C) Shallow depth

Explanation: Lagoons are typically characterized by their shallow depth, which influences their physical properties and ecological dynamics.

C) High evaporation rates with low freshwater inflow

Explanation: Hyper-salinity occurs in tidal embayments and wide shallow estuaries when high evaporation rates are present alongside low freshwater inflow, resulting in increased salinity levels.

C) It flows into the estuary over the top of the saline layer

Explanation: In an inverse estuary, seawater of lower salinity flows into the estuary over the top of the denser saline bottom layer, creating a distinct stratification of water layers.

B) They have multiple channels and experience surface currents

Explanation: Restricted lagoons feature multiple channels leading to the sea, allowing for surface currents caused by wind, which facilitates some mixing of water between the lagoon and the sea, unlike choked lagoons.

B) It transports sediments and wastes

Explanation: Vertical mixing in estuaries is crucial for transporting sediments and wastes, as well as circulating nutrients and oxygen, which are vital for the health of the estuarine ecosystem.

A) Sedimentation

Explanation: Sedimentation is a common process in estuaries, where sediments are deposited by river flow and tidal action, shaping the estuarine environment.

C) Tidal movements

Explanation: Tidal movements play a significant role in affecting water circulation in lagoons, influencing salinity levels and nutrient distribution.

C) Salt-wedge

Explanation: The salt-wedge estuary is classified based on water balance and is characterized by a distinct layer of saltwater that forms a wedge under the freshwater, influencing the estuarine ecosystem.

C) Threatened ecosystem function

Explanation: Greater nutrient introduction, along with pollution and sedimentation, can threaten the function of estuarine ecosystems, disrupting the natural balance necessary for their health.

B) It varies both vertically and horizontally

Explanation: In partially mixed coastal waterways, salinity is not uniform; it varies both vertically and horizontally due to the incomplete mixing of the water column.

B) Fjord type

Explanation: Slightly stratified estuaries, such as fjord types, exhibit layers of water with varying salinity and temperature, which can affect the distribution of organisms and nutrients.

B) It settles on the bed

Explanation: During periods of neap tide and slack water, sediment captured by the up-estuary near-bottom flow settles on the bed, indicating a temporary stabilization of sediment in the estuarine environment.

C) Desert dunes

Explanation: Desert dunes are not a habitat found in estuaries, which are characterized by diverse habitats such as mangroves, tidal pools, and intertidal flats.

C) Sufficient turbulence from tide, river, or wave energy

Explanation: Fully mixed conditions occur when there is enough turbulence generated by tide, river, or wave energy to mix the water column effectively, leading to uniform salinity.

C) It becomes denser than oceanic waters

Explanation: Under hyper-salinity conditions, estuarine water can become denser than oceanic waters, causing it to sink and form a highly saline bottom layer that flows seaward.

C) It results in lateral salinity gradients

Explanation: The salinity front is not advected at the same speed at different lateral locations, leading to the formation of lateral salinity gradients within the estuary.

B) It leads to greater coral reef die-off

Explanation: Ocean acidification, in combination with other stressors, can lead to greater coral reef die-off, threatening aquatic life and the success of coastal estuary programs.

B) Estuaries have variable salinity

Explanation: Estuaries are characterized by variable salinity due to the mixing of freshwater from rivers and saltwater from the ocean, unlike lagoons which may have more stable salinity levels.

D) Salinity is uniform but varies between riverine and oceanic ends

Explanation: In fully mixed conditions, salinity is uniform throughout the water column, but it varies between the riverine and oceanic ends of the estuary, indicating the influence of both freshwater and saltwater.

B) Inundation of lowlands

Explanation: Rising sea levels will inundate lowlands, displacing wetlands and altering the tidal range in rivers and bays, which significantly impacts estuarine ecosystems.

B) Mixing of seawater with outflowing river water

Explanation: Estuarine circulation is maintained by the mixing of seawater with river water, which is essential for the dynamics of estuarine environments.

C) At the channel center

Explanation: During flood (high tide), the salinity is higher at the channel center than near the channel banks, indicating a change in salinity distribution with tidal movements.

B) Lunar tides

Explanation: Lunar tides are identified as the primary driving force behind the changing water depths in estuaries, influencing the tidal patterns and water levels.

