Previously regarded as the passive drains of watersheds, over the past 50 years, rivers have progressively been recognized as being actively connected with off‐channel environments. These connections ...prolong physical storage and enhance reactive processing to alter water chemistry and downstream transport of materials and energy. Here we propose river corridor science as a concept that integrates downstream transport with lateral and vertical exchange across interfaces. Thus, the river corridor, rather than the wetted river channel itself, is an increasingly common unit of study. Main channel exchange with recirculating marginal waters, hyporheic exchange, bank storage, and overbank flow onto floodplains are all included under a broad continuum of interactions known as “hydrologic exchange flows.” Hydrologists, geomorphologists, geochemists, and aquatic and terrestrial ecologists are cooperating in studies that reveal the dynamic interactions among hydrologic exchange flows and consequences for water quality improvement, modulation of river metabolism, habitat provision for vegetation, fish, and wildlife, and other valued ecosystem services. The need for better integration of science and management is keenly felt, from testing effectiveness of stream restoration and riparian buffers all the way to reevaluating the definition of the waters of the United States to clarify the regulatory authority under the Clean Water Act. A major challenge for scientists is linking the small‐scale physical drivers with their larger‐scale fluvial and geomorphic context and ecological consequences. Although the fine scales of field and laboratory studies are best suited to identifying the fundamental physical and biological processes, that understanding must be successfully linked to cumulative effects at watershed to regional and continental scales.
Key Points:
Hydrologic exchange prolongs physical storage and reactive processing in river corridors
Consequences for water quality, ecological metabolism, and wildlife habitat provision
Challenge linking small‐scale physical drivers with larger‐scale ecological consequences
Urbanization-induced land use changes in riparian area alter soil and water regimes in complex ways, which may also affect the migration and transformation of soil heavy metals and increase the risk ...of release. In this study, soil samples from the riparian zone of Beiyun River, which located in the rapidly urbanized Beijing metropolis, were collected and analyzed for heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn). Then their zoning distribution pattern along river (section 1 to section 4 from upper to low reaches) and the correlation of heavy metals between riparian soils and riverine sediments were investigated. Results showed that the average soil heavy metal concentrations of Cd, Cr, Cu and Zn in riparian zone were approximately 2.2, 1.7, 1.9 and 2.0 times higher than the background values. Sectionally, the concentrations of Cd, Ni, Pb and Zn displayed a decreasing order with section 2 > section 3 > section 4 > section 1, while the highest values of Cr and Cu were found in section 3. The concentrations of all heavy metals except Cr in artificial garden land were higher than those in other land use types, and the concentrations of Cr among five land use types were in the order of grass land > farmland > artificial garden land > forest land > forest-grass land. Generally, most of the heavy metals in the riverine sediments had higher contents than those in riparian zones, especially Cu and Zn. There was a decreasing order for the average geo-accumulation index (Igeo) of measured heavy metals in the soils of riparian zone: Zn (0.15) > Cr (0.08) > Cu (0.07) > Cd (−0.08) > As (−0.57) > Pb (−0.67) > Mn (−0.75) > Ni (−0.86), whereas they had different “high-low” orders in different land use types. The Igeo index indicated most regions of riparian zone were moderately polluted with Cd, Cr, Cu and Zn, especially in grass land and forest land. Also, Cd, Cr and Zn in riparian zone have positive relationships with the concentrations in riverine sediments. Health risk assessment showed that the contribution of ingestion HQ to HI was the highest among the three exposure pathways (ingestion, inhalation and dermal contact), and children had higher non-carcinogenic risk and carcinogenic risk index than adult. Our findings suggest that land use and soil in riparian zone should be protected and managed scientifically to control the riverine pollution and ensure human health.
•Heavy metals in riparian varied greatly along different urbanized river gradients.•The riparian soils made various contributions to the riverine sediments.•The distribution of heavy metals was not same under different land uses.•Children had higher non-carcinogenic risk and carcinogenic risk index than adults.
