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TheRealSmallBean t1_jaa4tds wrote

Oh! I can actually answer this!

Fertilizers have a lot of nitrogen and phosphorus. When they enter a waterway, that causes algae to grow really rapidly and form “algae blooms” that cover the surface of the water. This blocks sunlight and makes it harder for plants to photosynthesize, which reduces the amount of oxygen in the water. As the plants and algae die, they’re also eaten by bacteria that require oxygen which limits the amount of oxygen in the water even further. The whole process is called eutrophication.

EDIT: Thanks for the awards!! This is my first comment that’s gotten more than like ten upvotes, how fitting for it to be about something nerdy.

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edXel_l_l t1_jabnr44 wrote

OOT, but I just wanna appreciate your enthusiasm. wish I have an award to give.

Edit: OMG thanks for the awards :"

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scottshilala t1_jac3tpt wrote

The algae bloom also limits the transfer of oxygen from the air to the body of water by creating a layer that blocks adsorption. The surface agitation is dampened dramatically by the floating mats, thus lowering the uptake of oxygen by a large percentage (that I can’t remember, so I don’t want to quote it, but it’s over 50%).

More simply, the floating mats of algae cut down the oxygen and create a blocking layer so very little oxygen gets through it.

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GeorgeCauldron7 t1_jacwrdf wrote

So does the algae itself consume oxygen (aerobic respiration?), or produce oxygen (photosynthesis?) in order to survive? Sorry, I study inorganic geochemistry but don't know much of anything about biology or botany.

Is there any difference between green algae and orange algae? I monitor water quality on a few streams, and the stream with the lowest dissolved oxygen (~30%) has both green and orange algae present, while the other streams have only green algae and have DO of 70-90%.

Also, are there any other plants that have a significant matting effect that dampens oxygen dissolution? Like a pond full of lily pads?

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RedditOR74 t1_jadidze wrote

Algae does both. During the day it contributes highly to oxygenating the water, but it consumes it at night. Since it also limits he surface area to replenish the oxygen, the water goes anaerobic during night time.

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Kingreaper t1_jadjc2x wrote

> So does the algae itself consume oxygen (aerobic respiration?), or produce oxygen (photosynthesis?) in order to survive? Sorry, I study inorganic geochemistry but don't know much of anything about biology or botany. > >

The Algae both consumes and produces oxygen - at first it's necessarily producing more than it consumes, in order to get the carbon it needs to grow in size, but when it's as big as it's going to get those numbers start balancing out.

Add in the fact that dead algae decaying take oxygen solely from the water, while living algae photosynthesising put their oxygen both into the water below and the air above, and you get a net decrease in oxygen over time (barring gas transfer, which as mentioned is blocked by the matting effect)

Another part of the problem is that the algae only produces oxygen in the daytime, and consumes it constantly, so at night the oxygen level in the water drops - and if something can't survive at night-time oxygen levels then it dies, and starts decaying, further lowering the oxygen levels.

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glampringthefoehamme t1_jadkekh wrote

Can we use the algae as fertilizer? As in, direct ask runoff to large ponds with non-harmful algae, allow it to absorb the leftover nutrients, harvest abs dry the algae, and then use it as fertilizer later?

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GeorgeCauldron7 t1_jadww4u wrote

So is it safe to say that if algae is present in a body of water, then you can expect the overall effect to be a net decrease in oxygen?

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Nero1022 t1_jabztb8 wrote

I just gave reward in your place, kind stranger. :)

​

Infact, have some yourself!

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Optimal_Hunter t1_jac7he8 wrote

What does OOT mean?

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edXel_l_l t1_jac89s7 wrote

Out of Topic. I wasn't contributing nor adding anything whatsoever, but I was commending his eagerness to explain something he knew.

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EquivalentCommon5 t1_jabn47x wrote

This is why it’s a great thing to have buffers for waterways, tiered gardens that funnel water runoff to be used again and not get into waterways. Other things that can help keep runoff out of waterways! But if the US can manage that, we still have animal fecal runoff (which can be mitigated but isn’t as much as should be), company pollution- which they can pay for off sets. Off sets aren’t available to farmers iirc, could be wrong! We need to supplement farmers not so many companies!!! Farmers feed us, companies- ugh, some ‘feed’ us but big corporations get major breaks that local farmers don’t! Wish people started to really look at what makes the US great. Unfortunately, they won’t! Liberals don’t see where their food comes from, conservatives don’t see how great diversity helps us, neither side on the outskirts seem to realize that politicians are about themselves. Politicians get away with bribes, stock fraud (buying knowing more than the public, pretty much corruption though there are other terms, insider trading comes to mind), oh not paying back loans that were for small business to stay afloat during the pandemic, or they get different health care, salaries and pensions that don’t make sense… they retire as millionaires. Sorry went off on a tangent I shouldn’t have. Summary from this- politicians on every side have a 70% chance of being corrupt in someway!

