Riparian Land Research Articles

The surrounding landscape influences the diversity of leaf-litter ants in riparian cloud forest remnants.

Riparian vegetation is a distinctive and ecologically important element of landscapes worldwide. However, the relative influence of the surrounding landscape on the conservation of the biodiversity of riparian remnants in human-modified tropical landscapes is poorly understood. We studied the surrounding landscape to evaluate its influence on leaf-litter-ant alpha and beta diversity in riparian remnants in the tropical montane cloud forest region of central Veracruz, Mexico. Sampling was carried out in 12 sites with riparian vegetation during both rainy (2011) and dry (2012) seasons. Ten leaf-litter samples were collected along a 100-m transect per site and processed with Berlese-Tullgren funnels and Winkler sacks. Using remotely-sensed and ground-collected data, we characterized the landscape around each site according to nine land cover types and computed metrics of landscape composition and configuration. We collected a total of 8,684 ant individuals belonging to 53 species, 22 genera, 11 tribes, and 7 subfamilies. Species richness and the diversity of Shannon and Simpson increased significantly in remnants immersed in landscapes with a high percentage of riparian land cover and a low percentage of land covers with areas reforested with Pinus, cattle pastures, and human settlements and infrastructure. The composition of ant assemblages was a function of the percentage of riparian land cover in the landscape. This study found evidence that leaf-litter ants, a highly specialized guild of arthropods, are mainly impacted by landscape composition and the configuration of the focal remnant. Maintaining or improving the surrounding landscape quality of riparian vegetation remnants can stimulate the movement of biodiversity among forest and riparian remnants and foster the provision of ecosystem services by these ecosystems. Effective outcomes may be achieved by considering scientific knowledge during the early stages of riparian policy formulation, in addition to integrating riparian management strategies with broader environmental planning instruments.

Riparian land uses affect the dry season soil CO2 efflux under dry tropical ecosystems

Riparian ecosystems are amongst the most vulnerable ecosystems of the world. The natural gradients and increasing human perturbations under these ecosystems can be explored for understanding the soil carbon (C) dynamics, especially soil carbon dioxide (CO2) efflux. However, studies on soil CO2 efflux and its governing variables under different land uses of dry tropical riparian ecosystems are limited. Therefore, the present study aimed (1) to assess the impact of riparian land use on soil CO2 efflux, and (2) to identify the key drivers of soil CO2 efflux along the river Ganga, Varanasi, India. The riparian land uses taken in this study were moist sandy flat (MSF), uncultivated sandy land (USL) and cultivated sandy land (CSL) depending upon their slope and distance from river body to upland, respectively. Soil CO2 efflux and other soil biophysical properties were measured at 54 locations distributed in six sites having these land uses, in dry season of 2014–15. Soil biophysical properties considered in this study were soil organic C, soil moisture, bulk density, porosity, fine particles, microbial biomass C and soil pH. Riparian land uses were found to have significant impact over soil CO2 efflux with a respective increase of 222, 424 and 63%, for MSF to USL, MSF to CSL, and USL to CSL land use transitions (P<0.01), respectively. Similarly, the regulators of soil CO2 efflux varied with the land uses. It showed strong positive correlation with soil organic C (r=0.81), fine particles (r=0.64) and porosity (r=0.61), whereas negative correlation with soil moisture (r=0.61) and bulk density (r=0.62) for overall dataset. However, soil organic C, fine particles, microbial biomass C and soil pH at MSF; soil organic C and microbial biomass C at USL; and soil moisture, porosity and microbial biomass C at CSL land uses were observed to regulate soil CO2 efflux. The findings revealed that riparian land uses have significant control over soil CO2 efflux and its biophysical regulators which have relative control over it. Soil organic C, soil moisture, fine particles, porosity and microbial biomass C were identified as prevalent regulators of soil CO2 efflux under dry seasons. Overall, the results indicate that the biophysical variables in addition to human interferences (CSL land use) have pronounced regulation over soil CO2 efflux in dry tropical riparian ecosystems.

Brazil's worst mining disaster: Corporations must be compelled to pay the actual environmental costs.

