Parameterization of biogeochemical sediment–water fluxesusing in situmeasurements and a diagenetic model

[摘要] Diagenetic processes are important drivers of water columnbiogeochemistry in coastal areas. For example, sediment oxygen consumptioncan be a significant contributor to oxygen depletion in hypoxic systems, andsediment–water nutrient fluxes support primary productivity in the overlyingwater column. Moreover, nonlinearities develop between bottom waterconditions and sediment–water fluxes due to loss of oxygen-dependentprocesses in the sediment as oxygen becomes depleted in bottom waters. Yet,sediment–water fluxes of chemical species are often parameterized crudely incoupled physical–biogeochemical models, using simple linearparameterizations that are only poorly constrained by observations.Diagenetic models that represent sediment biogeochemistry are available, butrarely are coupled to water column biogeochemical models because they arecomputationally expensive. Here, we apply a method that efficientlyparameterizes sediment–water fluxes of oxygen, nitrate and ammonium bycombining in situ measurements, a diagenetic model and a parameteroptimization method. As a proof of concept, we apply this method to theLouisiana Shelf where high primary production, stimulated by excessivenutrient loads from the Mississippi–Atchafalaya River system, promotes thedevelopment of hypoxic bottom waters in summer. The parameterizedsediment–water fluxes represent nonlinear feedbacks between water column andsediment processes at low bottom water oxygen concentrations, which maypersist for long periods (weeks to months) in hypoxic systems such as theLouisiana Shelf. This method can be applied to other systems and isparticularly relevant for shallow coastal and estuarine waters where theinteraction between sediment and water column is strong and hypoxia is proneto occur due to land-based nutrient loads.

[学科分类] 地球化学与岩石