Limnological Role of Aquatic Macrophytes and Their Relationship to Reservoir Management
Reservoir biologists often consider aquatic macrophytes an undesirable form of primary production. Techniques for controlling macrophytes have limited effectiveness. A consideration of recent research indicates that a balance between phytoplankton and macrophyte production is desirable in most reservoirs. Methods for eliminating especially troublesome macrophytes and encouraging more desirable species should be developed. Many macrophytes produce large standing crops and are intricately involved in aquatic food webs. The nutritive value of different species varies considerably. Therefore, a distinction should be made between the quality and quantity of production. The quality of food is often more important than its energy content when aquatic food webs are considered. Macrophyte communities often accumulate large quantities of inorganic nutrients early in the growing season and thereby compete with phytoplankton for nutrients. Phosphorus concentrations are apparently very important in regulating macrophyte growth. The phosphorus cycle of the littoral zone is considered in detail. In shallow, macrophyte-infested reservoirs, a considerable proportion of the phosphorus is cycled through pathways in which vascular plants are involved. In nutrient polluted reservoirs, certain macrophyte species could be cultivated in specified areas to deny space and nutrients to nuisance species. Macrophytes could be harvested to reduce nutrient levels. The macrophyte flora of tropical reservoirs represents an important source of fodder or leaf protein that could be exploited for food.