In marine and freshwater
ecology
Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...
, a particle is a small object. Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined by
Stokes' law) and accumulate as sediment. Some can enter the
atmosphere
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
through wave action where they can act as
cloud condensation nuclei (CCN). Many organisms
filter particles out of the water with unique filtration mechanisms (
filter feeders). Particles are often associated with high loads of
toxins which attach to the surface. As these toxins are passed up the food chain they accumulate in fatty tissue and become increasingly concentrated in predators (see
bioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended by
dredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes much
oxygen and can cause the water to become
hypoxic.
Particle analysis
Particle levels in water (or air) can be measured with a
turbidity meter and analyzed with a
particle counter. They can also be scanned with an underwater microscope, such as
ecoSCOPE.
Contaminant kinetics
It takes a few days until
plankton
Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
organisms have filtered the particles and incorporated the toxins into their body fat and
tissue: In the southwards flow of the waters of the Hudson off the coast of
New Jersey
New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...
, the highest levels of mercury in
copepod
Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...
s have not been found directly in front of the river off
New York but 150 km south, off
Atlantic City.
Many copepods are then captured by
mysidae,
krill and smallest
fish
A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
like the juveniles of
atlantic herring - and in each step of the
foodchain the toxin concentrations increase by the factor of 10.
Filter of
krill: The first degree
filter setae carry in v-form two rows of second degree
setae, pointing towards the inside of the
feeding basket. The purple ball is one micrometer in size. To display the total area of this fascinating particle filtration structure one would have t
tile7500 times this image.
Filter basket of a mysid. These 3 cm long animals live close to shore and hover above the sea floor, constantly collecting particles. Mysids are an important food source for
herring,
cod,
flounder,
striped bass. In polluted areas they have high toxin levels in their tissue but they are very robust and require much poison to die.
{{marine pollution
Environmental chemistry
Bioindicators