Time and monitoring will tell impact of Irene on Bay health

When it became clear that Hurricane Irene would move through the Bay region, the Chesapeake Bay Program’s (CBP) monitoring program coordinators, like Bruce Michael at Maryland’s Department of Natural Resources, adjusted the Bay water quality monitoring cruise schedules to get data just following the hurricane.

Now in the days since the hurricane, recent data from Maryland’s Eyes on the Bay program is showing that the Bay received a short term water quality boost from the hurricane. This is a result of the physical mixing of the Bay’s waters by extreme winds and waves that sent oxygen-rich surface waters into the deeper channels that are normally lacking oxygen at this time of year.

It’s all in the timing

When it comes to hurricanes and their impact on the Bay, it’s the timing that makes the big difference in terms of whether there is a short term (weeks to a month) or a long lasting (months to years) impact on the Bay ecosystem.

In this case, timing is made up of two important components: the point during the hurricane season when the hurricane moves through Bay country and how long the hurricane lingers over the Bay and its surrounding watershed.

When hurricanes strike during important growing seasons for fish, oysters and underwater bay grasses, the results can over longer lasting effects. Hurricane Agnes back in 1972 (a tropical storm by the time it hit the Bay), hit in June at the peak of the underwater Bay grasses growing season, tipping an already declining Bay ecosystem into a tailspin lasting into the early 1980s.

Also, when a hurricane stalls and hangs around the Bay and its watershed for days, the amount of rain and resultant flooding can increase dramatically compared to the effects of Irene who moved all the way through the region over in less than a 24-hour period.

And it’s good to be “late” sometimes

Fortunately in the case of Hurricane Irene, we are at the tail end of the peak growing season for bay grasses, so the clouded water and increased amounts of sediments entering the Bay’s tidal waters via runoff will not have as big of an impact compared to if the hurricane hit us in June or July.

We are also not in prime oyster spawning season (later in the fall to early winter) nor are we in any critical fish spawning period (late winter to late spring) so we missed those opportunities for a bigger, more direct impacts on our fish, crabs, oysters and grasses.

To surge or not to surge

Unlike Hurricane Isabel, Irene’s track and, therefore, wind directions meant that we did not experience a devastating storm surge that resulted in the extreme shoreline erosion the region witnessed in the fall of 2003.

The flood waters will continue to bring in extra nutrient and sediment pollution loads into the Bay for days and even weeks to come. But again, timing is on our side. With cooler temperatures and shorter days coming, those excess nutrients will not feed algal blooms which love hot, sunny, calm days.

Lingering effects

Some of the excess nutrients that flowed downstream during the storm will remain in the Bay’s tidal waters and will support next year’s algal growth. However their impact is likely less than if the hurricane had struck later in October or November when the nutrients have a greater opportunity to hang around until the next year.

All about the wait

The bottom line on Hurricane Irene’s impact is that we will have to wait for weeks (mixing up of the water column with good oxygen levels; short term algal blooms), and really months (impact on the next spring’s algal blooms, early summer’s re-growth of underwater Bay grasses, and mid-summer’s dissolved oxygen conditions years), to fully answer the question, “What was the impact of Hurricane Irene (and even the fall 2011 hurricane season) on the Bay?”

Fortunately, the CBP partnership has an extensive monitoring program in place which continues to measure various indicators of the Bay’s health — in this case, prior to the hurricane and in the weeks and months following the storm.

In a nutshell?

Given the timing of this storm, the Bay likely dodged a potentially serious bullet thanks to Irene’s timing, rapid movement through the region, and track.

For more information about the effects of Hurricane Irene on the Chesapeake Bay, visit these links from our partners:

• Monitoring Irene's Effects on the Bay - NOAA Chesapeake Bay Office
• Impacts of Hurricane Irene on the Chesapeake Bay Watershed (.pdf) - Maryland Department of Natural Resources
• Hurricane Irene Flooding Activities - U.S. Geological Survey