In November 2015, a large mine-tailing dam owned by Samarco Corporation collapsed in Brazil, generating a massive wave of toxic mud that spread down the Doce River, killing 20 people and affecting biodiversity across hundreds of kilometers of river, riparian lands, and Atlantic coast. Besides the disaster's serious human and socioeconomic tolls, we estimate the regional loss of environmental services to be ~US$521 million per year. Although our estimate is conservative, it is still six times higher than the fine imposed on Samarco by Brazilian environmental authorities. To reduce such disparities between estimated damages and levied fines, we advocate for an environmental bond policy that considers potential risks and environmental services that could possibly be impacted by irresponsible mining activity. Environmental bonds and insurance are commonly used policy instruments in many countries, but there are no clear environmental bond policies in Brazil. Environmental bonds are likely to be more effective at securing environmental restitution than post-disaster fines, which generally are inadequate and often unpaid. We estimate that at least 126 mining dams in Brazil are vulnerable to failure in the forthcoming years. Any such event could have severe social-environmental consequences, underscoring the need for effective disaster-management strategies for large-scale mining operations.

Analyzing riparian zone ecosystem services bundles to instruct river management

ABSTRACTThe ecosystem service framework is now well accepted for focussing management strategies to preserve and restore ecosystems. Its implementation remains challenging, however, due to the environment’s complexity and dynamics that interfere with ecosystems’ ability to provide the services. Here, we question whether we can show where and how to intervene in riparian corridors to restore specific ecosystem services without endangering others. Specific hypotheses in this context are for the spatial aggregation of ecosystem services delivered by riparian corridors with respect to naturalness (1), to the existence of bundles of ecosystem services (2), and finally for the scale sensitivity of this congruence (3). Within a Geographical Information System framework, we analyse the capacity of riparian corridors to provide ecosystem services over three river basins in the Bresse region (France) based on high-resolution data of the riparian corridor hydromorphology and land use. Specifically, we compare the capacity to provide two services: in-stream water purification and riparian retention of nutrients that are critical goals for river management and rehabilitation strategies. We observe little spatial association and high spatial variability for the two emphasized ecosystem services. Surprisingly, no congruence of ecosystem services with riparian corridor naturalness is present. The absence of associations between ecosystem services and their spatial variability will oblige environmental managers to identify underpinning environmental processes and patterns at local scales. In conclusion, we plead for fine-grained multifunctional assessment of ecosystems’ capacity to deliver services, especially in environments such as river corridors that exhibit high environmental heterogeneity.EDITED BY Neville Crossman

Assessment of River Ecosystems and Environmental Flows: Role of Flow Regimes and Physical Habitat Variables

Globally, rivers are under tremendous anthropogenic stress caused by flow fragmentation, land use changes and regulation. Floodplains had been cut out from rivers by embankments due to urban extension and most of the riparian lands in the river basin are under intensive agriculture. There was also widespread water quality degradation due to the industries and municipal wastewater causing a steep decline in the freshwater biodiversity across the world. It was recognised in the literature that the integrity of flowing water systems depended largely on their natural dynamic character which in turn maintained the habitat. Habitat characteristics and presence and absence of particular species suggests that most fishes of flowing water streams are habitat specialists and physical habitat variables including flow regimes played critical roles in the maintenance of their richness. This paper integrated broad environmental flow concepts and defined a new framework for e-flow assessment and implementation based on a review of supportive understanding of variable flow regimes and their benefits to river ecosystems. The main purpose of the framework was to stimulate the emerging discussion on environmental flows prospects in India and other parts of the world. The paper provided an example of the framework applied to River Ganga in India. We end by examining research needs and gaps in our understanding of the role of variable flow regimes and physical habitat variables and their ecological effects on river ecosystems.

The influence of habitat structure on fish assemblages in Amazonian streams of Machado river basin.

