Small streams and creeks, part of a vast tributary system, play a big part in an estuary's health
Miles from Delaware’s coast, in the heart of Sussex County, water from the Morris Millpond joins with the Stockley Branch to form Cow Bridge Branch. That stream flows southeast about 2 miles before it runs into Millsboro Pond, which ultimately spills into the Indian River, the largest tributary of Delaware’s inland bays system.
Cow Bridge Branch, and the meadows, wetlands and forests through which it flows, form “one of the last relatively [unaffected] watersheds of the inland bays,” says Bart Wilson, science coordinator with the Center for the Inland Bays. On the grounds of the state-owned Stockley Center (which serves people with developmental disabilities), the creek meanders through an old-growth floodplain that a 2008 article in Outdoor Delaware described as an “intact, high-quality, functioning ecosystem, something that is very hard to find these days.”
Cow Bridge Branch is just one of dozens of tributaries that feed the inland bays. The network of branches, streams, creeks, ditches, canals, prongs and guts supplies nearly half of the freshwater that mixes with saltwater from the ocean to form the bays. (The remaining freshwater is groundwater that has seeped into the earth and over a period of decades gradually makes its way into the bays.)
That saltwater/freshwater mix is very important: The brackish blend is what makes the inland bays an estuary, a natural ecosystem that globally is right up there with coral reefs and rainforests in production of the nutrients that are at the base of the food chain. Estuaries are chock-full of “primary producers” — plants, phytoplankton and bottom-dwelling organisms that use energy from the sun or from chemical reactions to transform oxygen, carbon and other elements into amino acids (the basics of proteins and vitamins) and carbohydrates to sustain themselves. Small animals eat those primary producers, larger animals eat the small animals and so on, until, at the top of the food chain, we can enjoy a meal of flounder stuffed with crabmeat.
Estuaries are also important breeding and nursery grounds for many species, including that flounder. The mix of salt- and freshwater means varying degrees of salinity, which enables many species of fish and invertebrates to live there.
“The tributaries are hugely important to the health of the inland bays,” says Sally Boswell, education and outreach coordinator for the CIB. “They bring in freshwater so that we get this whole diversity of micro-habitats that make the bays so productive.”
And, of course, the geology of an estuary only adds to that productiveness, with mudflats, marshes, reeds and grasses (which juvenile fish use as hiding places from predators). According to the U.S. Environmental Protection Agency, estuaries provide spawning, nursery and feeding grounds for more than 75 percent of the nation’s commercial fish catch and up to 90 percent of its recreational fish catch. Each acre of Atlantic Coast estuaries is estimated to produce up to 125 pounds of commercial fish, the EPA says.
In addition to the Indian River, which flows into the Indian River Bay, large tributaries of the inland bays include Love Creek and Herring Creek, both of which flow into Rehoboth Bay, and Dirickson Creek and Miller Creek, which feed Little Assawoman Bay. Primary tributaries of the Indian River are Lingo Creek, Pepper and Vines creeks (which start in the Great Cypress Swamp and merge at Derickson Point, about a mile before reaching the river) and Swan Creek.
In a healthy ecosystem, tributaries carry into estuaries adequate nutrients to enable the primary producers, and therefore all inhabitants, to flourish.
But other than Cow Bridge Branch, the inland bay tributaries in the 21st century “all have issues,” Wilson says.
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