FEATURE
CLEANER WATER THROUGH SITE-SPECIFIC FLOATING TREATMENT WETLANDS By Michael Ross, SITES AP, ASLA, Assistant Professor, Department of Plant Sciences + School of Landscape Architecture, University of Tennessee and Mia Roark, graduate student, School of Landscape Architecture, University of Tennessee
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saw its tail move first. The Guadalupe Bass, Micropterus treculii, was hiding under the mass of willow roots rippling in the current. The undercut bank and riparian vegetation, particularly the exposed willow roots, provided a great ambush spot for Texas’s state fish, which is closely related to the smallmouth bass. The guad, as we lovingly refer to them, is a sucker for crayfish patterns. With my friend on the oars and a moderately accurate cast, scarcely had the fly hit the water and began to sink than the predator rushed out from cover and inhaled it. Experiences like this one on the San Marcos River in Central Texas shaped my view of urban creeks, streams, and rivers and particularly the biodiversity possible when water and habitat quality are high. These types of habitat conditions have been key to many great fishing experiences as well as being essential to my early development as a budding herpetologist as copious numbers of turtles, salamanders, and snakes can be found in root curtains and shady bank overhangs. As I have moved around the country and traveled, I have seen the impact of urbanization on watersheds and waterways. Water quality issues and lack of good habitat have impacted streams, creeks, and rivers globally and it is particularly impactful in our state as Tennessee is known for the diversity of its aquatic organisms. But there is hope.
Floating Treatment Wetlands: An Opportunity for Cleaner Water Maintaining effective interplay of aesthetics and function is one of the on-going balancing acts of contemporary landscape design, especially design based on ecological principles. Traditional approaches to landscape design often have embraced a Eurocentric approach to aesthetics that largely ignores ecological assemblages, species interactions, and habitat complexity. Given the environmental challenges facing our communities, the landscape industries are uniquely positioned to intercede.
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One of the issues that arises with ever greater frequency is water quality. As our land development patterns continue to sprawl, impervious surfaces increase, as does the associated runoff pollution, volume, and velocity. As private land owners, municipalities, communities, and commercial entities begin to see their role in mitigating these by-products of growth, new tools that allow for tailored site-specific approaches gain in popularity. One such approach is the application of floating treatment wetlands (FTWs). These floating islands utilize regenerative systems inherent in plant growth to mitigate pollutants in the water, provide biodiversity and habitat, as well as aesthetic opportunities with seasonal flowering times and colors.
How FTWs Work Floating treatment wetlands work by floating at or slightly above the surface of the water. Plants that have evolved to grow in saturated, moist, or emergent conditions are placed in planting pockets with a small amount of soil (Image 1). These planting pockets or moisture levels can be tailored to meet the design goals based on what conditions the individual plants prefer. In time the plants send roots out through the island and into the water. These roots represent the primary mechanism for phytoremediation. The roots pull in water, extract excess nutrients, and develop biofilm. These mechanisms are particularly useful in conditions where excess nutrients or suspended solids might be problematic. They also provide excellent habitat for fish, amphibians, and invertebrates that help fuel a larger food web. In effect, the roots act much like the bank overhang with the root curtain I described above. The shade and accompanying cooler temperatures, lower light intensities, cover, food, and cleaner, less turbid water provide meaningful benefits to highly impacted urban streams. These are all positives from the perspective of aquatic organisms as well as those critters that feed on them.
TENNESSEE TURFGRASS AUGUST / SEPTEMBER 2021 Email TTA at: info@ttaonline.org
