Gull contributions of phosphorus and nitrogen to a Cape Cod kettle pond

Nutrient excretion rates and the annual contribution of P from the feces of the gulls Larus argentatus and L. marinus (and of N from L. argentatus) to the nutrient budget of Gull Pond (Wellfleet), a soft water seepage lake, have been estimated. Intensive year-round gull counts by species were combined with determinations of defecation rate and the nutrient content of feces to quantitatively assess the P loading rates associated with regular gull use of this coastal pond on a seasonal and annual basis. Total P loading from gulls was estimated to be 52 kg yr⁻¹, with 17 kg from L. argentatus and 35 kg from L. marinus, resulting from about 5.0 × 10⁶ h yr⁻¹ and 1.7 × 10⁶ h yr⁻¹ of pond use. This compares with P loading estimates of 67 kg yr⁻¹ from upgradient septic systems, 2 kg yr⁻¹ from precipitation and 3 kg yr⁻¹ from unpolluted ground water. Fifty-six percent of annual gull P loading was associated with migratory activity in late fall. Estimated annual N loading by L. argentatus was 14 kg TKN, 206 g NO₃-N, and 1.85 g g NH₃-N.