Fig 1 - uploaded by Vishnu Mohan S
Content may be subject to copyright.
Geology of south India (modi? ed after Santosh and Sajeev, 2006; Santosh et al, 2009) showing the Trivandrum Block (TB); Madurai Block (MB;) Nagercoil Block (NB) and Achankovil Shear Zone (ASZ). Extrapolation of the ASZ has been done based on observations of present study.
Source publication
The southern Kerala coast, south of the Achankovil Shear Zone (ASZ) is endowed with many freshwater lakes of variable dimensions close to the landward end of the major estuaries, like the Ashtamudi, Paravur and Nadayara estuaries. The largest freshwater lake in the category is the Lake Sasthamkotta, which is recently declared as a Ramsar site of in...
Citations
... The eastern end of the estuary is encircled by many satellite freshwater bodies like Sasthamkotta Lake, Chelupola Lake, Chittumala chira etc. As seen from the bathymetric map, it is revealed that the estuary exhibits a few funnel shaped depressions in its eastern margin (Fig. 2); Vishnu Mohan and Padmalal, 2014). At present, the Ashtamudi estuary is connected with the Arabian Sea by a comparatively narrow outlet (locally known as pozhi), which is being dredged annually as part of the developmental activities of the Neendakara port. ...
... A systematic fieldwork was carried out in the Ashtamudi estuarine basin to collect relevant primary and secondary data on various landform features, geological setting of the area and also locating the borehole sites. Depth measurements for the preparation of bathymetric maps of the estuarine basin were made using an Ecosounder (Model: Reson Navisound 215); Vishnu Mohan and Padmalal, 2014). A total of two borehole cores, one each in Puthenthuruthu (08 55 0 55 00 Ne76 33 0 01 00 E) and Munrothuruthu (08 58 0 43 00 Ne76 36 0 36 00 E) islands where retrieved from the estuarine basin using rotary drilling method (Fig. 1). ...
The southern Kerala coast in SW India has experienced dramatic changes in climate and sea level during Holocene. These changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched on the uplifted Neogene deposits. Here we report the sedimentary processes, palaeoclimate and sea level records decoded from two borehole cores – Puthenthuruthu and Munrothuruthu borehole cores – retrieved respectively from the marine and fluvial ends of the second largest estuarine basin in SW India, the Ashtamudi estuary, using sedimentology, palynology and stable isotopes as the major proxies. The heavy rainfall event at the latter half of Early Holocene (6117 ± 101 BP) is reflected well in the isotopic signatures of the Puthenthuruthu borehole core. The higher level of lighter isotopes of oxygen and carbon at 10–15 m below ground level is a clear indication of freshwater influx from the hinterland due to intensified monsoon activity. This, in turn, was responsible for the development of Bay Head Delta in the fluvial end of the estuary during Early–Middle Holocene period. Palynological contents below the level indicate a facies change as freshwater and terrestrial elements dominate over marine contents. Further, the occurrence of desmids shows the marine facies is being gradually replaced by freshwater to continental facies. This was followed by the deposition of littoral sands as Flood Tide Islands within the estuarine basin. The palynological investigations of sediments with radiocarbon age of 4350 ± 90 BP in the Munrothuruthu borehole core show a dry phase with high saline depositional environment in the beginning which is followed by influx of freshwater as indicated by the higher content of lighter isotopes of carbon and oxygen in the calcareous nodules (algal pisolites) embedded in the sediments. The occurrence of pteridophytic spores and a few pollen of Cullenia in the palynological preparations in the upper half of the silt and clay dominated intervening layers reiterate this view.
Freshwater quality studies all over the world have received significant attention, as these are vulnerable to external forces like over exploitation, pollution, unplanned development, and other environmental degradation issues. Several methods like index analysis, statistical analysis, and model simulations are generally done to estimate the quality of freshwater resources. A freshwater quality model utilizing fuzzy logic is a comprehensive artificial intelligence approach for the assessment of different types of freshwater resources. The present research aims at developing a new freshwater quality model and a standard index called “Fuzzy Lake Index (FLI)” for the routine assessment of inland water bodies especially for nonflowing freshwater systems based on fuzzy logic in MATLAB software employing both Water Quality Index (WQI) and Heavy Metal Pollution Index (HPI). WQI was computed with pH, Turbidity, TDS, Total Hardness, Ca, Mg, Cl, NO3, SO4, and Dissolved oxygen, while HPI was computed with Fe, Mn, Al, Zn, Pb, Cr, Cu, Cd, and Ni. Here, 20 parameters were included based on their critical importance for the overall water quality and their potential impact on human health. To assess the functioning of proposed model under actual conditions, a case study was conducted employing WQI and HPI data of three selected freshwater lakes of varying terrains, viz., Vellayani, Sasthamkotta, and Pookot in Kerala state, India, since this type of hybrid component freshwater quality model generation is first of its kind in water quality-related studies. A five-category ranking system from 0 to 10 with different classes is proposed in this study to denote the degree of freshwater quality. Results of this study indicated that Vellayani lake and Pookot lake belonged to ideal category with 5.52 and 5.58 as FLI values, whereas Sasthamkotta lake (1.5) belonged to moderately polluted category. The results of the study further suggest that freshwater lake quality model can be used as a complementary tool in water quality assessment methodologies.
Investigation on the physico-chemical parameters and bacteriological examination of surface waters of Sasthamkotta, Vellayani, and Pookot lakes of Kerala, SW India has been performed to assess the quality of lake waters for drinking purposes. For this study, a total of 60 surface water samples, 20 samples each from the three lakes were collected along S-N-W transects that cover the entire area and was performed during the year 2016–2017. The results obtained during the analyses were compared with maximum permissible limit values recommended by World Health Organization (2017) and Bureau of Indian standards (2012). The results showed that the annual concentration of a majority of the constituent parameters showed an increasing trend in their concentration. Acidification (mean pH 5.6) of Pookot lake owing to the forest canopy and spring water intrusion may deteriorate the species diversity of Pookot lake. TDS values of Sasthamkotta lake (mean TDS > 500 mg/l) and Vellayani lake (mean TDS > 500 mg/l) reflect the turbid and contamination scenario of the freshwater ecosystems. Increased concentration of primary nutrients like NO3⁻ (mean >4mg/l) and PO4³⁻ (mean >3mg/l) in Vellayani lake depict nutrient enrichment, both from anthropogenic influences and runoff from point and non-point sources in a swift pace. The observed hydro-chemical facies were NaHCO3 for Pookot lake, NaCl with subordinates of Ca and Mg for Sasthamkotta lake and NaHCO3 with subordinates of SO4²⁻ for Vellayani lake, based on Piper trilinear diagrams. Water Quality Index (WQI) were calculated for evaluating influence of natural and anthropogenic activities based on several key parameters (pH, EC, TDS, HCO3⁻, Cl⁻, SO4²⁻, NO3⁻, Ca²⁺, Mg²⁺, Na⁺, K⁺) in surface water chemistry. As per the WQI, majority of the samples in the three lakes, based on the observed chemical constituents were falling under ‘good’ category but the real havoc was existed due to bacteriological contamination. It was observed that there was an increased count of coliforms in the lake waters of Vellayani (140 MPN/ml), Sasthamkotta (260 MPN/ml) and Pookot (90 MPN/ml), which must be zero for drinking needs, according to WHO (2017) and BIS (2012) drinking water guidelines. The increased microbial population in all the three lakes indicate the unhealthy practices in the lake catchments. Therefore, sustainable management measures should be taken to improve the water quality of the fresh water resources of Kerala.
