Nematode assemblages in a nature reserve with historical pollution

Nematodes, and especially nematode communities, have significant potential as bio-indicators. The present studyaimed to assess the nematode community structure of several sites with different historical pollution. Long-term polluted municipal waste-, tar- and sludge- sites were compared with less disturbed annex sites. At each site heavy metal and PAHs concentrations were measured together with soil texture classes, pH and total organic matter. Identification of three hundred nematodes at each location resulted in the discrimination of 63 genera from 32 different families of which the Cephalobidae, Belonolaimidae, Tylenchidae, Hoplolaimidae, Belonolaimidae and Plectidae were the most abundant families. The sampling sites harbour significantly different nematode communities and significant differences of life-strategy-related parameters (cp-groups, MI indexes) wereobserved. The significant augmentation of the proportion of the cp 2 nematodes in historically-polluted sites was especially informative. Omitting the cp 1 group from the MI (=MI2-5) better reflects putative historical pollution-induced community changes. However, the current study did not reveal significant relationships between historical pollution and the feeding type composition, or the Shannon-Wiener diversity. The observed results are critically assessed in the light of possible flaws such as sampling and analyzing limitations

Nematode communities of small farmland ponds

The nematofauna of 14 farmland ponds, selected according to a gradient of surrounding agricultural land-use intensity, from five regions in North-West of Belgium were studied. The total nematode density (9-411 ind./10 cm(2) per pond), and especially the number of species (4-12 species per pond) was especially low in these ponds. In total, 17 genera of free-living benthic nematodes, belonging to 15 families, are identified. Tobrilus gracilis and Eumonhystera filiformis were the most common species and were found in 13 and 12 of the 14 sampled ponds, respectively. The genera Tobrilus and Eumonhystera jointly comprise 77% of the total nematofauna. Consequently, the investigated water bodies were dominated by deposit feeding Monhysteridae and/or by chewing Tobrilidae. Diplogasteridae and Rhabditidae, normally related with eutrophic habitats, were almost absent. In order to explain the variation of total density, diversity, feeding-types composition and the individual density of the six most important species within ponds as well, sets of environmental variables were statistically selected. It was demonstrated that morphologically very similar species can show highly different ecological properties. The presence of a substantial mud layer and of an overall high level of eutrophication as well as the presence of possibly associated anaerobic conditions are put forward as the main factors explaining the observed low density and diversity. Total phosphate concentration and sediment characteristics seem to be the most important variables to explain the nematode community structure. However, a clear pattern of environmental variables, agricultural land use and nematode assemblages was not observed