Grantee Research Project Results

Nitrogen Removal by Beaver Ponds in Nutrient Enriched Coastal Watersheds

EPA Grant Number: FP917819
Title: Nitrogen Removal by Beaver Ponds in Nutrient Enriched Coastal Watersheds
Investigators: Whitney, Christopher Thomas
Institution: University of New Hampshire
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2015 through August 31, 2018
Project Amount: $132,000
RFA: STAR Graduate Fellowships (2015) RFA Text |  Recipients Lists
Research Category: Academic Fellowships

Objective:

The shallow-sloped watersheds of northeastern Massachusetts that drain suburban Boston have been undergoing increasing urbanization, resulting in greater inputs of nitrogen pollution from non-point sources such as septic systems, fossil fuel combustion, and runoff from urban areas. These watersheds have also been experiencing a resurgence in the beaver population due to altered trapping laws and conservation efforts. As beaver have returned to many forested and suburban landscapes, the abundance of dams and beaver associated wetlands has also increased. Additionally, this expansion of beavers has led to increased inundation and connection of fluvial wetlands to channels and could enhance the capacity for attenuating high nitrogen inputs from upstream suburban areas. This research project will investigate the effectiveness of fluvial wetlands to control nitrogen at the scale of an entire river network and determine how their effectiveness has changed over time. The results will add new understanding to how the return of beavers affects the capacity of river systems to influence watershed nutrient exports.

Approach:

First, a geographic information systems (GIS) approach will be used to analyze the change in fluvial wetland area over the last 20 years. This analysis will use existing datasets as well as digital orthophoto images dating back to 1994 to quantify the change in fluvial wetland area in the study watersheds. Second, measurements of nitrogen removal rates will be made in a variety of beaver ponds spanning a range of wetland sizes, land use types, and locations relative to sources to account for the diversity of wetlands with the watersheds. These small-scale measurements will be used to develop functional relationships between nitrogen removal and various wetland attributes. Finally, an existing river network-scale nitrogen removal model that focuses on channel-dominated streams will be adapted to explicitly incorporate the role of wetlands at the river network-scale. This model will account for wetland abundance and nitrogen removal rates to understand how nitrogen removal of the entire river network has changed as both nitrogen loading and fluvial wetland abundance has changed and also to predict how river network nitrogen removal will change in the future as wetland abundance and nitrogen loading shift with increasing urbanization.

Expected Results:

This research will add new understanding to how the return of beaver affects the capacity of river systems to influence watershed nutrient exports. Ongoing wetland research has focused on site-specific nitrogen removal while the proposed work will scale these measurements up to investigate nitrogen removal by beaver ponds at the river network-scale. The watersheds of the Plum Island Ecosystems Long Term Ecological Research site are the ideal locations to conduct this work because there are more than 20 years of long-term data on the nitrogen fluxes reaching the coast. Furthermore, this location is ideal to test the hypothesis that beaver ponds can be important nitrogen sinks at watershed scales due to the high and potentially increasing abundance of these systems. The proposed approach couples field measurements with GIS and modeling techniques to arrive at a broad-scale understanding of nitrogen removal and to make predictions on future nitrogen removal in a dynamic landscape. The techniques and insight gained through this project on the natural processes that improve water quality can then be applied to other coastal systems, particularly those with large non-point source nitrogen inputs related to increasing urbanization

Supplemental Keywords:

water quality, nitrogen, nitrogen removal, beaver ponds, wetlands, urbanization, ecosystem services,

Progress and Final Reports:

2016

2017

Final