Tufts University SolarBees® Inafective on Milfoil

SolarBee on Lake Cochituate

SolarBee on Lake Cochituate

Tufts University scientists presented a paper at the NE Aquatic Plant Management Society meeting in Stowe, VT this January titled “Effectiveness of Solar Powered Water Circulators for Reducing Eurasian Milfoil Growth in a Recreational Lake”. They concluded that the SolarBees® had no measureable impact on Eurasian Milfoil populations in the lake.

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The response provided from SolarBee, Inc.


Lake Cochituate, Nadik, MA. This was to be a collaborative research project with the Massachusetts Dept. of Conservation and Recreation (DCR), Tufts University, and SolarBee, Inc. The study, designed as a Masters thesis for a Tufts University student, was to analyze nitrogen chemical transformations across the sediment-water interface to examine the hypothesis that the significant reductions of the aquatic weed Eurasian watermilfoil (EWM) observed in dozens of other lakes where SolarBees were installed are due to the nitrification of ammonia (the main source of nitrogen for EWM) to nitrate, which is essentially unavailable to EWM. This hypothesized increase in sediment nitrification comes from the increased oxidation of superficial sediments due to the flow of oxygen-rich water back to the SolarBee intake hose. This hypothesis has strong support from several leading aquatic plant scientists. As part of the experimental protocol, 2 SolarBees were to be placed in two different locations in the lake in the fall, and remain in place throughout the winter/spring in order to anticipate any EWM reductions the following summer. The units were installed in October 2006.

Unfortunately, proper experimental conditions were never met for several reasons: 1) one unit moved during the winter of 2006-07 due to ice flow, and, 2) the DCR moved the units around to accommodate local boaters and residents. Furthermore, without informing us the DCR and Tufts University decided that this was to be an evaluation of the SolarBee rather than trying to study the underlying science; as such, they intentionally kept us completely uninformed with regards to the data they were collecting, the assumptions they were making, and the conclusions they were drawing from the data. Having provided more than $100,000 in SolarBees, service and maintenance, and having explicitly agreed at the beginning that this was to be “collaborative” research, we reasonably expected better communication and cooperation. We discovered that they had changed the rules only after the Masters student had presented her results at two professional meetings, concluding that there were no significant differences between “treated” and untreated areas.

Nevertheless, we do not dispute the conclusion of the student. In fact, this study identified environmental constraints that can limit the applicability of long-distance circulation for EWM control through sediment oxidation. Not appreciated at the time, Lake Cochituate is considered by local residents as a “slow moving river”. Water flowing parallel to the shore will naturally disrupt SolarBee-induced near-laminar flows perpendicular to the shore (i.e., from the shore back out to the unit). That, and the fact that proper experimental conditions (i.e., standard application criteria of maintaining sediment oxidation beginning in the fall throughout the winter/spring and summer) were never achieved, the results were not surprising. What was surprising was the lack of scientific interpretation, and not analyzing these results with respect to the broader hypothesis we had thought the thesis was supposed to address. Instead, they made overly broad negative conclusions based on an inherently flawed design. It may be relevant that for years the DCR has actively and publicly campaigned for the use of toxic chemical herbicides to combat aquatic weed problems in Massachusetts, and that this study was a result of strong public pressure for the DCR to seriously consider “greener’ technologies.

1 Comment

Filed under Performance, Solarbees

One response to “Tufts University SolarBees® Inafective on Milfoil

  1. Charlie Robbins

    We have two solar bees in our 88 acre lake that has a good population of native aquatic plants of many types and also has an increasing population of invasive milfoil. In my observation the solar bees are not the quick fix that everybody wants.However I observe increased native plant growth increased water quality and no real decline in milfoil growth. The only decline has been through manual harvesting by the root ball.Milfoil seems to be quite cyclical and on a down year for milfoil the solar bees seem to accelerate native plant growth which seems to be helping .In another year
    it seems just the opposite.

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