B) Narrow channels with high wave energy

Explanation: Choked lagoons are characterized by their narrower channels and high energy waves, which block the tides from transferring water between the sea and the lagoon, limiting water mixing.

C) They have a wide channel and fast water currents

Explanation: Leaky lagoons are characterized by their wider channels to the sea and fast water currents, which promote significant mixing of water between the lagoon and the sea.

C) Freshwater input

Explanation: In classical estuaries, freshwater input is the main driver of long-term circulation, contributing buoyancy that influences water movement over months.

B) Brackish water

Explanation: The combination of freshwater and seawater in an estuary results in brackish water, which is slightly salty, distinguishing estuarine environments.

B) Vertical mixing and stratification

Explanation: Estuarine water circulation patterns are influenced by vertical mixing and stratification, which can significantly affect residence time and exposure time in the estuary.

B) It is uniform throughout the water column

Explanation: In fully mixed estuaries, salinity is uniform throughout the water column, although it varies between the riverine and oceanic ends, reflecting the mixing of freshwater and saltwater.

B) Near the channel banks

Explanation: Tidal velocities are lower near the channel banks than at the channel center, indicating a variation in flow dynamics within the estuary.

C) Threat to the availability of minerals needed for coral skeletons

Explanation: Ocean acidification, caused by rising CO2 levels, leads to increased acidity in marine waters, which threatens the availability of essential minerals needed for building and maintaining coral skeletons and supporting other estuarine species.

C) It is lower at the channel center than near the banks

Explanation: During ebb tide, the salinity at the channel center is lower than near the channel banks, reversing the salinity distribution observed during flood tide.

B) Low river flow and moderate-to-strong tidal currents

Explanation: A vertically mixed estuary occurs when river flow is low and tidal currents are moderate to strong, allowing for mixing of water layers.

C) It is the same from the surface to the bottom

Explanation: In vertically mixed estuaries, the salinity of water is uniform from the surface to the bottom due to strong tidal currents that eliminate vertical layering.

B) A coastal zone depression below mean high water

Explanation: A lagoon is defined as a naturally existing coastal zone depression that is below mean high water and has communication with the sea, protected by a natural barrier.

D) They promote vertical mixing but do not fully mix the water column

Explanation: Tidal currents in partially mixed conditions promote vertical mixing, but their strength is insufficient to achieve complete mixing of the water column, leading to variations in salinity.

C) It decreases

Explanation: In natural estuaries, the depth decreases towards the lateral boundaries, which is a key characteristic of their physical structure.

C) Raises salinity and allows saltwater to mix upstream

Explanation: Droughts reduce fresh water input into tidal rivers and bays, which raises salinity levels in estuaries and enables saltwater to intrude further upstream, posing risks to coastal drinking water infrastructure.

B) To transport organisms and circulate nutrients

Explanation: Water movements in estuaries play a vital role in transporting organisms, circulating nutrients and oxygen, and managing sediments and wastes, which are essential for maintaining the ecosystem's health.

C) Threat to coastal drinking water infrastructure

Explanation: The intrusion of saltwater into groundwater and further upstream poses significant risks to coastal drinking water infrastructure, highlighting the impact of changing salinity levels due to drought.

C) Mangroves

Explanation: The upper estuary is typically characterized by sheltered habitats such as mangroves, which provide important ecological functions.

B) Sandbars, barrier islands, or coral reefs

Explanation: Lagoons are shallow bodies of water that are protected from larger bodies of water, typically the ocean, by natural formations such as sandbars, barrier islands, or coral reefs.

C) Tidal currents generate turbulence promoting vertical mixing

Explanation: In partially mixed coastal waterways, tidal currents create turbulence that facilitates vertical mixing, although they are not strong enough to fully mix the water column.

B) It has steep, glacially-carved sides

Explanation: Fjord-type estuaries are known for their steep, glacially-carved sides, which create a unique habitat and water dynamics compared to other estuary types.

B) They lead to increased erosion and sedimentation

Explanation: Increased frequency and intensity of rainfall can result in greater storm water runoff, which contributes to erosion and sedimentation, threatening the function of estuarine ecosystems.