Igarapés are Amazonian streams that are extremely susceptible to environmental changes. Due to the rapidly occurring riparian land use changes, and the several impacts these may have on fish assemblages, it is highly valuable to describe and understand the current relationships between these assemblages and the local environmental conditions, especially in barely know areas. In this research, we studied the taxonomic composition and fish assemblage attributes variation in three streams with different riparian conservation conditions: forest, intermediate and pasture. Samplings were performed every two months from October 2011 to September 2012, in three 1st order streams in the Machado River Basin, Rondônia. Fish were collected using trawls (seine net with a mesh size of 2 mm) and dip nets (2 mm mesh) along the entire stretch; the obtained samples were preserved and identified per site type. A total of 2 141 fish specimens belonging to 59 species, 17 families and five orders were recorded. Unlike the intermediate and pasture streams, the forest stream showed a high richness and low abundance. The forested stream exhibited the highest diversity and evenness value, and had low dominance, unlike the other streams. The variance partitioning and partial Redundancy Analysis (pRDA) indicated that assemblage composition was significantly explained by the environmental variables such as: depth, water velocity, pteridophytes and grasses, but not by spatial predictors. The non-metric multidimensional scaling (NMDS) analysis showed that intermediate and pasture streams separated from the forested stream. We concluded that both, the stream environmental variables and fish assemblage attributes were influenced by the different conservation status and land cover. Given the influence of regional processes, which have a pervasive role in local fish assemblages, land use at the watershed scale is important, especially to explain the higher richness and diversity found in forested streams.

Impact of current riparian land on sediment retention in the Danube River Basin

Abstract Riparian land supports multiple ecosystem services that are essential for good water quality and aquatic biodiversity, providing habitat and hydrological connectivity, and retaining pollutants and sediments. Riparian land reduces sediment fluxes in the freshwater systems by trapping sediments generated on the hillslopes before they reach the stream network, and by stabilizing stream banks. The aim of this study was to assess the impact of current riparian land in reducing sediment fluxes in the stream network of the Danube River Basin. The Soil and Water Assessment Tool (SWAT) model was used to assess sediment yields across the basin and quantify sediment retention by riparian vegetation. Europe-wide spatial information on riparian land type and extent was used to set up agricultural to riparian land ratio and the streambank reach vegetation cover. SWAT sediment simulations for current conditions, i.e. including riparian land parameterization, were calibrated and validated for the period 1995–2009. The impact of riparian land was quantified by analyzing differences in mean annual specific sediment yields between scenarios without riparian land and current conditions. Sediment yield reductions and efficiency of riparian land were quantified at several spatial scales across the basin, considering hillslopes, stream order, and administrative regions. The impact of riparian filtering in reducing sediment fluxes to the stream network at the hillslope scale was always positive, with median efficiency of 50%. Efficiency was higher where incoming sediment and water yields per unit of area were larger, and in smaller HRUs (areas lower than 10 km 2 ). Sediment filtering in riparian buffers was more efficient in smaller reaches, and decreased from about 17% to 5% with Strahler’s order. Streambank protection was important locally in about 8% of reaches characterized by high stream power, where current streambank protection reduced potential sediment yields by more than 5 t/km 2 /y, and in large reaches, like in the Sava and Danube Rivers. At the Danube outlet to the Black Sea, the reduction in sediment yield attributable to current riparian land was estimated at 480 kt/y. Although riparian efficiency declined with spatial scale in terms of sediment yield reduction, filtering of sediments in riparian buffers abated in-stream sedimentation substantially. While occupying only about 2% of the Basin, current riparian land in the Danube Basin reduces sediment fluxes in river networks by about 8% regionally, and contributes to the improvement of the ecological conditions of freshwater ecosystems.

Shifts in leaf litter breakdown along a forest-pasture-urban gradient in Andean streams.

Tropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.

