2. Study Area

2.1 Kolleru Lake area

The Kolleru Lake has situated between 16⁰ 24′ 10″ and 17⁰ 23′ 44″ North latitude, and 80⁰ 41′ 5.5″ and 81⁰ 39′ 27.5″ East longitude in the south-eastern part of India (Fig.1). It is the largest freshwater lake in India located in the state of Andhra Pradesh and forms the largest shallow freshwater lake in Asia, with a catchment area of 5,052 km2, a water surface area of 901 km2at +10 MSL (mean sea level). The average water depth of 1 m and a maximum water depth of 3 m can be monitored during the southwest monsoon period (Barman 2004). The minimum and a maximum temperature range from 14 ⁰C to 22 ⁰C from November till February and 35 ⁰C to 46 ⁰C from March till October, respectively. The annual mean precipitation is 1,094 mm. The lake receives water from seasonal rivers, namely, Budameru and Thammileru. Apart from this, 68 minor irrigation channels are flowing into the lake. It has only an outlet river, the Upputeru, which connects the Kolleru Lake to the Bay of Bengal. The lake has a rich biodiversity, and thereby, the international Ramsar Convention declared it as a wetland of international importance in November 2002.
The two perennial rivers of the Krishna and the Godavari formed its catchment, which gives the lake a unique characteristic and has led to its role as a natural flood-balancing reservoir between these two river basins. The catchment is also one of the most developed agricultural areas in Andhra Pradesh state, as well as the state, which is historically called the “Rice Bowl of India.” With a massive fertilizer application and a high crop yield production, the Kolleru lake catchment accounts for 22.7% of chemical fertilizer consumption in the Andhra Pradesh state. According to the Andhra Pradesh Pollution Control Board (APPCB), reports that more than 17,000 tons/yr of fertilizers enter into the lake. Because of the high proportion of agricultural land and diverse agro-climatic conditions in this region, encourage the cultivation of different crops, a large number of chemical fertilizers considerably replaced the traditional organic fertilizer. In recent decades, besides the sewage inflow from nearby towns, diffuse agricultural pollution was accounted for a significant pollution source. In most cases, adding more quantities of N & P fertilizers to the soils does not result in increased crop yields and significantly led to proliferating eutrophication of the lake (Vijayalakshmi & Brahmaji 2017; Krishna et al., 2016; Bassi et al., 2014).
Kolleru lake is one of the most polluted lakes (Kolleru Lake, Pulicat Lake, Chilika Lake) in India. Therefore it is under the control of the Ministry of Environment, Forest and Climate Change (MoEF & CC), along with Central Pollution Control Board (CPCB) and State Pollution Control Boards (SPCBs). These organizations are responsible for the legal and regulatory framework for environmental protection in India (CPCB, 2005; MoEF, 2007). MoEF is accountable for the preparation of environmental policies through the Central Empowered Committee (CEC) in coordination with the Kolleru Lake Development Committee (KLDC), whereas the “Operation Kolleru” was implemented. The main objective of this voluntary program was to minimize the pollution from fishponds across the lake, the Supreme Court of India initiated the “Operation Kolleru” in 2006 to clear all encroachments and their water pollutants. It divided into three phases between 16 February 2006 and 13 June 2006. As a result, approximately 1,776 fish ponds became destroyed, and 89.08 lakh cubic meters of earth, forming tank bunds, were removed (Azeez et al. 2011).

2.2 Significance of the study

It is generally acknowledged that the following essential criteria are prerequisites for the Kolleru Lake pollution control measures and implement the adequate BMPs between point and diffuse sources:
Due to the lack of a comprehensive environmental policy, the Kolleru lake is still facing severe threats by, firstly, agricultural runoff. In the catchment area, paddy cultivation carried out twice a year, the first crop cultivated between July and September is known as a summer crop, whereas the second crop grown between October and March is a winter crop (Azeez et al., 2011). According to Rao (2005), the usage of fertilizers varies between these two seasons, and the first crop utilizes 40 kg/ha of chemical fertilizers and that of a second crop 120 kg/ha. Besides, around the catchment area, approximately used of 1,16, 800 tons/yr inorganic fertilizers, and one-fourth of them end up in the lake via run-off and leaching (Sreenivas and Kumar, 2013). The level of chemical fertilizer application is far beyond the maximum trend in this region, and the decrease of fertilizer application would be beneficial.
Secondly, the water quality of the lake is deteriorated by point sources; thus, untreated industrial effluents released into the lake from nearby cities (Azeez et al., 2011). According to the list of critical pollution industries of the Kolleru Lake, there are 36 industrial pollutants located in the catchment. The major industries such as rice mills, paper industries, sugar factories, milk factories situated around the lake, alternately sewage sludge from nearby cities have contributed to its depletion and pollution. The pollution sources of the lake have highlighted by several studies and still continuous effort on point source pollution control not yet implemented – the management of the Kolleru Lake wetland ecosystem has received inadequate attention in the Central Water Commission (CWC) agenda. As a result, it is subjected to severe anthropogenic pressure.
As more and more studies conducted on the Kolleru Lake ecosystem (Vijayalakshmi & Brahmaji 2017; Azeez et al., 2011; Jayanthi et al., 2006; Rao & Pillala 2001; Narender 1993), it is possible to use the accumulated information for the development of pollution control measures and their responses to environmental changes. Apart from the point and diffuse sources, damages and losses due to massive flooding during the monsoon season, and partly drying out during summertime, as a result of inadequate management planning and action, are seen as areas of improvement (RIS, 2002). These natural and anthropogenic processes are influencing the lake. Both local drivers and features originating in the whole catchment of the lake occur. Since the 1990s, the lake has gone through enormous changes; more information about these changes can be found in Azeez et al. (2011). Based on the complexity of the existing threats of the lake, first, it is necessary to identify priority or test areas for applying management practices in the Kolleru Lake catchment, at least for lake protection. This paper reports on the priority control areas aiming at socio-economic development linking with the “Operation Kolleru for demolishing the fish ponds to restore the past glory of the lake” (hereafter the “Operation Kolleru scheme”) and in the long turn protection of the lake water quality by applying the Best Management Practices (BMPs).