Coastal Fluxes in the Anthropocene: The Land-Ocean Interactions in the Coastal Zone Project of the I

In global coastal zones, the major fabric of goods and services for and the LOICZ II (Land-Ocean Interactions in the Coastal Zone) Project.
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Palm Jumeirah Island was created using 0. Palm Jebel Ali island was created using 0. Palm Deira island, when completed, will have used 2. The fourth example is the construction of the How large is 0. The Great Wall of China is approx. The major means to reduce the delivery of river sediment to the coast is through sediment retention in reservoirs [ 24 ].

Large reservoirs on average offer trapping efficiencies of 80 per cent [ 25 ]. Prior to , there were eight dams in China: There were no dams in Each reservoir affects the conveyance of sediment to the coastal zone to some degree. Type examples of the impact of dams include the Nile and Colorado [ 26 ], Yenisey [ 27 ], Ebro [ 28 ], Danube [ 29 ] and Sao Francisco [ 30 ]. Except for coastal lagoons enclosed by barrier islands and spits, most of the water bodies are man-made reservoirs. This enhanced satellite Moderate Resolution Imaging Spectroradiometer Terra image taken on 15 January is processed from near-infrared wavelengths.

Black is clean water; blue defines water with high suspended-sediment concentration. The BQART model inherently incorporates the scaling of sediment production chemical, mechanical and human erosion , sediment storage lakes, reservoirs, floodplains and flood-wave dynamics, 2. The BQART formula provides a value on average within 38 per cent of the measured loads on global rivers that drain 63 per cent of the global land surface. BQART is particularly aimed at capturing the wash load, as the observations were mostly from gauging stations near river mouths.

The formula has since been shown to be successful in predicting the within-basin suspended load [ 33 ]. Rivers also deliver a coarser load in contact with the channel bed, known as bedload, which ranges from less than 1 to 20 per cent of the total sediment load for locations near river mouths, with a global average of 6. Applying BQART using modern climatology and no human influences appendix A , the pre-human suspended-sediment load or discharge to the coastal ocean is calculated as To calculate this sediment discharge as affected by humans, two datasets are merged: The twentieth century global sediment load is calculated to be Flux of river water Q and sediment Q s for pre-Anthropocene and Anthropocene conditions ca late twentieth century after [ 35 ].

These values represent continental coastline fluxes. Unfortunately, we have modest information on the historical variation in the sediment load of rivers: Some rivers show loads increasing during the twentieth century e. Others such as the Yellow [ 6 ], Po [ 36 ] and Mississippi [ 37 ] had early increases in their sediment loads owing to human impact, but have since strongly decreased owing to the proliferation of dams and diversions within their drainage basins.

This pattern is similar to the eastern seaboard of the USA [ 38 ], where pre-European settlement pre saw sedimentation rates in estuaries increase eight times through early deforestation and agriculture — , increase another three times during the period of peak deforestation and intensive agriculture — and finally reduce 10 times during the period of dam building and urbanization to present.

Relative changes in the sediment loads carried by select rivers. Note that climate variability has been removed from these trends, by taking averages across 10—20 years. Danube, Yenisey are carrying much less sediment [ 22 ], and some rivers transport virtually no sediment: Sediment interception by reservoirs has reduced the global sediment delivery to the coast by about 10 years of pre-dam sediment transport.

River pathways were thus fixed in location with stop-banks and levees. Some rivers are free to meander between these stop-banks within widths 10— times narrower than the natural floodplain widths. Other rivers even have their meanders fixed in space with hardened channel banks. Extensive flooding and the deposition of cover deposits accompanied channel switching, until a new route was notched into the floodplain.

Loss of life and infrastructure forced fifteenth to nineteenth century Chinese engineers to spatially fix the Yellow river within artificial levees, during the time when soil erosion of the Loess Plateau was near its maximum [ 6 ]. When the levees failed, a crevasse splay grew until the levee was repaired.

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Yellow River Huanghe floodplain. Channel 1 is the main route between AD and AD SRTM data have been modified to accentuate low-level topography.

