Streambanks: A net source of sediment and phosphorus to streams and rivers

Authors: FOX, GAREY - North Carolina State University; PURVIS, REBECCA - Oklahoma State University; Penn, Chad

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2016
Publication Date: 8/5/2016
Citation: Fox, G.A., Purvis, R.A., Penn, C.J. 2016. Streambanks: A net source of sediment and phosphorus to streams and rivers. Journal of Environmental Management. 181:602-614.

Interpretive Summary: Excess phosphorus (P) and sediment transported to surface waters are a major cause of water quality degradation. Streambanks themselves are often overlooked as sediment and P sources. This review was conducted to summarize the current knowledge-base of streambank erosion, streambank P concentrations, and streambanks as P sources to surface waters. The following summarizes the highlights: -Limited data exist on watershed-scale sediment and nutrient loading from streambanks. -Streambank total phosphorus concentrations consistently exceed 250 mg/kg soil. -Streambanks reported to account for 6–93% of total phosphorus loads. -Significant research still needed on quantifying the dissolved and particulate P contributions from streambanks.

Technical Abstract: Sediment and phosphorus (P) are two primary pollutants of surface waters. Many studies have investigated loadings from upland sources or even streambed sediment, but in many cases, limited to no data exist to determine sediment and P loading from streambanks on a watershed scale. The objectives of this paper are to review the current knowledge base on streambank erosion and failure mechanisms, streambank P concentrations, and streambanks as P loading sources and then also to identify future research needs on this topic. In many watersheds, long-term loading of soil and associated P to stream systems has created a source of eroded soil and P that may interact with streambank sediment and be deposited in floodplains downstream. In many cases streambanks were formed from previously eroded and deposited alluvial material and so the resulting soils possess unique physical and chemical properties from adjacent upland soils. Streambank sediment and P loading rates depend explicitly on the rate of streambank migration and the concentration of P stored within bank materials. From the survey of literature, previous studies report streambank total P concentrations that consistently exceeded 250 mg kg-1 soil. Only a few studies also reported water soluble or extractable P concentrations. More research should be devoted to understanding the dynamic processes between different P pools (total P versus bioavailable P), and sorption or desorption processes under varying hydraulic and stream chemistry conditions. Furthermore, the literature reported that streambank erosion and failure and gully erosion were reported to account for 7–92% of the suspended sediment load within a channel and 6–93% of total P. However, significant uncertainty can occur in such estimates due to reach-scale variability in streambank migration rates and future estimates should consider the use of uncertainty analysis approaches. Research is also needed on the transport rates of dissolved and sediment-bound P through the entire stream system of a watershed to identify critical upland and/or near-stream conservation practices. Extensive monitoring of the impact of restoration/rehabilitation efforts on reducing sediment and P loading are limited. From an application standpoint, streambank P contributions to streams should be more explicitly accounted for in developing total maximum daily loads in watersheds.