Coastal Environments

Coastal Environments

Why do coastal landscapes vary? Lithology (Rock Type): Hard rocks (granite + basalt) give rugged landscapes such as Giants Causeway in N. Ireland, whereas Soft Rocks (sands + gravels) give low flat landscapes like the Nile Delta. Geological Structure: concordant (Atlantic) or accordant (Pacific) coastlines occur where the geological strata lie parallel to the coastline. Whereas, discordant (Atlantic-type) coastlines occur where the geological strata are at right angles to the shoreline. Processes: Erosional landscapes contain many rapidly retreating cliffs, whereas areas of rapid deposition contain many sand dunes and coastal flats. Sea Level changes: interact with erosional and depositional processes to produce advancing coasts (those growing either due to a deposition and/or relative fall in sea level) or retreating coasts (those being eroded and/or drowned by a relative rise in sea level)Human impacts: some coasts are extensively modified whereas others are more natural Ecosystem types: such as mangrove, coral, sand dune, saltmarsh and rocky shores add variety to coastlines.

Coastal ZonesThe coastal zone includes all areas from the deep ocean (up to 320km offshore) to 60km inland. At the coast there is the upper beach or backshore (backed by cliffs or sand dunes), the foreshore (periodically exposed by the tides) and the offshore area (covered by water) The coastal zone is a dynamic area with inputs and processes from land, sea and atmosphere.

Wave, marine and sub-aerial processes Waves are a medium through which energy is transferred. They are created by the wind blowing across the surface of the sea. Frictional drag increases as the wind speed increases, making the wave bigger.Wave energy depends upon three things:The strength of the wind.The length of time the wind has blown for.The fetch of the wind (the distance it blows over).

The wave orbitThe wave orbit is the shape of the wave: varying between circular and elliptical. The orbit diameter decreases with depth to a depth roughly equal to wavelength, at which point there is no further movement related to wind energy this point is called the wave base.

Wave definitions Wave fetch: The distance of open water over which a wave has passed. Wave crest: Highest point of a wave.Wave trough: Lowest point of a wave.Wave height: Distance between trough and crest.Wave length: Distance between one crest/trough and the next.Swash: Water movement up a beach.Backwash: Water movement down a beach.

Why waves break When out in open water there is little horizontal movement of ocean water, the bulk of the motion is up and down or vertical. However, this changes slightly when waves approach the coastline. As the water approaches the coastline it encounters increasing contact with the shelving sea bed, which exerts a frictional force on the base of the wave. This changes the normal circular orbit of the wave into an elliptical orbit. As the waves gets closer and closer to the coast the impact of friction grows, with the top of the wave moving faster than the base of the wave. Eventually a critical point is reached where the top of the wave (the CREST) curves over and creates a breaking wave. This breaking wave can be further disrupted by water returning down the coastline back out to sea.

Type of breakers Spilling breakers: are associated with gentle beach gradients and steep waves (wave height relative to wave length) They are characterized by a gradual peaking of the wave until the crest becomes unstable; resulting in a gentle spilling forward of the crest. Plunging breakers: tend to occur on steeper beaches, with waves of intermediate steepness. They are distinguished by the shore-ward face of the wave becoming vertical, curling over, and plunging forward and downward as an intact mass of water. Surging breakers: are found on steep beaches with low steepness waves. In surging breakers the front face and crest of the wave remain relatively smooth and the wave slides directly up the beach without breaking. Once the breaker has collapsed, the wave energy is transmitted onshore as a wave of translation. The swash will surge up the beach, with its speed gradually lessened by friction and the uphill gradient. Gravity will draw the water back as the backwash gradient.

Breaker waves

Waves of translationConstructive waves: Constructive waves have a short amplitude and a long wavelength. They have a low frequency of around 6-8 waves per minute, particularly when these waves advance over a gently shelving sea floor (formed of fine material: sand). These waves have been generated far offshore creating a gradual increase in friction and thus a gradual steepening of the wave front. This creates a spilling breaker, where water movement is elliptical. As this breaker collapses, the swash surges up the gentle gradient with maximum energy.Constructive waves produce a strong swash, but a weak backwash, which produces a gentle beach as material is deposited but not removed from the beach.The supply of new material and the constant action of pushing the material up the beach eventually produces berms.

Waves of translation2. Destructive waves: Destructive waves are the result of locally generated windsThey have a high amplitude and a short wavelength. They also have a high frequency of 10-14 waves per minute, resulting in a steeply shelving coastline, where rapid friction and steep circular plunging breakers are formed. The waves have a strong backwash but a weak swash, so they remove a lot of material from the beach producing a steeper beach profile. The force of destructive waves can fire material to the back of the beach where a ridge known as a storm beach forms.

Processes and landforms in coastal areas Wave DominatedTide DominatedWind DominatedShore platformsCliffsBeachesSpitsDeltasMudflatsSand flatsSalt marches MangrovesDeltasSand dunesHigh Energy Low EnergyHigh Energy

Tides and the tidal cycleTides are regular movements in the seas surface the rise and fall of sea levels, caused by the gravitational pull of the moon and sun on the oceans. Out of the two, the moon accounts for the larger share of the pull. When the earth, moon and sun are aligned the gravitational pull is at its greatest. This creates a Spring tide. A Spring tide results in a high, high tide and low, low tide. This creates a high tidal range (difference between the highest and lowest tide). Low spring tides occur just after a new moon whereas high spring tides occur after a full moon - when the Sun and moon are aligned. When the sun and moon are at a right angle to the earth we experience Neap tides. The gravitational pull of the sun partially cancels the moons. This results in a low, high tide and a high, low tide. This creates a low tidal range and results in weaker tidal currents than normal.

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Types of tides

What influences tides? Tides are influenced by the size and shape of ocean basins. The characteristics of the ShorelineCariolis forcesAnd Meteorological conditions.

In General: Tides are greatest in bays and along funnel-shaped coastlines. In the Northern Hemisphere water is deflected to the right of its path. During low pressure systems water levels are raised 10 cm for every decrease of 10mb.

Tides and the tidal cycleThe difference between high tide and low tide is called the tidal range. Tidal range varies with distance from the amphidromic point (place where there is no tidal range) & according to the shape of the coast; the strength of tidal currents varies enormously.If the coast is funneled, a tidal bore can be created due to tide advances being concentrated in a narrow space. Coastal areas can be classified intoMicro-tidal: (very low tidal range less than 2m)Meso-tidal: (2-4m)Macro: (over 4m)

Tidal ranges influence on coastal processes: It controls the vertical range of erosion and depositionWeathering + biological activity is affected by the time between tidesVelocity is influenced by the tidal range and has an important scouring effect.

