Date of Graduation
Eberly College of Arts and Sciences
Richard B. Thomas
Kevin C. Daly
William T. Peterjohn
Mark R. Walbridge
R. Kelman Wieder
Phosphorus (P) commonly limits productivity in freshwater ecosystems; thus, increased P loading, either in dissolved (DP) or particulate (PP) form, can lead to eutrophication. The central goal of my dissertation research is to understand these biogeochemical mechanisms of P retention and transformation in rivers and streams and their associated FFs in the Atlantic Coastal Plain of the southeastern US (VA, NC, SC, GA).;To assess the nature of P removal during flooding events, I conducted a detailed study of DP and PP forms (inorganic, Pi and organic, Po) in waters from alluvial (AL) and blackwater (BW) FFs. At each FF site, floodwaters were collected both from the river inflow point (RI), from within the floodplain (FP) near the outflow point, and analyzed P forms by 31P nuclear magnetic resonance (NMR) spectroscopy. In both AL and BW samples, total DP and dissolved orthophosphate (DP i) declined significantly from RI to FP, while dissolved pyrophosphate (complex DPi) and total DPo were significantly higher in FP than in RI waters. Orthophosphate monoesters comprised the majority of the DPo pool and were significantly higher in FP floodwaters in both AL and BW systems. This suggests that in both AL and BW systems, DPi was converted to DPo form during flooding events, reducing its bioavailability and potential to cause the eutrophication of downstream waters.;In a second study, I added 32Pi dissolved in river water to soil cores collected AL and BW FFs to identify specific mechanisms of P retention and transformation during flooding. As much as 77 % of added 32Pi was transformed to 32Po within 2 h of addition in BW river waters, while in AL river waters, all added 32Pi remained in inorganic form. However, when labeled river waters were added to soil cores, upon contact with the soil surface, additional transformation was observed resulting in an increase in the proportion of 32Po in headwaters, averaging 68 and 80 % of total 32P recovered in AL and BW cores, respectively. These results suggest that floodplain soils act as a second line of defense protecting water quality, by retaining P inputs that are not initially transformed within the water column (river- and head-waters) during flooding events.;In a third study, I compare changes in microbial community composition in AL and BW FFs. Soil chemical properties reveal that total P (TP) concentrations were significantly higher in AL compared to BW soils, whereas total C (TC) was significantly higher in BW compared to AL FF soils. Similarly, the bacterial and fungal community composition was taxonomically different in AL compared BW FF soils. Detrended correspondence analyses of the microbial profiles and the subsequent fitting of environmental variables to ordination plots, revealed that TP and pH were associated with the composition of bacterial and fungal communities in AL soils, whereas, TC was strongly correlated with the microbial community profiles in BW FFs. These results indicate that differences in FF type (AL vs. BW) are associated with differences in soil TC, TP and pH, that are important predictors of microbial composition.;My findings clearly indicate that FFs are indeed valuable ecosystems that have profound effects on the biogeochemical retention and transformation of excess P loadings carried with floodwaters, playing an important role in maintaining water quality in downstream aquatic ecosystems. It is forecasted that by 2025 as much as two-thirds (an estimated 5 out of the 8 billion people) of the world population will experience severe water scarcity due to climate change impacts and poor water quality resulting from the eutrophication of potable freshwater reservoirs. North America is likely to be impacted by these trends, and as such future policy decisions may be dependent on the prioritization of riparian wetlands (particularly FFs) based on their ecosystems functions and values. (Abstract shortened by UMI.).
Navaratnam, John A., "Phosphorus Retention and Transformation in Floodplain Forests of the Southeastern United States" (2013). Graduate Theses, Dissertations, and Problem Reports. 666.