Abstract
The Experimental Watershed Liming Study (EWLS) was initiated to evaluate the application of CaCO (sub 3) to a forested watershed in an effort to mitigate the acidification of surface water. The objective of the EWLS was to assess the response of the Woods Lake watershed to an experimental addition of CaCO (sub 3) . During October 1989, 6.89 Mg CaCO (sub 3) /ha was applied by helicopter to two subcatchments comprising about 50% (102.5 ha) of the watershed area. The EWLS involved individual investigations of the response of soil and soil water chemistry, forest and wetland vegetation, soil microbial processes, wetland, stream and lake chemistry, and phytoplankton and fish to the CaCO3 treatment. In addition, the Integrated Lake/Watershed Acidification (ILWAS) model was applied to the site to evaluate model performance and duration of the treatment. The results of these studies are detailed in this volume. The purposes of this introduction and synthesis paper are to: 1) present the overall design of the EWLS, 2) discuss the linkages between the individual studies that comprise the EWLS, and 3) summarize the response of the lakewater chemistry to watershed addition of CaCO3 and compare these results to previous studies of direct lake addition. An analysis of lake chemistry revealed the watershed treatment resulted in a gradual change in pH, acid neutralizing capacity (ANC) and Ca (super 2+) in the water column. This pattern was in contrast to direct lake additions of CaCO (sub 3) , which were characterized by abrupt changes following base addition and subsequent rapid reacidification. Over the three-year study period, the supply of ANC to drainage waters was largely derived from dissolution of CaCO (sub 3) in wetlands. Relatively little dissolution of CaCO (sub 3) occurred in freely draining upland soils. The watershed treatment had only minor effects on forest vegetation. The watershed treatment eliminated the episodic acidification of streamwater and the near-shore region of the lake during snowmelt, a phenomenon that occurred during direct lake treatments. Positive ANC water in the near-shore area may improve chemical conditions for fish reproduction, and allow for the development of a viable fish population. The watershed CaCO (sub 3) treatment also decreased the transport of Al from the watershed to the lake, and increased the concentrations of dissolved organic carbon (DOC) and dissolved silica (H (sub 4) SiO (sub 4) ) in stream and lakewater. The watershed treatment appeared to enhance soil nitrification, increasing concentrations of NO (sub 3) (super -) in soilwater and surface waters. However, the acidity associated with this NO (sub 3) (super -) release was small compared to the increase in ANC due to CaCO3 addition and did not alter the acid-base status of Woods Lake. Acid neutralizing capacity (ANC) budgets for 12-month periods before and after the watershed treatment showed that the lake shifted from a large source of ANC to a minor source due to retention of SO (sub 4) (super 2-) , NO (sub 3) (super -) , Al and the elevated inputs of Ca (super 2+) associated with the watershed CaCO (sub 3) application. In contrast to the direct lake treatments, Ca (super 2+) inputs from the watershed application were largely transported from the lake.