|Dewalle d r,|
|Pionke h b,|
Submitted to: Chesapeake Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/3/1994
Publication Date: N/A
Citation: Interpretive Summary: The primary water quality issue in Chesapeake Bay is too much inflowing nitrogen (N). Because the dominant land use in the drainage basin is forest (over 60%) and the N outflow from this basin is budgeted by land use using assumed N export rates, the N export from forests must be accurately known. If not accurately known, the N export from the other less-extensive eland uses (agriculture at less than 30% area) and particularly, its controllability, will be badly estimated. This could lead to the selection of inappropriate land-based N control policies and remediations. This paper presents new and collects existing data over the basin that shows currently used estimates of N outflows from forests to be high. Modelling and budget based estimates of N losses from the basin to the Bay, and the resulting interpretations should be developed using these more defensible lower values.
Technical Abstract: Since forest land occupies over half of the total area within the Chesapeake Bay drainage system and nitrogen has been identified as a major cause of eutrophication in Chesapeake Bay, the export of N in streamflow from forested catchments is of great importance in the modeling and management of the Chesapeake Bay. Nitrogen export data for forested basins savailable from several sources in the Chesapeake Bay region were compiled in order to determine the magnitude of N loads lost from forested basins and better understand those factors which cause N loads to vary. Although only a small fraction (<15%) of atmospheric N deposition appears to be exported from most of these forested catchments, the N loads exported from different forested catchments in kg N ha-1 yr-1 varied by a factor of 10. Variations in N loads among years and basins were analyzed to determine factors controlling variability in N loads from forested basins. preliminary analysis suggests that the condition of the forest, especially as it has been affected by repeated past insect defoliations and long-term atmospheric deposition, may be related to N load variations on some of these basins. Nitrogen export data from these forested basins are discussed in relation to current nitrogen saturation hypotheses.