Evaluation of Land Cover changes of Mangroves along Mandovi, West Coast of India using RS and GIS

Mangroves habitats are highly adoptable halophytes found in intertidal regions of tropical estuaries, are threatened by variety of anthropogenic activities including mining. Many mining sites and loading points are located along the course of Mandovi estuary, West Coast Of India, Goa which sustains mangrove habitats. Mangroves are of a great significance in arresting mining rejects and recycling its constituents and have proved to be a good indicator for detecting and quantifying short-term changes in the coastal zones. Time lapse satellite data suggested changes in land use patterns. The present study showed that mangrove cover along the stretch of Mandovi increased by 116.68% during 1997-2011, a decline of 12.52% from 2001-2006. The increased in mangrove cover could be attributed to government's rehabilitation initiatives and invasion by mangroves on agricultural farms; besides a new mangrove formations in the areas on deposited mudflats between the existing mangrove and open mudflats. Isle within the mid-stream of river was noticed with more proliferation with mangroves due to sediment deposition due to mining rejects and also from spilling of ores during transported. Mangroves have inherent characteristics to withstand pollutions to certain extent due to its robust nature. All these lead to tremendous improvement of mangroves. Mining may not affect mangrove distribution (area, content and canopy cover) to greater extent but its associated biological, hydrological and sediment logical features could get adversely affected. Current findings will serve in understanding the land cover changes of mangrove habitants and in devising effective strategies for their conservation and rehabilitation.


INTRODUCTION
Many global coastal zones are currently subjected to stress owing to spur of anthropogenic activities associated with economic consideration, land use, and resource development. India, in particular, is facing increasing stress as a result of cumulative environmental changes driven by urbanization, industrialization, unsustainable growth, and ever increasing population leading to degradation of coastal zones and ecosystems (Jagtap et al., 2003). Though, land cover change is a complex environmental indicator from regional to global level, but is an important aspect of resource management and environmental mitigation. Therefore, any unplanned interference can prove detrimental to its inherent value. Trends in vegetation cover dynamics, is an important aspect as it provides information about landscape processes and ecological status (Nagi, 2008). Remote Sensing data having good spectral and spatial resolution are found to be very effective in evaluating and monitoring land use and land cover changes (Lillesand et al., 2004). Mangroves form an ecological sensitive habitat in the tidal influenced intertidal regions of tropical estuaries and are of a great significance in arresting mining rejects and recycling its constituents, particularly metals (Kathiresan, 2000). Marine vegetation, particularly mangrove, plays a significant role in stabilizing the shores by preventing soil erosion. Besides, mangrove ecosystems inhabit various kinds of fauna of ecological and socio-economical significance (Ajana, 1980;. These habitats have proved to be a good indicator for detecting and quantifying the short-term changes in the coastal zones (Filho et al., 2006). Many estuaries of Goa namely, Terekhol, Chapora, Mandovi, Zuari, Sal, Talpona, Galgibag and along its coastline (~120 km) sustain mangroves. The Chorao island of Mandovi estuary sustains the best mangrove formation in the State. The major mangrove plantations (~ 80%) in Goa are located along the Mandovi-Zuari-Cumbarjua estuarine complex (Jagtap, 1986). This particular complex is extensively used to transport mining ores from loading points located along the bank of the Mandovi to Mormugoa harbour for shipment to other countries. Mining, a centrepiece of Goa's economy, forms the major source of sediment and oil to the close-by estuary areas. During recent years, Goa has been undergoing tremendous changes in its land use patterns (Murali et al., 2006). Mangrove ecosystems are important for fish production and serve as nursery, feeding and breeding grounds for many fish and shellfish. The healthy ecosystem of mangroves is vital in context of Goa since many mining sites are located around the catchment areas of many estuaries and also significant number of its population from the coastal areas are in the fisheries occupation. The objective of this work is to assess the changes in mangrove vegetation along Mandovi estuary during last fourteen years (1997-2011) and to assess its prevailing situation using remote sensing (RS) and Geographical Information Systems (GIS) techniques. This will greatly help in monitoring and management of major mangrove habitats of Goa and also help to evaluate the extent of possible impact of mining on mangrove ecosystem along the course of Mandovi estuary.

