CONTENTS / Oiled Wildlife Response / Habitats:
The River Thames, Habitats and Oiling
Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption
Click here to return to Wildlife: Oil Spill Response CONTENTS
CONTENTS

Introduction and General Information

"The physical impact and fate of a spill will depend on the type of oil, location of the event, and climatic conditions. Estuaries and salt marshes are particularly sensitive because they trap oil and thereby delay or prevent it from weathering." (B368.1.w1)

The River Thames winds all the way through London, through 17 London Boroughs, and out into the Thames Estuary. The Tidal Thames includes all of the Thames downstream from Teddington Lock. Within the Tidal Thames different areas are considered to be freshwater (upstream of Lambeth), brackish (between Lambeth and the confluence with the River Darent) and marine (further seaward).

The River Thames is an important water feature through London. It is important for shipping and it is also important for birds. While the majority of the sites of particular importance for birds are outside Greater London, the river, its tributaries, and adjacent waters and wetlands within Greater London do provide important habitats for birds, and are also used by certain mammals.

Birds use the Thames as a migration corridor and as a feeding site. (J322.56.w1) The Thames is particularly important in severe winters and cold spells, because it provides an area of ice-free water for wintering water birds. (J322.53.w1)

The River Thames is an important recovering ecosystem; many fish and aquatic invertebrates are found within the river and marine mammals sometimes venture up the river into London.

The Thames Estuary is one of the five most important sites in the UK for wintering water birds, holding internationally important numbers of dark-bellied Brent geese (Branta bernicla - Brent goose), Haematopus ostralegus - Eurasian oystercatcher, Charadrius hiaticula - Ringed plover, Pluvialis squatarola - Grey plover, Calidris canutus - Red knot, Calidris alpina - Dunlin, Limosa limosa - Black-tailed godwit, Limosa lapponica - Bar-tailed godwit, Tringa nebularia - Common greenshank and Tringa totanus - Common redshank, as well as nationally important numbers of various other species. (B45)

Published Guidelines linked in Wildpro General Oil Spill Effects & Response Documents

Thames/ London Wetlands Habitats Documents:

Return to top of page

Key Habitats of the Tidal Thames

The following table, taken from the Tidal Thames Habitat Action Plan, lists key habitats of the Tidal Thames in London, Kent and Essex:
Habitat Site Examples Description
Artificial Structures/ Built Areas Concrete Barges, Rainham, LB of Havering Redundant or low disturbance structures exposed at high tide, providing roost sites for wildfowl, and some also serve as nest sites for oystercatcher [Haematopus ostralegus - Eurasian oystercatcher] and gulls.
Flood Embankments Dartford Marshes, South Thames Estuary and Marshes (Higham, Cliffe, Cooling, Grain and Allhallows), Dartford Creek Vegetated earth embankments, valuable for specialised plant and insect populations.
Gravel Foreshore Isleworth, LB of Hounslow Intertidal substrate comprising gravel and sands.
Islands Chiswick Eyot, LB of Hounslow Mid-channel islands, some densely vegetated with trees and scrub, others dominated by tall herbaceous vegetation. Most serve as roost sites and some wooded islands e.g. Isleworth Ait are important for nesting grey heron [Ardea cinerea - Grey heron]. Several islands also support rare molluscs.
Mudflats  Mucking Flats, Blyth Sands, Yantlet Flats, Benfleet & Southend Marshes Intertidal substrate comprising mud and sands. Rich source of invertebrates (shellfish, worms and crustaceans) and provide feeding grounds for large numbers of wintering waterfowl. Priority habitat under the UK BAP.
Natural riverbank  Syon Park, LB of Hounslow Inter-tidal and terrestrial habitat forming the transition between the river and land.
Open Water Royal Docks, LB of Newham Adjacent areas of open water, valuable for high tide roosts, breeding sites (common tern [Sterna hirundo - Common tern]) and refuges for fish fry.
Reedbeds  LB of Newham; LB of Barking and Dagenham  Expanses of reed along the main river and within creeks.
River Walls  Strand-on-the-Green, LB of Hounslow Vertical walls of timber, brick and concrete which can support a wide diversity of plants and invertebrates.
Saline lagoons Cliffe Pools Saline lagoons at Cliffe represent 10% of the English resource of this habitat. They support nationally important numbers of invertebrates and are also important for feeding and roosting waterfowl. Priority habitat under the EU Habitats Directive. Subject of HAP under the UK BAP.
Saltmarsh Rainham, LB of Havering; Higham Saltings, Cliffe Creek, Yantlet Creek, Benfleet & Southend Marshes Transitional mud habitat in the mid to lower river, predominantly vegetated, ranging from inter-tidal to terrestrial communities. Important feeding and roosting areas for wintering waterfowl. Priority habitat under the UK BAP.
Seagrass beds (Zostera spp.) Nr. Two Tree Island close to Canvey High to mid-shore. Support many invertebrates and are spawning grounds for fish. UK BAP and Local BAP priority habitats.
Semi-natural grasslands of Thames Terrace Sand & Gravels Broom Hill, Northwick Road Canvey Island, West Thurrock Lagoons, Old sand & gravel extraction sites A combination of unimproved, often flower-rich grassland areas for invertebrate foraging and hunting combined with open sandy free draining soils, south-facing banks and slopes for nesting.
Sublittoral sands and gravels Putney, LB of Wandsworth Sands and gravels found below the lowest tides, continuously submerged loose sediment. Habitat for invertebrates and spawning substrate for fish e.g. smelt. Priority habitat under the UK BAP.
Tidal Creeks Deptford Creek – LB of Lewisham/ Greenwich, Holehaven Creek (Essex), Yantlet Creek - (Kent) Tidal areas at the mouths of tributary rivers acting as ‘mini-estuaries’ and providing off-line refuge for fish. Support much of the remaining saltmarsh in the lower part of the Estuary. Provide sheltered feeding and roosting habitat for waders and wildfowl.

