Kennebec Estuary

• Category: Marine and Oceanic Biomes.
• Geographic Location: North America.
• Summary: This unique estuarine resource in northern New England provides critical fish, plant, and waterfowl habitat off the Gulf of Maine.

Maine’s Kennebec River Estuary is one of northern New England’s most significant natural areas, where the fresh water from several of Maine’s largest and most important rivers meets the salty North Atlantic Ocean. This meeting creates a blending that provides a unique estuarine environment; it is critically important for numerous plants, fish, and other wildlife, including imperiled species such as the bald eagle, spotted turtle, harlequin duck, tidewater mucket, ribbon snake, redfin pickerel, and Atlantic salmon.

The Kennebec Estuary—the largest tidal estuary north of the Chesapeake Bay on the east coast of the United States—contributes, on a seasonally adjusted basis, more than 6 billion gallons (22.7 billion liters) of freshwater to the Gulf of Maine daily. It also provides a marine habitat that has a substantial effect on the health of Maine’s coastal waters and fisheries, and beyond. The area contains over 20 percent of Maine’s tidal marshes, a large percentage of Maine’s sandy beaches, dune habitats, and globally rare pitch pine woodland communities.

Overall, this estuary on the midcoast of Maine is comprised of two distinct components: Merrymeeting Bay and the lower Kennebec River.

Merrymeeting Bay and the Kennebec River

Located on the upper section of the river, Merrymeeting Bay is formed by the confluence of six rivers meeting the Atlantic Ocean. These rivers—the Kennebec, Androscoggin, Cathance, Abagadasset, Muddy, and Eastern—drain 40 percent of Maine’s land, as well as part of New Hampshire. Overall, Merrymeeting Bay is an inland bay of fresh and saltwater approximately 15 miles (24 kilometers) from the Atlantic Ocean.

Merrymeeting Bay provides an extensive expanse of shallow and nutrient-rich waters; vital plant cover; and more than 4,500 acres (1,821 hectares) of habitat for waterfowl, supporting critical foraging, nesting, and wintering activities. The benefits accrue to a significant number of waterfowl within the Atlantic Flyway, as well as a host of other flora and fauna.

The section downstream from Merrymeeting Bay consists of the lower Kennebec River as it runs between a series of forested uplands and rocky shorelines for approximately 15 miles (24 kilometers). The deep water and strong currents that typify the lower Kennebec provide additional types of habitat, including critical shelter for fish such as the Atlantic salmon, alewife, herring, and shad. Notably, the high salt content and significant tidal shifts of more than 5 feet (1.5 meters) prevent the Kennebec River from freezing over in this section, which allows many bird species to winter in this area.

Biota

The Kennebec Estuary biome is home to a wide range of plant life offering distinct rare and exemplary natural communities, including alder thicket, pitch pine bog, dune grassland, mixed saltmarsh, salt-hay saltmarsh, pitch pine woodland, both brackish and freshwater tidal marshes, maritime spruce-fir forest, and rose maritime shrubland.

Characteristic plants in the ecosystem include mudwork, yellow pond-lily, pygmy weed, tidal spikerush, water pimpernel, mountain laurel, long-leaved bluet, estuary monkeyflower, smooth sandwort, Long’s bitter-cress, sweet pepper-bush, and horned pondweed.

There are significant wildlife habitats here, hosting such hallmark species as the seabird roseate tern (Sterna dougallii) seabird, and providing deer wintering area.

More than 50 species of freshwater fish and 10 species of anadromous fish (those that migrate from the ocean to spawn in freshwater rivers) use Merrymeeting Bay, including Atlantic salmon (Salmo salar), shortnosed sturgeon (Acipenser brevirostrum), Atlantic sturgeon (A. oxyrinchus), striped bass (Morone saxatilis), American shad (Alosa sapidissima), the herring species alewife (Alosa pseudoharengus), blueback herring (Alosa aestivalis), and rainbow smelt (Osmerus mordax). At least one rare mussel species, the tidewater mucket (Leptodeaochracea), lives here. One of the bay’s small tributaries is Maine’s only known location for the redfin pickerel (Esox americanus). American eels, declining in much of their geographic range, are abundant here.

