Abundance and Microdistribution of Larval Chironomidae in Stabilizaton Lagoons1, 2

Abstract

Two different population structures of larval Chironomidae present in a 3-celled vs. a 1 cell 1 stabilization lagoon were studied from 1964 to 1966 in Oregon. Statistical analysis of dredging results from the 3-celled lagoon showed that total larval abundance was greater in winter, greater in the primary cell, and consistently greater in peripheral zones. Significant differences in larval population densities showed the following order of abundance: Glyptotendipes barbipes (Staeger) > Chironumus riparius Meigen > Anatopynia dyari (Coquillett). The established order of abundance resulted from greater tolerance on the part of G. barbipes than either C. riparius or A. dyari for physicochemical stress. Moreover larval A. dyari required more space for growth and development than did the tube-dwelling species. Dredging data from the 1-cell lagoon showed that total larval abundance was greater in the summer, greater for G. barbipes than for A. dyari, and greater for G. barbipes in both peripheral and central zones. The absence of C.riparius populations resulted from sustained sewage loading. The main factors affecting midge populations in both lagoons are considered to be: sewage influent quality and quantity, depth of water, degree of peripheral slope, and availability of dissolved oxygen at the soil-water interface.