streams.

1. With climate change and rising temperatures, the timing of spring is advancing in many parts of the world. Such environmental changes may have immediate effects on species communities, but also carry-over effects into later seasons. However, little is known about the extent of such carry-over effects for communities consisting of short-lived species with multiple life cycles in a year.
2. We used a 26-year dataset to explore the immediate and carry-over effects of spring temperature on freshwater zooplankton communities consisting of three taxonomic groups (Rotifera, Cladocera and Copepoda), sampled at three locations in a lake in central Norway. We first described the seasonal dynamics of zooplankton community abundance and species richness, as well as the ratio between abundance and species richness, using generalised additive mixed models (GAMM). Next, we used a sliding window analysis to identify the most important time during spring for which temperature affected community abundance and species richness, and the impact of this window on different parts of the seasonal curve of abundance and species richness of the community. This allowed us to explore whether spring temperature affected overall abundance and species richness, whether there were seasonal differences in the strength of the effect, how any effects varied between the three phyla, and whether they were consistent among the three localities.
3. Cladocera and Rotifera roughly followed the expected seasonal pattern, with a peak in total abundance. Copepoda, on the other hand, showed lower abundance in the middle of the sampling season. The shape of the curve also varied between localities. Spring air temperature affected the overall abundance, species richness, and abundance: species richness ratio throughout the season. In some cases, models with an interaction between spring temperature and Julian day were the best, indicating that the effect of spring temperature varied temporally in strength and direction.
4. Given the short life cycles of most zooplankton species present in our dataset, it is surprising that effects of spring temperature are visible throughout the summer and into early autumn. This implies that pulse disturbances may have long-lasting, multigenerational effects even in communities of short-lived species. Our study also illustrates how different zooplankton groups may vary in their response to temperature variations.