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y_ .. Corrtittued frarn pale T
<br />inviting. But it suffers from two major
<br />pollution problems: excess sediment
<br />that is washing into the lake at 10 times
<br />the rate it did before European settlers
<br />reached the Mississippi, and excess
<br />phosphorus that feeds summertime
<br />algal blooms and depletes the oxygen
<br />needed to sustain plants and fish.
<br />Since 2004, the Minnesota Pollution
<br />Control Agency has been researching
<br />Lake Pepin's water quality and the
<br />sources of its pollution, planning how
<br />to reduce the sediment and phosphon.Ts
<br />and modeling how the lake would
<br />respond to reductions.
<br />This fall the agency will make public
<br />a plan calling for significant~l0 percent
<br />to 50 percent-reductions in both pollut-
<br />ants in watersheds khat feed Lake Pepin.
<br />The plan-called a TMDL, for Total
<br />Maximum Daily Load-is the biggest
<br />such water quality plan the MPCA ever
<br />has written, and it is one of the biggest
<br />such plans undertaken anywhere in
<br />the country. It will be followed within
<br />a year by a plan proposing how to
<br />achieve those reductions.
<br />The plan, backed up by regulations
<br />that require sewage treatment plants
<br />to obtain permits for their discharges,
<br />will force Twin Cities plants to further
<br />crank down the levels of phosphorus
<br />they release into the Mississippi River.
<br />Lacking any similar enforcement
<br />mechanism to demand sediment and
<br />phosphorus reductions by farms and
<br />individual residents along the river, the
<br />plan almost certainly will call for vol-
<br />untary cuts in the two pollutants and
<br />propose state financial inducements for
<br />adoption of management practices that
<br />alleviate the pollution.
<br />The Freshwater Society interviewed
<br />Gaylen Reetz, who directs the MPCA's
<br />efforts to clean up lakes and rivers
<br />statewide, about the effort to improve
<br />Lake Pepin's water quality. Reetz'
<br />responses have been edited for brevity
<br />Q. In qualitative terms, what are Cake
<br />Pepin's problems?
<br />A. Phosphorous loading, which is
<br />Gaylen Reetz, MPCA regional director
<br />nutrient enrichment that results in algal
<br />blooms. And the second part is turbidity
<br />in the water column. When you com-
<br />bine the two, we have too much algae,
<br />and it shades out the rooted macro-
<br />phytes, which. are water celery, a favor-
<br />able food for migrating ducks. Algae
<br />create an additional oxygen demand in
<br />the water, so some of the more desir-
<br />able Eish species cannot survive, such as
<br />walleye and sauger and bass. The Eish
<br />that will probably thrive are carp and
<br />other rough fish.
<br />Q. Are the problems getting better or get-
<br />ting worse?
<br />A. What I'd like to say is both. When
<br />we plot some of the da#a, long-term, it
<br />appears to be getting worse. Now, at the
<br />same time, if you look at 40 to 50 years
<br />ago, I think we`d say there have been
<br />significant improvements in Lake Pepin
<br />as a result of improvements made in the
<br />metro area with wastewater treatment
<br />and combined sewer overflow.
<br />Q. In quantitative terms what are Cake
<br />Pepin's problems? Haw much phosphorus
<br />and sediment flaw into the lake every
<br />year, and haw much can the lake handle?
<br />A. Lake Pepin is subject to nuisance
<br />algae blooms when river flows decrease.
<br />To reduce the frequency of nuisance
<br />blooms, phosphorus concentrations in
<br />the Mississippi need to be reduced from
<br />180 parts per billion to 100 parts per bil-
<br />lion. Annual loads of suspended solids
<br />need to decrease by 40 to 50%, from the
<br />current average rate of 850,000 metric
<br />tons per year to around 500,000 metric
<br />tans per year.
<br />If current sedimentation rates con-
<br />tinue, the entire lake will fill in in 300
<br />years, and the upper third will be gone
<br />this century. tE we halve the annual
<br />average load of sediment, fife expec-
<br />tancy will increase to 600 years.
<br />Q. Does the current plan examine the
<br />nitrogen that flows dawn the Mississippi
<br />and contributes to the axygen-depleted
<br />zone in the Gulf of Mexico?
<br />A. It may Iook at it, but that really isn't
<br />the focus of the study we're doing.
<br />Q. What is the timeline for releasing the
<br />current study, proposing aclean-up plan
<br />and-finally-cleaning up the lake?
<br />A. The goal we`ve had is to try to have
<br />a study prepared, in draft, for public
<br />comment and review in September or
<br />shortly thereafter, and then try to have
<br />a cleanup plan in place within a year of
<br />that being finally approved.
<br />As far as ultimately cleaning up the
<br />Lake, it's going to take some time. When
<br />you're dealing with the size and scale of
<br />the system we're looking at, it did not
<br />deteriorate in five to 10 years, and it's
<br />not going to turn around in five to 10
<br />years. It's going to be more like 10, 20,
<br />30 years.
<br />Q. if you could immediately implement
<br />all the changes in behavior the clean-up
<br />plan is likely to recommend, would Cake
<br />Pepin get cleaner? Flaw long would it
<br />take?
<br />A. Yes, it will get cleaner, and I think if
<br />everything was done tomorrow, I would
<br />say it still may take a 10-year kind of
<br />timeErame for the response to fully
<br />occur. But it would respond.
<br />Q. What has Minnesota spent an the plan
<br />so far, and what will it cast to put into
<br />practice?
<br />A. At this point, I think we're in the $3
<br />million range. I don't even have a good
<br />estimate of the dollars as far as imple-
<br />menting the whole thing. It will cer-
<br />tainly be expensive, but we need to look
<br />at that not only as the improvement to
<br />Lake Pepin, but also the improvement to
<br />all those contributing waters that people
<br />Lake Pepill CirlltllTUt'S nn page 11
<br />FACETS June 2009
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