Drought Gives Rodman Parting Slap
by Bob Andry
During the weekend of September 16 and 17, while hurricane Gordon was passing, Rodman had a fish kill. This was the result of a long, clear, dry spell that ended with torrential rains preceding Gordon by about a week. It takes a special sequence of events in nature to set up a fish kill, and this was a classic example. A long drought must be followed by a "frog strangler". We had both.
For many months the sun had been shining through Rodman's clear water, and the hydrilla and other aquatic vegetation had been growing vigorously, much more so than normal. This vigorous, excessive growth set the stage for the fish kill. The water had been so clear because no rain had fallen upstream from the creeks and river that empty into Rodman. Normal rainfall washes the tannic compounds from the flood plains of Rodman's tributaries in a constant infusion of colored particles that darken the stream's water and thus Rodman's.
To understand how too much of a good thing (aquatic vegetation) can cause a problem you must consider what plants do in the aquatic community. Aquatic plants are responsible for placing the dissolved oxygen into the water during the day when the sun is shining. This process is called photosynthesis. Photosynthesis is the process by which certain living plant cells combine carbon dioxide, water, and light energy, by means of chlorophyll, to form sugar and release oxygen as a waste product. The total amount of oxygen that will be placed into the water is dependent on the quantity of plants and sunlight. You say, "OK! We've got lots of plants and plenty of sunlight so everything should be great." You are right up to a point. The problem is that the process is more or less reversed at night, or on cloudy days with NO sunlight. During these dark times oxygen is removed from the water and replaced with carbon dioxide. The more plants you have, the more severe is the daily shift from high to low oxygen content in the water. When several cloudy days occur in a row the oxygen content in the water drops near the critical point of 2.0 parts per million, beyond which fish cannot survive.
What we have now is a "cocked gun", a critical situation, but the gun will not fire unless something causes the trigger to be pulled. That something is usually drought breaking torrential rains. Rainwater has NO dissolved oxygen in it. When it falls on the watershed surrounding a stream or lake it falls on land that will not allow the water to soak into the ground because of the surface tension developed during the drought. It flushes all sorts of decaying organics into the water body so you have a double "whammy": no dissolved oxygen in the water and a lot of stuff that will use oxygen like mad in its process of decomposition.
By the first of September the shallow areas in Rodman were heavily covered with hydrilla; in some cases the cover was heavy enough to reroute currents. The rain came! Over seven inches of rain fell on Rodman during the second week in September while close to ten inches fell on places in the Orange Creek watershed. The third week in September brought reports of the water in the river rapidly getting dark and stinking. That weekend, during the overcast days while Hurricane Gordon passed, the fish died.
The kill was triggered by the water from Orange Creek. Dead fish were recorded from about where the Orange Creek boat ramp access canal junctions with the creek, then across the Orange Creek Delta to the old river channel. The kill progressed north, along the west side of the river channel to the old Fort Brook site. No dead fish were found south of the Orange Springs power lines, and likewise it appeared the kill was at most minimal east of the river channel between Orange Springs and Fort Brook. We have no idea what was in the water from Orange Creek, but the Orange Creek watershed stretches up towards Payne's Prairie. There was plenty of opportunity to flush out organics that had been decaying over the past three years..
The kill progressed to the Kenwood area with fish dying north of the barge canal. A few fish were killed further west along the canal south of Deep Creek, but upstream along Deep Creek there was no evidence of dead fish. You can sort of follow the kill as the bad water from Orange Creek progressed through the reservoir to Kirkpatrick Dam. It took about two weeks for the bad water to work through the reservoir.
A few large fish were killed, but most were small fish (brim, yellow catfish, suckers) that you would expect to find in shallow, heavily vegetated areas.
Florida's Fish and Wildlife Commission (WFC) investigated the fish kill on September 20. The commission estimated the number of fish killed initially at about 35,000, however 86.7% were small brim. Of the remaining 13.3 %, 5.1% were shiners; 3.9% were jacks with small bass, specks, suckers and catfish finished the remaining 4.3%. In other words the fish killed were the types of fish one normally finds hiding in shallow water grass beds. Those fish that normally live in deeper water at this time of year escaped.
My own observations closely agree with these estimates. Almost all the brim were under 3 inches in length. The few bass that I saw were about 6 to 8 inches long. The majority of the larger fish were yellow cats estimated to be about one to two pounds in weight. I did see a few tilapia (Nile Perch), a very few jacks and one small gar. The jacks and the gar were only about fourteen inches long.
The FWC's Bob Hujik closely monitored the progress of the fish kill. He estimated the total number of fished killed to be about 1.9 million. Hujik said, "It sounds like a lot, but we don't know how many fish are in the reservoir. It's probably not that much. Anglers probably won't see any drop off in the number of fish taken. In fact, sportsmen may appreciate the outcome. We didn't see large numbers of big bass. Those fish are still there and they're probably hungry."
To see this many fish die is a very sad thing, however, after looking at the size and types of fish killed, I believe the impact on fishing in Rodman will be minimal. Rodman is so rich with fish that the only lasting impact that I think will be felt might be in brim fishing and that only in the distant future. It was the youngsters that were killed. Who knows? If the next spawn is a good heavy spawn, there may be no noticeable impact at all.
Probably the biggest impact will not be in nature but in politics. Those who wish to destroy Rodman will again holler, "Rodman had another fish kill. We need to get rid of Rodman to stop killing all those fish." It is a shame the fish died, but if it weren't for Rodman all that junk that is being flushed down Orange Creek and down the Ocklawaha would have a straight shot at the St. Johns River with nothing to stop it. Perhaps, what we need to do is try to manage Rodman just a little bit better in the future so that when the next drought sets up conditions of low oxygen and a possibility for a fish kill, we can control the situation a little bit better.