The Tidal Thames Habitat and Species Audit (D170) lists the following important tidal creek systems: 

  • "Deptford Creek (south bank of the Thames - confluence of the river Ravensbourne)
  • Bow Creek - River Lee (north bank at Canning Town)
  • Barking Creek - River Roding - north bank at Barking)
  • Cliffe Creek (south bank at Cliffe)
  • Mucking creek (north bank at Mucking)
  • Holehaven Creek (north bank west of Canvey Island)
  • Bentfleet Creek (incorporating Oyster Creek & Smallgrains Creek) (north bank east of Canvey Island)"

(D170)

  • Of these, the last four are considered to be the most ecologically valuable, with extensive mosaics of inter-tidal mud and saltmarsh habitats, general isolation and lack of disturbance by human activity, making them locally valuable as feeding, roosting and breeding habitat for various waders and waterfowl. (D170)
  • Deptford Creek is noted to hold the nationally rare Phoenicurus ochruros - Black redstart. (D170)
Associated techniques linked from Wildpro

Return to top of page

Statutory Conservation Areas

The whole of the River Thames and its tidal tributaries are considered a Site of Metropolitan Importance: "River Thames and Tidal Tributaries Site of Metropolitan Importance SMI - The River Thames supports a diverse mix of habitats, including open water, intertidal mud, sand, shingle and small areas of relatively poor saltmarsh. The SMI is particularly important for a range of bird and fish species,  including Common Tern (Sterna hirundo), Reed Warbler (Acrocephalus scirpaceus) [Acrocephalus scirpaceus - Eurasian reed-warbler], Grey Heron (Ardea cinerea) [Ardea cinerea - Grey heron] and Teal (Anas crecca) [Anas crecca - Common teal], and Bass (Dicentrarchus labrax), Eel (Anguilla anguilla) and Flounder (Platichthys flesus)." (D225)

The following table, taken from the Tidal Thames Habitat Action Plan, lists statutory conservation areas along the Tidal Thames.

Site Description Designation
Barn Elms [The Wetland Centre, WWT]
Former reservoirs, now wetland
nature reserve
SSSI
Benfleet and Southend Marshes 
Mosaic of habitats including grazing
marsh and inter-tidal areas
SPA, Ramsar, SSSI
Chiswick Eyot
Island supporting osier and reedbed  LNR
Crayford Marshes
Coastal Grazing Marsh SSSI (p)
Crossness Nature Reserve
Grazing marsh and reedbed  LNR
Dartford Marshes 
Coastal Grazing Marsh and fresh
marsh
SSSI (p)
Duke’s Hollow  Hydrocere flora and wet woodland
supporting rare molluscs
LNR
Ham Lands
Flood Meadow  LNR
Holehaven Creek Tidal 
Creek with a mosaic of habitats
including mudflats and saltmarsh
SSSI [status now confirmed]
Inner Thames Marshes
Grazing marsh and reedbed SSSI
Lonsdale Road Reservoir
Former reservoir now nature reserve  LNR
Medway Estuary & Marshes 
Mosaic of habitats including grazing
marsh and inter-tidal areas
SPA, Ramsar, SSSI
Syon Park
Tidal Flood Meadows  SSSI
Thames Estuary and Marshes
(comprises of South Thames Estuary
& Marshes, and Mucking Flats &
Marshes SSSIs)
Mosaic of inter-tidal habitats,
saltmarsh, coastal gazing marsh,
saline lagoons and chalk pits

SPA, Ramsar, SSSI
West Thurrock lagoons and Marshes
SSSI
Saline lagoons and grazing marsh  SSSI

Key: LNR – Local Nature Reserve, SSSI – Site for Special Scientific Interest, SSSI (p) - proposed Site for Special Scientific Interest, SPA - Special Protection Area

Syon Park, in the freshwater zone of the River Thames, is the largest stretch of natural river bank between Teddington and Dartford. (D169)

Note: The River Thames and its tidal tributaries have been designated by the Greater London Authority as a Metropolitan Site of Importance for Nature Conservation (SINC). (D207)

Associated techniques linked from Wildpro

Return to top of page

Large Rivers

Definition/Description
  • Large rivers have high flow rates, with currents usually greater than one knot, meandering channels and varying salinities. The water levels in large rivers vary seasonally and at high water flow of water may reverse up tributaries and into backwater lakes. They commonly have associated floodplains. In flood, rivers have high suspended sediment and debris loads. (D195.w3)
  • Navigable large rivers may have a variety of manmade structures such as locks, dams and pools. (D195.w3)

