Will Solarbees increase fish mercury levels in Jordan Lake?
Recent science shows a clear connection between algal blooms and decreased mercury levels in fish.
Algal-bloom reducing Solarbees could increase fish mercury levels about 50 percent, taking Jordan Lake fish above the EPA’s advisory level.
Stormwater is the problem.
When it’s not raining, roads, parking lots, and houses collect pollutants like nitrogen, phosphorus, and mercury from the smokestacks of coal-fired power plants.
Rains wash these pollutants down stormwater pipes, into streams, and on into drinking water reservoirs like Jordan Lake.
Gushing stormwater leads to even more problems.
Deeply eroded streams drain groundwater near the stream, drying out stream-side vegetation, and that change reduces the nutrient and pollution processing abilities of these important stream-side ecosystems.
Because no one wants to halt economic development or drink dirty water, the National Academy of Sciences tackled stormwater in a 2009 book, “Urban Stormwater Management in the US”, freely available at bit.ly/1ky1GNV.
In order of decreasing importance to nation’s stream and lake water quality is (1) mercury, (2) pathogens (leaking sewer pipes), (3) sediments from land disturbance and stream erosion, (4) metals other than mercury (from vehicles), (5) nutrients (from fossil fuel use), which causes (6) oxygen depletion.
To solve simultaneously these many problems, the National Academy recommends approaches like pollution control, low-impact development, and things like rain gardens distributed throughout a watershed, as well as using stormwater as a resource to reduce volume and pollution loads.
However, using Solarbees our legislature is tackling problem No. 6 without addressing watershed-scale problems.
We learned long ago that nutrients make crops grow better, and in lakes it makes algae flourish and bloom. Algae-eating animals can’t keep up, and when all that algae dies, bacteria break it down and use up all of the oxygen in the water. That lack of oxygen makes fish die, the water stinky, and creates bad drinking water.
But the legislature’s misplaced focus is dangerous.
It’s a complicated process, but mercury works its way into reservoirs where algal cells take it up. Zooplankton eat algae, little fish eat zooplankton, big fish eat little fish, and birds eat big fish. Along with PCBs and flame retardants, mercury progresses up these trophic levels and biomagnifies in fish and birds.
Jordan Lake was included in a 2000-2004 EPA study that measured mercury in carp and largemouth bass, finding levels of 178 parts per billion and 288 ppb, respectively. Scary levels given that the EPA’s mercury limit for four fish meals per month sits at 300 ppb. Be warned: don’t eat big fish from Jordan Lake.
Here’s where the science of ecology is so fascinating.
High algal blooms dilutes the mercury that flows up to fish, resulting in fish with lower mercury levels.
One study, for example, by Celia Chen and Carol Folt (our new UNC-CH Chancellor), showed a clear connection between mercury levels in predatory fish, lake algal densities, and nutrient levels. It’s hard to say how much of a change in one begets a change in the other, but likely 30 to 50 percent.
So, preventing algal outbreaks with Solarbees in Jordan Lake might just push mercury levels in fish from 288 ppb to the mid-400 ppb, well above the EPA advisory of 300 ppb.
Our legislators’ experiment could harm people eating fish from Jordan Lake.
As a scientist, I’m thrilled the legislature is funding science, but I hope they’ll share with citizens the independent scientific reviews of their research proposal for the Solarbee experiment.
Did the reviewers note the possibility of enhanced mercury levels?
Did the reviewers recommend a few years of monitoring fish mercury levels, nutrient and algal concentrations prior to the Solarbee installations?
Even the most cursory review would note that measuring changes requires measuring pre-treament levels.
They did do a scientific review, right?
Will Wilson is an associate professor of biology at Duke, author of “Constructed Climates: A Primer on Urban Environments” and is writing a book on stormwater.