Year Established: 2014 Start Date: 2014-03-01 End Date: 2015-02-28
Total Federal Funds: $27,478 Total Non-Federal Funds: $55,096
Principal Investigators: Gretchen Rollwagen-Bollens, Stephen Bollens
Abstract: Seasonal blooms of cyanobacteria and other algae are natural occurrences in lakes, and may naturally increase in frequency as lakes evolve from oligotrophic states (deep, clean and unproductive) to eutrophic states (shallow and infested with aquatic plants and phytoplankton). However, increasing evidence demonstrates that the eutrophication process in lakes is being accelerated by human activity, and is contributing to an increase in frequency and intensity of cyanobacteria blooms. Excessive abundance of cyanobacteria may have detrimental effects on lake ecosystems and water quality, including development of surface scums, depleted oxygen levels, and (in some cases) production of toxins that can negatively affect aquatic life and humans. This phenomenon is of great concern to water resource managers, particularly with respect to human health, as well as to the public whose use and enjoyment of these environments may be prohibited as a result. A number of lakes in Washington state currently experience harmful and/or noxious cyanobacteria blooms, while others remain relatively unaffected. Past research in Pacific Northwest lakes and reservoirs, as well as in other temperate regions, suggests there is a strong relationship between nutrient availability and cyanobacteria blooms; however to date no clear correlation has been identified between nutrient concentration and cyanobacteria abundance. Similarly, past studies also show that grazing on cyanobacteria and/or other planktonic algae by zooplankton influences cyanobacteria bloom dynamics, but rarely has grazing been observed to directly control cyanobacteria populations. Thus, it remains difficult to generalize and predict the specific conditions under which to expect cyanobacteria blooms for any particular lake. One possible explanation for this lack of correlation between nutrient concentrations or zooplankton grazing rates and cyanobacteria blooms is that these two factors may be interacting to modulate the timing and magnitude of such blooms. Moreover, the interactive effect of nutrients and grazing on bloom dynamics likely varies with the degree of lake eutrophication. Thus, we propose to investigate and quantify the interactive effects of nutrient availability and zooplankton grazing in four lakes/reservoirs in Washington that span a eutrophication gradient, from eutrophic systems (Vancouver Lake and Lacamas Lake, both in Clark County) to more oligotrophic systems (Lake Merwin, Cowlitz County; Cle Elum Lake, Kittitas County). We will perform a series of 2x2 factorial experiments in each lake at three time periods over an annual cycle: once prior to the bloom period, once during peak bloom period, and once in the post-bloom period. Each experiment will measure the impact of enhanced nutrients and zooplankton grazing on cyanobacteria and algal growth in separate treatments, as well as a treatment with both factors, to assess how each influences cyanobacteria growth and abundance. The results of these experiments will allow us to more accurately define the balance of factors that influence cyanobacteria blooms in Washington lakes, and to better predict when or if cyanobacteria blooms may occur. This information will be critical for assisting resource managers in decisions about mitigation efforts; moreover what we learn about these 4 lakes in Washington will have broad implications for other temperate lakes in the region and around the globe.