Effects of future sulfate and nitrate deposition scenarios on Linville Gorge and Shining Rock Wildernesses
We used the Nutrient Cycling Model (NuCM) to simulate the effects of various sulfur (S) and nitrogen (N) deposition scenarios on wilderness areas in Western North Carolina. Linville Gorge Wilderness (LGW) and Shining Rock Wilderness (SRW) were chosen because they are high elevation acidic cove forests and are located on geologic parent material known to be low in base cations and thus sensitive to acidic deposition. We used five sulfate (SO42-) and nitrate (NO3-) deposition scenarios to compare with the current (base case) deposition: Scenario 1, SO42- at 94 percent and NO3- at 95 percent of current deposition; Scenario 2, SO42- at 58 percent and NO3- at 63 percent; Scenario 3, SO42- at 42 percent and NO3- at 51 percent; Scenario 4, SO42- at 35 percent and NO3- at 48 percent; and Scenario 5, SO42- at 22 percent and NO3- at 48 percent. For both sites, soil exchangeable calcium (Ca2+) increased while exchangeable aluminum (Al3+) changed very little over the 90-year simulation period with greater reductions in SO42- and NO3- deposition; and the increase in soil exchangeable Ca2+ improved soil Ca/Al molar ratios. Soil solution SO42- was much lower at all soil depths with greater reductions in SO42- and NO3- deposition. This reduction in SO42- in solution resulted in greater soil solution acid neutralizing capacity (ANC). At LGW, soil solution ANC of shallow soil was improved with the deposition Scenarios 2-5 compared to current deposition. By 2040, solution ANC of deep soil had increased above 20 μeq L-1 for Scenarios 3-5 at LGW suggesting that stream ANC will be improved as well with further reductions in acidic deposition. Soil and solution cation concentrations will be improved for both wildernesses based on Scenario 2; however, further reductions in acidic deposition (e.g., Scenario 5) will be needed to increase stream ANC to a level that could support trout and other fishes.