Treating Squam’s water through floating wetlands

Starting in June, keep an eye out for floating mats of plants on Squam Lake – our Floating Islands project is back! These floating wetlands use native plants to naturally remove toxins from the lake. Anchored foam mats hold the plants in place while their roots dangle into the water, grabbing contaminants from both the water and sediment, accumulating in the stems and leaves. At the end of the season, the plants, now containing toxins, will be removed from the lake and composted away from the watershed. Water samples will be collected throughout the season to measure the effectiveness of treatment.

Benefits of plants in aquatic ecosystems

Plants provide many essential components to an aquatic ecosystem. Their roots provide areas for fish to hide, nursery habitats, spawning sites, and food for animals. Aquatic roots can help alleviate pressures from shoreline erosion and wave action. Above the water, the leaves and stems also provide habitats, food, resting points for migratory birds, and hunting grounds for predators. Floating leaves of emergent pond weeds can be used for laying eggs for insects. Without aquatic plants, entire bird communities would disappear.  

Aquatic Plant Zonation

Aquatic plants grow in four different zones uniquely contributing to a balanced ecosystem.

• Shoreland – Grow along the water’s edge, and prefer moist soils, but not saturated soils.
• Emergent – Grow in water between 6 to 15 inches, and are rooted underwater with stems above the surface.
• Floating – Grow freely on the water’s surface and have adapted leaves. The leaves and stems absorb the nutrients directly and have air bladders to aid in floating, they have “false” roots they do not sequester.
• Submerged – Grow in water deeper than 15 inches, with long stems reaching up. The roots anchor them, often with branching stems. 

Plant Roots

There are two types of root growth forms: a tap root or a fibrous root. A tap root system has a primary root that grows straight down with secondary and tertiary roots growing outwards off of it. A fibrous root system has branching roots directly from the stem, which takes up more area in the top of the soil, but does not penetrate as deeply. Fibrous roots grow in all directions rather than just down from a primary root.

For this project, we are using fibrous-rooted plants to maximize the water column. Growing off of roots are tiny unicellular outgrowths that grab nutrients from the water or soil. Root hairs increase the surface area that the roots can reach, aiding in nutrient acquisition and anchoring the plant. They can even secrete substances that solubilize minerals, making them ionically available.  Root hairs are 80% effective in obtaining nutrients from the roots into the shoots.

What We’re Targeting

According to studies funded by the Loon Preservation Committee, pollutants of concern in the Squam Lakes Include:

• Phosphorus
• PCBs
• DDT (Dichlorodiphenyltrichloroethane) and DDE (Dichlorodiphenyldichloroethylene)
• PBDEs (flame retardants)
• PFOS (stain guards)
• Chlordane (a pesticide)

These toxins are legacy contaminants bound in sediment, and they still affect wildlife. There is little in the natural environment that can break down these materials, however, plant roots are able to make the continents biologically available. There were three areas of concern: the Kesumpe pond outlet, Bennett cove, and Swainey cove. These areas have high road runoff and historical pesticide use in upstream areas. Birds are especially vulnerable to DDT contamination. The presence of DDT leads to soft shells of loon eggs that can be deadly. Efforts like  NH LAKES ‘Lake Smart’ or the Squam Lake Conservation Society are working to reduce runoff impacts on the environment. 

Our Proposed Remediation

Our floating wetland treatments are modeled after global best practices. Five different species of native aquatic plants show promise in remediation projects: Pickerel weed, Softstem Bulrush, Common Soft Rush, River Bulrush and Sweet Flag. These emergent species have potential in remediation projects throughout the world and have promising existing research. We included considerations of reproductive technique, wetland status, pH range, mature height, shade potential, native range and growing season.

Deployment Sites

Starting in 2025, floating islands will be installed at six inflowing locations of high concern:

1. Evans Cove
2. Piper Cove
3. Kesumpe Pond outlet (Sandwich Bay)
4. Swainey Cove
5. Rockywold-Deephaven Camps
6. Bennett Cove