Phosphorus source tracking, bioavailability, and cycling in the Murderkill River, Delaware
Date
2020
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Publisher
University of Delaware
Abstract
Excess phosphorus (P) is a major cause of water quality issues, such as nutrient enrichment and eutrophication. While the Delaware Estuary overall is less prone to eutrophication, one of its sub-estuaries, the Murderkill Watershed, has experienced historically high P influx and seasonal eutrophic conditions. To identify sources of P in the watershed and their relative contributions to sinks in the Murderkill River, soils from various land uses including farm, residential, and forest, influent and effluent from the wastewater treatment facility, and particulate matter from the Murderkill River were collected. These samples were analyzed in accordance with three different methods of source tracking: 1) concentrations of P-pools, 2) stable isotopes of carbon (δ13C), nitrogen (δ15N), and phosphate-oxygen (δ18OP), and 3) elemental fingerprint modeling. ☐ The NaOH-P pool was found to have the highest concentration in all soils, to best be replicated by the model, and to be the most reliable pool for source tracking based on narrow confidence intervals of percent contribution from soil to PM. Furthermore, based on the elemental fingerprint model from the NaOH-P pool and δ13C and δ15N values, area normalized loading in particulate matter (PM) from farm and residential soils in the watershed was 2.9 (±0.7) and 1.5 (±1.9) times higher than forest soil, respectively. Additionally, a distinction among farm and residential soil δ18OP values was found, which points towards the possibility of future use of this proxy for source tracking of P. Overall, coupling concentration data, stable isotope values, and elemental fingerprint modeling aided in identifying particular sources for P and highlighted land use types where P abatement may be appropriate to avoid exceeding the TMDL limitation set for the Murderkill River.
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Keywords
Phosphorus source tracking, Bioavailability, Cycling, Murderkill River, DE, Delaware