Man's Influence on Freshwater Ecosystems and Water Use (Proceedings of a Boulder Symposium, July 1995). IAHS Publ. no. 230, 1995. 67 Lake Imandra water contamination dynamics from space images VALENTINA KRAVTSOVA Department of Geography, Moscow State University, Vorobjevy Gory, Moscow 119899, Russia Abstract Lake Imandra, in the Kola peninsula at the North of European Russia, has experienced pollution by effluent discharges from industry along its shores, especially the apatit-nefelin industry in Kirovsk and Apatity. At the end of the 1950s the southern bay of the lake - Guba Belaya — was isolated by a dike in order to use the bay as a reservoir for industrial wastes. But in spite of the dike, water pollution continued until the middle of the 1980s, when the factories introduced new processing technology. Multi-temporal remote sensing images have been used to identify the changes in water contamination throughout this period. Air photos and space images from Kosmos and Landsat satellites, taken in 1958, 1973, 1978, 1986, were used to compile maps of Lake Imandra water contamination. They show that the maximum extent of pollution was in 1973 and 1978, when half of the Big Imandra surface was conta­ minated. In 1986 the plume of pollution was reduced, due to the intro­ duction of the closed-cycle processing system. INTRODUCTION Lake Imandra in the Kola peninsula is the largest lake in Northern Russia, with an area of 885 km2 and a volume of about 11 km3. Formerly the lake's water was very clear; penetration by a white Secchi disk reached 11m and it was known for its large harvest of valuable kinds of fishes. We have investigated the northern part of the lake named Big Imandra, which is 60 km long in the north-south direction, and 3-8 km wide. Its depth is typically 10 to 40 m, with a maximum of 62 m. Currently this lake is suffering major impacts from the factories working around it, and the need for monitoring of water contamination, especially using remote sensing methods, has become very great. The goal of this paper is to show the potential of multi-temporal remote sensing for the control of water conta­ mination by suspended material, and to analyse the dynamics of such contamination in the Big Imandra area since 1958. SITUATION During recent decades, Lake Imandra has been damaged by industrial emissions from major industries especially the apatit-nefelin factory in the Khibiny mountains, nickel- 68 Valentino Kravtsova copper at Monchegorsk and mining processing at Olenegorsk and Kovdor. Monche­ gorsk, Olenegorsk and Kovdor are the sources of chemical pollution, which is not seen in space images (although this may be reflected by change in phytoplankton densities), but the apatit-nefelin plants in Kirovsk and Apatity discharge a slurry with a very high content of suspended material which greatly decreases the transparency of the lake water. Investigations carried out by the Kola department of the Russian Academy of Sciences have shown that light penetration, measured by a white Secchi disk, has reduced in the 1960-1970s: in the summer months of 1968 it was 3.3 m, in 1969 - 3.0 m, in 1973 - 3.2 m, in 1974 - 2.0 m, and in 1978 - 1.9 m (Chizhikov, 1980). Plumes of suspended material are seen very clearly in space images. The dynamics of the lake water contamination are connected with the history of the industrial plant. The mine processing factory ANOF-1 began to work in 1930 (Sazonov, 1971) and its waste reached the southern bay of Big Imandra - Guba Belaya - with the waters of the River Belaya. The Second World War halted the development of the plant, but after the War it developed very quickly. New mines began to be worked in the Khibiny mountains, Yuksporr, in 1951, Raswumchorr in 1959, Central in 1964, and Eastern in 1981. A waste-containing reservoir, constructed near Kirovsk, was full, and it was decided to use the Guba Belaya bay for containing the waste, constructing a protecting dike to separate it from the lake. But in spite of this dike, polluted water pene­ trated to the lake. New mine processing factories, ANOF-2 and ANOF-3 were built in 1964 and 1984 respectively, and a new waste-containing reservoir was constructed on the plain to the South of the Khibiny mountains. The technology of mine processing improved with the waste being used for the production of nefelin concentrate, but the projected level of waste content in the wastewater runoff from the reservoir of 30- 40 mg l"1 (Feldman & Roslyakov, 1980), had not been reached in the 1980s and pollu­ tion of the lake continued to the middle of the decade when processing factories changed the technological process to a closed-cycle system. MATERIALS Multitemporal air