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sweetpotatokumquat t1_jaby1pl wrote

One thing that annoys me about the rise of agrocorp is how the deck is stacked against existing farmers.

We know that tiered taxation systems are generally a good thing, where individuals who earn more pay progressively higher percentages in tax. They still take home more money overall by earning more, but it shifts the burden of income tax away from those who have the least.

This doesn't happen for corporations. The mom and pop farm managing 2 hectares is paying the same tax rate as HappyValleyAgroCorp which manages 100000 hectares spread across the country.

But it gets worse. Mom and pop either have old inefficient equipment they've inherited, or have to rent in equipment when needed, cause they can't afford to drop $500k on a new tractor that will get used for 50 days a year. So they're paying more for their equipment than HappyValleyAgroCorp which has their own fleet of gear that's in constant use.

Mom and pop are stuck paying whatever price the local farmer supply store charges for feed and fertiliser. HappyValleyAgroCorp is buying so much that they can negotiate heavily with suppliers and ship stuff in from across the country.

Mom and pop will struggle to access any subsidies that might be available, either having to jump through hoops or simply not knowing about them. HappyValleyAgroCorp's got a lawyer on retainer who goes golfing with the subsidy administrator.

Mom and pop are stuck taking whatever price HappyValleyGroceryCorp offers them for their produce. HappyValleyAgroCorp is pumping out so much produce for cheaper costs that they can undercut mom and pop into the ground, and negotiate higher wholesale rates by threatening to disrupt HappyValleyGroceryCorp's supply chains. But they hash it out over their weekly golf round, and the only ones that get hurt are mom and pop and us buying groceries.

And so mom and pop are stuck working for very little their entire lives, until they die, and their kids are left with a tiny farm that brings in very little, and forced to choose between slaving away like mom and pop did, or sell off the land to HappyValleyAgroCorp who's willing to step in with "quite a reasonable offer really for this tiny plot, in cash, cause we know in this difficult time you don't want to be wasting time dealing with this. It's what mom and pop would have wanted, that the land continues to be farmed."

And 40 years later, we still think of farmers as mom and pop but really it's 3 or 4 mega corps owning the entire thing.

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Trewarin t1_jabov1t wrote

There is also a lot of acid production during the phases where bacterial like organisms convert agricultural ammonia into nitrites, and then nitrates, especially if oxygenation of the waterway is low or temps high. The pH swing also kills fish rapidly

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PastelFlamingo150 t1_jabrh47 wrote

Are there animals that eat the algae rather than let bacteria decompose it? Is there a way to reinforce a food chain with the algae at the bottom such that it replenishes fish stocks or whale populations?

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pdpi t1_jabz6p9 wrote

“Can we solve the problem with one invasive species by adding another invasive species?” Is well-documented as a disastrous strategy

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gl00mybear t1_jacv0mz wrote

Specifically in this case, why the Illinois river is infested with carp.

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GeorgeCauldron7 t1_jacw5i8 wrote

Don't worry, when winter rolls around, the gorillas simply freeze to death.

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PastelFlamingo150 t1_jac0fox wrote

That's not at all what I'm talking about. I'm talking about using the wasted nutrition to rebuild oceanic food chains from the bottom up while simultaneously pulling CO2 out of the atmosphere.

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Kaisermeister t1_jac3dbk wrote

You are directionally thinking of a geoengineering method called ocean fertilization. Using iron in the middle of the ocean where plankton normally couldn’t grow to stimulate blooms.

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PastelFlamingo150 t1_jac5ut1 wrote

That sounds very expensive compared to utilizing free fertilizer runoff.

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Kaisermeister t1_jac6us1 wrote

Fertilizer is much more expensive to produce than iron which is cheap and plentiful. Using runoff would be much more expensive (extremely so) as they would have to build millions of miles of piping and collection systems, evaporate it out, and transport it into the middle of the ocean.

And in the end, the effects would be minimal, since the nutrient the phytoplankton are limited by is usually iron.

