Nutrient fluxes estimation

In the context of saltmarsh/coastal flux studies, a flux is the net exchange of a substance between these two ecosystems. The fluxes of several types of material, including nutrients, trace metals, herbicides and radionuclides, have been studied by researchers. Although this paper primarily appraises the methodology of nutrient flux estimations, many of the problems are also shared by researchers working on other types of material fluxes. 

First flux estimates through larger parts of its metabolism were based on constraining assumed reaction networks with measurement of uptake and production rates [74]. A number of studies utilized stoichiometric balancing to assess the flexibility of the metabolic network [11, 75] and to investigate the influence of environmental conditions such as dissolved oxygen level [88], salt content [89], or nutrient status [12,90, 91]. However, this conventional approach cannot yield reliable information about parallel or bidirectional reactions and has to rely on balances for NADH or NADPH, which may not be accurate [34]. Moreover, it is limited to derive new conclusions since the results are strongly based on the taken assumptions and not on data [92],... 

Moore, W. S., Blanton,., and oye, S. B. (2006). Estimates of flushing times, submarine groundwater discharge, and nutrient fluxes to Okatee estuary. South Carolina. J. Geophys. R s 111. 

It is important to realise that the flume method should not be used to estimate the overall flux from the saltmarsh. It is only suitable for assessing the importance of surface processes, such as diffusion of substances between pore-water and inundating tidal water, uptake by vegetation and wash off" processes. The results can not be extrapolated to determine the total flux between the saltmarsh and the coastal water, as the nutrient transforming processes associated with the marsh surface only play a small role in determining the overall nutrient flux (see Figure 4.2). 

The difference the field methodology makes to the estimation of the nutrient flux between a saltmarsh and coastal water can be illustrated using studies conducted on North Inlet marsh. South Carolina. Wolaver Spurrier (1988), used the flume technique to estimate the budget for a whole marsh. They concluded that North Inlet marsh imported both phosphate and particulate phosphorus. However, an earlier direct tidal... 

To obtain good estimates of nutrient fluxes, it is important to determine accurately the variation in its concentration over a tide. Therefore a sufficient number of samples should be taken to reflect the temporal variability. It should be noted that the concentration of particulate material is prone to greater short-term fluctuations than dissolved constituents and so the former requires more intensive sampling than the latter. In addition to temporal variability, spatial variability needs also to... 

Basically, flux is calculated as the difference between the amount of nutrient in the flood and ebb tide, but there are several ways of doing this. The amount of nutrient is estimated by combining discharge and water sample concentration. Calculation details are normally glossed over in published papers, and the absolute method is not defined, e.g. The transport was calculated on the basis of the weights of a component imported or exported on each tide (Boorman et al., 1994) and By multiplication with concentration values obtained from the sample, the particulate and dissolved matter could be calculated for each period (Bankers et al., 1984). This does not help readers assess the confidence they may place in the final flux values. 

There have been no studies measuring both carbon and nutrient fluxes in different morphological zones, nor studies relating net carbon sources and sinks to nutrient fluxes. For many reefs, errors in gross production and respiration are too high (10-15%) to get reliable estimates of net community production (Crossland etal, 1991) while changes in nutrient concentrations are nearly undetectable. Such experimental restrictions have limited our ability to understand the relationship between carbon and nutrient cycles in coral reefs. 

The Black Sea shows up as an area of very high chlorophyll throughout the year. This is expected since it is dominated by river inputs and estuarine circulation. The sea of Marmara also has high chlorophyll throughout the entire year. While there is a higher chlorophyll plume from the Black Sea into the northern Aegean, the amount seems to be relatively small and certainly smaller than the plumes observed from the Po and the Nile. Qualitative observations on the biomass produced by these extra-basin inputs are entirely compatible with recent estimates for the amount of nutrients fluxed into the basin from the sources (Krom etal., in preparation). In addition to these natural increases in biomass there is a major increase in colour off the Tunisian coast. This corresponds to an area of shallow water where there is both an increase in chlorophyll and particulates in the water column. 

Two widely used practical inverse approaches are presented in the next two sections ( Estimating absolute velocities and nutrient fluxes across sections and Estimating carbon export fluxes with the adjoint method ). These serve as examples to describe details of the mathematical methods and to list achievable results. The first method, the section inverse approach, infers nutrient, carbon, and tracer fluxes across sets of sections, based on hydro-graphic, tracer, and nutrient data along these sections. The second example describes an application of the adjoint method for the determination of ocean currents, biological productivity, and downward particle fluxes. This method is specifically adapted for the utilization of many different tracers and can handle problems with heterogeneous and sparse data coverage. 

Estimating Absolute Velocities and Nutrient Fluxes across Sections... 

Liu SM, Zhang J, Li DJ (2004) Phosphorus cycling in sediments of the Bohai Sea and Yellow Sea. Estuar Coast Shelf Sci 59(2) 209-218 Liu XC, Shen HT, Huang QH (2002) Concentration variation and flux estimation of dissolved inorganic nutrients from the Changjiang River into its estuary. J Oceanol Limnol Sin 33(3) 332-340 (in Chinese with English abrtract)... 

The rates in which the nutrient is fixed by phytoplankton and transferred upward in the food web to zooplankton can largely determine the productivity of fish in the marine system. Traditionally, studies of nutrient flux rates have been conducted using incubation experiments with artificial C or N isotope tracer and the transfer of activity over time into the various size classes of phytoplankton and zooplankton examined. The difficulty with such types of research is that they involve significant perturbations to the system of interest. For example, samples are first separated from the ecosystem before incubation. Bottle incubations will, at best, miss sporadic bloom events and provide rate estimates that are only valid for discrete depths and time. Recently, naturally produced and have been used to investigate directly the uptake rates... 

Human activity has an enormous influence on the global cycling of nutrients, especially on the movement of nutrients to estuaries and other coastal waters. For phosphorus, global fluxes are dominated by the essentially one way flow of phosphorus carried in eroded materials and wastewater from the land to the oceans, where it is ultimately buried in ocean sediments. The size of this flux is currently estimated at 22 x 106 tons per year. Prior to increased human agricultural and industrial activity,... 

It appears that Narragansett Bay retains less than 5 % of the nutrients, less than 10 % of the Mn, and perhaps 15-30 % of the Cd that is input to the system each year. The removal of Cu (70-95 %) and Pb (80-100 %) is much more effective. Somewhere between 25-65 % of the petroleum hydrocarbons entering the Bay remain in the sediments. These estimates are in agreement with the behavior of the different materials in sediment-water flux measurements and in experiments using the large MERL mesocosms. 

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