Soil Contamination and Remediation Effects on the Structure and Activity of Soil Microbial Communities

Soil can be defined as the space time continuum forming the upper part of the earth's crust. It is a natural body comprised of solid, liquid and gases that occur on the land surface. Joffe (1949) defined soil as a natural body differentiated into horizons of mineral and organic constituents usually unconsolidated of variable depth, which differs from the parent material below in morphology, physical properties and constitution, chemical properties and composition, and biological characteristics. Soil is one of the most fundamental resources for sustainability and survival. It is one of the most important assets to protect and pass on to future generations.
Soil contamination due to anthropogenic and natural sources is increasing day by day because of increasing population, industrialization, and urbanization. Soil is the receptor of many contaminants from various sources. Contamination decreases the quality of the soil and adversely affects soil organisms.
For this study, soil samples from thirteen locations contaminated from agricultural, industrial, and organic sources spread over the districts of Alappuzha and Kottayam in Kerala in the south west coast area of India were analyzed to study the changes in soil characteristics and its influence on soil microbial communities and their activities.

Autorentext

M.V. Bindu is Technical Officer at the Project Implementation Unit, Kerala Sustainable Urban Development Programme, Local Self Government Department, Thiruvananthapuram, Kerala India. After securing her Master s Degree in Environmental Management from Mahatma Gandhi University, India, she received her PhD (Biotechnology) in 2009 from the University of Kerala, India. Her area of interest is remediation of contaminated environment through microbial manipulations.

Leseprobe
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Chapter 3. 1. Soil temperature and moisture:
Soil temperature and moisture were significantly (P 0.01) influenced by soil contamination (Table. 3. 1) irrespective of locations, sources of contamination and season. Soils received agricultural contaminants (AC) recorded a general increase in soil temperature over control (uncontaminated soil) followed by soil contaminated with organic wastes (OW) during monsoon season (Fig. 3. 1). The increase in soil temperature even with the availability of sufficient moisture could be due to the fast rate of organic matter decay in the availability of water emanating heat (Chonkar et al., 2000). Soil temperature showed positive relationship with soil properties such as pH and EC and negative relationship with soil moisture and TOC (Table. 3. 7).
Soil moisture like temperature showed an increase in AC and OW soils (Fig. 3. 2) though their relationship was inverse (Table. 3. 7). The moisture retaining capacity is controlled primarily by the number of pores and their size distribution and the specific surface area of the [...] soils (Haynes and Naidu, 1998). Further, total pore space is typically increased by the addition of organic matter owing to increased aggregation (Sanchez et al., 1989). Though the AC and OW soils received organic matter in varied forms, the data on soil moisture and TOC did not yield a significant positive linear relationship. Therefore the high moisture retention capacity of these soils is presumably due to the physical nature (Cosby et al., 1984) rather than contamination.

3. 2. pH and EC:
      AC soils generally exhibited an acidic tendency in all the seasons (Table. 3. 2) probably due to the reason that the soils received continuous application of synthetic fertilizers and manure. Significant positive correlation could be drawn out in the present study between soil pH and nutrients particularly P and K (Table. 3. 7) confirming soil nutrients as a factor determining pH in soil. Increase in soil acidification due to long-term application of large amount of fertilizers and manures in a vegetable cropped soil has been reported earlier by Ju et al. (2007). In general, the industrially contaminated (IC) soils showed an alkaline range of pH. The results suggest a more pronounced increase over control in petrochemical contaminated soil (Fig. 3. 3) in contrast to the earlier finding of Ekundayo and Obuekwe (2000) who observed a low value for soil quality parameters including EC, exchangeable cations, total N and available P in an oil spill site of the Niger Delta basin of Nigeria. Li et al. (2000) found a near neutral pH (6.0 ± 7.0) in a petrochemical contaminated soil in Zihe valley in eastern China. Among IC soils, the soil contaminated with lime showed an increase (more alkalinity) over control. This is in line with the finding of Tomko and Hall (1986) that liming material when added increase the pH of the surface layer of soil. Changes in soil pH due to contamination of lime sludge have been reported earlier (Medhi et al., 2005). The OC soils recorded an acidic to neutral pH which appeared to be due to organic humic acids that are formed from the decay of organic matter in the waste (Krishna et al., 2005).
      [...] Soil EC was significantly affected by OW contamination which showed a general increase over control in all sites irrespective of season (Fig. 3. 4), but its relationship with pH was negative (Table. 3. 7). The increase in EC might be due to the release of salts of Ca, Mg and Na into the soil from organic wastes (Krishna et al., 2005) as leachate. However, offering such comments need more in depth investigations.
4. 3. Soil organic carbon:
      AC and OW soils recorded maximum values for TOC over control during post-monsoon and pre-monsoon seasons respectively (Fig. 3. 5), while the relationship of TOC with other soil parameters were negative (Table. 3. 7). Intensive agricultural practices with organic manure or better crop growth with concomitantly high