Quantifying and Characterizing the Legacy Phosphorus Pool in a Mississippi Delta Waterbody
Abstract
Agricultural soils in the Mississippi Alluvial Plain (i.e. the Delta) are notoriously rich in legacy phosphorus from natural and anthropogenic sources. Delta farmers rarely apply phosphorus fertilizer and aquatic environments are typically nitrogen-limited due to excessive phosphate. Despite this widespread local knowledge in the Delta, few studies have been conducted to quantify the legacy phosphorus present in sediments in this region and to quantify fluxes. Soils are typically clay textured and highly erosive. Therefore, large quantities of this nutrient-rich soil end up as sediment in aquatic waterbodies. To begin to quantify the legacy phosphorus in this region, lake sediment cores were collected from Beasley Lake, an oxbow lake in an agricultural watershed. Twelve sediment cores were collected from two locations: six from the littoral zone (depth = 1.5 m) and six from the limnetic zone (depth = 2.8 m). Cores were incubated for two weeks with either aerobic or anaerobic treatments. Sediment samples were also taken from each lake coring site and sequential phosphorus extractions and phosphorus isotherm analyses were performed. Results indicate that lake sediments are storing large amounts of phosphorus, up to 279 μg-P per g dry sediment. Core incubations demonstrated that phosphorus is easily desorbed from the sediment in anaerobic conditions. Average sediment phosphorus fluxes were 0.77 and 1.72 mg/m2/day under aerobic conditions and 15.26 and 22.33 mg/m2/day under anaerobic conditions from the littoral and limnetic zones, respectively. With additional phosphorus-rich sediment entering aquatic systems annually, there is an immense pool of available phosphorus. From a scientific perspective, ongoing work on this problem will provide data to improve phosphorus components in aquatic ecosystem models. With an eye to policy and practice, these results provide further evidence that it is critical to capture eroded soil at the edge of field or before it is transported into aquatic ecosystems through such practices as riparian buffers and sediment retention ponds.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H51D..05Y
- Keywords:
-
- 1803 Anthropogenic effects;
- HYDROLOGYDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGYDE: 1879 Watershed;
- HYDROLOGY