Vulnerability to oil

  • Large rivers are considered to have medium sensitivity to oil. They have high natural removal rates but also have extensive biological (and human) use. (D195.w3)
  • In flood conditions, river floodplains include highly sensitive habitat areas which may be important for a variety of species. (D195.w3) [An indication of such areas associated with the River Thames is given in the sections above, Key Habitats of the Tidal Thames and Statutory Conservation Areas]
  • Intakes of drinking, industrial and cooling waters from rivers are quite vulnerable to oil due to turbulent mixing of oil and water. (D195.w3)
  • Boat facilities such as marinas and harbours, moorings, boat ramps and slipways, are sensitive to oiling. (D226)
  • Sites of historical, culture or scenic significance close to the river shore may become involved. (D226)
  • Spill responses may be complicated by high currents, eddies, mid-river bars, flooding and (in colder areas) ice formation, water flow over weirs and dams, which is often turbulent and may produce emulsions, and adsorption of oil onto sediment particles followed by settling in quiet backwaters, which may cause contamination of such habitats. (D195.w3)
    • The presence of ice can cause considerable difficulties in both oiled wildlife response and in oil spill cleanup. (V.w73)

Vulnerability to spill response

  • The least adverse habitat impact is caused by:
    • Booming. This may be used to deflect spills from sensitive resources and divert slicks to collection points in low-current areas. This is of limited use for gasoline spills due to safety concerns. (D195.w3)
    • Skimming/vacuum. This is not useful for gasoline spills due to safety concerns. (D195.w3)
  • Some adverse habitat impact is caused by:
    • Natural recovery. This may cause little habitat impact with light oils (gasoline and even diesel) since surface slicks will be rapidly removed by evaporation and natural dispersion. It is less appropriate for heavier oils: recovery of the oil and/or protection of sensitive habitats should be attempted. (D195.w3)
    • Physical herding (which may be required to flush oil which is trapped in debris or eddies). (D195.w3)
    • Sorbents (may not be practical due to the rapid spread and drift of oil). (D195.w3)
    • In-situ burning (may not be practical on rapidly spreading oil. It is difficult to contain oil into the minimum thickness (1-3 mm) for burning in fast current. (D195.w3)
    • Emulsion-treating agents (not useable on gasoline). (D195.w3)
    • Vegetation removal (where oil is trapped in floating vegetation; used to prevent secondary oiling of wildlife, and chronic sheening), 
    • Debris removal (to remove associated trapped oil). (D195.w3)
    • Visco-elastic agents/solidifiers (may not be practical in rivers due to rapid spreading of oil) and manual or mechanical oil removal conducted from boats or barges.
  • Adverse impact is probable with dispersants, since the limited dilution of the dispersed oil may result in toxicity. Additionally, the impact on water intakes further downstream must be considered. (D195.w3)
    • Note: Use of dispersants is not permitted in inland waters in the UK. (W39.21Jun05.w1)
  • The greatest adverse habitat impact is probable with herding agents. (D195.w3)
Associated techniques linked from Wildpro

Return to top of page

Small Rivers, Streams, Tidal Creeks and Canals

Definition/Description
  • "Small rivers and streams are characterised by shallow water (generally 1-2 meters) and narrow channels." (D195.w3)
  • Water flow may be variable with season as well as with distance downstream. (D195.w3)
  • "Canals are artificial waterways constructed for the purpose of inland navigation." Canals in London act as a network of linear waterways providing habitat for various wetland species of plants, birds, mammals, fish and invertebrates. (D201)
  • "Tidal creeks [of the Thames] are the downstream sections of tributary rivers that are directly influenced by the daily tidal cycle of the river Thames. The most ecologically valuable creeks, are likely to be those with open channels associated with the lower reaches of the river that are undisturbed by human activity, possess mosaics of inter-tidal mud and saltmarsh habitat, and have completely unimpeded hydrological links to the river. Although the ecological functioning of these specific systems has not been extensively researched to date, they are considered to provide particularly important habitat for feeding and roosting wading birds and waterfowl, and also provide refuge and feeding areas for developing fish fry." (D170)

Vulnerability to oil

  • Medium to high sensitivity to oil spills. Lower flows, lower dilution and a lower overall energy, as well as the greater range of natural habitats, mean that these waterways may be more sensitive than are large rivers. (D195.w3)
  • Oil spills are likely to contaminate both banks, while non-viscous oils in shallow streams may easily be mixed into the whole water column so that both aquatic and benthic organisms may be exposed to oil. (D195.w3)
  • Fish, amphibians, reptiles, birds and mammals using these habitats may be exposed to oil; high localised mortality may occur with oil spills. (D195.w3)

Vulnerability to spill response

  • The least adverse habitat impact may be seen with:
    • Booming. This may be used to divert oil to collection sites in low-current areas. Effectiveness is low with fast currents, shallow water and steep banks. and thy are limited for use with gasoline spills due to safety concerns. (D195.w3)
    • Skimming/vacuum. (D195.w3)
    • Sorbents, used in booms to recover oil from sheens along shores and in low current areas, although deployment and recovery may result in trampling of both bank and streambed habitats, and risks driving oil into the sediments. (D195.w3)
    • Barriers/berms. There is the possibility that these may cause physical disruption and sediment contamination in their immediate area. Additionally, if much flow is diverted water requirements to downstream habitats must be monitored. (D195.w3)
  • Some adverse habitat impact may be seen with: (D195.w3)
    • Physical herding;
    • Natural recovery;
    • Debris removal;
    • Visco-elastic agents/solidifiers;
    • Vegetation removal;
    • In-situ burning.