River corridors, acknowledged as "blue-green infrastructure," have gained increasing attention due to their potential benefits on individual quality of life and social well-being in urban areas. ...However, there remains a lack of a comprehensive synthesis of evidence through a systematic literature review on the usage and associated constraints of urban river corridors. The paper aims to systematically review those attributes that influence the usage of urban river corridors and to analyse their complex interactions from a socio-ecological perspective. Results comprise an overview of the reviewed literature, including authorship, journal, geographical distribution, sample characteristics, data collection and analysis methods, and critical findings. Fifty-nine peer-reviewed papers published between 2012 and 2023 met the authors' inclusion criteria. The findings highlight the significant influence of individual, social, and physical factors on the usage of urban river corridors. Additionally, time reason also impact users' decisions regarding the usage of urban river corridors. Finally, a conceptual framework was proposed to guide urban planners, designers, and policymakers in enhancing urban river corridors' design and management standards, ultimately creating a sustainable, resilient, and inclusive leisure space catering to diverse needs.
Fertilized agroecosystems may show considerable leaching of the mobile nitrogen (N) compound NO3−, which pollutes groundwater and causes eutrophication of downstream waterbodies. Riparian buffer ...zones, positioned between terrestrial and aquatic environments, effectively remove NO3− and serve as a hotspot for N2O emissions. However, microbial processes governing NO3− reduction in riparian zones still remain largely unclear. This study explored the underlying mechanisms of various N-loss processes in riparian soil horizons using isotopic tracing techniques, molecular assays, and high-throughput sequencing. Both anaerobic ammonium oxidation (anammox) and denitrification activity were maximized in the riparian fringe rather than in the central zones. Denitrifying anaerobic methane oxidation (damo) process was not detected. Interestingly, both contrasting microbial habitats were separated by a groundwater table, which forms an important biogeochemical interface. Denitrification dominated cumulative N-losses in the upper unsaturated soil, while anammox dominated the lower oxic saturated soil horizons. Archaeal and bacterial ammonium oxidation that couple dissimilatory nitrate reduction to ammonium (DNRA) with a high cell-specific rate promoted anammox even further in oxic subsurface horizons. High-throughput sequencing and network analysis showed that the anammox rate positively correlated with Candidatus ‘Kuenenia’ (4%), rather than with the dominant Candidatus ‘Brocadia’. The contribution to N-loss via anammox increased significantly with the water level, which was accompanied by a significant reduction of N2O emission (∼39.3 ± 10.6%) since N-loss by anammox does not cause N2O emissions. Hence, water table management in riparian ecotones can be optimized to reduce NO3− pollution by shifting from denitrification to the environmentally friendly anammox pathway to mitigate greenhouse gas emissions.
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•Horizontally anammox and denitrification rate maximized in riparian fringe zones.•Denitrification and anammox separately dominate N-loss in upper unsaturated and lower saturated soil horizons.•Anammox contribution increased with water-level rising accompanied with N2O reduction.•Optimizing water-table management can reduce NO3− moreover mitigating N2O emission.•Ammonium oxidation coupling DNRA promote anammox in riparian zones.
Nitrate contamination in ground- and surface water is a persistent problem in countries with intense agriculture. The transition zone between rivers and their riparian aquifers, where river water and ...groundwater interact, may play an important role in mediating nitrate exports, as it can facilitate intensive denitrification, which permanently removes nitrate from the aquatic system. However, the in-situ factors controlling riparian denitrification are not fully understood, as they are often strongly linked and their effects superimpose each other. In this study, we present the evaluation of hydrochemical and isotopic data from a 2-year sampling period of river water and groundwater in the riparian zone along a 3rd order river in Central Germany. Based on bi- and multivariate statistics (Spearman's rank correlation and partial least squares regression) we can show, that highest rates for oxygen consumption and denitrification in the riparian aquifer occur where the fraction of infiltrated river water and at the same time groundwater temperature, are high. River discharge and depth to groundwater are additional explanatory variables for those reaction rates, but of minor importance. Our data and analyses suggest that at locations in the riparian aquifer, which show significant river water infiltration, heterotrophic microbial reactions in the riparian zone may be fueled by bioavailable organic carbon derived from the river water. We conclude that interactions between rivers and riparian groundwater are likely to be a key control of nitrate removal and should be considered as a measure to mitigate high nitrate exports from agricultural catchments.
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•Hydrochemical and isotopic data of 2-year sampling period in a riparian zone.•Temperature can explain 67.8% of the variance in DO and 66.2% in δ15N.•The higher the river water content in groundwater the higher is δ15N enrichment.•Reactions depend on bioavailable carbon delivered by infiltrating river water.
