Lake Bistineau September 28, 2009 Update

 

The Department of Transportation and Development opened the gates on the Lake Bistineau water control structure to commence the 2009 drawdown of the lake. The lake level will be reduced by seven feet. However, recent rain events have kept the lake up, extending the amount of time required to reach minus seven feet.

This week, LDWF biologists will conduct an aerial assessment of the lake to determine a base line for giant salvinia coverage. In addition, they will evaluate the watersheds that contribute runoff to the lake to determine the extent of giant salvinia in the upper reaches. Lastly, they will take a look downstream of the dam. Several more aerial assessments are planned as the lake level lowers.

The purpose of the drawdown is to strand giant salvinia in the lake. Many have expressed concern that the water control structure does not create a situation where the plants can exit the lake. In this instance, it is not necessary. Salvinia is a fern, and if unable to access water, will dry out and die. Last year’s drawdown, along with foliar herbicide treatments, reduced giant salvinia coverage from 4,500 acres to about 850 acres.

At this time, there are no plans to close the gates. During the drawdown period, the department will evaluate the use of water fluctuation to facilitate plants to move from areas that will not drain. In order to do so, the gates may be closed; the lake will be allowed to fill to a certain level below pool stage and then opened after the plants move to stranding areas. The long-term plan to control giant salvinia in Lake Bistineau will place heavy emphasis on managing water level fluctuations.

The problems associated with Lake Bistineau extend far beyond the salvinia crisis. Many human activities have and continue to contribute to the degradation of the lake’s ecosystem. Over the past few weeks, we’ve spent a great deal of time developing a better understanding of water quality issues in the lake and watersheds. Our discoveries answer some very important questions as to why giant salvinia grows exponentially in this water body. There are many outdated, poorly maintained sewage treatment facilities throughout the watersheds that are responsible for a constant influx of nutrients. As a result, giant salvinia is being nourished, or fertilized in Lake Bistineau.

Sewage discharge is regulated by the Department of Environmental Quality and Department of Health and Hospitals as well as the parishes. Going forward, this issue must be addressed. This department will make the case with those government entities that have jurisdiction over this matter that non-compliance with state and local ordinances is contributing to lake degradation and ultimately giant salvinia growth. Addressing this situation will require routine monitoring of all sewage discharge, which in some instances will include maintenance or new installation.

Therefore, the rapid growth rate and resulting immense coverage of giant salvinia on Lake Bistineau can be directly linked to sewage discharge present in the water body.
Neglecting to address contributing factors will undoubtedly lead to less than desirable long-term results.

Mark McElroy
Fisheries Biologist