| Abstract |
Ore mining is among the most environmentally destructive anthropogenic practices, particularly in developing
countries. Correct assessment of its impacts on soil ecosystems requires an understanding of the response of soil
food webs. Nematodes, often the most abundant invertebrates in soils, occupy various positions in food webs,
and their assemblages are commonly used to reflect soil health. In October 2014, we collected soil samples from
five sites of a small-scale mining area in Sibutad, southern Philippines, to assess the influence of mining activities
on nematode assemblages. Two sites were considered undisturbed as there were no visible signs of mining, while
the other three sites were disturbed. Nematodes were extracted live and identified to genus level using morphology-
based identification. We analysed genus composition, genus and trophic diversity, and the life-history
based maturity index. We measured soil environmental variables (pH, organic matter, granulometry and several
heavy metals), and correlated variation in nematode genus composition to variation in these environmental
factors. Small-scale mining activities had variable but generally non-significant impacts on soil properties, altered
vegetation and caused increases in concentrations of Hg and Pb, but not consistently so in all impacted
sites. The high patchiness in vegetation and heavy metal content were reflected in a high within-site variability
of nematode assemblages. Total nematode abundance was significantly lowest in the most physically disturbed
site, but not so in the most metal-polluted one, suggesting that abundance is not a good indicator of pollution
status. Nematode genus composition significantly differed between disturbed and undisturbed sites. By contrast,
only few differences between sites were found for diversity or maturity indices, demonstrating that genus
composition was a better indicator of mining-related effects than many common indicator indices and highlighting
that detailed assemblage analysis is required for a correct interpretation of moderate pollution effects on
soil nematodes. Measured environmental variables together explained 60% of the variation in nematode assemblages
in the area; the three 脙垄脗聙脗聵single best脙垄脗聙脗聶 explanatory variables were the concentrations of Pb, Hg and N, but
none of these by itself explained more than 8% of the variation in nematode data, while their combination
explained 24%. Some genera of predacious and omnivorous nematodes, which are generally expected to be
sensitive to both chemical pollution and physical disturbance (e.g., Ironus and Eudorylaimus), were most
abundant in sites with elevated heavy metal concentrations, which can have repercussions for the interpretation
of nematode-based indices such as the MI. |
Mindanao State
University - Iligan Institute of Technology