Abstract:
Muthurajawela is the largest wetland in Western Province of Sri Lanka, is characterised as a
complex peat-dominated system influenced by natural processes. Heavy metals, such as arsenic
and lead, are described as serious environmental and health threats because of their persistence
potential for bioaccumulation and toxicities even at trace levels. Seasonal variations in precipitation,
temperature, and biological activity generate the dynamic environment that affects the
speciation of metals and mechanisms of metal transport. The seasonal variation of arsenic and
lead contamination in relation to pH dynamics in a selected area of the Muthurajawela wetland
were analysed through water quality measurements. Accordingly, thirty-six (36) water samples
were collected from twelve stations at radial distances of 50 m, 100 m, 250 m, 500 m, and
1000 m from the Kerawalapitiya open waste dump site during the dry, wet, and intermediate
seasons, revealing significant spatiotemporal heterogeneity in heavy metal concentrations and
pH levels in this vital surface water network. This involves developing standard physical and
chemical characteristics of surface waters, comparing them with the parameters of the National
Ambient Water Quality Standards of Sri Lanka, and identifying significant pollutants that have
affected the ecological integrity of the wetland. Additionally, the research aims to develop an
advanced contamination audit using critical inspection of matrices of water quality and identify
the extent of surface water pollution from direct waste dumping activities. It was shown that
arsenic concentrations were found to range from 0.012 to 1.247 mg/L across the seasons, with
the highest values being recorded during the dry seasons (mean: 0.35 mg/L). Similarly, lead
concentrations were determined to range from 0.0017 to 5.13 mg/L, showing the highest levels
noted during intermediate seasons (mean: 1.48 mg/L). The range of pH levels was observed
between 5.16 and 12.4, which exhibited an extreme negative correlation with heavy metal solubility.
The findings of this research are summarised in this analysis to explore the complex
interaction between arsenic and lead contamination, pH regimes, and seasonal variation in the
context of the Muthurajawela wetland. The data and analysis of this study reveal that the major
contributor to heavy metal contamination of surface waters in the Muthurajawela wetland is the
Kerawalapitiya open waste dump site and its discharges.
