Long-term ecological research in Loch Vale Watershed, Rocky Mountain National Park : Annual Report 1992

Baron, Jill; Edwards, Robert; Newkirk, Brian; Back, Jennifer

The National Park Service and Colorado State University, as part of the Watershed Studies Cooperative Park Studies Unit of the Water Resources Division, studies the biogeochemical processes of alpine/subalpine watershed ecosystems to determine how they are affected by atmospheric deposition. Begun in 1981, this project assesses current precipitation patterns and ecosystem responses of the Loch Vale Watershed in Rocky Mountain National Park and evaluates them with the context of past conditions and trends. This research will be used to protect sensitive Rocky Mountain National Park ecosystems from damage from urban and industrial pollution. The Loch Vale Watershed project is an ecosystem study, attempting to quantify major elemental and pollutant flux, identifying sources, sinks and controls of the major ions. We defined the boundaries of our ecosystem with the physical boundaries of Loch Vale Watershed, and adopted the small watershed technique as the overall context for study. Instead of "black-boxing" internal processes while quantifying watershed inputs and outputs, we attempt to understand and quantify inputs and outputs from each of the major ecosystem components of the landscape: bedrock, soils, vegetation and surface waters.Because so little was known about these components of the alpine and subalpine zones, early effort went into documenting basic characteristics and processes. Rocky Mountain National Park is sensitive to acidic deposition. Much of the park area is exposed granitic rock with 147 alpine and subalpine lakes and over 700 stream km. Naturally-reproducing populations of trout are present in 59 lakes. It is well documented in the literature that deposition of strong acid anions can rapidly exhaust the acid neutralizing capacity of systems underlain by slow weathering bedrock types, allowing lakes and streams to acidify. The acidity itself, and, more importantly, aluminum which becomes soluble at pH levels below 5.0, are extremely toxic to aquatic organisms. Loch Vale Watershed was chosen for study for a number of reasons. A reconnaissance in 1981 of over 40 lakes and streams within four major drainages of Rocky Mountain National Park provided a chemical and geographical base of information which aided in the selection of a specific watershed study site. Of the drainages sampled, Loch Vale Watershed exhibited the lowest summertime alkalinities, and showed an inverse gradient of ANC with elevation. There are four lakes within the watershed, three alpine, and one located below tree line. This allows for comparison of alpine with subalpine lakes. There is sufficient soil development to allow characterization of different soil types and their influence on surface water chemistry. An old-growth Engelmann spruce-subalpine fir forest is within the valley basin. A controlled surface water outlet from the entire basin allows us to quantify stream discharge. One final reason for the selection of LVWS is that the watershed is accessible, although remote, throughout the year.