Freshwater marshes ring the bay; these provide wild rice and other plant foods for waterfowl, and support a number of rare plants. Among these are American bulrush (Schoenoplectuspungens), wild rice (Zizania aquatica), pickerelweed (Pontederiacordata), bullhead lily (Nupharvariegatum), Parker’s pipewort (Eriocaulonparkeri), water pimpernel (Samolusvalerandi), pygmy weed (Crassulaaquatica), estuary bur-marigold (Bidenshyperborea), Eaton’s bur-marigold (Bidenseatonii), mudwort (Limosellaaustralis), and spongy arrowhead (Sagittariacalycina ssp. spongiosa). Submerged aquatic vegetation includes tapegrass (Valisneria americana) and pondweed (Potamogetonperfoliatus).

Effects of Human Activity

Historically, the Kennebec River estuary was a significant cod fishery, providing both a spawning and nursery habitat for many marine species. Over time, however, human settlements and the corresponding heavy use of the estuary’s resources have imposed a significant and lasting toll. By the mid-20th century, the biota of several of the rivers contributing to Merrymeeting Bay had collapsed. Massive summer fish kills resulted from depleted dissolved oxygen levels in the waterway, while pesticide use in the watershed had strong negative reproduction effects on native bald eagle populations, among other harmful effects stemming from industrial activities surrounding the waterway.

This degradation, as well as similar harm to river habitats across the United States, led to the passage of the Clean Water Act in the early 1970s. The Act focused public attention on the negative impacts of overfishing, land clearance, damming, and water pollution, all of which have caused environmental damage to this ecosystem. Fortunately, the attention has led to at least a partial recovery of this resilient biome through concentrated actions. One such action was the removal of the Edwards Dam from the Kennebec River in Augusta, Maine in 1999. The removal of the dam led to a revitalization of the habitat, with large groups of wildlife returning to the area, including seals, river otters, bears, minks, bald eagles, and ospreys. The brining down of the dam helped conservationist realize what was possible in terms of restoration. Nevertheless, a full recovery may never occur or may require a substantially longer time window. However, new challenges may later manifest other obstacles, such as the recent appearance of harmful algae blooms (red tides) that have periodically paralyzed the region’s biota.

Ongoing, the estuary faces pressure from residential development that is damaging some habitats, as well as inappropriate recreational use, and the introduction of harmful invasive species. Climate change and the subsequent rise in sea level pose lasting threats to the Kennebec. Tidal marshes and other shoreline habitats may flood from rising seas, while the entire ecosystem could be altered by rising air and water temperatures, shifts in ocean circulation, saltwater intrusion, and increased erosion from more intense storms.

Conservation priorities include preserving habitat for migratory fish; maintaining undeveloped shoreline for bald eagle nesting and roosting; and maintenance of beaches and dunes, freshwater and saltwater tidal marshes, and the upland forests that buffer these shoreline ecosystems.

Bibliography

Burroughs, Franklin. Confluence: Merrymeeting Bay. Tilbury House, 2006.

Coffin, Robert P. Tristam. Kennebec: Cradle of Americans. Down East Books, 2002.

"Kennebec Estuary Land Trust." Maine Land Trust Network, 9 Sept. 2021, www.mltn.org/trust/kennebec-estuary-land-trust/. Accessed 9 Oct. 2024.

Köster, D., J. Lichter, et al. “Historical Land-Use Effects on a Freshwater Tidal Ecosystem.” Ecological Applications, vol. 17, 2007.

Lichter, J., et al. “The Ecological Collapse and Partial Recovery of a Freshwater Tidal Ecosystem.” Northeastern Naturalist, vol. 13, 2006.

Lohan, Tara. “How Removing One Maine Dam 20 Years Ago Changed Everything.” The Revelator, 11 Feb. 2019, therevelator.org/edwards-dam-removal/. Accessed 9 Oct. 2024.

McLane, Charles and Carol McLane. Islands of the Mid-Maine Coast. Tilbury House, 2003.

Sitterly, Laura. “Communities Weigh Whether Kennebec River Dams Should Come Down.” The Press Herald, 25 Sep. 2024, www.pressherald.com/2024/09/25/communities-weigh-whether-kennebec-river-dams-should-come-down/. Accessed 9 Oct. 2024.

Wippelhauser, Gail. "Recovery of Diadromous Fishes: A Kennebec River Case Study." Transactions of the American Fisheries Society, vol. 150, no. 3, 2021, pp. 277-90, doi:10.1002/tafs.10292. Accessed 9 Oct. 2024.