On Chesapeake cleanup, field studies and computer predictions don't always agree
"Here are some questions about the Chesapeake Bay restoration effort that might have surprising answers:
- Is the Bay region successfully curbing nutrient runoff from farms?
- Is nitrogen runoff from developed lands really increasing?
- Is the region actually on track to meet its phosphorus reduction goals?
A recent modeling exercise by U.S. Geological Survey scientists suggests the answers to all of those questions might be “no” — conclusions that run counter to conventional notions within the Bay cleanup effort.
The results published in a paper last year are based on a computer modeling exercise that relied heavily on water quality monitoring data within the Bay watershed over a 20-year period.
The exercise found fewer nitrogen reductions from agriculture than estimated by the state-federal Bay Program for the same period, and sharply different phosphorus trends. It also concluded that nitrogen runoff from cities and suburbs is decreasing.
To be sure, there are many caveats to those conclusions, and they do not necessarily mean that Bay Program estimates are wrong.
But the analysis highlights the longstanding question about whether on-the-ground nutrient reduction efforts are producing the expected water quality improvements. It’s an issue scientists have highlighted for years, and it’s drawing increased attention from the scientific community as the region approaches its 2025 Bay cleanup deadline.
The implications are huge. The region has been working since the mid-1980s to reduce the amount of two nutrients, nitrogen and phosphorus, reaching the Bay. In the Chesapeake, they spur water-staining algae blooms that draw oxygen from the water when they die, creating “dead zones” that are off-limits to most aquatic life.
Both the USGS analysis and Bay Program agree that most nutrient reductions achieved to date are from technology upgrades at wastewater treatment plants. With those largely completed, states are counting on greatly ramped-up efforts on agricultural lands, which generate the majority of the nutrient runoff, to meet Bay goals
But the USGS analysis indicates that it’s uncertain when and if those farm-based practices — such as nutrient-absorbing cover crops, vegetated buffers along waterways or plans to guide manure management — will achieve clean water goals.
A second USGS paper published this summer laid out a number of reasons for that uncertainty. For one, it can take a long time for some on-the-ground actions to benefit the water. But other factors could be at play, too. For instance, runoff control practices may not be as effective as thought. . ."