MAP Technical Reports Series No. 106 UNEP

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and flux pattern of nitrogen and phosphorus is also of importance. This concept has been
pioneered by Bernhardt and his Commission (Bernhardt, 1978) for phosphorus in Germany. A
simplified version of Bernhardt's methodology has been elaborated by Vollenweider (1992) for,
and adapted to the prevailing conditions of the Emilia-Romagna Region as an example. Data
needed are: imports and exports through all external systems boundaries, definition of
compartments within systems boundaries, size of, and fluxes between compartments. In
addition to data used from Chiaudani and Premazzi (1988) others have been taken from the
most varied statistics available. The pieces are brought together in Figure 7 showing the major
features of the internal basin structure, and the prevailing flow and exchange patterns. The figure
illustrates both, the complexity, and also how incomplete our knowledge about the various
compartments and flows still remains. Regarding the input output balance, of the roughly 35,000
t of phosphorus that enter the Region in the form of fertilizers and polyphosphates, some 16,000
to 18,000 t leave the Region in the form of farm products (wheat, produce, fruit, meat and bones,
dairy products etc.) and others, while only some 10 to 15 % end up in the sea.
Implicitly, this balance sheet accounting contains a warning that managing fertilizers
for the sake of phosphorus load reduction to the sea has its limitations, which not only depend
on technological constrains but also on implicit constraints that derive from the potential impact,
which fertilizer reduction may have on regional economic activities. In other words, fertilizer
imports cannot be below those of equivalent product exports. Simple source data listings would
hide this problem.
On the other hand, the conclusion regarding nitrogen, may be different, because it
seems that nitrogen fertilizers are used in excess of the amounts required to maintain crops at
the actual level of production. Unfortunately, no corresponding analysis has been made yet.
ii) Basin load to the Mediterranean. No comprehensive estimate of the total nutrient
load to the Mediterranean Sea as a whole seems to have been made yet by any author. This is
a lacuna difficult to fill because of the lack of exhaustive source and reliable input data for all
countries bordering the Mediterranean Sea. As already discussed, Italy is an exception.
Therefore, any estimate that is made from partial information must remain tentative.
Partial budget estimates have been made by Béthoux (1979; 1981; 1986), who
discusses the exchange balance between the Mediterranean and the Atlantic, and estimates
possible contribution of nitrogen fixation to the nitrogen budget. River inputs have been estimated
in a UNEP study (UNEP, 1984). Estimates about atmospheric input have been made by Martin
et al. (1989). Uncertainty remains, however, about the magnitude of retention in the basin of
nitrogen and phosphorus by processes of sedimentation and accumulation in sediments. A
wealth of information is available for the Adriatic Sea, and therefore it would be possible to draw
up reasonable balance sheets for this basin. Partial nutrient budgets have been proposed by
Vukadin (1992), but some of his figures are questionable. Bombace (1985; 1992) gives figures
for total fish catch, which further could be elaborated in terms of nitrogen and phosphorus
removed from the sea by fisheries. For the Mediterranean as a whole the extended FAO
Fisheries Statistics are available.
The following attempts to estimate the total inputs of nitrogen and phosphorus from
land-locked sources are based on the resident population of the Mediterranean basin, the