Varying redox potential affects P release from stream bank sediments

Abstract

Sediments in streams that drain agricultural watersheds may be sinks that can adsorb P from the stream or sources that can release P to the stream. Sediment characteristics and environmental factors, including the oxidation-reduction (redox) potential of the water associated with the sediment, determine whether P will be adsorbed or released by the sediment. We investigated P adsorption and release by four sediments [three Holocene-age sediments (Camp Creek, Roberts Creek and Gunder) as well as Pre-Illinoian-age Till] that occur in Walnut Creek, a second-order stream in Jasper County, Iowa, that is representative of many small streams in the glaciated upper Midwest of the US. The effects of two redox potentials on phosphorus buffering capacity (PBC) and equilibrium phosphorus concentration (EPC) were evaluated in batch adsorption experiments. We also simulated aerobic and anerobic conditions over a 24-day period and measured solution-phase P concentrations in stirred systems where the sediments were isolated from the water by dialysis tubing. The batch experiment indicated that the EPCs of the three Holocene-age sediments were similar to one another and increased with decreasing redox potential. In the stirred flow reactors, more dissolved P was released from the Camp Creek and Roberts Creek sediments under anaerobic conditions than from the other sediments. This observation suggests that these two sediments, which are younger and higher in the stratigraphic sequence, are more likely to be P sources in suboxic settings. The P buffering capacity was greatest in the till. Where it is in contact with the stream water, the till is likely to serve as an adsorbing sink for P in the water column.

Sediment phosphorus buffering in streams at baseflow: A meta‐analysis

“…However, Rahutomo et al. (2018) demonstrated either no or little increase in EPC 0 when sediments were stored under anaerobic conditions for 30 d; further, the redox effect was magnified only with the addition of labile C, illustrating the fact that C limitation, which is prevalent among stream sediments (Hill et al., 2012), likely limits the decrease in redox potential necessary to bias EPC 0 on reasonable timescales. Hence, the bias due to pretreatment can and should be avoided by analyzing sediments fresh as soon as possible and within 1–2 wk of sampling.…”

“…Much of the P stored in sediments is with varying Fe species (adsorbed and precipitated), which are sensitive to reductive dissolution (Casillas‐Ituarte et al., 2020; Hoffman et al., 2009; Lewandowski & Nützmann, 2010; Machesky et al., 2010; Peryer‐Fursdon et al., 2014; Weigelhofer, 2017). Indeed, in slow lotic systems (e.g., riverine wetlands) or in parts of the stream channel with long residence times (e.g., deeper subsurface), there tends to be greater reducing conditions, which can influence EPC 0 (House & Denison, 2000; Palmer‐Felgate et al., 2011; Rahutomo et al., 2018). Consequently, this may lead to greater decoupling of DRP and EPC 0 in situ (McDowell et al., 2020).…”

Phosphorus Pool Composition in Soils and Sediments of Transitional Ecotones under the Influence of Agriculture

“…Subsequently, fine sediments preferentially accumulate in areas of slower flows, which locally turns drainage ditches, small streams, and riparian zones into important accumulators for PP (Meals et al, 2010). Similar to the Pi in buffer strips, Pi in streambed sediments can be mobilized to the aqueous phase by several processes (e.g., desorption processes, redox dynamics, and hydrolysis of Po) (Rahutomo et al, 2018; Reddy et al, 1999). …”

Streambank Legacy Sediments in Surface Waters: Phosphorus Sources or Sinks?

“…While we did not measure EPC 0 at multiple times of the year, other studies suggest that sediment EPC 0 could also be temporally variable, driven by sediment conditions and stream water concentrations. For example, EPC 0 can increase under reducing conditions due to the loss of crystalline forms of Fe oxides resulting in a release or reduced retention of P [44,50]. EPC 0 values could also fluctuate as a result of stream water concentrations with an increase in EPC 0 with increasing stream water concentrations, resulting in a reduction of the sediment buffering capacity [51].…”