Quality Assessment of Soils in Thiruvananthapuram District,South India Using Nematodes as Bio-indicators

Nematodes represent a very abundant group of soil organisms in the food web and are important for soil quality. They are both taxonomically and functionally diverse, respond quickly to soil perturbation and have much potential as indicators of soil health. In the present study, the impact of contaminants on soil health has been addressed through the measurement of nematode abundance. Different categories of land use areas in the rural and urban sites of Thiruvananthapuram District receiving different types of contaminants were selected for this study after conducting a reconnaissance survey of the study area. Control areas which are in a benign environment were also identified in both rural and urban areas of Thiruvananthapuram District. Soil samples were collected from the selected stations in pre-monsoon, monsoon and post-monsoon seasons during the period April 2009 to January 2010 from the selected stations, and the physico-chemical characteristics, heavy metal content and nematode abundance were determined. The results showed that the soils of market area having the highest amount of decaying matter were rich in nematode density. The reason for this may be due to the fact that saprophytic nematodes can flourish well in that environment. It was also noted that the nematodes were scarce in the soils of gasoline station area contaminated with hazardous wastes and chemicals which will unfavourably affect the nematode population. The nematode abundance in the soils of the study stations are in the order: market area > sewage disposal area > agricultural area > benign environment > industrial area > road-side area > gasoline station area > coastal area. Nematodes were abundant in areas where the heavy metal concentrations were low, thus indicating a negative correlation.