Estuaries: an appreciation
Global heating and sea level rise threaten these productive and beguiling landscapes that I have grown to love
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I’ve been working part-time as a gardener at a small aquarium/zoo in Chula Vista, California, for the last ten years. The job has a lot of joys. I work with plants native to Southern California and interact with enthusiastic volunteers and interns. The facility is also in the middle of a wildlife refuge, resting on an island that skirts the San Diego Bay and an estuary.
Growing up in landlocked West Virginia, coasts were always an odd thing for me. I visited Virginia Beach as a kid and thought of the coasts of this country and the rest of the world as one long beach interrupted from time to time by a bluff or two. Now, over the years, I’ve learned about estuaries and grown more and more fascinated by them.
Estuaries are formed where rivers meet the sea, the deposits of the river creating expanses that are neither sea nor solid ground. And their waters are not entirely the salt waters of the ocean nor the fresh waters from the rivers but an often complex mixture that is referred to as brackish. If you spend any time at or around an estuary, the first thing you’ll notice after the pickleweed, cordgrass, and other low-growing plants, are the immense number of crabs, mussels, and oysters. Estuaries support a high level of fish as well. During high tide, you’re guaranteed to see lots of mollies and other fish. Many of these species use estuaries as breeding grounds and places to harbor their young before they grow up and set out to sea. I’ve even seen bat rays swimming through our estuary during high tide.
Estuary, the word, comes to us from the Latin for tide, aestus, and aestuo, to boil, which suggests the dynamics involved in these bodies of land/water. Tides are always rising or falling, with living creatures responding to the higher and lower water levels. At the Sweetwater River Estuary where I work, widgeons, pintails, and other waterfowl swim through the high tides, while egrets and herons wade through the shallow waters stalking their prey. Flocks of godwits and curlews descend on the estuary during low tide to feast on crustaceans.
Historically, people have had little regard for estuaries as they were considered nether regions or lowlands. They have often been dredged and turned into marinas or ports. Recent estimates have put the loss of estuary habitat along the West Coast as high as 85 percent. This has great implications for the species that rely on these habitats, even threatening the existence of such creatures as the endangered Ridgway’s rail.
Estuaries and sea level rise
As they are environments where land and sea meet, estuaries are vulnerable to sea level rise. In 2018, researchers conducted a comprehensive study of sea level rise and its effects on 14 estuaries along the Pacific Coast of the United States, including the Sweetwater River Estuary. Their findings suggest that all of them will suffer extensive habitat loss, with as much as 83 percent of the estuaries transitioning to unvegetated habitats in less than 100 years.
Estuaries are built and maintained by deposits of silt, sand, and other material carried by their rivers. Many of the rivers along the Pacific Coast, however, won’t be able to provide enough of this depositional material to keep up with the rate of the predicted rise of the ocean. This has been found to be the case with large estuaries worldwide.
In most low-lying coastal areas, rising seas translate into coastlines advancing landward. If coastal marshes have adjacent land to advance into, the estuary could just move with the rest of the coastline. Most Pacific Coast estuaries, however, have nowhere to go, largely due to the high amount of development we’ve built up adjacent to their borders.
On the East Coast, sea level rise is exacerbated by the subsidence of much of the coastal lands. This is occurring from Maine to the southern tip of Florida. The sinking of the land is caused by the over extraction of groundwater. Areas of particular risk are the Chesapeake Bay and the coast from Brunswick, Georgia, north to Charleston, South Carolina.
But it’s not all bad news. The U.S. Geological Survey, whose scientists examined the estuaries of Puget Sound in Washington State, found that the dynamics of the coastal wetlands, most importantly the sediment deposits of the rivers, can maintain the estuaries that are part of that body of water as the waters of the sound rise.
I have grown to love the Sweetwater River Estuary, and it saddens me to think that 60 to 70 years from now it might be all gone. Do you live by an estuary? Do you live someplace threatened by sea level rise? By climate change? Please share your experience by clicking “Leave a comment.”