High Inter‐ and Intra‐Lake Variation in Sediment Phosphorus Pools in Shallow Lakes. Issue 7 (6th July 2022)

• Record Type: Journal Article
• Authors: Albright, Ellen A.; Rachel, Fleck King; Shingai, Quin K.; Wilkinson, Grace M.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 7(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-07-06
• Subjects: sediments -- phosphorus -- shallow lakes -- spatial heterogeneity; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2022JG006817
• Languages: English
• ISSNs: 2169-8953

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. Plain Language Summary: Phosphorus (P) is an essential nutrient in freshwater ecosystems; however, in excess it can cause blooms of algae and cyanobacteria. P enters lakes from the watershed (external loading) or when released from lakebed sediments into the overlying water (internal loading). Sediment P chemistry controls internal loading because some forms of P are more susceptible to release. However, we lack a quantitative understanding of how sediment P chemistry can vary within individual lakes and among different waterbodies. We measured variation in sediment P composition within and among seven shallow lakes. We found that sediment P composition varied across lakes based on lake and watershed characteristics. We also found that a higher abundance of mobile P forms in the sediments was correlated with higher concentrations of phytoplankton pigments, indicating that sediment P composition may influence phytoplankton biomass in shallow lakes. Within individual study lakes, sediment P was highly variable, meaning that multiple samples are required to capture this heterogeneity. Our results reveal the scale of spatial variation in sediment P forms in shallow lakes. Since sediment P composition is a primary mechanism controlling sediment P release, this knowledge is critical to building accurate models to predict internal P loading. Key Points: The size and chemical composition of sediment phosphorus pools are spatially heterogeneous both within and among shallow lakes Lake basin morphology, water depth, and watershed characteristics drive variation in sediment P pools within and among lakes Understanding intra‐lake variation in sediment P informs the spatial sampling resolutions necessary for accurate P stock assessments