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St. Paul, Minn.— A new technical support document (TSD) released by the
Minnesota Pollution Control Agency (MPCA) details how the agency has refined
its draft proposal to protect wild rice in response to more than 600 comments.
The agency released its initial Draft Proposal for Protecting Wild Rice from
Excess Sulfate in March 2015, and requested comments on the proposal in October
2015.
In response to comments and questions received, the MPCA re-analyzed its
wild-rice study data using different statistical approaches. The agency has
revised its conclusions in four areas:
Categorizing wild rice waters
2015 proposal:
The proposal released last year includes a draft list of wild rice waters where the standard would
apply, along with a process to add waters to the list over time. The planned definition
for a “wild rice water” is a water that:
Contains a
self-perpetuating population of wild rice— now or any time since November 28,
1975 — with at least 8,000 wild rice
stems over the surface of a lake or wetland, or a minimum of 800 wild rice
stems over a river-mile reach.
Refinements
to the proposal:
The definition
of a “wild rice water” has been revised:
Since November 28,
1975, a lake, stream, or wetland has had a documented history of wild rice
harvest or contained a natural bed of wild rice of at least:
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0.25
acres, with a stem density of at least 8 stems per square meter OR
-
0.5
acres, with a stem density of at least 4 stems per square meter
The correct sulfide level
2015 proposal:
Sulfate in lake or stream water can diffuse into the sediment where wild rice
grows and turn into sulfide, which can be toxic to wild rice at high
concentrations. MPCA evaluated the effect of sulfide on wild rice and used
statistical analysis (EC10 developed through regression) to identify a
tolerable sulfide concentration to be able to develop a sulfate standard.
Refinements
to the proposal:
Based
on feedback, MPCA used a new approach (graphing the study data) and has revised the concentration
of sulfide in the sediment that wild rice can tolerate, detailed in the MPCA
draft technical support document.
Calculating appropriate sulfate levels
2015 proposal:
Iron
and organic carbon in the sediment affect the rate at which sulfate in the
water is converted to sulfide in the sediment. Iron in sediment binds to
sulfide and neutralizes it, making it non-toxic to wild rice. Organic carbon,
on the other hand, causes more sulfide to be produced. Sulfate is converted to
sulfide differently in each body of water, depending on the concentrations of
iron and organic carbon in the sediment. The MPCA proposed an equation that
accounts for iron and organic carbon levels. Plugging a site’s iron and carbon
concentrations into the equation would identify a sulfate concentration that allows
for wild rice growth and regeneration.
Refinements
to the proposal:
The
equation has been adjusted using a new statistical approach (multiple binary
logistic regression) that has a lower error rate than the approach used in the initial
proposal (structural equation modeling).
Implementing the standard
2015 proposal:
In order
to implement the standard in Minnesota lakes and streams, the MPCA will collect
sediment samples in wild rice waters, measure the iron and organic carbon
concentrations, and plug them into the equation to find a protective sulfate
level.
Refinements
to the proposal:
Based
on a 2015 survey of wild rice bed sediments in six bodies of water, the MPCA is
now proposing that five composite sediment samples consisting of five cores
each be collected in wild rice beds to more accurately represent iron and
carbon levels. The sulfate standard derived from these samples would apply as a
12-month average.
Go to the MPCA web site to see the full draft technical support
document. The public will have an opportunity to formally comment on the
proposed standard during a rulemaking process in 2017. Feedback on the
information being released today is appreciated by September 6; send it to wildriceTSD.pca@state.mn.us.
Broadcast version
A new technical support document released by the Minnesota Pollution
Control Agency (M-P-C-A) details how the agency has refined its proposed wild
rice standard in response to more than 600 comments. The agency released its a
Draft Proposal for Protecting Wild Rice from Excess Sulfate in March 2015, and
requested comments on the proposal in October 2015.
In response to comments and questions received, the MPCA re-analyzed its
wild-rice-standard study data using different statistical approaches. The
agency has revised its conclusions in four areas. Go to the M-P-C-A web site to
see the full technical support document.
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The mission of the MPCA is to protect and improve the environment and enhance human health.
St. Paul • Brainerd • Detroit Lakes • Duluth • Mankato • Marshall • Rochester • Willmar
www.pca.state.mn.us • Toll-free and TDD 800-657-3864
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