I'm Kevin Rose, the corresponding author for a paper recently published in Nature on widespread declines in lake oxygen - Ask me anything!

I work on Mfangano Island (Kenya) and Buvuma Island (Uganda) in Lake Victoria. I’m a PhD student in global health at Drexel University developing a program for economic empowerment of adolescent girls to reduce the spread of HIV/AIDS that occurs during transactional sex with older men in the fishing industry. Fish catch is significantly reduced due to the impact of the invasive Nile Perch and nutrification of the lake from runoff of agricultural products amid deforestation (as wood is used to make charcoal to sell).

My question is, what kinds of strategies can community members and public health workers implement to prevent, slow down, or reverse deoxygenation of Lake Victoria? Fish in this lake are a major staple of the local diet and drive the economy. We are in desperate need of tangible solutions to protect and revive Lake Victoria in any way possible.

Wow - the work you're doing sounds really important and impactful. Thank you!

I'm not too familiar with the details of Lake Victoria and if it is losing oxygen over time, but papers by O'Reilly et al 2003 and Cohen et al. 2016 shows that productivity in nearby Tanganyika has been declining over time. This is due to stronger stratification (warmer surface waters sitting on top of colder deep waters, and the difference in temperature and density between these layers is increasing over time). This same phenomena is driving long-term dissolved oxygen declines in many lakes.

One method to reduce stratification strength may be to work to improve water clarity. Higher water clarity enables more light (and heat) to penetrate to greater depths, so that the density gradient through the water column is less steep. Dark/turbid water traps more heat right at the surface, increasing stratification strength and reducing upwelling of nutrients and mixing of oxygen. More generally, working to strengthen the legitimacy and activity of watershed management organizations may be an important first step toward this goal.

The papers I mentioned:

https://www.nature.com/articles/nature01833

https://www.pnas.org/content/113/34/9563

Why don't we start at square one, for the link adverse among us? I assume "lake oxygen" is the amount of oxygen in a lake. Is that correct, why is it changing, and why should we care?

Yes, "lake oxygen" refers to the amount of oxygen that is dissolved in water. All complex life depends on oxygen. In aquatic ecosystems, whether it be lakes, ponds, rivers, streams, or the oceans, oxygen is in a dissolved form. Declines in oxygen threaten the survival of many species. When oxygen goes to zero (termed "anoxia") you also get other chemical reactions occurring. Sediments release phosphorus, which is a nutrient limiting algal growth. So more anoxia tends to increase phosphorus, which tends to increase algal growth. Too much, and you often get harmful algal blooms which are harmful to people and wildlife. Anoxia also tends to result in more methane release, which is a potent greenhouse gas.

Now, why is it changing? The solubility of oxygen in water goes down as temperatures goes up. So part of the story is that climate warming results in lower oxygen concentrations. But that's only part of the story. In deep waters, temperatures aren't warming. But warmer water in the surface effectively "caps" exchange with the atmosphere. Longer summer seasons mean less mixing with the atmosphere, giving more time for seasonal draw-down of deep-water oxygen concentrations. In many places, water clarity losses also contribute to oxygen losses. Water clarity losses mean less oxygen producing photosynthesis, especially in deep waters.

tl; dr: just like you depend on oxygen for survival, so does every other complex life form on the planet. And losing oxygen also reduces water quality, too. The trend toward deoxygenation is driven by climate change and water clarity losses.

I guess we all going to die

Said in jest? I hope so! I'm an optimist. Sure, dissolved oxygen is declining in many waterbodies, and that threatens water quality and many oxygen-sensitive organisms. But there are lots of environmental success stories, too. Some are at a local level, and it could be as simple as cleaning up trash on a street. I've seen pictures like that regularly on reddit, and hopefully it inspires people to recognize that we can be agents of positive environmental change in the world. At a larger scale, there have been things like the Montreal Protocols, which regulated CFC emissions, which deplete the ozone layer.

