Contamination of Lukha river system has damaged aquatic life and resulted in loss of livelihoods; write Aparajita Mukherjee & Debapriya Mukherjee
Meghalaya has a generous water supply with a number of perennial rivers, lakes and waterfalls that beautify the landscape. This state is also rich in minerals particularly limestone, coal, shale and laterite. Also, Narpuh reserve forest, deep inside the Jaintia Hills of Meghalaya, is among the few good forest patches which are under the intense pressures of growth, non-sustainable development and mindless extraction of natural resources like coal and limestone. The environmental problems associated with mining, urbanization, industrialization, road construction and other developmental activities have been significant because of the fragile ecosystem and richness of biological and cultural diversity.
The Meghalaya coalfield has a long history of disorganized "rat-hole" mining. The current modus operandi of surface mining in the area generates huge quantities of mine spoil or overburden (consolidated and unconsolidated materials overlying the coal seam) in the form of gravels, rocks, sand and soil, that are dumped over a large area adjacent to the mine pits without any consideration of environmental issues. The absence of post-mining treatment and management of mined areas are making the environment more vulnerable to degradation and leading to large-scale land use changes.
Furthermore, the thousands of rat-hole pits, abandoned after coal extraction, fill with water during rainstorms. This water percolates into the groundwater or flows into the rivers causing severe contamination of groundwater and river water respectively. The rainwater percolates through spoil heaps, leached metals, metalloids, and sulphate to receiving streams much like other mining regions. Also, the soil eroded in this area ultimately finds its way to the rivers. The rivers flowing through the mining belt are now severely contaminated with complex, ill-deﬁned mixtures of contaminants due to mining activities. The precipitated iron and the blue colour at the confluence of the Lukha river are evidence of AMD discharge and dust from the mining areas and cement industries.
In addition to coal mining, limestone mining in Meghalaya has remarkably increased from 2006 in order to meet the requirements of cement manufacturing units. Meghalaya possesses 9 per cent of the total limestone resources of the state, distributed mainly along the southern border. Limestone is the second most important mineral extracted in the state after coal. Preliminary observations reveal that limestone mining has degraded the ecosystem of the area through deforestation, removal of top fertile soil, disturbances in the surrounding ecosystem near the mining sites as well as contamination of the water in the nearby area. The total loss of forest in the area due to mining activities was found to be around 1,260 ha between 2005 to 2011, with maximum expansion during 2005-2009 and within 5 km radius. Loss of forest cover due to urbanization and mining activities further increases soil erosion. Appearance of blue colour along with fish mortality (all fish, irrespective of their size and species) in Lukha is an example of the adverse effects of mining activities on aquatic ecosystems. Annual occurrence of this episode may cause mortality of all fishes including vulnerable, endangered and critical species. Ecosystem function and evolutionary processes become imbalanced with loss of many invertebrates. The aquatic systems in this hilly area are highly sensitive to loss of flora and fauna.
In spite of several studies into this phenomenon, none have put sincere efforts to explore the actual cause of fish mortality. After the blue colour of the river and the fish mortalities were brought to the attention of regulatory authorities, there were speculations that it was due to the presence of copper sulphate, deposition of dust originating from cement industries, and the presence of aluminum, but a clear understanding of the source and mechanism of contamination remained elusive. Many villagers do not believe that coal mining is responsible for the blue colour and fish mortalities because coal mining has occurred since colonial times. According to them, the expansion of the cement factories that have been operating since 2007 has caused the problem and therefore closure of these industries will solve them. This perception is highly controversial. Many local communities and non-governmental organizations are raising their concerns about this environmental impact. the fact puzzled researchers as to what makes the water pollution so poisonous to fish. Researchers have focused on the presence of acid, sulphate and metals in the water, but they are still unable to understand the mechanism that causes the blue colour and fish mortalities.
The possible reason is that the earlier monitoring programmes were not properly designed. Critical analysis of these data clearly revealed that there may be certain flaws and inconsistencies in the selection of variables, environment components (water and sediment), analytical accuracy, and reassessment of the appropriateness and effectiveness of the existing monitoring programmes with reference to defined objectives and interpretation of data based on our literature survey.
Later on, considering the combined effect of pyrite oxidation on the Lunar river upstream and then mixing of slightly alkaline water, originating from a limestone quarry at the Lunar downstream, a monitoring programme was framed based on thorough literature survey. The study revealed that the combined effect of AMD and limestone discharge caused slow precipitation of white particles on the bottom with an increase of pH during low-flow conditions. Further mixing of this water at the confluence with the Lukha river increased the pH and caused coagulation of aluminosilicate particles (with some calcium and sulphate) as a thin layer of white precipitate on the river bed for 5-6 km downstream. These larger aluminosilicate particles scatter light in the blue spectrum. The cause of fish mortality is related to the accumulation of white particles enriched with Aluminum on fish gills as inferred from the physical appearance of fishs. The blue colour disappears slowly with the onset of rainfall and increasing discharge flushes out the white particles.
Further confirmation of this study is an emergent need so that prudent water quality management practices may be framed to improve economic, environmental and social conditions. This river pollution not only threatens the water use but also the supply of fish, an important source of nutrients to the villagers. The people in this area are also facing severe difficulties to sustain their livelihood due to the ban imposed by the National Green Tribunal on coal mining practices. Priority remediation must be based on water chemistry data, metal loads, and the areas of greatest risk to the public. The availability of lime water from the tributary could be engineered to neutralize acid water and prevent fish kills.
Views expressed are personal