Rainfall Effects on Bacterial Contamination, a Clam Purging Study and a Monitoring Plan

摘要

Monitoring Plan has been drafted that includes six chapters focusing on issues determined to be of most significance for the NHEP. The structure of the chapters includes a review of existing monitoring programs, identification of monitoring gaps, and a list of monitoring objectives for each issue. Each objective is then delineated in terms of performance criteria, hypothesis testing, sampling locations, statistical methods and analytical methods. Text, summary tables, and responses to review comments have been completed. The Jackson Estuarine Laboratory analyzed samples collected by NHEP/NHDHHS staff and volunteers from the shoreline of the Atlantic Coast, Isles of Shoals, Hampton Harbor and Little Harbor of New Hampshire. The samples were collected for determining shoreline sources of fecal contamination as well as more directed sampling of culverts in Hampton Harbor. Samples were analyzed for fecal coliforms, E.coli and pH. The results were routinely sent to NHEPINHDHHS staff to enable follow up investigations of sources and to direct further sampling efforts. In all, 232 analyses on 116 samples collected from culverts in Hampton Harbor, 54 analyses on 27 samples collected from the Atlantic Coast and the Isles of Shoals, and 54 analyses on 27 samples from Little Harbor were conducted, for a total of 340 analyses. In addition to fecal coli forms and pH, Escherichia coli counts were determined on all samples, and the salinity was recorded for some samples. E.coli counts were included as a check on the relationship between fecal coliform levels and the levels of the target organism of the fecal coliform test: E. coli. Many of the bacterial concentrations were >5001100 mI, reflecting the success of the sampling strategy to identify pollution sources. Rainfall events caused elevated concentrations of bacteria in culverts and in Little Harbor, where contaminant concentrations then decreased to low levels soon after the event. The response of clams following storm-related contamination events in the field were mixed. There was no clear demonstration of purging of bacterial contaminants in clams up to four days after storm events at both Middle Ground and Common Island. Other contamination events that occurred during the studies could have complicated interpretation of the results. More studies could provide better conditions for determining how long clams need to be exposed to clean water after a storm event in order to purge bacteria to lower levels.