    (D195.w3)

  • Adverse habitat impact is probable with:
    • Manual or mechanical oil removal. (D195.w3)
  • The greatest adverse habitat impact is likely with dispersants or herding agents. (D195.w3)
    • Note: Use of dispersants is not permitted in inland waters in the UK. (W39.21Jun05.w1)
Associated techniques linked from Wildpro

Return to top of page

Saltmarshes

Definition/Description
  • "Saltmarsh vegetation develops on sheltered shores between approximately high water level of neap tides (MHWN) and the highest high waters of spring tides." (D176)
  • Saltmarshes provide important habitats for birds, including many migratory birds. Fish may feed in marshes at high tide, and plant detritus from marshes can contribute to food webs in estuaries and other nearshore areas. (D176)

Vulnerability to oil

  • Saltmarshes tend to trap oil because they occur in sheltered conditions, because much vegetation is present within the strandline zone, and because vegetation, particularly species such as Spartina spp. with corrugated leaf surfaces, provide a large surface area to hold oil. (D176)
  • Damage from oiling, and time to recovery following oiling, can be very variable. This is affected by:
    • Oil type: fresh lighter, more penetrating oils tend to cause more toxic damage than do heavier or weathered oils. (D176)
    • Season at which oiling occurs: all species are more vulnerable in spring; summer oiling may have greatest effect on annuals, which have less well developed underground parts than do perennials; plants are relatively protected in winter, with most live parts of perennials not exposed. (D176)
    • The thickness of the oil deposit. (D176)
    • The degree to which oil penetrates into the sediment. (D176)
  • Note: oil on the surface of the marsh may be a threat to birds or other wildlife. (D176)
  • While good recovery may occur after a couple of years following light to moderate oiling with little penetration of the sediment, recovery may be delayed with thick deposits of oil or water-in-oil emulsion (mousse) which kill vegetation and inhibit recolonisation. Even when the area becomes revegetated, the type of vegetation which takes hold may not be the same as the dominant vegetation prior to the spill. (D176)

Vulnerability to spill response

  • "The protection of saltmarshes should be afforded a high priority at an early stage in oil spill response since cleaning of oiled vegetation and sediments is very difficult and may cause more damage than the oil itself." (D176)

Further information is available in IPIECA REPORT SERIES Volume Six - Biological Impacts of Oil Pollution: Saltmarshes (full text provided)

Associated techniques linked from Wildpro

Return to top of page

Saline Lagoons

Definition/Description
  • Saline lagoons are natural or artificial bodies of saline water which are partially separated from the adjacent sea. They may be brackish, saline or hypersaline. The type of saline lagoon is defined by the nature of material separating the lagoon from the sea and the degree of separation, while the salinity is affected by input of freshwater in the form of groundwater or surface waters. (W569.May05.w2)
  • Saline lagoons often have soft sediments which can support filamentous brown and green algae, stoneworts and tasselworts, and may contain invertebrates which are rarely found in other habitats. They provide important habitat for waterfowl, marshland birds and seabirds. (W569.May05.w2)

Vulnerability to oil

  • Small lakes and ponds have medium to high sensitivity to oil: they have low physical removal rates, limited dilution is possible and they have high biological use. (D195.w3)
  • Wind is likely to affect the spread of oil, containing it against a lee shore or spreading it along a shore. (D195.w3)
  • High doses of oil may have an adverse impact on floating vegetation. (D195.w3)

Vulnerability to spill response

  • The least adverse habitat impact will be produced by booming, skimming or vacuuming and use of sorbents. (D195.w3)
  • Some adverse impact may result from allowing natural recovery (more impact with heavier oils which will persist and affect shoreline habitats), in-situ burning, herding agents, debris removal, removal of vegetation which is trapping oil, physical herding of the oil (taking care not to drive it into the water column or into sediment) and visco-elastic agents/solidifiers. (D195.w3)
  • Manual or mechanical removal of oil is likely to have more adverse impact on the environment. (D195.w3)
  • Dispersants and likely to have the greatest adverse impacts, since the shallow water and low rate of dilution may result in high toxicity of oil/dispersant mixtures to aquatic organisms. (D195.w3)
    • Note: Use of dispersants is not permitted in inland waters in the UK. (W39.21Jun05.w1)
Associated techniques linked from Wildpro

