Is there any latest research on understanding the problems of estuarine deltas lately?

1.The tropical rainforest area in the basin is extensive, the vegetation coverage rate is high, and the soil erosion is relatively light. 2..Sediment is deposited in the middle of the river, and very little is deposited at the mouth of the river 3The terrain is different, the river flows rapidly, and the sediment at the mouth of the river is not easy to deposit.

Oceanographers have revealed the relationship between size and productivity in one of the world's most complex ecosystems

Nick Nidzieko, a professor of geography, said: "Estuarine issues are tricky because they don't quite fit well with either terrestrial or marine science. We can call it a delta, a depression, a salt marsh, a harbor, or a bay.

An estuarine system is neither a complete ocean nor a complete river or riparian system. The combination of these traits and habitat diversity and variability in quality makes it difficult for scientists to draw conclusions about how these systems work together to contribute to global processes, particularly in coastal carbon and nutrient cycling. ”

"We think of the metabolism of an ecosystem as the metabolism of all living things in the estuary, including all the animals and all the plants," Nidzieko said. It is a composite measure of how much organic carbon is produced or consumed in a place.

"Estuaries, which are vital for fisheries, transport, shipping and wastewater treatment, have been largely studied, but their combined impact on the ocean carbon budget remains unknown," he explained. ”

The results show that larger estuarine systems are generally less productive per unit area than smaller estuarine systems. The concept of "bigger is better" has its roots in evolutionary biology.

This is very common in animals," Nidzieko explains, "and this theory, known as Kreber's law, holds that an animal's metabolic rate is equivalent to three-quarters of its mass. The larger the animal, the slower its metabolism. A rat only lives for a few years, its heart beats so fast that it needs to eat constantly to survive.

An elephant eats occasionally, has a slower heartbeat, and can survive for decades. ”

The same 'three-quarters' ratio applies to estuaries. After studying a series of published surveys on ecosystem metabolism, Nidzieko argues that the productivity of estuarine systems is generally not linearly related to size: larger, deeper estuarine systems are less productive per unit volume than smaller and shallower estuarine systems.

"The explanation for why elephants have a slower metabolism than rats can also be used to explain why productivity per unit volume in San Francisco Bay is not as high as Goleta Slough," Nidzieko said. "It's basically driven by physics.

This article shows that metabolism is related to nutrient retention time (in other words, the speed at which nutrients move through the system).

These findings may affect the way the benefits of estuaries, their place in the wider global carbon cycle, and the planning of their use in these areas. Incorporating scale and depth into an estuary's productivity calculations could also allow scientists to reconsider what is lost to intrusion into coastal wetlands — such as San Francisco Bay, ports around the world, and wastewater treatment systems.

Compiler: Jessica Ji Reviewer: devin

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Estuarine deltas, i.e., estuarine alluvial plains, are a common surface topography.

The estuarine delta is the sediment and other impurities carried in the river flow, and the seawater with a much higher salt content than fresh water is encountered at the estuary, which is condensed and silted, and gradually becomes a new wetland at the estuary, and then forms a delta plain. The top of the delta points upstream of the river, and the outer edge faces the sea, which can be seen as the "bottom edge" of the triangle.

Delta is translated from the English delta, which is a transliteration of the Greek word δ, and the Greek meaning comes from the fact that the delta is shaped like a triangle, and some believe that this is the pictographic origin of the alphabet triangle. Typical deltas in the world: Ganges Brahmaputra River Delta, Mekong River Delta, China's largest delta is the Yangtze River Delta, which is also the second largest delta in the world.

Formation of estuarine deltas

A delta is an alluvial plain that gradually develops into an alluvial plain when a river flows into an ocean, lake or other river due to the decrease in the flow velocity, and the sediment it carries is deposited. The delta formed by the confluence of lakes and rivers is also called the inland river delta. There are some rivers that burst out of the delta directly on land without joining other water systems.

Such a delta is called an inland delta and is a type of inland river delta. The delta is also called the estuarine plain, from the plane, like a triangle, the top points upstream, the bottom edge is its outer edge, so it is called the delta, the area of the delta is larger, the soil layer is deep, the water network is dense, the surface is flat, the soil is fertile, and it is easy to flood.

An estuarine delta refers to a fan-shaped alluvial plain in the estuarine section.

When it flows into the sea, due to the decrease in the flow velocity, a large amount of sediment is carried by sedimentation, which extends in the estuary section, reclaiming the land, and gradually forming a fan-like accumulation during flooding.

From the perspective of the dynamic characteristics of the estuary area, within the range of the tidal boundary, the river is supported by the tidal current, and the flow velocity is small, which is most likely to form the heart beach and the river center island, which makes the river bifurcate. At the mouth of the estuary, due to the diffusion of the current, the flow rate slows down, and the sediment often accumulates into shallows, blocking the estuary.

Special circumstances

Of course, there are also rivers whose estuaries do not form deltas. For example, there is no delta at the mouth of the Qiantang River in China. This is because the sediment content in the Qiantang River is scarce, and the estuary is a very wide trumpet-shaped estuary, and the huge scouring force of the rising tide makes the sediment unable to be deposited, even if some sediment is lucky to stay.