Bank erosion and large wood recruitment along a gravel bed river

Riverine environments can be very dynamic and complex systems, particularly because of the interaction between active channel and riparian land during flood events of different magnitude. In recent years increasing attention has been paid to large wood (LW), focusing on its role and impact along riverine systems and fluvial landscapes. This research aims to analyze the characteristics of LW recruitment as a consequence of a flood event along a reach of a gravel-bed river. The study was conducted on a 3 km-long reach located in the middle course of the Piave River (north-eastern Italian Alps). A 20 m-wide buffer zone was considered along the floodplains and islands. Every standing tree in this buffer with diameter ≥0.10 m was measured manually (diameter breast height; height), whereas shrubs were not considered. The most common species in the study area are: &lt;em&gt;Populus&lt;/em&gt; sp., &lt;em&gt;Salix&lt;/em&gt; sp., &lt;em&gt;Alnus&lt;/em&gt; sp., &lt;em&gt;Carpinus&lt;/em&gt; sp., &lt;em&gt;Fraxinus&lt;/em&gt; sp., &lt;em&gt;Pinus&lt;/em&gt; &lt;em&gt;sylvestris&lt;/em&gt; and &lt;em&gt;Robinia&lt;/em&gt; &lt;em&gt;pseudoacacia&lt;/em&gt;. An over bankfull flood (Q=1329 m&lt;sup&gt;3&lt;/sup&gt;s&lt;sup&gt;–1&lt;/sup&gt;; recurrence interval=6 years) in November 2014 caused erosions along the floodplain (15,565.5 m&lt;sup&gt;2&lt;/sup&gt;), pioneer islands (25.2 m&lt;sup&gt;2&lt;/sup&gt;) and building islands (2085.6 m&lt;sup&gt;2&lt;/sup&gt;), recruiting 690 trees. Four of these trees were recruited from the pioneer islands (0.16 tree m&lt;sup&gt;–2&lt;/sup&gt;), 79 from building islands (0.04 tree m&lt;sup&gt;–2&lt;/sup&gt;) and 607 from floodplains (0.04 tree m&lt;sup&gt;–2&lt;/sup&gt;). Accurate dendrometric measurements were used to define the input volume of LW from the floodplains (86.25 m&lt;sup&gt;3&lt;/sup&gt;), pioneer islands (0.14 m&lt;sup&gt;3&lt;/sup&gt;) and building islands (6.62 m&lt;sup&gt;3&lt;/sup&gt;). The maximum distance traveled by LW recruited from the floodplain, pioneer and building islands was 8927, 1021 and 3727 m, respectively. Statistical analysis showed no significant relationship between the displacement and LW characteristics considered (diameter, length, volume, density). These results demonstrate that the recruitment and subsequent transport of LW is a complex mechanism that requires further study. To better characterize these mechanisms, it appears clear that it is important to consider not only the LW characteristics but also the connection between LW, morphological settings, and flood event characteristics.

Brown trout growth in Minnesota streams as related to landscape and local factors

ABSTRACTBrown trout (Salmo trutta) are ecologically and socioeconomically important throughout the world. As such, understanding population dynamics is critical for brown trout management. Brown trout support a valuable recreational fishery in the Driftless Ecoregion of southeast Minnesota, where growth (i.e. mean back-calculated length-at-age) varies among streams but the relative effects of landscape (i.e. watershed level) and local (i.e. reach-level) factors on growth are unclear. Thus, the objective of this study was to evaluate effects of drainage area on individual brown trout growth relative to the effects of local factors (i.e. thermal regime, riparian land cover, relative abundance) to provide managers with strategies for increasing growth and the abundance of large individuals in southeast Minnesota streams. Linear mixed-effects models with combinations of these factors were compared using information-theoretic model selection and multimodel inference. Age, which explained 63% of variation in growth, differed among streams for age-1 and age-2, but not age-3 brown trout. Model averaging indicated growth of age-1 and age-2 individuals increased primarily with drainage area and secondarily with forested riparian area. Brown trout relative abundance did not affect growth, so it is realistic for managers to sustain high-quality, high-quantity brown trout populations. Overall, this synthetic landscape and local study advances brown trout management by illustrating that systems with large watersheds and forested riparian zones are suitable for management strategies (e.g. harvest regulations, habitat restoration) to increase growth and the abundance of large brown trout in socioeconomically valuable southeast Minnesota streams.