Return to top of page

 Wetlands including Reedbeds

Definition/Description
  • Wetland habitats include a variety of habitats characterised by the presence of water, usually with vegetated areas at or below the water level, vegetation adapted to wet conditions and soils differing from those of adjacent upland areas. (D195.w3)
  • Wetlands generally have considerable biological diversity and provide critical habitat for many animal and plant species. Many species rely on wetlands during reproduction and early life stages. (D195.w3)
  • Reedbeds
    • Reedbeds are wetlands where the water table is at or above ground level for most of the year, with the vegetation dominated by the tall wetland grass Phragmites australis - Common reed. (D199, D204)
    • These areas of vegetated shallow water are found at the margins of all sorts of waterbodies (e.g. lakes, rivers, reservoirs) and alongside other habitats such as willow-dominated scrub and wet woodlands. (D199, D204)
    • Reedbeds may be natural or may be created during restoration of gravel workings, development of reservoirs for conservation etc. (D199, D204)
    • Reedbeds in London are used as roosting sites by many birds including migratory birds and raptors, and in winter are used by bearded tit, while bittern are winter visitors to reedbeds, particularly in the Lea Valley. (D199)
    • Tidal reedbeds in the Thames act as particularly valuable sheltered feeding areas for fish fry. (D199)
    • Reedbeds may also be important for other species such as water voles, harvest mice, water rail, reed warblers, sedge warblers and various invertebrates. (D204)

Vulnerability to oil

  • Wetlands are highly sensitive to oil spills. (D195.w3)
  • Oil spills affect the vegetation and sediments of the wetland habitat, and the organisms which rely either directly or indirectly on the habitat. (D195.w3)
  • Oil spilled into wetlands may directly oil animals using the wetlands. (D195.w3)

Vulnerability to spill response

  • These habitats are vulnerable to habitat impact caused by trampling, erosion or disturbance of substrate or vegetation, removal of vegetation either physically or by burning. (D195.w3)
  • The least adverse habitat impact may be caused by: (D195.w3)
    • Natural recovery. This may cause the least impact for small to medium spills, avoiding cleanup-associated damage. However some cleanup may be warranted if large numbers of animals using the wetlands are likely to become oiled. (D195.w3)
    • Sorbents. These should be used with care during both placement and recovery to minimise substrate and vegetation disturbance. Excessive waste may be produced. (D195.w3)
    • Flooding. This may be used to remove localised heavy oiling, but it can be difficult to direct the flow of water and oil towards recovery devices. It may cause erosion of substrate and vegetation, leave large amounts of oil residues if the oil is heavy, and with gasoline may transport the oil to more sensitive habitats. (D195.w3)
    • Low-pressure cold-water flushing. This may leave large amounts of oil residues if the oil is heavy, and with gasoline may transport the oil to more sensitive habitats. With too high water pressures it may cause erosion of substrate and vegetation. (D195.w3)
  • Some adverse habitat impact may be caused by: (D195.w3)
    • In situ burning. This may be a means of removing heavy oils while limiting physical damage, and also for gasoline trapped in ice. The roots of the vegetation may be protected by a layer of water on the surface. Its use varies depending on the time of year. (D195.w3)
    • Vacuum. This may be useful to remove surface pools of oil. Use of boards and limiting traffic can limit trampling of the vegetation and substrate during vacuuming. (D195.w3)
    • Debris removal. This may reduce tracking of oil off the site and contamination of wild animals. (D195.w3)
  • Adverse habitat impact is probable with:
    • Vegetation removal. Despite its impact this may be used to prevent oiling of oil-sensitive animals using the wetland. It is most appropriate for medium and heavy oils which form a sticky coating over the vegetation. Both the impact of the oil and physical destruction during the cleanup may delay recovery of the vegetation following removal. Control of access routes, use of boards placed on the surface or conducting the removal from boats may reduce trampling of vegetation. (D195.w3)
    • Manual removal of oil. This can be used for removal of large amounts of persistent oil and where sensitive species using the wetlands are likely to become oiled. It must be remembered that crews removing oil may both trample roots and mix oil deeper into the sediment. (D195.w3)
  • The greatest adverse habitat impact is likely with: (D195.w3)
    • High-pressure cold-water flushing. High-pressure water will disrupt the sediments, root systems and animals using the habitat. (D195.w3)
    • Low pressure or high pressure hot water flushing. Hot water is likely to kill vegetation. (D195.w3)
    • Mechanical removal of oil. Extensive physical disruption is likely where vehicles are used in areas of soft substrate, resulting in extensive and prolonged (years) alteration of the substrate, hydrology and vegetation. It may nevertheless be used "in heavily oiled wetlands when all other techniques have failed and there is an overriding reason for oil removal." (D195.w3)
    • Reworking of sediment. This will mix the oil deeper into the soil and produces no benefit. (D195.w3)
    • Solidifiers. These are not beneficial. Use of solidifiers is likely to increase oil adherence to vegetation and slow down weathering and natural removal of residual oil. Additionally, solidifiers are not useful on gasoline (which evaporates rapidly) or heavy oils (viscosity too high to allow mixing). (D195.w3)
Associated techniques linked from Wildpro

