Excessive nutrient loading from watersheds causes nutrient enrichment and water quality issues in very small streams to large rivers. Nutrient enrichment is exacerbated by urbanization and agricultural land use; however, the magnitude of the problem differs by regional landscape and environmental characteristics. Currently, we do not understand how regional variables moderate these relationships. Thus, the overall objective of this thesis was to investigate how regional landscape and environmental variables moderate developed land cover–stream nutrient relationships across the United States. The first study examined how climate and land use influences the scaling of phosphorus, total nitrogen, ammonia and nitrate loads for very large regions (Mid-Atlantic, Upper Mississippi, Ohio and Missouri) of the U.S. Results show the scaling relationships of nutrient loads with watershed size depends on the nutrient species and differed by region; the magnitude of the relationships was greater in wetter climates and developed watersheds. The second study determined 1) whether the relationships between urban and agricultural land cover intensity and concentrations of phosphorus, total nitrogen, ammonia and nitrate across the U.S., differed by ecoregion, and 2) whether regional landscape and environmental factors explained those differences. The relationships were found to differ by ecoregion and the differences were moderated by regional agriculture, topography and climate where stream nutrients increased more rapidly with anthropogenic land use in regions with high agricultural land use, wetter climates and flatter topography. The study findings will enable water quality managers create region-specific water management strategies for streams impacted by excessive nutrient loads. / Master of Science / Several factors affect the loading and concentration of nutrients, which in high amounts cause harmful algal blooms in streams. The size of watersheds and the level of urban and agricultural land use influence how much nutrient is added to streams. The main goal of this study was to determine how the effect of watershed size and urban and agricultural land cover on stream nutrient loading and concentrations, respectively, are controlled by particular environmental variables, such as climate, topography and land cover. To understand these effects, phosphorus, total nitrogen, ammonia and nitrate concentrations and loads were analyzed using statistical models. In the first study, the degree to which nutrient loading is affected by watershed size in four regions of the U.S. (Mid-Atlantic, Upper Mississippi, Ohio and Missouri) was assessed. The study found that the effect of watershed size on nutrient loading depended on the nutrient type and differed by region, and nutrient loads were greater in wetter climates and watersheds dominated by human activities. In the second study, regional differences in the effects of urban and agricultural land on nutrient concentrations was assessed. The study found that the effects of human land use differed by region and that these effects were greater in wetter, flatter regions, and those with a high degree of agricultural use. This study facilitates understanding and identification of important regional factors that regulate water quality in streams and therefore, will facilitate region-specific water management strategies for streams impacted by excessive nutrient loading.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106543 |
| Date | 14 May 2020 |
| Creators | Ogunmayowa, Oluwatosin Thompson |
| Contributors | Crop and Soil Environmental Sciences, Steele, Meredith K., Stewart, Ryan D., Sample, David J. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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