B) It transports fine sediments and facilitates sedimentation

Explanation: Estuarine circulation is highly relevant for the transport of fine sediments and sedimentation, playing a crucial role in the dynamics of sediment movement within estuaries.

C) It leads to a strong increase in turbidity

Explanation: High tidal currents can re-suspend sediment that has settled, leading to a significant increase in turbidity, which affects water quality and light penetration.

B) Tides, rainfall, evaporation, wind, and oceanic events

Explanation: Estuarine circulation is controlled by a combination of factors including river inflow, tides, rainfall, evaporation, wind, and other oceanic events such as upwellings and storms.

A) It increases residence time

Explanation: Estuarine circulation patterns, influenced by mixing and stratification, can affect residence time, which is the duration that water remains in the estuary before moving out to the ocean.

B) They support high biodiversity

Explanation: Lagoons are important ecosystems that support high biodiversity, providing habitats for various species and contributing to ecological balance.

B) They flood existing river valleys

Explanation: Rising sea levels flood existing river valleys over several millennia, leading to the formation of coastal plain or drowned river valleys.

C) Decreased salinity

Explanation: Decreased precipitation can affect the salinity of coastal waters, disrupting the natural balance of freshwater and saltwater that estuaries require for their ecosystems to thrive.

C) Estuaries have fast and strong water flow

Explanation: The primary distinction is that estuaries experience fast and strong water flow due to the inflow of rivers or streams, while lagoons have more sluggish and shallow water flow.

C) Stronger flood currents than ebb currents

Explanation: Tidal asymmetry due to non-linear tidal propagation in shallow water results in stronger flood currents compared to ebb currents, which influences sediment transport dynamics in estuaries.

B) The movement and circulation of water

Explanation: In the context of estuary classification, hydrodynamics refers to the movement and circulation of water, which includes parameters like stratification and circulation.

B) It has free communication with the ocean

Explanation: A defining feature of an estuary is that it has free communication with the ocean, allowing for the mixing of ocean water with freshwater from land.

C) Nearest the ocean

Explanation: The salinity in a vertically mixed estuary is highest nearest the ocean and decreases as one moves upstream toward the river.

B) Elongated/barrier islands lagoons

Explanation: Elongated/barrier islands lagoons are defined by their irregular stretches of water that exist between coastal areas and the shoreline, making them distinct from other lagoon types.

B) Delaware Bay

Explanation: Delaware Bay is identified as an example of a large, shallow estuary that exhibits characteristics of a vertically mixed estuary.

B) A salinity maximum zone

Explanation: Inverse estuaries form a salinity maximum zone where both riverine and oceanic water flow towards this zone, creating distinct salinity gradients.

C) To separate the estuary from the ocean

Explanation: The sand bar in a bar-built estuary serves to separate the estuary from the ocean, creating a semi-enclosed environment that influences the estuarine ecosystem.

B) An elongated, deep channel with a sill

Explanation: Fjords are characterized by their elongated, deep channels that include a sill, which is related to deposits from either currently active or extinct glaciers.

B) Tidal flow along the estuarine bottom

Explanation: Vertical mixing in estuaries occurs due to turbulence generated by tidal flow along the bottom, which helps to distribute nutrients and organisms throughout the water column.

B) Decomposition of organic material

Explanation: In the high turbidity zone, the decomposition of organic material can lead to oxygen depletion, particularly in lower water layers where mixing with oxygen-rich surface water is restricted by stratification.

B) A semi-enclosed coastal body of water

Explanation: An estuary is defined as a semi-enclosed coastal body of water that has free communication with the ocean and is where ocean water is diluted by freshwater from land.

C) Estuaries, sounds, bays, or lakes

Explanation: Lagoons can be referred to by various names, including estuaries, sounds, bays, or even lakes, indicating their diverse classifications.

C) They have a single small inlet for ocean communication

Explanation: Some bar-built estuaries feature a small inlet, typically a few hundred meters wide, which allows communication between the estuary and the ocean.

C) Earthquakes and fractures of the Earth’s crust

Explanation: Tectonic estuaries are formed specifically by earthquakes or fractures in the Earth’s crust, which create faults that lead to the sinking of part of the crust and the formation of a hollow basin.

