WINTER ASSESSMENT OF MICROBIAL BIOMASS AND METABOLISM IN LAKE ERIE
Project Number: R/ER-081, Progress Report
Start Date: 2/1/2009
Completion Date: 1/31/2011
Revision Date: 4/1/2009
| Principal Investigator(s) | 1. | Robert M.L. McKay, Bowling Green State University |
| Associate Investigator(s) | 2. | George S. Bullerjahn, Bowling Green State University |
| 3. | Scott O. Rogers, Bowling Green State University |
Funding Record
| Source: Ohio Sea Grant College Program | |||
| Source Fund | State Match | Pass Through | |
| First Year | $ 53,348.00 | $ 36,498.00 | $ 0.00 |
| Second Year | $ 55,531.00 | $ 38,173.00 | $ 0.00 |
Objectives
In late February 2007, we voyaged the length of Lake Erie on an icebreaker during a period in which the lake surface was 90% ice-covered. We sought to measure phytoplankton and bacterial abundance across the lake to answer the question: What microbes are in the lake in the dead of winter and what are they doing? A notable discovery was the documentation of high phytoplankton biomass dominated by a nutrient-replete, low-light adapted, filamentous centric diatom, Aulacoseira spp. Visible accumulations of Aulacoseira were associated with ice cover and were evident at levels far exceeding chl-a levels (up to 10-fold) normally observed in summer. We termed these visible concentrations of phytoplankton biomass CACHEs (Concentrated Algal Community and Heterotrophic Ecosystems), and feel they may be unique to Lake Erie. We also believe that the robust Aulacoseira spp. bloom observed during the February cruise is likely an important precursor to the formation of late summer central basin hypoxia. Unfortunately, our present understanding of CACHE contribution to the annual phenomenon is limited to measurements conducted at a single CACHE site and our best estimates of CACHE frequency and magnitude made during the final day of the research cruise.
Thus, our objectives for the proposed research are:
1. to quantify CACHE frequency and magnitude during ice cover in Lake Erie.
2. to measure physiological and biogeochemical activity in CACHEs and in the water column.
3. to uncover the diversity (bacterial, algal and fungal) of ice-associated microbes.
4. to assess the fate of winter diatom blooms in Lake Erie (i.e. are CACHE diatoms important as precursors to summer central basin hypoxia?)
Rationale
We hypothesize that if lipid synthesized on a vast scale in Lake Erie during winter is trapped in the hypolimnion of Lake Erie during the summer then the hypoxia evident in Lake Erie can be attributed not to plankton in the epilimnion during summer months but instead to plankton productivity in the lake that occurs up to six months earlier.
The implications of this hypothesis, if proven correct, are manifold. The mass of plankton, nutrient geochemistry, and the productivity of plankton in the lake under ice cover must be determined so that models can be developed that can incorporate situations that impact hypoxia in summer. Thus, better lake management decisions based on ecological
forecasts will be made if ecosystem response can be predicted more accurately.
Ice cover is attributed to reducing phosphorus levels in surface waters of the Great Lakes during the winter (e.g. Eadie et al. 1984; Nicholls 1998) by reducing fine grained sediment resuspension. If regional climate change forecasts predict less ice cover in Lake Erie in the future then marked changes can be predicted on the basis of current information and basic limnological principles. The longer ice-free period will allow water to mix more deeply prior to the onset of thermal stratification. This may lead to enhanced production (bacterial and phytoplankton; albeit temporally decoupled) as a result of resuspension of nutrients from the sediments (e.g. Cotner et al. 2000). The increased algal biomass will be exported to a warmer and shallower hypolimnion (due to extended mixing) and this will exacerbate hypoxia. The lake will be warmer in the summer, and algal blooms - including toxigenic cyanobacteria, prevalent now in the western basin of Lake Erie; Rinta-Kanto et al. 2005) - will be greater due to increased internal (wind-driven) phosphorus loading owing to increased epilimnion depth.
Overall, we feel this proposal is most responsive to thematic area VI (Ecosystems and Habitats) listed as “high priority” in the Ohio Sea Grant 2005-2010 Strategic Plan. Within this theme, the proposal addresses section A (Understand the impact of and reduce stresses on coastal systems) which has as its goal to: “Support research to improve our ability to understand and forecast ecosystem changes in Lake Erie caused by stresses to the system and reduce the impact of these stresses with particular emphasis on fisheries, harmful algal blooms, nutrient and contaminant loading, sewage outflows, and the Central Basin Dead Zone.”
Methodology
Central to the success of our project is the opportunity to conduct monitoring and sampling on a Canadian Coast Guard icebreaker. The Regional Operations Centre of the Canadian Coast Guard (Central and Arctic Region) has reviewed our request and is willing to assist us with a sampling program. We will also use aircraft surveillance to map CACHE size and distribution in Lake Erie during winter.
On board the icebreaker, we will sample CACHEs and conduct physiological experiments under controlled conditions (in incubators on board a research vessel) and in situ, though the ice. We will measure rates of primary production and respiration. We will also determine community structure of ice microbes using microscopy, flow cytometry and molecular (16S- and 18S rDNA) approaches.
In late fall 2008 and 2009, Environment Canada will deploy sediment traps at Sta. 340 and Sta. 84 that will over-winter. Material from these traps will be used to assess the ecological fate of winter phytoplankton biomass.
