Process-Based Modeling of the Dairy- McKay Watershed to Inform Monitoring for Agricultural Best Management Practices


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Process-Based Modeling of the Dairy- McKay Watershed to Inform Monitoring for Agricultural Best Management Practices is a well-researched Physical Sciences and Mathematics Thesis/Dissertation topic, it is to be used as a guide or framework for your Academic Research.


The project described in this paper specifically looks at the influence of land management practices on water quality, specifically total phosphorus (TP) loads in the Dairy McKay Watershed (DMW). The project is being used to inform a water quality monitoring plan for the Oregon DEQ via outputs from a SWAT model.

The DMW is known to have high TP levels that are linked to low dissolved oxygen levels in the Tualatin River. There is a total maximum daily load (TMDL) for the Tualatin River that specifies target TP levels coming out of the DMW, if met these targets are met, the DO levels should remain acceptable for aquatic life in the Tualatin River.

As there is little current water quality data within the DMW, it is difficult to identify where the high levels of TP are located and where they can be reduced. The DMW-SWAT model outputs were analyzed, via Linear Regression analysis, to gain a better understanding of which stream segments are most sensitive to TP loading, based on their land use and management. These sensitive stream segments are recommended as future monitoring locations for continuous water quality data in the DMW.


1.1. Point and Nonpoint Source Pollution A combination of societal and environmental factors places increasing pressures on local, regional and national water supplies. Adequate water provisions are required for energy and industrial
production, agricultural and domestic purposes, as well as protecting ecosystem services (Abbaspour et al., 2015).

While the quantity of water constitutes one critical aspect of water demands, the quality of water also has an important role. In developed areas, water systems can become contaminated with excessive nutrients, sediments, heat, heavy metals, and other chemical pollutants. Elevated concentrations of any of these contaminants can impair human and/or environmental health.

Therefore, it is important for regulatory authorities to improve the understanding of sources and loading rates of pollutants, a critical step in both restoring and managing water quality and quantity in watersheds. Water supplies can be contaminated via either point or nonpoint sources (NPS). Point sources are identifiable as direct sources of contamination to water sources, such as sewage outfalls or industrial waste outlet (EPA, 2018).

In Oregon, the Department of Environmental Quality (DEQ) regulates point source discharge through permits as required by the federal Clean Water Act (CWA), established in 1972. The CWA makes it unlawful to discharge any pollutants from a point source into navigable waters unless a National Pollution Discharge Elimination System (NPDES) permit is attained (EPA, 2018).

This permitting system, controlled at the state level, allows Oregon’s DEQ to regulate any industrial, municipal, or other facilities that discharge to surface waters. From its formation in 1938 to the development and implementation of NEEDS permitting, DEQ’s focus was assessing and controlling major point sources of pollution.

This consisted of addressing and limiting the sources of pollution, implementing wastewater treatment plants, and implementing water quality monitoring networks to document trends in water quality (ODEQ, 2005). Although point source pollution was the original focus of DEQ efforts, NPS pollution resulting from broad land-use practices and urban development has been increasingly recognized as critical for water quality management.

Uncovering the associations between land use and water quality is useful for managing land-based pollution (Zhou et al., 2016). Identification and regulation of NPS can be difficult, sourced mainly from land management activities without an immediate known, identifiable source.

NPS pollution tends to vary across study areas, particularly among watersheds that have various land uses (Huang et al., 2015). NPS pollution results from contamination during precipitation run-off, atmospheric deposition, leaching, or
erosion and is associated with practices in urban, forestry, and agricultural land management (Vymazal and Brezinova, 2015). Agricultural activities, such as fertilizer and pesticide application, are recognized as important factors influencing water quality (Smith et al., 2013).

As water moves through landscapes, via runoff or underground flow, it picks up and carries contaminants to finally deposit them in surface or ground waters, making for the difficulty in identifying the source of contamination (EPA, 2018). NPS pollution is recognized globally as a key factor responsible for waterways degradation (Fraga et al., 2016).

The Environmental Protection Agency National Water Quality Inventory indicates that NPS pollution is the major factor preventing the achievement of water quality goals in the United States (Bekele and Nicklow, 2005).


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