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The post Yellow delta is one of a number of global deltas e. Po, Ebro, Colorado in Texas that have formed during the Early Anthropocene period of elevated sediment loads [ 34 ]. These same deltas and many others have entered a destructive phase, concomitant with the upstream sediment sequestration in reservoirs, and accelerated compaction.

For many deltas, aggradation rates have either substantively decreased or nearly eliminated e. In addition to sediment sequestration in upstream reservoirs, the sediment flux across a delta plain is engineered through stop-banks to bypass the floodplain and directly enter the coastal ocean [ 30 ]. Deltas are also subsiding faster than in pre-Anthropocene times, as humans mine for groundwater and petroleum and thereby collapse their structure [ 40 ]. The Chao Phraya, Niger and Po are type examples [ 39 ]. Some deltas now suffer from virtually no aggradation and very high rates of accelerated compaction e.

The relative rate of sea-level rise on selected deltas is many times faster than the ambient pre-Anthropocene sea-level rate of less than 0. Deltaic subsidence relates to natural and accelerated compaction, greatly reduced aggradation and the weight of the sediment load of the delta isostasy. Humans have also reduced the number of distributary channels that carry floodwaters across deltas, in aid of year-round shipping [ 30 ].

Fewer channels decrease the rate of delta-plain aggradation, locally increasing the rate of coastal-zone sedimentation near the remaining channel mouths, but also increasing the rate of coastal erosion in areas that once received distributary sediment flux [ 41 ]. Distributary channels divide up the discharge from the main stem and thereby increase the hydraulic radius over which the river water flows [ 32 ]. Consequently, the velocity of effluent in a set of distributary channels is reduced relative to a main stem flow, along with its inertial ability to transport sediment away from the coast.

With reduced momentum to power the seaward-flowing plumes emanating from these distributary mouths, more suspended sediment is trapped near these river mouth. As humans have reduced the number of distributary channels, greater dispersal of the fluvial-suspended load would occur. However, dam operations have reduced the magnitude of the seasonal flood wave [ 34 ] and consequently the dispersal of river sediment. If sediment retention on deltas is reduced i. From a coastal-ocean perspective, this may in fact make up for the lower conveyance of sediment to the delta owing to up-stream sequestration of sediment in reservoirs.

Human influence on sediment dispersal is at the very least complex. Most rivers deliver their sediment load through momentum-driven surface hypopycnal plumes given the strong density barrier to freshwater entering the coastal ocean.


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A river plume and its sedimentation depend on the discharge magnitude, the rate particles flocculate, the settling velocities of the flocs and the ambient currents and density structure including bottom boundary-layer dynamics. Rivers that carry the requisite sediment concentration for hyperpycnal activity are typically small mountainous rivers that directly enter the ocean without an intervening floodplain. Hyperpycnal flows differ from surface plumes in that they hug the seafloor; bathymetry plays an important role in defining the flow path, along with ambient bottom currents as influenced by coastal upwelling or downwelling [ 45 ].

The bathymetry of shelves often offers a steeper gradient than the riverbed, and it is not uncommon for a hyperpycnal current to accelerate and become erosive as it plunges into the coastal ocean [ 46 ]. In contrast, surface plumes are more influenced by coastal winds, ambient surface currents, river momentum and buoyancy [ 47 ].

The pre-Anthropocene sediment concentrations of the Yellow River, for example, would have been 5—10 times less than the twentieth century concentrations, assuming modern climatology. Thus, the pre-Anthropocene Yellow River would have generated only hypopycnal plumes [ 43 ]. The Waipaoa River, New Zealand, experienced an eightfold increase in its sediment load for the last years over the pre-Anthropocene flux [ 52 ].

Specifically, the establishment of Polynesian settlements years ago was associated with an increase in suspended-sediment discharge by per cent, whereas the wholesale land-use changes effected by European colonists initially caused suspended-sediment discharge to increase by per cent, and by per cent once the headwaters were deforested [ 52 ].

Model simulations show that 25 per cent of the total sediment discharge of the Waipaoa into the coastal ocean is presently via short-lived hyperpycnal flows, a process that began in the s [ 53 ]. Prior to that for the previous years, only four hyperpycnal floods occurred. Other studies have shown the increased likelihood of Anthropocene hyperpycnal activity when, in more pristine times, a river was unlikely to generate hyperpycnal discharges e. In contrast to these situations, the Apennine Rivers of Italy have lost most of their capability of producing hyperpycnal flows owing to dam operations [ 36 ], as has the Tet River with the onset of dam operations [ 55 ].

