Long-Term Temporal Water-Quality Trends within the Barnegat Bay Watershed, New Jersey

This regional water-quality assessment compiles and analyzes water-quality data within the Barnegat Bay watershed (Ocean County, New Jersey) to determine if significant changes and trends occurred over decadal spans. Data evaluated spanned from the 1970s through July of 2013. Trends were evaluated after regionalizing sampling locations into 17 geographic zones. Over 1700 sampling stations within freshwater and Bay zones provided over 280,000 data results for 20 parameters. The parameters evaluated include: temperature, salinity, dissolved oxygen (DO), pH, nutrients, indicator bacteria, and solids. Temperature data comparing the 1970s with the present show statistically significant increasing trends in 13 of 17 zones during the summer months. Seven of those zones also saw increasing temperatures in at least one other season. Increasing trends were also seen for salinity in 8 of the 10 estuarine zones for two or more seasons. Potentially related to the increasing trends in salinity and temperature, DO concentrations were often decreasing or unchanged. Significant decreases in DO concentration can be seen in 12 of the 17 zones for one or more seasons. The pH was shown to be increasing in 10 of the 17 zones during one to four seasons. Four zones experienced a decreasing trend in pH, but only during one to two seasons. The interpretation of the nutrient data over this long time period proved to be a challenge, with multiple species of nitrogen and phosphorus reported but often with insufficient data to draw significant conclusions. Where data were sufficient, nutrient results were mixed, with many zones showing no changes in trends.