PARENT SESSION
Oral Session 1: Aquatic Ecology I: Rivers, Nutrients, and Water Quality.
Presiding: D Kashian
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 105.

Nutrient transformations in forested floodplains during overbank flooding: Do they exist?

Whitmire, Stefanie ^*,1, Dress, William ¹, Walbridge, Mark¹, ¹ West Virginia University, Morgantown, WV

ABSTRACT- Forested floodplains are common wetland ecosystems that can affect downstream water quality. As part of a larger study, we examined how forested floodplains retain and transform nutrients in floodwaters. Water samples were collected from floodplain forests adjacent to 2 alluvial and 2 black water rivers in late winter 2003. Samples were collected along upstream and downstream transects during overbank flooding to characterize the chemical changes that occur as water moves across the floodplain. We hypothesized that nitrogen (N) and phosphorus (P) concentrations would be lower at the downstream transect due to nutrient retention or transformation. Orthophosphate (SRP) concentrations ranged from 1.5-256 g P/L in upstream transects, to 5-151 g P/L in downstream transects. Dissolved organic P ranged from 9.2-22.1 g P/L and 1.2-26.7 g P/L respectively, in upstream and downstream transects. Contrary to our hypothesis, there were no clear trends in P retention or transformation from upstream to downstream in these 4 sites. One blackwater site had significantly lower SRP downstream. At one alluvial site, total P (TP) and particulate P (PP) decreased as water moved through the floodplain, although concentrations upstream were significantly higher than in river waters. Total P and PP concentrations at the other 3 sites increased across the floodplain, possibly indicating resuspension of PP during flooding. As expected, nitrate and ammonium concentrations tended to be lower at the downstream transects. Nutrient retention and transformation in floodplains during overbank flooding is highly variable. Variations in floodwater volume, floodplain size, and flow rates could explain observed variations in P retention functions.

Key words: phosphorus, floodplain