Hydrogeochemical Study of Western Ghats Region between Goa and Mangalore, India

Hydrogeochemical Study of Western Ghats Region between

Goa and Mangalore, India

SANJAY KUMAR SHARMA*, DHIRAJ KUMAR SINGH and V. SUBRAMANIAN

School of Environmental Sciences, Jawaharlal University, New Delhi- 110067

*E-mail- [email protected]

Abstract

Systematic hydrogeochemical survey has been carried out for understandingthe sources of elements in the West Coast Rivers of Western Ghats and the coastalplains of western parts of India. The ecosystems of these basins are under pressurefrom mining, beach tourism, sewage outfall, coastal construction and indiscriminatedumping which have deteriorating qualitative impacts on water, sediments andaesthetic quality. The Western Ghats Rivers are slightly alkaline irrespective ofseasons. Electrical conductivity (E.C.) is observed to be lower during monsoondue to high fresh water input in all the rivers. High E.C. occurs in all the seasonsnear the mouth of the river due to marine influence. The effective CO

2 pressure of

each of the Western Ghats Rivers is higher than the atmospheric pressure of 10–3.5

atm., which is in conformity with the global trend. Correlation of Na and Cl indicatesthe influence of marine aerosols and sea water intrusion in these rivers. Ageochemical survey of the Western Ghats region between Goa and Mangalore wascarried out in order to define concentrations and distribution patterns of selectedheavy metals (Fe, Mn, Cu, Cd, Cr, Ni, Pb, and Zn) in the coastal system and estuarinearea of the West Coast Rivers. The results indicate that the sediment chemistry isdominated by Si, Al, Na, K, Mg and Ca which show pronounced variation alongthe downstream. The Chemical Index of Alteration (CIA) over the surface sedimentsof Western Ghats Rivers indicates very low weathering. The contamination factor(C.F.) and pollution load Index (PLI) values of Western Ghats Rivers indicate thatthe sediments are moderately polluted. Remote sensing and geographical informationsystem on certain broad aspect of land use/land cover changes in the region indicatethat the coastal length of the study area has not changed much but the coastal belthas increased considerably.

Keywords: Hydrogeochemistry; landuse and land cover changes; Western GhatsRivers

MEMOIR GEOLOGICAL SOCIETY OF INDIA

NO. 73, 2008, PP. 405–420

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INTRODUCTION

This study initiated a baseline hydrogeochemical survey of seven westflowing rivers draining through Western Ghats between Goa and Mangalore. Inthis study, two rivers from Goa i.e. Mandovi and Zuari and six other rivers fromUttara Kannada and Dakshina Kannada districts of Karnataka state namelyKalinadi, Gangavali, Agnashini, Sharavati, and Netravati have been studied.Kalinadi, Gangavali, Agnashini and Sharavati are the prominent rivers of NorthKarnataka. Sharavati is the shortest river and is famous for the mighty Jog falls,the site of the hydel project. Though considerable studies (Alagarsamy, 2006;George et al., 1984) have been conducted on different chemical aspects of theMandovi-Zuari estuarine system, no comprehensive hydrogeological investigationhas been done so far in this region.

River water quality depends on local geology, distance from sea andindustrial zone, agricultural area and urbanization. Generally, lithology controlsmajor and minor contents but in some special cases lithology causes pollution inand around mining areas. Thus hydrological and hydrogeochemical investigationshelp us to identify the recharge-discharge area and rock-water interactions in thebasin. The interaction with adjacent groundwater may also play important rolesin determining the quality of the river water during lean period. Atmosphericinputs are an important source of dissolved elements in rivers, in particular forcoastal rivers where large parts of the catchment are under marine influence (Gibbs,1970; Stallard and Edmond, 1981; Meybeck, 1983).

