The restoration of drained agricultural soils to wetlands may result in the dissolution of P from reduced soils, causing the eutrophication of nearby surface waters. Therefore, continued improvements in the ability to predict P dissolution are necessary to minimize its potential environmental hazard. The objectives of this project were to determine if P dissolution would occur when soil material from a drained Carolina bay wetland was reduced, and to hypothesize explanations of differences in P dissolution between soils based on aqueous solution chemistry. Suspensions (15 g kg-1) of < 53 μm separates from surface samples (0-10 cm) of six poorly drained soils were subjected to microbial reduction for 25 d in a continuously stirred reactor. In a separate experiment, saturated whole soil samples (2.5 g H2O g-1 solids) were incubated under O2-free conditions for 62 d. In addition to total P, Fe, Mn, and Al; dissolved reactive phosphate (DRP), Fe(II), and dissolved organic carbon (DOC) were measured in filtrate samples from both experiments. A net increase in P dissolution (two-fold increase, up to 1.2 mg L-1) was observed for only one of six suspensions (Ponzer 1) in the continuously stirred reactor experiment. In that suspension the molar P:Fe(II) suggested that reductive dissolution of Fe(III)-bound P could not fully account for the P that dissolved, and DOC was highly correlated with P dissolution. For reactor suspensions in which no net P dissolution occurred, oxalate-extractable Al was negatively correlated (p < 0.05) with final [DRP], and DOC concentrations were approximately 2-fold lower than in the Ponzer 1 suspension. In the static incubation experiment, P dissolution occurred in all four samples, and the highest concentration was seen in the Ponzer 1 sample (three-fold increase, up to 2.2 mg DRP L-1). Dissolved organic carbon concentrations were between 2 and 4 fold higher in the static incubation experiment than the highest concentration observed in the stirred reactor experiment, and offer a qualitative explanation for the additional P dissolution that occurred in static incubation experiment. The results of these experiments suggest that P concentrations in soils of the restored wetland will increase upon reduction to levels that are environmentally threatening, and that interaction of DOC with PO4 or minerals that bind PO4 plays an important role in the release of P.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-05092007-122444 |
| Date | 01 August 2007 |
| Creators | Brownfield, Christopher Scott |
| Contributors | Dr. Mike Vepraskas, Dr. Dean Hesterberg |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-05092007-122444/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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