May 4, 2017
By Bettina Abe
NARA Pond Ecology
The nine-acre pond at NARA park has a maximum depth of 12 feet.
The park and the excavation for the pond were shaped by bulldozers and excavators. Gravel was excavated to the underlying granite bedrock.
NARA pond is a self-contained, groundwater-fed ecosystem. It does not have tributaries flowing into it. During springtime high water periods, the pond drains through an overflow pipe, flowing into Nashoba Brook, part of the “SuAsCo” (Sudbury, Assabet, Concord River) watershed. NARA pond’s water level changes seasonally depending on precipitation.
The plant community in and around the pond creates habitat for many animals. Stems and leaves create microhabitats between the grains of sand and mud and the undersides of rocks and stones.
Burrowing larvae, mussels, snails and worms live in the mud and feed on the decaying plant matter. Marginal irises, cattails, and rushes are shelter and food for other animals. The leaves and flowers of water lilies float on the surface and have their roots in the mud on the bottom of the pond. Other submerged plants like milfoil are rooted in the mud and provide shelter, food and sites for egg-laying. They also produce oxygen that dissolves in the water.
Algae, photosynthetic creatures, grow in fresh water and are neither plant nor animal. Insect larvae and tadpoles eat the algae. There are essential microscopic organisms in healthy ponds such as Phytoplankton that inhabit the upper, sunlit layer of fresh water. They photosynthesize, create oxygen and sustain the aquatic food web. Zooplankton (crustaceans) eat the phytoplankton, and are a keystone species.
Plant eaters like snails and mussels turn plant matter into energy. They live on the river bottom and are filter feeders, straining plant food from the water.
Ducks and geese eat these herbivores and benefit from the plant energy stored in their prey. Great great blue heron, green heron, spotted sandpiper, mallard, mute swan, gulls, kingfishers, and egrets feed in the shallow edge waters.
Some animals begin life in an egg mass, metamorphose and leave the pond. The dragonfly egg hatches into a nymph and molts up to 15 times during 2 years of growth to adulthood! It’s a fierce predator crawling along the bottom eating other insects or small fish. It climbs up the stem of a plant and molts into a dragonfly, usually at night. They are superb fliers and hunters, with huge compound eyes, speeding over the water and consuming insects. Dragonflies are an indicator species. Their presence and multitude tells us about the overall health of a local pond.