Distribution of inorganic nitrogen and phosphorus concentrations in stream flow of two Southern Piedmont watersheds

Innate distributions or variability of nutrient concentrations within the fluvial system must be better understood to establish nutrient guidelines that are applicable and to discern which areas or landscape positions within the watershed are more vulnerable to nutrient losses. This work was conducted to (1) determine the system-wide spatial distribution of N and P concentrations in biweekly stream samples from two Southern Piedmont watersheds, and (2) determine the relationship between N and P concentrations in biweekly samples and watershed morphological features. From December 1998 through December 2000 samples were collected biweekly from 17 sampling sites located on Rose Creek and from 18 sampling sites located on Greenbrier Creek. The samples were analyzed for ammonium (NH4), nitrate (NO3), and dissolved reactive phosphorus (DRP) concentrations. We found that spatial autocorrelation of nitrate concentrations was evident and that some spatial autocorrelation of DRP concentrations was also present. We further found that the fluvial network morphological feature, drainage density, explained part of the spatial autocorrelation found for nitrate but did not for DRP. These results indicate that innate variability of nutrient concentrations within streams exists and suggest that decision makers should begin to consider location within the watershed when making nutrient management guidelines and decisions.