2000-06-08_AgendaPacket - Laserfiche WebLink

Home

APPENDIX A PLANNING FORTf1E SHALLOW LAKE BONUS Dick Osgood, Ecosystem Strategies Reprinted from LAKELINE, 20(I ), Spring 2000 A quarterly publication of the North American Lake Management Society When planning for the management of aquatic plants in lakes, we must balance protecting the benefits that these plants provide with controlling the nuisances they present. But really, most aquatic plant management plans tend to emphasize control. After all, why are you even considering aquatic plant management, if there is not some need to control excessive growths or nuisance conditions? Aquatic plants love shallow lakes. It seems that shallow lakes, those lakes where rooted aquatic plants do, or at least could, grow almost everywhere, are either I) wall-to-wall aquatic plants or 2) a turbid algae soup devoid of rooted aquatic plants. Most often, neither condition is desired. Here I want to discuss a new way to approach aquatic plant management in shallow lakes to realize the shallow lake bonus. The Shallow Lake Bonus I attended a symposium at the University of Leicester, England, in 1996 where they had gathered saentists and lake managers to explore the topic of The Ecological Basis for lake and Reservoir Management. Much of what we heard dealt with classic management approach for lakes and reservoirs to deal with common problems. However, there was a particular theme among some of the delegates from the United Kingdom and Scandinavia - it seems that many people in these parts of the world value and enjoy aquatic plants. Their recreational use of lakes includes the opportunity to appreciate the plant life, in much the same way we would visit an arboretum or conservatory. As a result, it is a common management objective to encourage, protect or even cultivate the growth of aquatic plants. Interestingly, what the lake managers discovered is that when they succeeded at providing healthy, diverse aquatic plants in shallow lakes and ponds, the water became clear. It turns out that the clear water condition in shallow lakes can be accomplished through management and protection actions. Professor Brian Moss of the University of Liverpool has developed a method for restoring and managing shallow lakes. Professor Moss describes two stable conditions for shallow lakes: I)plant-dominated and 2) algae-dominated. The aquatic plants that can inhabit nearly the entire lake, practically eliminates the open water aspect. From a water quality point of view, this can be a benefit because the algae can be released from nutrient control -meaning something else control algae growth. When this happens, the lake is referred to as `plant dominated,' which means that rooted plants dominate the system instead of algae. Simply, there are abundant rooted plants and there is very clear water. healthy aquatic plants in the lake buffers the effects of excessive nutrients, so the lake is very clear - typically about 50% clearer with three-times less algae that an `algae-dominated' lake with the same nutrient concentrations in the water. When managing a shallow lake, the prevailing lake management paradigm -nutrient control -may be put aside in favor of aquatic plant protection. The reason for this is shallow lakes can switch from the plant- dominated to the algae-dominated condition. Unless or until that switch actually occurs, nutrient control has little potential effect. Protecting aquatic plants means the lake will stay very clear.