ENVIRONMENTAL AUDITING: Impoundment Productivity in the Prudhoe Bay Oil Field, Alaska: Implications for Waterbirds

/ To evaluate impoundments as habitat for waterbirds, we compared impoundments and natural ponds in the Prudhoe Bay oil field, Alaska, from 1991 to 1993, with respect to macroinvertebrate productivity, phytoplankton biomass (chlorophyll a), and nutrient availability (phosphorus and nitrogen). High variability in these limnological characteristics, particularly among impoundments, obscured potential differences between impoundments and ponds. No significant differences were found in chlorophyll or nutrient concentrations, and in only two cases were there differences in invertebrate production: gastropods were significantly more abundant in impoundments than in ponds in June, and trichopterans were significantly more abundant in impoundments than in ponds in July. For comparisons within impoundments and ponds, there were significant differences in invertebrate abundance between habitats and between wetland types. For example, plecopterans, trichopterans, and gastropods (all taxa combined) were consistently more abundant in shallow-Arctophila impoundments and ponds than in shallow-Carex impoundments and ponds. Thus, ponds and impoundments may differ significantly in invertebrate production, but we lack information on the amount of different habitat types (i.e., center versus emergent vegetation, Carex versus Arctophila) used by these taxa within each water body type. It is a reasonable speculation, based on results of this study, that impoundments and ponds may have similar value as feeding habitat for invertebrate-eating waterbirds. Thus the presence of impoundments may be consistent with waterbird management goals on the Arctic Coastal Plain.KEY WORDS: Arctic impoundments; Production; Macroinvertebrates; Nutrients; Phytoplankton; Impact assessment