THE SENSITIVITY OF ECOSYSTEMS TO ACID INPUTS IN THE HUNTER-VALLEY, AUSTRALIA

This study assesses the importance of H+ generation in the Hunter Vall ey from land use and coal-field power stations. The Hunter Valley is a temperate coastal landsystem approximately 150 km north of Sydney. La nd uses include forestry and national parks, grazing and fanning. coal mining coal-fired electricity generation and manufacturing. The H+ ge nerated from land use is estimated from land suitability classes. Wet deposition is estimated from 10 years' rainwater chemistry data and dr y deposition is estimated from modelled SO2 concentrations and a depos ition velocity constant. The pH and pH buffer capacity of 51 soils wer e measured. H+ loads from landuse ranged from 0.05 to 12 kmol H+/ha/ye ar for forests and prime agricultural land respectively. Estimated Hdeposition ranged from 0.27 to 0.65 kmol H+/ha/year, depending on the distance and direction from the power stations. The H+ load that will lead to critically low pH values in 50 years is 0.27, 0.60, 1.77 and 2 .14 kmol H+/ha/year for four broad soil classes. The two most sensitiv e classes, with target loads of 0.27 and 0.60 kmol H+/ha/year, occupy 26% and 56% of the study area respectively. Although the total contrib ution of H+ from land use is larger than from deposition (970 vs. 220 Mmol H+/year), H+ deposition may be important on low fertility nonagri cultural soils with low pH buffer capacity. More detailed study of the areas with sensitive soils is warranted.