B) By flushing the system and providing nutrients

Explanation: Tides flush the estuarine system and provide essential nutrients, which are crucial for maintaining functional food webs within the ecosystem.

E) Delta

Explanation: The classifications of estuaries based on geomorphology include coastal plain/drowned river valleys, fjords, bar-built, and tectonic. A delta is a different type of landform and is not classified as an estuary.

B) Mixing

Explanation: Mixing is essential for flushing pollutants out of estuaries, as it helps to distribute water and nutrients, thereby reducing concentrations of harmful substances.

B) Because fresh water is less dense than saltwater

Explanation: Fresh water is less dense than saltwater, which causes it to float above the seawater in a salt-wedge estuary, creating a sharp boundary between the two water masses.

C) Fjord

Explanation: Fjords are estuaries that are formed in steep, glacially carved valleys, often resulting in deep, narrow inlets that are characteristic of this type of geomorphology.

B) Old Woman Creek

Explanation: Freshwater estuaries are found in Old Woman Creek, located on the south-central shore of Lake Erie in Ohio, highlighting a specific example of this type of estuary.

B) They can increase areas subject to periodic inundation

Explanation: Storm surges resulting from more extreme weather events can increase the areas subject to periodic inundation, further impacting estuarine environments and their ecosystems.

B) Absorption of carbon dioxide in the ocean

Explanation: Ocean acidification is primarily caused by the rising concentration of carbon dioxide (CO2) in the atmosphere, which is subsequently absorbed by the ocean, leading to increased acidity in marine waters.

B) Toward the right channel bank

Explanation: The up-estuary residual flow is shifted toward the right channel bank when looking in the up-estuary direction, indicating the influence of Coriolis acceleration on flow patterns.

C) Littoral drift

Explanation: Bar-built estuaries are formed due to littoral drift, which leads to the creation of a sand bar or spit that encloses an embayment, making it semi-enclosed from the ocean.

D) Wind erosion

Explanation: Wind erosion is not a water movement process; instead, processes like evaporation, tidal exchange, and riverine discharge are essential for understanding estuarine dynamics.

B) The shape and structure of the estuary

Explanation: Geomorphology in estuary classification refers to the shape and structure of the estuary, which is crucial for understanding its physical characteristics.

C) Brackish, marine, or hypersaline

Explanation: Lagoons can have varying salinity levels, including brackish, marine, or hypersaline, depending on their location and environmental conditions.

C) Earth's rotation

Explanation: The primary factor influencing estuarine circulation patterns in the Northern Hemisphere is the Earth's rotation, which affects the direction of currents through Coriolis acceleration.

C) It increases toward the tidal inlets

Explanation: In brackish lagoons, salinity typically increases toward the tidal inlets due to the influx of seawater and runoff, creating a gradient of salinity.

B) A long, narrow arm of the sea bordered by steep cliffs

Explanation: A fjord is specifically defined as a long, narrow arm of the sea that is bordered by steep cliffs, typically formed by glacial erosion.

C) Fine-grained sedimentation and brackish marshes

Explanation: Elongated/barrier islands lagoons are noted for fine-grained sedimentation and the presence of brackish marshes, which are key features of this lagoon type.

C) They help prevent erosion and stabilize shorelines

Explanation: Salt marsh grasses and other estuarine plants play a crucial role in preventing erosion and stabilizing shorelines, which is vital for maintaining coastal ecosystems.

C) They cause part of the crust to sink

Explanation: Faults are crucial in the formation of tectonic estuaries as they cause part of the Earth's crust to sink, leading to the creation of a hollow basin that can be filled by ocean water.

B) Water Balance

Explanation: Estuaries can be classified based on various criteria, one of which is water balance, indicating the importance of hydrological factors in their classification.

D) Temperature

Explanation: The classification of estuaries is based on water balance, geomorphology, and hydrodynamics, but temperature is not a criterion mentioned for this classification.

C) By wave actions

Explanation: Small lagoons are formed primarily by wave actions, which shape the coastal landscape and create these shallow water bodies.

C) It ensures a healthier estuary

Explanation: Rapid flushing prevents sediment accumulation and dissolved oxygen depletion, making a well-flushed estuary intrinsically healthier than a poorly flushed one.

