Internal Phosphorus Load in an Oligotrophic Precambrian Shield Lake with an Anoxic Hypolimnion

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Abstract
The release of phosphorus from sediments into the anoxic water of oligotrophic Chub Lake, Ontario, determined with three different methods, showed that the average release rate of 2.2 mg∙m−2∙d−1is much smaller than release rates of more eutrophic lakes (14 mg∙m−2∙d−1). Our hypothesis that anoxic release rates depend on lake trophy was confirmed by the significant positive regression of release rates on lake phosphorus concentrations for 56 lakes from the literature. Despite a comparably small phosphorus release rate, the sediments play an important role in Chub Lake as a source of phosphorus because phosphorus from internal sources is in a highly available form and external loads are small.