Nitrogen Removal from Agricultural Subsurface Drainage by Surface-Flow Wetlands: Variability

Abstract

Agriculture has long been considered a great source of nitrogen (N) to surface waters and a major cause of eutrophication. Thus, management practices at the farm-scale have since attempted to mitigate the N losses, although often limited in tile-drained agricultural catchments, which speed up the N transport, while minimizing natural removal in the landscape. In this context, surface-flow constructed wetlands (SFWs) have been particularly implemented as an edge-of-field strategy to intercept tile drains and reduce the N loads by re-establishing ecosystems services of previously drained water ponded areas. These systems collect the incoming water volumes in basins sufficiently large to prolong the hydraulic residence time to a degree where biogeochemical processes between the water, soil, sediments, plants, macro and microorganisms can mediate the removal of N. Despite their documented suitability, great intra and inter-variability in N treatment is still observed to date. Therefore, it is essential to thoroughly investigate the driving factors behind performance of SFWs, in order to support their successful implementation according to local catchment characteristics, and ensure compliance with N removal goals. This review contextualizes the aforementioned issue, and critically evaluates the influence of hydrochemistry, hydrology and biogeochemistry in the treatment of N by SFWs.

Exploring Operational Procedures to Assess Ecosystem Services at Farm Level, including the Role of Soil Health

“…In BASIS, reduced tillage and organic farming did not result in lower risks of nitrogen leaching looking at the residual N in the soil at the start of the leaching season. Other measures to improve water quality are: (i) a sound crop rotation design where residual nutrients are used by following crops or catch crops; (ii) crop breeding to improve nutrient use efficiency; and (iii) various hydrological measures and the removal of nutrients in drains and agricultural ditches that can improve water quality [30,31]. As phosphate thresholds may not be met in the soil being considered, high-tech precision procedures, to be discussed in Section 4.2, are now available to fine-tune fertilizer applications to the needs of the plant, which vary during the growing season.…”

Low temperature Moving Bed Bioreactor denitrification as mitigation measure to reduce agricultural nitrate losses

“…Remarkably, all systems showed a certain variability in performance, comparable to the variable removal efficiencies of the MBBR during the first 158 days. This high variability prompted the study of Mendes (2021), which examined the drivers behind the performance of surface flow constructed wetlands. As outcome of the J o u r n a l P r e -p r o o f…”

“…The large variety in land use can be explained by the recent efforts to intensify wetlands for area reduction (Ilyas and Masih, 2017;Saeed et al, 2021;Wu et al, 2014). Studies investigating the driving factors behind their performance also enhance the applicability of the systems (Mendes, 2021). A tremendous reduction in footprint, towards values in the order of magnitude of a few to a dozen m 2 /ha, was already achieved by woodchip bioreactors (Bell et al, 2015;Christianson et al, 2013Christianson et al, , 2017David et al, 2016).…”

Upstream Solutions to Downstream Problems: Investing in Rural Natural Infrastructure for Water Quality Improvement and Flood Risk Mitigation

“…Success would be more likely with a system of NI measures, each targeted to particular landscape locations where they will provide the greatest benefit [75] and arranged in series along hydrologic flow paths to form "treatment trains" [76,77]. Recognizing that climate change is anticipated to increase the severity of storms and that high-flow conditions potentially reduce the treatment effectiveness of wetlands and other NI measures [78], we encourage watershed planners to include high levels of upland water storage, even in systems designed solely for water quality improvement, to ensure that the NI measures further downstream are able to perform as intended.…”