Islands in the Pond

ON JUNE 15TH, the Oak Spring Horticulture and Landscape Team implemented a unique and ecologically friendly strategy for the restoration of the Spring House Pond and Eliza’s Pond on the property. The ponds have been facing an annual algae problem caused by an overabundance of nitrogen and phosphorus in the water, producing algal blooms that rapidly cover the ponds’ surfaces during the summer months. Not only is the algae unsightly, but it is disruptive and potentially harmful for the plants and animals inhabiting the area. If the algae were to get out of hand, it could deplete oxygen from the water, block out sunlight, and cause significant die-off of the aquatic life in both ponds. The short of it? The algae had to be managed.

There are several options for treating excess algae in aquatic systems, including a number of herbicides. But spreading chemicals on and around the water would neglect the root of the issue; if the algae was killed chemically, there would still be a surplus of nutrients in the water. Decidedly against chemicals, then, the team looked into other solutions. By the end of their research, they saw promise in a durable, harvestable “plant island” product which had been successfully installed in habitats in Hanover County, VA, the Baltimore Bay, and elsewhere. The solution was called the Beemat.

The Beemat is comprised of floating mat “cells” that are perforated like giant slices of Swiss Cheese. The holes in the cells are used to keep wetland plants–– potted in reusable or biodegradable pots–– on top of the water. Because the plants do not need a soil medium to absorb nutrients from the water, they are wrapped in either burlap or coconut fiber to keep them secure in their pots. Additionally, each cell sports puzzle-piece edges that can dovetail into neighboring cells, creating one lush, sustainable, nutrient-facilitating island.

According to studies on the Beemat website, the mats need to cover 3 to 8% of the surface area of whatever body of water they occupy in order to adequately uptake the excess nutrients. For the Spring House Pond and Eliza’s Pond, The Oak Spring Horticulture and Landscape Team ordered 1024 square feet of Beemats, amounting to roughly 5% of the pond’s total surface. The mats also require an average of 2 ½ plants per square foot, making a grand total of 2500 plants spanning over 11 different species. Aquatic plant species used in the project include Swamp Sunflower, Green Bulrush, Blue Flag Iris, and Cardinal Flower among others. They were all selected considering studies provided by Beemats.

This is not the first time The Oak Spring Horticulture and Landscape Team has faced a big project surrounding the ponds. From 2016 to 2017, the ponds on the property were dredged for the first time in 60 years. When the crew restored the ponds then, they also fixed the connected outflows and dams that had become riddled with leaks.

Without a doubt though, the Beemat solution poised a difficult job for the Oak Spring Team, who focussed their initial efforts on the Spring House Pond, then Eliza’s Pond. The logistics of placing thousands of plants in the mat cells, binding the mats together, and getting them into the water before their roots dried out were not the only challenges either. Hungry Canada Geese, frequent around the Foundation’s landscape, are a looming pest. In order to deter interested geese from feasting on the fresh vegetation, the team is experimenting with an organic spray derived from grape seed extract. In a perfect world, the extract application will turn away geese from the appetizing food source while still inviting turtles, snakes, and smaller birds to the pond’s new feature.

By the end of the day, The Oak Spring Horticulture and Landscape Team successfully installed all of their Beemats into the water. But their efforts will not stop there. In the fall, the Oak Spring Team will harvest the plants from the islands to ensure that the absorbed nutrients do not return to the water as the plants go dormant in the winter months. Two-thirds of the plants were installed in reusable pots which will be harvested and used as a significant compost feedstock. The other third were placed in biodegradable pots which will be directly transplanted from the mats into neighboring wetlands, streambanks, and pond margins. Potential sites for transplanting include Goose Creek, which has banks bordering Oak Spring, as well as one of the Team’s on-site wetland habitat ecosystems, which they established this past winter by planting nearly 1,000 wetland shrubs. Effectively, the Oak Spring Horticulture and Landscape Team now has two beautiful-looking plant nurseries growing on the Spring House Pond and Eliza’s Pond.