2.2.1 Biogeochemical budgets – background
The LOICZ project set up a “globally applicable” method of estimating fluxes of carbon, nitrogen and phosphorus within the coastal ocean, especially the bays and estuaries of the inner coastal zone (Gordon et al. 1995). It was necessary to erect a methodology that could depend largely on secondary data, that had minimal data requirements and that was widely applicable and uniform, in order to allow effective comparison among sites. Finally, the method had to be informative about processes influencing CNP fluxes.
The implementation strategy for developing a biogeochemical
budget database was to mount a two-pronged attack on acquainting the scientific
community with the budgeting procedures. The first prong has been publication
of a web-page (http://data.ecology.su.se/MNODE
)
that summarizes and updates the budgeting procedures, provides tools for implementing
the procedures, provides various forms of teaching materials, and posts existing
budgets as they are developed. The second prong has been to hold a series of
workshops around the world, in order to teach people how to do the budgets and
to get them to prepare budgets that can be used by LOICZ. At time of writing,
about 170 budgets have been developed, largely as products of more than 15 workshops
held around the world. The sites budgeted are indicated in Figure 2.1.
Figure 2.1 Map of LOICZ budget sites, October 2001.
The LOICZ approach is based on one of the most fundamental
concepts of the physical sciences: conservation of mass. Details of the approach
are given in Gordon et al. (1995) and on the LOICZ Modelling web page
(http://data.ecology.su.se/MNODE).
Steady-state conditions are assumed in which water volume and salt content in
the system remain constant over time, as water flows through the system and
mixes with adjacent systems. The net flow of water can be described by a water
budget. Information about mixing can be deduced from a salt budget of non-reactive
materials. The data to establish at least first-order water and salt budgets
can be found for many sites around the globe.
Nutrients not only move with the water but also undergo reactions within the system. Nutrient data (especially data on the dissolved inorganic forms of phosphorus and nitrogen, here termed DIP and DIN) can be found for many of these same sites and used to establish nutrient budgets. These nutrient budgets include water flow and mixing, as defined by the water and salt budgets, and an additional term that describes net uptake or release of these nutrients within the system. In the jargon of oceanography, these are termed “nonconservative fluxes,” because the nutrients do not follow exactly the flux pathways of water and salt.
The nonconservative flux of DIP can be used as an approximation of net uptake of phosphorus into organic matter during primary production, or release from organic matter by respiration. While it would be desirable to have direct measurement of carbon uptake into organic matter, such data are not available for most locations. Therefore the flux of DIP becomes a proxy for net carbon flux. In the open ocean DIN is often scaled in exactly this manner to carbon. That scaling in general does not work well in the coastal ocean, for a reason that contains a great deal of information itself. Nitrogen fixation and denitrification are important metabolic processes in bottom-dominated systems and can account for most of the observed nonconservative flux of DIN. Therefore calculations are derived from the budgets:
1.) using DIP flux as a proxy to calculate how much net carbon uptake or release has occurred,
2.) scaling DIP flux to estimate the expected nitrogen (DIN) flux (typically using the Redfield N:P ratio of 16:1), and
3.) using the deviation between the observed DIN flux and the expected DIN flux to estimate the net of nitrogen fixation and denitrification.
2.2.2 Interactions with the regional typology workshop process
Development of biogeochemical budgets through workshops has continued in parallel with the regional synthesis workshop process, with budget node personnel heavily involved in the synthesis workshops. This ensured that the latest information on developments in the budget process were available to the synthesis workshop participants, and provided critical opportunities for developing the needed interconnections among the developing biogeochemical budget database, the typology database (Section 2.1, Appendix IV) and the Web-LOICZView (WLV) clustering and visualization tool (Section 2.3, Appendix VI).
The close coordination of synthesis (typology) and budget efforts through the workshop process developed both a cadre of scientists familiar with the developing combined effort, and a series of data integration and analysis trials that led ultimately to the combined database system. This process was augmented by key ‘mini-workshops’ held among the technical resource personnel in August and October 2001 to work through and test the practical details of the joint database operation and the applications of WLV to the combined data.
2.2.3 The joint “Synthesis Database” product
The budget sites (Figure 2.1) vary dramatically in their characteristics: from lagoons and estuaries of less than 1 km2 in area, to the 106 km2 East China Sea; from sites that are decimeters deep to sites that are hundreds of meters deep; from sites that are virtually devoid of loading from land to sites that receive heavy loads of inorganic nutrients derived from human wastes, agriculture, and other sources; from sites that are river-dominated estuaries to hypersaline embayments; and from tropical to arctic climatic zones. For some sites, data quality and quantity are both high; other sites suffer in the quality and quantity of information available. For the initial analysis we have identified a “preferred” subset of budget site data that excludes systems for which the basic data are incomplete, open shelf systems, and systems with an average depth >100 m, in order to facilitate comparisons among sites. This preferred dataset includes about 80 systems.
Initial experiments have shown the importance of data transformations and scaling in developing relationships that will be useful for upscaling as well as interpretation. The basic biogeochemical budget dataset has therefore been augmented with alternative presentations of many of the variables, so that users can take advantage of the accumulated experience without having to reformulate the data set.
The entire biogeochemical budget database has been
incorporated into the Oracle-based, web-accessible Typology database at http://www.kgs.ku.edu/Hexacoral/Envirodata/envirodata.html.
It can be accessed as either the complete or the preferred budget dataset, and
in combination with either the full inventory of environmental variables, or
a more concise set of variables selected for their appropriateness to representing
the ecosystems processes. The budget database includes descriptive and transformed
variables, and all of the budget variables can be manipulated (separately or
in combination with typology variables) by the database and WLV features described
elsewhere in this report.
Appendix V provides a summary list of the budget variables accessible through the integrated database.