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.