Transcript Pollution in coastal seas

Pollution in Coastal and Shelf Seas:
An Overview
Huge topic; 766,000 hits on Google!
An overview of key points,
Some of more important topics in more detail (* )
Case study of Black Sea.
What is pollution (UN version)?
“Marine pollution is the introduction by humans into the
marine environment, directly or indirectly, of substances
or energy that can lead to deleterious effects on e.g.
biological systems, human health, fisheries, or reduce
the quality of the environment for use by the leisure
industry”
Types of pollutants- major categories
Sewage discharges (high organic carbon, plus
other materials)
Nutrients* (at high levels)
Metals*
Hydrocarbons/oil*
Chlorinated compounds, and other synthetic organics
(endocrine disrupters, herbicides, unknown organics etc.)
•Plastics/garbage
Radio-nuclides (power/reprocessing plants- Cs-137,
Sb-125, Chernobyl Cs-134)
Heat (power stations; impact on species
composition & > bacterial respiration)
Some pollutants may be naturally present
However, Human activity often has enhanced releases,
e.g.
Metals released from mine spoil
Eutrophication may enhance occurrence of
toxin release from HABs, (Harmful Algal
Blooms)
Natural oil seeps
Origins of pollutants:
Domestic effluents
Industrial effluents [direct
(outfalls) and indirect (e.g.
via atmosphere)]
Ship origin (sinking
tankers, washing tanks,
anti-fouling agents etc)
Impact of pollutants
Function of toxicity
Sub-lethal effects- pressure on species
Bio-accumulation through food web
Control of Marine Pollution requires knowledge of:
Pathways by which pollutants reach the coastal
and shelf seas
Rates of inputs and dispersal of pollutants
Forms in which pollutants occur and how they
behave in marine systems
Note that as the coastal and Shelf seas systems are
open to inputs from land and atmospheric source,
controlling pollution here is synonymous with
controlling Global Pollution!
It is clear that knowledge of relevant marine physics,
biology, chemistry and geology/sedimentology are all
needed to provide an interdisciplinary view of pollution.
From Simpson, 1994
Nutrients in coastal waters
Referring to N, P and Si, as essential nutrients for
phytoplankton growth
Major input through rivers, although atmosphere can be
important for N (ammonia, nitrate)
Human impact principally through use of fertilisers and
detergents
Recent estimates of impact of human activities on P
fluxes = 2.4 X pre-human
Nitrate in the southern North Sea 1989, µM
Phytoplankton, organic carbon inputs, bacteria
and oxygen demand
(highly simplified!)
oxygen
produces
Humans
algae
supplies
NP
CO2
Dead
organic
matter
Low or no oxygen:
Eutrophic conditions
respiration
bacteria
Oxidation
provides energy
Sewage/C
inputs
Increase in biomass, on dying high bacterial
respiration and oxygen reduction = Eutrophication
Impact in terms of fish mortality, red-tide
incidence etc.
Particularly important when no or limited mixing
with oxygenated waters
Major impact in restricted exchange environments
(e.g. Baltic Sea)
Can be large-scale impact – e.g. Gulf of Mexico
Controls include reduced use of fertilisers, ban
on P based detergents
Oxygen minimum zone (shaded) that develops annually in
response to nutrient and other inputs to the Gulf of Mexico
Metals as Pollutants in the coastal zone
•Example of metals released from mining in Spain
•Mining since Roman times, of Iberian pyrite belt in
Andalucia
•Build up of mine tailings- residue after most metals
removed from sulphide ores, but still high metal content
•Sulphides oxidised in air- products sulphate and acid!
•Very low pH waters
•Tailing dams typically contain acid (pH2) waters and
sulphide sludge
•Background source of Zn and other heavy metals to S
Spanish coastal waters
•Zn signal can be followed for very long distances and
into Mediterranean Sea
•Los Frailes mine spill, April 1998, released circa 6 x
106 m3 sludge and water released into Guadiamar river
•Concern over damaging Doñana Park (UNESCO world
biosphere reserve)
•1.5 m thick layer of sludge covered 4000-5000 Ha of
flood plain but was diverted from park
Image showing grey
layer of metal laden
sludge deposited on
the flood plain of the
Guadiamar.
(c/o Dr E. Achterberg)
Main rivers
draining
mining areas
Manganese
Strait of
Gibraltar
Copper
Oil pollution
•Crude oil formed from organic remains of dead organisms
over geologic time-scales.
Thousands of organic compounds may be present
50-98% of compounds hydrocarbons (C and H only)
Class of
hydrocarbon
Toxic?
Biodegradable?
Alkane (chains)
Relatively non-toxic Many organisms can
biodegrade
Cycloalkanes (3060% of petroleum)
Toxic
Very resistant to
bio-degradation
Aromatic (2-4% of
petroleum)
Generally highly
toxic
Few microbes can
degrade these
compounds
Oil introduced into marine environment
through variety of routes:
Major incidents- sinking tankers- most
Washing out tanks at sea (now banned)
Land based inputs
Fate of Crude oil spilt on seawater:
Fate and behaviour of spilt crude oil will depend on
composition (origin)
As oil is hydrophobic and < dense that water, will
form thin layer at interface with atmosphere
100-200L of oil will cover 1 km2 to about 0.1 µm-
thicker if major spill
Film moves with wind and tides
Evaporation Generally the lower the molecular weight, the more volatile the
compound.
 Evaporation greatest in first few hours after a spill, but can
continue for months as compounds evaporate in MW sequence
 Evaporation function of T, wind action (directly related)
 For large spills most important factor for oil disappearance
Dissolution The lighter fractions dissolve most easily
 Micro droplets may also form
 Dissolved/micro droplets more readily destroyed by UV
Emulsification With adequate agitation, water absorbed by oil
“chocolate mousse”
Microbial Biodegradation Major ultimate process by which oil destroyed
 Oil degrading bacteria typically small in number; takes time for
numbers to build up
 Degradation function of T, nutrient availability etc.
Fate of residual oil at sea Formation of ubiquitous “tar balls”- gradual
physical/photochemical/ microbial degradation
 Oil may be entrained with denser particles and sink
Beaching Most dramatic evidence of spills
 Once in sediments, slow degradation
Oil pollution impacts
 Larger organisms major impact on e.g. birds
 Benthic and inter-tidal organisms- variable
response depending on species, level of
contamination etc.
Strategies to deal with Oil Spills
 If remains offshore, shore line impact limited
 Containment for use particularly near shore, ports etc
 Dispersants have been used to aid break-up and degradation-
however some dispersants may be more toxic than oil!!
Ultimately leave to natural processes to remove with time, the oil
residues
Examples of legislation to reduce pollution:
Tri- butyl Tin (TBT)
•Major impact on
certain molluscs
•Impact on oyster
growth (deformed
shells; reduced
growth)
•Now banned, even on
larger vessels
Banning of
“over the side”
dumping of
garbage at sea
(1988)