Rip Currents Rip currents are strong offshore flows, and often occur when breaking waves push water up the beach face. This piled-up water must escape back out to the sea as water seeks its own level. Typically the return flow (backwash) is relatively uniform along the beach, so rip currents aren't present. However, If there is an area where the water can flow back out the ocean more easily, such as a break in the sand bar, then a rip current can form. When water from the highest sections of breakers travels upshore upon returning as backwash it moves through the points where lower sections have broken, creating a strong backwash current. Once rip currents are formed they modify the beach by creating cusps which perpetrate the currents.

Rip currents

Discordant Coasts On a discordant coastline, alternating layers of hard and soft rock are perpendicular to the coast. Because the soft rock is exposed, it is eroded faster than the hard rock. This differential erosion creates headlands and bays along discordant coastlines.

Concordant CoastsConcordant coasts have alternating layers of hard and soft rock that run parallel to the coast. The hard rock acts as a protective barrier to the softer rock behind it preventing erosion. If the hard rock is breached though, the softer rock is exposed and a cove can form (e.g., Lulworth Cove).

Storm SurgesStorm surges are changes in the sea level, caused by intense low pressure systems and high wind speeds. For every drop in pressure of 10mb, sea water is raised by 10cm. Therefore during tropical cyclones, pressure may drop by 100mb resulting in a sea level rise of 1m! Storm surges can bring catastrophic consequences and are intensified on funnel shaped coastlines.

Storm Surge

Wave refractionIt is very rare for waves to approach a regular uniform coastline, as most have a variety of bays, beaches and headlands. Because of these features, the depth of water around a coast varies and as a wave approaches a coast its progress is modified due to friction from the seabed, halting the motion of waves.As waves approach a coast, due to the uneven coastline, they are refracted so that their energy is concentrated around headlands but reduced around bays. Waves then tend to approach coastline parallel to it, and their energy decreases as water depth decreases.However, due to the complexities of coastline shapes, refraction is not always fully achieved resulting in long shore drift (which is a major force for transporting material along the coast).

Coastal erosion processesHydraulic action: As waves break against the face of cliffs, any air trapped in cracks, joints and bedding planes is momentarily placed under great pressure. As the wave retreats this pressure is released with explosive force. This stresses the coherence of the rock, weakening it and aiding erosion. This is particularly obvious in well bedded rocks such as limestone, sandstone, granite and chalk, as well as poorly consolidated rocks such as clays and glacial deposits. It is most notable during times of storm wave activity.

Coastal erosion processes2.Abrasion/Corrasion: This is the process whereby a breaking wave hurls pebbles and shingle against the coast breaking bits off and smoothing surfaces. 3. Attrition: Takes place as other forms of erosion continue. Rocks and pebbles constantly collide with one another as they are moved by waves action, resulting in reduced size of beach material and increased roundness as the impact of 2 hitting smooth's away rough edges.

Coastal erosion processesSolution: Is a form of chemical erosion whereby rocks containing carbonates such as limestone and chalk are dissolved by weak acids in the water supplied by organisms such as barnacles and limpets. Calcium carbonate + weak acids = Calcium bicarbonate (soluble).

Sub-aerial processesSalt crystallization: The process whereby sodium and magnesium compounds expand in joints and cracks by 300% when temperatures fluctuate between 26-28 degrees thereby weakening rock structures. Freeze thaw= water becomes trapped in cracks in rocks, freezes when temperatures drop below 0 degrees and therefore expand by 10%. As they expand they put extra pressure onto the rock, until the ice melts when temperatures rise. After many repeated cycles the rock fragments and weakens. Biological weathering: where living organisms such as mollusks, sponges and sea urchins on low energy coasts physically break up structures. Solution weathering: the chemical weathering of calcium carbonate by acidic water, which tends to occur in rock pools due to the presence of organisms secreting organic acids.

Sub-aerial processes cont.Mass Movement: Mass movement can be defined as the large scale movement of weathered material in response to gravity. Essentially, its when a cliff or other structure that is not horizontally orientated has been weathered to the point at which it starts to collapse. Rock falls: Freeze thaw weathering on a cliff breaks the rocks up into smaller pieces which can then free fall. This occurs commonly on cliffs with lots of joints as the joints make it easier to break up the rock. If the cliff is undercut by the sea, it can loose some of its stability, increasing the likelihood that a rock fall will occur.Soil Creep: Soil creep is an incredibly slow process. It occurs on very gentle slopes and produces an undulated (wavy) surface. Damp soil moves very slowly down hill due to the increase in its mass (since its wet).Landslides : After being soaked by water, cliffs made from soft rock will begin to slip due to the rock being lubricated. (Rotational) Slumping: Slumping happens for similar reasons to landslides. Heavy rainfall makes the rock heavier due to it absorbing the water and the water also acts as a lubricant. The difference with slumping is that it happens on a concave surface, which causes the cliff to form a crescent shape.Mudflow: Mudflow is a very dangerous form of mass movement which occurs on steep slopes with saturated soil and little vegetation. The lack of vegetation means that there is nothing to bind the soil together, promoting mass wasting. The saturated soil becomes heavier and is lubricated, leading to the rapid movement of a lot of mud downhill.

Wave transportation:Traction: Grains slide or roll along the sea floor a low form of transport. In weaker currents sands may be transported, whereas in stronger currents pebbles and boulders may be transported. Saltation: Is when grains hop along the seabed in a skipping motion. Moderate currents may transport sand, whereas strong currents may transport pebbles and gravel. Suspension: Suspension is when grains are carried by turbulent flow and are held up in the water. Suspension occurs when moderate currents are transporting silts or strong currents transporting sands. Grains transported as wash loads are permanently in suspension and typically consist of clays and dissolved materials. Solution: Solution is when particles, invisible to the naked eye are carried in the waters current.

Longshore driftLongshore drift is a process responsible for moving significant amounts of sediment along the coast. This usually occurs in one direction as dictated by the prevailing wind. For example the prevailing wind along the Holderness Coast is north-easterly. As the result waves break on to the beach obliquely at an angle of around 45 degrees. The swash moves beach material along the beach and the backwash, under gravity, pulls the material back down the beach at right angles to the coastline. Over time this creates a net shift of material along the coast.

