Originally Posted By: Smalma
Bonaro -
Not sure that the paper that you generously provided the link to makes your case of limited impacts to stream habitat, water quality and biota from dredging. I admit that I only quickly read the paper (to lazy to go through it in great detail.

However it is clear that the paper was looking at fishless streams (or at least did not consider direct impacts on fish resources. It should be obvious by now that most of many of our concerns are fish based. Further the authors were unable to tease out what the chronic effects from mining/dredging. Did returning to "original" conditions mean historic conditions pre-mining or what had become the new "norm"?

It is clear that while a year or so after the dredging activities things looked more or least "norm" there also short term and localized impacts. The importance of those impacts likely would vary depending on the specifics of the particular situation. A couple things that jumped out to me if there were co-existing fish populations was the release of heavy metals at the site (and downstream for some distance). Those heavy metals are lethal to fish eggs and young fry are surprising low concentration. Of further concern was the concentration of some of those metals in the insects. Not only what those metals might do to the potential biomass of insects but how those metals may be further concentrated in the fish communities that may exist in the same system.

The authors did say that there were reductions in the biomass of periphyton (the foundation of the food chain) that in at least one case lasted into the following year. In the discussion of invertebrates the point was made that species richness and density remain more or less the same however the question of the biomass of those invertebrates was left unanswered.

Sorry cherry picking papers and data does not necessarily make your case.

Curt




Yes, the Fortymile is fishless as it freezes solid each year. This report did not study direct fish impacts but it is did examine impacts to the habitat and invertibrates fish depend on. The impacts were slight expecially considering this is a commercially dredged river. Seeing the difference between these commercial dredges and what is allowed in Washington is key

Here is some dredge trivia for comparison. I have dredged the Fortymile river in Alaska using a 8" dredge like they profiled in this report. I was able to move about 60 cubic yards per day because of the much greater capacity and the fine grained stream bottom. The dredges on the Fortymile River are each capable of moving more material in a day that I am allowed move under my HPA in 5 years. Even with this substantially larger scale, dredge impacts were still hard to find the following year

The report said there were reductions in periphyton...it also said it was localized and short lived.

The heavy metals - I have heard claims that dredges pollute the river by stirring up heavy metals. Pollution is an additive...ie...a car pollutes the air by adding exhaust to it. If a dredge discharges heavy metals into the water its because the metals were already in the water. No matter how deeply they are covered by sediment, the is still a constant circulation of water and those metals are already present. In this report it state the metals had settled out to background levels in a short distance

A modern gold dredge is able to capture heavy metals with 97% efficientcy. No other machine has been invented that can do this with such effectiveness. Below is a pic I took today. It shows about 8 pounds of lead steel copper and even a silver spoon and a couple bullets. I removed this with my dredge in one week of dredging. I have many more pounds of lead that I have already melted into ingots. Also in the pic is 4 pound of mercury that I also removed with my dredge....all from one river.
I dont need a PhD to know that if you have toxic material in the river and you remove a significant quantity, you have a lot less toxic material in the river and the river is healthier.

I will be out of town for a while but will provide more info later.
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