Nutrient Enrichment and Marine Ecosystem Disturbance:
A Deterministic and Stochastic Analysis of the Black Sea
By Duncan Knowler and Edward B. Barbier
ABSTRACT
Pollution of the marine areas that support much of the world's commercial fisheries is regarded as a pressing global environmental problem. One often-cited issue is nutrient enrichment, but this may be a mixed blessing: it contributes to primary productivity and increases the sustainable fish catch, while simultaneously causing occasional and damaging ecosystem events. Thus, enrichment's aggregate impact on the economic value of fisheries may be ambiguous. This research develops a method for analyzing such problems, using the example of the Black Sea anchovy fishery. Employing a bioeconomic model that incorporates nutrients directly into fish population dynamics, the problem is formulated in deterministic and stochastic terms and the results compared. The deterministic model assumes that nutrients only contribute positively to fish production for a given ecological state, and ignores stochastic events leading to shifts between states. Accordingly, a 50 percent nutrient abatement policy leads to welfare losses in net present value terms of US$ -152,000 to -2.7 million per year (1989/90 prices), depending upon the ecosystem state. The stochastic formulation recognizes that planners may have some knowledge of potentially damaging shifts in ecological states, and wish to take this into account. When these shifts are related stochastically to the level of enrichment, nutrient abatement is shown to have an indeterminate welfare effect. However, an experimental empirical analysis indicates that a 50% nutrient abatement policy generates positive aggregate benefits for the Black Sea anchovy fishery. The general applicability of such an approach for analyzing a range of marine environmental problems is discussed.
KEYWORDS: marine fisheries, marine environment, nutrient enrichment, anchovy, Black Sea
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