Impact of Coal Mining on the Tzuong River System of Mokokchung, Nagaland

The Changki valley area is traditionally regarded as the rice bowl region providing the supply of stable food to a large population of the Ao Naga tribe dwelling in the foothill regions of Nagaland, India. Rampant and unscientific coal mining in and around the Changkikong range has painted a grim future for the area due to severe environmental degradation. Mine tailings and the lack of treatment or mitigation measures have led to the spread of acid mine drainage (AMD) in nature and are the primary source of contaminants for the Tzuong River system. The pollution has also threatened the livelihood of the indigenous people and endangered numerous aquatic species that once thrived in these streams with extinction, some of which are still yet to be identified. Fourteen samples of water are collected at the Tzuong river as well as from its tributaries for physicochemical analyses. Results show that the natural water is significantly compromised and is highly acidic besides high total dissolved solids (TDS), iron and copper concentrations. Assessment of the index of water quality (WQI) by employing the weighted arithmetic indexing (WAI) approach categorizes the stream waters under “unsuitable for drinking purpose” status with WQI scores >100.


Introduction
Coal mining contributes significantly to a country's economic development, although it greatly impacts human health and the environment.A vast area of farmland, mountains, and forests are cleared to make way for coal mines which is of great concern.2][3] Furthermore, the disposal of waste materials from the coal mines interacts with nearby water bodies, which has an irreversible impact on the aquatic and terrestrial environment. 4ADEO et al., Curr.World Environ., Vol.18(1) 223-234 (2023)   The mining of coal is often accompanied by the generation of huge quantities of dust and loose materials during the excavation of overburden and the mineral.The severity of the effects of coal mining is mainly influenced by factors such as the area's geology, and composition of overburden and minerals in the coal, mining type, the scale of mining operations, rainfall, etc. [5][6][7][8][9] The waste material mainly in the form of overburden, that is removed before the extraction of coal usually contains many toxic chemicals and pollutants such as heavy metals.This leaches out specially during the rains and pollutes the surrounding area. 10ne major cause of water contamination is the generation of acid from the oxidation of sulphurbearing minerals like pyrite in coal mines. 11,12Acid mine drainage (AMD) results due to the reaction of Pyrites with water and air, forming sulphuric acid and some dissolved iron.The resulting contamination from AMDs lowers the pH of the affected water bodies leading to acidity, which in turn facilitates the leaching of toxic metals into the water. 13,14galand forms part of the mobile morpho-tectonic unit of the Indian Plate that collided with the Burma Plate. 157][18] All of these major structures have NE-SW trends.0][21] The BoS, bounded by Naga Thrust on the northwest and by the Disang Thrust on the southeast, 22 covers an area of ~4500 sq km and has a length of ~300 km. 23Sediments in this belt range from Eocene to Oligocene and Plio-Pleistocene, comprising Barail, Surma, Tipam Groups, Namsang, and Dihing formations.
Coals in Nagaland are of sub-bituminous rank deposited under the influence of the marine environment. 24A similar depositional environment has been revealed in the study of Singh et al.,  (2012)  25 from the Tiru valley coalfield.Within the BoS, tertiary coal occurs associated with the Tikak Parbat formation of the Barail Group, which is composed of fine to medium-grain sandstone with minor intercalations of shales.
Extensive coal mining in and around the Changkikong range of Mokokchung has irreparably changed the landscape and highly degraded the water bodies.The deterioration in the quality of water and soil because of activities related to coal mining in the Mokokchung region of Nagaland was stressed by workers such as Tiakaba (2016), 26 Semy and Singh (2019, 2021a, 2021b), [27][28][29] and Semy et al., (2022). 30The purpose of the study is to determine the ramification of coal mining on the Tzuong River and its tributaries.It involves the analysis of physicochemical properties and evaluation of the Water Quality Index (WQI) of samples collected from Tzuong River and its tributaries.The use of WQI for this study is to assess whether the water quality in the Tzuong River system is affected by coal mining.

Study Area
Area considered for investigation has been taken up from the Changkikong valley of Mokokchung district, Nagaland.It is part of Survey of India (SOI) topographic map No. 83/J7 and lies between the latitude 26°28'18.321"N and 26°24'31.308"Nand longitude of 94°24 '18.291"E and 94°19 '19.254"E, with a coverage of about 21 sq.km (Fig. 1).The preferred method of coal mining is rat-hole mining; however, open cast mining is also becoming quite popular in the recent years (Fig. 2a, b).Coal mining is primarily seasonal, and mining activities are undertaken during the month of October to April before the onset of the Indian Monsoon.The majority of the mining activities are managed and controlled by individual landowners.Coal mining is assumed to be more lucrative, and the appeal of making monetary income quickly has led to a decline in the age-old traditional practice of agriculture and farming as a source of livelihood in the area.The contamination of the irrigation water source from mines and degradation of cultivable land into wasteland areas are also responsible for the weaning away from such agrarian occupation (Fig. 2c).Tzuong river (Fig. 2d) which originates from Mangkolemba town as the Tsujenyong river, flows in the NE-SW direction and eventually drains as 4 th order stream into Tsurong river in the neighbouring district of Wokha.Analysis of pH (Potential of Hydrogen) was done with a digital pH meter (EcoTestr pH1, Eutech Instruments) at the sampling site, while research for TDS was done using the gravimetric method according to Bureau of Indian Standards (BIS) 3025 (1984). 31][34] Nitrate, iron, and copper analysis were done with Spectroquant Pharo 300, Merck KGaA, Germany, using the test kit.
WQI was calculated to estimate the status of water using the physicochemical parameters of the samples.Here, the general quality of the water during a specific location or time is expressed by a single number by incorporating several quality parameters of water.][37] The method, Weighted Arithmetic Index (WAI) 38 was employed to determine WQI following: Here, Q n = Quality rating of nth water quality parameter, W n = Unit weight of the nth water.Q n is determined using equation, Here, V n = real amount of the nth parameter present, Vi = ideal parameter value [V i = 0, except for pH (V i = 7)], V s = standard permissible value 39 for nth water.W n (Unit weight) is derived using the equation, where, k is the proportionality constant and is derived by following where ∑ (1/V s = 1//V s (pH) + 1//V s (TDS) + 1/V s (total hardness) + 1/V s (calcium hardness) + 1/V s (magnesium hardness) + 1/V s (nitrate) + 1/V s (iron) + 1//V s (copper).The BIS standard for drinking water category, as well as weightage accorded to each of the physicochemical parameter, are used for calculating the WQI, as shown in Table 1, while the range of the WQI and its status are shown in Table 2.

