The satellite images on this page were recorded by the Moderate Resolution Imaging Spectroradiometer (MODIS) now orbiting aboard two of NASA’s satellites, Terra and Aqua. Unless otherwise noted, the actual colour renditions were prepared by the MODIS Rapid Response Team out of the University of Maryland who provide near-real time colour composite images on their web site http://rapidfire.sci.gsfc.nasa.gov/realtime/ -- except that I have changed the tone curve to emphasize colour differences in the lake, at the expense of brighter areas like clouds.
Click on each underlined date below to view a larger copy of the image.
the 26th of November and the 1st of December,
19:25 26 November 2004
cover looks pretty solid over the shallow bays, and has started to form in the
Note that the colours in these images have been adjusted differently compared to images from earlier this year – trying to deal with the high contrast and still discriminate colours in the lake. As a result, the intensity of greens and tans is exaggerated and their relationship with water quality parameters is not quantitatively the same as in the ealier images.
the turbid plume created during the strong winds of early October is still
visible in the central
can also see the turbid plume of the
27, 30 September & 6 October 2004 The
was a strong blow. It peaked at a mean
hourly speed of 82 km/h measured at the
Surface algal blooms in the
and waves on the north shore at George’s
I posted the group of North Basin images on the right to show how quickly the apparent intensity of an algal bloom viewed from space can change. The first of the set were recorded at 12:05 and 13:50 on the 24th. You can see the same patterns in the colours, but the green in the northeast quadrant, north of Georges Island, is much brighter in the earlier image. And in exactly the same region, there is no sign of the bloom a day later. The blue-greens actively regulate their buoyancy and work their way up into the bright near-surface environment when they can. I suspect that it was calm enough on the 24th to do just that, though the winds may have started up sometime before the second image. (I don’t have the weather data for the 24th, though I do for the 25th. Environment Canada allows a few days’ delay between posting the latest 24 h weather and posting the historic climate record – the data for the 24th will be posted sometime next week. You can get both current weather and historic climate by following the links at http://www.weatheroffice.ec.gc.ca/canada_e.html.) On the afternoon of the 25th, winds at Norway House (just to the north of Lake Winnipeg) were strong westerly, gusting to 30 km/h all afternoon. With winds like that, there would have been 1 or even 2 m waves in the eastern region, so that algae that had floated to the surface would have been mixed back deep into the water column. The lesson I take from this is that these images are showing us only surface blooms. Any single image cannot indicate the absence of algae in the water column (it didn’t all die between the 24th and 25th – it was merely mixed downwards for the time being) although a bright green patch does definitely indicate its presence in abundance. Its only through a cumulative look at a lot of images each year – and knowing weather conditions associated with each -- that we can fairly compare frequency of blooms from year to year. But there are a lot of images, and these blooms can be identified on weather satellites that have been recording scenes of the lake every day or so since the early 1980s. So we’re doing just that – looking at as many cloud-free images as we can find each year and finding out what the historic record of satellite imagery can tell us about whether/how much the frequency and extent of such surface blooms may have changed over the last couple of decades.
By the way, for anyone who wonders. Yes, there are often two images of the lake on a given day. And then often not another for a couple of days, even without the problem of clouds. NASA now operates two satellites with the MODIS instrument on board. Each covers most of the earth each day. Unfortunately, Lake Winnipeg is centred in only about every third day’s image by each satellite – and that on the same day. When Lake Winnipeg is way off to the side, the image is so distorted as to be unuseable. You can see some distortion (they are only partly corrected) in the images on the 24th compared to the 25th, above. The satellite passed nearly overhead on the 25th, but it captured the scene at 12:05 on the 24th in its peripheral vision from way out over Saskatchewan.
sign of the surface blooms of August in these September images, but it would
have been difficult for algae to have concentrated near the surface given the
very strong south winds of the last few days.
The soft greens in the eastern and central
those of you who read Helen Falding’s article in the
Free Press a couple of weeks ago, you can see Limestone Lake clearly in this
image. It’s the bright blue lake just
northwest of Lake Winnipeg. In the
article, Derek Ford of McMaster University explained the colour as the result
of calcite precipitating – a phenomenon called a ‘whiting’ which he said turns
the lake a beautiful chalky blue, or turquoise, or even emerald green depending
on the temperature. It’s a karst lake, meaning that its in a
terrain formed partly by dissolution of the limestone bedrock – hence the high
calcium carbonate content of the water.
