Understanding Aquacultured Bivalve Growth and Climate Change Impacts in the Damariscotta River using a Coupled Modeling Approach

Project Description

The Damariscotta River has been a successful oyster aquaculture area since the mid-1980s with other bivalve aquaculture beginning in the river in more recent years. Due to its unique bathymetry, the Damariscotta River forms three basins with dramatically different conditions; water temperature differences can be as much as 10 °C between the upper basin and the mouth of the river. This difference creates opportunities to grow species that have maximum growth rates in different conditions within the same system (i.e. oysters and mussels). This makes the Damariscotta an ideal estuary to study in regards to understanding the driving factors of bivalve growth and how growth might be impacted by environmental variations due to climate change. Research can also help personnel learn to assess how much bivalve aquaculture the River can support.

This analysis was conducted using two different models: a hydrodynamic model and a biogeochemical model. The models are being calibrated and validated using historic data, data collected by the SEANET buoys, and discreet water sampling and conductivity, temperature, depth (CTD), and acoustic Doppler current profilers (ADCP).

Phase 1 of the project was to build a model domain. In order to capture accurate flow of the Western Maine Coastal Current (WMCC) and offshore buoys, the model domain included the offshore area between western Penobscot Bay to the area between the Kennebec and New Meadows Rivers. Five rivers are also included in the domain, with highest resolution in the Damariscotta River (Kennebec, Sheepscot, Medomak, and St. Georges River).

Phase 2 included implementation of the FVCOM model for this domain. A summary of this project is provided in the Hydrodynamic Modeling of Saco-Casco Bays, the Damariscotta River and Eastern Maine section of this document.

Phase 3 began once the FVCOM model was fully operational (2017). Preliminary runs were conducted for the 2016 growing season. The data from the model that pertain to the Damariscotta River has been extracted and used as input to the biogeochemical model – Row-Column Aesop (RCA). This model has been widely used as a water quality model because it includes parameters pertaining to chemical cycling of nutrients, oxygen, phytoplankton, grazers, and a sediment flux model. This model was run on the same mesh (for the Damariscotta River only) as the FVCOM model and will be used to understand how the nutrients, primary production, and grazing function in this river, and to understand how bivalves grow efficiently in this area. The RCA model was calibrated and validated using the data from the two land/ocean biogeochemical observation (LOBO) buoys located in the Damariscotta River and the data from the bi-weekly water sampling.

Phase 4 will begin once both models are complete. Project personnel will run climate change scenarios reflecting future Gulf of Maine temperatures, increased fresh water run off (which will decrease pH), and increasing sea level. Researchers will monitor how these changes affect estuarine circulation. These scenarios will help researchers understand how bivalve aquaculture in the Damariscotta might change in the future, and what it means in terms of resource management. The modeling approach will help identify the largest growth drivers, which can be used to locate potentially high growth sites in other areas along the coast.

Results and Accomplishments

Over the last year, climate projections capable of providing highly spatially resolved estimates of future conditions in the Gulf of Maine have taken major strides. For example, NOAA’s Geophysical Fluid Dynamics Lab (GFDL) has recently significantly increased the spatial resolution of the Climate Modeling Intercomparison Project (CMIP 2.6) to include the northwest channel, which influences the model to be more responsive to the influence of the Gulf Stream on the temperature of the Gulf of Maine. Researchers analyzed output from this model and created new boundary conditions for SEANET’s nearshore models. One key finding informing these efforts is that the Eastern Maine Coastal Current (EMCC) is projected to warm faster than the Western Maine Coastal Current (WMCC), due to processes mediated by nearshore mixing (EMCC is well mixed and the WMCC is highly stratified). The implications of differential warming on temperature sensitive aquacultured species will be explored in the next year.

Summary of Data Being Collected

Data Type Quantity Location
Buoy Observations at 1m: temperature, salinity, dissolved oxygen, pH, chlorophyll-a, CDOM, turbidity, current velocities, PAR, Nitrate Field Hourly Upper and Middle sections of Damariscotta River
Buoy Observations at 2m, 5m, 10m, 15m, and 25m: temp, salinity. Current velocity (all depth), chlorophyll-a (5m only) Field 15 minutes Mouth of Damariscotta River
Water samples analyzed for suspended particulate matter, chlorophyll-a, plankton size fractions, flow cam for species ID, primary production (via C-14 method), isotope analysis, POC and PON Field Bi-weekly Head to mouth of Damariscotta River
CTD profiles Field Bi-weekly Head to mouth of Damariscotta River
Acoustic Doppler Current Profiler (ADCP) profiles Field Monthly Head to mouth of Damariscotta River