Sediment cells`The coastal sediment system or `littoral cell system is a simplified model that examines coastal processes and patterns in a given area. Each sediment cell is a self-contained cell in which inputs and outputs are balanced. There are 11 such cells around the UK.

Dynamic equilibrium The concept of dynamic equilibrium is important to Littoral cells. The concept states any system is as a result of inputs and processes operating within it. Changes to an input i.e.. Sediment increase, has a knock on effect on processes such as Longshore drift, and a resulting change in landforms will occur. The balance changes in sync.

Coastal landforms

Wave cut platform The sea cliff is the main landform along coasts where marine erosion is dominant. The basic formation of a sea cliff is the same everywhere. Waves attack the base of the newly exposed rock faces. By hydraulic action and abrasion, and the other processes of coast erosion, the base of the cliff is undercut to form a wave-cut notch. The rock face above the effects of wave action begins to overhang. As waves continue their relentless attack upon the base of the cliff, the size of the overhang increases until the weight of the rock above can no longer be supported and a section of the cliff collapses. Active marine erosion begins again at the base of the cliff after the waves have removed the loose rock, leading to further collapses and gradual retreat inland of the position of the cliff. Therefore every cliff coastline is a sign that land is being lost. As a consequence of cliff retreat another landform. The wave-cut platform, is formed.

Headlands and BaysHeadlands and bays, such as Swanage Bay, form on discordant coastlines, where hard and soft rock run in layers at 90 to the water. Alternating layers of hard and soft rock allow the sea to erode the soft rock faster, forming a bay but leaving hard rock sticking out, known as a headland. The altering rate of erosion of hard and soft rock is known as differential erosion. As the bay develops, wave refraction around the headlands begins to occur, increasing erosion of the headlands but reducing the erosion and development of the bay due to a loss of wave energy. Headlands and bays can form on concordant coastlines too, as has happened with Lulworth Cove, but this requires the rock to have already been weakened, possibly during an ice age. Irrespective of whether the coastline is concordant or discordant, as wave refraction takes place around the headlands and erosion of the bay is reduced, sub-aerial weathering such as corrosion and corrasion begins to weather the bay, furthering its development.

CliffsA cliff is a vertical, near vertical or sloping wall of rock or sediment that borders the sea. They generally differ in their angle of slope because of their rock structure and geology, but the processes involved in their formation are the same.They result from the interaction of a number of processes:Geological.Sub-aerial.Marine.Meteorological.Human activity.

CliffsRocks tend to form in layers of different rock types known as beds. These beds are subjected to tectonic forces that tilt and deform them so they dip at an angle. The angle the beds dip at affects how they are eroded and the profile of the resulting cliffs. As well as this rock structure plays an important role in variation between cliff profiles: Vertical dipping beds, produce steep cliffsBeds that dip seaward produce gentler cliffs but are less stable because loose material can slide down the bedding planes by mass movements. Landward dipping beds produce stable and steeper cliffs.

Cliffs

Where dip or foliation lies to seaward then the cliff face is inherently unstable. Removal or collapse of rock towards the cliff base leads to rock slides/land slides (depends on material)

Cliffs

Where rocks dip inland, steep, but sub-vertical and relatively stable cliffs form.

Cliffs continuedMany cliffs are composed of more than one rock type - these are known as COMPOSITE CLIFFS. The exact shape and form of the cliff will depend on such factors as strength and structure of rock, relative hardness and nature of waves involved:Cliffs that are composed of strong, hard rocks such as granite will be eroded slowly with little cliff retreat. Whereas, cliffs composed of weaker rock strength experience cliff retreat more rapidly.

Cliffs continued.Depending on the relative position of the weaker rock in composite cliffs determines the different landforms that are created. For example: If less resistant, weak rock is at the base of the cliff, undercutting and collapse may occur. If the less resistant rock is near the top of the cliff, it may be subjected to sub-aerial processes.

Cliffs cont.Cliff morphology also is influenced by the permeability of a rock. For example: Cliffs which have impermeable rock overlying permeable rocks limit percolation and therefore are more stable, preventing mass movement. Whereas, cliffs in which permeable rock overlies impermeable rock, water may soak into the cliff, making slope failure more likely as water builds up between the junction of the two rocks.

Cliffs continued Cliff form can also be related to latitude. In the tropics, low wave energy levels and high rates of chemical weathering produce low gradient casts. Coastal cliffs in high latitudes are also characterized by relatively low gradients since the per glacial processes produce large amounts of cliff base materials. Temperate regions tend to have the steepest cliffs. The rapid removal of debris by high energy waves prevents the build up of material at the base,.

BeachesThe term beach refers to the accumulation of material deposited between high and low tidal limits, which shelves downwards towards the sea. A typical beach has three zones BackshoreForeshoreOffshore A whole variety of materials can be moved along the coast by waves, fed by longshore drift. The coarse material is found deposited in the backshore and foreshore zones as littoral deposits. The finer material, worn down largely by attrition is usually found in the offshore zone as neritic deposits.

The Backshore: The backshore is a cliff or is marked by a line of sand dunes. Above and at HWM (high water mark) there may be a shingle/storm ridge. This is an area of coarse material pushed up the beach by spring tides, aided by storm waves which fling material well above the level of normal tidal waves. This coarse material then usually cannot be reached and remains largely untouched. There are often a series of smaller ridges formed beneath the storm ridge known as berms. These are build ups of finer material that mark the successive high tides that follow the spring tide through to the neap tide.The seaward edge of the berm is often scalloped and irregular due to the creation of beach cusps. Cusps are semi-circular depressions; they are smaller and more temporary features formed by a collection of waves reaching the same point. The sides of the cusp channel the incoming swash into the centre of the depression and this produces a stronger backwash which drags material down the beach from the Centre of the cusp. The spacing of cusps is related to wave height and swash strength.

Depositional landforms: Backshore/Foreshore

The foreshore: The foreshore is exposed at low tide. Ridges and runnels form parallel to the shore line in the foreshore zone.Ridgesare areas of the foreshore that are raised above the adjacent shore which dips into aRunnel. Ridge and runnel systems are formed due to the interaction of tides, currents, sediments and the beach topography. They only form on beaches with a shallow gradient. They form as a simple drainage route for tides. Water flows in and out via the runnel.

The offshoreOffshore, the first material is deposited. In this zone, the waves touch the seabed and so the material is usually disturbed, sometimes being pushed up as offshore bars, when the offshore gradient is very shallow.

