Contemporary and historical comparisons of chemical and biological characteristics of lakes and ponds on the arid Columbia Plateau, Washington

Background/Question/Methods

Anthropogenic alterations to natural systems can have severe consequences for ecological processes, changing the conditions under which species have adapted and interactions between species. Globally, aquatic habitat has been rapidly and irreversibly altered by damming and irrigation projects. The Columbia Basin Project in arid eastern Washington built six dams and >300 miles of canals for irrigation, flood protection, and power production, permanently flooding areas of the geologically significant channeled scablands. An important early ecological study determined that the many small natural lakes and ponds of this region ranged across broad environmental gradients of salinity, seasonality, and productivity, and contained distinct assemblages of invertebrate species. However, hydrological manipulations have changed both abiotic and biotic conditions in waterbodies through varying groundwater levels and altered connectivity via dams and irrigation canals. Thirty-eight lakes and ponds were sampled during the summer of 2012, including 23 that were originally sampled prior to the completion of the Columbia Basin Project.  By design, waterbodies were chosen from both within and outside the zone of influence of the project, allowing for consideration of other environmental changes.

Results/Conclusions

Almost all waterbodies within the zone of the Columbia Basin Project have declined in salinity from historical records, whereas waterbodies outside the Columbia Basin Project have been more variable, with some increases and some decreases in salinity.  There were no consistent changes in pH between historical and contemporary samples, though some waterbodies have shifted pH by several orders of magnitude.  Correspondingly, there have been shifts in zooplankton community species, functional composition, and similarity. Quantifying the effects of abiotic and hydrologic changes on aquatic community structure is imperative to improve understanding of how humans alter freshwater ecosystems, particularly in light of the rapid pace of irrigation development on a global scale.