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United States Department of Agriculture

Agricultural Research Service

Title: WATERSHED-SCALE WATER QUALITY IMPACTS OF RIPARIAN FOREST MANAGEMENT

Authors
item Perry, Calvin - UNIVERSITY OF GEORGIA
item Vellidis, George - UNIVERSITY OF GEORGIA
item Lowrance, Robert
item Thomas, Daniel - UNIVERSITY OF GEORGIA

Submitted to: Journal of Water Resources Planning and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 12, 1999
Publication Date: December 10, 1999
Citation: Perry, C.D., Vellidis, G., Lowrance, R.R., Thomas, D.L. 1999. Watershed-scale water quality impacts of riparian forest management. Journal of Water Resources Planning and Management 125:117-126.

Interpretive Summary: Riparian (streamside) forest buffers are important for water quality maintenance in agricultural watersheds and can be used to help improve water quality. Yet, very few reliable estimates are available for the potential of riparian forest buffer management to help restore water quality on a watershed scale. This is partly due to lack of information on nthe condition of riparian areas. Remotely sensed data and geographic information systems can be used to estimate and map vegetation condition of riparian areas. We used land use information, GIS and understanding of the nutrient (nitrogen and phosphorus) retention of riparian forests in the Little River Watershed (Suwannee River Basin), GA to demonstrate the potential for water quality improvement or degradation due to riparian forest rstoration or removal. Although general perception is that there is extensive riparian forest in the study region, analysis showed that over r1/3 of the riparian area is not in forest cover. If the riparian forest was restored on half of the land were nonforest is near the stream, nutrients in streams could be reduced by at least 10-17%. Conversely, if the forest was removed from 50% of area which now has riparian forest, nutrients in streams would increase by at least 7-13%. Even in areas with a lot of riparian forest, problems exist due to forest being chopped into small strips. GIS analysis showed that in the entire watershed of 333 sq km (134 sq mi) that there were only six stream areas with 2 km (1.2 mile) of riparian forest.

Technical Abstract: A geographic information system (GIS) and Georgia Landcover Database were used to identify land use within the Little River Watershed and assess impact on riparian forests on water quality. GIS analysis was used to extrapolate field scale measurements of riparian forest nonpoint source pollution control capacity to the watershed scale and to evaluate water quality impact of inreasing or decreasing existing amount of riparian forest. Watershed contains a dense dendritic stream pattern typical of the middle coastal Plain. About 65% of the 30m buffer on either side of all 2nd order or greater streams was occupied by forest or cutover forest. Thus about 35% of riparian area was occupied by nonforest, mainly agriculture. It is likely that smaller 1st order streams (not detected in this data set) have a lower percent of forested riparian zone. Three scenarios for increasing and decreasing riparian forest were examined for their potential leffect on nutrient loading. Increased or decreased loadings were based on estimates of net N and P removal by mature riparian forests and do not consider other nutrient transport effects of land use changes. N and P loadings at watershed outlet could increase by at least 17 and 10%, respectively, if 50% of nonforest riparian area was restored to forest. Fragmentation analysis indicated that only 6 blocks of riparian forests at least 2 km long remained in the entire watershed, confirming the fragmented nature of the riparian forest.

Last Modified: 9/1/2014
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