SPATIAL, TEMPORAL, AND HYDROLOGICAL VARIATIONS IN PHOSPHORUS RETENTION IN A LARGE CATTAIL WETLAND

Abstract

ABSTRACT: Wetlands are now heavily regulated and recognized as key landscape features because of their roles in improving water quality through the removal of dissolved and sediment bound contaminants. However, wetland filtration processes are still the subject of considerable research, and limited evidence suggests that wetland filtration varies considerably as water levels follow natural rise and fall cycles. From April 2002 until April 2003, research was conducted in the Ellison Park Wetland, an 87-hectare cattail-dominated marsh near Rochester, NY, to determine how spatial and temporal variations in phosphorus (P) retention mechanisms, as well as a varying hydrological regime, affect P dynamics. A mass balance approach was used to determine how P retention processes vary seasonally or spatially. Groundwater and surface water hydrology of the study site were carefully monitored, using stage gages and seven nests of piezometers distributed throughout the study site, to determine potential influences it has on the wetland?s biogeochemistry. Replicated samples of the wetland substrate, plant tissues, litter, surface water and groundwater were collected at 18 stations seven times between May 2002 and April 2003 and analyzed for P content. Our findings show distinct differences in P dynamics spatially, in near-stream vs. interior plots, with different sets of processes driving retention in these wetland environments. The near-stream environment accounts for 70% of P retention whereas interior sites account for 79 % of surface area. Near-stream P retention is driven by long-term and short-term deposition of silt and clay-rich sediment associated with over-bank flood events, creating a greater capacity for P retention on a per volume basis. In contrast, the marsh interior has a more organic substrate with a lower total P content and lower aboveground plant growth. The combined effects of cattail phenology and two distinct hydrologic phases during the study period (wet spring and dry summer) on P processes show that a wetland?s ability to filter P is more dynamic over space and time than often assumed. As precipitation patterns become variable due to climate change, improved knowledge about P retention mechanisms in natural wetlands will be useful for water quality improvement.