Riparian ecosystems are particularly prone to heavy metal (HM) contamination, acting as a sink for HMs coming from human activities upstream or on adjacent uplands. An advanced understanding of the ...spatio-temporal dynamics, environmental drivers and the likely sources of HM contamination in riparian soils will be necessary for the conservation of riparian ecosystems. Thus, we conducted a nine-year study across a 600 km stream gradient along the Yangtze river, which has come under immense pressure in recent years partly due to the establishment of the Three Gorges Dam (TGD), the largest hydropower dam in the world. Levels of soil As, Cr, Pb, and Cu in the TGD's water level fluctuation zone (WLFZ) have consistently increased since the TGD's establishment. This increase tended to be more rapid at the upstream reaches of the WLFZ, where most HMs (As, Cd, Pb, Cu, and Zn) also tended to be particularly high. Our analyses suggest that the spatio-temporal dynamics of these metals are strongly influenced by soil phosphorus (P), organic matter, texture and manganese. In many cases HM levels exceeded acceptable pollution levels according to multiple indices. However, from 2008 to 2010 Hg and Cd presented great threat to ecosystem health, but from 2011 to 2016 levels of As and Pb became the primary concern due to increases in their concentrations of 152 and 38%, respectively, relative to 2009 levels. Factor analysis indicated that the major identifiable anthropogenic sources of HMs were traffic exhaust, sources associated with organic matter output (e.g. sewage), and sources associated with P output (e.g. agricultural runoff), with the latter generally dominant in the upper and middle reaches of the TGD watershed. These results indicate that the prioritization of As and Pb pollution and control of agricultural runoff will play an important role in the ecological protection in the TGR's riparian ecosystems.
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•Long-term, large-scale study of heavy metal pollution in riparian soils•Heavy metals concentrated in upstream riparian soils•Riparian soil was moderately contaminated by As and Pb according to several indices.•Heavy metal dynamics were strongly related to soil P, organic matter, Mn and texture.•Dam operation and local human activity affect heavy metal distribution in riparian.
How milldams alter riparian hydrologic and groundwater mixing regimes is not well understood. Understanding the effects of milldams and their legacies on riparian hydrology is key to assessing ...riparian pollution buffering potential and for making appropriate watershed management decisions. We examined the spatiotemporal effects of milldams on groundwater gradients, flow directions, and mixing regime for two dammed sites on Chiques Creek, Pennsylvania (2.4 m tall milldam), and Christina River, Delaware (4 m tall dam), USA. Riparian groundwater levels were recorded every 30 min for multiple wells and transects. Groundwater mixing regime was characterized using 30‐min specific conductance data and selected chemical tracers measured monthly for about 2 years. Three distinct regimes were identified for riparian groundwaters—wet, dry, and storm. Riparian groundwater gradients above the dam were low but were typically from the riparian zone to the stream. These flow directions were reversed (stream to riparian) during dry periods due to riparian evapotranspiration losses and during peak stream flows. Longitudinal (parallel to the stream) riparian flow gradients and directions also varied across the hydrologic regimes. Groundwater mixing varied spatially and temporally between storms and seasons. Near‐stream groundwater was poorly flushed or mixed during storms whereas that in the adjacent swales revealed greater mixing. This differential groundwater behavior was attributed to milldam legacies that include: berm and swale topography that influenced the routing of surface waters, varying riparian legacy sediment depths and hydraulic conductivities, evapotranspiration losses from riparian vegetation, and runoff input from adjoining roads.
Plain Language Summary
Riparian zones can buffer streams from upland nitrogen pollution and are thus considered as important water quality management practices. How the presence of milldams affects groundwater flow paths and their buffering capacity is not known. This study showed that milldams back up stream water above dams, reduce the groundwater gradients from the upland to the stream, and also result in their reversal during summer dry conditions and floods. Milldams reduced the mixing of groundwaters for near‐stream sediments. This response was attributed to the topographic and sediment conditions associated with the milldams.
Key Points
Milldams raise riparian groundwater levels, decrease hydraulic gradients, and cause reversals in groundwater flow
Milldam legacies contribute to reduced groundwater mixing in near‐stream sediments
Altered groundwater regimes due to milldams could affect riparian water quality processes
•Hydrologic changes enhanced CH4 emission, but inhibited CO2 and N2O fluxes.•N and N + P addition increased N2O fluxes, which is contrary to p addition.•No interactive effects of hydrologic changes ...and nutrient additions on GHGs fluxes.•Global warming potential was reduced by continuous flooding and enhanced by N + P.
