Reactive oxygen species (ROS) are ubiquitous in the natural environment and play a pivotal role in biogeochemical processes. However, the spatiotemporal distribution and production mechanisms of ROS ...in riparian soil remain unknown. Herein, we performed uninterrupted monitoring to investigate the variation of ROS at different soil sites of the Weihe River riparian zone throughout the year. Fluorescence imaging and quantitative analysis clearly showed the production and spatiotemporal variation of ROS in riparian soils. The concentration of superoxide (O
) was 300% higher in summer and autumn compared to that in other seasons, while the highest concentrations of 539.7 and 20.12 μmol kg
were observed in winter for hydrogen peroxide (H
O
) and hydroxyl radicals (
OH), respectively. Spatially, ROS production in riparian soils gradually decreased along with the stream. The results of the structural equation and random forest model indicated that meteorological conditions and soil physicochemical properties were primary drivers mediating the seasonal and spatial variations in ROS production, respectively. The generated
OH significantly induced the abiotic mineralization of organic carbon, contributing to 17.5-26.4% of CO
efflux. The obtained information highlighted riparian zones as pervasive yet previously underestimated hotspots for ROS production, which may have non-negligible implications for carbon turnover and other elemental cycles in riparian soils.
•Long-term effects of selective thinning along two small streams were investigated.•One of the streams was bordered by broadleaf trees and the other by conifers.•Water chemistry and benthic ...macroinvertebrates were monitored.•A few differences in water chemistry were detected.•Benthic macroinvertebrates responded to selective thinning.
The maintenance of narrow strips of trees (forest buffers) along the shorelines of surface water bodies during logging is a common measure to protect freshwater habitats. The functionality of forest buffers may be improved by actively managing the streamside forest early in the rotation for their eventual function as buffers, including by increasing the proportion of broadleaf trees in spruce-dominated stands. In this study, long-term effects of different selective thinning regimes along two small forest streams were investigated in south-central Sweden. In a young coniferous forest, a c. 10 m-wide band along the streams was selectively thinned in 1998 to create a band with purely broadleaf trees along one of the streams and purely conifers along the other. Forest stand characteristics, water chemistry and benthic macroinvertebrates data were collected during 1996–2003 (before and after selective thinning). The streams were re-investigated 20–22 years after thinning, together with three streams representing operational forest management. The forest adjacent to all five streams was inventoried and litterfall, stream water chemistry, and benthic macroinvertebrates composition were monitored between spring and late autumn during 2018–2020. Twenty years after thinning, the thinned bands beside the streams were still dominated by either broadleaf trees or conifers, depending on the stream. Over the longer term, the differences in water chemistry between the streams with selective thinning were mainly related to lower pH, ANC, Tot-P and Tot-N concentrations in the stream bordered by mainly broadleaf trees. Analysis of benthic macroinvertebrates was based on environmental quality indices (ASPT and EPT), diversity and abundance metrics, and relative abundances of functional feeding groups. Streams with higher broadleaf litter inputs tended to score better on the ASPT and EPT indices than those with lower broadleaf inputs, as well as supporting higher relative abundances of one or more groups of invertebrate detritivores (leaf shredders, collector-gatherers and/or passive filter feeders). This suggests that management of the density of broadleaf trees beside these streams might support higher ecological status and will support a greater proportion of detritivores in benthic food webs.
•Forest managers use tree buffers to protect streams from clear-cutting operations.•Functional diversity measures are critical indicators of forest disturbance.•Riparian buffer size has little impact ...on spider or vascular plant functional diversity.•Biotic and abiotic buffer conditions are more important for system function.•Forest management should promote species richness to increase ecosystem function.
