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Phosphorus (P) is an essential nutrient for sustaining life and agricultural production. Transformation of readily available P into forms that are unavailable to plants adds costs to P replenishment, which eventually translates into lower agronomic benefits and potential loss of soil P into runoff may degrade water quality. Therefore, understanding the sources and pathways of the formation of residual P pools in soils is useful information needed for the development of any technological or management efforts to minimize or inhibit the formation of such P pool and thus maximize availability to plants. In this research, we paired phosphate oxygen isotope ratios (δ18OP) with solid-state 31P NMR and quantitative XRD techniques along with general soil chemistry methods to identify the precipitation pathways of acid-extracted inorganic P (Pi) pools in an agricultural soil. Based on the comparison of isotope values of 0.5 mol L−1 NaOH-Pi, 1 mol L−1 HCl-Pi, and 10 mol L−1 HNO3-Pi pools and correlations of associated elements (Ca, Fe, and Al) in these pools, the HNO3-Pi pool appears most likely to be transformed from the NaOH-Pi pool. A narrow range of isotope values of acid-Pi pools in shallow (tilling depth) and below (where physical mixing is absent) is intriguing but likely suggests leaching of particle-bound P in deeper soils. Overall, these findings provide an improved understanding of the sources, transport, and transformation of acid-Pi pools in agricultural soils and further insights into the buildup of legacy P in soils.
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Loading and Bioavailability of Colloidal Phosphorus in the Estuarine Gradient of the Deer Creek‐Susquehanna River Transect in the Chesapeake Bay
Abstract Phosphorus (P) overloading is a major cause of surface water eutrophication and bottom water hypoxia. The incomplete understanding of different P pools and their corresponding bioavailability in the continuum from sources and sinks has limited the development of appropriate nutrient management strategies. Here we apply multistable isotope proxies to track colloids and identify whether specific P pools in colloids are biologically cycled at the Deer Creek‐Susquehanna River mouth stretch. Results showed that NaOH‐Piis the most dominant P pool in the summer and winter seasons. Oxygen isotope values (δ18OP) of NaOH‐Piand HNO3‐Pipools of different size fractions of colloids are much heavier than the ranges of equilibrium values in the ambient water, which suggest that these two pools are recalcitrant against biological uptake. It further means isotopic signatures of these P pools could be used to identify the sources of colloids. Carbon (C) and nitrogen (N) isotope compositions of colloids showed that the contribution of terrestrial sources gradually decreases downstream of the river toward the bay and Deer Creek contributes disproportionately high amounts of colloids to the Susquehanna River. These findings provide valuable information on the loading of colloids and relative bioavailability of colloidal P pools in estuarine ecosystems.
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- Award ID(s):
- 1654642
- PAR ID:
- 10458076
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 124
- Issue:
- 12
- ISSN:
- 2169-8953
- Page Range / eLocation ID:
- p. 3717-3726
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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