Terrestrial Contribution of N to Stream Water in Managed and Undisturbed Forested Watersheds

The overall objective of this study was to understand the physical mechanisms responsible for the release of organic N, NO3-N, and NH4-N from a variety of terrestrial ecosystems to streams. Specific objectives were:

1. quantify the output of nitrogen forms from gaged watersheds in relation to precipitation, temperature, soils, and vegetation type. This information is necessary to understand natural levels and variation in streams;
2. using laboratory experiments, identify the influence of temperature and precipitation on changes in the forms of nitrogen in soil and the flushing of nitrogen from the soil;
3. evaluate man-caused disturbances (i.e. ski area development, timber cutting in aspen) in terms of increased nitrogen levels in streams.

The amount of soluble nitrogen forms which can enter a stream is dependent on a number of factors:

1. nitrogen contained in precipitation entering the system;
2. mineralization of organic nitrogen during tissue decomposition;
3. uptake (and immobilization) of nitrogen primarily by plants and microbes;
4. volatilization (NH3) and denitrification losses;
5. and the presence of sufficient water to transport nitrogen into the drainage system of the watershed.

These factors all represent variables which can be expected to vary between ecosystems and with time in a particular ecosystem. The complexity of reactions which can, and no doubt do occur among these factors in the soil system preclude a detailed analysis; however, estimates of the “free” nitrogen of the soil solution plus precipitation and temperature patterns should allow an explanation of the variability of nitrogen levels in watershed drainage systems.

Project No. B-053-NMEX