Air and Water Quality

Urban forests have considerable effects on water and air quality. Trees and/or shrubs can help to absorb storm run-off and improve the quality of the water that makes its way to larger bodies of water. Trees also can improve air quality by reducing air temperatures and directly removing pollutants, and altering building energy use and consequent pollutant emissions from power plants. Northern Research Station (NRS) scientists are conducting research on the environmental effects of trees to help urban planners and residents configure urban vegetation to improve the quality of their air and water.

Selected Research Studies

Organic Matter Fluxes in Urban Catchments and Streams
In urban areas leaf litter represents an important “gutter subsidy” to stream food webs and also provides habitat for aquatic biota.  It likely affects other pollutants (e.g., binding metals, disinfection by- products) and so is a key component of the aquatic ecosystem. 

Urban Streams and Runoff
Urban streams are intimately connected to their landscapes through highly engineered drainage networks, resulting in excessive stormwater runoff (from roofs, streets, parking lots), lower groundwater levels and increased loads of many kinds of urban pollutants (e.g., pathogens, metals, deicers, nutrients.)   This leads to water quality problems (e.g., dissolved oxygen deficits, toxics, sediment), and damaged riparian areas, civil infrastructure and aquatic habitats and communities. This “urban stream syndrome.” presents a challenge for managers seeking to minimize degradation of streams so that these are available to people in both a recreational and ecosystem services context.

Role of Thermal Fluxes and Patterns in the Ecology of Urban Streams
Urban streams are intimately connected to their landscapes through highly engineered drainage networks, and stormwater runoff from impervious surfaces (e.g., roofs, streets, parking lots) causes greater runoff and an increased frequency of runoff events.  These flows also carry greater thermal loads, both because of the direct transfer of heat from surfaces from air and solar insolation, etc  These thermal impacts, are part of the “urban stream syndrome” and present important stresses on aquatic communities and microbial processes.  Minimizing these thermal transfers presents a challenge for managers seeking to minimize degradation of streams so that these are available to people in both a recreational and ecosystem services context.

Pathogens in Urban Streams and Runoff
Urban streams are intimately connected to their landscapes through highly engineered drainage networks, and this results in increased loads for many urban pollutants, including pathogens.  This is part of the “urban stream syndrome”, and is particularly salient because contamination of recreational and potable waters presents potentially serious health hazards.  The ubiquitous and frequent contamination of Baltimore streams with fecal coliforms presents a poignant challenge for managers seeking to minimize degradation by pathogens from runoff, leaking sanitary sewers, and urban animal populations because these streams are so often located in back yards and urban stream valley parks.

Tools to Assess Ecosystem Services and Values
To improve urban forest planning, management and design, managers need the ability to quantify their local urban forest composition and its associated ecosystem services and values.

Tree Influences on Climate of Urban Areas
What effects do urban tress have on local air temperature, relative humidity, and wind speeds, and how can urban vegetation be configured to increase human comfort and reduce thermal stress? NRS scientists are currently measuring the climatic variables and seeking methods to predict and map differences in the variables, particularly differences in air temperature, caused by trees across a city.

Tree Influences on Human Exposure to Ultraviolet Radiation
Vegetation can significantly reduce ultraviolet (UV) radiation loads reaching the ground. Our scientists study how vegetation designs will modify people's exposure to UV radiation, information that is needed by medical authorities for cancer epidemiology and in advising people on behaviors to avoid inappropriate UV exposure.

Adapting Forests to Climate Change
Climate models have projected significant increases in temperature over the next century for the Northeast and Midwest.  Climate change will also affect rainfall patterns, but scientists cannot yet predict how regional rainfall patterns will change.  Growing seasons will lengthen further in both spring and fall.  According to the Intergovernmental Panel on Climate Change, there is very high confidence that the vulnerability of North America depends on the effectiveness and timing of adaptation and the distribution of coping capacity, which vary spatially and among sectors. Climate change will constrain North America’s over-allocated water resources, increasing competition among agricultural, municipal, industrial and ecological uses (very high confidence).

Mid-Atlantic Forests and the Chesapeake Bay Watershed
Forest landscapes are changing as a consequence of climate and environmental change. These changes affect people and the forest ecosystems they depend on for clean water, clean air and forest products, and recreation. How can we best manage our forest resources to sustain this array of ecosystem services under increasing environmental stress and a changing climate?