Tucked behind the Harlem Meer's duck island, a blue and white machine about as large as a mid-size car floats inconspicuously. Twice a week, the machine is piloted by trained field staff across the Meer as its front-facing conveyor belt churns upward and collects debris and vegetation from just below the Meer's surface. Though it has the welcome side effect of collecting litter, the harvester's target is algae. Mostly unseen below the Meer's surface, algae (plural of "alga") are the biggest threat to the Park's water bodies.
In the early spring, algae begin growing from the floor of the Park's water bodies toward the surface, threatening its fish and other plants. Like other plants, algae grow through photosynthesis. During the day algae collect sunlight and carbon dioxide and release oxygen. At night, the process reverses and the algae consume oxygen to continue growing. The rate of oxygen consumption is elevated as the process of decomposition occurs. Left uncontrolled, a widespread algae bloom, along with rising water temperatures and slow moving water, can trigger a fish kill.
Algae are sometimes confused with duckweed, a small light green flowering plant that grows in vast clusters on the Park's water body surfaces. "A lot of people think of duckweed as a problem and it's not really," says Maria Hernandez, the Conservancy's Director of Horticulture. "It's wildlife food, it maintains the temperature of the water, it maintains oxygen in the water. Duckweed contributes whereas algae, if too abundant, depletes."
Algae develop so well in Central Park precisely because of the aquatic health it threatens to disrupt. The Park's water bodies are rich with nutrients from surrounding plants, leaves and mowed grass that fall into them, along with waste from animals like ducks, geese, turtles and fish. Despite the addition of these nutrients, the New York City municipal water that fills the water bodies remains clear. The combination of these nutrients with clear water and shallow depths that allow in sunlight makes for an almost ideal environment for algae during warm months.
Algae are harvested as part of the Conservancy's Invasive Plant Management program. Before the harvester was purchased over a decade ago, the Conservancy's horticulture team had to remove algae manually, which was labor intensive and time consuming. A few times a year, the New York City Parks Department generously lent its algae harvester, but scheduling was difficult. The algae harvester enables a gradual collection of algae that frees up the horticulture team's time to work on other projects. The collected algae are transported to the Mount, where they are composted and recycled with the rest of the Park's horticultural waste.
Note on the title: Spores are just one way that algae reproduce. Algae are extremely adaptive and has developed a wide range of reproductive strategies, including sexual, binary fission, fragmentation and, as the title mentions, spores. If you have questions about algae or how the Conservancy cares for the Park's water bodies, post your questions on our Facebook page or ask us on Twitter (@centralparknyc). We'll do our best to answer.
This nautically themed playground is located just north of Summit Rock, near the Park's Mariners' Gate entrance. It provides a variety of play experiences for younger children.