Integrating hydrogeomorphological concepts in management approaches of lowland agricultural streams: Perspectives, problems and prospects based on case studies in Quebec

Alternative management approaches for agricultural streams based on hydrogeomorphological principles such as a two-stage channel are promising, but need to be further tested in contexts other than the Midwestern United States. In Quebec (Canada), the presence of many deep drain outlets may limit their applicability. The objectives of this research are to (1) assess the feasibility of implementing the two-stage channel design in Quebec; (2) determine how alternative management approaches compare with traditional management from an economical point of view, and (3) evaluate the impact of modifying the drain outlet design using small horseshoe wetlands to accommodate hydrogeomorphological adjustments of the channel. A combination of case studies and numerical modelling (HEC-RAS, Hydrologic Engineering Center’s River Analysis System) was used for three study sites located in the Montérégie region (QC). Based on regional hydraulic geometry curves, additional space on each bank required for a two-stage channel ranged between 1.3 and 2.8 m for a width equal to 3 times the inset channel. Hydraulic modelling confirms previous findings of improved drainage capacity at high flow, (up to a 54% increase). Cost analysis reveals that two-stage and over-widened channels are 3 to 4 times more expensive to implement when compared to traditional trapezoidal clean-out dredging operations, mainly due to spoil removal and transportation. However, self-formed channels are less expensive since they only require additional riparian land. A crop yield analysis in the near-stream zone at three sites which are frequently flooded revealed markedly lower productivity in zones within the flooding space. The horseshoe wetland design for drain outlets could also be maintained at low cost, and would promote more heterogeneity than the traditional trapezoidal ditches. Using alternative agricultural stream management approaches based on hydrogeomorphological concepts would be feasible in the Quebec context without compromising the overall productivity of this key economic sector.

Development of a statistical tool for the estimation of riverbank erosion probability

Abstract. Riverbank erosion affects river morphology and local habitat, and results in riparian land loss, property and infrastructure damage, and ultimately flood defence weakening. An important issue concerning riverbank erosion is the identification of the vulnerable areas in order to predict river changes and assist stream management/restoration. An approach to predict areas vulnerable to erosion is to quantify the erosion probability by identifying the underlying relations between riverbank erosion and geomorphological or hydrological variables that prevent or stimulate erosion. In the present work, a statistical methodology is proposed to predict the probability of the presence or absence of erosion in a river section. A physically based model determines the locations vulnerable to erosion by quantifying the potential eroded area. The derived results are used to determine validation locations for the evaluation of the statistical tool performance. The statistical tool is based on a series of independent local variables and employs the logistic regression methodology. It is developed in two forms, logistic regression and locally weighted logistic regression, which both deliver useful and accurate results. The second form, though, provides the most accurate results as it validates the presence or absence of erosion at all validation locations. The proposed tool is easy to use and accurate and can be applied to any region and river.

Effect of Riparian Land Use on Phytoplankton Characteristics of Kwadon Stream, Gombe State of Nigeria

Effect of Riparian Land Use on Phytoplankton Characteristics of Kwadon Stream, Gombe State of Nigeria

Beyond cool: adapting upland streams for climate change using riparian woodlands.

Managed adaptation could reduce the risks of climate change to the world's ecosystems, but there have been surprisingly few practical evaluations of the options available. For example, riparian woodland is advocated widely as shade to reduce warming in temperate streams, but few studies have considered collateral effects on species composition or ecosystem functions. Here, we use cross-sectional analyses at two scales (region and within streams) to investigate whether four types of riparian management, including those proposed to reduce potential climate change impacts, might also affect the composition, functional character, dynamics and energetic resourcing of macroinvertebrates in upland Welsh streams (UK). Riparian land use across the region had only small effects on invertebrate taxonomic composition, while stable isotope data showed how energetic resources assimilated by macroinvertebrates in all functional guilds were split roughly 50:50 between terrestrial and aquatic origins irrespective of riparian management. Nevertheless, streams draining the most extensive deciduous woodland had the greatest stocks of coarse particulate matter (CPOM) and greater numbers of 'shredding' detritivores. Stream-scale investigations showed that macroinvertebrate biomass in deciduous woodland streams was around twice that in moorland streams, and lowest of all in streams draining non-native conifers. The unexpected absence of contrasting terrestrial signals in the isotopic data implies that factors other than local land use affect the relative incorporation of allochthonous subsidies into riverine food webs. Nevertheless, our results reveal how planting deciduous riparian trees along temperate headwaters as an adaptation to climate change can modify macroinvertebrate function, increase biomass and potentially enhance resilience by increasing basal resources where cover is extensive (>60m riparian width). We advocate greater urgency in efforts to understand the ecosystem consequences of climate change adaptation to guide future actions.

