Defining salinity limits on the survival and growth of benthic insects for the conservation management of saline Walker Lake, Nevada, USA

Abstract

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.