Soil solution chemistry and ion leaching in northern hardwood forests across an 800 km pollution gradient

TitleSoil solution chemistry and ion leaching in northern hardwood forests across an 800 km pollution gradient
Publication TypeConference Proceedings
Year of Conference1991
AuthorsMacDonald NW, Burton AJames, Liechty HO, Mroz GD, Witter JA
EditorIn A,
Conference NameEmerging Issues in Northern Hardwood Management: Air Pollution, Climate Change & Biodiversity
VolumeMiscellaneous Publication 91-1
Date PublishedMay 20-23,1991
PublisherMichigan Technological University, Ford Forestry Center
Conference LocationMackinac Island, MI

The presence of a pronounced gradient of H, SO4, and NO3 deposition across the Great Lakes region raised concerns over potential effects on ion leaching from forest ecosystems. Five study sites representing similar northern hardwood forest ecosystems were established from northern Minnesota (site 1) to central lower Michigan (site 5) with pollutant deposition increasing from site 1 to site 5. Lysimeters were installed at two soil depths on replicated plots within each study site and sampled over a two-year period from September, 1988 to May, 1990. In soil solution collected at 15 cm depths, SO4 deposition was positively correlated with solution concentrations of SO4 (r=0.74**), Ca (r=0.71**), Mg (r=0.65**), and K (r=0.60). These solution chemistry parameters were also positively correlated with H ion depositon (r=0.59* to 0.76**). In soil solutions collected at deeper soil depths, deposition effects were less noticeable, but still present. Solution SO4 concentrations were highly correlated with SO4 deposition (r=0.89**), as were SO4 to total inorganic anion ratios (r=0.65**). Comparison of atmospheric ionic inputs with ionic outputs from B horizons showed that net leaching of Ca and Mg was occurring from all sites along the gradient. Sulfate and K outputs exceeded inputs at the three southern sites (3,4,5). Sulfate outputs above background levels at these three sites contributed 207, 505, and 376 eg/ha/yr, respectively. These excess mobile anions accounted for increased cation leaching equivalent to 8% to 34% of annual cation outputs at sites 3, 4, and 5. Calcium losses at sites 3, 4, and 5 were in excess of estimated weathering rates, suggesting that depletion of cation reserves is a likely consequence of continued pollutant deposition.