The increasing level of turbidity observed in Salem Harbor and its possible link to concomitant degradation of eelgrass beds is an increasing cause for concern for the ecological health of the Salem Sound embayment. Salem State University explored the possible causes of these turbidity events in this project. From May to December 2012 continuous water quality monitoring was conducted at five buoy monitoring stations in Salem Harbor. Surface and bottom temperatures, conductivity, turbidity, water level, and meteorological data were measured to test four specific hypothetical causes for increased turbidity: wind events, runoff events, tidal currents, or phytoplankton increases.
Seasonal increase in phytoplankton appears to dominate the turbidity data during the summer months, overwhelming potential signals from the other causes. Wind events appear to initiate turbid conditions during periods in which winds are high and shifting. Although the linkage between wind and turbidity is likely due to boats shifting on their moorings, results after most boats were removed in the fall suggest that other processes, such as shallow water wave resuspension may provide an additional mechanism. Weak linkages were observed between precipitation and turbidity, suggesting that runoff may provide particulate matter to the harbor. The absence of a correlation between tidal currents and turbidity suggests that tides may not be a cause of significant turbidity in Salem Harbor. Seasonal stratification of the water column in deeper sites complicates resuspension dynamics.
Details of the study as well as management recommendations and next steps are provided in the final report. Hubeny, J. B. 2012. Determining the Nature and Causes of Turbidity Events in Salem Harbor (MA) Through Estuarine Water Quality Monitoring. Salem State University. file size 3MB
Further monitoring of particulate matter in Salem Harbor is recommended in order to further refine the results and interpretation. Due to the apparent importance of organic productivity to turbidity dynamics in Salem Harbor the team recommended that further study to characterize the particulate matter that is suspended in the water column. Funding secured by the Mass Bays Salem Sound regional partner, Salem Sound Coastwatch, from the Massachusetts Environmental Trust (funding 2013 – 2014) was used to further refine the data.