Estuarine management strategies and the predictability of ecosystem changes

Abstract

The Dutch Delta Region (S-W Netherlands) origi- nally consisted of interconnected estuaries, interfacing the rivers Rhine, Meuse and Schelde with the North Sea. The ecosystems were immature, with physical rather than bio- logical control of population dynamics. Main functions were shipping and shellfisheries. An emergent function of the inter- connected estuaries was the buffering and upgrading of river- borne substances before they entered the sea. Execution of the Delta Project in the period 1960-1986 resulted in isolation of several water systems disconnected from rivers and sea, and loss of gradients within these systems. Population dynamics were now controlled by chemical and biological rather than physical factors. Vulnerability to exter- nal perturbation increased. These changes also affected the buffering capacity, i.e. reduced the utility of the area as stabi- liser of the geosystem. Recreational use and appreciation of natural values increased, potentially conflicting with shipping and shellfisheries. Retrospective analysis of the environmental policy and management revealed three consecutive strategies in the Delta Project. 1. Reactive one-issue management, focusing on safety against flooding only. This strategy aimed at complete closure of the estuaries thus transforming them into fresh water lakes. It has destroyed feed-backs and buffering between coastal and inland waters. This strategy has not promoted sustainable development and has increased the vulnerability of the area to future catastrophes. 2. Protective bio-ecological management focused on the preservation of existing values of landscape and environment, and resulted in the maintenance of saline condi- tions and preservation of marshes by shore protection meas- ures. The drawback of this passive orientation to existing values Owhere they are nowO is the necessity of continuous intensive care because the natural adaptive ability is not being restored. 3. Constructive geo-ecological management is based on understanding functional properties within and between ecosystems as integrated elements of the landscape structure. This strategy aims at environmental protection, restoration and development of values Owhere they must beO. Re-establish- ment of gradients by e.g. re-introducing tidal influence and by restoring salt marshes should contribute to sustainable devel- opment.