Man’s activities have increased the quantity and distribution of heavy metalsin the atmosphere, on the land and in rivers, lakes and seas. The extent of thiswidespread but generally diffuse contamination has caused concern about itspossible effects on plants, animals and human beings. The study of river sedimentsrepresents a useful tool for determining the actual state of environmental pollutionand for understanding the origin and mechanism of the phenomena. Sedimentsprovide both a record of the past climatic and geological events and an indicationof the activities of man in the surrounding watershed. Mining operations, ironand steel production, general industry, coal combustion, oil and gasolinecombustion, waste incineration and fertilizer manufacture all discharge heavymetals in the atmosphere providing a steady but generally diffuse source of metalsto sediments. Thus, an effluent containing high concentrations of heavy metalsmay reasonably be expected to lead to highly contaminated sediments, priordilution by air or water can result in the contaminating particles being spreadthinly over large sedimentary areas. For contaminated sediment to have a clearlymeasurable ecological effect it needs to cause a change in the pattern of distributionand/or the numbers of individuals of the various species originally present (Ward,1979). It is not easy to measure such changes in the abundance and diversity oforganisms. In addition, the contamination is rarely due to heavy metals alone so

SANJAY KUMAR SHARMA, DHIRAJ KUMAR SINGH and V. SUBRAMANIAN

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that there may also be effects due to excess nutrients, other toxic substances,changes in pH, temperature and so on. The determination of metals in suspendedand bed sediment is more sensitive than the dissolved concentrations as theindicators of contamination in hydrologic systems (Salomons and Forstener, 1984).A variety of factors such as basin geology, physiography, chemical reactivity,hydrology, vegetation, landuse pattern and biological productivity regulate themetal load of the river system (Garrels et al., 1975; Zhang and Huang, 1993). Inview of this degree of contamination by heavy metals these river basins has beenundertaken for the study.

Thus the present work was aimed to get baseline data to determine thehydrogeochemical processes by major and minor elements in wet and dry seasonsof west flowing rivers draining the Western Ghats and to identify sourcescontributing them and to determine their distribution pattern in water andsediments. In the present study we report the analysis of selected heavy metals inthe chosen rivers with a view of establishing a baseline data of their levels.Increasing population pressure on finite land resources and implications of landtransformations to sustenance of human population call for an immediate need tounderstand the consequences of these transformations. In the light of the abovebackground, it is a necessary prerequisite to understand the landuse/ land coverchange. An attempt has been made in present study of Western Ghats region usingremote sensing and GIS on certain broad aspects of land use/ land cover changestaken place between Goa and Mangalore during the period of 1963 -2003.

MATERIALS AND METHODS

Study area and environmental setting

To the west of the Deccan plateau and close to the western coastline of theIndian peninsula are the Sahyadris, or Western Ghats. They extend southwardfrom about 20oN to the Malabar Coast, where they merge into the NilgiriMountains. The rivers in the Western Ghats region generally originate at anelevation ranging from 400 meters to 1600 meters above the mean sea level, closeto the Western Ghats ridge. The rivers generally flow westward and meet theArabian Sea after a short run varying from 50 kms to 300 kms. The rivers are verysteep in the upper reaches and fairly steep in the middle reaches. It is only nearthe sea that they have relatively flat gradients and some sort of flood plain.

River system and basin characteristics

With the Western Ghats (Sahyadri) forming a major water divide, there areshort and swift flowing rivers in the west draining into the Arabian Sea. Notableamong them are Mandovi [length 87 km and basin area 2032 km2

(Rao, 1975)]

and Zuari (34 km long and drainage area of 550 km2) in Goa state, Kalinadi (184

HYDROGEOCHEMICAL STUDY OF WESTERN GHATS REGION, GOA INDIA

408

km long; drainage area of 3376 km2), Gangavali (152 km long and catchmentarea of 3574 km2), Agnashini (84 km long; drainage area 1330 km2 ), Sharavati(122 km long; catchment area of 3592 km2), and Netravati [148 km long(Jayaprakash, 1988); drainage area about 3432 km2] in Karnataka state of India.

The Western Ghats provides a principal geographical barrier in the path ofthe Arabian Sea branch of the Southwest monsoon, and is principally responsiblefor the heavy rainfall over the western coastal belt having tropical evergreen forest.The Southwest monsoon season (June to September) is the principal rainy season;over 90% of annual rainfall is realized in this period. The annual average rainfallin Goa region is around 2500 mm (Das et al., 2005). Dakshina Kannada receivesan average rainfall of 3500–4500 mm annually, and has an average temperatureof 28°C (Gangadhara, 1992).

