Defining salinity limits on the survival and growth of benthic insects for the conservation management of saline Walker Lake, Nevada, USA
- 293 Downloads
Walker Lake, Nevada, a saline desert lake, has been undergoing loss of stream inflows, lowering of lake level, and concentration of dissolved salts for over a century due to agricultural diversions of water. This lake is or has been inhabited by native fish and visited by many species of waterbirds that depend on productive invertebrate life for food resources. The extent to which salinity limits the present and future viability of resident invertebrate fauna was evaluated using salt-tolerance bioassays and studies of salinity effects on growth and behavior in larval stages of the midges Cricotopus ornatus and Tanypus grodhausi, and nymphs of the damselfly Enallagma clausum. We found that salinities into and above a range of 20–25 g/L present either lethal limits or sublethal inhibitions to survival and growth that will eliminate or substantially reduce the current community of common benthic invertebrates. All species survived best at salinities below the current ambient level, suggesting these populations are already under stress. The 72-h LC-50 for Cricotopus was 25 g/L, and while mature damselfly nymphs were somewhat more tolerant, early instars survived for only short times in increased salinity. Damselflies also grew more slowly and fed less when salinity increased from 20 to 30 g/L. A conservation level for the lake that incorporates survival of native fish and recovers diversity and viability of invertebrate life should be within the range of 10–15 g/L salinity of Walker Lake water.
KeywordsSalinity tolerance Walker Lake Enallagma clausum Cricotopus ornatus Tanypus grodhausi Salt lake conservation
This work was conducted with the support of the Lahontan National Fish Hatchery Complex of the United States Fish and Wildlife Service (Agreement #81332-5-G004, Desert Terminal Lakes Program). We thank program managers Lisa Heki and Stephanie Byers for their enthusiasm for the project and for background information about fish physiology, and Robert Jellison for assistance with salinity calibrations. Helpful edits were also provided by Graham Chisholm. Senator Harry Reid deserves credit for his instrumental role in establishing a conservation program for the saline terminal lakes of Nevada.
- Bradbury JP, Forester RM, Thompson RS (1989) Late quaternary paleolimnology of Walker Lake, Nevada. J Paleolimnol 1:249–267Google Scholar
- Cooper JJ (1985) Age, growth, and food habits of tui chub, Gila bicolor, in Walker Lake, Nevada. Great Basin Nat 45:784–788Google Scholar
- Lauer GJ (1969) Osmotic regulation of Tanypus nubifer, Chironomus plumosus, and Enallagma clausum in various concentrations of saline lake water. Physiol Zool 42:381–387Google Scholar
- Lopes TJ, Smith JL (2007) Bathymetry of Walker Lake, West-Central Nevada. US Geol Surv Sci Investig Rep 2007–5012 p 26Google Scholar
- Milne W (1987) A comparison of reconstructed lake-level records since the mid-1800’s of some Great Basin lakes [M.S.]. Colorado School of Mines, Colorado, p 219Google Scholar
- NDEP (2004) State of Nevada surface water monitoring network: Walker River Basin (http://ndep.nv.gov/bwqp/WalkerMap.html). Nevada Div Environ Prot Carson City, Nevada
- Sigler WF, Helm WT, Kucera PA, Vigg S, Workman GW (1983) Life history of the Lahontan cutthroat trout, Salmo clarki henshawi, in Pyramid Lake, Nevada. Great Basin Nat 43:1–29Google Scholar
- Williams WD (1993) The worldwide occurrence and limnological significance of falling water levels in large, permanent saline lakes. Verh Int Ver Limnol 25:980–983Google Scholar