User:EJMimosa/sandbox

Iodine Cycle Draft

The iodine cycle is a biogeochemical cycle that primarily consists of natural and biological processes that exchange iodine through the lithosphere, hydrosphere, and atmosphere.

Biogeochemical iodine cycle: Inventories are in Tg iodine per year. Labeled flux arrows are in Gg iodine per year. Unlabeled inventories (sinks) and fluxes are of unknown quantities. Iodine cycles through the lithosphere, atmosphere, hydrosphere, and biosphere. Freshwater iodine is calculated by subtracting oceanic iodine from total iodine in the hydrosphere. In oceans sediments and crust, iodine is replenished by sedimentation and is cycled into seawater through release as brine during subduction. Marine biota uptake iodine from seawater where it may be volatilized by transformation to methyl iodide. Sea spray aerosolization, volcanic activity, and fossil fuel burning cycles iodine from the hydrosphere and lithosphere into the atmosphere as well, while wet and dry deposition remove iodine from the atmosphere. In soil, small quantities of iodine are cycled through weathering of parent rock. Terrestrial biota uptake and remove iodine from soil, and bacteria volatilize iodine by methylizing it.

Iodine exists in many forms, but in the environment, it generally has an oxidation state of -1, 0, or +5.

Oceanic cycling

Iodine in the ocean exists primarily in oceanic sediments and seawater. During subduction of oceanic crust and seawater, most of the iodine cycles into seawater through brine, while a minor amount is cycled into the mantle. Marine biota, including seaweed and fish, accumulate iodine from the seawater and return it during decomposition. Sedimentation of free iodine replenishes the ocean sediment sink.

The primary loss of iodine from the oceanic sink is by loss to the atmosphere. Sea spray aerosolization accounts for a portion of this loss. However, the majority of the iodine cycled into the atmosphere occurs through biological conversion of iodide and iodate to methyl forms, primarily methyl iodide. Algae, phytoplankton, and bacteria produce volatile methyl iodide which leaves the oceans and forms aerosols in the atmosphere.

Terrestrial cycling

Iodine rarely occurs naturally in mineral form, so it comprises a very small portion of rocks by mass. Sedimentary rocks have higher concentrations of iodine compared to metamorphic and igneous rocks. Due to the low concentration of iodine in rocks, weathering is a minor flux of iodine to soils and the freshwater hydrosphere.

Soils contain a much higher concentration of iodine compared to their parent rock, though most of it is bound to organic and inorganic matter, potentially due to microbial activity. The major source of iodine to soils is through dry and wet deposition of aerosolized iodine in the atmosphere. Due to the disproportionate production of atmospheric iodine from the oceans, both the concentration of iodine and the flux of iodine to soils is greatest near coastal regions. Plants uptake iodine from the soil through their roots and return the iodine when they decompose. Flora that consume plants may uptake this iodine but similarly return it to soils upon decomposition. Some iodine may also be cycled into the freshwater hydrosphere through leaching and runoff, where it may return to the oceans.

Similar to oceanic iodine, the majority of iodine cycled out of soil is volatilized through conversion to methyl forms of iodine by bacteria. Unlike ocean volatilization, however, bacteria are thought to be the only organisms responsible for volatilization in soils.

Anthropogenic influences

Iodine is a necessary trace nutrient for human health and is used as a product for various industries. Iodine intended for human use and consumption is taken from brines, which accounts for a minor perturbation to the global iodine cycle. A much larger anthropogenic impact is through the burning of fossil fuels, which releases iodine into the atmosphere.

Iodine-129, a radioisotope of iodine, is a waste product of nuclear power generation and weapons testing. Unless present in high concentrations, I-192 likely does not present danger to human health. Early research has attempted to use the I-129/I-127 ratio as a tracer for the iodine cycle.

Article Evaluation

Article 1: Nitrogen Cycle

With the exception of some organization issues, the content of the article appears to be fine. Much of the information is holistic and presented without bias, and links to other articles are abundant. Subsections could be introduced into the marine nitrogen cycle section, and the two human impact sections could be combined with subheadings. Though I am personally unaware of the topic myself, Earth history of the nitrogen cycle could be an interesting and productive section to be included in the future. Finally, though figures are helpful, it looks like there are almost too many figures in the article that border on redundancy. For example, there are four different representations of the terrestrial nitrogen cycle, two of which cover almost complete same topic.

Overall, the tone is effective in conveying the information in a concise, scientific, and unbiased way. Some of the text edge on being too colloquial in a way that is undescriptive of the processes they discuss, such as in the use of "different players." While using jargon is undesired, better, equally simple words can convey the meaning of the information.

Some of the sources used are probably not the most authoritative. For example, citation number 16 links to a book about ecology in gardening. While this book definitely has applications to the nitrogen cycle, it is used as evidence for the nitrogen sink in the atmosphere; better and more reputable sources that address this sink as a primary discussion topic probably exist. Additionally, there are long pieces of text that go uncited. The entire first paragraph of the "Nitrification" section presents definitive facts and statements about the process without sources to support the claims. Some of the sources do seem to be from the 2000s, which are on the cusp of being a little old, especially with rapidly changing environments. However, most of these sources are regarding the terrestrial and marine nitrogen cycles, which probably do not have too much novel literature that requires a complete revision of past review papers. Still, these sources can probably be updated. Most sources do seem to be scientific and from reputable journals or publications, so in that regard, the article succeeds.

The first figure in the article is very helpful in depicting the fluxes of the nitrogen cycle. I like the simplicity of the figure and its organization. However, some of the design choices seem haphazard, with arrows and text being different sizes and orientations in a way that neither represents the data nor assists in its readability. Additionally, I would have liked to see some of the inventory of the sinks to be able to quantify the size of the fluxes. The figure description is also helpful, though a more explicit reassertion of the flux units would be appreciated.

Article 2: Silica Cycle

This article has good information and uses links to other articles well, though not to the degree of the first article reviewed. Sources and information appear to be mostly up to date, but the article reads a bit "bare-bones." Some rewriting and padding could be added to improve it.

The tone of this article has some interesting choices. Some of the information is presented in a way that appears to be an addendum, and it is unclear what is central to the point and what is supplemental information. Another minor issue is that the writing is sometimes a little choppy, making it appear that the distinct thoughts are not interconnected. In addition, some of the topics discussed had disproportionate amounts of information. It was odd to me that discussion about the silica-carbonate cycle, arguably one of the more important points, was so short.

As in article 1, some of the sources seem to discuss the topics they are used to cite only tangentially. Other, more "on topic" sources should be used instead to facilitate ease of information access. However, article 2 is an improvement from article 1, as no fact goes uncited with some facts having multiple good citations. Like article 1, some of the sources could use an update, but article 2 overall does a better job in this regard.

Article 3: Mercury Cycle

Though this article was shorter than article 2, its writing style and presentation of information felt more complete and easy to read. Information is concise yet to-the-point. The main criticism I have is that the description of the cycling processes feels incomplete. If a proper review article exists, it seems like there could be a lot more discussion on how certain processes occur. Additionally, some of the major cycling processes could have their own subsection. Bioaccumulation, in particular, could be discussed in more detail regarding methyl mercury. However, I do commend this article for having good use of linking articles in topics that it does not go into with great depth.

The tone of the article, as mentioned earlier, is very satisfactory. The discussion is concise and unbiased, and it feels scientific without possession jargon.

The article citations appear to be pretty recent with some good review papers to back up the topics discussed. All facts were cited appropriately with some having multiple citations like article 2.