Results and Discussion Physicochemical Parameters
Table 3 shows the physicochemical properties of all the samples tested.pH is a very important criterion for evaluating water quality as it affects the behaviour of metals in the environment. 41,42The pH level of the water samples ranges between 2.7-5.7,which exceeds the limit of permissibility according to the BIS standard (Table 1).The sample collected at sampling site C10 with a pH of 2.7 is the most acidic.TDS, which is the measure of dissolved ionic concentrations, ranged between 32.1-587 mg/L, where 587 mg/L (highest value) was recorded at C10.As per BIS standard, samples collected at sites C10 and C11 exceeded the permissible limit with values of 587 and 525 mg/L, respectively.[45] The total hardness in all the sampling sites is found to be in the permissible limit of BIS standard and ranges from 36-184 mg/L.The concentration of calcium hardness ranges from 12-56 mg/l.Calcium values of all the water samples are found to be within the BIS permissible limit.Magnesium hardness range from 2.92-34.16mg/L.The sample collected at site C12 has the highest magnesium value of 34.16 mg/L exceeded the BIS permissible limit, while the rest fell within the permissible limit.
The amount of nitrate in all the samples is found to be low and occurred within BIS permissible limit with values ranging from 0.5-1.7 mg/L.Nitrogen in soil and bedrock is released as nitrate in the presence of air and water during the excavation process and mining. 46Low nitrate levels in the samples may be attributed to a lower level of nitrogen in the soils and bedrocks of the study area.[29] The concentration of iron ranges from 0.27-4.77mg/L.The sample collected at site C8 has the highest concentration of iron at 4.77 mg/L.All the samples, with the exception of site C5 (0.27 mg/L), have a high iron concentration that exceeds the BIS permissible limit.Concentration of copper in the samples varied between 0.02-0.09mg/L.The samples at site C2, C6, C12, and C13 with a copper concentration of 0.08, 0.08, 0.09, and 0.06 mg/L respectively, occurs beyond the BIS permissible limit while the remaining samples lie within the permitted limit.Pyrite (FeS 2 ) and Chalcopyrite (CuFeS 2 ), which are released during coal mining operations, are accountable for the high iron and copper in the samples. 44,47,48 le 4: Calculation of WQI for sites C1, C2, and C3

Water Quality Index Analysis
The highest W n value of 0.85 assigned to copper followed by iron at 0.14 (Table 1) suggests their significance in impacting the result of WQI.
The observed value for each physicochemical parameter of all the sample areas and their WQI values is shown in Tables 4, 5, 6, 7, and 8. From the WQI scores, iron and copper were found to have the highest influence among all other parameters considered for the study.The low WQI value of site C5, is due to the fact that it is located upstream and away from the influence of coal mines (Fig. 1).The sample with the highest WQI value was recorded at sampling site C11 with a score of 290.68.The high WQI value of site C11 can be attributed to the three streams that converge after passing through the coal mines.
It is observed that the sampling site C5 with an initial WQI value of 29.41 on reaching site C6 is seen to have drastically increased to 284.64 (Fig. 4).
The abrupt rise in the WQI value can be directly attributed to contamination from surface run-offs from coal mines as the stream at site C6 passes through the mining area.

Conclusion
The majority of the water source in the area of study has been highly contaminated by mining activities.Effluents from coal mines in the form of AMD have greatly deteriorated the quality of water of the Tzuong river through its tributaries as evidenced by high acidity, high TDS, iron, and copper concentrations.The overall quality status of the Tzuong river and associated tributaries from WQI values indicate the water to be unsuitable for drinking with iron and copper as the dominant parameters of influence in the WQI scores.Although the pollution levels are still high with high WQI values, the water quality along the Tzuong river is observed to be gradually improving downstream due to the dilution of pollutants by inflow from unpolluted tributaries.
As the entire operation of coal mining is carried out haphazardly by the landowners/locals, with no governmental control or EIA/environmental considerations/legislations in place, there is a strong need for the creation of awareness so that proper environmental protection procedures are followed before any mining activities are initiated as well as to encourage the stakeholders to come forward and volunteer for restoration activities and where possible, minimize and reduce the negative impacts associated with coal mining and its associated activities.

Fig. 1 :Fig 2 :
Fig. 1: Location map of the study area with sampling sites