My research is being conducted in the Cromwell Brook watershed from Cadillac Mountain down to the tidal boundary of Frenchman Bay in Bar Harbor. The research is part of a multiyear interdisciplinary project funded by the National Science Foundation and focused on strengthening the scientific basis for decision-making to improve the management of coupled coastal systems.
My work focuses on watershed processes that govern the sources, delivery and residence time of runoff and pollutants carried by runoff. The reason for this focus is that the loading of pollutants from coastal watersheds — bacteria in this case — drive management policies related to the closure of shellfish beds and beaches to protect public health. Better understanding of the watershed processes governing the loadings will help managers make decisions related to customized closure rules in the varied settings along the Gulf of Maine coast.
To do this research, we have created a watershed model that links precipitation with surface and subsurface hydrologic systems in the Cromwell Brook watershed. This required a lot of information related to the watershed hillslope topography, stream network, vegetation, land cover, and soils. It also required the measurement of freshwater discharge rates and the concentration of materials moving in the stream flows.
Several overarching questions drive our research in the park: How do coastal watersheds respond to rainfall events? What landscape characteristics and watershed features have dominant influence on pollutant loadings to tidal estuaries? Can watershed pollutant loads be predicted from knowledge of the relation between rainfall and runoff patterns governed by measurable watershed characteristics?
During the process of developing the coastal analyses used in our project, we noticed inaccuracies in many spatial data layers that are important to quantification of watershed properties linked to surface runoff. For example, we find that delineations of stream and watershed boundaries in the spatial data sets that are readily available online are often inaccurate. The errors can produce incorrect estimates of runoff volumes and rates important to the prediction of pollutant loads, not to mention engineering criteria for public safety related to flooding.
I often tell students it is surprising that we have a remote vehicle measuring the surface of Mars but we still don’t have accurate maps of streams in our parks. So we have spent a lot of time measuring stream channel dimensions, including the upper limits downstream from the mountaintops. We are now close to having the most accurate stream maps ever compiled from observations within the park.
Many Earth and climate science questions bubble up from this exploration, including the causes for variable points of stream channel initiation in the landscape. Are the upper limits governed by tectonics, glacial erosion or surface runoff? We intend to use our data to find out.
Dams, culverts conveying flows under roadways, and drainage pipes collecting stormwater from paved areas are present throughout the park and surrounding areas. At the bottom of the watershed, we have focused interest in quantifying the effects of wetlands and ponds on runoff delivery, many of which have been altered by humans.
Our measurements of the engineered controls and incorporation of the features in our model will help us identify watershed runoff processes directly linked to human activities and then provide managers with information to target the modern watershed features that have the greatest influence.
Working in Acadia National Park to sleuth coastal runoff pollutant source and delivery culprits provides multiple advantages. Watershed assessments and research are difficult because they require information from relatively large spaces. The ability to measure and simulate processes in a location dominantly controlled by a single landowner makes it much easier to assemble data and information important to our research.
The National Park Service also is a uniquely diligent and attentive custodian of the land areas they oversee. The staff knows a lot about the landscape they manage, including its history. They often have archived information of the research that has occurred in the park that can be helpful for starting new investigations.
Further, the ability to simultaneously conduct research on watershed processes that is transferable to other locations along the Gulf of Maine and feed into a knowledge base that helps manage a park used by millions of visitors makes the returns on research investments focused in Acadia large in comparison to other locations.
Mainers should be interested in the research we are conducting in Acadia National Park because it is focused on a coastal pollution issue that has substantial influence on the state’s economy. Both seafood industries and tourism can be affected by coastal pollution, making it important to develop appropriate and efficient management strategies involving stakeholder engagement and improvements to the fundamental knowledge base for the region.
The substantial increase in the number of visitors to the park this year provides a good example of the pressure that may be building and the management responses that will be necessary. More broadly, understanding the connections between climate, modern watershed conditions, runoff and pollution is at the heart of sustainability solutions for Maine’s coastal areas.
Sean Smith is an assistant professor of watershed geomorphology in the School of Earth and Climate Sciences and the Senator George J. Mitchell Center for Sustainability Solutions