While the role of agricultural practices on soil erosion has been well studied, only recently has the role of resuspension by bottom trawling on continental shelves been investigated. Areas of strong fishing activity can modify the scale of natural disturbance by waves and currents [ 56 ].

The impact of bottom trawls on fine sediment resuspension per unit surface is comparable with that of the largest storms, and is responsible for more than 30 per cent of the total export of suspended sediment from the shelf of the Gulf of Lions [ 56 ]. Unfortunately, the global impact of seafloor trawling on the magnitude of sediment disturbance has not yet been made, but is expected to be large. Major impacts by humans on soil erosion began years ago following growth in human population in a few river basins. Impacts accelerated more widely years ago.

By the sixteenth century, soil disturbance was rampant as modern societies began engineering their environments. By the early twentieth century, mechanization related to Earth removal, mining, terracing and deforestation led to global signals in increased sediment discharge in most large rivers.

By the s, this sediment-discharge signal reversed for most major rivers owing to the proliferation of dams. A trend of subsidence outstripping sedimentation began in the s for some deltas and for many deltas has become a dominant signal in terms of relative sea-level, overwhelming even the global warming imprint on global sea level. These collective impacts have given rise to major changes on how water and sediment flows across continents and is subsequently discharged into the sea.

The marine environment remains cloaked in mystery, being largely hidden from satellite surveying. Simplified calculations on the phenomena of trawling suggest that even continental shelves have received a significant Anthropocene impact.


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    4. Other studies support this sediment-flux magnitude-level comparison [ 57 ]. This Anthropocene signal deal is thus much broader than the recent global warming signal much discussed by governments. Further, because the human imprint on sediment flux to and through coastal environments is a developing story with complex scenarios, its impact remains under-appreciated. Discussions with John Milliman and Bob Meade have led to insights incorporated in this article. L is the basin-averaged lithology factor defined as: For example, water storage schemes and managed retreat schemes along coastlines have been proposed and enacted as soft-engineering works, for dealing with long-term problems in a environmentally friendly and sustainable way.

    Dredging mainly causes physical disturbance and may result in the redistribution of contaminants through release from the sediment. Offshore sand mining for beach nourishment and land reclamation and aggregate extraction for the construction industry causes temporary disturbance of benthic communities and in some cases permanent loss of habitats. Contaminants might be resuspended and remobilised from sediments and create new entries in the food web. Any increase in suspended matter will impede growth of filter feeding organisms bivalves and alter the burial capacity of benthos.

    It is well known that changes in substrate quality are synonymous to changes in the structure of benthic communities. The bulk of material disposed in the sea comes from dredging of navigation channels. Sewage sludge dumping increases the fallout of organic material and associated contaminants to the seafloor.

    It can contribute to eutrophication in coastal waters, see Eutrophication in coastal environments and other links in this article. Marine litter is derived from land-based and marine sources. It is found in large quantities on the coastal seabed, floating in the water column and on the shore. It is brought to the sea by rivers but originates also from activities at sea such as shipping, fishing and mariculture or recreation and tourism. Entangling and drowning of biota birds, mammals may happen and inflict physical injury to animals turtles or even an obstruction of digestive system after ingestion of plastic objects.

    Once in the food-web, plastics release toxic substances.

    Land–Ocean Interactions in the Coastal Zone: Past, present & future - ScienceDirect

    Containers or all sorts bottles, boxes will host alien species and help in the transportation of invasive species, see the article Non-native species invasions for an introduction to this topic. Flow of fresh water and entrained materials to the coastal zone has been grossly altered by human activities [4]. In some arid regions where freshwater is diverted for irrigation, the discharge to the coastal zone has diminished to a small fraction of the natural flow.

    In other regions the issue is management of water, as the seasonal pattern of discharge has been greatly modified. Either water loss or alteration of the seasonality of discharge can have major impact on coastal ecosystems. Human activities have also altered the patterns of sediment discharge. In some regions increased soil erosion has occurred associated with human land use especially agriculture and has led to increases in sediment delivery. However, in most cases an overriding effect has been increased trapping of sediments in water reservoirs.