Retention of forested buffers around streams following forest cutting operations is a common management technique used to protect aquatic resources and conserve the surrounding ecosystem services. Species richness, or α-diversity, is commonly used as an indicator of the effects of forestry management although it provides very little information about those effects on ecosystem processes and function. Functional diversity links species traits and ecosystem function incorporating species diversity, community composition, and functional guild and is more suitable to investigate the direct and indirect effects of forestry on ecosystem function. We sampled spiders and vascular plants in buffered and unbuffered stream-forest systems in southern Sweden and used a trait-based approach to assess the effects of buffer size and environmental variables on functional diversity. We used structural equation modeling (SEM) to explore the effects of buffer size and condition on spider and vascular plant diversity. We found no effect of buffer size on the functional richness or functional redundancy for spiders or vascular plants. Buffer size had a slight effect on the α-diversity of spiders within small buffers and fully forested sites but the effect was small. Other buffer variables including canopy closure, buffer density, bare ground coverage, and soil fertility had direct effects on spider and vascular plant functional diversity. The main driver of functional richness was α-diversity, but our SEM analysis illustrated other environmental variables working jointly to drive functional diversity. Using a trait-based approach, we showed that forested buffers have a minimal overall impact on spider and vascular plant functional diversity. However, it is important to maintain high levels of α-diversity to preserve and promote both spider and plant functional richness in production forests and we suggest that forest management conserves and encourages high levels of α-diversity to increase overall functional diversity.
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•EEM-PARAFAC was applied to probe DOM fractions in four types of riparian zones.•2DCOS was used to explore variations of DOM fractions with depth.•PLS-SEM was employed to reveal ...latent factors of DOM from four riparian soils.•The forest soils were distinguished from the grassland and cropland.
Dissolved organic matter (DOM) plays key roles in species-distribution of contaminants and the biogeochemical cycle of carbon in ecosystems. Riparian zone is the representative of water-land ecotone and controls the DOM exchange between water and land. However, the variance of DOM in different landcover areas of an urban river riparian zone is unknown. In this study, fluorescence excitation-emission matrix (EEM) spectroscopy coupled with parallel factor analysis (PARAFAC) and partial least squares structural equation model (PLS-SEM) was applied to character dissolved organic matter (DOM) fractions in four types of landcover riparian areas (natural forest, artificial forest, semi-natural grassland, and cropland) of Puhe River and trace latent factors. Soil samples were collected at 0–20 cm, 20–40 cm, 40–60 cm, and 60–80 cm. The results showed that soil DOM components and humification varied between forests with grassland and cropland samples, and soil humification was obviously higher in the forest samples than that in the grassland and cropland samples. In the natural and artificial forest soils, the humic/fulvic-like were the dominant fractions of DOM, whose variations were smaller than the protein-like with soil depths. However, the tyrosine-like was the representative component in the grassland and cropland soils, whose variation was smaller than the humus substances. According to the PLS-SEM, the DOM components and humification were affected by soil physiochemical properties and DOM sources. The humification in the forest soils had a positive correlation with tryptophan-like, which derived from blended source of the autochthonous and terrigenous. Nevertheless, a positive correlation was observed between humification and humus substances, which could derive from microbial degradation of tyrosine-like, in the grassland and cropland soils. Moreover, the soil physiochemical properties were negatively related to DOM components in all soil samples, which could affect indirectly soil humification. Therefore, EEM combined with PARAFAC and PLS-SEM might be an effective method to investigate DOM fractions and trace the latent factors in different landcover areas of the riparian zone.
Riparian zones of rivers are transitional environments between land and water ecosystems with distinct hydrological gradients, soils and habitats strongly related to their functioning. When these ...functions are intact, they integrate multi-directional processes across the land-river channel (e.g. canopy shade effects on the stream, flood inundation effects on the land) with mutual beneficial effects. In many managed landscapes these functions have been degraded. To restore them, considerable efforts have been directed over the last 20 years to understand and place effective riparian ‘buffer’ zones, particularly to enhance water quality and biodiversity. Since water quality targets are not easily met by current practices in many managed landscapes (as additive pressures increase), catchment managers will have to increasingly restore riparian functions to enhance aquatic ecosystem resilience to land and climate change. Targeting effective restoration within site-specific contexts requires availability of spatial data, in combinations that inform on individual and multiple functions. There are accelerating developments with spatial data, arising from increased spatial resolution of key underlying datasets, availability of soil and landcover data and increasing secondary derived attributes. Hence, a review is timely into the best practices in the use of these data for delineating riparian functions and management zones for rivers.
