Relative Roles of Sediment Transport and Localized Erosion on Phosphorus Load in the Lower Susquehanna River and Its Mouth in the Chesapeake Bay, USA
Date
2022-08-05
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Journal of Geophysical Research: Biogeosciences
Abstract
Particle size greatly influences the fate of phosphorus (P) in estuaries as P adheres more readily to the larger surface area in smaller sized particles. Here, data on two size fractions of particulate matter, permanently suspended particulate matter (PSPM, ≤40 μm) and resuspended particulate matter (RSPM, >40 μm), from field and controlled laboratory erosion experiments were analyzed to determine their relative contribution to water column P in the mouth of the Susquehanna River in the upper Chesapeake Bay. Based on the composition of sequentially extracted P pools, C and N isotopes, and elemental data, all PSPM and the majority of RSPM are most likely derived from allochthonous sources through river transport. A minor fraction of particulate matter in the water column was derived from sediment resuspension, which had a dominant role above the sediment-water interface in the river's mouth. The proportion of biologically available P pools to recalcitrant P pools in suspended particulate matter decreased with water column depth, indicating their preferential removal or biological utilization during settling. Suspended particulate matter (SPM) mobilized during sediment erosion experiments, regardless of particle size, was richer in biologically available P pools than SPM in the field, suggesting higher mobility of these pools in the field. These complementary results from field and field-simulated laboratory erosion experiments provide unique insights into the composition of particulate matter under different hydrodynamic regimes in the river estuary.
Plain Language Summary:
Phosphorus (P) is often the limiting nutrient for eutrophication. Of importance is the P load from the Susquehanna River into the Chesapeake Bay, as it contributes about a fourth of the total bay load. Paired field measurements and erosion experiments showed that the majority of suspended particulate matter and P load was derived from external, upstream riverine sources. Localized sediment erosion was present only in the mouth of the river in the northernmost Chesapeake Bay. Comparative analyses showed that P was more likely to be transported in fine grained suspended particulate matter and in forms that were more biologically available.
Key Points:
- Concentration of total particulate matter increased downstream with water column depth but P content decreased with water depth
- P pools and δ13C and δ15N values of in situ and eroded particulate matter indicated riverine input as the major source
- Sediment resuspension marginally contributed to P load
Description
© 2022. American Geophysical Union. All Rights Reserved. This article was originally published in Journal of Geophysical Research: Biogeosciences. The version of record is available at: https://doi.org/10.1029/2022JG006944. This article will be embargoed until 02/05/2023.
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Citation
Li, Q., Gray, K. E., & Jaisi, D. P. (2022). Relative roles of sediment transport and localized erosion on phosphorus load in the lower Susquehanna River and its mouth in the Chesapeake Bay, USA. Journal of Geophysical Research: Biogeosciences, 127, e2022JG006944. https://doi.org/10.1029/2022JG006944