Return to top of page

Rocky Shores

Definition/Description
  • Rocky substrate which may vary considerably in permeability. (D194)
  • May be exposed or sheltered. (D194)
  • May have more or less rubble overlying bedrock; more rubble may accumulate on sheltered rather than exposed shores. (D194)

Vulnerability to oil

  • On exposed rocky areas, wave reflection tends to keep oil offshore and generally no clean-up is required. (D171, D194)
  • On sheltered rocky shores, oil may persist much longer, even for years. (D171)
  • Normally oil is not retained on rocky shores in a form/quantity causing long-term impacts. (D177)
  • Most marine organisms inhabiting rocky shores have "considerable potential for re-establishing populations." Therefore in general communities recover within two to three years. (D177)
  • In some circumstances long-term impacts may occur: for example if large amounts of viscous oil land on a sheltered rocky shore and an asphalt pavement forms. (D177)
  • Organisms inhabiting rocky shores vary considerably in their sensitivity to oil: (D177)
    • Brown seaweeds have a mucilaginous coat, from which oil washes off in the next high tide; (D177)
    • Barnacles and intertidal sea anemones may be killed after smothering with viscous oil for a few tides; (D177)
    • Grazing molluscs such as littorinid snails, and limpets, are more susceptible, particularly with toxic gasoline products which may kill directly or have a narcotic effect so that the organisms lose their grip on the rocks and either die of desiccation or become susceptible to predation. (D177)
  • Effects also vary depending on the type of oil: weathered crude may have much less effect than fresh diesel or gasoline which has greater immediate toxic effects (see above), as well as bleaching effects on red algae. (D177)
  • Note: spills may alter predator-prey relationships causing changes in the species composition in the spill-affected area. (D194) For example, when grazing molluscs are removed by the effects of oil this may be followed by rapid proliferation of microalgae on the rock, after which spores of macroalgae settle and dense seaweeds may grow. Juvenile limpets and snails then gradually repopulate, although some years may be required for the ecology of the system to stabilise. (D177)
  • Effects on amphipods and other small crustaceans, and on crabs and starfish are generally temporary (less than one year) unless oil is trapped long term or species which are long-lived and reproduce slowly are affected. (D177)
  • Further information is provided in: 

Vulnerability to spill response

  • Aggressive clean-up methods may increase the detrimental ecological effects of oil on rocky shores. This has been demonstrated following use of large quantities of toxic chemicals for oil dispersal, mechanical scraping of rocky shores, and high pressure hot water flushing. (D177)
  • Clean-up techniques which are able to remove bulk oil without causing severe damage (physical or chemical) are preferred. 
    • Suction devices may be used to remove pooled oil if equipment can reach the site without causing physical damage due to its weight. (D177)
    • Sorbent pads may be used to remove small oil pools where suction devices cannot be used. (D177)
    • If flushing is to be used then low pressure flushing with ambient temperature seawater is the best option; flushed oil must then be held by a containment boom and removed using skimmers. Care should be taken not to wash oil down over more sensitive lower areas of the shore, so this method should be used only at higher tides. (D177)
      • High pressure flushing with hot or cold water, and steam cleaning, should be avoided since they are very destructive to the ecological community. (D177)
    • Low toxicity modern dispersants may have some use but it must be remembered that the dispersed oil may then affect areas below the water level. (D177)
    • While manual removal of tarballs and detached oiled seaweed may be carried out, the potential impact of trampling by personnel should be considered. (D177)
    • Further information is provided in: Biological Impacts of Oil Pollution- Rocky Shores- IPIECA Report Series Volume 7 (full text provided)
Associated techniques linked from Wildpro

Return to top of page

Mudflats: Sedimentary Shores

Definition/Description
  • Sedimentary shores are found as intertidal habitats worldwide. The sediments range in size from mudflats (including silt and clay) with sediment particles less than 0.06 mm diameter, through sand (particle size 0.06-2mm), granule /gravel (2-4 mm) and pebble/shingle (4-64 mm) to coarse cobble (64-256 mm) beaches. The slope of the shore and the size of the particles are determined mainly by wave and current action: strong waves result in a steep beach profile with large, highly mobile particles, while gentle wave action results in a gently sloping beach with small, relatively stable particles. In general, sheltered areas have shallower gradients and are made up of finer particles. In estuaries, mudflats develop due to the sheltered conditions and the flocculation of suspended material from the river. (D179)
  • Cobble and pebble sediments are generally unstable and drain rapidly, and do not support many species. In contrast, in mud and sand, capillary action in the interstitial spaces between particles holds water after the tide retreats and these types of sediments can support a variety of species including bacteria and diatoms on the surface of particles, meioflora (0.05 to 0.5 mm) and larger species. (D179)
  • Intertidal sands and mudflats are used as feeding grounds by wading birds when the tide is out. (D179)