Laterite, Saline and sodic soils also occur in the patches in the summits ofthe Western Ghats. Most of Goa’s soil cover is made up of laterites which are richin ferric aluminium oxides. Further inland and along the river banks, the soil ismostly alluvial and loamy. Goa, being in the tropical zone and near the ArabianSea, has a warm and humid climate for most of the year. Rice is the mainagricultural crop, followed by, cashew and coconut.

GEOLOGICAL SETTING

The geology is largely composed of greenstone belts, high-grade schists,and charnockites set in a vast expanse of migmatitic gneisses, all forming part ofthe shield area of peninsular India. The coastal margins of the state, bounded bythe Arabian Sea, show a thin cover of recent and sub-recent sediments and alluvium.The area is largely covered by pre-Cambrian Dharwars represented by quartzites,phyllites, chlorite-schists, gneisses, metabasalts, metagreywackes and bandedhematite quartzites. Besides, rocks belonging to Cuddapah age occur fringing thenorthern stretch of the coast. A patch of Deccan Traps covers the crystalline rockstowards north-east. Lithology of the basins is dominated by plutonic andmetamorphic rocks, which are weathering resistant. However, in the basinslimestones are present at few places, which can have a strong impact on the waterchemistry. Limestone weathers almost 20 times more rapidly than granite (Amiotte-Suchet and Probst, 1993, 1995) and even smaller area of limestones can stronglyinfluence the water compositions of the basin. An important feature is the extensivelateritization over most of the region owing to the tropical, moist climate withvast seasonal changes. The laterites are associated with iron and manganese oresalong a linear belt within the midland of the state.

SAMPLE COLLECTION AND ANALYTICAL METHODS

Hydrochemical informations were gathered from a sampling network oftwenty two points (3 each from the Mandovi, Kali, Gangavalli, Aghanashini,Sharavathi, and Netravati Rivers and 4 from the Zuari river) in the hydrological


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basins of Goa and Mangalore (Fig. 1) during 2003-2004; pre-monsoon, monsoonand post-monsoon to compare the water properties.

Once samples were brought to the laboratory, they were preserved at 4oCin the cold room. Parameters like pH, Conductivity, TDS (Total Dissolved Solids)and Bicarbonate contents of the samples were measured from unfiltered samplesimmediately after the sampling. Water samples collected from each location werefiltered through 0.45μm membrane filter in the laboratory. Sediment collected onthe filter paper was weighed after drying for determination of total suspendedmatter (TSM). About 100 ml sample was acidified with HNO

3 to a pH ~2 to

stabilize the dissolved metals and rest of the portion was kept unacidified.

Cations were analyzed in acidified fraction whereas all anions were analyzedin unacidified fraction. Bicarbonate content was determined followingpotentiometric titration method (APHA, 1998). Na and K were determined byFlame-photometer while Ca and Mg concentrations were determined by usingShimadzu AA-6800 AAS.

Anions were determined by Ion Chromatograph. Dissolved silica (H4SiO

4),

and DOC (Dissolved Organic Carbon) were determined from the unacidified watersamples by Molybdosilicate Method (APHA, 1998), and Vial digestion methodusing COD reactor respectively and finally absorbance were taken by CecilSpectrophotometer (model no.594) for both the parameters.


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Sediment samples, after being brought to laboratory, were kept in cold room at4oC. Fine ground homogengenized sediments were taken in the beaker and heatedwith 30% (v/v) H

2O

2 for removal of organic matter. The treatment was repeated

until the CO2 emission stopped. 0.1gm of finely ground sample was transferred to

the Teflon crucible and 2ml of aqua regia (HNO3 and HCl ratio 1:3) and 5ml HF

were added to each crucible, these were then sealed in metallic cases. The cruciblewas heated for 1.5 hrs at 100°C and then allowed to cool down to room temperature.5.6gm of Boric acid crystal (H

3BO

3) was dissolved in 20 ml distilled water and

then added to the bomb content that was made up to 100ml. The solution wastransferred to polypropylene bottles for storage. The sample was left undisturbedovernight to allow the formation and setting of borosilicate from the solution.The gelatinous precipitate is separated by centrifugation. The solution thus obtainedwas used for analysis of metals by using Shimadzu-AA-6800, Atomic AbsorptionSpectrophotometer using air-acetylene flame.

