The Role of Long-Lived Zooplankton Diapausing Eggs Response and Recovery of Impacted LakesEPA Grant Number: R824771
Title: The Role of Long-Lived Zooplankton Diapausing Eggs Response and Recovery of Impacted Lakes
Investigators: Hairston Jr., Nelson G. , Mills, Edward L.
Institution: Cornell University
EPA Project Officer: Packard, Benjamin H
Project Period: March 1, 1996 through February 1, 1999
Project Amount: $350,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water
Description:The response of freshwater ecosystems to anthropogenic perturbations depends in part upon the kinds of organisms already present. This is true whether the perturbation is detrimental (e.g., introduction of toxicants, changing temperature, or invasion by exotic species), or a recovery after remediation. For plankton, the single most significant source of organisms often lies in the millions of dormant eggs, cysts and spores residing in the lake sediments. Although these stages survive in sediments for decades or even centuries, and thus store a live sample of past ecological communities and processes, they are little studied and their responses to perturbation practically unknown.
The relationships between the density of zooplankton diapausing eggs and the concentration of heavy metals in the sediments of two lakes in New York State are under investigation. One, Onondaga Lake, has a history of substantial pollution; the other, Oneida Lake, has a cleaner record. Both lakes have experienced significant changes in their zooplankton communities over the past three decades. Diapausing (dormant) egg densities are being quantified as a function of sediment depth, and as a function of sediment location within the lake basins. The statistical relationships between egg density and viability on the one hand and heavy metal concentration (especially mercury) on the other are being determined. Egg hatching rates will be compared with the water-column zooplankton population dynamics. Field and laboratory experiments on the effects of sediment mixing quantify the enhanced effects of sediment disturbance (e.g., lake dredging) on hatching rate. Comparisons of cladoceran microfossil densities with densities of viable eggs and empty egg cases, in dated cores, will be used to infer past histories of egg production and water-column recolonization.
During the first year of funding, analyses of sediment cores from Onondaga Lake show substantial zooplankton species replacement during the period of peak pollution (1960s to mid-1980s). Diapausing eggs have been isolated and many are viable and have begun to hatch, despite burial in sediments containing mercury concentrations in excess of 50 µg g-1. One remarkable discovery is the appearance in high densities of Daphnia similis during the period of peak pollution. This large species has only previously been reported from salt lakes west of the Mississippi River. D. similis was apparently able to survive in Onondaga Lake as a result of the salt brine deposited in the lake by industry. How it colonized is unknown.
Can eggs buried in sediments be returned to the sediment surface and hatch? What is the role of sediment disturbance in this process? A field experiment in Oneida Lake during the past summer showed that sediment mixing significantly enhanced hatching of Daphnia diapausing eggs.
Through this study we are gaining insight into the role played by long-lived diapausing eggs in the responses of lakes to perturbations. The information and approaches provided by this study will help in predicting and tracking the recovery of impacted lakes after remediation actions have been taken.