Lake Catchment Interaction Analysis by Using Remote Sensing and GIS Techniques – the case study of Kolleru Lake, South India
Wetlands belong to the most productive ecosystem on Earth. They provide many essential services to humans. They play an important role and possess ecosystem services, for example, in biodiversity conservation, for the hydrologic cycle, to buffer regional climate change, and for human health. Among t...
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| Format: | Dissertation |
| Sprache: | Englisch |
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Philipps-Universität Marburg
2020
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| Zusammenfassung: | Wetlands belong to the most productive ecosystem on Earth. They provide many essential services to humans. They play an important role and possess ecosystem services, for example, in biodiversity conservation, for the hydrologic cycle, to buffer regional climate change, and for human health. Among the different types of wetlands, lakes (lacustrine wetlands) play a crucial role in maintaining global and regional water balances, natural and socio-economic resources, and habitats. Over the last decades, the lakes have gone through enormous changes derived from both natural processes and anthropogenic activities. Particularly, freshwater lakes are endangered through point and non-point pollutions, and such impacts are coming from agricultural runoff and industrial pollution, domestic waste, through municipal sewage, which may deteriorate the water quality and their ecological integrity. The Kolleru Lake wetland ecosystem in South India has been taken here as a case study, based on a comprehensive data analysis and modeling of Spatio-temporal variability of the pollutant loads, to achieve a better understanding of the man-environmental problems of the lake and its surrounding catchment. This is a necessary requirement for both better management of the agricultural, industrial, and water resources in the whole area and better lake protection and conservation.
Kolleru Lake is the largest freshwater lake in India. It is a huge natural flood balancing reservoir and also a wildlife sanctuary. In 2002, the Ramsar Convention recognized the lake as a wetland of international importance. The lake is predominately fed by rivers. Among them, Budameru and Tammileru rivers are contributing to the lake influx substantially, plus supported by 68 minor irrigation (drainage) canals. The Kolleru Lake covers a total area of more than 90,100 hectares and holding approximately 1,350 cubic miles of freshwater. Additionally, Kolleru Lake provides drinking water to the inhabitants of the surrounded villages. The lake area up to 3' ft contour is consistent with water, while the 5' ft contour level of the Kolleru Lake belongs to the wildlife sanctuary. Further, it is mostly occupied by aquacultures followed by paddy cultivation, weed infests, and marshy land. There are many small scales to large scale industries growing steadily in order to support successful aquaculture. Before the 1970s, the lake area up to 5' ft contour was not occupied by any type of economic activity; however, the lake is saturated with water during the rainy season, and it remains dry during summer. Furthermore, it was completely free from contamination by aquaculture and agricultural activities before the 1970s. After the 1970s, the State Government had distributed the Kolleru Lake up to 5'ft contour area the poor people, migrant workers, and local inhabitants in the promise of whenever the government again needs the lake area, and they can take it back by paying compensation to them. Then farmers have started paddy cultivation in and around the lake. All bed villages in the lake region are frequently severely affected by massive flooding in connection with the submersion of paddy fields. Despite the fact that the state Government had encouraged the farmers to convert the paddy fields into fishponds by providing loans in order to overcome the floods. However, the maximum of lake area up to wildlife sanctuary is practiced by the aquaculture in the 1990s.
Since 1970 until the current situation, the lake has been facing some severe environmental threats, such as degraded water quality, deteriorated aqua species and birds, and habitat losses, induced by human activities and accelerated by climate change. A major cause of the environmental problems was identified within the lake by the construction of fishponds resulted in pollution by using pesticides and waste food (exposed to bacterial diseases and infection) to enrich the fish growth. As a result, it causes biological magnification diseases, fertility, and respiratory problems to the animals, birds, and humans who live near to the lake. Thereby the ecosystem will become an inhospitable environment for those aqua species and birds. The fish ponds occupied approximately 42% of the lake area while aquaculture had encroached another 8.5%, together covering 50% of the lake region. If the human-induced debasement of the lake will continue, the lake will no longer cease to exist, and the wildlife species soon will disappear. Apart from the aquaculture tradition, the Kolleru Lake catchment is known for its intensive paddy cultivation. However, the massive application of pesticides and chemical fertilizers to agricultural lands across the catchment area is one reason for the eutrophication in Kolleru Lake. In addition to the several factors that influence the lake ecosystem, industrial pollution causes deteriorating water quality and makes them unfit for drinking water for the inhabitants of the villages around the Kolleru Lake. Both point and non-point sources issued threatens to the lake area becomes more sensitive by anthropogenic activities.
