Effects of a managed three zone riparian buffer system on shallow groundwater quality in the southeastern Coastal Plain

Riparian forest buffers can help improve agricultural water quality. USDA g uidelines are for riparian forest buffers of three zones. Zone 1 is permane nt woody vegetation near the stream. Trees can be harvested in Zone 2, whic h is upslope from Zone 1. Zone 3 is a grass filter upslope from Zone 2 at f ield edge. In order to test USDA guidelines, a site runs established in the southeastern Coastal Plain near Tifton, Georgia, with an 8 m wide grass bu ffer (Zone 3) situated between a field and a mature Riparian forest. In the Zone 2 forest, mostly 50 year-old pine trees, one block was harvested by c learcut, one block was thinned and one block was left as a mature forest co ntrol. Care was taken to minimize soil disturbance during the timber harves t operation. The Zone 1 forest [15 m wide (49 ft)] was left undisturbed. Sh allow groundwater wells were used to monitor the effect of the managed Ripa rian forest buffer on N, P, and Cl concentrations. Groundwater nitrate conc entrations decreased from 11 to 22 mg L-1 adjacent to the field to less tha t 2 mg L-1 at 5 m (16 ft) into the forest. Nitrate concentration decreased under the grass filter strip as well as in the forest. Nitrate concentratio ns increased in one corner of the Riparian forest near the stream. This inc rease may be due to flow patterns of groundwater that bypasses the Riparian forest buffer. Chloride concentrations increased under the buffer indicati ng that the nitrate removal was due to biological processes such as plant u ptake and denitrification rather than dilution. Concentrations of other pot ential pollutants such as ortho-p, ammonium, and organic N moved in very sm all quantities and did not show consistent spatial patterns. There was no e ffective to harvesting of the Zone 2 forest on either nutrient concentratio ns or water table elevations. These results indicate that Zone 2 trees, alo ng small streams in the southeastern coastal plain, can be harvested with l ittle effect on groundwater nutrient movement to streams.