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PastelFlamingo150 t1_jacd7ua wrote

What about setting up at the mouth of the rivers? I imagine the operation would be easier if it was operating in New Orleans rather than Midway.

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madbird406 t1_jacqiur wrote

Eutrophication already occurs at these places, because of, again, overabundance of fertilizer runoff and plankton growth. They often create "dead zones" that cause marine life to suffocate when they pass through.

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PastelFlamingo150 t1_jacsey2 wrote

Right. I'm asking if there is a way to avoid the dead zones by having something further up the food chain eat the algae before the bacteria rots them. Someone had suggested filter feeding shell fish.

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TheRealSmallBean t1_jacrwg5 wrote

I’m not sure if there is some animal that can “fix” it, but I know one of the biggest problems is that the lack of oxygen kills fish. If there’s an abundance of food, the fish will reproduce at rates that the oxygen in the water can’t support. It’s a good idea though!

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flareblitz91 t1_jacb8m8 wrote

Slightly less ELI5 expansion: Nitrogen and Phosphorous are both considered “limiting nutrients” basically every ecosystem on the planet is limited by one of these two nutrients, naturally speaking phosphorous only comes from the weathering of minerals and bio available nitrogen only comes from nitrogen fixings bacteria in anaerobic environments (such as nodes in some symbiotic plant roots) and lightning…until the invention of the Haber-Bosch process the amount of useable nitrogen on earth was functionally fixed….people were scraping guano off of rocks to make TNT…

Anyway, with industrial processes and fertilizers we’ve cranked these nutrients up to 11 to disastrous result on the environment, seriously this might be worse than climate change unless we stop what we’re doing (we won’t).

Nutrient pollution not only causes these aquatic issues, it can also heavily favor invasive species, as native plants are typically adapted well to a specific environment, which includes nutrient availability, invasive plants more suited to higher nutrients can take advantage of higher levels of available nitrogen and phosphorous, grow rapidly and displace the native plants.

This is actually one of the reasons why wetlands are so critically important, not only to they tend to collect the nutrient pollution and prevent it from being washed downstream, they are also a critical site for nutrient cycling, in this case specifically Denitrification.

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FakeLoveLife t1_jaby99q wrote

So algae thriving will end up killing algae? Thats quite interesting

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Patmarker t1_jacqduv wrote

It’s the natural order of all things. Good conditions for any organism will allow it to reproduce and grow the population rapidly. They’ll then use up all the resources and go through a massive population crash, after which the population tends to recover towards a stable level.

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alreadyhaveanaccou t1_jabznks wrote

Ambrose Furey couldn't have said it better himself. There'd be a tangent about Domoic acid though.

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where-is-sam-today t1_jac9r9l wrote

Oh! And i can reverse the problem!

The process is called amelioration - it comprises of two stages - aeration, and bio manipulation.

Compressed Ozone is funnelled through tubes to the bottom of the lake / water body, and is released through stainless steel disks. It completes the oxidation process of the decay/ decomposition of organic matter all the way from the depth to the surface. Decayed matter starts to surface and is collected. Gradually the lake literally "vomits" out the crap. That's aeration.

All this while the water quality is measured, and once it reaches optimum level, specific species of fishes are introduced , and that's bio manipulation.

The lake shines again!🍀

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arztnur t1_jac4mhd wrote

Very brief and perfect explanation. A true Eli5 should be like that.

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AnnonymousRedditor86 t1_jacimtu wrote

Thank you for explaining this so succinctly. Would you please come with me to Congress to explain this to all the states bordering the Mississippi River so that we might begin to reduce the huge dead zone in the Gulf of Mexico when half the nation's fertilizer runs off into it?

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TheRealSmallBean t1_jacs5c9 wrote

I’m in college right now to (hopefully) double major in political science and environmental studies, so that’s exactly what I want to be doing in the future!

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UntamedStream t1_jacl37e wrote

Yes! This is something that is also taught in schools nowadays (at least here in Finland)

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ColdDesert77 t1_jadayu4 wrote

Why do nitrogen and phosphorus cause algae?

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TheRealSmallBean t1_jadg90q wrote

Someone in the comments explained it really well, but plants need nitrogen and phosphorus to grow. Usually those are in limited quantities, so growth is limited by the amount available. Fertilizer is designed to provide an abundance of nitrogen and phosphorus to plants, so if those high quantities end up in the water, algae growth isn’t limited and can grow more rapidly.