Its also near a potential mine development, and the lake that the
Canadian Parks and Wilderness Society are lobbying to have it incorporated in
the National Park being developed along the shore of Lake Winnipeg. There is another pale blue lake to the
southeast of Limestone, Clearwater Lake.
(You can see the area a little more clearly in two other images wo images, from August
of last year and
of this year). Its not as bright a gem as
Limestone, but still a beautiful robin's egg blue from space. And from its colour at various times, I think
that whitings occasionally colour Talbot Lake, the
larger lake to the east -- and probably also parts of the Moose Lakes, although I suppose their
colours to be a more complicated mix due as well to algae in the summer and
occasional sediment resuspension events.
I have wondered at various times if the pale greens that I often see in
Lake Winnipegosis might be some combination of calcite and algae. Though they could simply be
different algal communities than we regularly see in
The picture has changed since mid-August (below). Where in early August the east side was all browns indicating either turbid water or water rich in dissolved organic carbon from the Shield watersheds (or very probably a mixture of the two), on the 31st of August along the same shore there was a surface bloom of algae as much as 10 km wide from the Narrows to somewhere near Poplar River, a distance of something like 150 km. You can see the antecedents of this bloom from the Narrows up to Berens Island on the 13th of August, but from Berens north at least to Georges Island there is no sign of it in the earlier image. Unfortunately, clouds prevent us seeing the fate of the large blooms in the northwestern part of the basin – as they have prevented us from seeing much of the lake through the whole last half of August. Again, I’ve included a vegetation index map on the left – with darkest green denoting most dense and most vigorous vegetation. Much of the bloom in this rendition is indistinguishably green from the forest just to the east of it. Its an indication that a thick green matte of algae completely covered the water surface there, on that day.
An image recorded Friday the 13th, when the Namao was probably near Georges Island doing fish trawls. The map on the right shows a vegetation index prepared by mapping the ratio of infrared light to red light. Chlorophyll in healthy green vegetation reflects infrared strongly, but absorbs red for photosynthesis. The vegetation index map shows increasing chlorophyll response in the colours brown (low) through yellow through increasingly dark green. The patches of these colours in Lake Winnipeg are surface blooms of algae, and in some parts, they are almost as green as some of the terrestrial vegetation around the lake – a sign that in those regions the algae is must be nearly carpeting the surface. Since water absorbs infrared light, for the vegetation index to produce even the browns and yellows out in the lake, it must be fairly dense on or near the surface. I expect that the Namao passed through one or both of the two blooms last week. We’ll know soon – they’re due back in Gimli tuesday.
The bright yellow-greens signalling algal blooms are if anything a little more widespread in today’s image than a couple of days ago, at least in the region between Reindeer Island and Long Point. Mike Stainton (by satellite telephone this evening) tells me that the Namao sampled from Berens River to George’s Island today – along the track marked in red. (They set out yesterday, but had to return to Berens to get one of the science crew to the nursing station. Happily, he is well again, today.) Today’s cruise will have taken them through mostly the brownish water along the west side of the lake. In fact, near Berens Island today, they did not encounter the dense algal blooms that we have seen there several times in recent years, though they did pass through a small bloom day before yesterday. You can see it on this image – small swirls of green just a few kilometres north of the Narrows. Tomorrow, their intention is to sample two transects across the centre of the North Basin – the blue circuit. That’s “weather permitting”. Mike tells me that there’s a strong wind from the south rolling waves into the harbour mouth at George’s tonight. Anyway, when they do set out, their planned path will carry them across a huge algal bloom that look as dense as any we saw last year.
they are on schedule the crew of the Namao should have left Matheson Island
this morning to arrive in Berens River this evening. That would take them through the tan-coloured
region along the route marked in red above.