Piled up at the mouth of the Qiantang River, it is also difficult to increase the height, and can only form an underwater sand barrier under the water surface, which cannot form a delta that is exposed to the water surface.

In addition, contrary to the delta formation process, the amount of sediment coming from the river is small, and the estuary is strongly scoured by the current, and there is no delta formation, and it is often trumpet-shaped, and this kind of estuary is called a triangle port or triangle bay.

For example, Hangzhou Bay is a typical triangular port. The Qiantang River carries less sediment, the estuary coast falls, and the tidal range is large, which not only makes the sediment carried by the river unable to accumulate in the estuary, but also causes a strong erosion, deepens and widens the estuary, and gradually forms a triangular port.

The formation process of the estuarine delta is as follows:

The estuarine delta is the river at the mouth of the sea or at the mouth of the river, because the terrain is flat and the flow rate is slow, so the sediment carried in the river water, a large amount of sediment, a large amount of sediment is deposited, and the river water also obtains the top of the seawater, therefore, the river water compromises a large amount of sediment to form a land.

The location of the estuary should be low and flat, the flow speed of the river channel is slow, the sediment-carrying capacity of the river channel is weakened, and the sediment accumulation forms a delta, so the delta is usually low and flat.

Causes of estuarine delta formation.

Estuarine deltas are sedimentary systems fed by rivers, which are the products of the interaction of "dynamics-sedimentation-geomorphology" and other factors, and are distributed in areas where rivers flow into oceans or lakes. Its planar shape is mostly triangular, with the top pointing upstream and the bottom facing the open sea. It is composed of two parts: onshore and underwater.

The basic conditions for the formation of estuarine deltas mainly depend on the basic laws of water flow changes in the estuarine area. Therefore, factors such as rivers, marine tectonics, climate, and natural geography of the basin all profoundly affect the sedimentary characteristics and morphological types of deltas to varying degrees. According to the different geomorphological parts, from the continent to the sea, the delta is generally divided into the top layer, the prelayer and the bottom layer.

The general plan shape of a delta is triangular, with the beginning of the delta pointing upstream as the apex and the shoreline facing the ocean as the bottom. However, due to the differences in river hydrology, the different geological tectonic movements of estuaries, and the role of marine hydrology, deltas often present a variety of forms.

Point-shaped delta: The bottom edge is a pointed protrusion extending to the ocean, which is the result of the continuous accumulation and extension of sediment in the eight seas of the river in a main waterway, such as the Yangtze River Delta.

Fan-shaped delta: The river is scattered into many rivers and waterways in the delta, radiating from the apex to the sea, and the bottom of the delta shoreline is advancing towards the sea in an arc, such as the Yellow River Delta.

Bird's claw-shaped delta: the estuary has no strong coastal flow and tidal action, the river carries rich sediment, and divides into several streams into the sea, and the distributary channel extends a long sand spit and sand bank to the sea, and the whole is like a bird's claw, such as the Mississippi River Delta.

The delta is a historical witness of geological changes and vicissitudes, and it is also one of the most active areas in the world in terms of economic and cultural development.

The delta region is also quite favorable for the formation of oil and gas, and many of the world's famous oil fields are located in the delta region. Therefore, it is also known as the "** Delta".

Reasons for the formation of estuarine deltas.

Estuarine deltas are a common surface topography. Delta, or estuarine alluvial plain, is a common surface topography. An estuary is the terminus of a river, where it flows into an ocean, lake, or other river.

An endorheic river that does not flow into a lake is called a tailless river and can have no estuary. At the estuary, the cross-section expands, the water flow rate decreases sharply, and a large amount of sediment is deposited to form a triangular sandbar, which is called a delta. The top of the delta points upstream of the river, and the outer edge faces the sea, which can be seen as the "bottom edge" of the triangle.

Geographical features:A delta is an alluvial plain that gradually develops into an alluvial plain when a river flows into an ocean, lake or other river due to the decrease in the flow velocity, and the sediment it carries is deposited. The delta formed by the confluence of lakes and rivers is also called the inland river delta.

However, there are some rivers that directly alluvial deltas on land and do not flow into other water systems, such deltas are called inland deltas, which are a type of inland river deltas.

The above content reference: Encyclopedia - Estuary Delta.

Reasons for the formation of estuarine deltas.

Soil erosion in the middle and upper reaches carries a large amount of sediment, and the river channel widens and the slope tends to be gentle at the estuary, coupled with the jacking effect of seawater, the river flow slows down, and the sediment is deposited at the estuary, forming a delta.

Soil erosion in the middle and upper reaches, sediment deposition due to slowing down in the downstream, sedimentation, and flowing water deposits.

The shape of the estuarine delta.

When the river carrying a large amount of sediment enters the ocean, if the slope of the underwater water at the mouth of the river is gentle, coupled with the supporting effect of the seawater, the river flow slows down, and the sediment carried by the river will accumulate in front of the estuary, forming a delta.

An estuarine delta refers to a fan-shaped alluvial plain in the estuarine section. When the river enters the sea, due to the decrease in the flow velocity, a large amount of sediment carried by it is silted up and extended in the estuary section, and the land is reclaimed from the sea.