Lake Apopka, Part 2

Part of a continuing series on Florida's Lakes.

I want to write about each of Florida's largest lakes. I hope to write 3 articles on each lake. One will be the history of the lake. I hope for the second piece to be about the environmental challenges facing the lake today. That was relatively easy for Lake Apopka, but I'm not sure I can get enough data on all lakes. 

The final piece will be about "ecotourism" opportunities near the lake. Specifically hiking, biking, kayaking and other outdoor activities that are available near the lake. Feel free to drop the names of nice parks, trails, or businesses in the ecotourism trade (kayak or bike rental, etc) near Lake Apopka in the comments here or on Facebook.

To review: Last week I wrote about the history of Lake Apopka. Lake Apopka was once a thriving commercial lake that gave local farmers a highway to get their produce to market and was ringed by a thriving sport fishing industry. Pollution brought fish kills and hurricanes in the 1940's destroyed the plants at the bottom of the lake. In 1999 a century of mismanagement culminated in thousands of migratory birds being killed by poisons in the lake.

Enough with the housekeeping. Let's talk about Lake Apopka today.

Beautiful water, at least on the surface

In 1998 the St John's River Water Management District (SJRWMD) took over management of the northern shore of Lake Apopka. The big thing they wanted to do was to remove the fertilizer residue, phosphorus and nitrogen, from the environment. They had several strategies for rehabilitating the lake. All are interesting, but I want to focus in the first 2 only.

The biggest change to North Shore was implementing a Marsh Flow-Way. The marsh flow-way pumps water through a series of wetlands to filter out the phosphorus. They claim it filters 2.6 metric tons of phosphorus per year.

Removing Phosphorus 

The other main way of removing phosphorus from the system is by removing gizzard shad. The gizzard shad is a fish that retains a large amount of phosphorus in its system. If the gizzard shad dies in the lake the phosphorus goes back into the environment. However if taken out of the environment the phosphorus is removed with them. This removes about 2.7 metric tons of phosphorus from the lake annually. 

Netting shad in lake Apopka

That and a few other strategies are what the SJRWMD is doing to clean up the lake. Next question: Is it working?

I downloaded water quality data from the SJRWMD website to look at overall trends. My  impression is that Lake Apopka is healing, but way more slowly than it needs to. And in the last few years there are hints that things may be getting worse instead of better.

All of the parameters I looked at are heavily influenced by the level of the water in the lake. When the lake is full the parameters look pretty good. In drought times the parameters look horrid. That is completely outside of what the SJRWMD is doing. Therefore to look at any parameter without reference to the lake level makes no sense. In each chart the lake level is given by the black line. The red line is the individual parameter -- visibility, chlorophyll, or temperature. 

Starting with visibility.  Visibility is the top line indicator of the health of Lake Apopka. As long as sunlight can't reach the bottom of the lake plants won't grow there. This is the problem that has to be solved before the lake recovers. Is it happening?

Lake Apopka's ugliest chart

The red visibility line is depressing. It has varied over the last 17 years with the level of the lake. In 2002 when the lake lost 80% of it's volume due to a drought there was a dip in the visibility. But visibility got better when the water returned in 2004-2006. A few more droughts in 2007 and 2011-12 also hurt visibility. But it recovered nicely afterwards.

But recent history is a disaster. Right now the lake level is higher than it has been in decades. But the visibility hasn't recovered from the last drought. Instead of increasing with more water in the lake like it did after previously the visibility hasn't moved much from the depths of the last drought and may even be falling this year. Ouch.

But in another sense it's even worse than it looks. After a couple decades of treatment it should be improving. Maybe if you squint hard enough you can see some improvement early in the graph that wasn't due to varying water levels. But why didn't that continue? Why no progress in the last decade? And especially why didn't visibility increase with higher water levels since 2013?

Another parameter to look at is the average chlorophyll content of the water. In water chlorophyll content can tell us about the algae content of the water. More chlorophyll means more algae is present. It tends to vary inversely with the water levels -- when water levels rise (black line) chlorophyll content decreases (red line). The overall trends are about as expected. The peak in 2008 that went way higher than the peak in the 2002 drought is disturbing because the 2008 drought was much milder than the earlier one.

Lake Apopka Chlorophyll

This is troubling, but maybe not as scary as the visibility line. At least it's falling now with the higher waters. But it really doesn't look like it's changing a lot over the years except for water level variation. Lake Apopka has not in recent years had large masses of floating algae like Lake Okeechobee, just decreases in visibility due to it. The chlorophyll content would have to get much higher for the large algae blooms to be an issue. But the fact that it's not going down after nearly 20 years of treatment is problematic.

One last chart and I promise I'll end this novella. The temperature of the lake is the missing piece to the puzzles above. When the lake level rises the temperature should drop since it takes more heat to raise the temperature.

Lake Apopka Temperature

The years 2013 and 2015 were extremely hot years for the lake. Year 2015 saw hot water despite the relatively high water level in the lake. I left in a point for 2016 even though we're only halfway through the year. It will probably raise some since water temperature tends to be higher in the last half of the year than the first. 

If the lake temperature stays this warm the restoration will remain a challenge. It doesn't take nearly as high of fertilizer load to upset a lake with such warm temperatures. Algae growth is a function of fertilizer availability in the water and temperature. I won't add another graph but the phosphorus levels look about the same as the others -- bouncing around with water levels but not a lot of long term progress in evidence.

Sunset on Lake Apopka. But will it rise again?

These graphs are only a small subset of what I went through to put this together. But after the analysis I came away feeling I understood it only a little better than I did in the beginning. It doesn't seem like a lot of restoration progress is being made. It's always hard to predict how natural systems will react to change. Annual rainfall amounts have varied a lot over the decade as have temperatures. The SJRWMD has been trying to turn the only control they have with Lake Apopka -- fertilizer loads. But it's hard to say that's doing the job at this point. Maybe when somebody sits down to write this story in another 20 years the progress will be clearer.

Sorry so long on this article. I started to break it up a couple of times but decided to let it run. I usually limit my articles to 700 words but this one will end up nearly twice that length. What’s being done and the current health of Lake Apopka just seemed like a story that needed to be told all at once.

Remember to send suggestions of outdoor adventures on and around Lake Apopka. Thanks.