Cladophora glomerata, commonly known as “blanket weed” or “water silk,” is a filamentous green algae found in freshwater environments worldwide. While a natural component of many aquatic habitats, its growth can become excessive under certain conditions, leading to nuisance blooms. These events have been documented in major bodies of water, such as the Great Lakes in North America.
Identification and Habitat
Cladophora glomerata is identified by its long, branching green filaments. These filaments are one cell wide and form growths that feel coarse or cottony. The frequency of its branching is influenced by water current strength, and the alga attaches to hard, submerged surfaces like rocks, logs, and aquatic plants.
This alga thrives in freshwater systems like rivers, streams, and large lakes. It is common in clear, hard, unshaded waters, especially during summer low flow. It grows most prolifically on rocky shorelines and in waters with high phosphate concentrations, appearing in climates from New Zealand to colder regions.
Causes of Nuisance Growth
The primary cause of excessive Cladophora glomerata growth is eutrophication, an overabundance of nutrients in the water. While the alga is a natural part of many ecosystems, high levels of phosphorus and nitrogen act as a fertilizer. This fuels rapid and dense growth beyond normal levels.
Elevated nutrient concentrations originate from human activities within the surrounding watershed. Agricultural runoff is a major source, carrying fertilizers from fields into nearby streams and lakes. Discharges from wastewater treatment plants and leaking septic systems also release high levels of phosphorus and nitrogen, creating ideal conditions for the alga to form massive blooms.
The link between nutrient levels and Cladophora growth is well-documented. For instance, widespread blooms in the Great Lakes during the mid-20th century were significantly reduced following a binational effort to abate phosphorus inputs. This history underscores the relationship between nutrient pollution and the proliferation of this alga.
Ecological Impact
While Cladophora provides habitat and food in a balanced ecosystem, its overgrowth has negative consequences. When large, dense mats of the alga decay, the decomposition consumes large amounts of dissolved oxygen. This leads to hypoxic (low oxygen) or anoxic (no oxygen) conditions that are lethal to fish and other aquatic organisms.
Nuisance blooms also create aesthetic and recreational problems. As algal mats wash ashore and decompose, they produce strong, foul odors. These accumulations can clog boat motors, interfere with fishing lines, and make shorelines unpleasant for swimming. The presence of these mats has been a recurring issue, prompting public concern and management efforts.
Dense algal mats can also become a habitat for harmful bacteria. Cladophora can harbor high densities of fecal indicator bacteria like E. coli and enterococci. Research has detected human pathogens such as Salmonella and Campylobacter within these mats, posing a potential public health risk.
Management and Control Strategies
Managing nuisance growths of Cladophora glomerata involves both short-term actions and long-term solutions. The most direct method is physical removal through raking, netting, or using mechanical harvesters to clear algae from shorelines. While effective for temporary relief, this approach does not address the underlying cause of the overgrowth.
A more effective long-term strategy is to reduce the amount of nutrients entering the waterway. Since phosphorus and nitrogen fuel the blooms, controlling these inputs is the most sustainable solution. This involves watershed management practices aimed at curbing runoff from agricultural and urban areas and creating buffer zones of vegetation along waterways.
Improving agricultural practices, such as optimizing fertilizer application and implementing better manure management, can also lower nutrient loads. Upgrading wastewater treatment facilities to enhance nutrient removal is another step. While chemical treatments like algaecides exist, their use is approached with caution as they can have unintended negative effects on other aquatic organisms.