photographs and space images were used for monitoring changes in Lake Imandra water pollution. Air photographs at a scale of 1:30 000, taken in August 1958, show the situation before the dike was constructed. We have used a mosaic of these pictures for the Guba Belaya area. A space image from the Landsat satellite, taken in July 1973 covers the main surface of the lake, excluding the upper part of the bay Guba Belaya; the plume of discharge from this bay is seen in band 4 of the image. A Landsat image taken in June 1978 covers the whole of Big Imandra, including the bay Guba Belaya. A colour composite was used for image interpretation. Space photographs from the Kosmos satellite, taken by the KATE-200 camera in June 1986, also cover the whole lake. Images in three bands (green, red, near infrared) and colour composites were used for interpretation. METHODS Black and white images of the green band, and colour composites were used for visual Lake lmandra water contamination dynamics from space images 69 interpretation. Areas with different degrees of pollution were identified using optical densities in seven ranges: D = 0-0.2; 0.2-0.3; 0.3-0.4; 0.4-0.5; 0.5-0.7; 0.7-0.9; 0.9- 1.2. The differentiation into four degrees of contamination (clear water, little, moderate, strong and very strongly contaminated) is relative, not quantitative, because there were no measurements of water pollution at the time the images were acquired. The 1978 and 1986 images were digitized and processed on a PC using the method of histogram brightness separation. This permitted regions of different degrees of pollution to be defined objectively. MULTI-TEMPORAL DATA ANALYSIS Air photographs of Guba Belaya in 1958 show this bay before it was transformed into a waste-containing reservoir (Fig. 1). Waste passing directly to the bay is the cause of its high brightness in the image. Space pictures, taken in 1973 and 1978 after construc­ tion of the protecting dike, show that when the bay became a waste-containing reservoir, some of the waste material, obviously only a small fraction, penetrated to the open lake. Plumes of suspended material are seen very clearly in the pictures; sometimes the waste was transmitted directly by the waters of the river Belaya, coming through the canal along the reservoir shore. Spreading of the turbid stream far to the North along the eastern shore of the lake is seen in the Landsat picture taken in 1973. The map, compiled from this picture (Fig. 2), shows that a stream of very strongly contaminated water spreads for 4 km to the north of the dike. Strongly contaminated water spreads for 8 km and moderately Fig. 1 The mosaic of air photographs of Guba Belaya, August 1958. Valentino. Kravtsova udnyj ji DID « ^3 MONCHEGORSK—4 ^ Imandra Fig. 2 Map of lake Imandra water contamination, July 1973. 1: clear water, 2: little contaminated, 3: moderately contaminated, 4: strongly contaminated, 5: very strongly contaminated water. \\JSf- . Fig. 3 Lake Imandra (a) in the Landsat image, June 1978 and (b) in the Kosmos image, June 1986. Lake Imandra water contamination dynamics from space images 71 contaminated water for 17 km. Little-contaminated water spreads to all the southern half of the lake. The Landsat image taken in July 1978 shows a similarly bad situation (Fig. 3(a)). At this time the wind condition did not promote the formation of a single stream, as in 1973. Strongly contaminated water occurs in all the southern part of the lake to 3-4 km from the southern shore (Fig. 4(a)). Moderately contaminated water spreads for 8-10 km to the north, to the group of big islands, and into the southern lake - Ecoostrovskaya Imandra. Little-contaminated water spreads along the eastern shore for 20 km and also reaches the bay Guba Kislaya and Ecoostrovskaya Imandra. A different situation is demonstrated by the images from the Kosmos satellite in June 1986 (Fig. 3(b)). The plume of strongly contaminated water is localized and spreads only 1 km from the dike (Fig. 4(b)). Moderately contaminated water also forms a very compact plume, spreading only 3-5 km from the dike. Little-contaminated water spreads into the southern part of Big Imandra 10 km up to the group of big islands, and a part of Ecoostrovskaya Imandra. The brightness of the former bay Guba Belaya has increased in this image - this reservoir has continued to fill with waste, and part of it has become dry. These changes are in good accordance with data on the waste content of the factory discharge: it was 210.18 mgl"1 in 1983 and became 102.18mgr' in 1986. A Landsat picture taken in July 1992 shows that this tendency to improvement continues: the plume of contaminated water is not seen in this image.