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

• Main Authors: Shreeram Inamdar, Nathan Sienkiewicz, Alyssa Lutgen, Grant Jiang, Jinjun Kan
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Soil Systems
• Subjects: legacy sediments; phosphorus; equilibrium phosphorus concentration; sorption; desorption; anoxic
• Online Access: https://www.mdpi.com/2571-8789/4/2/30

Streambank legacy sediments can contribute substantial amounts of sediments to Mid-Atlantic waterways. However, there is uncertainty about the sediment-bound P inputs and the fate of legacy sediment P in surface waters. We compared legacy sediment P concentrations against other streambank sediments and upland soils and evaluated a variety of P indices to determine if legacy sediments are a source or sink of P to surface waters. Legacy sediments were collected from 15 streambanks in the mid-Atlantic USA. Total P and M3P concentrations and % degree of phosphorus saturation (DPS) values for legacy sediments were lower than those for upland soils. % DPS values for legacy sediments were below the water quality threshold for P leaching. Phosphorus sorption index (PSI) values for legacy sediments indicated a large capacity for P sorption. On the other hand, equilibrium phosphorus concentration (EPC₀) for legacy sediments suggested that they could be a source or a sink depending on stream water P concentrations. Anoxic conditions resulted in a greater release of P from legacy sediments compared to oxic conditions. These results suggest that legacy sediment P behavior could be highly variable and watershed models will need to account for this variability to reliably quantify the source-sink behavior of legacy sediments in surface waters.