Phosphorus Cycling in Southeastern Piedmont Lakes: An Alternative Pathway
Parker, Amanda K.
Rasmussen, Todd C.
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The phosphorus cycling paradigm in lakes is based on data from systems in northern temperate regions. Anoxic respiration in the hypolimnion of north-temperate lakes creates strongly reducing conditions that liberate dissolved inorganic phosphorus (DIP) from settling particulates. Hypolimnetic DIP steadily increases during summer stratification as phosphorus is liberated, and is mixed throughout the water column at fall overturn. This paradigm fails to explain phosphorus cycling in Southeastern Piedmont lakes. No increase in DIP is found in the anoxic hypolimnion during summer stratification; nor is an increase in DIP observed during fall overturn. We hypothesize that the conventional paradigm is not appropriate in iron-rich Southeastern Piedmont lakes because: a) iron-oxide sorption reduces the bioavailability of DIP, and b) the abundance of oxidized iron prevents DIP accumulation in the anoxic hypolimnion. We use iron-oxide chemistry to develop an alternate phosphorus cycling pathway: DIP is released from iron-phosphate particulates when pH increases due to photosynthesis. This mechanism forms a biogeochemical feedback loop that enhances algal blooms.