“is plume of fine-grained sediments” another word for pollution now…there’s a reason most people who would swim in the ocean do not swim in the mississippi…

So there is “natural pollutants” like volcano/wildfire ash, and sand/dust storm debris, but this is neither of those things. And this isn’t ocean pollution like the dumping of waste into the ocean or from storms dragging out debris/sediment from land or from harmful ocean mining practices (well not from dumping mining waste water filled with radioactive/chemically destructive sediments anyway). The truth is a bit more complicated but pretty easy to understand.

The Mississippi River has a huge watershed so naturally when the river leads out to the ocean a lot of sediment will go out with it. “Louisiana’s millions of acres of coastal wetlands were created over the past 7000 years as the Mississippi River fanned out and deposited its sediment at its delta before emptying into the Gulf of Mexico. The Mississippi River accumulates large quantities of sediment from water flowing overland and into streams in the river’s 3.2-million-km² (1.2-million-mi²) watershed. Much of this sediment originates from the Missouri River basin, which drains America’s agricultural heartland.”

However the reason for the sediment plumes happens because sediment *ISN’T* being dispersed from the Mississippi river mouth. So now the question is “why is there sediment plumes in the Gulf if there isn’t enough sediment being dispersed?”.

The answer has to do with how the estuary works: “The salt marshes in the river’s delta naturally compact over time. This compaction lowers the level of the marsh bottom and submerges vegetation under increasingly deeper waters. When waters become too deep, the vegetation dies, and soils are then washed away by the Gulf of Mexico. The natural compaction is offset, however, by inputs of sediment from the river and from the deposition of organic matter from marsh grasses. These additions keep soil levels high, water depths relatively stable, and vegetation healthy.”

Okay so that explains why the sediment plumes mostly come from the erosion of the coastal wetlands, but then why is sediment that comes downstream from the watershed not offsetting the soil level? What is happening to that sediment upstream? If this isn’t caused by pollution what is the problem here?

Human alteration to the environment of course! Altercations to the coast is causing the coastal wetlands to erode away and an altered coast leaves no barrier to stop sediments entering the Gulf. “13,000 km (8000 mi) of canals [have been cut] through coastal wetlands to facilitate shipping and oil gas exploration. These canals fragment the wetlands and increase erosion rates because they enable salty ocean water to penetrate inland and damage vegetation and wildlife in freshwater marshes.”

(here is a picture of Louisiana’s coastline erosion)

Okay so the coast has something to do with it but we can’t just fix the coast and be done with it! You still haven’t told me where the sediment upstream went!

You’re right! Damming rivers and building levees is the other major human altercation that is slowing down the rivers waters and causing the sediment suspended in the water to settle (mostly in reservoirs) before it can even reach the coast!

But we can’t just take down dams and levees so easily! Dams are used to create water reserves to provide potable water for hundreds/thousands of people and is also used to irrigate crops. Hydro-power plants are also used on dammed rivers to use the waters natural flow to turn turbines and create energy. Hydro-power is a “clean” energy in the fact it does not produce emissions and has one of the highest EROI values (Energy Return On Investment) over fossil fuel powered plants and renewable/bio energy power plants. However hydro-power energy can’t expand more because most of the suitable rivers have been dammed. Fortunately for Louisiana and the Gulf, damming for hydro-power plants has been recognized for having large impacts on their local ecosystems and many dams are slowly being phased out. (A win for the Louisiana coastal wetlands and local ecosystems but maybe not so much for the environment depending on how demands for electricity and water are met after dams are torn down) Levees protect against personal losses and public losses due to the destructive forces of flooding so they are seen as a good thing. Although extensive leveeing should be discouraged because it causes the river to slow allowing sediments to settle and preventing these sediments from ending up where they are needed.

So that pretty much explains what these sediment plumes are and what causes them.

Oil spills among other types of pollution and storms can also cause serious damage to the coastal wetlands damaging vegetation and wildlife that keeps the wetland healthy and soil/water levels to remain stable. However the main source of the problem has to do with the human altercation to the environment explained above.

Eventually the sediment disperses in the ocean but the plumes themselves cause hypoxic zones which is bad news for fish and even more bad news for Louisiana whose main economic income comes from their fishing, tourism and offshore oil businesses. The fishing industry is devastated by this and by offshore oil practices, the tourism industry goes down because the coast is no longer “aesthetic” (who wants to swim in water that looks like that? Or water that is polluted by the oil industry?), eco-tourism goes down too because the ecosystem’s wildlife/marsh vegetation is dying from the disruption of habitat. And we can’t just stop mining oil from the Gulf because local oil keeps us away from politically and ethically “unclean” oil (in the middle-east and south america) the US is trying to steer clear of. We can’t just point fingers at the oil industry for dirty practices: we also need to make it so that there isn’t heavy demand for fossil fuels by increasing reliance on renewable energy, decreasing reliance on nonrenewable energy, demanding fuel-efficient cars (with added tax on fuel to offset increased mileage per gallon), demanding emission-safe cars, demanding cars that are fueled by renewable energy sources (with incentives to build fuel stations for solar/hydrogen cars, making fuel more accessible), seeking subsidies for renewable energy, decreasing subsidies on nonrenewable energy, and increasing eco-laws that increase restrictions on mining pollution and that charge businesses for mining cleanup funds. (I could talk for years about the fuel/ecosystem/us-politics/climate-change crisises but I will spare you all that (for now))

In conclusion (AKA TL;DR) sediment plumes are not necessarily “pollution”, sediment moves naturally down the Mississippi watershed to build Louisiana’s shores but the shores are eroding away so sediment is ending up in the Gulf in plumes. Sediment Plumes can be caused by pollution but they are mainly caused by human alterations to the environment made to meet the demands of society, pollution should be addressed but that is another Gulf of Mexico/US/international issue, Louisiana is fucked.

(All written sources from my Essential Environment textbook. Picture sources all from Google Images.)

It appears the video posted earlier today motivated a good thousand word discussion, so I ought to share that.