Satellite Imagery of Manitoba's Great Lakes - 2009
The satellite images below were taken by the Moderate Imaging Spectroradiometer (MODIS) on the NASA satellites Terra and Aqua. Image preparation is consistent with previous satellite images prepared by Dr. Greg McCullough. For more background information on the imagery and to view previous year’s images, please visit Dr. McCullough’s website at http://home.cc.umanitoba.ca/~gmccullo/LWsat.htm.

Water bodies, such as Lake Winnipeg, contain particles (silt and clay), dissolved substances and living organisms (algae). These constituents, as well as the water itself, absorb and scatter light. This affects both the transparency (how clear the water is) and colour of the water. In these images, clear water (with few particles) will appear dark since most of the light is absorbed and a small amount of light (of the visible colour) is reflected. For example, very dark brown water is due to high concentrations of dissolved organic carbon, much like a cup of strong, black tea. Increasing inorganic particle concentration will cause a range of colours from blue to green to tan. The south basin of Lake Winnipeg often appears tan in colour due to high turbidity caused by particles carried in from the Red River, as well as high winds which stir up the sediment from the bottom of the lake. Highly turbid water due to an algal bloom will appear bright green in colour due to the algal cells at the surface of the lake. The edges of a bloom will appear crisp in the image when the bloom is at the surface of the lake, and less defined when it is below the surface of the lake.

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The north basin bloom is less evident today, perhaps dispersed or sunk in the last few days. The plumes of high DOC water that have been largely confined to the east shore river outflows appear to be mixing further offshore. Considerable erosion is occurring on the north shore and influencing the clarity of the water in that area as well as the west side of Playgreen Lake. Similarly, high turbidity continues to predominate south of Berens Island.

The north basin algal bloom persists largely in the northeast quadrant with a thin extension down the centre of the basin toward Reindeer Island and a less dense extension to near Berens Island. Both images show how remarkably heterogeneous this lake can be. September 9th includes Lake of the Woods in the bottom right corner of the image - note the large algal bloom covering much of the east basin.

Finally some unobscured images of Lake Winnipeg reveal interesting changes occurring in the north basin over the last few days. A notable algal bloom has formed in the northeast quadrant of the north basin, curling around Long Point and reaching the east shore, extending south to near Berens River. The high turbidity in the south basin and narrows is likely preventing any large-scale bloom formation in those areas - so far at least. The Winnipeg River plume extends well into the south basin and north along the east shore.

Until early August, it had been fairly uneventful in terms of visible cyanobacterial blooms. By the second week of August, however, surface blooms were becoming more visible in the north basin - at the tip of Long Point and north of Grand Rapids (August 6th), and offshore of Poplar River and north toward Warren's Landing (by August 13th). Results by Hedy Kling indicate that this bloom consisted of a mix of Anabaena flos aquae, A. mendotae, some A. lemmermannii and low numbers of single filaments of Aphanizomenon species (see photomicrograph above). Preliminary results from the summer research cruise (ended late July) indicate that the algal community is considerably different this year than in past years with a predominance of diatoms and cryptophytes, instead of primarily cyanbacteria with some diatoms. In addition, the biomass of algae is lower so far this year than in previous years. The summer thus far has been quite wet, cool and windy - with a change in weather to calm and warm, the characteristic cyanobacterial blooms may still form this year, especially given that there is plenty of phosphorus in the lake to fuel their growth.

Three relatively unobscured images recorded in the third week of July reveal a highly turbid lake for the most part. No substantial algal blooms have developed yet, although the small wisp of bright green in the far north of the July 25th image indicates a small surface bloom.

These two images were taken on the same day. Again, highly turbid water dominates much of the lake with the exception of the area near the mouth of the Saskatchewan River, which remains clear. Interestingly, this dark, clear water is making its way around the tip of Long Point. July 12(2) includes the mouth of the Nelson River at Hudson Bay - note the influence it has on the receiving waters. Quite remarkable!

With the exception of the area north of Long Point, near Grand Rapids, the lake appeared increasingly turbid during the first week of July.

Just three images for June. The Red River continued to influence the southern half of the south basin, and the Winnipeg River, with its high dissolved organic carbon (DOC), dominated the north half of the south basin. The east shore rivers, with their high DOC concentrations, were still visibly influencing the lake as well. However, by the last week of June, this distinction was less apparent as the lake mixed and appeared more turbid overall - note the interesting flow pattern just north of Moose Island in Fisher Bay in the June 30th image (you will need to zoom in). The distinctive dark, clear water in the north basin near the Saskatchewan River outflow, north of Long Point, contrasts greatly with the bright, highly turbid, clay-rich water along the far north shore and flowing into Playgreen Lake via Two-Mile Channel.