Bioirrigation refers to the process of
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
organisms flushing their
burrow
An Eastern chipmunk at the entrance of its burrow
A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of s ...
s with overlying
water. The exchange of dissolved substances between the
porewater and overlying seawater that results is an important process in the context of the biogeochemistry of the oceans.
Marine coastal ecosystem
A marine coastal ecosystem is a marine ecosystem which occurs where the land meets the ocean. Marine coastal ecosystems include many different types of marine habitats, such as estuaries and lagoons, salt marshes and mangrove forests, seagrass me ...
s often have organisms that destabilize
sediment. They change the physical state of the sediment. Thus improving the conditions for other organisms and themselves. These organisms often also cause
bioturbation
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a pr ...
, which is commonly used interchangeably or in reference with bioirrigation.
Bioirrigation works as two different processes. These processes are known as
particle
In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass.
They vary greatly in size or quantity, from s ...
reworking and
ventilation, which is the work of benthic macro-
invertebrates (usually ones that burrow). This particle reworking and ventilation is caused by the organisms when they feed (faunal feeding),
defecate
Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging fro ...
, burrow, and
respire.
Bioirrigation is responsible for a large amount of
oxidative
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
transport and has a large impact on
biogeochemical cycle
A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the ...
s.
Bioirrigation's Role in Elemental Cycling
Bioirrigation is a main component in element cycling. Some of these elements include:
Magnesium,
Nitrogen,
Calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
,
Strontium
Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...
,
Molybdenum, and
Uranium. Other elements are only displaced at certain steps in the bioirrigation process.
Aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
,
Iron,
Cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pro ...
,
Copper,
Zinc, and
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
are all affected at the start of the process, when the larvae begins to dig into the sediment. While
Manganese,
Nickel,
Arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
,
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
and
Caesium
Caesium ( IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
were all mobilized slightly after the burrowing process.
Challenges to Studying Bioirrigation
When trying to describe this biologically driven dynamic process, scientists have not been able to develop a 3D image of the process yet.
New Mechanisms to Study Bioirrigation
There is a hybrid medical imaging technique using a position emission tomography/computed tomography (
PET/CT
Positron emission tomography–computed tomography (better known as PET-CT or PET/CT) is a nuclear medicine technique which combines, in a single gantry, a positron emission tomography (PET) scanner and an x-ray computed tomography (CT) scan ...
) to measure the ventilation and visualize the
pore water advection
In the field of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is a ...
that is caused by the organisms in 4D imaging.
Ecological Importance of Bioirrigation
When coastal ecosystems do not have bioirrigating organisms, like lugworms, it results in a lot of sedimentary problems. Some of these problems include clogging of the sediment with
organic
Organic may refer to:
* Organic, of or relating to an organism, a living entity
* Organic, of or relating to an anatomical organ
Chemistry
* Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
-rich fine particles and a drastic decrease in sediment
permeability. It also makes it so the oxygen cannot penetrate deeply into the sediment and there is accumulation of reduced mineralized products in pore water. These problems disrupt the foundations of a coastal ecosystem.
Economic Impacts
Two organisms that contribute to the bioturbation of soil are
Nephtys caeca (Fabricius) and
Nereis virens (Sars)
annelidae. They dig, bioirrigate, and feed in the sediment and they homogenize the particles found in the sediment when they partake in these activities because of their erratic movements. The bioirrigation generated by these organisms modifies the distribution of
dinoflagellate cysts
Dinocysts or dinoflagellate cysts are typically 15 to 100 µm in diameter and produced by around 15–20% of living dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic ...
in the sedimentary column. They either bury them or raise them back to the surface, keeping them rotating. One of the most important
dinoflagellates that these organisms help distribute is called noxious
microalgae and it is responsible for the formation of toxic
red tides
A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are sometimes ...
. These red tides poison
mollusks and
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s which results in very important economic losses in the fishing industry.
Case Study:
Boston Harbor
Boston Harbor is a natural harbor and estuary of Massachusetts Bay, and is located adjacent to the city of Boston, Massachusetts. It is home to the Port of Boston, a major shipping facility in the northeastern United States.
History
Since ...
The sediments of marine environments are important sites of
methylmercury (MMHg) production. This production provides important sources of
this MMHg to near-shore and off-shore water columns and
food webs. Scientists
have measured the flux in production across 4 different stations in the Boston
Harbor which had different bioirrigation site densities. There is a strong
linear relationship between the amount of MMHg exchange and the
infaunal
Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is ''funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zool ...
burrow
density. In the Boston Harbor, it was shown that bioirrigation stimulates the production of
methylmercury and water column flux.
[{{Cite journal, title = Effect Of Bioirrigation On Sediment-Water Exchange Of Methylmercury In Boston Harbor, Massachusetts, last = Benoit, first = Janina, date = 2009, journal = Environmental Science & Technology, doi = 10.1021/es803552q, volume=43, issue = 10, pages=3669–3674, pmid = 19544871, bibcode = 2009EnST...43.3669B]
References
Irrigation
Articles containing video clips