Nickel mining threatens Lake Matano, Central SulawesiPublished by MAC on 2003-05-15
Nickel mining threatens Lake Matano, Central Sulawesi
Pasi Lehmusluoto Ph.D., Limnologist
Little fieldwork has been done on Indonesian lakes compared to forests and coral reefs. Occasionally expert missions have prepared reports on lakes and their ecology, invariably basing conclusions on few field observations and rapid assessments. Some lakes have larger size and volume and/or a higher value than others, targets for human interest and economic revenue, the classic conflict between economic, sustenance and preservation perspectives.
In Indonesia, there are 521 natural lakes, the greatest number of lakes in Southeast Asian countries, and over 100 reservoirs covering 21,000 square kilometers. Many of the natural lakes are small but of the great lakes 14 are over 100 meters, 8 over 200 meters and 3 over 400 meters deep (Matano, Toba and Poso). In the world, there are only 20 extremely deep lakes with depth exceeding 400 meters. Matano is the seventh deepest lake in the world. In addition to lakes and reservoirs, wetlands and floodplains cover 119,000 and swamps 394,000 square kilometers.
The lakes contain some 500 cubic kilometers. Lake Toba alone contains 240 cubic kilometers of good quality freshwater, the largest volume of lake water in Southeast Asia. The lakes and reservoirs are valuable as storehouses of water and in preventing floods, important ecological entities and sources of food. They supply water for humans, sanitation, trade and industry, support economic livelihoods like fisheries, hydropower generation, irrigation, transport and recreation, and are important for religious ceremonies. For indigenous waterfront communities, lakes are the foundation for livelihood. The Malili lakes (Matano, Mahalona, Towuti) in Central Sulawesi are famous for their endemic macrophyte, mollusc and fish species. However, algal growth and subsequent fish production are among the lowest in Indonesia. The introduced fish species may have had a manipulative effect on the food web.
There is only a very rudimentary understanding of the couplings with watersheds, complexity and functions of the Indonesian lake ecosystems. It would be presumptuous to think that lakes can be managed without adequate knowledge. The findings of the joint LIPI and University of Windsor of Canada study claims that the water column of Lake Matano is homotherm, continuously mixing with only near-surface transient density layering during the day. The Indonesian national lake and reservoir inventory, Expedition Indodanau, showed that the lake was at the time of the study stratified with lack of oxygen in deep water.
The two degree Celsius temperature difference between surface and deep water, common in tropical lakes, may give the 'feeling' that the lake is "homotherm". One-degree temperature difference in the tropics represents a water density change equivalent to a temperature difference of 10-12 degrees in the colder climates. Thus, one-degree temperature change causes in the tropics 35 times higher density change than in the temperate region. Expedition Indodanau evidenced stratification not only by temperature but physical and chemical gradients and lack of nitrate in deep water below 300 m. At zero latitude, it takes 10-200 days deep water to become anoxic, depending on the rate of biological and chemical processes in a stratified lake. Nitrate will be eliminated within a couple of days after the onset of anoxia but nitrite will be present.
Stratification was also evidenced by e.g. lower pH and higher carbon dioxide, electrical conductivity, ammonia, total nitrogen and silicate, calcium, magnesium and iron values in deep water than in surface layers. Already in 1931 professor Ruttner, one of the early developers of lake ecology, evidenced anoxia in Indonesian lakes. If Lake Matano were continuously mixing, oxygen demand should be high in the deep water to cause oxygen deficiency. However, it is possible that every year during hemispheric "winter" the lake becomes isothermal and mixes deeply, but water does not homogenize completely.
It is presumed that the stratification and mixing patterns of Lake Matano and many other Indonesian lakes cannot be explained by the generally given definitions. It is a combination of several patterns of hydrodynamic processes, with varying ecological importance. This is an issue, which needs to be recognized throughout the tropical belt and occasionally in the temperate region, making lake management guidelines prepared for temperate lakes often ambivalent, the higher chemical reaction and metabolic rates adding to the complexity. The long water residence time makes another complication by increasing lifetime of pollutants.
In the LIPI, University of Windsor study it is argued that high heavy metal concentrations are related to ground water inputs. However, in the effluents of PT Inco the concentration of manganese was 70, cobalt 1, nickel 23, zinc 1.5, and of plant nutrients, total nitrogen 30 and total phosphorus 1, all in mg/l. Rain water pH in the Lake Matano area has been 1 pH unit lower than in the surrounding areas. The threats of the wastewater discharges and air emissions of the mining and smelting operations of the Canadian PT Inco at Soroako to the lake's ecology and endemic flora and fauna were not addressed. Concentrations of chromium, iron, manganese and nickel in the sediments were well above levels that are considered to induce toxicological stress. Ground water is a common explanation, - an alibi to increased heavy metal concentrations in lakes and sediments adjacent to mining and smelting operations.
The Canadian mining company PT Inco is planning to expand its present operational capacity in the close vicinity of the lake. Nickel ore reserves in the Soroako concession are the world's third largest source of nickel after New Caledonia and Cuba. PT Inco has embarked on an expansion programme both in mining and smelting at Soroako, intending to increase production from its current 40,000 + tons to around 70,000 tons of nickel. To meet the challenge, the company is adding a fourth smelting line to the Soroako plant and building a second hydropower plant on the Larona River. The programme seems to be the most extensive of its kind in the world and will cost US$ 1.5 billion. Increased wastewater discharges and air emissions will increase heavy metal load of Lake Matano.