Our review evaluates the application of spatial data and is structured around three conceptual methods of riparian delineation; fixed width, variable width by river corridor features and variable width by context of local pressures or required outcomes. We explore process representation and incorporation into management across main riparian functions (hydrological connectivity, water quality, shading, resource transfers and habitat provision). Translating spatial data into functions informs the ability to go beyond contemporary, generally fixed width approaches using basic structural components towards planning to better target functional attributes to optimise ecosystem protection.
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•Understanding riparian functions in space is necessary to manage rivers.•We review use of spatial datasets to represent riparian functions.•Key datasets on soil, topography, water flows and vegetation inform on processes.•Data spatial resolution, parameter classifications groups and coverage are key.
Dam construction significantly influences riparian ecological functions and environmental conditions in the reservoir region. Despite the importance of diazotrophic mediation of nitrogen cycling in ...riparian ecosystems, knowledge concerning the impacts of dam construction on diazotrophic function and community composition remains very limited. Here, riparian soils were collected from control sites and dam-affected sites located in six cascade dam-formed reservoirs on the Lancang River, China. Diazotrophic activity was assessed by measuring nitrogen fixation rate, while bacterial abundance and community composition were determined with the nifH gene, using quantitative real-time polymerase chain reaction and MiSeq sequencing, respectively. The results indicate that the activity, abundance, and ɑ-diversity of diazotrophs in the affected sites were significantly higher than those in the control sites. The diazotrophic community composition was differed between the control and affected sites, with the latter showing significantly lower community dissimilarity than the control. Both geographic distance and environmental heterogeneity varied in the diazotrophic community, while environmental heterogeneity was the primary factor controlling diazotrophic assemblage in riparian soils, especially at the affected sites. Moreover, co-occurrence network analyses revealed a much higher possible network connectivity at the affected sites than at the control sites. This study suggests distinct activity, abundance, distribution pattern, and network structure of the diazotrophic populations in riparian soils between dam-affected and control sites; thus, providing a novel insight into the potential ecological effects of dam construction on nitrogen cycling.
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•Dam-affected sites had higher nitrogen fixation rates than control sites.•The abundance and ɑ-diversity of diazotrophs were increased in dam-affected sites.•The affected sites had significantly lower community dissimilarity than the control sites.•Environmental heterogeneity was a primary factor affecting diazotrophic assemblage.•Diazotrophic networks were more complex in dam-affected sites than the control sites.
The biota of European rivers are affected by a wide range of stressors impairing water quality and hydro‐morphology. Only about 40% of Europe's rivers reach ‘good ecological status’, a target set by ...the European Water Framework Directive (WFD) and indicated by the biota. It is yet unknown how the different stressors in concert impact ecological status and how the relationship between stressors and status differs between river types. We linked the intensity of seven stressors to recently measured ecological status data for more than 50,000 sub‐catchment units (covering almost 80% of Europe's surface area), which were distributed among 12 broad river types. Stressor data were either derived from remote sensing data (extent of urban and agricultural land use in the riparian zone) or modelled (alteration of mean annual flow and of base flow, total phosphorous load, total nitrogen load and mixture toxic pressure, a composite metric for toxic substances), while data on ecological status were taken from national statutory reporting of the second WFD River Basin Management Plans for the years 2010–2015. We used Boosted Regression Trees to link ecological status to stressor intensities. The stressors explained on average 61% of deviance in ecological status for the 12 individual river types, with all seven stressors contributing considerably to this explanation. On average, 39.4% of the deviance was explained by altered hydro‐morphology (morphology: 23.2%; hydrology: 16.2%), 34.4% by nutrient enrichment and 26.2% by toxic substances. More than half of the total deviance was explained by stressor interaction, with nutrient enrichment and toxic substances interacting most frequently and strongly. Our results underline that the biota of all European river types are determined by co‐occurring and interacting multiple stressors, lending support to the conclusion that fundamental management strategies at the catchment scale are required to reach the ambitious objective of good ecological status of surface waters.
