Composition, structure, and formation factors of bottom invertebrate communities in lakes of the southern Ob-Irtysh interfluve
A three-year project on the benthic community of salt pans (shallow saline lakes) in the Seewinkel area of Eastern Austria has been carried out since 1996. Most of the salt pans investigated are very shallow (mean depth mostly < 0.5 m), highly alkaline and inorganically turbid. Salinity ranged from 1.6 to 4.5 g l-1in 1996 and 1997, but reached its highest values (> 50 g l-1) during the dry summer of 1998. A comparison of the benthic community in 20 salt pans at two sampling dates in 1997 revealed a negative relationship between salinity and species richness of Oligochaeta and benthic Crustacea. However, the decline of diversity was observed at salinity values much lower that those reported in the literature for most benthic invertebrates. It is thus doubtful whether or not salinity has in fact directly affected the benthic community in the salt pans of Seewinkel. Rather, it is suggested that biotic interactions controlled by changes in the hydrochemical situation are responsible for the reduction in diversity of the benthic community. Actual experiments or more detailed data on changes over a full gradient of salinity will be necessary to attribute changes in the species composition of benthic invertebrates to any environmental impact with certainty. The phenology of benthic invertebrates in Unterstinker, a sub- to hyposaline (0.5–20 g l-1) salt pan studied in greater detail, was distinctly influenced by the development of submerged macrophytes. Abundances of chironomids and crustaceans, the two dominant major benthic groups, were high only in June and July, when Charophyceae had stabilized the lake bottom and prevented further erosion of fine sediments. Substrate characteristics and the abundance of macrophytes appeared to determine the seasonal development of the benthic community as long as the ion concentration remains low (< 3 g l-1).