Water quality monitoring in response to young-of-the-year smallmouth bass mortality in the Susquehanna River Basin, Pennsylvania

Mortalities of young-of-the-year smallmouth bass were observed in the Susquehanna River basin in the summers of 2005, 2007, and 2008.  Although relations among water-quality, streamflow, and fish mortality in the Susquehanna are poorly understood, elevated water temperature and low dissolved oxygen are suspected stressors, especially during times critical for development of smallmouth bass (May 1-July 31).

In 2008-09, environmental conditions in nursery microhabitats (microhabitats) and main-channel habitats were compared by measuring dissolved-oxygen concentration and water temperature twice hourly. During critical months of 2008, daily minimum dissolved-oxygen concentration was significantly lower in microhabitats than the nearby main channel; dissolved oxygen in microhabitats fell below the national criterion of 5.0 mg/L on 20-30% of days in the critical months. Dissolved-oxygen concentration in 2008 was 1-2 mg/L less than 2009 for both habitats owing to streamflows twice those of 2008. Water temperatures were warmer in 2008 and in both years were closely correlated with sun exposure rather than habitat type.

Data from 2008-09 indicate microhabitats are more stressful than the main channel. Comparing dissolved-oxygen and water-temperature data from the Susquehanna River to data from the Delaware or Allegheny Rivers indicates fish in the Susquehanna are most likely to experience stress from these factors.