Phosphate concentrations in lakes

Abstract

Phosphate is an important nutrient that restricts microbial production in many freshwater and marine environments. The actual concentration of phosphate in phosphorus-limited waters is largely unknown because commonly used chemical and radiochemical techniques overestimate the concentration. Here, using a new steady-state radiobioassay to survey a diverse set of lakes, we report phosphate concentrations in lakes that are orders of magnitude lower than estimates made spectrophotometrically or with the frequently used Rigler radiobioassay. Our results, combined with those from the literature, indicate that microbes can achieve rapid turnover rates at picomolar nutrient concentrations. This occurs even though these concentrations are about two orders of magnitude below the level where phosphate uptake is estimated to be half the saturation level for the pico-plankton community. Also, while phosphate concentration increased with the concentration of total phosphorus and soluble reactive phosphorus in the lakes we sampled, the proportion of phosphate in the total phosphorus pool decreased from oligotrophic to eutrophic lakes. Such information, as revealed by the phosphate assay that we use here, should allow us to address hypotheses concerning the concentration of phosphate available to planktonic microorganisms in aquatic systems.

Periphyton responses to eutrophication in the Florida Everglades: Cross‐system patterns of structural and compositional change

“…In all but the most hypereutrophic settings, the majority of P is in the biota (Hudson et al 2000), which, in shallow water, are mainly benthic rather than planktonic. However, water column measures are still used to assess P transport in wetlands…”

“…In all but the most hypereutrophic settings, the majority of P is in the biota (Hudson et al 2000), which, in shallow water, are mainly benthic rather than planktonic. However, water column measures are still used to assess P transport in wetlands and, together with sediment P accretion rates, provide the input for loading models used to calculate nutrient assimilation efficiency (Richardson and Qian 1999).…”

Information Processing by Cyanobacteria During Adaptation to Environmental Phosphate Fluctuations

“…4,5 The biological significance of this behavior can be deduced from the nutrient situation in oligotrophic lakes, in which the formation of phytoplankton biomass is limited by the amount of inflowing phosphate. 6 Under this condition the phosphate concentration decreases to such low levels that the uptake system has not sufficient energy to overcome the existing concentration gradient across the cell membrane. 2,3 In such a situation cyanobacteria and algae can only grow, when the external concentration exceeds, at least occasionally, a characteristic threshold value above which available energy suffices for the transport into the cell.…”

MAGIC method for subnanomolar orthophosphate determination in freshwater

“…At these low concentrations, phosphate availability can be a critical control on carbon fixation and cycling in diverse environments, including the subtropical gyres in the North Pacific (Karl and Tien 1992) and North Atlantic (Wu et al 2000;Ammerman et al 2003), the Eastern Mediterranean Sea (Thingstad et al 2005), and a number of brackish and freshwater systems, including coastal wetlands (Sundareshwar et al 2003;Childers et al 2006) and lakes (e.g., Levine and Schindler 1992;Hudson et al 2000;Bergström et al 2005), specifically Lake Superior (USA/Canada) (Baehr and McManus 2003), which was studied using the new method presented here.…”