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Spiritual_Jaguar4685 t1_ja9jfxy wrote

Fertilizer is basically "small creature food" and the algae and other micro-organisms eat it up and grow like crazy, sucking up all the oxygen from the water because they need to breathe too. They call this effect a "bloom", so the missing piece for you is the algae, they eat the food, they grow like crazy, they breathe up all the water-oxygen, everything else dies..

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finn_enviro89 t1_ja9sz6h wrote

Also, when the algae die, they’re eaten by decomposers, which take in a ton of oxygen, causing more things to die, causing more decomposers to thrive…

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paid2fish t1_jaap5el wrote

The algea bloom also limits the depth light can penetrate, reducing the amount of o2 produced by submerged plants and phytoplankton

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Veritas3333 t1_jaanasq wrote

To help clear up some confusion, what gets used up is "Dissolved Oxygen", which is oxygen that's in the water, that fish and plants need to survive. Fish and plants aren't separating the hydrogen and the oxygen in the water molecules, they're using the dissolved oxygen suspended in the water.

Some ways to aerate water are fountains, bubblers, or in the case of flowing water you just put a bunch of rocks in the water to create rapids, also called riffles.

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Psychological-Dog994 OP t1_ja9kopn wrote

How does water gain dissolved oxygen does it come from photosynthesis?

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Spiritual_Jaguar4685 t1_ja9lnyy wrote

A liquid will absorb a portion of any gas it's exposed to, for example water on Earth will absorb gases from the air above it. It's just a natural process called "Boyle's Law", something we've learned from physics and chemistry.

The amount of overall gases a liquid absorbs is complicated, but has to do with pressure (for example, this is why soda and beer bubble like crazy when you open them, because you're removing the pressure in the can and the beer can't hold that much gas at room pressure) and the proportion of the gases dissolved is the same as the proportion of the gases in the air (again, using beer as our example, this is why carbonated beers are so bubbly but only for a short time [lots of CO2 in the beer, barely any in the air, hence it all wants to come out quickly] and why nitrogenated beers like Guinness don't bubble as much and stay bubbly for so long [lots of nitrogen in the, but also lots of nitrogen in the air, it doesn't have any place to go])

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Fat_Doinks408 t1_jaacbqb wrote

This is why i f*cken love reddit!! Learn something new everytime!

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BudoftheBeat t1_jaav4ay wrote

Right? Like it's osmosis but for gases using liquid as the membrane

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TheRichTurner t1_jaahyry wrote

Boyle's law: 'The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.'

Boyle's law has nothing to do with water absorbing gasses.

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ThepunfishersGun t1_jabiieu wrote

Henry's Law (I believe, been awhile since college/grad school) partial pressure of dissolved gas in liquid is proportional to partial pressure of undissolved gas. IIRC, it goes: p1/a1 = p2/a2 where one side of the equation describes gas dissolved at a given atmospheric pressure and the other side describes gas dissolved at a changed atmospheric pressure.

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Revenge_of_the_User t1_jaaesjn wrote

The astronaut everyone loves, cant remember his name, demonstrated this not too long ago by being pretty deep below water level where the pressure is just...much greater than on a beach.

He shook a soda pretty vigorously, and then cracked it. Since the pressure was so high down there, the pop only slightly fizzed.

This is also why deep divers have to surface slowly, or spend time in a hyperbaric (pressure) chamber if the need to surface quickly. The nitrogen gas in their blood/tissue expands as they go up, and needs to be done slowly or you get "the bends". Think meat balloon on a cellular level. Can be fatal, or cause life long problems. One guys body swelled up like crazy after an emergency deep dive surfacing (lost his air hose) and survived; though the hyperbaric chamber didnt really help him like it can others - he stayed unfortunately very swollen. But at least he didnt die. The bends are very painful, im told.

All because of gasses in liquids at varying pressures.

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BaconIsAVeg2 t1_jaaipsl wrote

> It's just a natural process called "Boyle's Law", something we've learned from physics and chemistry.

Example of it in action here.

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paid2fish t1_jaapief wrote

Also, the amount of o2 that water can absorb is significantly affected by water temperature. Colder water holds more o2

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Mvpeh t1_jaarwus wrote

Boyle’s law doesn’t apply here.

Moveover, Nitrogen is less soluble than CO2 in H2O, and equilibrates quicker.

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breckenridgeback t1_ja9o92e wrote

Ultimately, yes: all of Earth's atmospheric oxygen is from photosynthesis. But in the more local sense, it's just dissolved into the water from the air around it.

