Ecosystem Thresholds

Despite thirty years of significant public investment, an ambitious management effort in the Chesapeake Bay has not reached its goals for ecological recovery. Some scientists argue that natural systems like the Bay are not likely to respond to restoration efforts in a simple, predictable manner. Instead, the Bay could cross certain thresholds that will cause quick changes, either for worse or — we hope — for the better.

What thresholds might exist — ecologically, spatially — that could trigger or hinder recovery, especially if nutrient levels drop as hoped? How will these thresholds be affected by climate change and variations in storm events, rainfall, and runoff? Looking toward the future, scientists and managers will need to anticipate a range of possible ecological responses and prepare to modify their management approaches accordingly.

Predicting the pathways that the Bay’s ecosystem will follow will not be a trivial matter. Improvements in water quality, habitat condition, and living resources probably won’t follow in lockstep with decreased nutrient loading. There may be time delays caused by the slow movement of groundwater, for example. On the other hand, the Bay may exhibit threshold-type behaviors, where certain levels of a controlling variable (like water clarity), may trigger a sudden burst towards recovery. With improved light conditions underwater grasses may reappear quickly.

One thing is certain. An understanding of the Bay’s likely responses in the context of such nonlinear or threshold events will be key if managers are to monitor recovery, manage public expectations, and maintain a clear and confident approach to the restoration of Bay ecosystems.

Useful links

Thresholds in the Recovery of Eutrophic Coastal Systems: A Workshop Report