Chironomidae (order Diptera) as hypolimnetic oxygen indicators in brook trout lakes of Nova Scotia: A paleolimnological investigation

Sport fishing is a multi-million dollar industry in Nova Scotia, of which brook trout (Salvelinus fontinalis) comprises a large component. One aspect of the 5-year Trends in Eutrophication and Acidification in the Maritimes (TEAM) project involves investigation of eutrophication in Nova Scotia brook trout lakes. Consistent long-term water chemistry data are not available for many Nova Scotia lakes, as data have been collected sporadically over the past twenty-five years. The limited long-term data base for these lakes challenges Nova Scotia Inland Fisheries in monitoring lake health and facilitating proper lake management. I applied paleolimnological techniques to these lakes in an effort to reconstruct the historic lake environments, thereby facilitating the formulation of sound management decisions.; Chironomidae (Diptera) have been long considered useful indicators of paleoecological conditions such as hypolimnetic dissolved oxygen. Using a combination of the 'top-bottom' paleolimnological approach and detailed sediment core analysis of 4 lakes, this study addresses the questions: Have hypolimnetic oxygen levels decreased in these lakes; If so, when and by how, much? Twelve lakes from Nova Scotia were selected for study based on usage patterns, environmental concern, historic data availability or economic importance. Top-bottom analysis, where bottom sediments represented ca. 1850 AD or older, displayed high taxonomic similarity. Heterotrissocladius and Micropsectra , two indicators of oxygen-rich hypolimnetic water, were present in both top and bottom intervals of most lakes. These taxa were also well represented in the four detailed lakes. Chironomus, an indicator of anoxia, was not abundant in any interval of this lake set.