In early November, Bay area newspapers were full of stories, columns, editorials and letters to the editor about whether the health of the Bay was improving or showing no signs of recovery.
Government agencies responsible for monitoring environmental conditions in the Bay announced signs of improvements at a press conference on Nov. 6. Among other indicators, they noted that despite the extensive “dead zone” observed early in the summer, dissolved oxygen conditions over the whole summer were really not that bad considering the near-record amount of freshwater inflow this year.
As reported in several newspaper accounts, a Bay Program official suggested that 20 to 30 years ago, we would have seen a much longer period of harmful, low-oxygen conditions, or hypoxia, suggesting that the interval of hypoxia was abbreviated because of steps taken to reduce nutrient inputs from agriculture and wastewater treatment plants.
Less than one week later, the Chesapeake Bay Foundation released its annual State of the Bay Report. The aggregate score dropped by one point, from 28 to 27 (out of 100) from 2002 to 2003, mainly because of declines in the component scores for nutrients, water clarity and dissolved oxygen. The foundation noted that one of the largest “dead zones” ever recorded in the Chesapeake occurred during the summer of 2003, containing about 40 percent of the Bay’s volume and stretching from Baltimore to the York River.
In the press flurry, Bay Foundation officials complained that the agencies presented too optimistic an interpretation of the evidence concerning hypoxia, thus misleading the public about the amount of progress that yet has to be made to restore the Bay to acceptable health.
What, then, are we to believe? Is the Bay, or at least its “dead zone,” getting better or worse?
In “Is the Chesapeake getting worse? It’s not as bad as some report,” [Bay Journal, November 2003], David Jasinski presented results from Chesapeake Bay Program monitoring on the average summer volume of anoxia (essentially no dissolved oxygen) and hypoxia (he used a dissolved concentration of 5 mg/l rather than the usual 2 mg/l as the upper limit of hypoxia) from 1985 through 2003.
Jasinski concluded that the mean volume of anoxia in 2003 was less than average, but the mean volume of hypoxia was greater than average, ranking fifth among 29 years of data.
To understand the apparent contradiction, it is necessary to look in more detail at the climatic and physical conditions that prevailed during this past summer.
In his commentary, Jasinski describes in some detail the effects of physical factors, including freshwater discharge, temperature, the salinity of water moving along the bottom of the Bay from the ocean, and mixing winds, which resulted in a highly variable hypoxia during the summer of 2003.
Early in the summer, unusually large areas of hypoxia developed in the Bay, extending south of the Rappahannock River for the first time since 1989. The volume of anoxic water reached record levels of nearly 4 cubic kilometers. This was a result of unusually high river runoff (bringing large volumes of less dense, fresher water and also a large pulse of nutrients) and the unusually cold and salty (and therefore more dense) water that moved up the Bay. These conditions caused strong density stratification and the isolation of bottom waters.
However, high winds from a series of storms in late July and early August mixed the well-oxygenated surface waters with oxygen-poor bottom waters. Consequently, while the hypoxia that had developed in the Bay by early July was probably as severe as ever recorded, the average conditions for the whole summer were not extraordinarily severe.
In his doctoral dissertation, James Hagy analyzed dissolved oxygen records from 1950 through 2000 and found that the proportion of the Bay’s volume experiencing severe hypoxia (<1 mg/l) during a year of average freshwater inflow increased from 2 percent in the 1950s to 12 percent in the 1990s. He noted that: “The trend in hypoxia during 1985-2000 was less obvious only because analyses based only on data for this period indicated no significant time trend. In contrast, within the context of the longer time series it appears that the upward trend in hypoxia was accelerating, rather than stabilizing, in recent years.”
Examining the period from 1985 to 2003, Jasinski concluded: “The scientific data do not suggest that dissolved oxygen conditions have gotten worse in the last 20 years.” Remember that Hagy also did not find a statistically significant trend when just examining data from 1985-2000.
Just as important, though, there is no basis to conclude from either statistical analysis of trends in the volume of hypoxia that dissolved oxygen conditions have gotten better over the last 20 years. In fact, both analysts agree that, prior to 2003, the worst years of severe hypoxia (average summertime conditions) were not in the 1980s, but during the 1990s, and corresponded with much higher than normal river inflows.
So, was the dead zone the worst ever in 2003? It depends on one’s perspective. If one were an analyst examining trends over many years, perhaps not. But, if one were a sturgeon trying to survive in the deep waters of the Bay and not having the ability to postpone respiring for a few weeks until oxygen conditions improved, it might have been.
