Changing agricultural practices: potential consequences to aquatic organisms

Area of Science:

• Environmental Science
• Ecotoxicology
• Freshwater Ecology

Background:

• Agricultural intensification, characterized by increased herbicide use and animal waste application, threatens freshwater biodiversity.
• Significant declines in fish and mussel populations have been observed in the Upper Conasauga River watershed over the past two decades.
• These declines coincide with prevalent agricultural practices in the region.

Purpose of the Study:

• To investigate the potential impact of agricultural practices on freshwater species populations in the Upper Conasauga River.
• To assess water and sediment quality for key agricultural contaminants, including glyphosate, metals, nutrients, and hormones.
• To correlate water and sediment chemistry with observed declines in aquatic biota.

Main Methods:

• Surface water and sediment samples were collected across the Upper Conasauga River basin.
• Samples were analyzed for glyphosate, aminomethyl phosphonic acid (AMPA), metals, nutrients (nitrate, phosphorus), and steroid hormones.
• Chronic toxicity tests were conducted using Ceriodaphnia dubia and Hyalella azteca.
• Water and sediment contaminant concentrations were compared to established impairment and toxicity levels.

Main Results:

• Few water or sediment samples exhibited toxicity, and metal concentrations were generally below impairment levels.
• Glyphosate was undetected, but its degradation product, AMPA, was prevalent in 77% of water samples and most sediment samples.
• Widespread nutrient enrichment (nitrate and phosphorus) exceeded eutrophication thresholds.
• Sediment hormone concentrations frequently surpassed levels known to cause endocrine disruption in fish, suggesting impacts from animal waste application.

Conclusions:

• Agricultural practices contribute to the degradation of freshwater ecosystems in the Upper Conasauga River.
• Elevated nutrient levels, potential herbicide surfactants (inferred from AMPA), and sediment-bound hormones are implicated in the observed declines of fish and mussel populations.
• Further research is needed to fully elucidate the complex interactions between agricultural contaminants and aquatic ecosystem health.