The chironomids (Diptera: Chironomidae) of shallow lakes of the humid Pampa region, Argentina: An approach to paleoproductivity reconstruction

Abstract

The Humid Pampa, center-east of Argentina, is the most important socio-economical area of the country. Several shallow lakes have been the focus of many studies due to the significant changes in their trophic status related to human activities and to global warming recorded since the beginning of the twentieth century. Although chironomids have been used extensively in paleoclimatic and paleoenvironmental research, they are rarely used for paleoenvironmental reconstructions of the Pampean shallow lakes. The aim of this paper is to contribute to the knowledge of the chironmids' community composition and distribution in the Pampa region, and to relate their distribution to selected climatic and limnological variables. The ultimate goal is to retrieve new ecological information for future paleoenvironmental and paleoclimate reconstructions by using chironomid-based inference models. In this study, chironomids head capsules were collected from surface sediments from 17 shallow lakes of the Humid Pampa. Our analyses indicate that the chironomid assemblages reflect the decreasing NE-SW rainfall gradient of the region as well as the land use intensity, which in turn affects the aquatic ecosystems, in terms of lake productivity. Some chironomids are associated with brackish conditions (e.g., Chironomus, Ablabesmyia, Tanytarsini D2). Additionally the occurrence of assemblages of detritivore taxa such as Goeldochironomus, Chironomus, Polypedilum, and Dicrotendipes reflect the natural eutrophic state of Pampean shallow lakes, whereas assemblages mostly dominated by Coelotanypus, Procladius, and Chironomus are indicative of hypertrophic conditions, which are usually the result of human activity. This is the first study of chironomids from surface sediments from the central temperate plains of Argentina, and our records extend the ecological information of the Diptera in temperate areas. Although more studies are necessary to fully understand the main factors determining the chironomid fauna distribution in the Pampa region, we conclude that chironomids are potentially good proxies for paleoproductivity and salinity reconstructions of Pampean shallow lakes.