Characterization and Comparison of Stream Nutrients, Land Use, and Loading Patterns in Maryland Coastal Bay Watersheds

Abstract

Land use and its relation to nutrient concentrations and loading via streams is an important issue in coastal lagoons and embayments worldwide including the Maryland coastal bays system, USA. As in many coastal areas around the globe, declining water quality in the bays is the result of nutrient inputs from the surrounding watershed. In this study, the sources of the nutrient inputs were examined. Monthly concentrations of total nitrogen (TN), ammonium (NH4+), nitrate (NO3-), phosphate (PO4-3), and total phosphorus (TP) were measured in six streams in the St. Martin River basin from July 2006 to January 2008. Current land use information for the basins of each stream was also compiled. Several significant correlations between nutrients and land use type were found. The most significant correlation was with the land area of feeding operations, which demonstrated a significant positive relationship with mean baseflow TN concentrations. A similar relationship was also found with anthropogenic land area (cropland + urban + feeding operations), and wetland area was also positively associated with hydric soils. Using local water yields from a US Geological Survey station, annual stream watershed export was calculated using the concentration data, which indicated that the watershed with the most crop agriculture had the highest N export coefficient (20.4 kg N ha-1 year-1), while the highest P export (0.47 kg P ha-1 year-1) was in a watershed containing a nonoperational chicken hatchery and a subsequently modified channel. This suggests that agricultural development, especially animal feeding operations, and landscape characteristics are important factors to understand nutrient loading in St. Martin River and Maryland coastal bays. The methods used and the results determined in this study have implications for determining nutrient loading in lagoons and embayments, in relation to land use in coastal regions globally.