This action funds an NSF Postdoctoral Research Fellowship for FY 2010. The fellowship supports a research and training plan entitled "Plankton phenology: how shifts at the species level propagate through a lake ecosystem." for Annika Walters. The host institution for this research is The University of Washington, and the sponsoring scientist is Daniel E. Schindler.
Ecological dynamics are strongly influenced by climatic conditions. In lakes, warmer water temperatures can shift the timing of key physical processes, including spring ice-breakup and thermal stratification, which can affect the phenology of freshwater plankton species. The challenge is to understand how climate driven effects, for example shifts in the timing of peak abundance for a phytoplankton species, propagate through complex communities. Inter-specific interactions may cause species level impacts to quickly dampen out or to transmit broadly to have effects at the ecosystem level. This study utilizes a 48 year dataset of phytoplankton and zooplankton species abundances from Lake Washington, which has experienced a 1.4 °C increase in water temperature. The aim is to explore variation between species level and aggregate community and ecosystem level responses of plankton to warming. An understanding of how responses "scale up" can inform efforts to detect ecosystem impacts associated with climate change.
Training goals include developing advanced skills in statistical analysis and modeling. The project will utilize a variety of time-series analysis techniques including dynamic linear models, multivariate autoregressive models, and spectral analysis. The study contributes to our understanding of climate change and provides opportunities for mentoring undergraduate students. The research supports long-term data collection at Lake Washington and the results will be presented at local lake association meetings, in addition to national scientific meetings and through publications.
Normal 0 false false false EN-US JA X-NONE In temperate and polar ecosystems we experience distinct growing seasons when plants accomplish the majority of their annual production and reproduction. The onset of this growing season in the spring is marked in terrestrial ecosystems by leaf and flower emergence and in lake ecosystems by the growth and reproduction of phytoplankton. In many places we are seeing these events shift earlier. These shifts in timing are often linked to climate warming, but could also be due to changes in nutrient loading or grazing regimes. We examined the timing of peak phytoplankton production in Lake Washington, Seattle, WA, USA and the mechanisms driving changes that we saw. We looked at the timing for each phytoplankton taxa individually and for the entire phytoplankton community. When we looked at the phytoplankton community we saw a clear shift earlier. Peak phytoplankton production has shifted earlier by 63 days from 1962 - 2000. When we looked at the phytoplankton taxa individually we saw that only 58% shifted earlier. Even after we weighted each phytoplankton taxa by their relative abundance the species level shifts could not explain the community level shift. However, when we examined community composition we found the explanation. Taxa differ in their seasonal timing and early season taxa had become more abundant while some late season taxa were less abundant. Several factors were driving these changes in timing and community composition. The first was improved sewage treatment which lowered the nutrient load of the lake. Once the lake was not nutrient rich, one group of phytoplankton (Oscillatoria sp. complex) that had been numerous during the period of high nutrient levels and had a distinct summer peak disappeared moving the community peak earlier. Climatic changes were also important; warmer temperatures are causing the lake to stratify earlier in the season and earlier onset of stratification is associated with earlier diatom blooms. Lastly, the addition of a new grazer to the system (Daphnia sp.) is associated with some shifts in timing and composition. This research has provided a clearer picture of what has been occurring in the Lake Washington phytoplankton community. However, the most important finding from this research is documentation that shifts in community composition can have a large role in driving community phenology. There is an increasing use of remote sensing technology to document shifts in the timing of primary production. The assumption is that shifts in primary production are driven by individual species shifting earlier. This research shows that one also has to consider potential shifts in community composition.
