Date of Award

Winter 2007

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

William McDowell

Abstract

Anthropogenic nitrogen (N) inputs in terrestrial and aquatic ecosystems can alter groundwater N cycling, which affects N fluxes in surface water and coastal environments. Increased N inputs can decrease the overall health of terrestrial and coastal ecosystems as well as pose serious human health threats. It is well documented that riparian zones can reduce N fluxes to surface water bodies as well as coastal environments. Recently, it has been determined that riparian denitrification potential is largely influenced by hydrogeologic characteristics.

Hydrogeologic characteristics and groundwater physical properties and chemical constituents were evaluated in the James Farm well field located in Lee, NH, USA from 1995 to 1996, and 2004 to 2006. The "push-pull" method estimated denitrification potential by adding different quantities of nitrate and dissolved organic carbon to riparian groundwater. The constituents measured were nitrate, ammonium, total dissolved nitrogen, dissolved organic carbon, sulfate, bromide, chloride, sodium, magnesium, potassium, calcium, and silica. Patterns of nitrogen concentration in ambient riparian groundwater suggested that denitrification might be occurring as groundwater flowed through the center of the well field. Field experiments with the push-pull method, however, showed that substantial N loss did not occur even with large amounts of added nitrate and dissolved organic carbon. Short groundwater residence times may have been responsible for the lack of denitrification. Because human population density is significantly correlated with NO3- concentrations in surface- and groundwater, and global human population continues to grow exponentially, an increase in NO3- concentrations is likely. It is essential to further examine denitrification control mechanisms to determine if riparian zones are important in regulating nitrogen loss from coastal New Hampshire watersheds.

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