Abstract
Thermal and chemical stratification of water bodies has a strong bearing upon the water quality since it regulates mixing of nutrients/pollutants and affects the aquatic life in it. The present study was undertaken in a shallow pond ecosystem to study thermal stratification and trophic status over a period of 4 months (January–April, 2015) to understand the seasonal variations associated with. Chemical stratification with respect to dissolved oxygen was also observed along the depth. The pond was weakly to strongly thermally stratified throughout the study. The redox potential of water varied from − 246 mV (February 15) to 137 mV (March 15) indicating dominantly reducing conditions. The dissolved oxygen profile with depth confirmed that reducing conditions prevailed in the hypolimnion. The surface epilimnion represented higher values of Trophic State Index for total phosphate (TSI-TP) and relatively lower values of total chlorophyll (TSI-Chl). The value of buoyancy frequency (N) and Richardson number (R) indicated complete and strong mixing in surface epilimnion due to the temperature, wind velocity, and current speed during the study with relatively stronger stratification and lower surface mixing during early summer (March–April). The higher value of TSI-TP compared to TSI-Chl indicated that zooplankton grazing or limitation of nitrogen plays a role in limiting eutrophication and algal growth. Although the wind velocity may be higher during summer, stronger thermal stratification can be formed due to temperature difference between upper layer and lower layer resulting in lower mixing of surface epilimnion, which may be a cause of concern if dissolved phosphate levels are high.
Highlights
Cultural eutrophication is a process that speeds up the rate of natural eutrophication by increasing the inflow rate of nutrients into the water body
The water body was classified as eutrophic throughout the study, and the details of water quality, thermal stratification, and the trophic status are discussed
The water quality on the basis of physico-chemical characterisation of collected water samples revealed that the water lies in slightly alkaline range with average pH ranging from 7.6 to 8.7 (Table 1) with dominantly reducing conditions based on values of oxidation–reduction potential (ORP)
Summary
Cultural eutrophication is a process that speeds up the rate of natural eutrophication by increasing the inflow rate of nutrients (nitrogen and phosphorous) into the water body. Turbidity of the water body is an important parameter to determine the water quality, and most of the eutrophicated lakes have low transparency because of algal growth, and Department of Environmental Engineering, Delhi Technological University, Bawana Road, Shahbad Daulatpur, Rohini, Delhi 110042, India dead and decomposing organic matter. It results in reduced sunlight penetration, reduced photosynthesis, and low productivity of the lake (Haritash et al 2015a, b). Many physical factors are responsible of the trophic state of water body; thermal stratification is one of them where density difference in the lake is primarily due to
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