An Evaluation of the Contribution of Macro- and Microelements from Colonial Nesting Waterbirds to Surface Water

Macro- and microelements contained in the feces of cattle egrets () and other colonial birds in heronries can be sources of contamination of nearby waterways. Concentrations of the macroelements potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S) and the microelements zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), and boron (B) were measured in water and fecal samples collected from four locations containing heronries during the breeding seasons of 2011, 2012, and 2013. Nitrogen and phosphorus were measured but not reported in this study. Concentrations of K in feces ranged from 8.19 × 10 ± 4.38 × 10 to 4.88 × 10 ± 7.57 × 10 mg kg, and concentrations in water ranged from 3.92 ± 0.05 to 17.93 ± 0.37 mg L. Similarly, concentrations of Ca in feces ranged from 4.17 × 10 ± 1.84 × 10 to 1.16 × 10 ± 4.14 × 10 mg L, and concentrations in water ranged from 25.28 ± 0.89 to 67.88 ± 2.02 mg L. When birds nested directly over water, concentrations of K, Ca, and Mg in water were significantly higher ( < 0.05) than concentrations in water adjacent to birds nesting on islands. The results from this study show that macroelements from avian feces have the potential to enrich surface water and to negatively affect surface water quality. These results provide information regarding the contribution of nutrients from heronries (comprised primarily by cattle egrets) to watersheds.