B) Semi-diurnal

Explanation: Estuaries typically experience semi-diurnal tides, which means there are two high tides and two low tides each day.

B) Tidal exchange

Explanation: Tidal exchange is a critical hydrodynamic aspect that influences circulation patterns in estuaries, affecting how water and nutrients are distributed.

B) Subtropical regions of the Americas

Explanation: Bar-built estuaries are commonly found in subtropical regions of the Americas, such as North Carolina, Florida, and northern Mexico, as well as in southern Portugal.

B) It is filled by the ocean

Explanation: After the hollow basin is formed due to tectonic activity, it becomes an estuary when it is filled by the ocean, creating a unique coastal environment.

C) They create saltwater currents that move seawater up into the estuary

Explanation: High tides generate saltwater currents that push seawater into the estuary, influencing salinity and nutrient dynamics.

C) Coastal plain/drowned river valleys

Explanation: Coastal plain/drowned river valleys are formed when sea levels rise and flood existing river valleys, creating estuaries characterized by their drowned river systems.

B) Discharge of river flow and tidal waters

Explanation: Water movements in elongated/barrier islands lagoons are primarily influenced by the discharge of river flow through the lagoon and the regular influx and outlet of tidal waters through inlets.

D) Amazon River

Explanation: The Columbia River, Hudson River, and Mississippi River are examples of rivers that form salt-wedge estuaries, while the Amazon River is not typically associated with this type.

B) High width/depth aspect ratios

Explanation: Fjords are characterized by low width/depth aspect ratios, meaning they are deep and narrow with steep side walls, contrary to having high aspect ratios.

B) Currents are deviated to the right

Explanation: In the Northern Hemisphere, Coriolis acceleration causes currents to be deviated to the right, which is a fundamental aspect of fluid dynamics influenced by the Earth's rotation.

B) Water sources and movements

Explanation: Understanding water sources and movements, such as evaporation, precipitation, and riverine discharge, is crucial for studying the distribution and cycles of particulates, pollutants, and nutrients in estuaries.

B) Dry climates

Explanation: Inverse estuaries primarily occur in dry climates where evaporation greatly exceeds the inflow of freshwater, leading to unique salinity dynamics.

C) Heavy metals, dissolved nutrients, and algal blooms

Explanation: Residence time influences the distribution of various parameters such as heavy metals, dissolved nutrients, suspended solids, and algal blooms, which are critical for the health of estuaries.

B) By serving as a source of water, fish, and wood

Explanation: Lagoons encompass wetlands that are essential for the livelihood, well-being, and health of nearby communities, providing resources such as water for washing, fish for food, and wood for building and fuel.

B) T = (Vol/Q f)(1 - S 1/S 0 - S f/S 0)

Explanation: The residence time formula incorporates the volume of freshwater within the estuary and the flow rate of the river, along with salinity factors, to determine how long water remains in the estuary.

C) They represent islands with multiple inlets

Explanation: Detached sand bars in bar-built estuaries can form islands that feature two or more inlets, allowing for communication between the estuary and the ocean.

B) The conservation of mass in estuarine inflow and outflow

Explanation: This equation illustrates that the inflow and outflow of water and the fluxes of salinity are equal, reflecting the principle of mass conservation in the estuarine system.

B) Chesapeake Bay

Explanation: Chesapeake Bay and Delaware Bay are cited as examples of coastal plain or drowned river valleys located on the eastern coast of the United States, illustrating the concept.

C) Circular/atoll/oceanic lagoons

Explanation: Circular/atoll/oceanic lagoons are specifically restricted to tropical open seas, often surrounded by coral atoll reefs or protected by barrier coral reefs.

C) River inputs

Explanation: Riverine fjords, which are related to extinct glaciers, derive their main source of buoyancy from river inputs, distinguishing them from glacial fjords.

B) They provide habitat for diverse species

Explanation: Lagoons serve as important habitats for a variety of species, supporting biodiversity and providing essential ecosystem services.

A) The time it takes for water particles to leave the estuary

Explanation: Residence time is defined as the duration it takes for water particles to exit the estuary, which is crucial for understanding the health of the estuarine ecosystem.

