Exposure times rather than residence times control redox transformation efficiencies in riparian wetlands

Frei, Sven; Peiffer, Stefan

doi:10.1016/j.jhydrol.2016.02.001

Cited by 18 publications

(14 citation statements)

References 35 publications

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“…For many compounds, such as pharmaceuticals and nitrate, hyporheic reactivity is, furthermore, dependent on redox conditions in the HZ. To properly assess the relative contribution of the HZ to overall in-stream removal of these compounds, it could, therefore, be more appropriate to not only quantify the overall residence time in the HZ but also to disentangle reach-scale exposure times to different redox conditions in streambed sediments [241]. The hyporheic turnover length (i.e., the distance that is required for streamflow to be entirely exchanged with the HZ) increases with river discharge [18].…”

Section: Innovative Modelling Approachesmentioning

confidence: 99%

Is the Hyporheic Zone Relevant beyond the Scientific Community?

Lewandowski

Arnon

Banks

et al. 2019

Water

138

102

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Rivers are important ecosystems under continuous anthropogenic stresses. The hyporheic zone is a ubiquitous, reactive interface between the main channel and its surrounding sediments along the river network. We elaborate on the main physical, biological, and biogeochemical drivers and processes within the hyporheic zone that have been studied by multiple scientific disciplines for almost half a century. These previous efforts have shown that the hyporheic zone is a modulator for most metabolic stream processes and serves as a refuge and habitat for a diverse range of aquatic organisms. It also exerts a major control on river water quality by increasing the contact time with reactive environments, which in turn results in retention and transformation of nutrients, trace organic compounds, fine suspended particles, and microplastics, among others. The paper showcases the critical importance of hyporheic zones, both from a scientific and an applied perspective, and their role in ecosystem services to answer the question of the manuscript title. It identifies major research gaps in our understanding of hyporheic processes. In conclusion, we highlight the potential of hyporheic restoration to efficiently manage and reactivate ecosystem functions and services in river corridors.

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Section: Innovative Modelling Approachesmentioning

confidence: 99%

Is the Hyporheic Zone Relevant beyond the Scientific Community?

Lewandowski

Arnon

Banks

et al. 2019

Water

138

102

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“…Whilst riparian wetlands have been shown to act as biogeochemical cycling hotspots, with the potential to transform and attenuate the nutrient and geochemistry signal from the catchment as it moves from land to water [1,3,[17][18][19], the efficacy of this function in real terms is controlled by the specific distribution of functional zones or biogeochemical cycling hotspots within the wetland. These in turn are controlled by the chemical character and distribution of contributing source areas of flow to the wetland between and within a water year, flow routing through the wetland, the residence time of water within the wetland and contact or exposure time between the microbial community and the nutrient parcel transitioning through the wetland; while soil organic carbon content and dissolved organic matter in porewaters acts as an energy resource to support denitrification, with redox status varying laterally, vertically and over time [7,11,20,21]. Reported denitrification rates vary widely within and between riparian wetlands, and over time, with annual rates reported to vary from <3 kg N ha −1 to >500 kg N ha −1 in denitrification hotspots in wet meadow systems, and <4 kg N ha −1 to >65 kg N ha −1 in riparian forests [22].…”

Section: Introductionmentioning

confidence: 99%

“…The latter might comprise any, or a combination, of diffuse flow into the wetland from adjacent hillslopes, road runoff, diffuse influx from groundwater recharge through the valley gravels underlying the wetland, or influx of water from the adjacent river. The dominant hydraulic gradient and thus the source of wetland soil porewaters is likely to vary both in time and space, altering the rate and origins of nutrient influx to the wetland, and the contact time between the wetland plant and microbial communities and the nutrient load in transit which has been reported in previous studies to be a key control on processes such as soil redox and ultimately denitrification in wetland soils [11,20]. This in turn would influence the speciation of the nutrient load as it moves through the wetland.…”