Factors affecting beach formBeach form is affected by the size, shape and composition of materials, the tidal range and wave characteristics. As storm waves are more frequent in winter and swell waves more important in summer, many beaches differ in their winter and summer profile. Thus the same beach may produce two very different profiles at different times of the year. For example, constructive waves in summer may build up the beach but destructive waves in winter may change the size and shape of the beach. The relationship between wave steepness and beach angle is a two way affair. Steep destructive waves reduce beach angle whereas gentle constructive waves increase it. In turn, a low gradient produces shallow water which in turn increases wave steepness. Hence plunging waves are associated with gentle beaches whereas surging waves are associated with steeper beaches. Sediment size affects the beach profile through its percolation rate. Shingle/pebbles allow rapid infiltration and percolation, so the impact of swash and backwash are reduced. As the backwash is reduced it will not impeded the next swash. If the swash is stronger than the backwash then deposition may occur. By contrast, sand produces a lower angle and allows less percolation. Backwash is likely to be greater than on a gravel beach. The pattern is made more complex because sediment size varies up a beach. The largest particles, the products of cliff recession, are found at the rear of a beach. Large, rounded material on the upper beach is probably supplied only during the highest spring times and is unaffected by average conditions. On the lower beach wave action is more frequent, attrition is common and consequently particle size is smaller.

Depositional processes and features There are two types of coastlines Swash Aligned Coasts: are produced where the waves break in line (parallel) with the coast. Swash and backwash movements move material up and down the beach producing many coastal features. Swash aligned beaches are smoothly curved, concave beaches. Drift aligned coasts: beaches are produced where waves break at an angle to the coast. The swash therefore occurs at an angle but the backwash runs perpendicular to the beach. As a result, material is transported along the beach via longshore drift.

Drift aligned beaches transfer sediment along the beach due to the angle of wave approaching the shoreline on an angle, under the influence of prevailing winds. As a consequence, large wide beaches struggle to establish. However, these beaches are associated with a range of depositional features that develop along the coast, including spits. Prevailing wind brings waves in on an angle which is slightly reduced in the nearshore by wave refraction. As waves break, their swash transports sediment up the beach at angle but the backwash under the influence of gravity bring it back perpendicular. As a result sediment is transported down the beach in a zigzag pattern. Most sediment is suspended in the water but when moved by the breaking wave it is transported through saltation and traction. A strong current is also present in the nearshore, called the longshore current. Sediment is also transported in the longshore current. The current varies in strength from beach to beach but works like stream down within trough between the beach and an offshore bar. It is these offshore currents that explain the all-too-common experience, when bathing at the seaside, you enter the sea at one point but when you come out you realize that you have drifted some distance down the beach. Many a time as a child this caused me great stressAt breaks within the offshore bar, surfers will be all-too-familiar with the powerful rip-currents that developDrift Aligned Beaches

LOCALISED DEPOSITIONAL FEATURESBars, spits and other localised features develop where: Abundant material is available, particularly shingle and sand. The coastline is irregular due to for e.g. geological variety. Deposition is increased by the presence of vegetationThere are estuaries and major rivers.

Spit FormationA spit is a stretch of sand or shingle extending from the mainland out to sea. They develop where there is a sudden change in the shape of the coastline such as at a headland. Normally, longshore drift transports beach sediment along a coastline. When the shape of the coastline changes substantially however, longshore drift continues to transport material in the same direction rather than following the coastline. This transports the material out to sea. As the strength of the drift weakens away from the coastline, the sediment is deposited. Deposition can be brought about earlier near estuaries. The flow of water into the sea at an estuary is stronger than the drift, forcing the sediment to be deposited.The deposition of sediment forms a spit but its shape changes as a result of wave refraction. Refraction around the end of a spit curves it into a hook forming a recurved spit. As the area behind a spit is sheltered from waves and the wind, it provides the perfect environment for salt marshes to develop.Spits are eroded by the sea and wind but a constant supply of sediment from longshore drift ensures their continued existence. Events such as storms change the shape of a spit drastically over short periods of time though. During a storm event, erosion exceeds deposition so a lot of material is removed from the spit, changing its shape

Bar formationA bar is a ridge of material that is connected at both ends to the mainland. It is located above sea-level. If a spit continues to grow lengthwise, it may ultimately link two headlands to form a bay bar. These are composed either of shingle, as in the case of the Low Bar in Cornwall, or of sand, such as the nebrung of the Baltic coast.

Barrier Islands Barrier islands are natural sandy breakwaters that form parallel to a flat coastline. By far the worlds longest series is that of roughly 300 islands along the East and Southern coasts of the USA. The islands are generally 200-400 m wide, but some are wider. Barrier islands form only under certain conditions and America's eastern seaboard provides the ideal conditions for barrier islands Over the last 15000 years, the sea level has risen by 120m as glaciers and ice caps have melted. Wind and waves have formed sand dunes and beach ridges at the edge of the continental shelf. As the sea levels rose, the water broke through the ridges and dunes, flooding the low area behind it forming a lagoon. This resulted in the former dune area becoming an island. Constant action by waves and continuing rise in sea levels caused islands to migrate landward as sand was removed from the beach and deposited inland.

Tombolo If a ridge of material links an island with the mainland, this ridge is called a tombolo. An example of this is Chesil Beach on the south coast of England.

Cuspate Forelands Cuspate forelands consist of shingle ridges deposited in a triangular shape, and are the result of two separate spits joining, or the combined effects of two distinct sets of regular storm waves.

Sand dunesSand dunes form where there is a reliable supply of sand, strong onshore winds, a large tidal range and vegetation to trap the sand. Extensive sandy beaches are almost always backed by sand dunes because strong onshore winds can easily transport inland the sand that has dried out and is exposed at low water. The sand grains are trapped and deposited against any obstacle on land, to form dunes. Vegetation causes the wind velocity to drop, especially in the lowest few cm above the ground, and the reduction in velocity reduces energy and increases the deposition of sand. Dunes can be blown inland and can therefore threaten coastal farmland and even villages. Special methods are used to slow down the migration of dunes Planting of special grasses, such as marram which has a long and complex tap root system that binds the soil Erecting brushwood fences to reduce sand movementPlanting of conifers which can stand the saline environment

Sand dunes continuedThere are several conditions that need to be met for sand dunes to develop. First, a large supply of sediment is needed. The best place to get this is from a large tidal flat. An area with a large tidal range (a big difference between the high and low tide) will result in a lot of sand being exposed to the wind, ready to be transported. This brings us to our next condition. A (relatively) strong and continuous wind is needed to move sand grains and transport them inland via saltation. The best place to find strong winds that dont change direction is in areas that face the prevailing wind direction.With these conditions met, its now only a matter of time until a sand dune starts to form. Obstacles such as rocks or human rubbish are deposited at the strandlineessentially the high water mark. These objects block the wind causing sand grains that are being transported to be deposited. Over time, the sand grains will build up and encompass the object forming a very small embryo dune.Eventually pioneer species of plants will start to grow on the embryo dune. As they do so, they bind the sand together, increasing the stability of the dune. The vegetation itself also traps sand causing the embryo dune to grow even more. As the dune grows it becomes a foredune and a new embryo dune begins to develop in front of it. This is the beginning of a sand dune succession.

