PREP Publications

Abstract

The Squamscott River has had extended episodes of low dissolved oxygen (DO) that have been recorded at a site near its mouth over the past few years. These episodes were recorded as a result of temporally intensive monitoring by a datasonde, whereas data for the rest of the river has been spotty. Thus, the spatial extent of low DO episodes is not known. This study was designed to better characterize the spatial extent of DO conditions along the full length of the river, as well as to determine nutrient and other water quality parameters along the transect to help understand possible causes of low DO levels. Sampling and measurements were taken on five dates in 2005 and one in 2006. Only one date, August 19, 2005, showed spatially extensive low DO levels. Results on the other sample dates were either acceptable levels or low DO levels were confined to small areas on two other dates. The areas where low DO levels occurred on the three dates were all distinctly different areas of the river, possibly reflecting different causes, tidal transport of low DO waters, or sample timing relative to conducive conditions. The nutrient and chlorophyll a levels at the different sampling sites in the Squamscott River did not appear to have any discernable relationship with DO levels. The Exeter WWTF was a consistently significant source of nutrients to the river, but DO conditions at the outfall pipe were never below target levels. This is not surprising because the oxygen demanding processes that are stimulated by nutrients may not take place immediately at the outfall pipe. Thus, the widespread low DO levels on 8/19/05 downstream of the WWTF may have been caused by discharged nutrients, as well as the more confined low DO levels observed on 8/5/05. Overall, conditions recorded by the datasonde for 2005 showed greatly diminished episodes of depressed DO levels compared to previous years. Future studies should focus first on verifying the spatial extent of conditions that are conducive to depressed DO levels as indicated by existing sonde data. Such spatially and temporally intensive measurements would provide the basis for follow up sampling for nutrient analyses in problem areas and under conducive conditions to discern possible causes of depressed DO.

Publication Date

4-2007

Publisher

New Hampshire Estuaries Project

Document Type

Report

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