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zaphrous t1_ja9w9d2 wrote

You can aerate water. This happens naturally where air meets water. You can do it more quickly by spraying the water in the air like a fountain. So a fountain can keep pond fish alive. Or you can use a pump to make bubbles underwater. So probably a waterfall would be the best natural way to get oxygen back into the water, but rough waters would also work well.

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takemybomb t1_jaabvkh wrote

Algae isn't creating oxygen as a process though? or there many type of algae.

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Revenge_of_the_User t1_jaafa0m wrote

Its misworded; the issue is that when the agae dies, the decomposition process eats up the oxygen....and as stated somewhere above, causes more stuff to die, causing more decomposition, causing less oxygen and more death......its pretty concerning honestly. There are pockets of no oxygen moving around in the ocean that just suffocate things.

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pleasegivemealife t1_jaalivb wrote

Just add bubbles maker like those aquariums! Problem solved. Jk

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thesquirrelhorde t1_jabtjte wrote

Nope, that just encourages more algal growth. It’s the high nutrient levels that are the problem.

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pleasegivemealife t1_jac0ns8 wrote

It's just a joke, but yes I believe the solution is more complicated than that

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thesquirrelhorde t1_jac18h9 wrote

No worries, I mentioned it as adding bubblers/fountains tends to be the go to solution for the well meaning but uniformed. I get why people do it, it seems logical. But it’s another example of why common sense is not always the right answer.

A much better solution (after reducing the nutrient input that is) is to increase the number of large aquatic plants (macrophytes). These take up the nutrients which suppresses the algae growth.

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Durris t1_jaad6hq wrote

Algae doesn't "breathe up all the water-oxygen" though.

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Book_Sea t1_jabg3u5 wrote

Algae doesn’t breathe up all the water oxygen. They are plants. It is the decomposers who eat all these small creatures who use the oxygen.

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Barneyk t1_jabjez6 wrote

>so the missing piece for you is the algae, they eat the food, they grow like crazy, they breathe up all the water-oxygen, everything else dies..

This is worded so badly.

Algae are plants that produce oxygen, they don't breathe it up.

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[deleted] t1_ja9kpl3 wrote

[removed]

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atape_1 t1_jaa9jyg wrote

Also in the top layers the algae is thick an blocks sunlight from reaching the bottom layers where decomposition is taking place, so it's even more so pronounced.

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patienceisfun2018 t1_ja9leg2 wrote

So how to prevent this or clean up the water quality in a large amount of water?

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VRFireRetardant t1_ja9nku9 wrote

The best preventions for excess fetilizer runoff are

Not using more than needed

Not spreading during wet weather

Ensuring creeks and streams next to the fields are well vegetated around the sides to slow the runoff, absorb nutrients, and slow the water in the creek which slows down the nutrients that do still get in.

There are other more complicsted methods but most follow those guidelines.

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Archaris t1_ja9u78b wrote

>Not spreading during wet weather

Farmers will respond: "Farming doesn't wait for weather"

So to get them to comply you need some laws, monitoring (water testing, sensors), and enforcement vehicle (serious fines that help pay for the monitoring).

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VRFireRetardant t1_jaa2cvd wrote

There often are laws and regulations around spreading and even for riparian zones (vegetation next to streams). The places with a lack of regulations for this are often the places nutrient run off is a signifcant issue in watersheds. A lot of the monitoring for my area is done by local watershed conservation groups who share their data with other authorities or authorities in their organization. They often work together with policy makers to find a good balance for the watershed and the economy.

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dbx999 t1_jabbqj1 wrote

You would think that fertilizer is expensive and you wouldn’t want to let it go to waste by running off places that won’t help you grow your cash crops.

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patienceisfun2018 t1_jaakvha wrote

But what about cleanup, past prevention

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VRFireRetardant t1_jaav27f wrote

Nutrient clean up is incredibly hard. The life in the water uses the nutrients quickly and exponentially multiply. Watershed restoration can help reduce impacts by increasing wetland and stream health and allowing these ecosystems to take up more nutirents before they enter the lake or ocean. These strategies can take a few years to fully reestablish and must be protected and maintained from invasive species or erosion removing the vegetated portions.

