Title page for ETD etd-10212005-123011
|Type of Document
||Kim, Dong Yeob
||Municipal wastewater effects on nitrogen cycling in a mature hardwood forest
|Burger, James A.
|Johnson, James E.
|Reneau, Raymond B. Jr.
|Seiler, John R.
|Zelazny, Lucian W.
- Nitrogen cycle
|Date of Defense
Land disposal of municipal wastewater is considered ecologically acceptable and
cost effective. The success of land treatment systems, however, requires proper
functioning of all ecosystem components. The impact of municipal wastewater irrigation
on the structure and function of an Appalachian hardwood forest in Virginia was
investigated. Four irrigation rates (17.5, 35, 70, and 140 em yr-l
) were applied in this
hardwood forest, and their effects on forest nutrient cycling were monitored for two
years. Tree growth, seedling reproduction, tree mortality, species diversity, and N
sequestering by vegetation were not changed significantly. Herbaceous ground cover
increased due to irrigation, except for the 140 cm yr-l treatment where the heavy spray
caused physical damage to the cover. Depending on the rate applied, the mature
hardwood forest system sequestered only -3.4 to 8.2 kg N ha yr-l in the above ground
biomass. Therefore, the fate of added N to the system became a function of N
transformation processes in the soil. Nitrogen mineralization and nitrification increased
as irrigation increased. Denitrification rates were not affected by irrigation; the process
of denitrification did not constitute a significant N output from the forest system. The
additional soil nitrate (N03) was left to leach because of the low assimilation by the
plant/soil system and the low denitrification rate. Nitrogen storage decreased in the
forest floor due to the increase in litter decomposition, and increased in the surface soil
due to the increase in microbial N assimilation. Total soil N increased on the low
irrigation sites and decreased on the high irrigation sites, indicating that high rates of
irrigation stimulated N loss from the soil by enhancing soil N transformations. The
health of the forest ecosystem was not adversely affected during this period, but the
forest did not serve as a net sink for N. There was little opportunity for N sequestering
in this mature hardwood forest. Without harvesting and regeneration, the system is likely
to lose system N when wastewater is applied. When wastewater is applied to lands, N
sequestering and denitrification should be maximized in order to minimize the pollution
potential of N03 leaching to groundwater systems.
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