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Cattail Farming for Water Quality: Harvesting Cattails for Nutrient Removal and Phosphorous Recovery in the Watershed

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Wetlands are a critical component of a healthy watershed, and can significantly improve the quality of water that flows downstream into our aquatic systems. Wetlands slow the movement of water and nutrients across the landscape during spring snow melt and following storm events. Reducing the movement of this nutrient rich runoff water increases retention time allowing nutrients to be either absorbed from the water or settle into the litter and sediment layer. Wetlands can store, remove, and assimilate a significant amount of nutrients, such as nitrogen and phosphorous, which are often the focus of enrichment issues in aquatic systems. Wetland plants play an important role in the nutrient storage and cycling of these natural systems, and their ability to absorb nutrients from sediment and water makes them potential tools to further remove stored nutrients and reduce nutrient export into lakes and streams.

Netley-Libau Marsh is one of the largest freshwater coastal wetlands in North America, and lies at the south end of Lake Winnipeg in Manitoba, Canada. This lake is considered one of the largest freshwater lakes in the world and also one that is experiencing severe nutrient enrichment problems. The Red River, the largest contributor of N and P to the lake, flows through the marsh on its way to the lake, and has had significant impacts to this freshwater ecosystem. Netley-Libau Marsh is not functioning as a healthy coastal wetland, and many benefits that it could provide in removing and storing nutrients that would otherwise enrich Lake Winnipeg, have been severely degraded or lost. The purpose of the current research program is to help understand the importance of this freshwater coastal wetland in the context of Lake Winnipeg nutrient enrichment, and to examine how restoring this large coastal wetland can help improve the quality of water flowing from the surrounding watershed into the lake. It has been recognized as a key component in the Red River and Lake Winnipeg watershed, and an important component of an integrated watershed management strategy needed to reduce nutrient loadings in the Lake Winnipeg Basin.

Harvesting of marsh plant biomass was examined as a management concept to remove stored nutrients from managed wetland zones. Removing nutrient rich plant material prevents release of nutrients back into the wetland, which naturally occurs during decomposition. Over time this could reduce loadings in the marsh and nutrient export to downstream water bodies. To evaluate the potential of harvesting wetland plant biomass for removal of stored nutrients and phosphorous recovery, cattails (Typha Spp.) were harvested from 2006 to 2008 in an area of Netley-Libau Marsh. Spring and summer harvests were also compared for seasonal nutrient loss. Regrowth following harvests was nearly 2 weeks earlier vs. unharvested areas, with greater plant density and biomass per sq m, and greater biodiversity. Highest phosphorous removal was during late summer harvests. Summer harvested cattail biomass contained significant stored N and P taken up from litter and sediment: 30 kg of P per ha of cattail in the pre-harvest year, and 30 to 60 kg of P per ha of cattail in years following harvest. Cattail lost significant nutrients over the winter months, with only an average 5 kg of P per ha of cattail remaining in the dead spring harvested biomass. Impacts of harvesting on plant community, regrowth, biodiversity, and nutrients were examined, and short term harvesting impacts were minimal.

An additional benefit was gained from the harvested cattail biomass by utilizing the plant biomass as a fuel source for bioenergy production. Plant material provides a valuable feedstock for producing bioenergy, and is considered to be a promising future renewable energy source. Cattail bales were burned in a gasifier system in 2006 and 2007 to produce carbon-neutral bioenergy, and was also shredded and compressed into cubes and pellets. Cattail pellets had a very high durability value of 97% and did not need any additional binding agent during the densification process. The pellets had a calorific heat value between 16 and 20 MJ/kg, comparable to commercial wood pellets at 17 MJ/Kg. This study demonstrates harvesting of cattail biomass for nutrient removal could hold promise, and has the greatest environmental and economic feasibility when combined for the purposes of habitat improvement, nutrient removal, and bioenergy production.
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Keywords: Cattail; Netley-Libau Marsh; Phosphorous; Wetlands; bioenergy; biomass; carbon sequestration; co-benefits; harvesting; integrated watershed management; nutrient management

Document Type: Research Article

Publication date: 2011-01-01

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