Observations on the dynamics and fate of dissolved organic phosphorus in lake water and a new model of eplimnetic P cycling

Abstract

Phosphorus (P) in lake water is commonly partitioned into particulate P and dissolved P by membrane filtration, and dissolved P is then fractionated into soluble reactive P (SRP, reactive with molybdate) and dissolved unreactive or organic P (DOP). Much of what is known about DOP is derived from radiotracer studies using gel chromatography, and summarized by a kinetic model (Lean, Science 179:678-680, 1973a; Lean, J Fish Res Board Can 30:1525-1536, 1973b. Since this work, several relevant discoveries have been made on the role of enzymes, viruses and zooplankton in regenerating dissolved P, and the role of filtration damage in generating dissolved P in filtrates. Herein we present the results of new radiotracer experiments on the fate of DOP in lake water filtrates, consistent with the hypothesis that some of the high molecular weight organic P breaks down spontaneously to smaller molecules, which in turn break down to PO 4 3− . We use inhibitors, including competitive inhibitors of phosphatases and a commercial product (RNA-later ® ) to support the hypothesis that the larger molecules include nucleic acids, and that the smaller molecules are substrates for alkaline phosphatase. We also find that colloidal P (i.e., P > 5000 MW according to gel filtration) includes some virus-sized material that can be collected on 0.02 or 0.03 µm filters. Finally, we provide a new model of the cycling of epilimnetic P that is consistent with these and earlier observations.

Ultraviolet‐visual spectroscopy estimation of nitrate concentrations in surface waters via machine learning

“…Concentrations of dissolved inorganic fractions of nitrogen (NO 3+2 ), phosphorus (PO 4 ), and carbon (CO 2 ), which are bioavailable to algae, are usually hidden by much larger concentrations of organic and particulate nutrient fractions. Measurements of hourly or daily turnover rates of inorganic fractions by living cells are even less common (Hudson et al 2000;Taylor and Lean 2018). Eutrophication studies usually rely on basic knowledge of whole-river or whole-lake inputs and outputs of nutrients on an annual basis; rarely do these studies have good estimates of internal recycling within waterbodies (Orihel et al 2017).…”

Editorial: Phosphorus Along the Soil-Freshwater-Ocean Continuum

“…Phosphate and other P forms can exchange with the water column through adsorption/desorption and precipitation/dissolution, and through uptake and remineralization by organisms in the sediment and in the water column. Within the water column, organic and inorganic P compounds can be dissolved, associated with colloids, or associated with larger particulates including plankton (e.g., Paytan and McLaughlin, 2007;Orihel et al, 2017;Taylor and Lean, 2018).…”

Journal of Water and Land Development

“…Additional nutrient loading from the surrounding catchment areas usually contributes to the trophic deterioration of lake waters, combined with an increase in the intensity of phytoplankton blooms, which in turn leads to a deterioration in water quality, hypolimnetic oxygen deficits, and changes in species biodiversity. The circulation of nutrients within the lake basin (subject to change in the different seasons) and the inflow of nutrients from direct and indirect catchments determine the condition of the lake waters [CHAPRA et al 2012;KAISERLI et al 2002;SEIP 1994;TAYLOR, LEAN 2018;TORRES et al 2014].…”