Nutrients in precipitation and the phytoplankton responses to enrichment in surface waters of the Albemarle Peninsula,NC, USA after the establishment of a large-scale chicken egg farm

Nitrogen (N) and phosphorus (P) released in waste from animal feeding operations can stimulate phytoplankton biomass production in local receiving waters. Changes in weekly wet atmospheric N and P were measured from 2005 to 2008 at monitoring stations located 0.8, 7.9, and 10.3 km downwind from a new chicken egg production facility on the Albemarle Peninsula, North Carolina. After this farm began operating, there was a significant doubling in mean wet NH₄ ⁺ concentrations (465–1,022 μg l⁻¹) at 0.8 km with no change at the other sites. To measure the phytoplankton responses to nutrient enrichment, we conducted seasonal N and P enrichment bioassays from 2006 to 2008 on nearby Phelps Lake and Alligator River. These low-nutrient waters responded to nutrient additions, with the highest increases in phytoplankton primary productivity (¹⁴C uptake) and biomass (chlorophyll a) occurring in the combined N and P treatments suggesting co-limitation of N and P. Although we did not find an increased nutrient signal in precipitation at sites >0.8 km from the farm, there is the potential for atmospheric deposition of N to these and other waters located N/NE of the farm given prevailing winds and distance that NH₄ ⁺ aerosols can travel. Furthermore, surface runoff from the farm may impact receiving waters downstream (e.g., Pungo and Pamlico Rivers). In order to prevent excessive phytoplankton productivity and biomass both N and P inputs should be carefully assessed and potentially controlled in these nutrient-sensitive waters.