Changes in global rainfall patterns and construction of artificial dams have led to widespread alteration of hydrological processes in riparian ecosystems. At the same time, many riparian ecosystems, such as those associated with the Yangtze, are being subjected to enhanced inputs of nitrogen (N) and phosphorus (P) due to intensified agricultural activity in surrounding uplands. Together, these environmental changes may alter the magnitude and direction of greenhouse gasses (GHGs) fluxes from riparian soils. We conducted an in situ experiment combined with quantitative PCR approach (qPCR) to elucidate the effects of hydrological alterations (continuous flooding (CF), periodic flooding (PF), and no flooding (NF)) and nutrient addition (N addition (urea, 100 kg N ha−1 y−1), P addition (P2O5, 20 kg ha−1y−1), N + P addition, and control (CK)) on three major GHGs including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes as well as the underlying mechanisms. Our results showed that hydrological alterations greatly affected GHGs emissions, possibly by altering soil moisture, soil organic C, and C:N ratios. The CF, with higher soil moisture and lower C:N ratio, increased CH4 emissions 13-fold and reduced CO2 and N2O emissions by 37.3% and 72.2% averaged over the growing seasons compared with no flooding. PF enhanced CH4 emissions 5.7-fold and decreased N2O emissions by 69.0% in comparison with no flooding. Nutrient additions had no significant effect on CO2 or CH4 flux, but P addition significantly lowered N2O flux. Interactions between hydrological alterations and nutrient additions were not detected for any GHGs. As a result, hydrological alterations and nutrient additions affected the global warming potential (GWP) of growing season GHG budgets on a 100-year time horizon, mainly by changing the CO2 emissions. CF reduced GWP from 597 to 439 g CO2-eq m−2, and N + P addition enhanced GWP from 489 to 625 g CO2-eq m−2. The qPCR analysis revealed that decreased CH4 oxidation potential may lead to the enrichment of CH4 emissions under the hydrological alterations, and reduced nitrification and denitrification potential contributed to the reduction of N2O fluxes under all the treatments. Our study indicates that continuous flooding could curb the contribution of riparian GHGs fluxes to global warming but that the combination of N and P additions may increase the greenhouse effect mainly by regulating the CO2 emissions of growing season in riparian ecosystem.
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Polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap) and phenanthrene (Phe) are organic pollutants of concern owing to their toxicity, carcinogenicity, and teratogenicity. Biodegradation ...is considered the most economical and efficient process to remediate Nap and Phe. The riparian zone between a river and a riparian aquifer, which is rich in indigenous microorganisms, may be important for PAH remediation. However, few studies have evaluated the ability of indigenous microorganisms to remove Nap and Phe. In this study, focusing on the typical PAHs (Nap and Phe) as target pollutants, the genus-level community structure of Nap- and Phe-degrading bacteria was identified. Batch static and dynamic biodegradation experiments were conducted to explore the biodegradation mechanisms of Nap and Phe in the riparian zone and identify the factors influencing Nap and Phe biodegradation in the binary system (i.e., where Nap and Phe are simultaneously present). According to the genus-level community structure test results, the dominant bacterial genus in the binary system was mainly the Phe-degrading bacteria. The Nap and Phe-biodegradation percentages were 19.20% lower and 19.49% higher, respectively, in the binary system than in the unitary system. The results indicated that functional bacteria can degrade Nap and Phe, and that Nap weakly promoted Phe biodegradation. Additionally, the initial Nap and Phe concentration ratio, hydraulic gradient, and temperature affected Nap and Phe biodegradation. Dynamic biodegradation experiments showed that the biodegradation percentage decreased as the hydraulic gradient increased, and biodegradation percentage of Phe was always higher than that of Nap. According to the results of the dynamic laboratory experiments, the removal percentages of Nap and Phe by indigenous riparian-zone microorganisms were 6.21–16.73% and 13.95–24.45%, respectively. The findings in this study will be useful for alleviation of Nap and Phe pollution in groundwater and will facilitate determination of appropriate treatment measures for groundwater exposed to this type of pollution.
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•Polaromonas, Pseudomonas, Janthinobacterium and Methylophilus degrade naphthalene (Nap) or phenanthrene (Phe).•Functional bacteria preferentially degraded Phe when Nap was also present.•Nap removal percentages by indigenous riparian-zone microorganisms were 6.21–16.73%.•Phe removal percentages by indigenous riparian-zone microorganisms were 13.95–24.45%.
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