Spatial variability of soil characteristics along a landscape gradient in Bellanwila-Attidiya area, Sri Lanka

Abstract

Wetlands are comprised of unique components of soil, water and biodiversity which are interconnected. This ecosystem provides important ecological, social and economic services which are often unnoticed and undervalued. Although water and biodiversity components of wetlands are being somewhat investigated, a very few research have been carried out to investigate soil properties.

This study focussed on spatial variability of soil chemical and physical parameters in a land use gradient around the Bellanwila-Attidiya Sanctuary, a wetland situated in Colombo suburbs. Main objective was to present a summary of spatial variation of soil characteristics and develop maps using GIS in different land use areas: natural-wetland; manmade-functioning paddy fields, non-functioning paddy fields, residential and industrial.

This study was carried out for a period of 3 months and several random soil samples were obtained from all land use areas. The following parameters were analysed in triplicate, from the samples taken at the surface and at one m depth in the soil: chemical properties; NO^3- , PO₄^3-, SO₄^2-, Cl^- and Fe³⁺ and physical properties; moisture content, pH, salinity, electrical conductivity, temperature, soil type and soil colour. All analysis were carried out according to Standard Methods and the GIS maps were developed using ArcView GIS 3.2.

The results indicated that all chemical and physical parameters of soil varied across the landuse gradient, except for temperature. According to the GIS maps there are apparent variations in distribution of soil properties. On the surface, the highest level of each parameter was found as follows: NO₃^- in industrial area, PO₄^3- in functioning paddy fields, SO₄^2- in residential area, Cl^- in residential area, Fe³⁺ in functioning paddy fields, moisture content in wetland, pH in industrial area, salinity in residential area, electrical conductivity in residential area. At 1 m depth, the pattern was different: NO₃^- in abandoned paddy fields, PO₄^3- in functioning paddy fields, SO₄^2- in wetland, Cl^- in wetland, Fe³⁺ in residential area, moisture content in wetland, pH in industrial area, salinity in wetland, electrical conductivity in wetland. The findings clearly exhibit the increases in anthropogenic pressure have resulted in wide-scale alternation of soil properties, at least in the surface soil, across a land use gradient. Managing land use in the watershed of the wetland thus needs adequate attention to conserve this natural ecosystem