Retrospective study of suspended sediment patterns on Lake Winnipeg using NOAA AVHRR satellite imagery

Over the last two decade there has been growing public and scientific concern about the health of Lake Winnipeg. In 1980, Brunskill et al. warned of a trend towards increasing nutrient supply from it watersheds, particularly in the Prairies where increasingly intensive agriculture was leading to higher nutrient loads in influent rivers. Since 1975, the lake has been controlled as a storage reservoir for hydroelectric production in the downstream Nelson River, increasing winter discharge at the expense of summer outflow. This changed regime would effectively increase nutrient storage by reducing outflow at the summer period of peak plankton productivity, and therefore peak suspended nutrient concentration. Over this same period, and particularly in the last decade, Lake Winnipeg fishermen have reported increasing frequency and magnitude of algal blooms. Suspended sediments are a critical component of freshwater aquatic systems, simultaneously supplying nutrients and reducing light necessary for biological production. In the last few decades, we have also come to understand their significance as agents of contaminant transport into and removal from aquatic systems. However, their discontinuous distribution and dynamic movement through lacustrine environments has made sediments difficult to monitor adequately by traditional limnological point sampling techniques. Although airborne photography has been used in the past to study patterns of turbidity, the most promising quantitative techniques for capturing this spatial dimension have employed calibrated multispectral scanners, especially those carried by satellites now continuously in orbit above the earth. This study begins an attempt to document suspended sediment and productivity patterns on Lake Winnipeg using satellite remote sensing. We have used a set of National Oceanic and Atmospheric Administration’s (NOAA) Advanced Very High Resolution Radiometer (AVHRR) images of Lake Winnipeg to create maps of suspended solids concentration (TSS) on Lake Winnipeg through the period 1985 to 2000. A primary data set of 15 TSS maps documents mid-summer TSS in each year, and a second set shows monthly TSS, June through September, in four selected years

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