User:Chloepm/sandbox

Chromium Cycle Draft

The chromium cycle is the biogeochemical cycle of chromium through the atmosphere, hydrosphere, biosphere and lithosphere.

Diagram of the Chromium Cycle. Chromium cycles through the atmosphere, soil, oceans, mantle, and freshwater. The arrows indicate fluxes given in gigagrams of chromium per year. The stocks indicate reservoirs of chromium given in gigagrams of chromium.

Terrestrial weathering and river transport

Chromium has two oxidation states: trivalent chromium, Cr(III), and hexavalent chromium, Cr(IV). Trivalent chromium adsorbs highly onto particles, whereas hexavalent chromium is highly toxic and soluble, making it a toxic contaminant in environmental systems. Chromium commonly exists as highly insoluble trivalent chromium, such as chromite, in soil and rocks. Terrestrial weathering could cause trivalent chromium to be oxidized by manganese oxides to hexavalent chromium, which is then cycled to the ocean through rivers. Estuaries release particulate chromium into rivers, increasing the dissolved fluxes of chromium to the ocean.

Oceanic cycling

Soluble hexavalent chromium is the most common type of chromium in oceans, where over 70% of dissolved chromium in the ocean is found in oxyanions such as chromate or hydrogen chromate. Soluble trivalent chromium is also found in the oceans where complexation with organic ligands occurs. Chromium is estimated to have a residence time of 6300 years in the oceans. Hexavalent chromium is reduced to trivalent chromium in oxygen minimum zones or at the surface of the ocean by divalent iron and organic ligands. There are four sinks of chromium from the oceans: oxic sediments in pelagic zones, hypoxic sediments in continental margins, anoxic or sulfidic sediments in basins or fjords with permanently anoxic or sulfidic bottom waters, and marine carbonates.

Methods for chromium tracking

Isotopic fractionation of chromium has become a valuable tool for monitoring environmental chromium contamination through recent advancements in mass spectrometry. Isotope fractionation during river transport is determined by local redox conditions based on dissolved organic matter in rivers.

Influence from other biogeochemical cycles

Manganese (III) can oxidize Cr(III) to Cr(IV) when complexed with organic ligands. This causes contaminant mobilization of Cr(IV), and also reduces Mn(III) to Mn(II), which can then be oxidized back to Mn(III) by oxygen.

Article Evaluation

Nitrogen Cycle

I read the article regarding the nitrogen cycle. The grammar in the article could be improved a bit as the sentences in the introduction are a bit short and redundant, but the language is accessible and the information is easy to follow. It was helpful that the Wikipedia pages for the full processes were linked under each process section above the blurb about how the process relates to the nitrogen cycle. The information seems to be up to date, and all the information in the article is relevant to the nitrogen cycle, although (as a Chemical Engineer I may be biased) the Haber-Bosch process could've been expanded upon more since it is one of the largest industrial processes that fixes nitrogen. The article is written without bias, and the tone of the article is neutral yet informative. It covers each aspect of the nitrogen cycle in depth.

The first figure on the page is aesthetically pleasing and easy to read, although it took me a minute to recognize that the numbers on the arrows related to the annual flux in TG/yr, so the legend could've been expanded upon in the caption of the figure or in a more central location in the figure. The figure is accurate scientifically, but I had to zoom in on the page to read the text on the figure because it is so small. Aside from those issues, the figure is done well, and I appreciate how the anthropogenic influence in the nitrogen cycle was included.

Checking sources on the page (1, 4, 19, 21), all of the links I clicked were accessible and linked to articles in reputable science databases/journals. The information in the Wikipedia article linked to a citation was drawn from the information in the citation. The sources and the article were accurately connected.

Calcium Cycle

I thought the introduction for the article on the calcium cycle was well-written and got all of the main points across that were to be covered later in the article. Everything in the article is relevant to the cycle. I think it might be valuable to name some non-dairy sources of calcium in the human/animal use of calcium since it's abundant in plants as well, but I fully admit that is my personal bias as a vegan speaking. I think that claiming dairy products as the main source of calcium in a diet as the article does, however, is a bit biased, especially with no source linked to that statement. Aside from that, the article seemed unbiased. The article is easy to read, although I personally would reword some of the sentences, and doesn't use complex language making it very accessible to the layman.

The first thing I noticed when opening the article was that a diagram of the calcium cycle was not the first figure on the page. I had to scroll down a bit to find it, and it was very sterile looking with no color or simple figures in the diagram. The other diagrams in the article were a bit complicated and not labelled very well. It was difficult to ascertain what was being modeled. Although the figures were lacking, I found the information in the article to be very interesting and well-presented.

Of the papers I clicked that were cited (1,3,8), all of them were from reputable journals. The information presented at each one of these citations lined with the information in the Wikipedia article. However, one citation I clicked (25), led to a "404 Not Found" page that seemed to be a blog post from a company that sells fertilizers, pesticides, and other chemical compounds. Although the section that has this citation is talking about the science behind calcium uptake into plants, this leads me to question the validity of the science about why calcium is important for plants when it comes from a company that sells calcium to farmers and gardeners for their plants.

Selenium Cycle

I think linking to the carbon, nitrogen, and sulfur cycles mentioned in the introduction would be a valuable edit to the Selenium Cycle introduction section. Something really small and inconsequential that bothered me was the lack of an Oxford comma when listing the oxidized forms of selenium that are metabolized by bacteria, fungi, and plants when an Oxford comma had already been used in the same sentence. I think that the information was concise, and provided the relevant information about the cycle itself, but it felt like the information was a lot less in depth than the other two articles (to be fair, there is a lot less research on the selenium cycle than there is about the nitrogen or calcium cycles). I think the information was still accessible and easy to understand.

There were no figures in this article, and I found it took a moment to visualize the cycle that was being discussed as a result. I think the cycle itself was described very well, and it would not be difficult to create a diagram of the cycle from the information provided in the article.

I thought the tone of the article was neutral and unbiased, and the sources were all from reputable research. The three citations were all linked to reputable journals, however, the link for the second citation was broken and I had to search online for the paper. The paper that had the broken link actually had some really good figures about the selenium cycle in it, so it is a bit surprising to me that inspiration was not drawn from the paper to make a diagram for the Wikipedia page. The sources all had solid information and matched the facts presented in the article. I would like to have seen more citations, especially in the "immobilization processes" section, though.