Temporal changes in the weather elements at Panangad region and their influence on the hydrography of a pond

Abstract

The present study was undertaken with a view to finding out the seasonal and diurnal changes of weather elements at Panangad region, seasonal and diurnal changes in the hydrographic parameters of a freshwater pond and finally to understand the possible influence of weather elements on hydrographic conditions of a pond during the four seasons viz. southwest monsoon season (June-September), post monsoon season (October-November), northeast monsoon season (December-February) and pre monsoon season (March-April) at the College of fisheries, Panangad, Cochin. Meteorological data were collected at 03 UTC (0830 IST) and 12 UTC (1730 IST) daily during the period from June 2003 to April 2004. Water samples were collected from a pond every fortnightly to analyse hydrographical parameters. To study the diurnal variation, 24-hour observation were taken at an interval of 3 hrs, once for each season. Meteorological observation includes air temperature, maximum temperature, minimum temperature, total rainfall, relative humidity, cloudiness, wind speed and direction. Hydrographic parameters like water temperature, pH, transparency, water level, total alkalinity, primary productivity, dissolved oxygen, nitrate, nitrite, phosphate and silicate were estimated. There was a considerable seasonal variation in water qualities. The surface temperature closely followed the air temperature and exhibits a clear double oscillation. Low pH values confined to the southwest monsoon period were due to heavy rainfall. pH showed a positive relation with air temperature. At higher temperature evaporation was more and water level decreased, which leads to the higher concentration of plankton bloom and low level of transparency. Presence of nutrient elements in optimum concentration and there by production of phytoplankton and algal bloom may be the possible reason for the high productivity during the northeast and pre monsoon periods. The low values of primary production during southwest monsoon period (June to September) and in October might be due to cloudy conditions before and during the sampling, which reduced light intensity, and along with incessant rains cut down production. The high concentration of alkalinity during pre monsoon may be due to decrease in water level due to evaporation. The effect of rainfall in decreasing bicarbonates is well known. Dissolved oxygen was at the highest level in ponds during colder months and was due to low temperature and intense photosynthetic activities. Subsequent fall of dissolved oxygen in pre monsoon period is attributed to the death and decay of plankton and presence of other organic matter. The plankton population in the pond was highest during the month of December/January to April, coinciding with the higher concentration of alkalinity and nutrients. Diurnal variations in water temperature, pH, dissolved oxygen, alkalinity and primary productivity were well marked. Among nutrients phosphate, nitrate and nitrite did not show any specific pattern, where as silicate concentration showed well-marked short-term variation in all seasons. Weather elements showed significant relationship with many hydrographical parameters and the variations might be due to the combined effects of all those factors. The influence may be direct or indirect. Among the weather elements the influence of air temperature and rainfall was most prominent. The seasonal and diurnal changes in weather elements were equally important for the changes in hydrographical parameters. Shallow water bodies quickly react to the changes in weather elements.