Effect of Sublethal Concentrations of Agricultural Herbicides on the Structure and Function of Estuarine Phytoplankton Communities
James L. Pinckney and Jean Marie Buschur
South Carolina Sea Grant
March 2006 - February 2007
Objectives:
To determine the short-term sublethal effects of environmentally-relevant concentrations of atrazine (under high and low nutrient concentrations) on estuarine phytoplankton community structure and function. The specific hypotheses that will be tested are
a. Short-term exposure of estuarine phytoplankton to low atrazine concentrations (1.00 µg liter-1) under low nutrient conditions promotes shifts in the relative abundance of phytoplankton taxonomic groups and species and a reduction in primary productivity.
b. Under high (non-limiting) nutrient conditions, the effects of sublethal concentrations of atrazine (1.00 µg liter-1) on phytoplankton biomass, community composition, and primary productivity are less severe (i.e., are significantly different) than the effects under nutrient-limiting conditions.
c. Trace concentrations of atrazine (0.10 µg liter-1) have no effect on estuarine phytoplankton biomass, community composition, or primary production.
Tasks and Methodology:
Short-term Phytoplankton Bioassays will be used to measure initial phytoplankton responses to different levels of atrazine and nutrient exposure. The purpose of these experiments is to determine the effects of a range of atrazine/nutrient concentrations on phytoplankton primary productivity and biomass of specific algal groups (i.e., diatoms, cyanobacteria, dinoflagellates, cryptophytes, etc.) in natural estuarine phytoplankton assemblages. These data will be used to assess "who" responds to the different levels of atrazine treatments under ambient (light, nutrient, temperature, etc.) conditions. This experimental approach is critical for understanding the mechanisms underlying phytoplankton community responses and dynamics in estuarine ecosystems.
Rationale:
Habitat alteration and loss of biodiversity due to pesticide contamination is rapidly emerging as major ecological threat for wetland and estuarine ecosystems. In aquatic ecosystems, phytoplankton are usually the most atrazine-sensitive biotic components. The proposed research will directly address SC Sea Grant Strategic Goal 3 under the Priority Topic "Investigations of the cumulative effects on key indicator marine organisms of low level, sub-chronic exposure to chemical contamination due to increasing human activities". In this project, the key indicator species will be phytoplankton and the ecological indicators will be phytoplankton community composition and primary productivity. The chemical contaminants will be a common herbicide (atrazine) in waters entering many South Carolina estuaries, growth-limiting nutrients (nitrate & phosphate), and the interactive effects of atrazine and nutrients to simulate pulsed river discharge events.