Spatio-Temporal Variability of Phosphorus Near the Groundwater-Stream Interface
Abstract
Agricultural practices can cause excess inputs of soluble reactive phosphorus (SRP) to freshwater catchments leading to eutrophication. This study evaluates spatio-temporal variability of SRP in an agricultural streambed including the influence of groundwater-stream interactions, and examines the associated geochemical and hydrological controls. High porewater SRP (>1000 µg/L) and high SRP sediment fractions were observed in low groundwater discharge zones, specifically in the shallow (≤ 0.1 m) streambed sediments. Porewater SRP concentrations were linked to iron redox cycling with SRP concentrations concordant with more reducing conditions. Porewater SRP varied temporally but distinct seasonal changes were not observed. The conditions in the shallow streambed sediments switched from less-reducing to more-reducing conditions between sampling times with SRP release to the stream more likely when the shallow streambed was more reducing. The study findings are needed to improve water quality predictions and management practices aimed at reducing P stream loads.