RESULTS AND DISCUSSION

Major element chemistry

The average results of chemical analysis of waters of rivers underinvestigation along with pH, EC and TDS for the pre-monsoon, monsoon andpost-monsoon seasons are given in Table 1. The analytical results show themarginally acidic to marginally alkaline nature of water. The pH in post-monsoonis slightly less as compared to monsoon and pre-monsoon seasons. These riversare characterized by high TDS and low alkalinity (HCO

3-). The higher conductivity

(EC) reflects the higher ionic concentration of the waters. In general, EC andTDS show low concentration during monsoon and higher values in pre-monsoonand post-monsoon periods (Fig. 2a-g). Such seasonal variation in EC indicates anincrease in concentration of major ions in the non-monsoon seasons, which is


411

probably due to evaporation duringperiods with low water levels, aidedby elevated temperature in theregions. The TDS in rivers includeinput of elements from all sourcesviz. chemical weathering,atmospheric and anthropogeniccomponents. The mean TDS in the

waters is 11157.88 mg/l (n = 66) (Table 1). The major anions constitute ~62% ofthe TDS. Chloride is the dominant dissolved ion, accounting for almost 57.53%of the TDS. On an equivalent basis, Cl- accounts for ~78% of the total anions andis followed by SO

42- and HCO

3-, which account for ~8% and ~6% of the total

anions respectively. It is estimated that most of the bicarbonate in the rivers isfrom carbonate weathering. Bicarbonate concentration from silicate weatheringis not significant. The average pCO

2 of the rivers during post-monsoon, monsoon

and pre-monsoon are 10-2.35 atm., 10-2.38 atm. and 10-2.40 atm. respectively. Theeffective internal CO

2 pressure of each of the Western Ghats Rivers (Table 1) is

higher than the atmospheric CO2 partial pressure value of 10-3.5 atm., which is in

conformity with the global trend. This would mean that rivers are commonly outof equilibrium with the atmosphere. High chloride and sulphate contents foundin waters of these river basins may probably be attributed to the distance to the


412

marine environment which controls the exponential decrease of ocean aerosolinput to land (Na+, Cl-, SO

42-, Mg2+) and to the morphology of the soils irrigated

by the rivers, which are formed mainly of limestone. Molar Na/Cl ratios rangingfrom 0.28 to 4.02 with an average of 0.95 indicate a significant marine contributionin these coastal river basins. Anthropogenic inputs such as discharge formindustrial, sewage and mining effluents and manure can be considered as othersources for Na and Cl abundances in the river basins.

The waters studied here are rich in sulfate ion. The sulfate ion in the riverwaters may have several sources, that is, dissolution of evaporites such as gypsum,oxidation of sulfides, and atmospheric input. It is certainly important to identifythese sources or their relative contributions to the water when considering sourceof major ion and rock/soil weathering rate in the catchments. Although dolomiteis present, there is no geological evidence of presence of evaporite strata exposedin the river basins.

Other potential sources of Cl- and SO4

2- dissolution of halites, suppliedfrom saline/alkaline soil, and discharge from groundwater and anthropogenicinputs. Oxidation of pyrite bearing shale and schist can be an additional sourcefor SO

42-. No sedimentary rock containing evaporates is reported in the basin,

which excludes the lithological origin of chloride in the river water. In the absenceof evaporite outcrops in the catchment, Cl in rivers can be entirely attributed tonon-weathering sources (Meybeck, 1983, 1996). Other measured anions (NO

3-, F-

and PO4

2-) contribute relatively less (<2%) to the total anionic budget. Undernatural conditions, the dissolved phosphate (PO

43-) concentration should not exceed

0.5 mg/l, as the solubility of phosphate mineral is limiting (Subramanian, 1994).The reported high concentration of these ions in the rivers can largely be attributedto anthropogenic activities, the likely sources being fertilizers and sewage.

The average dissolved organic carbon (DOC) concentration of these westflowing rivers is 2.91 mg/l (Table 1). Most of the values are comparable to theDOC (2.7 mg/l) in Rio Branco (clear water) but are well below the DOCconcentrations (7.7-8.6 mg/l) in Rio Salimoes (white river) and the mean DOCvalue (11.4 mg/l) detected in the Negro Basin (black water) (Kuchler et al., 2000)except at few gauging stations. These river basins are, therefore, non-organic innature.

