Modelling sedimentary biogeochemical processes in a high nitrate, UK estuary (the Gt. Ouse) with emphasis on the nitrogen cycle
Modelling sedimentary biogeochemical processes in a high nitrate, UK estuary (the Gt. Ouse) with emphasis on the nitrogen cycle
The description, calibration and application of a reaction-diffusion model of early diagenesis is presented. Unlike previous models it has been developed for a temperate latitude estuary (upper and lower Gt. Ouse, UK) impacted by high nitrate concentrations (annual mean 700 mM). Five variables, O2, NO-3, NH4+, SO4= and S=, are modelled from the steady state distributions of bulk total organic carbon (TOC).
Different representations of the first order rate constant, k, for TOC mineralisation are tested. Use of separate k values for individual mineralisation pathways is the only way to reproduce the data but at the cost of 1) increasing the degrees of freedom in the model and 2) conceptual simplicity. This casts doubt over the universal applicability of diagenetic models in high NO3- environments. Underestimation of the observed ammonium fluxes leads to the inclusion of dissimilatory nitrate reduction to ammonium (DNRA) into a diagenetic model for the first time. Use of an empirical temperature function successfully simulates rates of denitrification and DNRA. It is concluded that temperature is an important control in partitioning nitrate reduction into DNRA and denitrification in the Gt. Ouse sediments. This temperature effects implies that during an extended warm summer in temperature estuaries receiving high nitrate inputs, nitrate reduction may contribute to, rather than counteract a eutrophication event. A literature review showing that DNRA can account for up to 100% of the nitrate reduction in different locations around the world, means that diagenetic models of the nitrogen cycle in coastal areas should include DNRA.
A parameter sensitivity analysis (PSA) reveals a highly non linear model response to parameter changes of ±50%. The variability in model response among the sites in the Gt. Ouse highlights the importance of accounting for differences in 1) the relative contributions of oxic, suboxic and anoxic mineralization to total organic carbon mineralization; 2) rates of oxygen consumption and 3) oxygen penetration depths.
University of Southampton
Kelly-Gerreyn, Boris A
0774749f-e27b-44e9-bad9-6c68391c060e
2003
Kelly-Gerreyn, Boris A
0774749f-e27b-44e9-bad9-6c68391c060e
Kelly-Gerreyn, Boris A
(2003)
Modelling sedimentary biogeochemical processes in a high nitrate, UK estuary (the Gt. Ouse) with emphasis on the nitrogen cycle.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The description, calibration and application of a reaction-diffusion model of early diagenesis is presented. Unlike previous models it has been developed for a temperate latitude estuary (upper and lower Gt. Ouse, UK) impacted by high nitrate concentrations (annual mean 700 mM). Five variables, O2, NO-3, NH4+, SO4= and S=, are modelled from the steady state distributions of bulk total organic carbon (TOC).
Different representations of the first order rate constant, k, for TOC mineralisation are tested. Use of separate k values for individual mineralisation pathways is the only way to reproduce the data but at the cost of 1) increasing the degrees of freedom in the model and 2) conceptual simplicity. This casts doubt over the universal applicability of diagenetic models in high NO3- environments. Underestimation of the observed ammonium fluxes leads to the inclusion of dissimilatory nitrate reduction to ammonium (DNRA) into a diagenetic model for the first time. Use of an empirical temperature function successfully simulates rates of denitrification and DNRA. It is concluded that temperature is an important control in partitioning nitrate reduction into DNRA and denitrification in the Gt. Ouse sediments. This temperature effects implies that during an extended warm summer in temperature estuaries receiving high nitrate inputs, nitrate reduction may contribute to, rather than counteract a eutrophication event. A literature review showing that DNRA can account for up to 100% of the nitrate reduction in different locations around the world, means that diagenetic models of the nitrogen cycle in coastal areas should include DNRA.
A parameter sensitivity analysis (PSA) reveals a highly non linear model response to parameter changes of ±50%. The variability in model response among the sites in the Gt. Ouse highlights the importance of accounting for differences in 1) the relative contributions of oxic, suboxic and anoxic mineralization to total organic carbon mineralization; 2) rates of oxygen consumption and 3) oxygen penetration depths.
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Published date: 2003
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Local EPrints ID: 464984
URI: http://eprints.soton.ac.uk/id/eprint/464984
PURE UUID: 981817ce-28f8-46b2-a7c9-d17eaa56a64e
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Date deposited: 05 Jul 2022 00:15
Last modified: 16 Mar 2024 19:52
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Boris A Kelly-Gerreyn
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