In 2018, we collected mussels from a total of 100 sites throughout Casco Bay and analyzed for nitrogen isotope ratios in their tissues to map out regions with higher levels of human-associated nitrogen (download the full report below for a more detailed explanation of nitrogen isotopes).
Green areas on the map indicate higher values of human-associated nitrogen (e.g., from sewage, septic, and livestock sources), whereas the blue regions represent values more consistent with natural nitrogen sources. Mussels are like continuous monitoring devices, as the nitrogen isotope values in their tissues may reflect weeks to months of average feeding conditions in one place. Other nitrogen monitoring activities may only provide temporal snapshots of nitrogen levels in just as wide of a geographic range. More traditional continuous monitoring methods use sophisticated sampling devices, or sondes, and are typically too costly to deploy over broad areas.
As of now, our nitrogen loading map doesn't necessarily indicate a nitrogen problem in any one location. Rather, our approach is intended to direct more targeted sampling strategies. We plan to repeat our sampling effort in Casco Bay in 2020 to reconstruct maps similar to those produced in 2018, but over longer periods of time. We will also expand sampling to Penobscot Bay to provide baseline data for any changes from land use practices in the area.
2018 Mussel Isotope Monitoring Report
In 2018, we collected mussels from a total of 100 sites throughout Casco Bay and analyzed for nitrogen isotope ratios in their tissues to map out regions with higher levels of human-associated nitrogen.
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