Vulnerability to oil

  • The depth to which oil penetrates sedimentary shores is affected by:
    • Particle size, with less penetration in areas of fine particles such as mudflats;
    • Viscosity of the oil, with less penetration by highly viscous oils and mousse than by lower viscosity oils;
    • Drainage, with greater penetration into well-drained coarse sediments and generally poor penetration into poorly drained fine sediments, since the water content can prevent oil penetration;
    • Root pores and animal burrows, into which oil can penetrate in fine sediments;
  • Oil may be naturally cleaned from sedimentary shores by wave action; this is generally faster on exposed coarse sediment areas than on sheltered fine sediments such as mudflats. (D179)
  • Crusts of oil can form on mud and sand, and asphalt pavements can form on coarser sediments, when large amounts of oil or mousse consolidate the surface layer of sediment; with weathering, the oil-and-sediment layer becomes hardened and may persist for some time until finally broken down as wave action undercuts the edges. (D179)
  • Biodegradation is likely only to be significant after most of the oil has been removed by physical processes and it is relatively slow where oxygen is limited (e.g. in thick oil layers and in poorly-drained fine sediments). (D179)
  • Sheltered sediments such as mudflats are likely to be worst affected by oil: they are most likely to retain oil, and these are also the types of sediments with the highest productivity. (D179)
    • Different species show different rates of recovery and populations of some opportunistic species may blossom briefly after a spill; (D179)
    • Recovery rates will be affected by the toxicity of the oil. (D179)
  • N.B. Birds and fish which feed on tidal mudflats could be adversely affected by long-term depletion of the fauna normally supported by the sediments. (D179)

Vulnerability to spill response

  • It is very important to protect mudflats from oiling if at all possible since it is difficult to access these areas for cleanup since they are not able to support heavy machinery. (D179)
    • Protection may involve booming to contain oil on water and recover it, or to direct oil to "sacrificial" beaches which are less sensitive, then the oil can be collected from those beaches. (D179)
      • Note that booms do not work effectively in the presence of strong currents or strong waves. (D179)
      • Anchoring of booms along shorelines can be difficult, particularly where long lengths of booms are required. (D179)
  • Machinery should not be driven over oil on sediments, as this may drive the oil further into the sediment. (D179)
  • For more exposed sedimentary shores, leaving the shore alone and allowing natural clean-up may be most appropriate. (D179)
  • In sheltered shores, natural clean-up may be the preferred option, despite the length of time it will require, if other techniques would cause unacceptable damage. (D179)
    • Natural clean-up of sheltered shores is more likely to be effective where oil penetration is limited by waterlogging of the sediment. (D179)

Further information on clean-up methods for sedimentary shores is available in: Biological Impacts of Oil Pollution- Sedimentary Shores- IPIECA Report Series Volume 9 (full text provided)

Associated techniques linked from Wildpro

Return to top of page

Gravel Beaches

Definition/Description
  • Gravel beaches, which tend to occur as bars along rivers and streams, as well as on lake shores, are beaches with substrate that is mainly granules (greater than 2 mm diameter) to boulder (greater than 256 mm) in size, usually with less than 10% sand at the surface, although this may increase to 20% deeper down. (D195.3.w3, D195.AppB.w7)
  • Gravels are highly permeable. They can have low bearing capacity and therefore not be suitable for vehicles. (D195.3.w3)
  • In general, gravel beaches tend to be steeper than mud or sand beaches. (D179, D195.3.w3)
  • Natural replenishment rates are much slower than for sand. (D195.3.w3)

Vulnerability to oil

  • The vulnerability of gravel beaches to oil spills can be described as moderate. The mobility of the sediment, desiccation, and low organic matter levels lead to very sparse biological communities. Insects such as midges, caddisflies, stoneflies and mayflies may be present, with their larvae living in the sediments. On the gravel undersides there may be flatworms, leeches and crustaceans. In the nearshore, fish may spawn, with the gravel providing protection for fry and larvae.  (D195.3.w3)
  • Gravels are more vulnerable to oil than are mixed sand and gravel beaches because the permeable structure allows penetration of oil into the substrate. Since the oil can penetrate below the depth of annual reworking of the substrate, it may persist long-term. (D194, D195.3.w3)
    • How long oil will persist depends on the depth of routine reworking of the gravel by wave action. (D194)
  • In sheltered areas, chronic sheens and (with persistent oils) asphalt pavements may form. (D194, D195.3.w3)
  • Natural recovery is likely with little adverse impact if light oils are involved, some adverse impact with heavier oils. (D194)

