Author
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Lowrance, Robert |
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Sheridan, Joseph |
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Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/1/2005 Publication Date: 9/1/2005 Citation: Lowrance, R.R., Sheridan, J.M. 2005. Surface runoff water quality in a managed three-zone riparian buffer. Journal of Environmental Quality, 34(5): 1851-1859. Interpretive Summary: Both grass buffers and forest buffers are increasingly used as conservation practices to control nonpoint source pollution from agriculture. We measured the amount of water in surface runoff and the nutrients (nitrogen and phosphorus) carried by that water in a three zone riparian buffer system consisting of a grass strip followed by a managed forest and an unmanaged forest. The managed forest consisted of a clear-cut section, a thinned section and a mature section. The grass filter was between the field and all of the forest buffers. Different parts of the buffer received different loadings from the adjacent field and this affected the apparent differences among forest treatments. The clear-cut forest was highest for most forms of nitrogen at the position nearest the stream compared to the mature and the thinned forest. There were no differences for forms of phosphorus among managed forest treatments. Although there was an increase in nitrogen in the clear-cut forest, it was not a large amount and there were not large differences among the managed forest treatments. It appears that cutting of the managed forest is possible without negative effects on water quality as long as the permanent forest along the stream is not cut. The average buffer was represented by the combination of all forest treatments. This is similar to a real situation on a farm where different parts of the riparian forest buffer would be in different stages of development but a grass buffer and a permanent (unmanaged) forest would be maintained. All loads decreased significantly within the average buffer but not all concentrations decreased. Concentrations of nitrogen did not change significantly within the buffer. Concentrations of phosphorus decreased significantly and chloride increased significantly. The largest percent reduction of the incoming nutrient load took place in the grass buffer zone because of the large decrease in flow within the grass buffer. The grass buffer removed most of the incoming load. The managed forest and grass buffer combined was an effective buffer system. Technical Abstract: Both grass buffers and forest buffers are increasingly used as conservation practices to control nonpoint source pollution from agriculture. We measured surface runoff volumes and nutrient concentrations and loads in a three zone riparian buffer systems consisting of a grass strip (zone 3) followed by a managed forest (zone 2) and an unmanaged forest (zone 1). The managed forest consisted of a clear-cut section, a thinned section and a mature section. The grass filter was between the field and all of the forest buffers. There were significant differences in the nutrient concentrations and loading entering the buffer and this affected the apparent differences among forest treatments. There were not consistent differences in nutrient concentrations among the Zone 2 forest treatments, although the clear-cut buffer was highest (significant difference) for nitrate, total Kjeldahl N (TKN) and total N at the position nearest the stream. Although the increased concentrations in the clear-cut Zone 2 were about 20%, they only accounted for a small absolute increase, about 1 mg/L. There were no differences for sediment TKN or P species among Zone 2 treatments. The average buffer (all treatments pooled) represented the conditions along a stream reach in different stages of growth. The runoff volumes at positions in the buffer had a large impact on the loads. All loads decreased significantly within the buffer but not all concentrations decreased. Concentrations of nitrate, TKN, and total N did not change significantly within the buffer. Ammonium and P species (dissolved molybdate reactive P, total P, sediment total P) decreased significantly and chloride increased significantly. The largest percent reduction of the incoming nutrient load (65 to 80%) took place in the grass buffer zone because of the large decrease (68%) in flow and smaller changes in concentrations. The entire buffer system reduced loadings for all nutrient species from 27% for TKN to 63 % for sediment P. The managed forest and grass buffer combined was an effective buffer system. Although there was elevation of most N species in the clear cut, there were not large differences among the managed forest treatments. It appears that cutting of the Zone 2 forest is possible without effects on water quality. |