II.
STUDY AREA Mandovi River originates in the Barwa Ghat of the Sahyadri hills in Karnataka, flows downstream as Mandovi estuary (Fig. 1) and after traversing a stretch of about 70 km joins the Arabian Sea through the Aguada bay near Panaji. Its width at confluence region is 3.2 km, while at upstream it narrows down to 0.25 km and is fed by monsoon precipitation from the discharges of a catchment area of ~ 1150 sq km . The Mandovi basin has an area of 1530 sq km and constitutes about 42% of the land area of the State . Its pre-and postmonsoonal flows are also regulated by the semidiurnal tide of 1.0-2.5 m range. Along its course, Mandovi has number of tributaries and islands with narrow bends and shallow depth. It is connected with Zuari estuary through a canal called Cumbarjua canal having a length of 17.0 km and an average width of 0.5 km. It is a natural course connecting the two estuaries.

Status of Mangroves:
Mangrove vegetation in the world has been declining at the assumed rate of 2 to 8% per year or 0.6 % of all inland forests (Spalding, 1997). The total area of mangroves in the year 2000 was 1,37,760 sq km in 118 countries and territories in the tropical and subtropical regions of the world; approximately 75% of world's mangroves are found in just 15 countries and only 6.9% are protected under the existing protected areas network (Giri, et al., 2010). Indonesia has the highest mangrove cover of 22.6% of total global mangrove area, while India accounts for only 2.7%. The Indian sub-continent harbours about 9700 sq km of mangrove area with major formations occur in the regions of the Indus, Sunderband, and Mahanadi deltas, the Gulf of Kutchchh, the Andaman and Nicobar group of islands, and a part of the West Coast and the Jaffana Peninsula in the north of Sri Lanka (Jagtap, et al., 2007). Mangrove habitats of India have been facing tremendous threats due to indiscriminate exploitation of mangrove resources for various uses. In recent past, the mangrove vegetation in the world and particularly in Indian subcontinent has deteriorated, mainly due to their poor management (Jagtap, et al., 1993;Khalil, 1999;Jayatissa, et al., 2002). Pollution is major common occurrences that dwindled mangrove area (Jagtap, 1983). According to Government of India report (1981), there was a loss of 40% of mangrove forests during the last century (Kumar, 2000 a). The National Remote Sensing Agency (NRSA, 1983) recorded a decline of 59.18 sq km of mangrove between 1972-1975 and 1980-1982. Owing to these threats, more than 33% of the Indian mangrove areas have been lost within the last 15 years; East Coast has lost an area of about 28%, West Coast lost about 44% and Andaman and Nicobar Islands approximately 32% (Jagtap, 1983;Babukuttyand Chacko, 1992;Chakrabarti, 1995;Elizabeth, et al., 2006;De Souza, 2006;Naskar, et al., 2008). In the context of Goa, as well, there are concerns of the mangrove habitats being put under threat due to anthropogenic activities of various kinds. Mining, being a major industry in Goa is believed to be one of such activities, which have a potential to cause a considerable damage to their existence and in their conservation efforts.

III.
METHODOLOGY Mapping of mangroves along Mandovi estuary was done using cloud free satellite data (Febuary, 2011) of LISS III sensor of IRS-P6 series during the low tide period in order to obtain maximum coastal zone and exposure of vegetation. IRS LISS III provides data in four spectral bands; green, red, Near Infra Red (NIR) and Short Wave Infra Red (SWIR). Density-wise classification details are obtained from LISS III data with the resolution of 23.5 m at 1:25,000 Scale. Geometric correction was performed to improve the geolocation to a root mean square error of half a pixel, an accuracy needed for subsequent change analysis. Each image was normalized for variation in solar angle and earth-sun distance by converting the digital number values to the top of atmosphere reflectance. The images were not enhanced prior to unsupervised classification, and the thermal band (band 6) was excluded. Prior to classification, satellite images were subsetted to include only areas where mangrove forest is likely to occur. Subsetting an area of interest helped to increase overall classification accuracy by reducing the number of land-cover types and spectral projection and WGS84 datum. Area of interest was separated using subset method and then subjected to unsupervised classification. From the results obtained, mangrove classes were visually separated and grouped into one common class. Google map was used as reference for confirmation of the classified area. These images were later opened in Arc Map 9.3 environment to spatially assess change detection in mangrove habitat ( Figure 6.2). Ground truth information was used to match the classified images to check the accuracy of the result and for the production of final maps.