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confidence: 97%

Determining the Impact of Riparian Wetlands on Nutrient Cycling, Storage and Export in Permeable Agricultural Catchments

Johnes

Gooddy

Heaton

et al. 2020

Water

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The impact of riparian wetlands on the cycling, retention and export of nutrients from land to water varies according to local environmental conditions and is poorly resolved in catchment management approaches. To determine the role a specific wetland might play in a catchment mitigation strategy, an alternative approach is needed to the high-frequency and spatially detailed monitoring programme that would otherwise be needed. Here, we present a new approach using a combination of novel and well-established geochemical, geophysical and isotope ratio methods. This combined approach was developed and tested against a 2-year high-resolution sampling programme in a lowland permeable wetland in the Lambourn catchment, UK. The monitoring programme identified multiple pathways and water sources feeding into the wetland, generating large spatial and temporal variations in nutrient cycling, retention and export behaviours within the wetland. This complexity of contributing source areas and biogeochemical functions within the wetland were effectively identified using the new toolkit approach. We propose that this technique could be used to determine the likely net source/sink function of riparian wetlands prior to their incorporation into any catchment management plan, with relatively low resource implications when compared to a full high-frequency nutrient speciation and isotope geochemistry-based monitoring approach.

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“…In the latter approach, the exposure to conditions suitable for a reaction was defined as a binary switch: the exposure‐time clock stopped in nonreactive zones while it progressed with a constant speed in reactive zones. Frei and Peiffer () defined the exposure time for denitrification as the travel time in which the oxygen concentration was below an inhibitory concentration, thus also using a binary, although dynamic, switch.…”

Section: Introductionmentioning

confidence: 99%

Accounting for the Decreasing Reaction Potential of Heterogeneous Aquifers in a Stochastic Framework of Aquifer‐Scale Reactive Transport

Loschko

Wöhling

Rudolph

et al. 2018

Water Resources Research

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Many groundwater contaminants react with components of the aquifer matrix, causing a depletion of the aquifer's reactivity with time. We discuss conceptual simplifications of reactive transport that allow the implementation of a decreasing reaction potential in reactive‐transport simulations in chemically and hydraulically heterogeneous aquifers without relying on a fully explicit description. We replace spatial coordinates by travel‐times and use the concept of relative reactivity, which represents the reaction‐partner supply from the matrix relative to a reference. Microorganisms facilitating the reactions are not explicitly modeled. Solute mixing is neglected. Streamlines, obtained by particle tracking, are discretized in travel‐time increments with variable content of reaction partners in the matrix. As exemplary reactive system, we consider aerobic respiration and denitrification with simplified reaction equations: Dissolved oxygen undergoes conditional zero‐order decay, nitrate follows first‐order decay, which is inhibited in the presence of dissolved oxygen. Both reactions deplete the bioavailable organic carbon of the matrix, which in turn determines the relative reactivity. These simplifications reduce the computational effort, facilitating stochastic simulations of reactive transport on the aquifer scale. In a one‐dimensional test case with a more detailed description of the reactions, we derive a potential relationship between the bioavailable organic‐carbon content and the relative reactivity. In a three‐dimensional steady‐state test case, we use the simplified model to calculate the decreasing denitrification potential of an artificial aquifer over 200 years in an ensemble of 200 members. We demonstrate that the uncertainty in predicting the nitrate breakthrough in a heterogeneous aquifer decreases with increasing scale of observation.

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Exposure times rather than residence times control redox transformation efficiencies in riparian wetlands

Cited by 18 publications

References 35 publications

Is the Hyporheic Zone Relevant beyond the Scientific Community?

Is the Hyporheic Zone Relevant beyond the Scientific Community?

Determining the Impact of Riparian Wetlands on Nutrient Cycling, Storage and Export in Permeable Agricultural Catchments

Accounting for the Decreasing Reaction Potential of Heterogeneous Aquifers in a Stochastic Framework of Aquifer‐Scale Reactive Transport

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