Preliminary investigation on anthropogenic impacts on the water quality and biota of “Madola” stream, Hiyare, Galle

Abstract

Sri Lanka's rich water resources are endowed with a high diversity o f aquatic fauna. Water pollution is becoming a major problem in many urban and even rural areas. The present study was carried out to determine the influence o f anthropogenic activities on physico-chemiacl and biological characteristics o f the “Madola " stream at Hiyare, which drains into the Gin River. Four sites (i.e. A, B, C and D) each o f about 20 m in length were selected using criteria such as nature o f the substrate, water level and water flow. Data on some physico-chemical and biological parameters were collected monthly for a period o f six months during 1998. To assess the influence o f anthropogenic activities, data on same physico-chemical and biological characteristics were collected for a period o f nine months after five years in 2003. Diversity o f fish and macroinvertebrates in each o f the sites were determined using Shannon Wiener diversity index. SPSS (version 10) statistical package was used to analyze the data on physico-chemical parameters. Anthropogenic impact on each site was surveyed using a questionnaire to gather information on the livelihood o f neighboring community, current and past nature o f the stream, different uses o f the stream, and views on the impact o f the stream. During the period o f five years from 1998 to 2003, in each site, physico-chemical parameters such as the biochemical oxygen demand, phosphate concentration, and alkalinity had significantly decreased, while the Secchi disk depth, conductivity and nitrate concentration had significantly increased. In 1998, thirty four fish species were recorded and this number had reduced to 30 in the year 2003. Conductivity in site D significantly decreased, while dissolved oxygen concentration increased in all sites except in site D. Shannon Wiener diversity index calculated for fish fauna decreased in all sites. Total number o f fish caught in each site significantly decreased from year 1998 to 2003. Majority ofpeople use the stream for washing, bathing and agricultural purposes, while a few households use the stream for drinking and fishing. Only site A, which is the closest to the origin o f the stream, is being used for consumption o f water. However, the decrease in diversity and abundance o f both fish and macroinvertebrates in all study sites o f the Madola stream, is comparatively low and these changes may be due to the change in the above physico-chemical parameters resulting from anthropogenic activities