Sand dune succession

Sand dune successionSand is moved by the wind. However, wind speed varies with height above the surface. As most grains protrude above this height they are moved by saltation. The strength of the wind and the nature of the surface are important. Irregularities cause increased wind speed and eddying resulting in more material being moved. On the leeward side of irregularities, wind speed is lower, transport decreases and deposition increases. For dunes to become stable, vegetation is required. Plant succession can be interpreted by the fact that the oldest dunes are furthest from the sea and the youngest closer to shore. On shore conditions are windy, arid and salty. The soil contains few nutrients and mostly sand hence the fore dunes being referred to as YELLOW DUNES. Few plants can survive, although sea couch and marram can tolerate these conditions. Once the vegetation is established it reduces wind speed close to the ground level. The belt of no wind may increase to a height of 10mm. As grasses such as sea couch and marram need to be buried by fresh sand in order to grow, they keep pace with deposition. As the marram grows it traps more sand. As it is covered it groves more and so on. Once established the dunes should continue to grow as long as there is a supply of sand. However, once another younger dune, a fore dune, becomes established the supply of sand is reduced. As the dune gets higher the supply of fresh sand is reduced to dunes further back. Thus marram dies out. In addition as wind speeds are reduced, evapotranspiration losses are less and the soil is moister. The decaying marram adds some nutrients to the soil, which in turn becomes more acidic. In the slacks, the low points between the dunes, conditions are noticeably moister and marsh vegetation may occur. Towards the rear of the dune system grey dunes are formed (grey due to the presence of humus in the soil). The climax vegetation found here depend largely upon the nature of the sand. If there is a high proportion of shells (providing calcium) grasslands are found. By contrast, acid dunes are found on old dunes where the calcium has been leached out, Here acid loving plants such as heather dominate. Vegetation at the rear of sand dune complex is quite variable/.

DefinitionsEmbryo dune: The first part of the dune to develop. Stabilisation occurs via marram and Lyme grass, which act as traps for sand. Conditions are dry and plants adapt to this via long roots, or thorny leaves to reduce evapotranspiration.Yellow dune: Colour is due to a lack of humus, but with distance inland they become increasingly grey due to greater amounts of humus. Heights can reach 5m and plants include sand sedge, sea holly, and red fescue.Fixed grey dunes: Limited growth due to distance from beach. Far more stable as shown by existence of thistle, evening primrose, bracken, bramble and heather.Dune slacks: Depressions between dune ridges, which will be damp in summer and water-filled in winter. Species include water mint, rushes, and weeping-willow.Blow outs: Often evidence of over use by humans. Large 'holes' that appear in the dunes

Mudflats and SaltmarshesThe intertidal zone the zone between high tide and low tide experiences severe environmental changes in salinity, tidal inundation and sediment composition. Halophytic (salt-tolerant_ plants have adapted to the unstable, rapidly changing conditions. Salt marshes are typically found in three locations: Low energy coastlinesBehind spits and barrier islandsIn estuaries and harbor'sSalt accumulates in these situation's and on reaching sea level forms mud banks. With the appearance of vegetation, saltmarshes is formed. The mud banks are often intersected by creeks.

Salt marsh formationSalt marshes only form in low energy environments where there is shelter from the wind and waves. Depositional landforms such as spits can help provide this shelter. Salt marshes require a large input of sediment which can arrive from the sea and rivers. The most likely place along a coastline where youll find this sort of sediment input is near a tidal flat. The low gradient of a tidal flat means that any rivers that flow into it will very quickly deposit any sediment theyre transporting. At the same time, the periodic flooding of the tidal flat by the tides will deposit even more sediment.Over time, sediment accumulates and the elevation of the tidal flat increases in a process known as coastal accretion. This reduces the duration of tidal flooding allowing a small selection of plants to grow on the now developing salt marsh. These plants are halophyticthey love saltand are capable of surviving underwater for several hours a day. Theyre often called pioneer species because of their hardy nature and, well, pioneering growth on salt marshes. These plants, which include species of cord grass (Spartina) and glasswort (Salicornia)1, have several adaptations that not only help them thrive in saline environments but also help aid coastal accretion.Long blades of cord grass trap sediment that is too fine to settle out of water in a salt marsh, building up a muddy substrate. At the same time, the roots of the cord grass plant (that are long to tap into the water table) help stabilize already deposited sediment, aiding coastal accretion. Pioneer species such as Spartina alterniflora (a species of cord grass) are invasive plants that spread rapidly. Once these plants are introduced to a salt marsh, coastal accretion takes place quickly and the elevation of the salt marsh increases greatly. This creates new environments that are submerged by the tide for shorter periods of time, allowing even more species of plants and animals to colonise the salt marsh.

Factors affecting salt marshes

Coral Reefs

Coral reefsCoral reefs are calcium carbonate structures, made up of reef-building stony corals. Coral is limited to the depth of light penetration and so reefs occur in shallow water, ranging to depths of 60m. This dependence on light also means that reefs are only found where the surrounding water contain relatively small amounts of suspended material. Although corals are found quite widely, reef- building corals live only in tropical seas, where temperature, salinity and a lack of turbid water are conducive to their existence. Coral reefs occupy less than 0.25% of the marine environment, yet they shelter more than 25% of all known marine life, including polyps, fish, mammals, turtles, crustaceans and molluscs. There are as many as 800 different types of rock-forming corals. Some estimates put the total diversity of life found in, on and around all coral reefs at up to 2 million species.