Its easy to be fatalistic and think that the environment is a goner, and there are plenty of stories of environmental loss out there. But as an example of a resounding success, the Montreal Protocols is an environmental treaty, and the only treaty in the history of the UN that's been signed by every country on the planet. That is amazing! It shows that when the science is clear, people care, and a solution exists, things can really change for the better.

Our research on dissolved oxygen in lakes is hopefully the first paragraph in this story. It demonstrates the science and highlights a challenge. The next steps, and what we do from here, are up to all of us.

Wow, scary. Is this deep water capping disruptable? I would guess that surface winds could break it up, given enough strength and time.

The stratification that develops that isolates deep waters is broken down seasonally. In most lakes in the temperate zone (e.g., most of the US and Europe), lakes mix fully in the spring and fall. The trouble is, in between these times of year oxygen can get very low. Many species, such as cold water fishes, depend on cold deep water habitat, so if oxygen declines (as it has been), it threatens their ability to survive in that waterbody.

Water is H2O. If there is not 2 oxygen with 1 hyrdrogen then it is not water. So what are these low oxygen lakes filled with? The single hydrogen should revert to gas under normal conditions, right?

Water is made of oxygen, yes, but what we're talking about is atmospheric oxygen (O2) that is dissolved in water, not the atoms that make up water. When you have a glass of water, even if filtered through the best filter out there, it is not just pure water. There are atmospheric gases dissolved in it. A little bit CO2, some nitrogen, and some oxygen. We're talking about the same thing in water.

Thanks for clearing that up. I do have a follow up question. Is it possible that a water electrolysis station could be built nearby and then pump the newly freed oxygen back into the water?

I’m no chemist, but I think if energy and purification could be addressed efficiently, then this seems plausible. Could be a great solution at local levels.

The generation of both hydrogen and oxygen gas can be a serious fire/explosion hazard, so if safety is addressed as well this might be a cool concept to expand on!

Worth bouncing off of some chemists and electrical engineers.

Theoretically, this sounds like it would work. But I see two problems. First, there are >100,000 lakes in the US alone. Would we put a station near, on, or in every lake? That doesn't seem feasible. Secondly, Mixing the oxygen at depth is a substantial challenge. Deep waters often have very limited mixing, which is part of the reason why dissolved oxygen gets depleted in the first place. Artificially mixing them would likely alter their temperature - likely warming them up - as they mix more with surface waters. That reduces the deep, cold water habitat we would be trying to protect.

Could the introduction of Oxygen producing plants help to mitigate this? Could it mitigate it for say 40 years?

Plants can help in some circumstances. But the biggest problem is dissolved oxygen losses deep in the water column, where light is too low for photosynthesis. In this case, a solution is to improve water clarity, to enable more oxygen producing photosynthesis at depth. But improving water clarity can be challenging, as it often depends on reducing watershed run off of nutrients and organic matter. Things like planting and maintaining buffer zones can help, as can better waste water treatment and reduced fertilizer application. The neighbor's bright green grass comes from fertilizer application, and often that comes at a cost of high nutrients in runoff.

I used to watch Diggnation every weekend with my girlfriend (now wife) years ago!

My question is, do you think in our lifetimes we will see some form of evolution or extreme adaptation but the wildlife that live in these lakes to compensate? Maybe not like, physical changes but perhaps more behavioral - like how raccoons adapted to the growth of cities?

Scientists have observed what is referred to as "rapid evolution" in the lab and in outdoor experiments, over the course of weeks to months. It occurs in short-lived organisms that go through many generations in a short time. Some evolutionary changes in some organisms, such as zooplankton, phytoplankton, and bacteria, is certainly possible.

More likely, as you mention, are behavioral and physiological adaptations. Organisms avoid waters with low oxygen concentrations. Some types of zooplankton look blood red when in low oxygen environments, because they produce more hemoglobin to compensate. So there are behavioral and physiological changes that occur in response to low oxygen.

