We chose locations that spanned water quality that ranged from good to impaired based on past data from the Buzzards Bay Coalition’s Baywatchers water quality monitoring program. The goals were to: (1) detect hourly and daily changes to dissolved oxygen that can’t be detected by traditional grab sampling of water; (2) identify the magnitude and duration of periods of low water low water quality that we likely miss with traditional grab sampling; and (3) gain experience with dataloggers that will help us plan for deployments of more dataloggers across Buzzards Bay in the future.
Map of locations of oxygen and salinity datalogger deployments in Buzzards Bay during the summer of 2024.
The dataloggers are made by Onset Computer Corporation and recorded temperature, salinity, and dissolved oxygen every 10 minutes from May through October. The high frequency readings allowed us to track how dissolved oxygen changes throughout the day with sunlight, wind, and tides, as well as see how water quality changes over the summer.
For example, station OB2 in outer Onset Bay and Station BD1 in inner Onset Bay had relatively similar dissolved oxygen in May and June but dissolved oxygen was regularly much lower in the inner Bay in July and August. Stations with lower overall water quality and greater abundance of algae such as BD1 also had much greater daily fluctuations in oxygen levels. As we gather more data and deploy dataloggers in more places, we will compare the data collected with the dataloggers with the data from continued traditional grab sampling. This will help us develop relationships between the continuous data and our historical grab sampling, such as the frequency of low-oxygen periods that grab sampling traditionally missed. It may also help us develop new metrics for water quality, such as the magnitude of oxygen fluctuations, that could provide more sophisticated metrics of water quality.
Plot of dissolved oxygen concentrations at two stations in Onset Bay during the summer of 2024. Station BD1 is farther inland in the embayment and measured much greater daily variations in dissolved oxygen. The fine-scale pattern over two days in late July is shown in the inset.
Although the dataloggers allow us to gather much more data, they still need maintenance. Researchers from the COMBB project visited each datalogger weekly to check on the dataloggers, clean them, and download data. We learned that this frequent cleaning ensures the quality of the data.