    Thus, some regions experience artificially elevated sediment discharge, whereas many others experience severe diminution. Either change can be detrimental to ecosystems acclimated to receive a particular level of sediment load. For example, severe erosion without sediment replacement may occur in systems poised to receive high sediment loads.

    By contrast, ecosystems such as coral reefs are generally acclimated to low sediment discharge, and large amounts of sediments can bury or otherwise damage reefs. Human activities have generally led to increased discharges of pollutants which affect water quality. Some countries have done better than others in effectively regulating and controlling these discharges. Although not as obvious as river discharge, continental ground waters also discharge directly into the sea. Like surface water, groundwater flows down-gradient.

    Therefore, groundwater flows directly into the ocean wherever a coastal aquifer is connected to the sea. Furthermore, artesian aquifers can extend for considerable distances from the shore, underneath the continental shelf. In some cases, these deeper aquifers may have fractures or other breaches in the overlying confining layers, allowing groundwater to flow into the sea. If polluted, groundwater flow into the sea will contribute to marine pollution.

    Coastal areas provide recreation opportunities for local people and for tourists who travel at present the whole world. Tourism causes pressures on coastal ecosystems by excessive influx of visitors. People movements rely on transportation systems which range from pathways for walkers to landing strips for airports. These movements contribute to the wandering of pests, construction and building with associated pollution and eutrophication and disposal of litter and other waste in tourist areas. The paradox is that, most often, tourism will disturb and threaten local populations and wildlife and their habitats, which attracted them to the area in the first instance.

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    Beaches are important areas for tourism. However, the increasing population and standard of living push many areas beyond their sustainable limits, both from a tourism and environmental point of view. In beach tourism there are clear feedback mechanisms: Tourism, a major source of income for many coastal communities, can have major effects on coastal environments unless the scale and type of activities are controlled. Biodiversity reduction, resource depletion, and human health problems may result from the accumulated environmental effects. Setting maxima to tourist numbers is a proper managerial measure, however, once these maxima are reached, pressure to relax the restrictions increase.

    Clear definitions of maxima, and scientifically adopted calculation methods are still lacking. Recreational boating increases with the increasing standard of living, and in some countries harbours and marinas built primarily for recreational use by small boats may disturb more of the coastal zone than commercial and industrial use.

    Sediment flux and the Anthropocene

    The environmental impacts of marinas and small harbours depend on site location, design, construction methods, and 'house-keeping'. Careful site planning can help avoid or minimize many of the impacts. Seabirds and marine mammals, particularly cetaceans , offer excellent opportunities for ecotourism in many parts of the world. Seabird colonies and seal rookeries are spectacular and increasingly popular places to visit. In many places around the world, whale watching trips are organized or specific advice is given by tourism organisations as to where and how whales can be observed from headlands and coastal promontories [5].

    This rapidly growing interest for ecotourism has been reason for concern [6] [7] [8]. Subsequently, codes of ethics and best practice guidelines for ecotourism have been published and most of the major tourism organisations have formally declared to follow such guidelines. This topic is further developed in Impact of tourism in coastal areas: The coastlines of many countries face high risks of damage from certain types of natural disasters. A major concern is death and property loss by winds and flooding by hurricanes or cyclones. Along many densely populated coastlines, the risks of natural disasters are being increased by population growth and unmanaged development projects, including residential urban development [2].

    Coastal natural disasters cut across all economic sectors. Wind or water damage from a cyclone hurricane , flooding by tsunami, wreckage from an earthquake, or coastal erosion from storms can affect tourism, fishing, port operations, public works, transportation, housing and industry. Tropical cyclones hurricanes form over the warm oceans at least 26 o C mainly over the western parts where no cold currents exist. Apart from wind and rain, a major impact is from the associated storm surge and storm waves. These have been responsible for major loss of life particularly in low lying densely populated coastal areas such as Bangladesh or China.

    Tsunamis are quite a different phenomenon and are associated with subsea earth movements. However, their speed and height can cause extensive coastal destruction with little warning and some distance from their origin see: