Examples of (human induced) shifts and thresholds in socio-ecological systems in the region include: The Delta Works closed two estuaries, that subsequently turned into freshwater bodies: the Haringvliet and the Volkerak-Zoom lake. The seemingly unlimited fresh water availability created opportunities for the development of agriculture and drinking water supply, thereby boosting economic development. At the same time water quality of the new fresh water lakes deteriorated. To reduce water-quality problems, it has recently been decided to establish a small fresh-saline gradient in the Haringvliet by operation of the Haringvliet sluices ('Kier besluit'). The relationship between operation of the sluices and the (recovery) of the ecological status of the lake / estuary is being debated and expected to be non-linear. In the second freshwater body, the Krammer-Volkerak Zoommeer lake, algal blooms especially are identified as a problem. Here the strategy is debated whether to restore estuarine dynamics (i.e. a saline gradient) by the year 2015. Re-introduction of a saline-freshwater gradient in the Krammer-Volkerak Zoommeer may reduce the occurrence of algae blooms, but it also reduces freshwater availability for agriculture, drinking-water supplies and greenhouse horticulture in the region. Possible additional measures are (a) increase of fresh water supply and distribution, inclusive alternative internal or external freshwater sources, (2) land-use and local water-management transitions geared at more efficient freshwater use and/or the introduction of other forms of agriculture (salt-water agriculture or aquaculture).
The discussions on partially opening the estuaries and reintroducing a saline-freshwater gradient are linked to the debates on using the estuary for discharging future Rhine peak flows, whereby relieving the Rotterdam / Rijnmond area. The effect of peak flow discharge on the region's socio-ecology is a new topic for debate.