The average concentration of dissolved silica (H4SiO

4) is ~5 mg/l, which is

lower than the Indian (7 mg/l) (Subramanian, 1979) and global average which is12 mg/l (Meybeck et al., 1996) for an aquatic system. At some stations the silicavalues are well compared to the world average and in case of Gangavali River,the average silica value (7.53 mg/l) is comparable to the Indian average but lowerthan the world average.


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The major cations contribute around 38.26% of the TDS. Sodium andmagnesium are the dominant cations accounting for 33.17% and 2.38% of theTDS respectively. Calcium concentration contributes 1.28% to TDS. The plot ofcalcite Saturation Index (SIc) against Dolomite Saturation Index (SId) for WesternGhats river estuary system (Fig 3) shows that maximum of the water samplesduring post-monsoon, monsoon and pre-monsoon seasons were undersaturatedwith respect to calcite and dolomite due to little input from land and most water isderived from the groundwater. Potassium is the least dominant cation.

The compositional variations of waters of these rivers reflect the variationin source rocks of the catchment areas of the river basins and proximity from thesea. The upstream sampling stations in the river basins are controlled mainly bynatural conditions, whereas the water quality further downstream is increasinglyaffected by human activities. As a consequence, chloride in the upstream stationsshould be strongly controlled by atmospheric inputs. In the downstream stations,however, the water composition changes without any visible connection tolithology. The ionic composition of the upstream and downstream waters showsall the major ions show a significant downstream increase dominated by therelevant increase in Na, Cl, and SO

42-. The downstream increase of these ions can

be ascribed to the sea water mixing and geological nature of the soils surroundingthe rivers. The rivers are characterized by high sodium and chloride due to theirproximity to the Arabian Sea. All the measured chemical parameters show muchhigher concentrations in the downstream than the upper reaches of the drainagesystems with some value more than 100 to 1000 fold higher in the downstreamthan upstream. Almost all the measured chemical parameters show systematicincreases from headwater areas to the lower reaches that appear to be associatedwith inputs of the domestic wastes and sea water mixing. Mining debris containingcontaminating effluents and the domestic sewage are the major pollutants

Figure 3. Saturation Indices with respect to calcite and dolomite (Slc and Sld) for Western GhatsRivers.


414

discharged in the estuary regions. Specific human activities and landuse associatedwith population density such as agriculture probably do have contribution in thechemical loads of the rivers under investigation. The Dandeli Paper Mills atDandeli on the banks of the Kali River releases large volumes of untreated effluentsdirectly into the river thus polluting the river. There is illegal sand mining alongthe banks of river Kali and its tributaries. It is reported to be rampant in the Supadam area.

The upstream sites are sparsely populated and anthropogenic inputs intothe streams are less than the lower reaches which are densely populated. Thusnatural and anthropogenic factors can promote the evidenced longitudinal variationof the chemical composition of the waters of the investigated rivers.

Sediment chemistry

In addition to water chemistry, surface samples of the river sediments havealso been investigated and the average elemental composition of surface sedimentsof the Western Ghats Rivers is presented in Table 2.

Chemical Index of Alteration (CIA)

Nesbitt and Young (1982) have derived a weathering index called ChemicalIndex of Alteration (CIA) in molecular proportions:

⎥⎦

⎤⎢⎣

⎡

+++=

OK ONa CaO OAl

OAl 100 CIA

2232

32

The average upper crust has a CIA value of about 47 (McLennan, 1993),CIA values of 45-55 indicate in essence no weathering. For individual clayminerals, kaolinite, chlorite, gibbsite have CIA values of 100, whereas smectiteand illite have values in the 70-80 range. Primary minerals have much lowervalues of CIA (Nesbitt and Young, 1982). The annual average CIA values for theWestern Ghats Rivers ranged between 27.44 and 47.44 (Table 2). The CIA valuesindicate that there is very low weathering in the river basin. Mineralogy of surfacesediments indicates that at few locations, kaolinite concentration is high. Therefore,


415

it can be inferred that different proportions of primary minerals and high contentof quartz in the surface sediments along with clay minerals cause such a widerange of CIA values obtained in these Western Ghats Rivers. The enrichmentratio was calculated for surface sediments of Western Ghats Rivers using theformula given by Lee et al. (1994).

