Snow pack levels across the Rocky Mountains are expected to decrease by 50 to 100% by 2050 causing lower in-stream flow and earlier seasonal exposure of streams to UV radiation.  Metal bioavailability is greatly decreased by its complexation with dissolved organic carbon (DOC).  Because UV destroys DOC and alters the composition of remaining DOC, UV exposure can greatly increase metals availability.  Based on field studies that quantified the effects of metals on macroinvertebrate communities in 11 streams over a 60-d period, we developed a dynamical model of how increased UV exposure due to shorter seasonal duration of snow cover, slowed stream flow, and lower water levels is predicted to shape the future structure of stream communities. 

Results/Conclusions

According to the model, the greatest effects of climate change will occur at sites having high concentrations of dissolved organic carbon because of increased availability of metals released from metal-DOC complexation.  In addition to direct UV effects on geochemistry, the model demonstrates how abiotic factors indirectly alter trophic interactions because species-specific susceptibility to metals removes dominant predators, promotes greater species richness among less-competitive predators and allows population increases in grazers.  Model results suggest how climate change will structure species diversity and trophic interactions in high-altitude streams impacted by heavy metals as well as those having only background levels of metals.