The main focus of the present research was to analyze the problems related to the lake catchment and give recommendations to the government about the insight view of the land use cover and enlighten the public perception towards the lake degradation. However, sedimentation in a lake is a natural consequence of the inflow of respected tributaries, rivers, and streams. In addition to the natural influence, man-made activities like land use and others are also responsible for erosion in the catchment and the sediment transport and accumulation of the sediments in both the lower sections of the catchment and the lake basin itself, as discussed in the first research objective. Extensive use of land and the indiscriminate rise of embankments for the construction of fishponds as well as agricultural functions has resulted in widespread soil erosion in the catchment and sedimentation over the deltaic part of the Kolleru Lake catchment. In addition, the perennial rivers of Krishna and Godavari drift down to the lake about 68,000 tons/yr of sediments that coming from the whole catchments after passage from the river banks and river beds. The objective of this part was to analyze both the average annual soil loss rate and its change from the catchment and the sediment yields by using the RUSLE model both for the terrestrial part and the semi-aquatic deltaic part of the Kolleru Lake catchment for the years 1972 and 2012. The results indicated that the average annual soil loss was estimated with 13.6 t/ha/yr, classifying the Kolleru Lake Basin under a very high erosion rate category. Whereas, the average annual sediment yield was determined with 7.61 t/ha/yr. The resultant difference of the sediment balance is temporally interbedded within the terrestrial sites and within the river banks and river beds. However, this study has found that tributaries and streamlines of the catchment carry high sediment loads to the lake.
This research has proved how intensive agricultural activities in wetland catchments interact with the pollution levels of the lake, causing a deteriorated water quality. Agricultural runoff (runoff from catchment areas dominated by agricultural use) is the main driving factor of accumulated non-point source pollution of the lake water, with side-effects on sediments and silts near the downstream areas of the Kolleru Lake catchment. It primarily caused eutrophication in the lake subsequently that led to proliferating the weeds. However, the second objective of the research was to estimate the tributaries' sub-basin loads and to highlight the diffuse critical sources against the village communities. For this purpose, the Soil and Water Assessment Tool (SWAT) was used to model the diffuse sources in the catchment. The spatial distribution of nitrate-nitrogen (NO3-N) and total phosphorus (TP) emissions were quantified. Some sub-basins contribute more pollutant load to the lake. Alternately, the first and second BMPs (Best Management Practices) level priority areas were identified. Further, suggestions for the implementation of agricultural management practices have been provided for the crucial protection of the lake ecosystem.
Consequently, the Kolleru Lake wetland ecosystem is known for its both abundant water availability as well as water scarcity. The river and streams water diverted into the agricultural lands, and still, there is a dire need for groundwater too. When the monsoon rain was weak, and after rainless summer periods, the lake falls more or less dry. Therefore there is a high demand for groundwater, which is continuously increasing. An effective way to analyze groundwater recharge and groundwater availability is a remote sensing and GIS based mapping. The theoretical concepts are involved in this objective is more useful for t further research of the link between surface emission and groundwater contamination. That is why the present research has been investigated as the third objective, the potential groundwater resources in the catchment. A simple mathematical equation was derived from the catchment hydrologic characteristics. The catchment characteristics were analyzed and based on the previous literature sources, and the thematic weight was assigned to evaluate potential groundwater zones. About 13% of the catchment area falls under poor conditions, 38% of the area falls under moderate conditions, 42% of the area falls under good conditions, and about 7% of the area is under excellent condition. These results are a contribution to future groundwater management projects and artificial recharge plans of the Kolleru Lake catchment to maintain sufficient groundwater levels.
Due to the still existing lack of observed data of the tributaries, i.e., runoff, sediment, water quality parameters, nutrient load, the used methods are limited and suitable just for an estimation. Sufficient calibration and validation of the results were also limited because the access to the study area and to an onside research institute was not allowed for the Ph.D. candidate, because of its status as a Ph.D. student from Germany. Field investigations on the interaction of pollutant loads with the runoff would be advantageous for a better calculation of the pollutant load and its dynamic. Because of the limited funding capacity, it is challenging to do a field survey to control every remote sensing and GIS result of this research. That is why, without a few exceptions, this study was conducted dominantly based on remote sensing data and accessible weather and soil data.
From the research results emphasized that the Kolleru Lake water level and water quality are highly degraded, respectively polluted with metals, agricultural contaminants, which makes the lake water not advisable for human consumption. The erosion and sedimentation loads are also high, and the priority management practices should be targeted already in the middle catchment region. These results give a general understanding of the pollutant levels in the lake, which should be useful for government management plans.
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| Umfang: | 145 Seiten |
| DOI: | 10.17192/z2020.0246 |