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[deleted] t1_ja9mcqj wrote

Preventing excess fertilizer and other pollutants from entering waterways is the best way to ensure the water quality stays high. But

  1. using less fertilizer and pesticides on plants and crops,
  2. using organic and natural alternatives to chemicals when possible And
  3. dispose of hazardous waste properly are other ways to prevent it
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sickeningly_sweet t1_jaaih6e wrote

'organic' and 'natural' are dangerous words to use, as they don't really mean anything, and often are worse for the environment than synthetic chemicals.

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Mr_BriXXX t1_jaavx7x wrote

They can be. But most are lower concentration and work by supporting microbial action which aids in carbohydrate exchange instead of heavy loading of nitrogen, phosphorus and potassium. Depends on a what they are using and how much. In poor soils in harsh growing environments organics alone aren't always sufficient or heavy applications of high urea content are required (not great for the waterways, to be sure). Ideally, you need to manage your soil carefully over a prolonged period - and even, then, it's not always possible if the environment is inhospitable. Like most things, the truth is complicated.

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Naive_Composer2808 t1_jaa0cqn wrote

Don’t discount mechanical aeration, as a fast way to remediate.

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Soranic t1_jaafguq wrote

Since these zones are usually dead anyway, could we detonate a nuke at the bottom of the dead zone so it mixes everything?

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CBus660R t1_jaavpnb wrote

That won't do anything except make it radioactive too. The dead zones are in shallow waters, they're not out past the continental shelf where the depths are in the thousands of feet deep.

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thebiologyguy84 t1_jaac3z6 wrote

Ok, I teach this to my biology students: Algae are members of the protoctists (essentially organisms that don't quite fit the definition of animal, plant, or fungus). They grow rapidly in fertiliser causing light to be blocked from water plants. They die leaving behind a smorgasbord of food for bacteria and fungi and other decay-eating microorganisms. As they live, like us they need oxygen to perform respiration.....taking oxygen from the water, leading to larger organisms such as fish to die, leading to more bacteria etc etc etc finally causing anoxic water which smells and nothing larger than a cell is alive in it.

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Mammoth-Mud-9609 t1_ja9pf3e wrote

Eutrophication or hypertrophication effects the water system. Excessive nitrates and phosphates from farms and sewage can promote the growth of algal blooms which then can choke the life out of rivers lakes and streams. https://youtu.be/gGDWsZNrF-8

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Birdie121 t1_jaathyt wrote

The waterways get "algae blooms" where all the extra nutrients from the fertilizer helps algae grow rapidly. However, this algae all dies fairly quickly and becomes food for a lot of microbes which breath oxygen just like us, releasing carbon dioxide. So those herbivores/decomposers end up using all the oxygen and the fish die as a result. So it's not the plants/algae that deplete the oxygen, it's the herbivores and decomposers that can grow rapidly from having a huge food supply.

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ruidh t1_jaahfuu wrote

Usually nutrients are the limiting factor in keeping plants from growing. Add a large amount of nitrogen and phosphorus and they no longer are the limiting factor. Oxygen in the water becomes the new limiting factor.

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Intelligent-Bat1724 t1_jab0fj5 wrote

Crops that require high concentrations of nitrogen, are usually the most treated with fertilizer.

For example, sugar cane fields in Florida are fertilized several times during the growing season. The fields are in south central Florida in or near the basin that drains into Lake Okeechobee. This causes blooms of blue-green algae. This is a highly toxic mess. It makes the lake unusable for boaters and outdoors people. This also aversely affects the St Lucie River which drains out of the lake to the east and the Caloosahatchee River to the west....These waterways and tributaries often become odoriferous nightmares. Anyone with allergies, asthma or other respiratory issues have to stay away from the water until such time as the blooms disappear.

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EpidemicRage t1_jaahwb2 wrote

Fertilizers give nutrients into the water. Since there are more nutrients, more algae and other plants grow. But eventually the nutrients are consumed and then the algae die. Then microorganisms decompose the dead algae/plants and in this process oxygen is consumed.

Hence, overall oxygen levels decrease.

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Dungwit t1_jacvuvw wrote

The nitrogen feeds algae.

Algae requires oxygen to survive.

With all the excess nitrogen feeding it the algae multiplies enormously until there is so much it is consuming all the oxygen and killing all the fish as a result.

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[deleted] t1_jaa5cli wrote

[deleted]

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Taibok t1_jabk81k wrote

Photosynthesis requires oxygen?

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Vergesso t1_jaby959 wrote

It does not, but plants on their own breathe too. They produce more oxygen that they need, but photosynthesis happens not in the same organella that breathing does, so there is some travelling oxygen has to make before it may be used in breathing.

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