USDA Forest Service

Pacific Southwest Research Station


Pacific Southwest Research Station
800 Buchanan Street
Albany, CA 94710-0011

(510) 559-6300

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Understanding the decline of deepwater sensitive species in Lake Tahoe: What is responsible, eutrophication or species invasions?

Proposal [pdf]

Lead Researchers:

Sudeep Chandra, University of Nevada-Reno
Eliska Rejmankova and John Reuter, University of California-Davis


A comparison of historical and contemporary benthic surveys showed a large decline in bottom invertebrate and plant occurrence in the deepwater environment of Lake Tahoe (Caires et al., 2010). The decline in plants may be directly related to reductions in water clarity over the past four decades, while reductions in the invertebrate community may be related to plant declines and invasive species introductions. Two of Lake Tahoe's unique bottom species (a blind amphipod and a deep-water stonefly), found nowhere else in the world, are at high risk given their significant reduction since the 1960s. Currently, the deepwater benthic environment in Lake Tahoe is not being monitored and is not well understood. We will examine the spatial distribution of these deepwater special status plant and invertebrate communities and, in doing so, gather information about their biology and ecology. Specifically, we will study the life cycles of special status plants and invertebrates and feeding strategies of endemic invertebrates. We will also measure native plant photosynthetic rates at varying light conditions and relate observed plant responses to long-term subsurface irradiance data in order to understand the depths at which light has been limiting for deepwater plants over the last four decades and how this has affected changes in their vertical distribution. The influence of future clarity improvement (as part of the Lake Tahoe Total Maximum Daily Load strategy) on the redistribution of this special deepwater plant community will be evaluated using a model to be developed for this purpose. Non-native invertebrate effects on special status communities will also be analyzed in the laboratory. We intend to determine mechanisms that have contributed to the decline of these unique deepwater plant and invertebrate communities and develop appropriate restoration strategies. A monitoring plan will be developed to allow managers to track special status community response to restoration strategies, such as changes in light penetration and/or reductions in non-native species. Monitoring of relatively long-lived organisms such as aquatic plants and invertebrates provides an important biological indicator of the overall health of the system, one that has received little attention in Lake Tahoe.

Relation to Other Research Including SNPLMA Science Projects

Of critical importance is the direct connection between this proposed research and current efforts to develop and refine an environmental indicators program and a monitoring and evaluation program for Lake Tahoe. The Tahoe Regional Planning Agency and collaborating partners have had numerous meetings in the last seven years to (1) determine environmental condition, (2) assess response to restoration efforts, (3) monitor status and trends, and (4) establish scientifically-based targets for indicators of choice. The proposed research will contribute significantly to these emerging efforts by focusing on an area that has not been previously considered in Lake Tahoe. Previous funding (2009-2010) by the Tahoe Regional Planning Agency recognized our lack of understanding of the benthic environment and the importance of baseline community characterization given recent invasive species discoveries and eutrophication to the lake. This was the first major funding for benthic biodiversity studies since the 1960s. This research will refine our understanding of benthic processes to develop indicators that are reliable and sensitive to the changing conditions in Lake Tahoe. Other large lake ecosystems have undergone much greater alterations due to eutrophication (oligotrophic to eutrophic) and have documented subsequent changes to benthic plant and invertebrate communities. Surprisingly, Lake Tahoe has only undergone progressive eutrophication with a slight change in trophic status; thus restoration of habitat for deepwater special status communities is possible.

Expected date of final products:

August 2015

Last Modified: Nov 12, 2014 03:47:45 PM