Hydrology and Nitrate Removal in Constructed Wetlands Receiving Agricultural Runoff: The Importance of Surface Water – Ground Water InteractionsEPA Grant Number: F6B30762
Title: Hydrology and Nitrate Removal in Constructed Wetlands Receiving Agricultural Runoff: The Importance of Surface Water – Ground Water Interactions
Investigators: Schmidt, Calla
Institution: University of California - Santa Cruz
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $109,742
RFA: STAR Graduate Fellowships (2006) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Hydrology , Water and Watersheds
Eutrophication poses a widespread risk to water quality throughout many regions of the United States. The primary cause of eutrophication in surface waters is enrichment of nitrogen and phosphorus from fertilizer application.Constructed wetlands have been shown to reduce the concentration of nitrate in agricultural run-off through enhancement of microbial denitrification, Because denitrification occurs under anoxic conditions, the rate of denitrification may be limited by the rate of diffusive and advective exchange between aerobic and anaerobic parts of the wetland system. The objective of this research is to quantitatively link physical hydrology to biochemical nutrient cycling within a treatment wetland. Specifically, I will investigate if the rate of seepage exchange between surface and subsurface waters is a primary control on the rate of denitrification within the wetland. Only with greater understanding of the mechanisms by which treatment wetlands meet (or fail to meet) design goals, can design parameters be optimized for nutrient load reduction.
The constructed wetland will comprise of a network of impoundments to treat agricultural runoff before it enters the Pajaro River. I will measure dissolved oxygen, electrical conductivity, temperature, pH, and dissolved nutrients (nitrate, ammonium, reactive phosphorous), total nitrogen, total phosphorous, major cations and anions within the wetland as well as at inflow and outflow points to evaluate the effectiveness of the treatment wetland on these water quality parameters. I will also develop two innovative components for this project: (1) determination of rates of seepage exchange using mass balance and geothermometry and (2) monitoring of wetland and subsurface conditions (physical, chemical) to assess denitrification rates, including a pilot study of nitrogen isotopes.
One anticipated result is that the rate of denitrification will vary significantly as a function of season, precipitation, through-flow, and seepage exchange. I expect that seepage exchange rates will vary as a function of water levels (both in the wetlands and in the subsurface) and time of year depending on vegetative density and the accumulation or erosion of sediment. I expect that denitrification rates will peak with intermediate rates of seepage exchange, when the transport of nitrate into the subsurface is optimal with respect to oxygen.