Because of the extreme climatic conditions leading up to it, the record hypoxia seen early in the summer should not be taken as a certain indicator that the health of the Bay is declining. On the other hand, one shouldn’t conclude that this was just a natural event—its root cause is excessive nutrient inputs. As Jasinski put it: “We therefore, cannot hold Mother Nature fully accountable for the dissolved oxygen problems in the Bay this summer.”
Also, it is not at all apparent that the improvements in oxygen conditions that occurred in midsummer were the result of steps taken to curb nutrient inputs, but rather were due principally to wind mixing, for which the Chesapeake Bay Program should not claim credit.
At the Chesapeake Bay Program press conference, scientists from the U.S. Geological Survey presented findings that the concentrations of nutrients in the major rivers discharging to the Bay have been declining since 1985. Statistical trends in the flow-adjusted concentrations of both total nitrogen and phosphorus measured at the fall lines of major rivers are significantly downward. This is a strong signal that efforts to reduce nutrient pollution are having an effect.
However, there has been no significant trend in the loadings of nitrogen and phosphorus delivered to the Bay, primarily because of the occurrence of several high flow years during the 1990s and now in 2003. Even as the concentrations of nutrients were reduced, the higher flows delivered a higher mass of nutrients.
The lack of significant trends in loadings may explain why a reduction in hypoxia is not yet apparent, despite the fact that nutrient concentrations in river discharges have declined as a result of management activities.
Keep in mind, also, that the loadings estimated at fall line gauges constitute only about 60 percent of the total nutrient loading in the estuary.
This counsels patience in watching results unfold and avoiding both irrational exuberance when dry years result in reduced loadings of nutrients and less hypoxia, and inconsolable depression when wet years deliver a wallop with large quantities of nutrients.
Another November 2003 Bay Journal article heralded “Monitoring reveals drought helped to improve Bay’s water quality.” While the reduced loadings, clearer waters and expanded submerged aquatic vegetation during the past four dry years (1999-2002) in some ways give us a glimpse of a recovering Bay, those years hardly represent a recovered, healthy Bay.
Abnormally low flows negatively affect anadromous fish, oysters and freshwater SAV species. Nutrients may build up in soils during dry years only to be flushed downstream during a following wet one.
What should be emphasized is not that the average annual loading of 119 million pounds of nitrogen during the four dry years nearly reached the 105 million pound goal set for the nontidal area, but that in order to reach the time-averaged goal, the loading during a similar dry spell in the future would have to be reduced to about 70 million pounds.
In any case, the goal for Bay restoration should not so much address the average condition but be directed to re-establishing the resilience of the system wherein the unusual climatic conditions of 2003 no longer produce the same widespread and severe hypoxia.
Here in the early 2000s, we may be seeing clear signs of recovery in the lowered nutrient concentrations in rivers and expansion of SAV, but more striking is not the progress we have made, but how much further we have yet to go in reaching Chesapeake 2000 goals. As a Bay Program official recently said, “we are on the right track,” but the train is well behind schedule.
I think that all would agree that our efforts in reducing nutrient inputs will have to be greatly strengthened and coupled with more active habitat rehabilitation and sustainable harvest management to restore the ecosystem to a state that the public desires and science indicates is possible.
The controversy over whether the dead zone is getting better or worse is a graphic example of the natural differences in how parties playing different roles chose to interpret environmental information.
Typically, governmental agencies like to demonstrate that progress has been made in the execution of policies. They fear that public support may wane if it appears that little progress is being made.
Environmental advocacy organizations are consequently distrustful of agency interpretations and also fear that the public will lose interest and commitment by being lulled into complacency.
Greater involvement by the independent scientific community, largely lacking in this case, could help keep interpretations objective.
This controversy also reveals shortcomings in science integration in the Chesapeake Bay Program. The annual variation in flows makes deciphering a trend in the dead zone nearly impossible. But the Bay Program’s assertion that hypoxia would have been worse 20–30 years ago given 2003 climatic conditions could be examined by comparing last year’s observations with water quality model predictions based on 2003 streamflow and physical conditions in the Bay, but with past observed nutrient concentrations.
The Mars of modeling and the Venus of monitoring must go beyond occasional dalliances and commit to a strong marriage. This would avoid the overreliance on the virtual reality of models for which the Bay Program has been criticized and greatly enhance our ability to detect—and understand—trends in a highly variable world.