Streambank Legacy Sediment Contributions to Suspended Sediment‐Bound Nutrient Yields from a Mid‐Atlantic, Piedmont Watershed

Abstract

Research Impact Statement: Streambank legacy sediments constitute a significant fraction of suspended sediment-bound nutrient exports and must be considered in watershed models, regulatory assessments, and management practices.

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

“…One other study [24] investigated anthropogenic signatures in legacy sediments through the use of elemental ratios. Our work showed that while P concentrations in legacy sediments were on the lower side (25-1293 mg/kg; [22]), streambank legacy sediment contributions to watershed fluxes could be as much as 50% and 32% for sediments and sediment-bound P, respectively [21]. Legacy sediments have been defined as deposits of historic sediments that have accumulated in the valley-bottoms of eastern US following European settlement [13,14].…”

“…Detailed description of the streambank sampling sites, coordinates, and methods is provided in [21,22,33]. Briefly, legacy sediment sampling was performed at 15 streambank sites across five streams in northern Delaware (DE), eastern Maryland (MD), and southeast Pennsylvania (PA) ( Figure 2 where all the M3 extractable values are in molar concentrations [27].…”

“…Many of the milldams, which were particularly ubiquitous across the mid-Atlantic region (every few kilometers), have now breached or have been removed, leaving incised streams vulnerable to bank erosion [14,17,18] (Figure 1). Not surprisingly, recent studies reveal that streambank erosion of legacy sediments could constitute as much as 50 to 100% of the watershed fine sediment exports [19][20][21] and need to be accounted for in watershed sediment budgets and management plans. Beyond sediments, however, very few studies have characterized the concentrations of P in legacy sediments and their contributions to sediment-bound and total P budgets [15].…”

“…Beyond sediments, however, very few studies have characterized the concentrations of P in legacy sediments and their contributions to sediment-bound and total P budgets [15]. We know of only three studies, including two of our own that have determined P concentrations in legacy sediments and estimated their contributions to watershed P loadings [21][22][23]. One other study [24] investigated anthropogenic signatures in legacy sediments through the use of elemental ratios.…”

“…and (3) What are the broader implications of legacy sediment P for water quality and watershed management? To address the first question we collated our recent legacy sediment P concentrations reported by [21,22], compared them to P values reported for other streambank legacy and non-legacy sediment sites, upland soil concentrations, stream bed sediments, and water quality thresholds. Comparisons were performed for total P, bioavailable fraction of P quantified by Mehlich-3 extracts [27], and the % degree of phosphorus saturation (%DPS; [27]).…”