Where the Rivers Meet the Sea : Oceanus Magazine
A place where Fresh Water and Salt Water Meet is called a Halocline. When Salt and Fresh Water mix it is called a mixing zone. Inside the natural feature named estuary, an amazing phenomenon happens continuously, which is the interaction of river fresh water and the. Brackish water is water that has more salt than freshwater, but not as much as seawater. Brackish water condition commonly occurs when fresh water meets seawater. In fact, the most extensive brackish water habitats worldwide are.
The continual bottom flow provides an effective ventilation system, drawing in new oceanic water and expelling brackish water. This circulation system leads to incredible ecological productivity.
Brackish water - Wikipedia
Nutrients and dissolved oxygen are continually resupplied from the ocean, and wastes are expelled in the surface waters. This teeming population of plankton provides a base for diverse and valuable food webs, fueling the growth of some of our most prized fish, birds, and mammals—salmon, striped bass, great blue heron, bald eagles, seals, and otters, to name a few.
The vigor of the circulation depends in part on the supply of river water to push the salt water back. The San Francisco Bay area has become a center of controversy in recent years because there are many interests competing for the fresh water flowing into the Bay—principally agriculture and urban water supplies extending to Southern California.
Estuarine circulation is also affected by the tides; stronger tides generally enhance the exchange and improve the ecological function of the system. The Hudson estuary, for example, is tidal for miles inland to Troy, N.
Some are self-inflicted; some are caused by the abuses of human habitation. An estuary, with all of its dynamic stirrings, has one attribute that promotes its own destruction: When suspended mud and solids from a river enter the estuary, they encounter the salt front.
Unlike fresh water, which rides up and over the saline layer, the sediment falls out of the surface layer into the denser, saltier layer of water moving into the estuary. As it drops, it gets trapped and accumulates on the bottom. Slowly, the estuary grows muddier and muddier, shallower and shallower.
Occasionally a major flood will push the salt right out of the estuary, carrying the muddy sediment along with it. Sediment cores in the Hudson River indicate that sediment may accumulate for 10, 20, or even 50 years, laying down layers every year like tree rings.
- What is an Estuary? The Areas Where Fresh & Salt Water Meet Are Known As Estuaries
- When Fresh Water meets Salt Water
- Where the Rivers Meet the Sea
But then a hurricane or big snowmelt floods the river, wipes out the layers of sediment, and sends the mud out to sea. It is good because a big storm can keep an estuary from getting too shallow too fast.
In fact, it appears that over the last 6, years, the natural dredging by large storms has maintained nearly constant water depth in the Hudson estuary.
Environmental regulations are far stricter now than they were 50 years ago, and we have stopped using many chemicals that play havoc with the environment. For instance, polychlorinated biphenyls PCBs were banned in the s because they were shown to be toxic to fish and wildlife, and to the humans who consume them. Trickle-down effects Billions of dollars are now being spent to clean up American estuaries contaminated by industrial pollution.
The Superfund program of the U. Environmental Protection Agency collects and spends billions of dollars more to remediate estuaries. Often the remediation strategies are complex and controversial. In the case of Hudson River, there is a heated debate about whether PCB-contaminated sediments should be removed—dredged with high-tech methods that theoretically minimize environmental harm—or left undisturbed.
That debate pivots on the episodic storm phenomenon: Are the contaminated sediments there to stay, or could they get stirred up when the next hurricane washes through the Hudson Valley?
Aside from cleanup initiatives, parts of the Hudson need to be dredged for navigational purposes. Dredging is not that costly or difficult, but finding a place to put contaminated sediments is a problem.
The Port of New York has been filling up abandoned Pennsylvania coal mines with its contaminated mud, but that is not a long-term solution. While the problems of American estuaries are complicated and expensive, they pale in comparison to Asian estuaries. The entire nation of Bangladesh lies within the estuary and lower floodplain of the Ganges-Brahmaputra River. Global sea-level rise is causing a loss of land, increased flooding, and increased salt intrusion in these estuaries.
The demand for water upstream for irrigation and domestic use significantly reduces freshwater flow through these systems. The Indus River and Huang Ho estuaries have suffered from drastic reductions of freshwater flow over the past several decades, and the impact of these human alterations is just now being recognized.
New policies about land use, water diversion, and even global carbon dioxide production which affects global warming and sea level rise will be needed to protect these vulnerable estuarine environments and their human inhabitants.
Stirring up new ideas One of the challenges of estuarine research is that most of the significant problems are interdisciplinary, involving physics, biology, chemistry, geology, and often public policy and economics. Salmon are anadromous, meaning they live in the sea but ascend rivers to spawn; eels are catadromous, living in rivers and streams, but returning to the sea to breed.
Besides the species that migrate through estuaries, there are many other fish that use them as "nursery grounds" for spawning or as places young fish can feed and grow before moving elsewhere. Herring and plaice are two commercially important species that use the Thames Estuary for this purpose. Estuaries are also commonly used as fishing grounds, and as places for fish farming or ranching.
Many, though not all, mangrove swamps fringe estuaries and lagoons where the salinity changes with each tide. Among the most specialised residents of mangrove forests are mudskippersfish that forage for food on land, and archer fishperch-like fish that "spit" at insects and other small animals living in the trees, knocking them into the water where they can be eaten.
Like estuaries, mangrove swamps are extremely important breeding grounds for many fish, with species such as snappershalfbeaksand tarpon spawning or maturing among them. Besides fish, numerous other animals use mangroves, including such species as the saltwater crocodileAmerican crocodileproboscis monkeydiamondback terrapinand the crab-eating frogFejervarya cancrivora formerly Rana cancrivora.
Where Fresh Water and Salt Water Meet is Called A Halocline
Mangroves represent important nesting site for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, shorebirds and seabirds. Although often plagued with mosquitoes and other insects that make them unpleasant for humans, mangrove swamps are very important buffer zones between land and sea, and are a natural defense against hurricane and tsunami damage in particular.
Brackish seas and lakes[ edit ] Some seas and lakes are brackish. The Baltic Sea is a brackish sea adjoining the North Sea. Originally the confluence of two major river systems prior to the Pleistocenesince then it has been flooded by the North Sea but still receives so much freshwater from the adjacent lands that the water is brackish. Because the salt water coming in from the sea is denser than freshwater, the water in the Baltic is stratified, with salt water at the bottom and freshwater at the top.