V.
DISCUSSION RS data in combination with GIS offers possibilities for effective and efficient analysis of detailed mangrove communities allowing qualitative and quantitative assessments of inaccessible area and is also able to retrieve, transform and display spatial data (Jensen, 1986;Davis and Quinn, 2002). GIS has been used with RS and field data to map and monitor regional and global environments, including the extent and dynamics of mangrove communities (Chaudhury, 1991;Hussain et al., 1999). Numerous researchers have carried out study on various aspects of mangroves in India Banerjee and Gosh, 1998;Singh, 1998;Nayak and Bhuguna, 2001;Singh, 2002). To arrive at the clear picture of status of mangroves, Kumar (2000 b) worked extensively on the status of natural regeneration in mangroves of Goa through sample surveys in all the estuaries and compared observations with Untawale et al. (1982). Upper reaches of the bank of Mandovi estuary is amidst of intense mining activities for considerable time. It has > 27 mines in its catchment area and 12 loading points on its bank or on the bank of its tributaries. About two third of mining operations are confined in its catchment area (Pathak et al., 1988) generating a reject of ~ 1500 to 6000 tonnes/day by each mine in this area (Nair, et al., 2003). Ore loading platforms are constructed along the bank of the rivers from where it is loaded on the barges and transported to Mormugoa harbour. Thus, the estuarine bed and associated mangrove of the Mandovi are exposed to an influx of metal affluent from ferromanganese mining (Attri and Kerkar, 2011). Mangrove cover in Goa was estimated to be around 20 sq km according to one mapping (Untawale, et al., 1982;Jagtap, et al., 2003). As per the report of Forest Survey of India (1999), the State had five sq km areas under mangroves, which appears to be an underestimate (Singh, et al., 2004). In the context of the presently study, it is revealed that there is an increase of 116.68% in mangrove vegetation from an area of 5.563 sq km to 12.054 sq km during the span from 1997 to 2011 along the Mandovi estuary. Whereas, from 1997 to 2001, a growth was noted from 5.563 to 7.783 sq km thereby, registering an increase of 39.90%. According to one study (Singh, et al., 2004), an increase in the mangrove vegetation in the important estuaries has been found during 1994 to 2001. During this period, the mangrove habitat increased by  (FSI, 1999 b). In 1988, The Government of Goa formed a State Level Steering Committee to oversee the improvement and conservation of the mangrove forest. In 1990, the State Government set up Multidisciplinary Project Formulation Team to facilitate the preparation of a Comprehensive Action Plan for the development of the mangrove ecosystem. In the same year, the government decided that no construction or development work would be allowed in the area earmarked by the Forest Department for mangrove conservation and declared that mangrove species should not be felled for a period of ten years. A five-year Mangrove Management Plan for Goa was prepared in 1991-1992 and implemented with financial assistance from the Government of India and one sq km of mangroves were planted each year as planned. The increase in the mangrove habitat in the study region can also be attributed to conservation and restoration mechanism initiated by the forest department of the State government and their well organized awareness programmes. As per the latest released India State of Forest report (2011) by government of Goa, the State has 22 sq km areas under mangrove cover and there has been increase in mangrove habitat in North Goa by 5 sq km over last two years. Ground truth observations revealed that mudflats due to the mining operations in the catchment region of Mandovi estuary provide a suitable substratum for the mangrove vegetation for its growth (Plate 1 a). Besides the increase in mangrove habitat could also be attributed to the reduction in agriculture activity in the area adjacent to mangrove plantation which is infested by mangrove (Plate 1 b). Further, Ground truth observations revealed that new mangrove formations have taken place, particularly in the area on the recently deposited mudflats between the existing mangrove and open mudflats along the waterways. More recently, an expansion of recently developed isle (Plate 1 c) was noticed in the mid stream of Mandovi estuary at Ribandar, close to station # 2, perhaps due to deposition of heavy sediments. The primary reason can be attributed to the flow of mining rejects from mining operations located along the bank of Mandovi estuary on its upper region. Spilling of ores from the barges while being transported from loading points situated either along its bank or its tributaries to Mormugoa harbour is also a contributing factor. Such types of new isles provide a good substratum for the growth of mangroves. This has proved to be blessing in disguise for the profusion of mangroves. Plantation efforts of the State forest department also assisted in a major way for the increase of mangrove cover. All these could be possible reasons of tremendous improvement of mangrove vegetation along the Mandovi estuary. Here, one side there is a heavy deposition of sediments in the Mandovi river and gets affected to such an extent that a small island of sort being formed whereas, on the other side, the sediments deposition acts as a good substratum for the growth of mangroves. Therefore, to conclude that there is no effect of mining operations on marine environment of Mandovi river on the basis of tremendous growth of mangroves in Mandovi river and along its bank would be erroneous and far from facts. The effects of mining pollutants on aquatic ecosystem of Mandovi estuary needs to be judged from the study of various marine hydrological parameters. One estimate suggests that on an average about 25 to 30 million tonnes of mining rejects per year is generated in the regions around Mandovi and Zuari estuaries. Along the basin of Mandovi estuary itself, an average reject amounting to 1500-6000 tonnes/day/mine is generated and about 27 major mines are located in the area (Nair, et al., 2003). Luxuriant growth of mangroves particularly in the Mandovi is attributed to favourable ecological conditions and substratum deposition . However, a study by Jagtap et al., (2007) revealed that an excess of sediments to a tune of > 9-12 cm thick per year due to natural and human activities has potential to threaten mangroves by way of clogging and ultimately may result in their deaths besides retarding new formations. Therefore, this parameter needs to be investigated regularly as a part of monitoring of mining to understand the impact on the mangrove habitats. Nevertheless, this work throws a light on healthy situation with regard to mangrove ecosystem and its potential for further growth and its conservation along the bank of the Mandovi estuary provided the various measures initiated by the government are continued further and if possible, strengthen the same. This study gives an updated geospatial database of these natural resources, which is the prerequisite for the management and conservation planning. Hence, to draw a conclusion that the mining pollutants do not exhibit visible impact on mangrove vegetation along the bank of Mandovi estuary is difficult to conclude, as there are multiple reasons for its growth as discussed above. However, various initiatives and mitigation steps taken by the government towards the conservation and protection of mangrove vegetation did help in yielding the desired result including steps taken to prevent the pollutants from mining operations reaching mangrove ecosystem.

