Malheur Lake Light Transmission Study

Science Center Objects

The Malheur National Wildlife Refuge provides habitat for a variety of highly valued ecosystem services, including shorebirds, waterfowl, and a diversity of other wildlife species. 

The health of the aquatic ecosystem in Malheur Lake has been strongly compromised by a lack of light that supports development of vegetation in the lake. Such emergent and submerged plants provide habitat for a variety of highly valued ecosystem services, including shorebirds, waterfowl, and a diversity of other wildlife species. The biggest limiting factor to the health of the lake is the common carp (Cyprinus carpio), a nonnative species with strong direct and indirect effects on water column turbidity. Indirect effects of carp include consumption and uprooting of aquatic vegetation, which leaves the bed sediment exposed and easily mobilized by winds. Direct effects include suspension of sediment by carp feeding activity.

Population modeling has determined that eradication of carp from the lake will be extremely difficult. Therefore, it is important to understand what other pathways can be used for restoration besides carp control. An important pathway that requires more exploration is the influence of basic physical factors (e.g., lake bathymetry, sediment, wind, suspended material) on light availability in the water column. A more complete and quantitative understanding of these factors, when combined with other important biological processes, can provide clearer direction for managing the Refuge over the following 15 years.

The goal of this work is to create a quantitative empirical model that describes light in the water column as a function of location on the lake, depth (lake stage), incident solar radiation, wind speed and direction, and aquatic vegetation coverage. Successful calibration of the model with data collected at several locations will allow the results to be extrapolated to the entire lake in order to provide, for example, the area of the lake the meets a certain light threshold under given conditions, or the average light in the lake as a whole, or in a defined area of interest.