The sediments of rivers were found to be polluted with respect to few metals(Table 3). Abundance of total concentrations of elements in the surface sedimentsof Western Ghats Rivers is depicted in Fig. 4(a & b). The sediment chemistry isdominated by Si, Al, Na, K, Mg and Ca which show pronounced variations alongthe downstream. Cd showed significant enrichment in almost all the rivers. Fe,

Figure 4(a&b). Abundance of total concentrations of elements inthe surface sediments of Western Ghats Rivers.


416

Mn, Cu and Pb also show some enrichment at certain locations. The sources of allthese metals in the rivers seem to be due to anthropogenic activities as industrialactivities and domestic sewage discharge. The contamination factor was calculatedas the ratio between the sediments metal content at a given sampling station andthe world average for that element reported for the world shale (Turkian andWedephol, 1961). Results on the contamination factor are presented in Table 3.For most of the metals at different locations, CF values may be considered asdominantly anthropogenic in origin and could be linked to industrial pollutionand mining of Fe and Mn along these river basins. Tomilson et al. (1980) proposedPollution Load Index, to assess the extent of metals in the sediments of rivers andestuaries. The PLI values of Western Ghats rivers indicate that the sediments aremoderately polluted (Table 3).

Landuse/Land cover changes in the Western Ghats region during the periodof 1963-2003

The changes in the landuse/land cover often produce serious threats to thehuman existence directly and indirectly. The knowledge of the land use/land coverpatterns helps in landuse planning, proper decision-making and policy framing aswell as its implementation. Hence, landuse/land cover is of great concern toplanners, academicians, researchers and the entire administrative set up. In thisRemote Sensing and Geographical Information System (GIS) plays one of themajor and an indispensable role as a decision making tool. An attempt has beenmade to present results of this study using remote sensing and geographicalinformation system on certain broad aspect of landuse/land cover changes (forest,agricultural land, coastline, water bodies, open scrub and settlement) that havetaken place in the Western Ghats region between Goa and Mangalore during theperiod of 1963 to 2003. Vegetation has been cleared by the inhabitants of thecatchments to give room to cultivation and settlement. The vegetation cover ofthe catchments presently being secondary in character consists largely ofagricultural crops. The entire study area shows quite large amount of deforestationand conversion of dense jungle to agricultural land and open scrub and also humanencroachment done through development of settlement areas {Fig. 5 (a-e)}. Thecoastal length of the study area has not changed much but the coastal belt hasincreased considerably. The Sharavati and Netravati have meandered to someextent and this has caused some land use and land cover changes in an around thesampling areas and also there is deforestation and an increase in agriculture andopen scrub area. Thus, the study area requires special attention regarding landuse and land cover planning, proper management and emphasis to preventenvironmental degradation and other types of hazards.


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Fig. 5 a.

Fig. 5 b.


418

Fig. 5 c. Fig. 5 d.

Fig. 5 e.


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CONCLUSIONS

1. The Western Ghats Rivers under investigation are marginally alkalineirrespective of seasons. High E.C. and TDS values particularly near themouth of the rivers reflect higher ionic concentration in water indicatingmarine influence.

2. The average bicarbonate concentration is in conformity with that of theIndian rivers. The effective CO

2 pressure of each of the Western Ghats

Rivers is higher than the atmospheric pressure of 10–3.5 atm., which is inconformity with the global trend.

3. The sediment chemistry is dominated by Si, Al, Na, K, Mg and Ca whichshow pronounced variation along the downstream.

4. The Chemical Index of Alteration (CIA) over the surface sediments ofWestern Ghats Rivers indicates very low weathering. The contaminationfactor (C.F.) and pollution load Index (PLI) values of Western Ghats Riversindicate that the sediments are moderately polluted.

5. The entire study area shows quite large amount of deforestation andconversion of dense jungle to agricultural land and open scrub and alsohuman encroachment done through development of settlement areas.

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Hydrogeochemical Study of Western Ghats Region between Goa and Mangalore, India

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