I'm reminded of Jeff Goldblum's character in Jurassic Park, when he says, "Life finds a way". Its often true. The challenge, though, is that oxygen is just one stress to organisms. Adaptations often come with tradeoffs, so adapting to one stress can make an organism more sensitive to another. That can become a problem.

Edit: BTW, I'm a different Kevin Rose. Not the founder of Digg. com. Sorry to disappoint! ;-)

Wrong Kevin Rose lol

This dude is a natural scientist, the other is the computer digg guy

Haha - thanks for catching that! Ya, different guy. Although I wish I had his bank account.

I wish I had his raccoon wrestling skills.

raccoon wrestling skills

I just watched that video. Racoons aren't to be messed with. They can get up to 70 lbs! That was impressive.

I thought about asking if he gets mistaken for the other Kevin Rose, but that's moot now.

The only other time I've been confused for that Kevin Rose was years ago: My wife's grandmother saw the other Kevin Rose on the cover of Businessweek magazine giving two thumbs up. The title on the magazine read something like, "How Kevin Rose made $60 million in 18 months". She gave the magazine to my wife and (jokingly) told her that I should be buying anything she wanted! :-)

This one: http://www.wordyard.com/2006/08/04/businessweek-on-digg/

What advice would you give an aspiring scientist in your field?

Somewhat depends on what you aspire to, as there are different things you may want to do, depending on if you want to work in academia, government, consulting, not-for-profits, or industry. But, my general advice is: Work hard, learn some solid technical skills (e.g., programming, statistics) and baseline knowledge in your focal area, and work to construct a strong professional network - those that can speak to your work ethic, skills, etc. If you're interested in academic research, then there are lots more specific advice I can provide.

Who pays for your research?

I'm a professor at Rensselaer Polytechnic Institute, a private R1 university in New York. I've obtained grants from places such as the National Science Foundation. This particular paper was supported primarily by NSF funding, but we had a large group of collaborators on it, who were supported by many mechanisms where they are located. We had >40 coauthors in total. The data we used in the paper was collected for decades with support from many organizations, including governments (Federal, State, Local), not-for-profits, and academic institutions.

Is it hard to do anything online when you share the name of a more famous Kevin rose?

Meh. I prefer the anonymity that can come with it. When you google my name I don't immediately come up. But, I'm relatively easy to find if you know something about me (e.g., that I study ecology and water quality), so its still easy for folks to find you if they are really looking.

This is exactly what Digg.com Kevin Rose would say if he was living a double life as a water ecologist but forgot to change his name.

hahaha - caught me! ;-)

Can and should artificial means of oxygenating the water be developed / deployed?

There are artificial aeration techniques used in many places. If you've seen a fountain in a small pond in a park, there is a good chance it was installed to ensure adequate oxygenation of the water column. There are other systems that work on slightly larger waterbodies, too, where bubbles are pulse injected at depth. But in general these systems are expensive and do not work on large lakes, where most aquatic habitat is located.

The best way to ensure adequate oxygen in the water column is to reduce runoff from the surrounding landscape. Oxygen is often one of the top managed-for water quality characteristics. And lakes with low oxygen in deep waters also often have other undesirable characteristics, such as low water clarity, surface scums and algal blooms, etc.

Is the issue mostly cost? As in, if the cost could be kept down then it would be doable? And what are the big expense items? Energy costs, maintenance, or the initial installation?

I *think* the costs would be in the initial installation and energy costs. It would be pretty expensive to implement a system in a large lake. And who would pay for it? Those living right nearby? The government (so shared by all)?

I live near Lake Mendota in Wisconsin, and the university Limnology department, as well as a couple of non profits, have been trying to convince people to reduce runoff into the watershed for years. But what they've done barely seems to help -- we've got "beaches closed due to algae" signs up all over. Does more need to happen at the federal level?

There are some regulations on water quality and runoff at a Federal level, but they are all geared toward point source pollution, such as that coming from waste water treatment plants. Non-point source nutrient pollution is not regulated at a Federal level.

The central issue in southern Wisconsin is the agriculture, and dairy is a large player in the issue. Wisconsin is America's dairyland, after all! What do farmers do (or should they do) with all of the manure waste the cattle produce? That waste is very high in nitrogen and phosphorus, which fuels algal blooms when it enters lakes like Mendota and Monona (which, incidentally, were both included in our study).

The biggest issue in a region like where you are is rain on snow events. During the winter months, dairy farmers often spread manure on their fields as a fertilizer, but also to get rid of it. There otherwise would be too much waste build up over the winter months. Well, come spring, you start to get rain on frozen ground. That flushes all of those nutrients into the lakes from the manure. Something like 80% of the nitrogen and phosphorus budget in Mendota comes in ~20 days a year.

How do solve the issue? Regulations could be put into place, but the manure waste has to go somewhere. Where should it go? Who should have to pay for it to be removed from the farms? If a farmer has to pay to dispose of it, it makes food costs for all of us go up. These aren't easy questions to answer, and they highlight that there are important tradeoffs.

Are we doomed?

I certainly hope not! The loss of oxygen is not exactly a good sign of how things are changing. But there are environmental success stories, too! Perhaps I'm just optimistic, but positive environmental changes can and do happen.

I'll have to read your paper but besides sustainable farming techniques already in practice, how else can eutrification be reduced in commercial agriculture? Is there any hope for a global solution?

Great question. Reducing fertilizer application is an excellent start, and applying it more timely (e.g., not before storms that wash it off fields, etc). More generally reducing the runoff of nutrients, sediments, and organic matter into waterbodies would be a big step forward, and there are many ways to do that. Planting buffer zones can help, as plants in this zone trap nutrients, sediments, etc, before they enter waterbodies.

Unfortunately, there is probably no "global" solution to eutrophication. It is an issue best addressed at the individual watershed. However, there are certainly best practices (e.g., buffer zone plantings) that can be applied across watersheds.

Is there a latitude line where this impact is higher or is it seen equally across all latitudes?

Our work focused on the temperate zone. We had a few lakes from other latitudes, but not enough to really understand what was happening elsewhere. We didn't see an effect of latitude. But, we did see that areas with faster warming had greater oxygen losses, especially in surface waters. So latitudes with faster warming would likely be losing more oxygen. While we had very few lakes from the Arctic (Toolik Lake in Alaska was one we had, though), the Arctic has been a region of very fast warming, and it is likely that lakes are losing oxygen rapidly there, as well. That is something I'd love to study in more detail to confirm or refute if it is true, because these same habitats are really important for global carbon cycling and habitat for cold water fishes.

Is this a decline in oxygen or a lack of circulation with anoxia at the bottom (as is typical in arctic lakes)?

The decline in oxygen is due to several drivers. Part of it is stronger stratification, which reduces circulation. Part of it is warmer temperatures. The solubility of oxygen in water goes down when temperature goes up. Finally, water clarity is also important. Lower water clarity means less oxygen producing photosynthesis.

Unfortunately, we didn't have many arctic lakes in the study - I wish we did!

Unfortunately, we didn't have many arctic lakes in the study - I wish we did!

Yes it's quite tough to look at these arctic lakes. My research (I'm a PhD student) is on high resolution, non-hydrostatic simulations of ice-covered lakes, so entirely below the temperature of maximum density. Certainly one of the biggest challenges for trying to connect my research to real geophysical flows is the general lack of measurements in these lakes.

Were any of the lakes you studied looked at in the winter season (with some ice-coverage) or entirely ice-free?

Sounds like interesting research. The Nature paper focuses on the late summer period (July and August in the Northern hemisphere). We chose that time period because it was when most lakes were sampled (larger data set) and it is also when dissolved oxygen tends to be seasonally lowest. We thought that if dissolved oxygen was going to be declining and causing a problem, it would be at a time of year that it is usually pretty low to begin with.