B) Daily tidal stage

Explanation: In vertically mixed estuaries, salinity is determined by the daily tidal stage, as strong tidal currents mix the water and influence salinity levels.

B) Toward the left bank

Explanation: The down-estuary residual flow is shifted toward the left bank in the Northern Hemisphere, demonstrating the effects of Coriolis acceleration on estuarine circulation.

A) Salt-wedge estuary

Explanation: Salt-wedge estuaries are noted for being the most stratified or least mixed of all estuaries, primarily due to the interaction between fresh and saltwater.

C) Lagoons have sluggish water flow

Explanation: Lagoons are characterized by shallow and sluggish water flow, contrasting with the fast and strong flow found in estuaries.

B) By filtering sediments and pollutants from water

Explanation: Estuaries filter out sediments and pollutants from water draining from uplands, creating cleaner and clearer water, which benefits both people and marine life.

B) San Francisco Bay

Explanation: San Francisco Bay is specifically mentioned as an example of a tectonic estuary, illustrating the concept of tectonic activity leading to the formation of estuarine environments.

D) 3 cm

Explanation: Most changes in water level in freshwater estuaries, specifically due to seiches, are about 3 cm, indicating the subtle yet significant impact of these processes.

D) Canada

Explanation: The examples provided include San Francisco Bay in the United States, Manukau Harbour in New Zealand, Guaymas Bay in Mexico, and some Rias in Northwest Spain, but Canada is not mentioned.

C) High latitudes, poleward of riverine fjords

Explanation: Glacial fjords are found in high latitudes, specifically poleward of riverine fjords, indicating their location in colder regions.

B) Estuaries are usually deeper than lagoons

Explanation: Estuaries are generally deeper than lagoons, which contributes to their different ecological characteristics and water dynamics.

B) Highly energetic beaches

Explanation: The ocean side of an estuary is often characterized by highly energetic beaches, contrasting with the more sheltered habitats found within the estuary.

B) They provide habitats for thousands of species to live, feed, and reproduce

Explanation: Estuaries are critical natural habitats that support a diverse range of wildlife, making them essential for the life cycles of many species, hence the term 'nurseries of the sea.'

B) A semi-enclosed area of the Great Lakes

Explanation: Freshwater estuaries are specifically defined as semi-enclosed areas of the Great Lakes where waters mix with those from rivers or streams, distinguishing them from brackish water estuaries.

B) A natural barrier

Explanation: A lagoon is protected from the sea by some type of naturally existing barrier, which allows it to maintain its unique ecological characteristics.

C) Resembles present-day rivers, but much wider

Explanation: Coastal plain or drowned river valleys have a shape that resembles that of present-day rivers, although they are much wider, indicating their unique formation process.

B) A former barrier island facing the Caribbean Sea

Explanation: The Hotel Zone refers to an area that sits on a former barrier island facing the Caribbean Sea, illustrating the relationship between lagoons and coastal geography.

C) By glacial erosion

Explanation: Fjords are usually formed by glacial erosion, which carves out underwater valleys that become flooded by seawater.

C) It is pushed downward and spreads along the bottom

Explanation: In the salinity maximum zone, water is pushed downward and spreads along the bottom in both seaward and landward directions, affecting the overall water dynamics.

B) Sedimentation and saltwater intrusion

Explanation: Tides play a crucial role in determining both sedimentation patterns and the extent of saltwater intrusion in estuaries, affecting their overall health and functionality.

B) Greenland

Explanation: Greenland is listed as an example of a location with fjords, along with other regions like Alaska and British Columbia, highlighting the geographical distribution of fjords.

B) Pleistocene increase in sea level

Explanation: Coastal plain or drowned river valleys were formed as a result of the Pleistocene increase in sea level, which began approximately 15,000 years ago, significantly altering the landscape.

D) Industrial waste disposal

Explanation: Lagoons provide a wide range of natural functions such as storm protection, river purification, and nutrient cycling, but they do not serve as a means for industrial waste disposal.

C) Freshwater input is greater at the seaward end

Explanation: In humid climates, inverse estuaries can occur where the freshwater input to a coastal region is greater at the seaward end of the estuary, affecting salinity distribution.

