PELAGIC FOOD-WEB STRUCTURE IN ADIRONDACK MOUNTAIN, USA, LAKES OF VARYING ACIDITY

Pelagic food web models were constructed for 50 softwater lakes of varying acidity (pH 4.17-7.32) in the Adirondack Mountains, and relationships between food web parameters and several abiotic variables (pH, monomeric Al, dissolved organic carbon (DOC), z(max) and area) were quantified. With declining pH, pelagic food web complexity was reduced, as the number of species, links, links per species, predator generalization, and prey vulnerability all declined. The declines were less pronounced in lakes having high DOC levels. Some web parameters, including the predator/prey ratio, the portion of basal, intermediate and top species, and species redundancy, did not decline with pH but were more variable among the acid lakes. Those trends are consistent with the view that at low pH, toxicity becomes the major factor controlling community structure.