That’s an area of fairly turbid water – turbid partly because it’s South
Basin water carried north through the channel and partly because the region is
shallow, at least compared to the basin north of Berens Island (generally only
10-12 m deep compared to mostly 16-18 m deep in the open North Basin) so that
bottom sediments may be brought into suspension whenever there are strong north
winds. It will be interesting to see the
water chemistry data from the mouth of the Berens River. The dark browns along the east shore have
been much more intense this year compared to last – that fits with the
relatively high runoff that I think has been coming off the shield. Like many of the Shield rivers
images recorded while we were sampling on the first few days of the summer
cruise. There’s a lot of variation in the colour of the
A press conference on board the Namao. On the left: Manitoba Minister of Water Stewardship, Steve Ashton, announcing $140000 support that will help pay the costs of keeping the Namao operating on Lake Winnipeg through this summer. Equally welcome was his announcement of additional resources for the riparian tax credit program, which supports the elimination of tillage and the limitation of grazing by livestock on lands adjacent to rivers and streams. The riparian tax credit now applies to land by lakes as well as streams. On the right: Claire and Keith identifying fish from a surface trawl – one of the many things they’ll be doing about 60 more times over the next month, only without the audience.
from the first days of the summer cruise.
The first three show some of the sampling that we do at stations. 1.
Alex taking a water sample at one of our
stations, for determination of the plankton concentration in the surface water
Its been a cloudy summer over
For those who can get out there, the ship will be docked for an Open House (Open Ship?) – everyone welcome to come, look and ask questions -- at Victoria Beach on Saturday the 31st of July and at Gimli on Sunday the 1st of August. Further afield (weather allowing) there are tentative Open Houses at Berens River on the 4th, at Grand Rapids on the 11th and at Matheson Island 16th of August.
The lakes are for the most part clear of opaque clouds; however, there is a soft haze over most of the scene – either thin haze or possibly smoke from the west. Reports back from the spring cruise of the Namao indicate that diatoms still dominate the phytoplankton community. Due to the cold spring, they may well persist longer and delay any blue-green bloom to later in the summer than last year. Clouds permitting, we’ll be able to watch. The northern half of the South Basin, the Narrows region and much of the east shore are much less turbid than at the same time last year (see, e.g. 3 July 2003) when at least the South Basin and Narrows were more homogeneously brown in these MODIS images. Turbid brown water at the south end persists as a result of the high May and June flows from the Red River. The darker regions this year are probably waters much diluted by the high runoff from the shield drainages to the east. Certainly, you can see a dilute plume of Winnipeg River water passing through more turbid water along either shore of Traverse Bay.
11:30 16 June 2004 The Namao is conducting fish trawls, along with routine plankton, benthos, water quality and optical sampling, today near Georges Island (circled in red on the thumbnail above). That’s Stephen, Claire and Kevin hauling in the trawl net, with Namao crew member George in the background, a few days ago. I was just talking with Christina by satphone from the ship this morning, who confirmed what you can see in the image above – it’s a beautiful, clear day, and for once near calm. (There’ve been a lot of wet, windy and rough days so far.) A day like today is what was needed to collect data on turbidity and chlorophyll concentration in order to improve our estimates of both from satellite images like these. The ship spent the last few days sampling at stations in the basin north of Long Point, and will be returning south tomorrow, overnighting at Berens River, Matheson Island and Gull Harbour, and finally back in Gimli sunday, all going well. By the way, the crew have completed installation of all three weather buoys on this trip. You can access real time air temperature, pressure and wind data from the buoys at http://weatheroffice.ec.gc.ca/marine/region_06_e.html.
In both the image above and the one on the 9th below, the muddy brown colour at the south end and in the Netley marshes is exactly what it looks like – muddy brown water from the Red River, which has been flowing high since the heavy rains of a week and a bit ago. And the pattern of dark water along the west shore of the North Basin looks a lot the same as last year at this time (10 June 2003) – this year we should get some well-positioned samples in that region to better understand the water quality (or plankton) differences underlying those colour patterns.
Most of the west side of the North Basin had opened up by the 27th. Although the ice covered much the same area on the 27th and 28th, you can see that it was much more broken up into separated pans on the 28th. By today, the 1st of June, there appears to be very little ice except north of Long Point, and a big sheet attached to the east shore of Reindeer Island. Not a very good quality image, but I thought the crew of the Namao might like to know that its pretty well ready for them up there. They’ll be leaving for the north end in a couple of days.
Though I am
studying the geography of plankton on