Spatio-Temporal Distribution of Water Quality Parameters in Ramsar Site-Kolleru Lake

India with its large geographical spread supports diverse wetland classes and being one of the signatory countries to the Ramsar convention for management of the wetlands for the conservation of the biodiversity and wise use of the wetlands. within the country. Kolleru is one of the largest freshwater lakes in Asia, 15 kilometers away from the city of Eluru, which is located between the alluvial plains of Krishna and Godavari river of  West Godavari and Krishna districts of Andhra Pradesh, India. It covers an area of 245 km² (Raoet_al1999) and is situated between 81° 04' 23" to 81° 24' 53" latitude and 16° 32' 03" to 16° 46' 49" longitude. The lake is a natural flood-balancing reservoir for the two rivers namely Tammileru and Budameru and sustained the rich native flora and fauna. Apart from these, nine major drains and seven medium drains empty their water into the lake. There is just one outlet referred to as Upputeru that runs a distance of sixty-four kilometer and connects to the Bay of Bengal. Most of the lake is freshwater, except in the southeastern part where brackish water conditions prevail especially during summer months, due to the incursion of tidal water through Upputeru (Karanam et al., 2019).
 
Kolleru lake undergone tremendous land use and land cover changes (LULC’s) due to the natural and anthropogenic activities (Settlement, agriculture and aquaculture etc). These changes have severe impact on the lake water quality, mainly on surface water degradation caused by agricultural, aquaculture runoff, factory discharge and sewage from household (Hong et al., 2011; Smith et al., 2013). Earliar studies also supported that this ecologically important lake is getting polluted due to the discharge of untreated effluents from industries located around the lake and by aquaculture, agricultural wastes and domestic sewage from neighbouring villages (Rao et al., 2004). Water is a major issue for the survival of all living organisms and it is a vital resource for any environment for their development. In the recent time the variation in water quality is affected due to the increased anthropogenic activities, domestic wastewater discharge and aquaculture activities in and around the lake (Kumar et al., 2016). The water quality assessment is based on the value of several physical, chemical and biological indices (Bhutiani et al., 2016). According to Vijayalaksmi et al., 2015 the organic-rich wastes which come through the non-point sources are another important reason to deteriorate the water quality including depletion of dissolved oxygen levels leading to mortality of aquatic fauna of the lake. As reported earliar, dispersal of pesticides like polycyclic aromatic hydrocarbons (PAHS) in the prawn ponds of Kolleru lake water and sediments have raised concerns against the quality of prawns harvested. The entire lake ecosystem has been highly disrupted by the activities of man, mainly by illegal encroachment of lake bed area for agriculture, human settlement and aquaculture to some extent.
       
This study is undertaken to evaluate the present water quality status existing in Kolleru Lake, which has been affected seriously. The spatial distribution maps of water quality is developed to locate the potential areas of pollution stress, along a seasonal gradient. The spatial maps depicting the seasonal hydrological parameters for the Kolleru lake can potentially act as a baseline for the efficient lake management plan and sustainable aquaculture development in the area.

The sampling locations were selected on the basis of inlets and, outlets of the lake and the extent aquaculture growth in and around Kolleru lake (Fig 1). To cover a large number of determinates, sampling network was designed that fairly represent the water quality of the lake system. Total ten (10) sampling sites were selected within the entire lake area to review the Physico-chemical parameters of the lake. The sampling locations were geographically identified using Global Positioning System (GPS) to locate them easily in the next sampling. Sampling was done from August 2017 to March 2018 covering the Post monsoon and Pre-monsoon seasons. A total of 11 water quality parameters such as pH, temperature, EC, TDS, TSS, total alkalinity, total hardness, dissolved oxygen, salinity, COD and nitrates were analysed by using a standard protocol (APHA 2012). Geographical description of the sampling sites were given in Table 1. Table 2 shows the method adopted for the analysis of the respective parameter Fig 1. Shows the study area.
 

 

 

       
Arc GIS is a powerful software used for computerized mapping and spatial analysis. Extracted lake boundary from NE 44-15 toposheet of 1938 has been used for the spatial distribution of physico-chemical parameters. For this study, the latest version of Arc GIS 10.4 by ESRI was used. Interpolation of Physico-chemical parameters were also carried out using IDW (Inverse Distance Weighted) Spatial Analyst tool under the Arc toolbox of Arc Map.

Physico-chemical parameters were estimated from 10 sampling locations selected at kolleru lake showed great variation from the post-monsoon to pre-monsoon. Results of post-monsoon and pre-monsoon water quality parameters from ten sampling stations are presented in Table 3 and 4 respectively. Spatial distribution maps for post-monsoon and pre-monsoon were presented in Fig 2 and 3.
 

