Phosphorus sources and demand during summer in a eutrophic lake

Abstract

In pelagic systems, phytoplankton biomass may remain abundant or near equilibrium while concentrations of the limiting nutrient are below detection. In eutrophic lakes, it has been thought that episodic algal blooms are due to mixing events that break down this equilibrium by adding nutrients to the mixed layer. Alternatively, rapid rates of biotic recycling among primary producers and heterotrophic consumers could maintain high phytoplankton biomass, yet the recycling process has been difficult to observe in situ. Here we use free-water oxygen measurements and an associated metabolic model to infer rates of phosphorus (P) uptake and biotic mineralization in the epilimnion of a eutrophic lake. The rates of uptake and mineralization were compared to "external" sources of P such as loading and entrainment. Also, model results were assessed using sensitivity analysis. We found that the majority of phytoplankton P demand during the period of low P availability could be accounted for by biotic mineralization, but that it was important to consider the effects of entrainment in order to account fully for P uptake. These general results were relatively insensitive to model parameterization, though the relative C:P ratio of material taken up versus mineralized was an important consideration. This study integrates modeling and measurement tools that monitor ecosystem processes at finer temporal resolution than has previously been possible, complementing other studies that use experimental incubation and elemental tracers. Extension of this approach could enhance models that aim to integrate biological and physical processes in assessment of water quality and prediction of phytoplankton biomass.

Lake metabolism and the diel oxygen technique: State of the science

“…(e.g., Cole et al 2000;Hanson et al 2003;Staehr et al 2010), we can achieve a wealth of strong empirical data to quantify in situ undisturbed processes and test the relations of GPP, NEP, and R to irradiance, temperature, nutrient availability, and food web structure. A most creative use of metabolism estimates has been estimation of nutrient recycling in the epilimnion of Lake Mendota (Kamarainen et al 2009). …”

In situ estimation of water quality parameters in freshwater aquaculture ponds using hyperspectral imaging system

“…The interrelationships between Chl-a and N and P have been explored during the past few decades (e.g. Brown et al, 2000;Kamarainen et al, 2009). These relationships suggest the potential use of Chl-a to estimate N and P concentrations.…”

Seasonality of Aulacoseira ambigua abundance and filament length: biogeochemical implications

“…Through sedimentation, spring diatom blooms can remove a significant fraction of phosphorus (P) from a lake early in the season (Kufel 2001). This removal subsequently limits the amount of P available for recycling in the photic zone, the principle source of P to primary pro-ducers during the stratified period (Kamarainen et al 2009). Reynolds (1998) referred to the removal of P from the water column through sedimentation of the spring diatom bloom as a nutrient-sponge which influences the community composition of phytoplankton during the stratified period.…”