Application of sewage sludge to non-agricultural ecosystems: Impacts of nitrogen on forests

The Clean Water Act (CWA) of 1977 directed EPA to establish standards for use and disposal of sewage sludge (biosolids). This report is part of a larger study evaluating nutrient and contaminant impacts associated with the land application of biosolids in non-agricultural ecosystems. Ecological risk assessments rarely focus on nutrients as stressors. The nutrient components of municipal sewage sludge may impact tree community composition, growth and production, habitat and forage quality for wildlife, and nutrient cycling. The focus here is on three forest ecosystems: northwestern Douglas-fir forest (Pack Forest, WA), southeastern loblolly pine plantation (Athens, GA), and eastern deciduous forest (Hubbard Brook, NH). A model called LINKAGES has been developed at ORNL to examine the relationships between nitrogen cycling and long-term forest stand dynamics, limited by climate and soil water status. Plant-available nitrogen from biosolids is added in several application scenarios and compared to the no-amendment case. All changes are noted, even if they may be viewed as benefits rather than risks. Model outputs include: above-ground biomass, individual species biomass, net above-ground production, leaf litter, evapotranspiration, available nitrogen, and dead trunks. The changes in plant community composition and production are dependent on the rate, frequency, and duration of sludge applicationmore » and on the age of the stand at the time of application. Model outputs are compared to empirical studies of forests where biosolids have been applied.« less