B) They are deviated to the left

Explanation: In the Southern Hemisphere, Coriolis acceleration causes currents to be deviated to the left, contrasting with the behavior observed in the Northern Hemisphere.

C) Provisioning, regulating, cultural, and supporting services

Explanation: Lagoons provide a variety of ecosystem services, including provisioning, regulating, cultural, and supporting services, which are vital for the economy and well-being of communities.

B) High latitudes with intense glacial activity

Explanation: Fjords are specifically associated with high latitudes where glacial activity is intense, indicating their formation is closely linked to glacial processes.

B) It restricts water circulation with the open ocean

Explanation: The sill in a fjord restricts water circulation with the open ocean, preventing dense seawater from flowing up over the sill into the estuary.

C) Continuous oceanic and fluvial processes

Explanation: Estuaries are subjected to continuous oceanic (wave and tidal) and fluvial processes, which influence their dynamics and ecological characteristics.

C) Stratification

Explanation: Stratification is a key parameter included in the classification of estuaries under hydrodynamics, as it relates to the layering of water due to differences in density.

B) The separation of water masses based on density

Explanation: Stratification in estuaries refers to the layering of water masses based on differences in density, which can affect mixing and the distribution of nutrients and organisms.

B) A rapidly flowing river discharging into the ocean where tidal currents are weak

Explanation: Salt-wedge estuaries occur when a rapidly flowing river discharges into the ocean, particularly in areas where tidal currents are weak, leading to the formation of distinct water layers.

B) Storm surges and seiches

Explanation: Freshwater estuaries are storm-driven, with water levels often regulated by storm surges and subsequent seiches, which act like tides in exchanging water between the river and the lake.

B) Water sports and tourism

Explanation: Lagoons offer recreational opportunities such as water sports and tourism, which contribute to the local economy and enhance the quality of life for residents.

C) Slight mixing might occur

Explanation: At the boundary between fresh and saltwater in a salt-wedge estuary, slight mixing might occur, but the two water masses generally remain distinct due to their differing densities.

B) It acts like a plug, inhibiting mixing

Explanation: The salinity maximum zone acts like a plug, inhibiting the mixing of estuarine and oceanic waters, which prevents freshwater from reaching the ocean.

D) Tectonic

Explanation: Tectonic estuaries are formed as a result of tectonic activity, such as the sinking or uplifting of land, which creates basins that can be filled with seawater.

B) They contribute to tourism, fisheries, and recreational activities

Explanation: Estuaries have significant economic value, providing benefits through tourism, fisheries, and recreational activities, which are vital for local economies.

C) Freshwater only

Explanation: Freshwater estuaries do not contain saltwater; they are unique combinations of river and lake water, which are chemically distinct from brackish water.

C) They dilute ocean water with freshwater from land

Explanation: Estuaries are characterized by the dilution of ocean water with freshwater derived from land, creating a unique brackish environment.

B) 10 m

Explanation: Coastal plain or drowned river valleys are typically shallow, with depths on the order of 10 meters, which is a defining characteristic of these geological formations.

B) Water deterioration and harm to aquatic life

Explanation: A lack of tidal flushing can lead to water deterioration, particularly in terms of dissolved oxygen levels, which can negatively impact aquatic life within the estuary.

B) By absorbing flood waters and dissipating storm surges

Explanation: Wetland plants and soils in estuaries act as natural buffers, absorbing flood waters and dissipating storm surges, which helps protect coastal areas from extreme weather events.

B) It is highly stratified

Explanation: Fjords experience very little tidal mixing, which results in highly stratified water layers, with distinct differences in temperature and salinity.

C) Mainly in Norway, Chile, New Zealand, Canada, Greenland, and Alaska

Explanation: Fjords are primarily found in regions such as Norway, Chile, New Zealand, Canada, Greenland, and Alaska, with Norway having over 1,700 named fjords along its coast.

B) An estuary formed by the accumulation of sandbars

Explanation: Bar-built estuaries are formed when sandbars accumulate along the coastline, partially enclosing a body of water and creating a distinct estuarine environment.

B) In the western Pacific and parts of the Indian Ocean

Explanation: Circular/atoll/oceanic lagoons are commonly found in tropical regions, particularly in the western Pacific, parts of the Indian Ocean, and isolated areas in the Caribbean.