We analyzed the effects of multiple stressors on ecological status of more than 50,000 European river catchments. Hydro‐morphological degradation showed the strongest effects, followed by nutrient enrichment and toxic substances. Interactive stressor effects were prominent. Our findings highlight the role of multiple stressors acting on Europe's rivers and call for fundamental restorative management strategies at the catchment‐scale.
Besides gas-water-exchange in surface waters, respiratory consumption of dissolved oxygen (DO) in adjacent riparian groundwater may trigger the addition of so far hardly explored sources from the ...unsaturated zone. These processes also systematically influence stable isotope ratios of DO and were investigated together with Cl− as a conservative tracer for water mixing in a near-river riparian groundwater system. The study focused on a losing stream section of the Selke River at the foot of the Harz Mountains (Germany). The study area exposed steep DO gradients between the stream water and riparian groundwater between April 2016 and May 2017. Our results indicated dominant influences of microbial community respiration with observed DO concentration gradients. These observations can be explained by DO from the river that is subject to fractionation by microbial respiration with a typical fractionation factor (αr) of 0.982. However, with such respiration dominance, we expected a simultaneous enrichment of δ18ODO towards values that are more positive than the well-known atmospheric O2 signal of +23.9‰ versus the Vienna Standard Mean Ocean Water standard (VSMOW). Surprisingly, our measurements revealed much lower δ18ODO values between +22‰ and +18‰ in the near-river groundwater. Mass balance calculations revealed that the DO pool in the shallow and unconfined aquifer receives contributions of up to about 80% by diffusion of oxygen from the vadose zone with a distinctly lower isotope value than the one of the atmosphere. This finding about additional oxygen sources from the unsaturated zone has numerous ramifications for oxygen related processes in near-river environments including the oxidation of pollutants, nutrients and ecosystem health.
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•DO gradients between river and riparian groundwater indicate dominant respiration.•Measurements of δ18ODO revealed much lower values than expected with respiration.•Diffusion in the unsaturated zone added oxygen with a distinct low isotope signal.•This finding effectively impacts oxygen related processes in near-river environments.
The construction and operation of the Three Gorges Reservoir (TGR), the largest hydropower dam in the world, has had significant consequences for the hydrology of riparian zones along the Yangtze ...river. Little is known about how such changes in hydrology might affect the levels of nutrients and organic matter (OM) in riparian soils. We conducted a nine-year study on the spatio-temporal dynamics and dominant environmental correlates of nutrients and OM in riparian soils along a 600 km section of the Yangtze. These soils have been exposed to a disrupted hydrological regime since the TGR's establishment in 2008. Vegetation surveys were also conducted from 2012 to 2016 to assess relationships between soil chemical properties and vegetation community properties under altered hydrology. Across the stream gradient, concentrations of total potassium (K) increased by 54% since the TGR's establishment. The opposite occurred for SOM and available K, concentrations of which were 35% and 33% lower in 2016, respectively, than those of 2008. The rate of increase in total K tended to be more rapid at the middle section of the stream gradient. Moreover, concentrations of SOM, total N, total K, and available phosphorus (P) and K tended to be particularly high at the middle section. The spatio-temporal distributions of nutrients were strongly positively related to the contents of fine soil particles (i.e., silt and clay). Moreover, the aboveground biomass was negatively correlated with the nutrient dynamics. Our results indicate that the control of the nutrient release in the middle reaches and lower elevations where fine particles tend to accumulate, will be essential for maintaining the health of aquatic and riparian ecosystems upstream of the TGR.
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•Nine-year study of riparian soil nutrients across a 600 km stream gradient•Nutrients accumulated most in the middle of the stream gradient.•OM and available K decreased but total K increased over time•Nutrient dynamics were strongly positively related to the contents of silt.•Aboveground biomass was negatively correlated with nutrient distributions.
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