Watermeal
(Wolffia spp.)
Description
Watermeal is the smallest flowering plant on Earth, belonging to the duckweed family (Lemnaceae). It appears as tiny, granular, green dots floating on the water’s surface. Individual watermeal plants typically measure less than 1 millimeter in diameter and lack roots, resembling green specks of grain or cornmeal. Unlike other aquatic plants, watermeal grows as a free-floating mat across calm water bodies and can reproduce rapidly. Because of its size and buoyant nature, watermeal is easily carried by wind and water currents, enabling it to quickly spread across ponds, lakes, and slow-moving streams.
Distribution
Watermeal is widespread throughout North America and is often found in nutrient-rich, still, or slow-moving water bodies such as ponds, marshes, and lakes. It prefers warm temperatures and can thrive in eutrophic conditions where excessive nutrients are present, leading to potential explosive growth. Watermeal can also be found in parts of Europe, Asia, and Africa.
Habitat
Watermeal thrives in freshwater environments with abundant sunlight and minimal water movement. It is commonly found in ponds, lakes, and ditches where nutrient levels are high. This floating plant often coexists with duckweed and can form thick mats that cover the entire surface of a water body. The dense growth of watermeal can lead to shading, negatively impacting submerged vegetation and altering aquatic habitats.
Impacts to the Aquatic Ecosystem
Watermeal can significantly impact aquatic ecosystems. Dense mats can reduce oxygen levels in the water by limiting gas exchange with the atmosphere, which may lead to fish kills and harm other aquatic organisms. The thick cover also blocks sunlight from penetrating below the surface, inhibiting the growth of submerged aquatic vegetation (SAV) essential for the ecosystem’s balance. Furthermore, watermeal competes for nutrients, making it difficult for native plants to survive. Its rapid growth may also lead to clogged water intakes and decreased water quality, exacerbating eutrophic conditions.
Prevention and Control
Mechanical Control
Manual removal of watermeal can be challenging due to its small size and rapid reproduction. Skimming devices, nets, and other mechanical methods may reduce biomass temporarily, but they often prove inefficient in providing long-term solutions.
Biological Control
The introduction of certain fish species, such as grass carp (Ctenopharyngodon idella), has shown limited success in controlling watermeal populations. However, this method must be carefully managed to avoid ecological imbalance. Biological control using specific weevils has also been researched, but practical applications remain limited.
Chemical Control
Effective management of watermeal often involves the careful application of specialized herbicides, which target the plant’s growth mechanisms. The precise method and selection of treatment can vary based on site-specific factors and desired outcomes. It is recommended that chemical control be managed by a professional aquatic specialist to ensure efficacy, compliance with regulations, and minimal impact on the surrounding ecosystem.
