Accumulation of atmospheric nitrogen and mercury

Ivan Fernandez, a professor of soil science and forest resources in the School of Forest Resources and Climate Change Institute, and Mike Jakubowski, a graduate student in the School of Forest Resources, collect water samples from the Hadlock Stream watershed.

Accumulation of atmospheric nitrogen and mercury

Our research is focused on two watersheds in Acadia National Park, and we take the classic paired watershed approach to the long-term studies of biogeochemistry in this project. We refer to the two watersheds as Cadillac (a 32-ha watershed that goes from the summit of Cadillac to Canon Brook) and Hadlock (a 47-ha watershed that is on the southwest face of Sargent Mountain and drains to Hadlock Brook).

Cadillac was intensively burned in the 1947 fire — a fire that burned the forest, including the ground and some of the mineral soils. Hadlock was not burned, and so represents conditions that would exist without that dramatic disturbance from the fire.

In the late 1990s, we established the study site with specific goals to look at how the contrast between these two watersheds might be used to understand the accumulation of atmospheric nitrogen and mercury in watershed soils and their export in streams. Interests in nitrogen stem from its role as part of the cause of acid rain, as well as its role as a nutrient and nutrient loading to the environment. Interests in mercury are because mercury is a dangerous metal in the environment that can come from both natural and industrial sources.

In addition, we studied the impacts of the fire on carbon because of its role in ecosystem processes in the form of soil organic matter and dissolved organic carbon in lakes and streams, and the increasing interest in carbon due to its participation as carbon dioxide in climate warming (as a greenhouse gas).

We saw dramatic declines in watershed burdens of these pollutants with the fire, which were lost to erosion and combustion, and marked changes in the forest, all compared to the undisturbed Hadlock watershed. Ironically, because Hadlock had a larger burden of accumulated pollutants in the soils, the Hadlock stream also had a higher concentration of mercury and nitrate compared to Cadillac.

Now, we are returning 15 years later to see how conditions have changed in order to better understand the rates of accumulation and recovery that occurs following the fire.

This addresses impacts of fire and fire risk on the stability of ecosystems in Acadia National Park, and ecosystem services, such as carbon sequestration, biodiversity, water yield and quality, visitor experience and recreation. This research gives us insight into the risks of accumulation and loss of atmospheric pollutants like mercury in ecosystems, and how disturbance alters that system. This study also is giving us a better understanding of the relationship between watershed soils and streams that is increasingly important in our changing climate.

From a scientific standpoint, this research also helps us understand the role of fire in ecosystem function. Certainly there is increasing interest in this in the fire-plagued western states where mega-fires have become more common. We have less risk of fire in the humid Northeast, although drier years like this one can increase our risk of fire disturbances and its consequences that can last from years to centuries.

Acadia is a beautiful place to work, and is one of the jewels of the National Park System that Americans today and for many generations to come will enjoy. Knowing how ecosystems function and respond to environmental disturbances is critical to making sure the Acadia of 2100 is as wonderful as it is today.

Scientifically, Acadia is a somewhat unique landscape along the Maine coast being influenced by marine processes, mountain processes, and interior processes of both ecosystems and climate. Because Acadia is a national park, it is protected hopefully forever, and therefore it offers the opportunity to do long-term ecological research that is otherwise difficult to support or preserve in privately held landscapes.

We also know research in Acadia is highly valued by Acadia staff and personnel as they strive to manage this unique resource in the face of increasing stresses from a changing physical and chemical climate and human use. The value of these long-term studies to Acadia, and to science in general, cannot be overstated. Many of the processes that influence our natural resources, from the biogeochemistry of soils and streams to bird populations or microbial communities, take place on scales from seconds and minutes to years, decades and centuries. Too often we are faced with making decisions of policy and management based on science that is overwhelmingly focused on short-term research as a function of typical three- to five-year funding cycles. Some of the watershed approaches being developed by Acadia management, and our watershed project as a research example, have the potential to unlock unknowns about how ecosystems function and respond to disturbance over the long-term of decades or more, which is ultimately the goal.

This research may be in Acadia, but what we are learning about how these forested watersheds function and respond to environmental stress have a lot to tell us about how the Maine landscape is responding to a change, including management, natural disturbances and a rapidly changing climate. We have been operating another paired watershed study about 60 km inland from Acadia to study nitrogen and sulfur, where we have manipulated one of the two watersheds by adding fertilizer for 27 years, something you could never do inside a national park, but research that complements our understanding of watershed processes in Acadia.

However, both the Acadia study and this other study, called the Bear Brook Watershed in Maine, reinforce and reveal many aspects of our understanding of how ecosystems function and allow us to test and validate insights from one site with data from another. These studies give us information on the effectiveness of the Clean Air Act, the risks and consequences of fire in our forests, the negative and positive consequences of declining atmospheric deposition of nitrogen, nutrient dynamics that are relevant to the sustainability of forests when used as fiber and bioenergy sources, impacts of changes in watersheds on the quality and quantity of freshwater draining them as lakes and streams, and impacts on wildlife and fisheries due to changes in the ecosystem.

Ivan Fernandez is a professor of soil science and forest resources in the School of Forest Resource and cooperating professor in the Climate Change Institute. Mike Jakubowski is a graduate student in the School of Forest Resources pursuing a master’s in plant, soil and environmental sciences.

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