(Posted by Bill Dennison.)
In a recent scientific publication by Rebecca Murphy and Bill Ball from Johns Hopkins University and Michael Kemp at the University of Maryland Center for Environmental Science, an analysis of 40 years of Chesapeake Bay data reveals some important new insights.
What Rebecca and her colleagues did was quite clever. Instead of simply looking at the annual “dead zone”– regions within Chesapeake Bay with very low dissolved oxygen levels (<0.2 mg/L)– they separated the low oxygen events into spring/early summer events vs. late summer/autumn events. Various different environmental factors influencing these low oxygen events were explored.
They found that the spring/early summer “dead zones” were largely due to increased stratification: warmer, fresher water floating in top of cooler, saltier water. This has led to earlier, more pronounced “dead zone” formation. Regional climatic factors were invoked to explain this trend, and it is just a bit of more bad news for Chesapeake Bay.
But what is really exciting about their analysis is what is happening in the late summer/autumn “dead zones.” Their analysis indicates a reduction in the “dead zones” which, by process of elimination, they have related to nutrient reductions that have been documented entering Chesapeake Bay at the river monitoring sites.
This is a very encouraging finding, as it is the first time that we can point to management actions having a positive impact on reducing the Chesapeake Bay “dead zone.” In a similar vein, the resurgence of aquatic grasses in some of the freshwater reaches of the Bay were related to nutrient reductions in a paper by scientists at the Virginia Institute of Marine Science, United States Geological Survey and the University of Maryland Center for Environmental Science. This trend was not evident when lumping all of the Bay grasses into one group, just as lumping all of the dissolved oxygen data into annual increments would have hidden the story of nutrient reductions leading to reduced late summer “dead zones.”
There are three features of the dissolved oxygen and aquatic grass stories that are worthy of mention.
- These stories rely on good, long-term monitoring data carefully collected and analyzed. We need to continue to monitor the Bay to track the progress of Chesapeake Bay restoration.
- The in-depth analyses that synthesize large, complex data sets require teams of talented researchers using sophisticated analytical techniques. The monitoring data, without this analysis, was not enough. Thus, ongoing monitoring needs to be accompanying with ongoing research.
- The connection between what we are accomplishing in terms of management implementation and the health of Chesapeake Bay is difficult, but not impossible, to discern. We need to continue to look for more of these stories in the data that we have at hand. In summary, we need continued monitoring and research and we need to apply this to Chesapeake Bay restoration.
This past summer was a fairly awful one for Chesapeake Bay water quality, largely due to weather extremes. The advantage of analyzing long term data sets is that year-to-year variability can be factored out of the equation. So as we sort through the combined impacts of high spring rains, and Hurricanes Irene and Lee, it is really nice to have this news that Rebecca Murphy and colleagues have given us.