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Advances in the aquatic sciences
RESEARCH ARTICLE

Phosphorus dynamics in sediments of a eutrophic lake derived from 31P nuclear magnetic resonance spectroscopy

Deniz Özkundakci A D , David P. Hamilton A , Richard McDowell B and Stefan Hill C
+ Author Affiliations
- Author Affiliations

A Environmental Research Institute, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand.

B AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand.

C Scion Research, Te Papa Tipu Innovation Park, 49 Sala Street, Private Bag 3020, Rotorua, New Zealand.

D Corresponding author. Email: d.ozkundakci@gmail.com

Marine and Freshwater Research 65(1) 70-80 https://doi.org/10.1071/MF13033
Submitted: 4 February 2013  Accepted: 19 June 2013   Published: 18 September 2013

Abstract

The determination of organic phosphorus (P) compounds in lake sediments can provide information on the potential for internal P loading. Settling seston and vertical sediment core samples from highly eutrophic Lake Okaro, New Zealand, were collected during a mixed winter and stratified summer period, representing, respectively, when the water column was well oxygenated and when the bottom waters were anoxic. Samples were analysed with 31P nuclear magnetic resonance (31P NMR) spectroscopy, which showed that both bottom sediments and settling seston contained orthophosphate, orthophosphate monoesters and diesters, pyrophosphates, polyphosphates and phosphonates. Phosphorus concentration in settling seston increased ~2.5-fold in winter as a result of seasonally induced changes in phytoplankton biomass, with a marked increase in the concentration of orthophosphate. Several potentially bioavailable P compounds in the bottom sediments were identified that were likely to contribute to recycling of P from the sediment to the water column. An ‘apparent half-life’ was used to quantify the time scales on which these compounds were recycled to the overlying water column. Orthophosphate monoesters that include inositol phosphates were the most persistent P compound. On the basis of half-lives, high internal P loadings may persist for more than 20 years, potentially hindering restoration efforts in Lake Okaro.

Additional keywords: internal loading, Lake Okaro, sedimentation, temporal variability.


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