DISTRIBUTION OF CHIRONOMIDS (DIPTERA, CHIRONOMIDAE) AND CERATOPOGONIDS (DIPTERA, CERATOPOGONIDAE) ALONG A COLORADO THERMAL-SPRING EFFLUENT

Chironomidae and Ceratopogonidae populations were studied in a thermal gradient at Poncha Hot Spring (T48N, R8E, S15) in South Central Color ado, U.S.A. Chemical analyses revealed moderate spring ion concentrati ons that ranged from trace amounts of nitrates to 210 mg/liter sulfate . Four new chironomid species in the genera Cricotopus, Polypedilum, T anytarsus, and Rheocricotopus were found. Paratendipes thermophilus To wnes, Cricotopus sp., Micropsectra sp., and Larsia sp. were collected from the thermal spring effluent with P. thermophilus being the most a bundant chironomid. The presence of P. thermophilus represents a new s tate record for Colorado. Dasyhelea cincta Coquillett and Palpomyia sp . were also found in the hot spring effluent with D. cincta being the most abundant ceretopogonid. The relationships between chironomid and ceratopogonid abundances and biomasses to temperature are described. C hironomid abundance and biomass decreased in a curvilinear manner as t emperature increased along the spring effluent's thermal gradient, whe reas, there was no significant relationship between ceratopogonid abun dance and biomass and temperature. The ceratopogonid distribution patt erns suggest they were thermophilic.