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GLERL 2000 Milestone Reports
GOAL: SUSTAIN HEALTHY COASTS
OBJECTIVE: PROMOTE CLEAN COASTAL WATERS TO SUSTAIN LIVING
MARINE RESOURCES AND TO ENSURE SAFE RECREATION, HEALTHY SEAFOOD,
AND ECONOMIC VITALITY.
PM: Develop better tools, predictive models and understanding related to water quality and coastal ecosystems management
Milestone: Complete the first field year of the 6-year
NOAA-NSF Coastal Ocean Program "The Impact of Episodic Events on
the Great Lakes" and
report results to NOAA-COP, NSF, and on the web
Scientists: B.
Eadie and D.
Schwab
Purpose: NOAA-GLERL, NOAA-Coastal Ocean Program and the National Science Foundation-Coastal Ocean Processes are conducting a jointly funded program to examine the impacts of massive storm events in late winter-early spring on sediment resuspension and transport of particles and associated materials and on subsequent spring ecology in Lake Michigan. This program, Episodic Events: Great Lakes Experiment (EEGLE), is being coordinated by NOAA-GLERL and is scheduled to include a pilot field year, two full field years and two years of subsequent interpretation and product development.
Efforts: We have just completed the pilot and first full field efforts. EEGLE program components include a retrospective analysis of satellite imagery, water intakes, and other historical data, process and survey cruises, moored current meters, traps and data acquisition instruments and coupled hydrodynamic/sediment transport/ecological modeling. There are presently 41 investigators from 17 institutions participating in this interdisciplinary project.
During this pilot year, the program was fortunate to have the opportunity to examine a very large event (Figure 1). Only once before, in its 39 years of intake turbidity records, did the St. Joseph water treatment plant (on the southeastern shore of the lake) experience an event of similar magnitude. Although not scheduled to be a full field year, efforts were made to exploit the opportunity of examining this rare event. Cruises were conducted on four different vessels, with activities shown in Table 1. A one day Coast Guard helicopter drifter deployment flight was also conducted. While it appears that the winter-spring storms occur annually, there is a large range in scale. As illustrated in figure 1, the 1999 storm event was much smaller than the very large 1998 storm event. The two images of AVHRR reflectance (channel 1 - channel 2) illustrate the approximate maximum of each years' event. A longer-term estimate of the scale of the event is illustrated by the yearly maximum of the 10 day running mean of winter-spring turbidity from the St. Joseph, MI Water Treatment Plant. The last bar represents 1999 and shows it to be somewhat below the average. The 1998 bar is similar to 1973 and they are the largest events for this 39 year period. Other water intake (and wind/wave) data are being accumulated for similar long-term evaluations. The relatively small 1999 event allows for an interesting contrast to the large 1998 event. During 1999, we've had successful survey cruises before, during and after the event, along with a number of process cruises. Water sample and Plankton Survey System (PSS) tows will continue on a monthly basis throughout the year. Table 1 shows program activities. There is one more field year, which should be similar in effort to 1999.
Figure 1. Examples of satellite images for the spring turbidity events in 1998 and 1999 and the turbidity at the St. Joseph Water Intake that results.
Preliminary findings from our efforts include: 1) high particle fluxes associated with the event and synchronized throughout the basin, 2) elevated phosphorus concentrations, low primary production (due to light limitation), elevated heterotrophic rates, elevated Th-234 activity (its use as a tracer looks promising), and elevated PCB concentrations within the plume region. Examination of the meteorological conditions during the storm that generated the March 1998 turbidity plume suggests the existence of a mesoscale atmospheric vortex above southern Lake Michigan coinciding with the generation of the observed eddy. Measured currents and the bulge in the nearshore turbidity pattern are consistent with the hypothesis that longshore convergence in the current field can generate sufficient offshore transport of fine-grained sediments to account for the visible features.
|
1997 |
1998 |
1999 |
|
| Cruises |
8 |
36 |
37 |
| Total Days at Sea |
22 |
109 |
166 |
| Water Samples |
12 |
144 |
294 |
| Plankton Survey Tows |
- |
22 |
53 |
| Trap Samples |
12 |
205 |
178 |
| ROV Dives |
- |
120 |
253 |
| Current Meters |
- |
11 |
27 |
| Drifter Days |
- |
40 |
350 |
| Papers and Reports |
2 |
1 |
8 |
| Presentations - Public |
11 |
20 |
12 |
| Presentations - Professional |
2 |
9 |
35 |
| Visits to EEGLE web |
- |
19,376 |
21,678 |
Customers: Special sessions have been convened at three
international scientific meetings ASLO-99 Santa Fe, NM, Feb.,
1999, IAGLR-99 Cleveland, OH, May, 1999, and Ocean Sciences, San
Antonio, TX Feb., 2000, and the program has made an effort to
communicate with the interested public via presentations,
newspaper articles and radio. In order to promote
interdisciplinary activities, the program has held an annual
all-hands meeting each fall, Milwaukee, WI Oct., 1997, Ann Arbor,
MI Oct., 1998 and Minneapolis, MN Oct., 1999. The NSF-CoOP
Steering Committee, and their invited experts, attended our last
meeting in Minneapolis and provided some feedback - virtually all
was positive. For more on EEGLE, please visit our extensive
website: EEGLE web page.
Significance: Our results imply that the mass of reflective substances in the plume is approximately equal to the total annual particle load to the lake. Since these fine-grained materials are excellent substrates for sorption it is hypothesized that this episodic event may play an important role in both the nutrient and contaminant cycling within the lake. Also, the offshore eddies in the southeastern portion of the plume coincide with the area of maximum sediment accumulation in the lake, implying that this event also plays an important role in shaping observed depositional patterns and in mediating subsequent sediment-water interactions.
The timing of this episodic sediment resuspension event, relative to lake warming and increased solar irradiance, may be important in the development of the spring diatom bloom and subsequent production. Biological recycling of nutrients within the upper layer of the water column is very efficient. The inventory of nutrients present in this layer when the lake thermally stratifies is the fuel that determines the magnitude of annual productivity. Our limited results from this effort allow us to pose the following hypothesis for further consideration:
1) that the forced, two-gyre vorticity wave response of the lake to episodic wind events, occasionally modified by stratification, is a major mechanism for nearshore-offshore transport of particulate matter and associated constituents in the Great Lakes
2) that the plume is a result of the first winter-spring storm after ice-out and represents the resuspension of particulate materials (and associated constituents) that have been stored in the lake as surface sediment "floc" for a distribution of times, during which they have undergone differential diagenesis, and
3) that physical processes, (e.g. resuspension, turbulence) associated with the plume event are important in determining the nutrient and light climate, and in structuring the biological communities throughout the spring isothermal period, and in setting the conditions for the critical `spring bloom' period
Success: The project has one more year of field work and two subsequent years of interpretation and modeling. As an interim product, we are defining success as the completion of sample collection and ongoing analysis. We did collect samples throughout the event in 1998 and 1999 and will be able to estimate the importance of these events in the cycling and transport of nutrients and contaminants.
Next Steps: Year three sampling is underway and data analysis and synthesis meetings are planned for June, September and December, 2000. These will help organize the foci for analysis and the products to be developed.
Last updated: July 9, 2002 mbl