All that being said, there is a subset of lakes with better seasonal coverage. I'm personally collecting temperature and dissolved oxygen data on several lakes 24/7/365. Send me an email if those data might be useful to your modeling (you can find my email on RPI's website, or our paper).

My apologies I have not reviewed your research. Do you see pattern distribution? Eg, It starts here and spreads to .....

No worries - that's why I'm doing this AMA! We saw that lakes were losing oxygen in many locations. Most of our data was from the US and Europe, where monitoring has been going on for decades now. It is likely occurring in other places, though, too, because the drivers of deoxygenation are occurring in other places (Drivers being climate change and water clarity losses). If you're interested, you can check out the abstract to the paper on Nature's website: https://www.nature.com/articles/s41586-021-03550-y

And some news outlets have pretty good coverage of the research, too, such as the Guardian: https://www.theguardian.com/environment/2021/jun/02/climate-crisis-is-suffocating-the-worlds-lakes-study-finds

Our paper is going to be summarized on NPR's Science Friday podcast today at 2PM EDT as well.

Has your research ID precursors that exists before a lake moves into the oxygen depletion stage?

Good question. Fast air temperature warming rates in the region would likely be a good indicator. As would water clarity losses.

Concerning the climate issue.. are you as inwardly optimistic as you are outwardly?

I tend to be optimistic. Part of this comes from seeing some success stories and recognizing that ecosystems almost always have some redundancy built into them that enables them to be resilient to disturbances and some human impacts. Of course, there are plenty of examples of substantial environmental losses, and human impacts so severe that ecosystems may take hundreds or thousands of years to recover. For example, it will take millennia to replace the biodiversity we've lost through species extinctions. But right now I see promising environmental trends on the horizon. The rate of solar and wind growth in energy production is growing by large double digits annually right now.

Many of the most pressing environmental problems require a combination of social and technological solutions. It can be difficult to predict these ahead of time, because change often occurs exponentially, whereas it seems like most thinking and awareness is more linear. But the indicators of positive changes are there, such as the growth in alternative energy production. In the US, we've also passed peak water and fertilizer use already. These are encouraging trends.

Is there a database or table where we can look at the data pertaining to individual lakes? I'm curious about lakes in my area.

We have supplemental tables in the paper that have the trends for all the lakes in the study. We worked to make as much data as publicly available as possible, too. Almost all of the data is available online at the Environmental Data Initiative at: https://portal.edirepository.org/nis/mapbrowse?scope=edi&identifier=698&revision=3

While a big study, this was still only about 400 lakes. There are well over 100,000 lakes in the US alone. So this is a drop in the bucket relative to all the lakes out there, and depending on where you live, there may be none nearby. But it was the best we could do: we can only analyze data when it exists! :-)

Is there anything that fishermen/outsdoorsmen can do to help?

Absolutely! Citizen scientists regularly help collect temperature and dissolved oxygen data on many lakes. Get in touch with your State DNR or local lake association, who can probably tell you more about any routine monitoring that is going on.

Hello, I hope you're still up. What do you think about the increasing phytoplanktons in seas? Can this positively effect oxygen levels? Sorry if it's been irrelevant

Fair question. Some places have seen increasing phytoplankton in the oceans, as well as in lakes. This can increase oxygen in surface waters. But excess phytoplankton in both lakes and the oceans eventually die and settle to deep waters. They undergo rapid decomposition, which consumes oxygen. This often results in low oxygen conditions in deep waters of lakes and coastal zones where phytoplankton are abundant. You can google the dead zone in the Gulf of Mexico as an example of this process in action.

Can you make the article open access? It would be nice to be able to read it, especially since it's funded with public money like NSF grants. Thank you.

I wish I could, but it cost something like $11,000 USD to make it open access. However, I believe I can share pdfs of it individually, and I can put it in a public repository six months after it is published, which I plan to do.

