Press vs. pulse disturbance in ecology as applied to the recent oil spills

Ecologists generally classify ecological disturbances as either “press” or “pulse” disturbances. Press disturbances are long-term disturbances that have long-term impacts on an ecosystem, often resulting from changes to the physical structure of an ecosystem. Pulse disturbances are temporary disturbances that, while influential, are recoverable because of the temporary nature of the problem. Press and pulse disturbances can be natural or human-caused (anthropogenic).

The recent oil spill in the Gulf, as well as the oil spill in the Kalamazoo River in Michigan (>1 million gallons in a small tributary) have me thinking a lot about press vs. pulse disturbances. The gulf spill dominated the national news for months. Rarely does the health of an ecosystem get this kind of attention. And when it does, it’s always due to a catastrophe.

These oil spills are certainly nothing to minimize. Oil spills can have huge impacts on ecosystem processes and wildlife (as we’ve all seen). And there are significant human health concerns that go along with these sorts of spills. However, the gulf and Kalamazoo River oil spills are temporary, anthropogenic pulse disturbances. Ecosystems are resilient, as people have begun to point out in reference to the gulf oil spill—the oil is gradually breaking down. But long after the oil is gone, these systems will continue to be impacted by chronic (press) anthropogenic disturbances that are much more significant in the long-term, and the media will hardly even notice (certainly not in any way like the oil spill).

Chronic (or press) disturbances in the gulf include loss of coastal wetlands, a huge dead zone resulting from excessive nutrients delivered from the Mississippi River basin, overfishing, and climate change. Chronic disturbances in the Kalamazoo River include high phosphorus loads from incompatible agricultural and urban-development practices, fragmentation from dams, altered hydrology from increased watershed impervious surfaces, and the introduction and spread of aquatic invasive species. These impacts have been cumulatively impacting these ecosystems (and systems like them) for decades. And there are substantial socio-economic costs that go along with these impacts as well. But the impacts are cumulative and gradual, so we generally overlook them. Rather than killing birds and fish in a gooey mess, their habitat is gradually degraded or destroyed so that they can no longer reproduce. Long after there is any sign of oil within either of these systems, these press disturbances will go on with insufficient action to effectively minimize their impacts. Don’t get me wrong; there are valiant efforts by conservation organizations, natural resource agencies, and dedicated citizens to conserve these systems--and these projects are critical (see brief example from The Nature Conservancy below). But these efforts rarely approach the conservation endpoint of “effectively conserved” against these anthropogenic impacts because the problems are so systemic and the media attention span isn’t sufficient to attain public awareness of the issues.

My fear is that as the oil (and alarm) dissipates, the message from the oil spill(s) will be that ecosystems are resilient and anthropogenic disturbances are always blown out of proportion. This message could ultimately cause more damage than the oil spills themselves. A better message, from the start, would have been that these ecosystems are already under major stress from a variety of chronic anthropogenic stresses, and the last thing they need is an oil spill to further degrade things. We need more attention on the chronic anthropogenic disturbances to the ecosystems upon which we depend. Hopefully the media will stay around for a while.

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The Nature Conservancy works with partners to address both press and pulse anthropogenic disturbances to conserve biodiversity, including work in the Gulf. A new report, Gulf 20/20: Case for Long-Term Restoration, highlights the need to balance short-term, reactive responses with long-term restoration.