Autotrophic-heterotrophic coupling in lake ecosystems: The importance of organic carbon and food web interactions

Net production in lakes depends upon the balance of autotrophic and heterotrophic processes. Bacterial metabolism is a major portion of total planktonic metabolism so factors influencing bacteria will affect total net productivity. In particular, the sources and supply rate of dissolved organic carbon have a major impact on bacterial metabolism and therefore overall ecosystem productivity. This dissertation focuses on dissolved organic carbon sources to lake ecosystems, heterotrophic response to DOC inputs and the potential influence of DOC on planktonic foodweb interactions. Dissolved organic carbon supply to lakes depends upon factors such as lake size, littoral zone area and phytoplankton production. Resident bacteria have a large capacity to respire excess organic carbon so DOC inputs directly stimulate heterotrophic metabolism. Additionally, DOC inputs can influence the outcome of nutrient competition between phytoplankton and bacteria and can further encourage heterotrophic dominance of lakes. Use of DOC by heterotrophic bacteria therefore provides a connection between physical properties and net production of lakes.