Despite computer models which suggest nutrient levels should be going down, recently compiled figures from water quality monitoring in the Bay’s largest tributaries have failed to show any discernible nutrient trends.
The real-world data, officials say, suggests that some nutrient reduction efforts in the watershed have either not taken effect, or are being overcounted.
“Even though we’re modeling predicted source reductions, the monitoring doesn’t actually show that is taking place,” said Scott Phillips, Chesapeake Bay coordinator for the U.S. Geological Survey, which, along with the states of Maryland and Virginia, develops the trend estimates.
He and others suggest that the Bay Program may need to revamp the way nutrient reductions are counted as it moves to set nutrient and sediment reduction goals aimed at cleaning up the Bay. Through the end of last year, the Bay Program’s computer model calculated that the amount of nitrogen entering the Chesapeake had been reduced 15 percent from 1985 levels, while the amount of phosphorus was reduced by 25 percent.
But when scientists looked at monthly nutrient loads from monitoring programs over that period, they saw a different picture. Monitoring data collected through 2000 failed a scientific “trend test” designed to detect significant changes in nitrogen loads. Nitrogen is the nutrient most responsible for algae blooms in saltwater portions of the Bay.
That analysis was in line with a recent USGS report which showed no significant trend through 1998 for nitrogen, although some progress was made with phosphorus. [See “USGS report finds no decline in nutrient loads from most rivers,” Bay Journal March 2001.]
The lack of progress helps to explain why key water quality indicators, such as dissolved oxygen and the amount of grass beds in the Bay, have remained largely unchanged in the past decade. Except for reductions at wastewater treatment plants, which are easily measured, river monitoring finds little evidence that any large nonpoint source — or runoff — reductions are taking place.
“It reinforces the fact that we need to become more sophisticated about how we approach nonpoint source reductions,” Phillips said. “We need improved information about the sources, the reduction actions, and how watershed characteristics and changes in river flow will influence the effectiveness of reductions.”
Some of the lack of progress can easily be explained, officials say. Several years of higher-than-normal river flows — which flush more nutrients off the land and into waterways — have probably obscured some nutrient reduction efforts.
“The four years of high river flow during the 1990s is one of the reasons we are not seeing a reduction in nutrient loads to the Bay,” Phillips said. “However, variability in river flow will always occur and we need to account for it in our planning to meet the new Bay water quality standards by 2010.”
Another explanation is that many nutrients travel through groundwater, taking years — even decades — to reach rivers, streams and the Bay. As a result, it can take years for the effect of some nutrient control efforts to be seen in waterways.
But, officials increasingly acknowledge that part of the difference between the model projections and real-world monitoring is that some nutrient reductions are not as effective as assumed in the model.
For example, the model gives credit for the widespread use of nutrient management plans across the watershed. Farmers use those plans as a guide for applying nutrients on fields, thereby reducing the use of excess fertilizers and animal manure, which can run off fields and into streams.
Despite the increased use of nutrient management plans — and a decline in farm land — reviews by the USGS and the Bay Program have failed to find a decrease in fertilizer sales in the watershed. Meanwhile, the amount of animal waste produced has gradually increased. Officials say that raises questions as to whether the nutrient plans have been fully implemented.
Also, the Bay Program model assumes nutrient control practices are equally beneficial regardless of soil type and local hydrology. USGS research strongly suggests those factors dramatically affect the nutrient runoff in different parts of the watershed.
Some “hot spots” yield far more nutrients than other areas. In particular, agricultural areas near big rivers tend to deliver far more nutrients to the Bay than those near smaller streams far away from major rivers. That’s because natural processes in small streams tend to be effective nutrient removers.
As a result, the model probably overcounts the effectiveness of nutrient reduction practices in areas where only low amounts of nutrients were making it to the Bay to begin with.
Assumptions about the effectiveness of nutrient reductions for various activities, such as use of nutrient management plans, construction of berms to slow runoff, or buffer strips, were developed in the early 1990s when the states developed tributary-specific nutrient reduction strategies.
Officials needed the figures to determine what had to be done to reach nutrient reduction goals for each river. Those same values were ultimately included in modeling assumptions.
In hindsight, nutrient reduction values assigned for specific actions were based on “overoptimism,” said Tom Simpson, of the University of Maryland’s College of Agriculture and Natural Resources, and chair of the Bay Program’s nutrient subcommittee. “For the most part, we used research-level reductions,” he said. “We assumed that they were properly and fully implemented and maintained appropriately, and we assumed they functioned well even in major rain events. We don’t know if they are fully implemented. I think they are dominantly implemented. We’re quite confident they are not all perfectly maintained or function properly all the time. And this is not just for agriculture. This is urban runoff and everything, too.”
In reality, Simpson said the effectiveness of many nutrient control practices decrease over time unless they are maintained. And some practices can be overwhelmed by large storms. But he defended the original tributary strategies as a good first effort toward accounting for nutrient reductions — something no one else was attempting at the time. “When you are trying something new, you do it, and learn how to do it better,”
The Bay Program next year will set new nutrient reduction goals aimed at achieving a “clean” Chesapeake by 2010. New tributary strategies aimed at achieving those reductions will be developed by fall 2003.
Simpson and others say it is critical that more realistic assumptions about the effectiveness of nutrient control practices be used when strategies are developed. Otherwise, the Bay Program will not achieve its goal of removing the Chesapeake from the EPA’s impaired water list by the end of the decade. In that case, the EPA would likely require that an enforceable, and potentially more costly cleanup plan, known as a Total Maximum Daily Load, be developed for the watershed.
Rich Batiuk, associate director for science with the EPA’s Bay Program Office in Annapolis, said the monitoring information reinforces the need to get better on-the-ground — and in-the-stream — information throughout the watershed.
While some nutrient reductions have probably been overcounted, Batiuk said others have been undercounted — particularly in New York, Delaware and West Virginia, which are not formal members of the Bay Program.
That needs to be coupled with more localized water quality monitoring that would serve as an early warning system as to whether — and where — nutrient and sediment control practices are achieving expected results. Further, Batiuk said, the Bay Program plans to start making computer model estimates of nutrient loads reaching the Chesapeake based on actual flow conditions, rather than average conditions.
He said the Bay states may need to undertake nutrient reduction efforts beyond those required to meet the 2010 goal as a “margin of safety” against the impacts of high flows, and the potential underperformance of some nutrient control practices.
“We’re moving in the right direction but some of our assumptions are a little optimistic,” Batiuk said. “If we really want to make something happen in the next decade, our restoration goals are going to have to reflect that a lot more needs to be done in the future to make up for those optimistic assumptions of the past.”