Species Composition and Spatial Distribution of Odonates as a Pollution Level Indicator in a aquatic ecosystem
Faculty Of Applied Science,University Of Rajarata
Madupa Hewapathiranage Santhushya Hewapathiranage
Introduction: What conservation problem or question does your study address?
Sri Lanka is a tropical country which posses a high biodiversity and high endemicity of it’s fauna.It has 118 discribed Odonates and out of them 47 are endemics. Maha Oya is one of the Sri Lanka’s largest perennial rivers providing invaluable ecosystem services during its 130 kilometre journey .It harbours many freshwater species.
Methods: What were the main research methods you used?
we selected four study sites, in Mawanella town,Aranayaka, Kondeniya and rambukkana which posses an urbanization gradient. For each site we selected 5 transects along marginal vegetation, and 5 transects along the river randomly, each of belt transect was 20 meter in length and possessed a 5 meter width.Dragonflies were identified, photographed and counted.Species diversity, species richness and relative aboundance was calculated. Also the aquatic temperature (oC),pH,Total dissolved solids (TDS)(ppm), Conductivity(μs/cm), dissolvedOxygen(DO)(mg/l), Nitrate(NO3)(mg/l), Phosphate(PO4-3)(mg/l),Calcium(CaCO3)(mg/l) were measured for each plot. A questionnaire survey which reflects the urbanization level,was also done with village officers who represesnts the divison of the selected site.
Results: What are your most important results?
Total number of thirty odonates was recorded during this study, Out of them fourteen were endemic to Sri Lanka.Species diversity and their abundance were negatively correlated with TDS(ppm),Conductivity (μs/cm), NO3(mg/l), PO4-3 (mg/l) and CaCO3 (mg/l) levels. Species diversity, abundance and richness were significantly lower in highly urbanized areas than the others.
Discussion: What are your important discussion points and what is the relevance of your results to conservation (if any)?
Water pollution is a serious threat to Odonates.As a result of agricultural production,industrial production many chemicals end up in the Maha oya river basin. It directly affects the odonates breeding sites. The increasing human population also puts pressure on water sources, causing increased extraction and use of water and pollutionThis is detrimental to the odonates not only directly but also indirectly.