Physical criteria for wetland targeting on a watershed scale

Wetlands are vital ecosystems that provide a wide range of services. Much attention has been focused on wetlands’ ability to retain and remove pollutants, in particular nitrogen, from streams and waterways. For example, nitrogen runoff from tile-drained fields in the Upper Mississippi River Basin is considered a major cause of hypoxia and the dead zone in the Gulf of Mexico. Wetlands have been shown to be a cost-effective solution for reducing nitrate pollution in the Upper Mississippi River Basin. To improve wetlands’ ability to remove nitrogen loads, research has suggested that sites should be targeted on a watershed scale. One method that has been applied in choosing wetland sites is the wetland-to-watershed ratio; for all suitable wetland sites, the upstream drainage area is calculated and the ratio is then calculated. The wetland’s suitability is determined based on the specific ranking of the ratio. However, in the literature on nitrogen removal in wetlands, the recommended ratio varies by an order of magnitude; when the ratio is used to determine wetlands, it is important to assess which ratio is the most appropriate for a specific biophysical and physical setting. In this thesis I build on previous work on wetlands’ ability to remove nitrogen and combine a biophysical and a physical model to target nitrogen removal on a watershed scale. I find that different wetland-to-watershed ratios should be used in different climatic settings. In areas of high stream discharge, wetlands should be located relatively farther upstream and have comparatively larger wetland-to-watershed ratios. The same is true for wetlands located in cold climates. If the nitrogen concentration increases or stays constant throughout a watershed, wetlands should be located in the bottom of the watershed (very small wetland-to-watershed ratios), but if the nitrate concentration decreases downstream, there may be an optimal location in a watershed, since lower wetland-to-watershed ratios mean a decrease in nitrogen removal. Lastly, given a choice between two sites with different nitrogen concentrations, the site with the highest nitrogen concentration should be chosen to maximize the mass of nitrogen removed. In general, I find optimal wetland-to-watershed ratios that are smaller than those previously used and reported in the literature and policy reports.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2012

Author dc:creator

• Lentz, Adam

Contributors dc:contributor

• Brozović, Nicholas

• Wetlands
• Nitrogen pollution
• Optimal site selection
• Wetland-to-watershed ratio

Statement dc:rights

• Copyright 2011 Adam Tobias Bank Lentz

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/29694

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/29694