 

 

 

 
Temperature
 
The water temperature of the Kolleru lake ranged from 25.4°C to 27.2°C during post-monsoon and 26.7°C to 29.5°C during pre-monsoon. This study shows that higher temperature levels 29.5°C were noticed at Chintapadu while lower temperature value of 25.4°C was noticed at Pratikolalanka. This variatipon tn temperature maybe due to the variation in the timing of water sample collection, from different areas and influence of season, as also reported by Jayaraman et al., 2003. The temperature of the surface water will change according to the sun intensity, while the bottom of the lake remains constantly cold (Jorgensen, 1980). Temperature changes in the lake could be explained in terms of climate influence, season and depth of the lake (Gupta and Gupta, 2006), as is also reported in the present study.
 
pH
 
pH is a measure of acidity or alkalinity present in water samples. The pH of the water samples in the study area varied in between 7.6 to 8.5 during post-monsoon and 7.8 to 8.9 during pre-monsoon respectively. All these results of the water samples representing the pH of lake water were neutral to slightly in alkaline nature. Higher pH level 8.9 was noticed at Paidichintapadu may be due to the rich organic matter in water. Comparitively low pH value 7.6 was observed at Chintapadu may be due to a decreased level of water in this area. Nandan and Patel, (1992) reported that the low pH values during post-monsoon might be due to dilution of rainwater and the water which consists of more level of pH promotes the growth of algae and results in a massive bloom of phytoplankton. Overall in all the selected sampling sites, pH levels suggested that slightly alkaline conditions which are generally favourable for the growth of aquatic macrophytes.
 
Electrical conductivity
 
Conductivity is used as an indicator of the quality of water. Conductivity values were recorded above the normal range in all the sampling sites. In the study area, the EC of watervaries between 1250.12 μmhos/cm to 6008.7 μmhos/cm during post-monsoon and 1350.12 μmhos/cm to 6850.4 μmhos/cm during pre-monsoon repectively. High conductivity was reported at Chintapadu which shows the high rate of anthropogenic input like agricultural wastes and municipal wastes from Vijayawada, Eluru, Gudiwada municipalities. Low rate of conductivity was noticed in Gudivakalanka due to its vast area of natural ecology. When the water level was high after the wet monsoon, EC was recorded low during the post-monsoon season (Pramod et al., 2011).
 
Salinity
 
The salinity in the study area was recorded as 0.1 ppt to 6.1 ppt during post-monsoon and 0.2 ppt to 7.6 ppt during pre-monsoon. This study shows that the high values of salinity were recorded at Upputeru-near Pandiripalligudem, Chintapadu sampling. Upputeru water may backflow entering into Kolleru Lake is another reason for the high value of salinity in Upputeru. The lower value of Salinity in Gudivakalanka suggested the small amount of salts as it is not connected to sea through uppeturu. The maximum value of salinity was recorded during the pre-monsoon season. Changes in the land use pattern and groundwater overexploitation are the main sources for saltwater intrusion in Kolleru lake (Karanam et al., 2019).
 
Dissolved oxygen
 
The biological processes have a dominant influence on the concentrations of oxygen. Thus, in areas where organic matter accumulates and become degraded, those areas may become anoxic or anaerobic and fish death will occur (Hale et al., 2016). DO values ranged from 2.4 mg l^-1 to 7.2 mg l^-1 during post-monsoon and 2.3 mg l^-1 to 5.6 mg l^-1 during pre-monsoon. The maximum value was recorded at Atapaka with 7.2 mg l^-1, which might be due to the least magnitude of disturbance, since the area is under the monitoring and protection by Kolleru board and the minimum value was recorded at Chintapaduwith 2.3 mg l^-1 may be due to the addition of a high amount of agricultural wastes, sewage and surface runoff in the area. The maximum value of dissolved oxygen was recorded during the post-monsoon season. Lake consists of more amounts of weeds; it affects significantly the dissolved oxygen concentration in water (Mironga et al., 2012).
 
Total alkalinity
 
The total alkalinity was varied between 195.2 mg l^-1 to 407.5 mg l^-1 during post-monsoon and 189.5 mg l^-1 to 356.5 mg l^-1 during pre-monsoon. The high value of alkalinity was reported at Kolletikota, due to high pH level which favours the growth of aquatic macrophytes like Phragmites, Ipomea, Azolla and decomposition of these weeds will again increase nutrient content which further leads to higher alkalinity in Kolletikota (Vijayalakshmi et al., 2016), While the low values of alkalinity reported at Chintapaducan be due to low nutrient input to the area. The peak value of alkalinity was recorded during the post-monsoon season. The degradation of plants and other organism and organic waste might also be one of the reasons for the increase in carbonate and bicarbonate thereby the alkalinity. Sarala and Babu (2012) opined that the high alkalinity of lake water might be attributed by the discharge of wastewater and microbial decomposition of organic matter in the water body.
 
