Ecological health and causal assessment of fish communities experiencing multiple stressors in Gap Stream, South Korea

Habitat evaluation, water chemistry, fish community data, and a chemical exposure biomarker were used to evaluate the effects of multiple stressors on fish community structure and identify the probable cause(s) of fish community degradation in the Gap Stream, South Korea during May-October 2000. Downstream of a wastewater outfall, there was a decline in the Index of Biotic Integrity of the fish community due to a decrease in the number of native species, an increase in the percentage of tolerant species, and an increase in external deformities and lesions. Five candidate causes of fish community degradation were identified including habitat alteration, chemicals including metals and polycyclic aromatic hydrocarbons (PAHs), low dissolved oxygen, and nutrient enrichment. The results of our causal analysis suggest that chemical contamination, habitat alteration, and nutrient enrichment were the principal probable causes responsible for the degradation of the fish community in the Gap Stream below the municipal wastewater treatment plant.