Planktonic Primary Production in the Offshore Waters of Dreissenid-infested Lake Erie in 1997

Phosphorus and chlorophyll a (Chl a) concentrations in 1997 decreased from the west basin, which receives most of the lake's nutrient loading, to the central and eastern basins. By contrast, average areal primary production varied little between basins, because higher Chl a concentrations in the west basin were offset by poorer light penetration. Sub-epilimnetic production in the deeper central and east basins, which might be favored by trends to greater water clarity over recent decades, was a minor contributor to total primary production. With additional data from the literature, it was shown that pre-dreissenid Lake Erie produced significantly less Chl a relative to total phosphorus (TP) than did other Great Lakes or smaller inland lakes. Chl a:TP ratios did not change significantly consequent to dreissenid colonization. Despite the continued low yield of Chl a, Lake Erie in post-dreissenid years had areal primary production relative to TP as high as other, dreissenid-free, Great Lake locations and much higher than comparably oligotrophic inland lakes. Absolute concentrations of TP and Chl a have decreased over the decades of nutrient controls and, in the west basin, in parallel with dreissenid colonization. The lake nonetheless remained highly efficient at translating TP into primary production up to 1997, revealing little or none of the depression associated with dreissenid impacts in shallower systems.