Total hardness
 
Hardness is a very important characteristic of water for various life processes. The Hardness values varied between the range of 198.5 mg l^-1 to 874.5 mg l^-1 during post-monsoon and 248.2 mg l^-1 to 901.7 mg l^-1 during the pre-monsoon. In the present study, the high value of total hardness noticed in Chintapadu might be due to the high degree of sewage and agricultural waste discharges while at Atapaka the high values of hardness was due to the migratory bird’s droplets. The low value of Hardness was observed in Gudivakalanka indicating low anthropogenic activities in the area. Similar results were reported by Vijayalakshmi and Brahmaji, (2016).
 
Total Dissolved Solids (TDS)
 
TDS are the solids present in water in the dissolved state. Total Dissolved Solids is a useful parameter to know the quality of water. The TDS concentration values ranged between 1165 mg l^-1 to 4580 mg l^-1 during the post-monsoon and 1348.4 mg l^-1 to 4850 mg l^-1 during the pre-monsoon. High TDS was noticed at Kolletikota and Chintapadu (near Pedayadlagadi) due to the discharge of sewage from minor drains because it is a large area and connected by small drains and channels which carries excess fertilizers from agricultural fields. The less TDS was reported in Gudiuakalanka and Pratikulalanka due to less human interventions. The high amount of TDS was recorded during the pre-monsoon season, maybe due to the addition of domestic wastewater, garbage, sewage, etc. in the natural surface water body. According to Singh and Mathur (2005), the high concentration of TDS rose the nutrient status of a water body which would ultimately result in eutrophication which also observed in the Kolleru lake.
 
Total Suspended Solids (TSS)
 
TSS concentration of the study area varied in between 16 mg l^-1 to 42 mg l^-1 during post-monsoon and 10 mg l^-1 to 28 mg l^-1 during pre-monsoon. High TSS is observed at Chintapadu (near Pedayadlagadi) and Upputuru is due to the silt formation in the lake area by the inflowing streams, rivers, drains and channels carry large quantities of sediment into it. The low value of TSS was reported at Chettunnapadu and Gudiuakalanka which not directly conneted with rivers, streams and drains. Relatively high amount of TSS was found during the post-monsoon season.
 
Chemical Oxygen Demand (COD)
 
The COD concentration in the present study area was ranging from 9 mg l^-1 to 49 mg l^-1 during the post-monsoon and19 mg l^-1 to 64 mg l^-1 during the pre-monsoon. Highest values were noticed at Upputeru near Pandiripalligudem due to the influx of domestic sewage, surface runoff, waste discharges as it is the outlet of the lake and the lower values were reported in Gudivakalanka maybe attributed by its nearness to the agriculture fields. The maximum values were recorded during the pre-monsoon season. According to Elayaraj and Selvaraju (2014), high COD values indicated the presence of non-biodegradable oxygen demanding pollutants in the water.
 
Nitrates
 
The nitrate concentration in the study area is varied in between 14 mg l^-1 to 96 mg l^-1 during post-monsoon and 9 mg l^-1 to 88 mg l^-1 during pre-monsoon. The high amount of nitrate recorded at Chintapadu due to excessive use of fertilizers on land or leaching from cess-pools. The high amount of nitrate was recorded during the post-monsoon season. Nitrates are introduced to freshwater through the discharge of sewage, industrial wastes and runoff from agricultural fields. Higher concentration may be due to the influx of nitrogen-rich flood water and bring about the massive amount of wastewater. According to Anderson et al., (1998), the monsoon season is the period with the highest nitrate-nitrogen level which is known to support the formation of blooms.

The Lake Kolleru is the largest freshwater body in India, and now the water is changing to brackish due to ingression of saltwater through the connected Upputeru drainage to the Bay of Bengal. In the present study the better water quality was observed in the Post-monsoon season than that of Pre-monsoon season because of water recharging due to rains. The kolleru lake has undergone chemical and biological changes that have contributed to its depletion and pollution. The extent of pollution occurred due to urbanization; anthropogenic activities increased human interventions in the groundwater have been ascertained. According to the results, the main issue faced by the lake is the high nutrient concentration resulting in high growth of weeds. Spatio-temporal analysis of water quality in the study area indicated that many of the parameters observed are higher than desired level. Observations based on present study necessitates for mass awareness and making policies for the protection of such productive habitats which acts as a shelter and nursery areas for important animals like fish, shellfish and migrating birds.

The authors are grateful to the Director ICAR-Central Institute of Fisheries Education Mumbai for providing Institutional fellowship to one of the researcher Mr A. Shivakrishna. The authors wish to express their gratitude to HOD, FRHPHM Dr B.B.Nayak for encouragement. Thanks are also due to Mr Dande Kranthi Kumar Ph.D. Scholar for his kind help during the sample collection at Kolleru Lake, Andhra Pradesh.