Influence of hydrological regime and land cover on traits and potential export capacity of adult aquatic insects from river channels.

Despite many studies highlighting the widespread occurrence and effects of resource movement between ecosystems, comparatively little is known about how anthropogenic alterations to ecosystems affect the strength, direction and importance of such fluxes. Hydrological regime and riparian land use cause well-documented changes in riverine larval invertebrate communities. Using a dataset from 66 sites collected over 20 years, we showed that such effects led to spatial and temporal differences in the density and type of larvae with winged adults within a river reach, altering the size and composition of the source pool from which adult aquatic insects can emerge. Mean annual larval densities varied 33-fold and the temporal range varied more than 20-fold between sites, associated with the hydrological regime and land cover and antecedent high and low flows, respectively. Densities of larvae with winged adults were greater in sites that had more algal coverage, agricultural land use, seasonally predictable flow regimes and faster water velocities. More interestingly, by influencing larval communities, riparian land use and the magnitude and frequency of high and low flows affected the size structure, dispersal ability and longevity of adults available to emerge from river reaches, potentially influencing the spatial extent and type of terrestrial consumers supported by aquatic prey. This suggests that anthropogenic alterations to land use or river flows will have both spatial and temporal effects on the flux and potential availability of adult aquatic insects to terrestrial consumers in many rivers.

Headcut Erosion in Wyoming's Sweetwater Subbasin.

Increasing human population and intensive land use combined with a warming climate and chronically diminished snowpacks are putting more strain on water resources in the western United States. Properly functioning riparian systems slow runoff and store water, thus regulating extreme flows; however, riparian areas across the west are in a degraded condition with a majority of riparian systems not in proper functioning condition, and with widespread catastrophic erosion of water-storing peat and organic soils. Headcuts are the leading edge of catastrophic channel erosion. We used aerial imagery (1.4-3.3-cm pixel) to locate 163 headcuts in riparian areas in the Sweetwater subbasin of central Wyoming. We found 1-m-the generally available standard resolution for land management-and 30-cm pixel imagery to be inadequate for headcut identification. We also used Structure-from-Motion models built from ground-acquired imagery to model 18 headcuts from which we measured soil loss of 425-720 m3. Normalized by channel length, this represents a loss of 1.1-1.8 m3 m(-1) channel. Monitoring headcuts, either from ground or aerial imagery, provides an objective indicator of sustainable riparian land management and identifies priority disturbance-mitigation areas. Image-based headcut monitoring must use data on the order of 3.3 cm ground sample distance, or greater resolution, to effectively capture the information needed for accurate assessments of riparian conditions.

Riparian land cover and land use effects on riverine epilithic fungal communities

Although fungi are important decomposers in lotic environments, few studies have investigated the spatial and temporal changes in epilithic fungal communities in rivers. If epilithic organisms grow using organic matter and nutrients ultimately discharge into rivers, it is likely that the taxonomic composition of epilithic fungal communities will change spatially depending on the land use and land cover (LULC) in the drainage area. To test this hypothesis, we examined the relationship between the taxonomic composition of fungi on cobbles and the LULC in the fall and in spring. The taxonomic composition of the epilithic fungi was significantly related to ambient water temperatures and concentrations of nutrients and dissolved organic carbon. Supporting our hypothesis, the taxonomic composition of the epilithic fungi differed largely among the reaches covered mainly by different forest types and land uses in both the fall and in spring. The results suggest that the quality of the dissolved organic matter differed among the catchment areas depending on the LULC. Further analyses indicated that the sum of the LULC and within-river variables could explain 36.4 and 41.2 % of the spatial variation in the fungal taxonomic compositions in the fall and in spring, respectively. The LULC variables alone explained 16.1–18.7 % of the variations, and a similar percentage was found for within-river variables. These results suggest that the organic matter from LULC was equally as important as physical and nutrient conditions in the ambient water for determining the community structure of epilithic fungi in rivers.

