Phosphorus limitation of bacterial growth in high Arctic lakes and ponds

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Water from lakes and tundra ponds on Banks, Melville, Ellef-Ringnes, Ellesmere and Devon Island (74–79°N, 82–116°W) in the Canadian high Arctic was studied in batch culture experiments to test whether nitrogen, phosphorus or organic carbon limited bacterial growth and biomass accumulation. Water samples containing indigenous bacteria were amended with carbon (glucose), nitrogen (nitrate) or phosphorus (phosphate), either alone or in combination, and were incubated in the dark at ambient temperatures. Bacterial growth was measured as the rate of protein synthesis and the accumulation of bacterial cells. Bacterial growth was significantly enhanced in all cultures amended with phosphorus. There was no indication of primary carbon or nitrogen limitation in either lakes or ponds, but the combined addition of phosphorus and either carbon, nitrogen or both, had a positive effect on bacterial growth in the lakes but not in ponds. This contrasting response in Arctic lakes and ponds can be predicted from in situ concentrations of dissolved nutrients: total dissolved phosphorus was low in all systems (= 10 μg L−1), whereas total dissolved nitrogen and organic carbon was on average 24 and 7 times higher in ponds. Pelagic bacteria in lakes and ponds of the high Arctic seem to follow the general pattern of phosphorus limitation previously observed in many temperate and tropical freshwater systems.