Summary and Conclusion:
The anthropogenic activities worldwide along with natural disturbances in the past have yielded varied results. Mining was the backbone of Goa's economy till recent past; however, illegal mining in the past decade has caused severe damage to the ecology, hydrology and agriculture. This study was aimed to understand possible effects of mining on mangrove ecosystem along the course of Mandovi estuary of Goa. The present study reveals that there was an overall increase of 116.68% in mangrove cover from an area of 5.563 sq km. to 12.054 sq km during the span from 1997 to 2011 along the Mandovi estuary. However, a decline in the mangrove vegetation was observed from 2001 to 2006 registering negative growth of 12.52% and the mangrove vegetation declined from 7.783 sq km to 6.806 sq km, further from 1997 to 2001, registered an increase of 39.90%. To conclude that mining activities do not have any tangible effect on mangrove ecosystem along the bank of Mandovi estuary is difficult to arrive at due to increase of its cover. It is observed that the proliferation of mangroves is greatly helped by the aforestration efforts of the State forest department's initiatives. Further, mudflats due to mining operations in the Mandovi estuary provides a substratum for the mangrove vegetation for its growth, besides the increase in mangrove habitat could be attributed to the reduction in agriculture activity in the area adjacent to mangrove plantation, which is infested by mangrove. Ground Truth Observations revealed that new mangrove formations have taken place, particularly in the area on the recently deposited mudflats between the existing mangrove and open mudflats along the waterways. Besides, of late formed isle within the mid stream of Mandovi river, close to St. # 2, was noticed with more proliferation with mangroves due to the deposition of sediments of mining rejects from mining operations and also spilling of ores from the barges while being transported from loading points to Mormugoa harbour. Besides, mangroves have inherent characteristics to withstand pollutions to certain extent due to its robust nature. All these could be the possible reasons of tremendous improvement of mangrove vegetation along the Mandovi estuary. As such, mining activities may not affect mangrove distribution (area, content and canopy cover) to greater extent but, its associated biological, hydrological and sedimentological features could get adversely affected. The present work will form a baseline data on mangrove habitats to monitor the changes in near future.