Introduction
Cattails are a genus of wetland plants known scientifically as Typha that are characterized by long, erect leaves shaped like swords or straps and distinctive, dense brown flower spikes. There are about 30 recognized species of cattails worldwide. They grow in dense stands in fresh to slightly brackish waters up to 2 meters deep.
Wetland plants like cattails are well-known for their ability to filter pollutants and improve water quality. As water flows through stands of cattails and other wetland vegetation, the plants and associated microbes can remove excess nutrients, absorb toxic compounds, and trap sediment. This natural process is called phytoremediation.
Cattails in particular have shown promise for cleansing contaminated water more effectively and efficiently than other wetland plants. However, their effectiveness depends on several environmental factors, and they also have some drawbacks. This article will examine the ability of cattails to remove specific pollutants from water and discuss the benefits and limitations of using cattails for phytoremediation.
Background on Cattails
Cattails are slender wetland plants that belong to the genus Typha. The most common species in North America is Typha latifolia, also known as the common cattail (Britannica, https://www.britannica.com/plant/cattail). Cattails have elongated, blade-like green leaves that can grow up to 2.5 cm wide and reach heights of 3 meters. The leaves emerge from a spreading rhizome below the water. At maturity, cattails produce a distinctive cylindrical, brown flower spike with tiny flowers (Nature Conservancy, https://www.nature.org/content/dam/tnc/nature/en/documents/UT_WingsWater_WetlandProducers_Jan19.pdf).
Cattails thrive in marshes, wet meadows, pond margins, ditches, and other wetland habitats. They grow throughout North America except for the extreme north. Cattails are among the first plants to colonize mudflats and shorelines. As pioneer species, they help stabilize sediments and provide shelter and food to wildlife. Their dense growth provides important habitat for wetland birds and aquatic animals (Cattail Facts, https://cattails.wordpress.com/facts/).
How Wetlands Filter Water
Wetlands act like natural water filters, removing pollutants and improving water quality through several processes. One key process is sedimentation, where suspended solids and particulates settle out of the water column. The slower moving waters in wetlands allow sediments to fall out, removing turbidity and associated pollutants (Vermont DEC).
Wetlands also remove pollutants through absorption and uptake by plants. As water flows through wetland vegetation, plants absorb excess nutrients like nitrogen and phosphorus. Trace metals and organic pollutants also adhere to plant stems and are incorporated into plant tissues (Wetlands Work).
Finally, microbes in the sediment break down organic matter and cycle nutrients. Anaerobic bacteria in particular transform chemicals like nitrate into harmless nitrogen gas in a process called denitrification. The wet conditions create an environment for diverse microbial communities to flourish and process contaminants.
Nutrient Removal Abilities
Cattails have a remarkable ability to absorb and remove nutrients like nitrogen and phosphorus from water. One study found that cattail stands can remove up to 2,460 pounds of nitrogen and 261 pounds of phosphorus per acre per year from wastewater (https://www.producer.com/crops/cattails-suck-floating-water-filters/). The dense root systems of cattails allow them to efficiently take up and store excess nutrients that would otherwise promote algae growth and eutrophication in water bodies.
Specifically, cattails absorb inorganic forms of nitrogen like nitrate and ammonium through their roots and leaves. The nitrogen is utilized for growth and incorporated into the plant’s tissues. For phosphorus, cattails can uptake phosphates and accumulate them in their shoots and rhizomes at concentrations far exceeding natural levels (https://www.sciencedirect.com/science/article/pii/S0011916409004263).
Compared to other common wetland plants, cattails have some of the highest nutrient removal capabilities. Species like bulrush and reed canary grass remove less than half the amount of nitrogen and phosphorus that an equal stand of cattails can take up. This makes cattails an excellent choice for phytoremediation projects aiming to lower excess nutrient levels in polluted waters (https://www.researchgate.net/publication/272212021_Cattail_Farming_for_Water_Quality_Harvesting_Cattails_for_Nutrient_Removal_and_Phosphorous_Recovery_in_the_Watershed).
Toxin and Contaminant Removal
Cattails have demonstrated an ability to remove a variety of toxins and contaminants from water through different processes. This includes heavy metals like lead, arsenic, and mercury, as well as organic pollutants like pesticides, explosives, and pharmaceuticals.
For heavy metals, cattails can uptake and accumulate the metals in their plant tissues through their roots. A study showed that cattails were effective at removing lead from contaminated soil over time [1]. The metals can become immobilized in the sediment as well. Cattails may also degrade certain pesticides and explosives through metabolic processes as the contaminants move through the wetland environment [2].
However, the ability to remove toxins and contaminants can vary depending on the specific pollutant, its concentration, the wetland conditions, and other factors. Not all metals or organic pollutants may be effectively removed. But overall, cattails have demonstrated an important capacity to help clean up a range of water contaminants when utilized properly.
Factors Influencing Effectiveness
There are several key factors that influence the effectiveness of cattails for phytoremediation in wetlands:
Plant density is important, as having more cattail plants per area increases the overall phytoremediation capacity. One study found that wetlands with higher cattail densities were able to remediate lead-contaminated soils more quickly [1].
