Combined Gel Probes for the In Situ Determination of Dissolved Reactive Phosphorus in Porewaters and Characterization of Sediment Reactivity

Diffusive equilibrium in thin films (DET) and diffusive gradients in thin films (DGT) were applied in situ to obtain high spatial resolution dissolved reactive phosphorus (DRP) sediment porewater profiles in two lagoons of the Gippsland Lakes (SE Australia) during summer. Although the DRP depth prof...

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Bibliographic Details
Published in:Environmental science & technology 2008-07, Vol.42 (14), p.5112-5117
Main Authors: Monbet, Phil, McKelvie, Ian D, Worsfold, Paul. J
Format: Article
Language:English
Subjects:
Applied sciences
Australia
Chemical reactions
Cyanobacteria
Diffusion
Environmental Monitoring - methods
Environmental Processes
Exact sciences and technology
Fresh Water - analysis
Gels - chemistry
Geologic Sediments - analysis
Lakes
Phosphorus
Phosphorus - analysis
Pollution
Sediments
Thin films
Water Pollutants, Chemical - analysis
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Summary:Diffusive equilibrium in thin films (DET) and diffusive gradients in thin films (DGT) were applied in situ to obtain high spatial resolution dissolved reactive phosphorus (DRP) sediment porewater profiles in two lagoons of the Gippsland Lakes (SE Australia) during summer. Although the DRP depth profiles were different in each lake, highlighting the sensitivity of DRP to the redox state of the sediment, spatial DRP variations obtained from DET and DGT showed striking similarities with depth in each lake. Comparison of DRP concentrations obtained from DGT and DET allows an assessment of the reactivity of the sediment. A dynamic numerical model of DGT-induced flux in sediments (DIFS) quantified reactivity kinetics. Sediment response time (T c) related to sedimentary phosphorus resupply resulting from DGT-induced lowering of the porewater DRP concentration was calculated. Values of T c ranged from 4128 to 183 400 s and from 55 to 149 400 s for Lakes Victoria and Wellington, respectively. These results indicate the limited capacity of the sediment to quickly resupply DRP to the porewater, especially in surface sediment, which was always characterized by the highest T c. Adsorption and desorption rate constants were also calculated from DIFS with values ranging from 2 × 10−3 to 2 × 10−2 day−1 and from 0.3 to 21 day−1 for Lake Victoria and from 2 × 10−4 to 0.8 day−1 and from 0.6 to 1558 day−1 for Lake Wellington, respectively. Diffusive fluxes estimated from the in situ DRP gradient at the sediment−water interface by DET were 558 and 1.2 μmol m−2 day−1 in lakes Victoria and Wellington, respectively. Despite only a single measurement, these fluxes highlight a substantial contribution of P from the sediment to the water column in summer for Lake Victoria which is likely to contribute to the recurring blooms of blue-green algae. These calculated fluxes obtained with minimal sediment disturbance and high spatial resolution were substantially different (by a factor of 6−180) from other reported values using more conventional quantitative assessments such as diffusive fluxes (from core slicing) and benthic chambers.
ISSN:0013-936X
1520-5851
DOI:10.1021/es8001663