PELAGIC FOOD-WEB STRUCTURE IN ACIDIC ADIRONDACK MOUNTAIN, NEW-YORK, LAKES OF VARYING HUMIC CONTENT

Pelagic food web models were constructed for 28 acidic (pH < 5.0) Adirondack Mountain lakes, and multiple regression analyses were done to quantify relationships between abiotic variables (DOC, monomeric Al, total P, and H+ concentrations and lake area) and three food web attributes (number of species, number of links, and links per species) Regression models contained log DOC and H+ as significant predictors of food web structure. The models explained over 35% of the variation in species, links and links per species; most of the variation was explained by log DOC. Species, links and links per species increased as DOC increased from <2 to roughly 4 mg . L-1. At higher DOC levels, the food web attributes reached plateaus at 35 species, 120 links, and 4 links per species. The results support the view that in acidic lakes, DOC ameliorates the toxic effects of Al, so that above a saturating DOC level of approximately 4 mg . L-1, Al-sensitive biota can exist in acid waters. Hence, food webs of high DOC acid lakes are larger and more complex than their low DOC counterparts.