Vulnerability to spill response

  • Flooding (deluge), low-pressure ambient temperature flushing, use of sorbents or nutrient enrichment are likely to cause the least environmental impact. (D194)
  • The least adverse impact on this habitat occurs with: 
    • Removal of oiled debris; (D195.3.w3)
    • Flushing with cold water at low pressure. This is effective only with fluid oil adhering lightly to the sediment. It is usually used together with vacuum and sorbent use. It is less useful with heavy oils and is likely to result in the residual presence of large amounts of oil; (D195.3.w3)
    • Leaving the habitat to recover naturally. This method is that with the least impact where light oils have been spilt, in small quantities, in remote or eroding areas. (D195.3.w3)
    • Use of sorbents. These are useful for recovering oil sheens however overuse of sorbents produces excessive oily waste. With heavy oils, physical removal is slow and less oil will be mobilised for recovery by sorbents. (D195.3.w3)
  • Some to severe ecological impacts is likely with high pressure ambient water flushing, low pressure hot water flushing, or high pressure hot water flushing, which may be required if heavier oils are to be removed (more with high/hot water flushing). (D194)
  • Some adverse impact on the environment will result from:
    • Vacuuming. This can be useful on pooled liquid oil soon after it has been spilled, to prevent deeper penetration of the oil into the sediment. 
    • Flushing with cold water at high pressure. This is likely to flush finer sediments into the nearshore submerged habitat. Very high pressures are required to mobilise very viscous oils. (D195.3.w3)
    • Nutrient enrichment. (D195.3.w3)
    • Manual removal of oil, reworking of sediment, shoreline cleaning agents, in-situ burning and solidifiers. (D195.3.w3)
  • Adverse impact on the habitat is likely with low-pressure hot water flushing, which may be needed to flush oil which is viscous or has penetrated deeply into the sediment, since any organisms will be adversely affected. (D195.3.w3)
  • Mechanical oil removal is likely to cause severe or very severe environmental impact. (D194)
    • Removal of oiled gravel is undesirable because of the length of time required for the gravel to be replenished. (D195.3.w3)
    • Mechanical removal is also likely to cause adverse impact, since it is probable that large quantities of gravel will be removed with the oil, and both pedestrian and vehicular traffic may mix the oil deeper into the sediments. (D195.3.w3)
  • The greatest adverse impact is likely with high pressure hot water flushing or steam cleaning. (D195.3.w3)
    • High pressure hot water flushing will both adversely affect any organisms and is likely to flush oiled sediments into nearshore submerged habitats. (D195.3.w3)
    • Steam cleaning will kill any organisms present in the sediment, and there is the potential for released oil to penetrate deeper into the gravel. (D195.3.w3)
Associated techniques linked from Wildpro

Return to top of page

 Seagrasses (Subtidal Areas)

Definition/Description

Vulnerability to oil

  • Generally no direct contamination, since the oil passes over subtidal seagrass beds. (D194)
  • If oil which is heavier than water is involved, this may be trapped in the beds, coating leaves and sediments, adhering to the leaves and causing defoliation. (D194)
  • When intertidal seagrass beds are oiled, rapid defoliation of oiled blades occurs. (D194)
  • Lighter, floating oil can contaminate seagrass beds if it becomes stranded on adjacent beaches, picks up sediment and is then deposited on the seagrass beds. (D194)
  • Natural recovery is likely with minimal environmental impact if the lighter oils are involved or some environmental impact with heavier crudes, residual products and non-floating oils. (D194)

Vulnerability to spill response

  • Use of sorbents will cause minimal environmental impact. (D194)
  • Seagrass beds are vulnerable to physical damage when booms are deployed and anchored; care must be taken to reduce this impact. (D194)
  • Care is also required to minimise sediment suspension and mixing with oil, and disturbance of roots and vegetation by either personnel on foot or boat traffic. (D194)
  • Use of dispersants directly over seagrass beds is not recommended as this may impact the highly sensitive ecological communities. (D194)
  • Note that if oil is burned in-situ near seagrass beds then the residues may sink, with variable effects on the environment. (D194)
  • Booming, skimming and manual removal of oil will all cause some adverse habitat impact. (D194)
  • Cutting and removal of vegetation will cause significant adverse habitat impact. (D194)
    • Seagrass should not be cut unless there is a significant risk of grazing species contacting or ingesting oil coating it. (D194)
  • Mechanical oil removal will cause the most severe environmental impact. (D194)
Associated techniques linked from Wildpro

Return to top of page

Artificial Structures

Definition/Description
  • These include seawalls, piers, port facilities, groins etc. and may be constructed of concrete, wood or metal. Their composition, design and general condition are highly variable. (D194)
  • Boat facilities such as marinas and harbours, moorings, boat ramps and slipways, and structures of e.g. historical or culture significance may be involved. (D226)

Vulnerability to oil

  • Oil readily adheres to the rough surfaces of many manmade structures and forms a distinct band above the high-tide line. (D194)
  • In the lower intertidal zone of these structures, oil is often prevented from adherence since the structure stays wet, particularly if covered in algae. (D194)
  • If left to recover naturally, there will generally be minimal or some adverse habitat impact (more with heavier than with lighter, more volatile oils). (D194)
  • Cleanup from riprap may be problematic because the large spaces between the boulders allows accumulation of oil and debris. This oil may be difficult to remove and provide a source of sheens. (D195.w3)

Vulnerability to spill response

  • Manmade structures can generally be cleaned using low- to high-pressure water, sprayed at ambient temperatures. (D194)
    • Such response methods cause variable habitat damage, minimal if low-pressure ambient temperature water is used to remove light oils, but some or significant adverse impact if used to remove heavier oils, and if high-pressure or hot water flushing is used. (D194)
  • Use of sorbents to remove oil from manmade structures generally causes minimal or some habitat damage. (D194)
  • Debris removal causes minimal habitat damage. (D194)
  • Steam cleaning or sand blasting both cause the greatest amount of habitat damage. (D194)
Associated techniques linked from Wildpro

Return to top of page

 

Authors & Referees

Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referees Dr Virginia Pierce (V.w73)

Return to top of page