Abstract
LANDSAT images are used to identify organic contaminants in water bodies, but, there is no enough evidence in present literature that LANDSAT is also good in identifying a mixture of organic and mineral contaminants such as agricultural waste. The focus of this paper is to evaluate the effectiveness of LANDSAT imagery to identify organic and mineral contamination (OMC) and to identify spread extent variations of pollution over the season/year in the Nagarjuna Sagar (NS) reservoir using only satellite images. A new band combination is proposed in order to detect OMC, because existing formulae based on band ratio proved to be inadequate in detecting the contamination in NS. Difference in reflectance values of Red and Green channel of an image helps clearly distinguish clear water from OMC water. This procedure was applied over LANDSAT data of the calendar years 2008, 2014 and 2015 to understand the contamination spread pattern through the reservoir. Results show that contamination is following a similar pattern over these calendar years. In January contamination starts at inlets and by May contamination spreads to almost 90% of the reservoir when the total area of water spread is also reduced by half. Contamination spread is low during the monsoonal period of June to September due to heavy inflow and heavy outflow of waters from NS reservoir. Post monsoon NS is contaminated again because of heavy inflow of runoffs from neighboring land use and limited water outflow. This contamination spread pattern matches the agricultural seasons and fertilizer application pattern in this region, indicating that agricultural use of fertilizers could be one of the primary causes of contamination for this waterbody.
Highlights
Natural and anthropogenic reasons are two major causes of water resource contamination; anthropogenic factors such as high urbanization, industrialization and intensive agricultural practices have increased and accelerated the contaminants that are being delivered to water resources, so, water bodies are not able to recover from these contaminations naturally (Rodriguez et al, 2007)
This can be attributed to two factors – while the increase in the contamination is due to immediate runoff from surrounding agricultural land use draining into the water bodies with the coming to an end of the main cropping season, the decrease may be due to increased water inflow into the reservoir due to North-east returning monsoon
This method gives good results when detecting organic and mineral contamination (OMC) from very large water bodies such as Nagarjuna Sagar (NS), located in tropical regions, using LANDSAT 5, and 8
Summary
Natural and anthropogenic reasons are two major causes of water resource contamination; anthropogenic factors such as high urbanization, industrialization and intensive agricultural practices have increased and accelerated the contaminants that are being delivered to water resources, so, water bodies are not able to recover from these contaminations naturally (Rodriguez et al, 2007). While the point source such as industrial and urban waste can be identified and handled for reduction in contamination, the non-point contamination sources such as agriculture runoffs are major problem throughout the world as these sources are hard to trace (Zeng et al, 2009, Linxu et al, 2010, Xue et al, 2008). Contaminants from these sources are both organic or inorganic. Chang et al, (2014), Palmer et al, (2015), Kutser, (2009) reviewed the sensors available, possibilities and methods available to detect contaminants in inland water bodies and agreed that using satellite imageries to study inland water contamination is one of the best available options
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