Water flow rates also matter. Slower flow allows for greater contact time between contaminants and the plant roots. Seasonal variations in growth cycles can impact efficiency as well, with greater contaminant uptake in peak growing periods [2].
Planting cattails together with other wetland species can have synergistic effects. Combining cattails with bulrushes, sedges, and reeds may increase overall wetland health and phytoremediation capabilities compared to monoculture cattail stands [3].
Optimizing these factors when engineering constructed wetlands with cattails can maximize their effectiveness at removing nutrients, metals, and other pollutants from contaminated water sources.
Limitations and Drawbacks
While cattails can be very effective at removing pollutants from water, they do have some limitations and drawbacks:
Cattails can spread rapidly and become invasive if not properly managed. Their dense root systems allow them to quickly propagate and colonize new areas (https://www.producer.com/crops/cattails-suck-floating-water-filters/). This can crowd out other native plants and reduce biodiversity.
Over time, the pollutant removal capacity of cattails can become saturated. The plants can only absorb so much before becoming overloaded. Regular harvesting and replanting is often needed to sustain water treatment capabilities (https://pub-saskatoon.escribemeetings.com/filestream.ashx?DocumentId=118236).
Cattail’s pollutant uptake is reduced in cold weather when the plants become dormant. Their water treatment abilities function best in warmer months (https://albany.cce.cornell.edu/environment/ponds/controlling-cattails). This can limit their year-round effectiveness in colder climates.
Usage in Constructed Wetlands
Cattails are commonly used in constructed wetlands for wastewater treatment, stormwater management, and land remediation applications. Constructed wetlands utilizing cattails provide a natural, low-cost alternative to conventional water treatment methods (https://www.epa.gov/sites/default/files/2015-10/documents/constructed-wetlands-handbook.pdf).
For wastewater treatment, cattails and other wetland plants help filter out organic pollutants, nutrients like nitrogen and phosphorus, and suspended solids (https://digital.library.unt.edu/ark:/67531/metadc3210/m2/1/high_res_d/thesis.pdf). As wastewater flows through the wetland, the rhizomes, roots, and stems of cattails physically filter out contaminants while also facilitating biological and chemical treatment processes.
In stormwater wetlands, cattails help capture runoff and remove pollutants like motor oil, fertilizers, pesticides, and road salts. The dense root systems slow down water flow, allowing contaminants to settle out. Cattails also take up and store excess nutrients, preventing them from entering waterways.
For land remediation of contaminated sites, cattails can help remove heavy metals and other pollutants from soil and groundwater through phytoextraction. Constructed wetlands with cattails are sometimes used as an ecological cleanup solution.
Proper design considerations for constructed cattail wetlands include appropriate hydraulic residence time, water depth, subsurface flow paths, plant density, adequate pretreatment, and maintenance of aerobic conditions (https://www.epa.gov/sites/default/files/2015-10/documents/constructed-wetlands-handbook.pdf). Following best practices for design helps ensure optimal water treatment performance.
Comparisons to Other Plants
Cattails have some key advantages over other common wetland plants when it comes to water filtration:
Cattails form dense stands that slow water flow and allow contaminants to settle out. Their complex root systems provide a large surface area for microbial activity to degrade pollutants. Cattail leaves and stems uptake and store excess nutrients like nitrogen and phosphorus. They produce abundant biomass that can be harvested to permanently remove accumulated nutrients and prevent them from cycling back into the water (https://www.producer.com/crops/cattails-suck-floating-water-filters/).
Some of the best plant combinations with cattails for water filtration include bulrushes, pickerelweed, arrowheads, iris, sweetflag, and rush. Bulrushes provide additional biomass for nutrient removal while pickerelweed, iris, and arrowheads can uptake different forms of nutrients than cattails. Sweetflag forms an interconnected root matrix with cattails to filter sediments, and rush provides habitat diversity (https://digital.library.unt.edu/ark:/67531/metadc3210/m2/1/high_res_d/thesis.pdf).
Conclusion
In summary, cattails have demonstrated an impressive ability to help filter contaminants from water in natural and constructed wetland environments. Through various complex physical, chemical, and biological processes, cattails can remove excess nutrients like nitrogen and phosphorus, absorb heavy metals and organic pollutants, and even mitigate bacterial contamination.
While cattails alone cannot purify heavily polluted wastewater, they can substantially polish effluent when used in sequenced treatment wetlands. Their effectiveness depends on factors like plant density, water flow rates, and seasonal changes. When conditions are optimized, cattails can remove over 50% of nitrates, 80% of heavy metals, and 99% of fecal coliform bacteria.
Given these pollution-fighting benefits, usage of cattails in constructed wetlands is highly recommended. They provide a natural, low-cost way to improve water quality. Cattail wetlands can be integrated into the drainage areas of farms, residential areas, wastewater plants, stormwater systems, and more to filter runoff and prevent pollutants from entering downstream waters.
However, cattail wetlands do require proper long-term maintenance. Periodic harvesting of cattails is needed to prevent over-accumulation of toxins in plant biomass and maintain optimal plant density and microbial communities. Overall though, cattails present an accessible, sustainable water treatment solution worthy of further application.
