The objective of this study was to examine the effects of flooding …

• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• References
• Figures
• Tables

Biology Articles » Hydrobiology » Phosphorus Availability in an Artificially Flooded Southeastern Floodplain Forest Soil » Introduction

Introduction

- Phosphorus Availability in an Artificially Flooded Southeastern Floodplain Forest Soil

INTRODUCTION 

FLOODPLAIN FORESTS have been shown to play an important role in improving downstream water quality (National Research Council, 1995; Brinson and Rheinhardt, 1996). This capability results in part from a landscape position that can favor the flow of both upstream (via overbank flooding) and upslope waters (via riparian transport) through the floodplain at various times during the year (Brinson, 1993; Lockaby and Walbridge, 1998). Interest in the ability of floodplain forests to remove suspended and dissolved constituents from the water column has generated extensive research (Brinson, 1977; Mitsch et al., 1979; Yarbro, 1983; Brinson et al., 1984; Elder, 1985; Mendelssohn and Burdick, 1988) and several reviews (Lowrance et al., 1984; Faulkner and Richardson, 1989; Kuenzler, 1989; Johnston, 1991; Walbridge and Lockaby, 1994; Lockaby and Walbridge, 1998). Phosphorus retention is of particular concern because P often limits primary production in downstream aquatic systems. Excess inputs of dissolved P to these systems can cause stream eutrophication and fish kills (NRC, 1995). Despite this concern, detailed studies of the effects of flooding on the distribution and availability of P in floodplain soils are rare and limited to alkaline soils (Fabre et al., 1996).

When upland soils are flooded for rice cultivation, P availability has been shown to increase because of the release of P from geochemical pools: (i) the reduction and dissolution of Fe (III) phosphates; (ii) the hydrolysis and dissolution of Fe and Al phosphates; or (iii) the release of clay-associated phosphates through anionic exchange (Ponnamperuma, 1972; Gambrell and Patrick, 1978). In contrast, more recent research has shown that in some systems, flooding can cause P availability to decrease by favoring the formation and persistence of amorphous (poorly crystalline) Fe and Al minerals (Kuo and Mikkelsen, 1979; Sah and Mikkelsen, 1986; Sah et al., 1989). Because their adsorptive surface area per unit soil volume is larger than more crystalline forms (Parfitt, 1989; Schwertmann and Taylor, 1989), these amorphous minerals tend to dominate soil P sorption reactions when present in significant amounts.

Several other factors might cause P availability to increase with flooding. In agricultural or urban areas, floodwaters themselves can carry significant loadings of available P, resulting from point and nonpoint source pollution within the watershed (Carpenter et al., 1998). Phosphorus availability might also increase following flooding because of a decrease in biological (plant and microbial) P demand under anaerobic versus aerobic conditions (Gambrell and Patrick, 1978; Schlesinger, 1997; Mitsch and Gosselink, 2000). Labile P can also be released from microbial biomass following flooding because of both the lysis of aerobic microorganisms under anaerobic conditions and the activities of facultative anaerobes specially adapted to fluctuating oxic/anoxic environments (Boström et al., 1985; Fleischer, 1985; Davelaar, 1993; Khoshmanesh et al., 1999).

The objective of this study was to examine the effects of flooding on P availability in a forested floodplain ecosystem along the Ogeechee River, Georgia. We hypothesized that P availability would increase with increased flooding duration and periodicity, primarily because of the flooding-induced release of P from Fe and Al phosphates, as observed in upland soils flooded for rice cultivation. Flooding duration and periodicity were manipulated experimentally in field mesocosms artificially flooded with river water. Previous research at this site emphasized organic matter (OM) and bacterial metabolism in the river and export of OM and bacteria from the floodplain (Findlay et al., 1986; Meyer, 1986; Cuffney and Wallace, 1987; Edwards and Meyer, 1987; Cuffney, 1988; Meyer and Edwards, 1990; Carlough and Meyer, 1991; Pulliam, 1992; Wainright et al., 1992). More recent research has focused on the effects of flooding on biogeochemical processes (Lockaby et al., 1996a, 1996b; Darke et al., 1997; Darke and Walbridge, 2000).