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Bioirrigation refers to the process ofbenthicorganisms flushing theirburrows with overlyingwater. The exchange of dissolved substances between theporewater and overlying seawater that results is an important process in the context of the biogeochemistry of the oceans.
Marine coastal ecosystems often have organisms that destabilizesediment. They change the physical state of the sediment. Thus improving the conditions for other organisms and themselves. These organisms often also causebioturbation, which is commonly used interchangeably or in reference with bioirrigation.[1]
Bioirrigation works as two different processes. These processes are known asparticle reworking andventilation, 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, burrow, andrespire.
Bioirrigation is responsible for a large amount ofoxidative transport and has a large impact onbiogeochemical cycles.
Bioirrigation is a main component in element cycling. Some of these elements include:Magnesium,Nitrogen,Calcium,Strontium,Molybdenum, andUranium. Other elements are only displaced at certain steps in the bioirrigation process.Aluminium,Iron,Cobalt,Copper,Zinc, andCerium are all affected at the start of the process, when the larvae begins to dig into the sediment. WhileManganese,Nickel,Arsenic,Cadmium andCaesium were all mobilized slightly after the burrowing process.[2]
When trying to describe this biologically driven dynamic process, scientists have not been able to develop a 3D image of the process yet.
There is a hybrid medical imaging technique using a position emission tomography/computed tomography (PET/CT) to measure the ventilation and visualize thepore wateradvection that is caused by the organisms in 4D imaging.[3]
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 withorganic-rich fine particles and a drastic decrease in sedimentpermeability. It also makes it so the oxygen cannot penetrate deeply into the sediment and there is accumulation of reduced mineralized products in pore water.[4] These problems disrupt the foundations of a coastal ecosystem.
Two organisms that contribute to the bioturbation of soil areNephtys caeca (Fabricius) andNereis 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 ofdinoflagellate cysts in the sedimentary column. They either bury them or raise them back to the surface, keeping them rotating. One of the most importantdinoflagellates that these organisms help distribute is called noxiousmicroalgae and it is responsible for the formation of toxicred tides. These red tides poisonmollusks andcrustaceans which results in very important economic losses in the fishing industry.[5]
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The sediments of marine environments are important sites ofmethylmercury (MMHg) production. This production provides important sources ofthis MMHg to near-shore and off-shore water columns andfood webs. Scientistshave measured the flux in production across 4 different stations in the BostonHarbor which had different bioirrigation site densities. There is a stronglinear relationship between the amount of MMHg exchange and theinfaunal burrowdensity. In the Boston Harbor, it was shown that bioirrigation stimulates the production ofmethylmercury and water column flux.[6]