The Development of CoralAll tropical reefs begin life as polyps tiny, soft animals, like sea anemones which attach themselves to a hard surface in shallow seas where there is sufficient light for growth. As they grow many of these polyps exude calcium carbonate, which forms their skeletonAs they grow and die these rock-forming corals create the reefs.Polyps have small algae zooxanthellae, growing inside them. There is a symbiotic relationship between the polyps and the algae (they both benefit from the relationship). The algae get shelter and food from the polyp, while the polyp also get some food via photosynthesis. This photosynthesis means that algae need sunlight to live, so corals only grow where the sea is shallow and clear.

Rate of growth in Coral reefsTropical reefs grow at rates ranging from less than 2.5cm 60cm per year, forming huge structures over incredibly long periods of time which makes them the largest and oldest living systems on earth. The 2600Km Great Barrier Reef off Eastern Australia was formed over 5 million years!!

Factors that influence the distribution of coral reefsTemperature: no reefs develop where the mean annual temperature is below 20c. Optimal conditions for growth are between 23-25C Depth of water: most reefs grow in depths of water less than 25m, so are generally found on the margins of continents and islands. Light: corals prefer shallow water because the tiny photosynthetic algae that live in the coral need light in return they supply the coral polyps with as much as 98% of their food requirements.Salinity: corals are marine organisms and are intolerant of water with salinity levels below 32 psu although they can tolerate high salinity levels (42 psu +) as found in the Red Sea or Persian Gulf.Sediment: sediment has a negative effect on coral it clogs up their feeding structures and cleansing systems and sediment-rich water reduces the light available for photosynthesis.Wave action: coral reefs generally prefer strong wave action which ensures oxygenated water and where there is a stronger cleansing action. This helps remove any trapped sediment and also supplies microscopic plankton to the coral. However, in storm conditions, the waves may be too destructive for the coral to survive. Exposure to air: coral die if exposed to air for too long therefore they are mostly found below the low tide mark.

Types of reefs

Types of Coral Reefs: Fringing ReefFringing Reefs are those that fringe the coast of a landmass. They are usually characterised by an outer reef edge capped by an algal ridge, a broad reef flat and a sand floored boat channel close to the shore. Many fringing reefs grow along shores that are protected by barrier reefs and are thus characterised by organisms which are best adapted to low wave energy conditions.

Barrier Reefs Barrier reefs occur at greater distances from the shore than fringing reefs and are commonly separated from it by a wide and deep lagoon. Barrier reefs tend to be broader, older and more continuous than fringing reefs. Barrier reefs forms as the oceanic island begins to sink into Earth's crust due to the absence of volcanic island building forces, the added weight of the coral reef, and erosion at the surface of the island. As the island sinks, the coral reef continues to grow upward.

Atoll Reefs Atoll reefs rise from submerged volcanic foundations and often support small islands of wave-borne detritus. Atoll reefs are essentially indistinguishable in form and species composition from barrier reefs except that they are confined to the flanks of submerged oceanic islands, whereas barrier reefs may also flank continents. There are over 300 atolls in the Indian and Pacific oceans but only 10 found in the western Atlantic.

Patch ReefDescribes small circular or irregular reefs that rise from the sea floor of lagoons behind barrier reefs or within atolls.

Origin: Charles Darwin theoryThe origin of fringing reefs is quite clear they simply grow seaward from the land. Barrier reefs and atolls, however, seem to rise from considerable depth, far below the level at which coral can grow, and many atolls are isolated in deep water. The lagoons between the barrier and the coast are usually 45-100m in depth, and often many kilometres in width and this requites some explanation. In 1842 Charles Darwin, explained the growth of barrier reefs and atolls as a gradual process, the main reason being subsidence (gradual sinking of land). In his book, Darwin outlined the ways in which coral reefs could grow upwards from submerging foundations. From this, it became clear that fringing reefs might be succeeded by barrier reefs and then by atoll reefs. A fringing reef grows around an island and as the island slowly subsides, the coral continues to grow, keeping pace with the subsidence. Coral growth is more vigorous on the outer side of the reef, so it forms a higher rim, whereas the inner part forms an increasingly wide and deep lagoon. Eventually the inner island is submerged, forming a ring of coral that is the atoll. Supporters of Darwin have shown that submergence has taken place, as in the case of drowned valleys along parts of Indonesia. However, in other areas, such as the Caribbean, there is little evidence of submergence.

Origin cont: Sir John Murrays theoryAn alternative theory was that of Sir John Murray, who in 1872 suggested that the base of the reef consisted of a submarine hill or plateau rising from the ocean floor. These reached within 60m of the sea surface and consisted of either sub-surface volcanic peaks or wave-worn stumps. According to Murray, as a fringing reef grows, pounded by breaking waves, masses of coral fragments gradually accumulate on the seaward side, washed there by waves and are cemented into a solid bank.

Origin: Dalys theoryAnother theory was that of Daly. He suggested that a rise in sea level might be responsible. A rise did take place in post glacial times as ice sheets melted. He discovered traces of glaciation on the sides of Mauna Kea in Hawaii. The water there must have been much colder and lower (about 100m) during glacial times. All coral would have died, and any coral surfaces would have been eroded by the sea. Once conditions started to warm, and sea level was rising, the previous coral reefs provided a base for the upward growth of coral. This theory helps account for the narrow, steep sided reefs that comprise most atolls, so of which have 75 slopes.

Which theory?!Darwins theory still receives considerable support. While Daly was correct in principle, it is now believed that erosion of the old reefs was much less rapid than previously believed, and that the time available during the glacial low sea-level stages was inadequate for the formation of these bevelled platforms. Much of the erosional modification is now believed to be due to sub-aerial karstic (limestone) processes such as carbonation solution.

The value of coral : $$$Coral reefs are among that most biologically rich ecosystems on Earth. Coral reefs resemble tropical rainforests in two ways: both thrive under nutrient-poor conditions (where nutrients are largely tied up in living matter), yet support rich communities through incredibly efficient recycling processes. Additionally, both exhibit very high levels of species diversity. However, corral reefs and other marine ecosystems contain a greater variety of life forms than do land inhabitants. Coral reefs are not only important for their biodiversity, they are important to people too: Seafood: in LEDCs, coral reefs contribute about of the total fish catch, providing food for up to a billion people in Asia alone. If properly managed, reefs can yield on average, 15 tonnes of fish and other seafood per km squared / year.New medicines: Coral reefs offer particular hope because of the array of chemicals produced by many of these organisms for self protection. Corals are already being used for bone grafts, and chemicals found within several species appear useful for treating viruses, leukaemia, skin cancer and other tumours. Other products: reef ecosystems yield a host of other economic goods, ranging form corals and shells made into jewellery and tourism curios to live fish and corals used in aquariums, and sand and limestone used by the construction industry. Recreational value: The tourism industry is one of the fastest growing sectors of the global economy. Coral reefs are a major draw for snorkelers, scuba divers and recreational fishers.Coastal protection: coral reefs buffer adjacent shorelines through wave action and the impact of storms. The benefits of this protection are widespread and range from maintenance of highly productive mangrove fisheries and wetlands to supporting local economies that are built around ports and harbours, which in the tropics is often sheltered by nearby reefs.

