Urbanization increases runoff, sediment, and nutrient loadings to freshwaters, causing flooding, harmful algal blooms, and increased costs for drinking water filtration. Most watershed models use runoff quality data from specific land uses; coupled with a variety of methods for quantifying loads, the most common being Build-up and Wash-off (BUWO) equations for which loading is a function of antecedent dry period (ADP). However, several studies have shown there is no significant correlation between urban runoff quality and ADP, suggesting predictions based solely on landuse and ADP are questionable. The objective of this study is to discover which parameters, climatological or catchment characteristics, are most significant and should be included in the BUWO relationship. Stormwater quality data was obtained from the National Stormwater Quality Database (NSQD), which is the largest and most recent database of its type in the U.S. Bayesian Network Structure Learner (BNSL) was used to assess the relationships between catchment characteristics, climatological information, and runoff quality for each land use. Given the optimal BN structure, it was determined which parameters affect water quality event mean concentrations the most, and which the least. The results demonstrated that for some constituents (i.e. particulate nitrogen, particulate phosphorous, and sediments), other factors (such as rainfall depth and duration, surface slope) exert a more important influence on urban runoff quality than ADP.

Sunlight plays an important role in regulating the nutrient cycle in streams. Throughout the years, more streams are buried to accommodate for residential or commercial facilities. This results in severe impacts on the health of streams due to altered exposure to sunlight, air, and soil; it subsequently affects the growth of aquatic and riparian vegetation, thus impairing the water quality of streams. Although urbanization effects on urban surface streams are well understood, the adverse effects of burying streams on dissolved oxygen (DO), reaeration, photosynthesis and respiration processes have been mainly remained theoretical. This study evaluated the effect of stream piping on DO for two sections of Stroubles Creek in Blacksburg, VA through comparing the water quality prior to entering, and post exiting the buried sections of the Creek. Monitoring DO was conducted through manual readings and continuous measurement for a number of days in Fall 2015 and 2016. The results indicated that the water DO level decreased by approximately 11% as water flowed through the buried sections. The covered section of the stream also caused variability of the water temperature, resulting a possible disturbance to the downstream ecosystem. The buried channels-induced DO variations effects on the Brook Trout (Salvelinus sp.), a sensitive species present at the Stroubles Creek headwaters was also assessed. Further, the photosynthesis rate, reaeration coefficient, and daily respiration rate were computed prior and after one of buried channels through a series of mathematical and empirical approaches to assess the buried channels effect on the aforementioned parameters. The photosynthesis and respiration rates were reduced at the inlet compared to outlet, primarily due to less solar radiation and aquatic vegetation oxygen uptake, however, reaeration rate was increased at the outlet compared to inlet. This study can assist the decision makers and resource planners in taking the appropriate decisions regarding daylighting stream channels to improve water quality or/and accommodate increasing demand for urbanization.