These results seem so important—can you speculate on why there hasn’t been more research into this habitat-threatening imbalance all around us?

Great question. Our study was five years in the making. That might give you a sense of the difficulty of compiling all of the data (>45,000 profiles from ~400 lakes) and figuring out what the data are telling us. It is important work, but it wasn't easy to do.

Assuming we cannot reverse deoxygenation in lakes, what do you believe we should do, individually, to prepare? For instance, do we each need to think about home filtration and purification of tap water?

We can reverse this, and some lakes in our data set had increasing oxygen levels. Reducing runoff, which includes organic matter and nutrients, and really help the issue.

Sure, I understand this perspective. My question, however, deals with a specific risk factor; namely: the non-reversal of deoxygenation of large bodies of water. And I’m particularly NOT focused on policy, rather, I’m interested specifically in individual protective behaviors: IF deoxygenation continues, what do individuals need to do to protect themselves from potential harm?

OK, I think I understand now. In reality, there isn't much threat to humans. The threat is really to the integrity of the ecosystem and to the species that inhabit it.

The potential threat to humans occurs after oxygen is depleted. At that point, the chemistry changes and anoxic chemical reactions occur that often release nutrients like phosphorus from lake sediments. That fuels algal blooms, and, when nutrients are high enough and other conditions are correct, harmful algal blooms. These harmful algal blooms are toxic to humans and wildlife.

As an example, Lake Erie regularly goes anoxic (zero oxygen) in its deep waters each summer. The lake also gets some pretty serious harmful algal blooms. The city of Toledo, OH, had to shut down the drinking water intake to ~400,000 people a few years ago due to high toxins from the harmful algal blooms in the lake. So there can be a human health impact, but it is not from low oxygen in the water. It is from the knock-on effects that occur after oxygen is depleted.

How to deal with that? Well, folks in Toledo had to drink bottled water for a few days.

I'm currently doing a project on predicting algae blooms but more in coastal areas thanks to aquaculture. I am wondering if I should be lagging the oxygen variables, what are your thoughts on it?

Collecting more data is usually a good thing, if you can do it relatively easily and have a research question or use of the data in mind.

There's been lots of work done in coastal zones on dissolved oxygen that you may want to check out. For example, see some of Denise Breitburg's research here:

https://scholar.google.com/citations?user=4qImBvgAAAAJ&hl=en

Could this be due to the increase of wildlife within them? More animals = More oxygen intake.

Great question and thought! Often, microbes (bacteria) are the biggest source of heterotrophic respiration (oxygen consuming organisms). So, in a way, yes, the loss of oxygen is, in some places, a reflection of the increase in organisms with heterotrophic metabolisms (as opposed to organisms with autotrophic metabolisms - such as oxygen producing algae). But bacteria are probably not exactly the charismatic type of animal you're thinking of.

Overall, the declines we saw were associated with changes in temperature, so while increases in respiration are occurring in many locations, our work doesn't indicate that it is the overall most important driver of the loss of oxygen in lakes.

There was an interesting documentary a few years back about Uncertain, Texas and a fisherman dependent on a lake there to earn a living.

An invasive weed was starving the lake of oxygen, which I had no idea could happen and killing off wildlife. The doc covers other subjects, but on this particular one it was a good example of the effects of something like this.

Interesting - I've never heard about this case. Usually, invasive weeds (such as Eurasian watermilfoil, Curly leaf pondweed, etc) are photosynthesizers, and hence produce oxygen. I'm totally speculating here, but these same invasives can and do often reduce turbulence in the water column. Essentially, they slow the movement of water. So it may be possible that, despite producing oxygen themselves, they also reduced mixing of oxygen to deep waters in this particular case. I'd be interested in checking out that documentary.

