UF/IFAS CAIP Lake Panasoffkee Outlet River Project


The Southwest Florida Water Management
District came to me and Dean Jones of biological scientists with the
University associated with the center about an issue on the outlet canal
between Lake Panasoffkee in the Withlacoochee River. The issue was there
was a heavy infestation of hydrilla in the outlet river and based on the levels
of both Lake Panasoffkee and the Withlacoochee River
the water flow out of the lake into the river was cut by about 50% based on
historical data. So, much of that reduced flow was associated with the vegetation
present in the canal and it was causing a lot of problems with local properties
being being flooded as well as reduced dissolved oxygen levels in the lake,
which resulted in some fish kill issues. So, hydrilla or hydrilla verticillata is
an exotic invasive aquatic plant. It’s a submerged aquatic species, so it
lives its complete life cycle underwater. It’s rooted to the bottom and sediment
and it has been coined and as the first nationally problematic aquatic weed. It
is probably it counts for the majority of state of Florida’s budget in terms of
management costs and it causes all sorts of problems from navigation, water flow,
out competing native submerged vegetation and we we focus a lot of our
research efforts on management of that species. So, Dean Jones and I were
instructed to help with what’s called a drip treatment or a pulse treatment of
herbicide called endothall. It’s a contact herbicide that needs a
shorter contact time with the plant to cause a response, but when you’re dealing
with trying to manage a submerge species in flowing water
we can’t just put a known amount of herbicide into the water once and let it
do its work. So, because we’re constantly exchanging water in that system, we have
to constantly add herbicide. So, in the drip or pulsing treatment we have small
peristaltic pumps that slowly trickle in herbicide over a period of time creating
a band or slug of herbicide in that system for a period of time to allow us
to absorb enough herbicide into the plant to cause death. Now, the other part
to that treatment was a mechanical harvest component and that took place a
few days after our herbicide treatment. That was primarily to get rid of as
much biomass in a short period of time as we could despite our herbicide
treatment, which takes a while for that biomass to leave. So, we tried to
monitor water quality before during and for a certain time period after our
herbicide treatments and that essentially from our end is to give us
insight into what’s going on chemically in the water in case there’s a scenario
where the treatment does not work. Also we need to monitor certain water quality
components such as dissolved oxygen due to the sensitivity of fish species to
low DO levels. Now the major concern in this system and treatment was because we
had such low dissolved oxygen in the lake prior
to treatment causing a fish kill, as we kill plants generally, we draw out more
dissolved oxygen from the water as the plant material starts to break down so
we were we were very conscious of not contributing to that fish kill and
dropping dissolved oxygen levels lower. But, from recent reports I’ve received
allowing more water flow through that system has actually increased our
dissolved oxygen levels in conjunction with the more sunny days we were able to
promote photosynthesis in the lake. So water flow, water quality, our efficacy on
on the actual plant will be monitored in the next couple of weeks as we move
forward and furthermore, after the mechanical harvest is over with that
will be monitored definitely by the Water Management District and FWC as
well as wildlife impacts, especially fish fish populations. The desire effect of
this project or operation essentially was to bring the water management’s
classification criteria down from an emergency level. We needed to get a lot
water off of the lake out the outlet canal into the river to recede those
those flooded properties as well as getting some water moving to help our
systems start developing a little bit more dissolved oxygen and obviously
because of the high water levels and the amount of vegetation, the the outlet
canal was basically only navigable by airboat as any conventionally propolsed
both would have a problem getting through the vegetation and even the
bridge that crosses that outlet canal was unpassable by any boat just because
of the water level differential height between the bottom of the
bridge and water. The outcome of this project up until this point has
been generally good from the reports I received. I think it was about four or
five days after our herbicide treatment prior to the mechanical harvesting
having any significant progress, we had already seen water outflow levels
increased by 100 cubic feet per second. So a little bit of background on
that our typical level of water flow in that system for this time of year based
on the lake level and the river level was supposed to be around 400
cubic feet per second. Prior to treatment, it had been reduced
down to around 200 and four to five days after treatment we were up to
about 300 cubic feet per second, which reflected the herbicide treatment able
to knock down some of the hydrilla and let more water through.

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