|
From: Doug Charles [dcharles@charlesaquatics.com]
Sent: Thursday, May 22, 2008 8:03 AM
To: Haller,William T
Subject: Lake Asbury
Dr. Haller,
I need your assistance again on Lake Asbury. The hydrilla has returned in the shallows primarily in the areas that were exposed during the draw down. I would guess 10 to 15 acres of hydrilla, it was difficult to estimate with the planktonic algae. There is also a planktonic algae bloom (18 inch water clarity.)
Tuesday the 27th of May 11:00 am at the boat ramp works for me and Dharmen. We all appreciate your help.
Douglas K. Charles
President
Charles Aquatics, Inc.
904-997-0044
------
From: Haller,William T [mailto:whaller@ufl.edu]
Sent: Sunday, June 01, 2008 11:40 AM
To: Doug Charles
Cc: 'dharmen.setaram@uniphos.com'; gstibolt@sky-bolt.com
Subject: RE: Lake Asbury
Doug/Dharmen/Ginny,
We visited North Lake last Tuesday and spent an hour or two sampling hydrilla and evaluating the treatment sites. Hydrilla was completely controlled in almost all the treated areas as we expected and usually
dragging a rake in these areas came up with either nothing or only a couple fragments. Of
course, the area above the 8 foot drawdown was not exposed to herbicide and tubers and fragments are starting to germinate and hydrilla is trying to re-establish in the dewatered areas....
Where the hydrilla is particularly bad, or almost to the surface is along a distinct band around the lake edge. This depth contour corresponds to the 7-9 foot contour where the edge of the water was when the lake was drawndown. It was an area that remained moist and root crowns and stem fragments under the collapsed hydrilla remained viable which was expected..
Also, the herbicides were not applied in water that was 0-12 inches in depth,, though it certainly moved into those areas but likely did not control all the vegetation there due to shallow water and really thick hydrilla... Recall, we took 7-9-11 feet of hydrilla and lowered the water and collapsed it all into 0 to 5 feet of water..
The objective of the drawdown was to reduce cost of herbicides and to get the hydrilla biomass greatly reduced so the Grass carp could get ahead of the growth curve.. This objective has been met for certain. Last fall hydrilla covered probably 80 % of the water
surface, so much so that I was concerned about fish kills if the entire lake was treated at one time... I expect the hydrilla biomass to have been reduced by at least 90%. In the 120 acre lake,, there maybe 10-15 acres of hydrilla remaining and the plants in most areas are well below the water surface, which really means that the weight per acre is still pretty low....
The algae bloom occurred due to the large amounts of hydrilla that were either dried out or killed by the herbicide.. Topped out hydrilla weighs about 12 tons per acre wet weight, really does not contain much
nutrients, but if we controlled 80 acres, you have released nutrients from nearly 1000 tons of hydrilla, and the dewatering and drying of organic sediments also released some nutrients; so
yes, the algae bloom has occurred, should have been expected, and I should have warned the Board that this was
likely, however,, it will not persist, if we can get some much needed rain and water starts
flowing, the water quality will greatly improve, it already has,, but until the water flows through the system you can expect some bouncing around of Algae concentrations,, may be good this
week, and bad next week,, etc...
We also noted plenty of Vallisneria around the lake, lots of coontail,, so there has been a resurgence of submersed native plants,, which occurs if you reduce the competition caused by hydrilla...So all looks pretty darn good at the present time...
The key to maintaining Hydrilla within tolerable levels now relies almost solely on the grass carp and this is where guesswork comes in... I would assume good fish survival following the last stocking.. so 2000 1 pound
fish, now weigh 2 pounds and are eating their body weight each day..
that's 4000 pounds of hydrilla daily, with 15 acres left, at most, it takes 5 days to eat an acre(20,000 lbs),, so there should be no increase in
hydrilla,,, and it should decrease in coverage...
There seems to be two options at this point, you can apply some herbicide in the very south inflow end of the lake where we saw most of the hydrilla and do a couple 1-2 acre plots in other
"bad" portions of the lake. Or you can just watch the lake closely to make sure that the hydrilla
area, does not increase. The fish are currently working in deep
water, and will gradually feed into the shallows as hydrilla in the deeper waters is
reduced, and it is.... Even the algae bloom helped reduce sunlight to deep water slowing hydrilla
growth, and the fish seem now to be working the outside edge of the bands referred to above....
Overall, you sure seem to be on track. You might want to treat 5-8 acres of hydrilla or you can leave it for the time
being... this is the tough time, no real science here,, ,, not sure what the carp are going to
do, but you really can't hurt anything by removing another few acres, Or just watch
closely???????????????
Bill H.
|
