High Inter‐ and Intra‐Lake Variation in Sediment Phosphorus Pools in Shallow Lakes
Ellen Albright, Fleck King Rachel, Quin K. Shingai, Grace M. Wilkinson
Abstract
Abstract Phosphorus (P) release from lakebed sediments may fuel phytoplankton blooms, especially in shallow waterbodies. A primary mechanism that controls internal P loading is the size and chemical composition of the sediment P pool. However, variation in sediment P within and among shallow lakes remains poorly quantified. We measured the degree of spatial heterogeneity in the size and composition of sediment P pools, both within and among seven shallow lakes. There was a 1.6× difference in total sediment P among the study lakes, and P composition varied across lakes based on differences in watershed soils and land cover and lake basin morphology. Differences in sediment P composition among lakes imply that the dominant mechanisms of internal loading will also vary among lakes. We also found that higher mobile P (as a fraction of total P) in the profundal sediments was positively correlated with long‐term mean chlorophyll ‐a concentrations ( p = 0.04), indicating the reciprocal relationship between sediment P composition and phytoplankton biomass in shallow lakes. Additionally, we measured substantial within‐lake heterogeneity in total and loosely‐bound sediment P within each lake. Concentrations were positively correlated with water depth such that extrapolating measurements from the deep site alone could overestimate whole‐lake mean P concentrations, reinforcing that single station methods produce unreliable estimates of mean sediment P stocks. Our results provide insight into the magnitude and pattern of inter‐ and intra‐lake variation in sediment P pools that should be accounted for when sampling, scaling measurements, and modeling sediment P dynamics.