HR: 10:38h
AN: H52C-02 INVITED    [Abstracts]
TI: Storms Induce Variable Changes in Phosphorus Release From a North Carolina Coastal Plain In-Stream Wetland
AU: Novak, J M
EM: jeff.novak@ars.usda.gov
AU: Szogi, A A
EM: ariel.szogi@ars.usda.gov
AF: USDA-ARS-Coastal Plains Research Center, 2611 West Lucas Street, Florence, SC 29501,
AU: Stone, K C
EM: ken.stone@ars.usda.gov
AF: USDA-ARS-Coastal Plains Research Center, 2611 West Lucas Street, Florence, SC 29501,
AU: * Watts, D W
EM: don.watts@ars.usda.gov
AF: USDA-ARS-Coastal Plains Research Center, 2611 West Lucas Street, Florence, SC 29501,
AU: Johnson, M H
EM: mel.johnson@ars.usda.gov
AF: USDA-ARS-Coastal Plains Research Center, 2611 West Lucas Street, Florence, SC 29501,
AB: Wetlands are a valuable tool for water purification but vary in their effectiveness at sequestering phosphorus (P). A long water retention time and an extensive amount of sediment surface area in the wetland create optimum conditions for slow P exchange between the water column and storage pools (i.e., sediment pore water, sorbed to sediments, etc.). These P storage pools can be overwhelmed through hydrologic disturbances caused by intensive rainfall events and flooding associated with storms. Events such as hurricanes and tropical storms can differ in their rainfall delivery and residence time overland, thus causing variations in their hydrologic disturbances to wetlands. In some cases, storms can increase inflow into wetlands that exceeds its water storage capacity, thereby flushing P storage pools and accelerating P releases with outflow (Q). Between 1996 and 1999, this study examined 10 different storm event and wetland hydraulic characteristics (rainfall totals, residence time over mainland, wetland Q, etc.) on dissolved phosphorus (DP) exported from an animal waste impacted in-stream wetland and evaluated shifts in P storage pools (sediment pore water and sediment total phosphorus concentrations) that would account for potential DP releases. The 10 storms (6 hurricanes and 4 tropical storms) were found to differ greatly in their ability to accelerate P releases. For example, turbulence within the wetland caused by a single hurricane event such as by Bertha (in 1996) and Bonnie (in 1998) released less than 50 kg DP/mo, whereas, a single tropical storm (in 1997) promoted the release of 117 kg DP/mo. The higher DP mass load after the single tropical storm in 1997 was explained by severe disturbance to internal DP storage pools that increased outflow DP concentrations from 0.9 to 3.3 mg/L. Correspondingly, the range in outflow DP concentrations after the pair of single hurricane events was only between 0.2 to 0.3 mg/L. On a gross scale, massive rainfall totals by successive hurricanes in 1998 (Dennis, Floyd, and Irene) precipitated huge hydrologic disturbances within this wetland resulting in 1,119 kg of DP released. These three hurricanes in a short time period (2.5 mo) delivered a cumulative rainfall total of 606 mm that caused the in-stream wetland to be flushed several hundred-fold with equivalent volumes of water as inflow. Multiple flushing of the wetland by storms over 4 yrs also resulted in significant reductions in sediment pore water DP contents and in sediment total phosphorus concentrations. The large difference in DP mass loads released from this in-stream wetland was explained using regression analyses to evaluate mass loads versus Q differences between storm events. Examining 4 yrs of storm activity showed that some tropical storms can cause similar or higher DP releases than a single hurricane; still, multiple successive hurricanes in the same season delivering heavy rainfall totals significantly increased DP export.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0496 Water quality
DE: 0497 Wetlands (1890)
SC: Hydrology [H]
MN: 2007 Fall Meeting