Disentangling environmental drivers of benthic invertebrate assemblages: The role of spatial scale and riverscape heterogeneity in a multiple stressor environment

It is broadly acknowledged that freshwater ecosystems are affected by multiple stressors, but the relative importance of individual stressors in impairing riverine communities remains unclear. We investigated the impacts of multiple stressors, incorporating in-stream water quality, riparian and catchment land use and stream morphology, on riverine benthic invertebrate communities, while considering the spatial scales of factors and the heterogeneity of riverscapes. We performed a stepwise regression procedure linking 21 abiotic and 20 community metrics using Generalized Linear Models on data from 1018 river sites spread across Germany. High impact stressors (e.g., nutrients and water temperature) were identified for various community metrics. Both the combination of relevant stressors and their explanatory value differed significantly across streams of different sizes and ecoregions. In large rivers, the riparian land use was less important in determining community structure compared to lower order streams. Thus, possible mitigating effects of revegetated riparian buffer strips are likely to be overwhelmed by the influence of catchment-wide land use. Our results indicated substantial variability in stressors for the range of metrics studied, providing insight into potential target parameters for effective ecosystem management. To achieve long lasting successes in managing, protecting and restoring running waters, it is of vital importance to recognize the heterogeneity of riverscapes and to consider large-scale influences.

Shifts in reciprocal river‐riparian arthropod fluxes along an urban‐rural landscape gradient

Summary We measured bidirectional arthropod fluxes at 12 river reaches distributed across an urban‐rural gradient of riparian land use and land cover in the Scioto River system of Ohio (U.S.A.). For the terrestrial‐to‐aquatic arthropod flux (i.e. inputs of terrestrial arthropods to the river from the land), urban development was positively related to density of inputs but negatively related to biomass, partially explained by shifts in community composition and body size. Riparian grassland, typical of rural (i.e. non‐urban) landscapes, was positively associated with both density (range: 2.8–18.9 individuals m−2 day−1) and biomass (range: 7.1–58.7 mg m−2 day−1) of inputs. For the aquatic‐to‐terrestrial flux of adult aquatic insects (i.e. emergent aquatic insects exported from the river), riparian grassland cover was positively associated with both density (R2 = 0.61; range: 12.8–116.8 individuals m−2 day−1) and biomass (R2 = 0.65; range: 1.4–27.9 mg m−2 day−1), with relatively larger‐bodied taxa dominating emergence at rural reaches. Riparian landscape composition relates to reciprocal fluxes of arthropods (aquatic insects out, terrestrial insects and other arthropods in) in river‐riparian systems as we found human landscape disturbances were associated with changes in the taxonomic composition of both aquatic emergence and terrestrial input, and an overall decrease in the magnitude of emergence and terrestrial input. Furthermore, landscape changes that alter arthropod fluxes may have broader consequences for linked river‐riparian biodiversity and food webs and should be taken into account in conservation, restoration and management of these systems.

Distribution and trophic dynamics of riparian tetragnathid spiders in a large river system

Development and agriculture are increasingly encroaching into riparian areas, with largely unknown effects on nearshore arthropods, which are important components of linked aquatic–terrestrial food webs. To assess the environmental determinants of the distribution and trophic dynamics of riparian spiders of the family Tetragnathidae, we characterised riparian habitat, collected emergent aquatic insects, and surveyed spiders in developed and rural landscapes of the Scioto River system, Ohio, USA, which provided a range of riparian land cover, nearshore vegetation types and habitat complexity. We also estimated the trophic position (TP) of Tetragnathidae and the proportion of energetic and nutritional subsidies derived from benthic algae (EBA) using naturally abundant carbon (C) and nitrogen (N) stable isotopes. Model-selection results revealed that tetragnathid spider density (1.57–3.80individualsm–1) was more sensitive to differences in overhanging vegetation than to those in aquatic food resources (i.e. emergent aquatic insects). Tetragnathidae TP, which averaged 3.16 across all 12 study reaches (range: 2.35–3.98), was largely driven by canopy density, shoreline shape, percentage overhanging vegetation and emergent-insect density. Emergent-insect density was the strongest driver of tetragnathid spider EBA (0.04–0.54, µ=0.24). Our study reinforced the notion that riparian spiders ecologically link aquatic and terrestrial ecosystems. In particular, our results further current understanding of the mechanisms affecting riparian spider distribution and trophic dynamics, particularly in the context of larger stream and river systems, given that the propensity of related research has occurred in small streams.