Human impact on Coral

Human impactOverfishingDestruction of the coastal habitatPollution from industry farms and households are endangering not only fish the leading individual source of animal protein in the human diet but also marine biodiversity and even the global climate. There are natural threats too Dust storms from the Sahara have introduced bacteria into Caribbean coralWhile global warming may cause coral bleaching.Many areas of coral in the Indian Ocean were destroyed by the 2004 tsunami. According the the World Resources Institute, 57% of the worlds coral reefs are at high or medium risk of degradation with more than 80% of SE Asias extensive reef systems under threat.

Coral Bleaching Reef-building corals need warm, clear water. Unfortunately pollution, sedimentation, global climate change and several other natural and anthropogenic pressures threaten this fundamental biological need, effectively halting photosynthesis of the zooxanthellae (algae inside polyps) and resulting in the death of the living part of the coral reef. Coral lives in a symbiotic relationship with algae called zooxanthellae. This algae lives within the coral animal tissue and carries out photosynthesis, providing energy not only for themselves but for the coral too. This algae is what gives coral its colour. However, when environmental conditions become stressful, zooxanthellae may leave the coral, leaving the coral in an energy deficit and without colour a process that is referred to as coral bleaching. If the coral is recolonized by zooxanthellae within a certain time, the coral may recover, but if not the coral will die. Coral bleaching can be caused by increases in water temperatures of as little as 1-2c above the average annual maxima. The shallower the water the greater the potential for bleaching. As well as being caused by unusually warm waters particularly if the water temperature exceeds 29c bleaching may also be the result of changes in salinity, excessive exposure to ultraviolet radiation and climate chance.

Climate change, coral and people About 500 million people depend on coral reefs for some food, coastal protection, building materials and income from tourism. Among these, about 30 million people are dependent on coral reefs to provide their livelihoods, build up their land and support their cultures. Global climate change threatens these predominantly poor people, with many living in 80 small developing countries. Human wellbeing will be reduced for many people in rapidly growing tropical countries: 50% of the worlds population are predicted to live on coasts by 2015. This growth is putting unstainable pressures on coastal resources. In 2009 the UN environmental programme estimated that coral reef area of 284000 km squared provides the world with more than $100 billion USD per annum in goods and services. Even moderate climate change will seriously deplete that value.

Evidence of climate change damage on coral reefsMass coral bleaching was unknown in the long oral history of many countries such as the Maldives and Palau, before their reefs were devastated in 1998. About 16% of the worlds corals bleached and died in 1998. In that year 500-1000 year old corals died in Vietnam, Indian ocean and Western Pacific. The hottest years recorded in the tropical oceans were in 1997/98- 2005. In this time major bleaching took place in Caribbean corals. The bottom cover of corals on Caribbean corals have dropped by more than 80% since 1977. The growth rate of coral species has declined by 14% on the Great Barrier Reef since 1990, either due to temperature stress of ocean acidification or both. Ocean temperature have risen in all oceans in the last 40 years as seen from satellite images and other measures over 135 years from the National Oceanic.

Sustaining CoralGlobal climate change seriously threatens the future of coral reefs. Current scientific thought is that coral reefs may become one of the first ecosystem causalities of climate change and could become functionally extinct if co2 levels rise about 450ppm which could happen by 2030. Having huge affects on the livelihoods of up to 500 million people. Global temperatures are expected to rise by at least 2 c leading to widespread coral bleaching, extinction of coral species, more fragile skeletons and greater risk of storm damage, making low lying coastal communities more vulnerable to coastal hazards. To avoid permanent damage and support people in the tropics it is recommended that.. The world community reduces the emissions of greenhouse gases and develops plans to sequester co2Damaging human activities (sedimentation, overfishing, blasting coral) are limited to allow coral to recover from climate change threats. Assistance provided to LEDCsLocal coastal management practices to be introduced. Strategies are developed to cope with climate change damage. Management, monitoring and enforcement of regulations improved etc.

Sustaining coral reefs

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Sustainable management of coastsHuman pressures on coastal environments create the need for a variety of coastal management strategies. These may be long-term or short term, sustainable or non-sustainable. Successful management strategies require a detailed knowledge of coastal processes. Rising sea levels, more frequent storm activity and continuing coastal developmental are likely to increase the need for coastal management.

Shoreline management plans (SMPs) SMPs are plans in England and Wales designed to develop sustainable coastal defence schemes. Sections of the coasts are divided up into littoral cells and plans are drawn up for the use and protection of each zone. Defence options include Do nothing Maintain existing levels of coastal defenceImprove the coastal defenceAllow retreat of the coast in selected areas.

Coastal management involves a wide range of issues Planning Coastal protectionCliff stabilisation Coastal infrastructure including seawalls, paths etc. Control of beaches and public safety Beach cleaning Pollution and oil spills etc.

Coastal defence Coasts are vulnerable locations that need protecting. They need protecting because of the economic value they bring to areas e.g. fishing, tourism and transport. Coastal erosion is mainly caused by hydraulic pressure, corrosion, Corrasion and wave pounding. However, sub-aerial erosion can also play an important role. Areas that are near to sea level and are made from soft rock are particularly vulnerable. If coastal erosion is allowed to happen, coastal roads, ports, holiday resorts, farmland and even whole villages may be lost.So how can coasts be protected? Through Hard and Soft engineering! .

