Sept. / Oct. 2010, Page 3
RESERVOIR CONDITIONS
by Bob Andry
The condition of the reservoir is pretty much what you would expect this time of year. Heat and sunlight have brought the hydrilla to the top in the shallower areas, but you can still get around in the reservoir without too much trouble. What has been the norm for the past few years and is different this year is the water lettuce crop. By this time last year we had a full blown channel blockage between Cracker Landing and Orange Springs. There is some lettuce on its way downstream and probably a blockage will occur soon about where it normally does, but it is a couple of months late in forming. The only reason for there being less water lettuce seems to be the unusually cold winter we just had. A graph of the water clarity records for the past three years show no similarity to each other, so that probably had little effect. Each year had its share of dark and clear water but all at different times. Perhaps, we had better just enjoy the absence of the pesky plant and not bother about what reduced this year's crop.
Fishing has been good all spring and summer, but now with the temperature in the high nineties and big afternoon thundershowers the only time to be comfortable and fish is the early morning and plan to be home by ten o'clock. There are spots in the riverine zone to drown a worm that are shady and not too uncomfortable after the sun is up, but even these get the full blast of the sun around noon.
LakeWatch
Since the year 2000, SRR members have collected water samples from Rodman and sent them to the LakeWatch laboratories at the University of Florida for analysis. The results of these efforts have allowed us to prove that the reservoir's plant life removes unwanted nutrients from the water. Thus, another reason to keep Rodman.
The water at nine sites throughout the reservoir, starting at Eureka and ending below the dam, were sampled for years. Unfortunately, last year budget cuts at the state level reduced LakeWatch's operating capitol. As a result the sampling activity in Rodman as well as in many other lakes in Florida had to be scaled back. We now sample four sites and only every other month rather than each month.
The laboratory analysis results are always sent to us a few months delayed from when the water samples are sent to the university. We have now received analysis results for the year 2009. The charts below show a summery of these results. Site 6 (Eureka) and Site Out-3 (Orange Creek) show the nutrient level that enters Rodman at these sites. Site 1 (above the dam) shows the nutrient level as the water leaves the reservoir.
The "High" and "Low" figures give you an idea of the amount of fluctuations that occur throughout the year. The "Average" is the average of all the values from 2009 for that site. All values are in micrograms per liter. The first table shows total nitrogen (Tn) and the second total phosphorus (Tp).
| Tn | High | Low | Average |
| Site 6 (in) | 1,510 | 300 | 1,192 |
| Site Out-3(in) | 2,800 | 330 | 1,330 |
| Site 1 (out) | 1,280 | 340 | 747 |
| Tp | High | Low | Average |
| Site 6 (in) | 44 | 29 | 39 |
| Site Out-3(in) | 169 | 20 | 73 |
| Site 1 (out) | 48 | 17 | 28 |
The "High" and "Low" values occur pretty much at both Eureka and Orange Creek in the same time period which would indicate they were caused by heavy rains flushing the flood plain. As a matter of fact the Tn value of 2800 at the Orange Creek site was a possible contributor to the fish kill which Rodman had last year.
It looks like we are still getting about a fifty percent reduction of the nutrients and they travel through the reservoir which is good for the St. Johns River environment and a very good argument for keeping our wonderful reservoir.
