Figure 4 . Map of the 20-year FC trends for all 466 water quality stations (points) along North Carolina’s coast alongside the developed change percentage of the HUC12 watershed areas (purple fill). The points representing the water quality station FC trends are colored by the τFC value with the red and orange colors illustrating the positive trends in FC concentrations while the green and blue colors indicate a negative trend in FC concentrations. These points are also sized by the magnitude of their βFCvalues (i.e., larger points represent steeper slopes in the FC trends and smaller points represent more gently sloping FC trends). The light purple watershed areas represent smaller proportions of developed land increase whereas dark purple areas represent a more intense increase in developed land proportions from 2001 to 2019; white, unfilled areas between watersheds correspond to watersheds that do not directly connect to a waterway. This map was created in R version 4.1.0 with ‘sf’ version 0.9 package.
The Pearson correlation coefficients for the water quality and environmental trends along the full coastal area are summarized in Table 1. These correlations include the relationships between τFC, βFC, τSal, βSal, τPrecip, βPrecip, developed land percentage, barren land percentage, wetlands land percentage, vegetated land percentage, cultivated land percentage, and distance to shore. We observed a clear negative relationship between both τFC & βFC and τSal& βSal (r values from -0.281 to -0.304). There was a weak positive relationship between βFC and τPrecip & βPrecip. The positive relationship between τSal & βSal and all land use classifications with wetlands had the strongest positive coefficients (r = 0.393 and r = 0.401, respectively). Distance to shore was weakly correlated with overall FC trends.