Table 4.

Ecological traits of the most typical species collected in the Toce River.

Taxa	Ecological Traits
Macropelopia spp.	The genus prefers waters with higher oxygen saturation and moderate water flow. No particular sensitivity to toxicants was observed. It is a predator of other chironomid larvae, or Oligochaetes [5].
Conchapelopia pallidula	The species prevails at the downstream stations in the summer. It prefers the pool habitat. It shows no flow type preference and no sensitivity to toxicants in the Toce River. It is a common predator of other chironomid larvae and Oligochaetes [5].
Diamesa spp.	The taxon includes Diamesa zernyi and Diamesa tonsa. It prefers running waters with high flow velocity and turbulence, such as upstream riffle habitats with lower water temperatures. It tolerates a moderate organic carbon concentration in sediments and high Hg levels, while it is mostly absent at sites with higher DDT concentrations.
Potthastia longimanus	This species prefers pool microhabitat, silty sediments, broken standing wave flow type, moderate organic matter content in sediments, and high DDT concentrations, while it is moslty absent at sites with higher Hg concentrations.
Sympotthastia spinifera	Abundant in February, this species is rare in October and April. It prefers pools rich in submerged macrophytes, but it is present at all microhabitat types and stations. It tolerates high organic carbon content (>3.2%) and is present at sites most contaminated by As and Hg, while it is mostly absent at DDT-contaminated sites.
Odontomesa fulva	Abundant in April, it is rare in October and February. It prefers pool areas with rippled flow type and sand and mesolithal microhabitats, tolerating organic carbon in sediments. It is present at all stations, including sites with higher Hg and DDT concentrations but lower As levels.