HomeMy WebLinkAbout20221013 Ken Wagner review Parker Pond Al reviewWater Resource Services Inc.
144 Crane Hill Road
Wilbraham, MA 01095
kjwagner@charter.net
413-219-8071
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October 13, 2022
Mr. Peter Duggan
351 Pleasant Street, Suite B, #135
Northampton, MA 01060
Barnstable Conservation Commission
Town Hall
367 Main Street
Hyannis MA 02601
Dear Colleagues:
I was asked to provide an evaluation of the phosphorus (P) inactivation proposal for Parker Pond.
As the Commission is aware, I have been involved with many such projects on Cape Cod for
close to 20 years now and can offer some insights. Overall, this is a rational proposal with an
appropriate dose to be applied over a three-year period.
By way of background, P accumulates in sediment in multiple forms with variable availability to
algae and rooted plants. Over a long period of time, these reserves can grow to a point where
they become a significant or even dominant source of P in the pond. Of greatest concern is P
bound to iron (Fe-P), as those elements can dissociate under low oxygen conditions and re-enter
the water column. Also of concern is biogenic P, which is P bound in easily decayed organic
matter. Biogenic P can be released by normal decomposition processes. If there is adequate iron
present, which is the case in most Cape Cod ponds, P released from organic matter should be
bound to iron and precipitate out, further increasing the Fe-P fraction. However, many types of
algae, including mat-forming green algae and some cyanobacteria, can grow at the sediment-
water interface in water shallow enough for light to penetrate to the bottom, absorbing P as it is
released from the sediment and eventually rising in the water column. Consequently, binding P
in the surficial sediment may be essential to preventing algal nuisances.
Watershed management is an important part of lake management, and the presence of a golf
course in the watershed of Parker Pond represents a threat, but even with the best watershed
management effort, addressing the internal load of P from sediment is often necessary to achieve
desirable conditions. The situation is akin to a leaky boat. Fixing the leaks is a good idea and
essential if the leaks are large enough, but if the boat is full of water, it won’t be useful until that
water is removed, even if the leaks have been patched. P inactivation, almost always by
aluminum addition in Massachusetts, addresses the internal load, equivalent to emptying the
water from the leaky boat and restoring utility until more water enters through the leaks. For
many Cape ponds, the long-term accumulation of P in the sediment and onset of low oxygen
conditions has been the primary trigger for cyanobacteria blooms. I have not seen any data to
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allow evaluation of the relative importance of external and internal loading to Parker Pond, but
the report by Water and Wetlands and the project plan from TRC convince me that P inactivation
(getting the water out of the boat) is a necessary step, just perhaps not the only step.
For Parker Pond, it appears that the primary issue is release of biogenic P, not release of Fe-P.
This is not the typical situation but has been observed in other Cape ponds. It is not clear why
there is inadequate iron to bind P released by organic matter, but the potential for algae to grow
at the sediment-water interface then move upward in the water column may require treatment of
those sediments even with adequate iron. P bound to organic matter is more challenging to
address with aluminum, as it will not bind most P currently bound in organic matter. Aluminum
can replace iron but not most organic complexes by chemical equilibria in the sediment, so
inactivation of P in this case depends on having that organic P released and then bound by
aluminum. The proposal explains this to some degree and proposes a typical total dose of
aluminum to be delivered over three years. Spreading out the dose is a logical approach and
doing it in the fall might help, as the most available P should be present then after a season of
decomposition under warmer temperatures.
The actual dose to be delivered appears to have been determined by Dr. Keith Pilgrim, who has
considerable experience in P inactivation projects and knows how to evaluate lakes for P
inactivation. The proposed dose of about 47 g/m2 is similar to that applied to many other Cape
Cod lakes that have shown considerable improvement post-treatment. An initial dose of 20-30
g/m2 is usually necessary to get the desired result, with subsequent additions enhancing the
longevity of those results. The proposal calls for an initial dose of about 24 g/m2 in year 1 with
two additional treatments of 11-12 g/m2 in subsequent years. For the conditions of Parker Pond, I
find this to be an appropriate approach.
Release of biogenic P may continue beyond the treatment period and may require further
aluminum addition, but that can be evaluated later after appropriate monitoring. I work with
several ponds in urban areas that receive annual low dose treatments with aluminum. Conditions
are very much improved in all of them, but with watersheds that cannot be practically managed
to minimize inputs, ongoing treatment is necessary. Lovells Pond in Barnstable was only treated
once at 50 g/m2 in water deeper than 15 feet, improved markedly, but has not achieved lasting,
acceptable conditions, likely a consequence of ongoing release of biogenic P. P inactivation is a
highly flexible approach with a reliable track record, but it is not the complete answer to all pond
problems.
In terms of adverse impacts, nearly all possible problems with aluminum treatments are related
to the initial dose and pH control, aluminum potentially being toxic at high concentrations
outside the pH range of 6-8 standard units. Fish or invertebrate kills can occur during treatment if
too much aluminum is applied at once and the pH is too high or too low. This occurred in
Hamblin Pond in Barnstable back in 1995. The treatment was very successful for algae control,
but a lot of fish died during treatment. Procedures have changed a lot since 1995 and there have
been no fishkills from New England P inactivation treatments in over two decades.
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Adverse impacts are virtually unknown with areal doses of <25 g/m2, so this project represents
little threat. We like to keep the volumetric dose <5 mg/L, although concentrations up to 10
mg/L have not caused problems within the desired pH range. With a typical mixing zone of
about 15 feet, a 25 g/m2 dose will result in an appropriate volumetric aluminum concentration,
the typical situation in most treated Cape Cod lakes. However, the Parker Pond proposal calls for
treating in water as shallow as 5 feet, given the expected contribution from decaying organic
matter, so there is potential for the aluminum concentration to be higher during treatment,
Shallow treatment has been done elsewhere with no adverse impacts as long as the pH remains in
the proper range. The key is careful monitoring during application.
My only other concern is that Water and Wetlands lists multiple vascular plants in the pond,
probably in 2-10 ft of water, but treatment is planned in water as shallow as 5 ft. If plants are
abundant at the time of treatment, there may be some issue with the aluminum getting to the
sediment interface in reactive form. The late timing of treatment this year may limit plant
abundance but having a lot of aluminum floc on plants is not desirable. It should also be noted
that four of the nine plant species listed for the pond (duckweed, watermeal, coontail and
bladderwort) are unusual in that they gain most of their nutrition from the water column and are
likely to be limited by the treatment. Most rooted plants utilize nutrients from the sediment,
usually well deeper that the aluminum treatment will affect, but the noted species have been
controlled in other ponds with aluminum treatments and this may be an additional benefit of the
proposed program.
I was provided with two likely permit clauses regarding monitoring. One calls for temperature
and oxygen measurements at 1 meter increments and mentions an aerator, which I suspect is left
over from some other Order of Conditions from which the condition was excerpted. The required
monitoring is still appropriate. The second clause calls for P and N monitoring near surface, mid-
depth and bottom on a monthly basis, and is also appropriate. However, I see no requirement for
monitoring during treatment, which will only last a day, but someone should be checking pH and
calling for alum to aluminate ratio adjustment if necessary. Additionally, we usually observe floc
formation and do a check for stressed or dead organisms before and after any treatment, which
would seem essential in light of treatment in shallow water.
So with minor adjustment of permit clauses to include monitoring during treatment and longer
term evaluation of results, I find the proposed project to be well conceived and worth doing. You
may contact me with any questions.
Sincerely yours,
Kenneth J. Wagner, Ph.D., CLM
Water Resources Manager, WRS Inc.