The impact of salinity pulses on the emergence of plant and zooplankton from wetland seed and egg banks

Murray-Darling Freshwater Research Centre

MDFRC item.

1. In this study we compared the emergence of aquatic biota from sediments under 14-daypulses of high (5000 mg L)1) and low (1000 mg L)1) salinity with emergence underfreshwater and equivalent constant salinity levels. We tested the hypothesis that pulses ofhigh salinity and short duration have no impact on the emergence of aquatic plants andzooplankton from wetland sediment.2. The way salt is moved through the landscape may alter the response of biota to increasesin salinity. Under natural hydrological regimes in rivers and floodplains salinity pulsesoccur often at concentrations that exceed predicted tolerance levels for aquatic biota. Theimpacts of natural pulses of high salinity followed by rapid return to fresh conditions maybe used to inform management guidelines for the potential release of non-natural salinewater into river systems with minimal impact.3. For both aquatic plants and zooplankton the abundance and richness of the emergingtaxa decreased at higher salinities kept at constant levels. In contrast, pulses of salinityfollowed by return to freshwater conditions did not have a negative impact on theemergence of aquatic plants or zooplankton. For many taxa of zooplankton a positiveimpact was demonstrated with higher emergence following the salinity pulse.4. The responses of aquatic plant and zooplankton taxa are grouped into five responsetypes. Type 1: negatively impacted by all salt regimes. Type 2: preference for constantsalinities. Type 3: no difference between fresh and either pulse regime. Type 4: preferencefor high concentration pulses. Type 5: emergence higher under a low concentration pulse.5. Although previous studies indicate that constant high-level salinity in rivers andwetlands can decrease the species richness of aquatic communities, this current studyshows pulses may not have the same impact. Our results support the hypothesis thatpulses of high salinity and short duration do not impact on the emergence of aquatic plantsand zooplankton from wetland sediments. For zooplankton, pulses of salt may triggeremergence.6. These trends may be used to explore the potential to use managed water releases to movesalt through the landscape with minimal impact of salinity on aquatic biota. However,before such preliminary results are applied in management of saline water releases weneed to determine the implications for interacting processes in natural ecosystems.