Hard engineeringHard engineering techniques are typically used to protect coastal settlements. They are used to deflect the power of waves. These are highly visible solutions which help reassure coastal communities. However, they are are expensive to install and maintain. In addition to this by installing hard engineering solutions in one place this can have a detrimental effect further along the coast.Types of Hard engineering include the following:Cliff base management7. offshore breakwatersSeawalls8. rock strongpointsRevetments9. cliff face strategiesGabions10. cliff drainageGroynes11. cliff grading Rock armour

Types of ManagementAims/MethodStrengthsWeaknessesSeawallsLarge-scale concrete curved walls designed to reflect wave energyEasily madeExpensiveLife span about 30-40 yearsRevetmentsPorous designed to absorb wave energyEasily madeCheaper than seawallsLifespan limitedGabionsRocks held in wire cages absorbs wave energyCheaper than seawalls and revetmentsSmall scale

GroynesTo prevent longshore driftRelatively low costsEasily repairedCause erosion on downdrift sideInterrupt sediment flowRock armourLarge rocks at base of cliff to absorb wave energyCheapUnattractiveMay be removed in stormsOffshore breakwatersReduce wave power offshoreCheapDisrupt local ecologyCliff drainageRemoval of water from rocks in cliffCost effectiveDrains may become new lines of weakness; dry cliffs may produce Rockfall

Hard engineering coastal management

Hard engineering Sea walls These are the most obvious defensive methods. Sea walls are exactly that. Giant walls that span entire coastlines and attempt to reduce erosion and prevent flooding in the process. Theyre big, ugly and very expensive requiring constant maintenance so that they dont fail. They also produce a strong backwash in waves which undercuts the sea wall making their long term sustainability questionable.Traditionally, sea walls are large flat walls however more modern sea walls have a curved structure that reflects waves back into incoming waves, breaking them up and further reducing erosion.

GroynesGroynes are relatively soft hard engineering techniques. Theyre low lying wooden walls that extend out to sea. The idea of groynes is to capture sand that moves down the beach via longshore drift and help build up a larger section of beach in front of an area thats experiencing coastal erosion. The new beach will increase the distance that waves have to travel to reach the coast and, in the process, theyll lose most of their energy, reducing their impact. Groynes are pretty effective but they have one major drawback. Groynes will remove a lot of the sand thats present down-drift of the beach which will result in a thinner beach at this area. This, in turn, means that sections of the coast will be more exposed to erosion down drift of the groynes which can create new problems relating to coastal management.

GabionsGabions are quite simply bundles of rocks in a metal mesh. Theyre placed at the base of a cliff in an attempt to reduce the impact of waves on the cliff and prevent the cliff from being undercut. Theyre not particularly effective and theyre quite unsightly but theyre sure as hell cheap.

RevetmentsRevetments are concrete (or in some cases wooden) structures that are built along the base of a cliff. Theyre slanted and act as a barrier against waves not too dissimilar to a sea wall. The revetments absorb the energy of the waves, preventing the cliffs from being eroded. Revetments can be modified so that they have rippled surfaces, which further help to dissipate the wave energy. Revetments are normally successful at reducing coastal erosion but they are expensive to build. Once built however, they dont require as much maintenance as a sea wall.

Riprap/Rock armourRiprap are just rocks and stones that have been put against the base of a cliff. Theyre similar to gabions in their purpose but they arent bound together in a mesh. This makes them look slightly more appealing as they blend into the environment better however the rocks are susceptible to being moved by the sea.

BreakwatersBreakwaters are offshore concrete walls that break incoming waves out at sea so that their erosive power is reduced to next to none when they reach the coast. Breakwaters are effective but they can be easily destroyed during a storm and they dont look particularly nice.

Soft EngineeringSoft engineering techniques are low tech, low cost solutions that work with nature to reduce erosion. Theyre no where near as effective as hard engineering techniques but theyre far more sustainable.

Type of managementAims/MethodsStrengthsWeaknessesOffshore ReefsWaste materials e.g. old tyres weighted down, to reduce speed of incoming waveRelatively cost effectiveLong term impacts unknownBeach NourishmentSand pumped from seabed to replace eroded sandLooks naturalExpensive and short term solutionManaged RetreatCoastline allowed to retreat in certain placesCost effective; maintains natural coastlineUnpopular; political implicationsDo NothingCost effectiveUnpopular; political implicationsRed-liningPlanning permission withdrawn; new line of defences set back from existing coastlineCost effectiveUnpopular; political implications.

Soft Engineering Techniques

Soft engineering techniquesBeach Nourishment: This is where sand and shingle are added to a beach in order to make it wider. This increases the distance a wave has to travel to reach the cliffs and so the wave will lose more energy and have less erosive power when it reaches the cliffs. The sand and shingle has to be obtained from elsewhere and is normally obtained from dredging.Land Management: Land management is often used to help protect and rebuild dunes. Sand dunes act as a good barrier against coastal flooding and erosion and they can be exploited as a natural defence against the sea. In order to do so though, the dunes must be left relatively undisturbed so boardwalks are constructed and sections of sand dune systems are marked as out of bounds to the general public in order to reduce the erosion of the dunes by humans. Marshland Creation: Marshland can be used to break up the waves and reduce their speed, reducing the waves erosive power. The marshlands also limit the area which waves can reach preventing flooding. The marshlands can be created by encouraging the growth of marshland vegetation such as glassworts.Beach Stabilisation: The goal of beach stabilisation is the same as beach nourishments goal, to widen the beach and dissipate as much wave energy as possible before it reaches the cliffs. Beach stabilisation involves planting dead trees in the sand to stabilise it and lower the profile of the beach while widening the beach too.

Pros and Cons of Coastal Defence!Disadvantages Advantages Cost of buildingMaintenance and repairIncreased erosion downdrift due to beach starvation or reduced longshore driftReduced access to beach during worksReduced recreational valueSmaller beach due to scourDisruptions of ecosystemsVisually unattractiveProtected buildings, roads and infrastructure (gas, water, sewerage, electricity services etc.)Land prices risePeace of mind for residentsEmployment on coastal defence works.

Relationship between human activities and coastal problemsHuman ActivityAgents/ConsequenceCoastal Zone ProbsUrbanisation and transportLand use changes for ports/airportsRoad, rail and air congestionWater abstractionWaste disposalLoss of habitats and species diversityLowering of groundwater tableWater pollutionEutrophicationAgricultureLand reclamationFertiliser & pesticidesLoss of habitatsWater pollutionEutrophicationTourism + RecreationDevelopment of land useWaste water disposalLoss of habitatsWater pollutionHuman health risksFisheriesPort constructionFishing gearFish farmsOverfishingHabitat damageChange in marine communitiesIndustryLand use changesPower stationsExtraction of natural resourcesLos of habitatsWater pollutionDecreased input of fresh waterCoastal erosion

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