Long-term hydrologic and water quality responses following commercial clearcutting of mixed hardwoods on a southern Appalachian catchment

Long-term changes (similar to 20 years) in water yield, the storm hydrograp h, stream inorganic chemistry, and sediment yield were analyzed for a 59 ha mixed hardwood covered catchment (Watershed 7) in the southern Appalachian mountains (USA) following clearcutting and cable logging. The first year a fter cutting, streamflow increased 26 cm or 28% above the flow expected if the forest had not been cut. In subsequent years, discharge increases decli ned at a rate of 5-7 cm per year until the fifth year when changes in flow returned to baseline values. Later in forest succession, between ages 15 an d 18 years, both significant increases and decreases in annual water yield were observed; these discharge dynamics are discussed in relation to vegeta tion regrowth dynamics. Flow responses predicted from an empirical regional scale model were within 17% of experimental values during the first 4 year s of regrowth. Intra-annual analysis showed that proportionally larger incr eases (48%) in flow occurred in the low flow months of August-October. Stor m hydrograph analysis showed that, on an average, initial flow rate and pea kflow rates increased 14-15% and stormflow volume increased 10%. Analyses of stream solute concentrations and catchment nutrient fluxes show ed small increases in nutrient losses following clearcutting and logging. R esponses were largest the third year after treatment with annual values of 1.3, 2.4, 2.7, 3.2, 1.4, 0.39, and 2.1 kg ha(-1) for NO3-N, K, Na, Ca, Mg, S, and Cl, respectively. Explanations for the retention of nutrients and hi gh ecosystem resistance and resilience are discussed in relation to interna l biogeochemical cycles based on long-term process level studies on the cat chment. A second, sustained pulse of NO3- to the stream (exceeding post-har vest values) observed later in succession is also discussed in the context of ecosystem processes. Large increases in sediment yield were measured imm ediately after road construction due to two major storm events. Subsequentl y, during logging, sediment yield from roads was,greatly reduced and insign ificant when logging activities were completed. In contrast, cumulative inc reases in sediment yield were observed downstream over the next 15 years wh ich illustrate the lag between pulsed sediment inputs to a stream and the r outing of sediments through a stream system. The relevance of sedimentation to stream sustainability is discussed in the context of long-term response s in the benthic invertebrate community structure and productivity measured on WS7. Published by Elsevier Science B.V.