Quantifying denitrification following floodplain restoration via the two-stage ditch in an agricultural watershed

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

“…The larger transect volume of two-stage ditches allows stream water to spread on to floodplains during high flows, relying on riparian connectivity to enhance reach-scale denitrification. Constructed floodplains have been shown to prolong water residence time and remove 2-13 % of stream NO 3 − loads (Mahl et al, 2015;Roley et al, 2012;Speir et al, 2020). However, denitrification can terminate with nitrous oxide (N 2 O) and potentially impose an environmental trade-off between water quality improvements and greenhouse gas emissions from constructed floodplains (Dee and Tank, 2020).…”

The Case for Studying Highly Modified Agricultural Streams: Farming for Biogeochemical Insights

“…This combination greatly reduces the efficiency (i.e., removal relative to export) of both dissimilatory (i.e., denitrification) and assimilatory pathways (Royer et al 2004), thereby limiting the ability of agricultural streams to mitigate nutrient export (Bernot and Dodds 2005). While agricultural streams support high rates of transformation compared to less disturbed systems, agricultural streams typically have inorganic N concentrations that are orders of magnitude higher than streams draining native vegetation (Bernot et al 2006), highlighting the fact that high processing rates do not necessarily equate to high nutrient retention rates (Bernot and Dodds 2005; Speir et al 2020).…”

“…Agricultural streams are highly reactive (top panels), yet also transport significant amounts of nutrients downstream, especially during storms (bottom panels). Denitrification data modified from Mulholland et al (2008), Findlay et al (2011), Roley et al (2012), Mahl et al (2015), and Speir et al (2020). Storm export data modified from S. L. Speir unpubl.…”

“…While agricultural streams are highly bioreactive, these streams are responsible for the majority of nutrient export to downstream waterbodies, which strongly impacts water quality (Alexander et al 2000; Vitousek et al 2009; U.S. Environmental Protection Agency 2017). For example, studies have measured high denitrification with increasing nitrate concentrations (Mulholland et al 2008; Speir et al 2020), yet the processing power of agricultural streams is not enough to reduce N and P loads to target levels set by the US EPA Mississippi River/Gulf of Mexico Watershed Nutrient Task Force (Porter et al 2015). Moreover, increased nitrate export from agricultural streams, especially during winter snowmelt and spring storms, has been identified as the primary driver of eutrophication in the Gulf of Mexico (Turner et al 2012), despite high rates of processing.…”

Water transport pathways influence the propagation of field‐scale NO3−‐N reductions to the watershed scale

“…In agricultural watersheds, farmers often implement conservation practices to reduce nutrient losses from their fields to adjacent waterways, and include conservation tillage practices (Allmaras & Dowdy, 1985; Phillips et al, 1980), the two‐stage ditch (Mahl et al, 2015; Roley et al, 2012; Speir et al, 2020), and the planting of winter cover crops in the fallow season (Hanrahan et al, 2018; Kaspar & Singer, 2011; Kladivko et al, 2014; Strock et al, 2004; Trentman et al, 2020). Given the pervasive water quality challenges in agricultural landscapes, effective conservation practices are needed, but the patchwork geomorphology of rivers means an alteration within the watershed at the field scale may be masked when exploring dynamics at the watershed scale (De Jager & Houser, 2012; De Paula, Gerhard, De Barros Ferraz, & Wenger, 2018).…”