Do you know why Aral Sea’s water has more oxygen on the bottom compared to the surface? I hear that’s the only lake to have this type of phenomenon

Interesting; I didn't know this was the case for the Aral Sea. I've never been there and don't know much about the lake. But, I'm fairly sure the salinities vary quite a bit among the basins. Salinity can impact how strongly stratified the water column is, so I suspect it might have something to do with density gradients among the basins and how much resistance to mixing there is, or where (at what depth) stream water inflow plunges to in the lake.

Intuitively, how can a relatively small change in temperature (about 1C above the pre-industrial level) cause such a dramatic decline in lake oxygen?

I do understand that oxygen is less soluble in warmer water, but the difference doesn't seem to be large enough to explain the effects you've found.

Its a solubility effect, but also due to changes in stratification. Surface temperature were warming, which reduces solubility. Meanwhile, deep water temperatures did not increase. So the temperature difference between surface waters and deep waters increased. This is called stratification, and stronger stratification resists mixing of oxygen from the atmosphere to deep waters. This enables deep water oxygen to be drawn down more each season, as there are many oxygen consuming organisms in deep waters. Meanwhile, water clarity is often low, so there is little to no oxygen producing photosynthesis at depth. Deep waters depend on the mixing of oxygen from the atmosphere, and when that mixing decreases due to stronger stratification, deep water dissolved oxygen falls as a result.

tl; dr: The effects of temperature increase are two-fold: reduced solubility as well as reduced mixing from the atmosphere to deep waters.

what are you top 3 favorite lake-dwelling fish/amphibians?

There's a frog that lives in Lake Titicaca that is really cool. Oxygen is low there (very high elevation). Frogs breath through their skin. The frog has evolved such that has plenty of extra skin. It looks like someone who used to be very large but just lots hundreds of pounds. Its really interesting. That might be my favorite. Closer to home, I'm a fan of Grey's tree frogs, as they sound like summer evenings to me. And Brook trout are beautiful.

Is this related to the crazy algae showing up every year in Lake Hopatcong in NJ? https://abc7ny.com/lake-hopatcong-algae-no-swimming-bloom/6376328/

Hey there - very close to my hometown (Sussex County, NJ)! What is happening in Lake Hopatcong is similar to what we talk about in our paper. Harmful algal blooms like those on Lake Hopatcong are often associated with deep water oxygen losses. That's because the algal blooms eventually senesce, die, and settle to the bottom of the lake. The algal cells are easily decomposed, and decomposition consumes oxygen. So large blooms can result in rapidly consumed deep water dissolved oxygen. That deoxygenation in deep waters then changes the chemical reactions that occur, often releasing phosphorus from lake sediments.

Phosphorus is a limiting nutrient, meaning that you often get increases in algal growth when phosphorus increases. So the blooms like you describe can "lock in" a feedback cycle that results in further blooms and low oxygen conditions.

1) What’s your favorite lake? 2) what’s your favorite lake that you’ve got to visit / study?

I love this question!

Favorite lake. Hmm. That is a tough one. It might be Crater Lake, Oregon, because it is just so beautiful. But also, lakes in the Adirondacks in New York are special to me, and I'm particularly fond of Upper Saranac. But I'm also a sucker for alpine lakes (those above treeline) and I studied lakes along the Beartooth highway in Wyoming/Montana for my PhD. So many excellent ones to choose from. I've also worked on lakes in the Canadian Rockies (e.g., Lake O'Hara) and they are absolutely gorgeous.

My favorite lakes are also ones I get to study. One of my PhD students just published a paper on Crater Lake, and I take every opportunity I can to visit new beautiful lakes. I study lakes because I love them.

Who should we look to for fixing/changing this problem?

Addressing the decline in oxygen in lakes can occur both locally and globally. The drivers of oxygen loss in lakes are due to both water quality losses (e.g., water clarity losses) and climate change. Improving water quality in a lake is often a local task, and there are many things folks can do locally to improve water quality. Addressing climate change, well...is a far greater and global issue. But things can be done locally, such as working to reduce fertilizer use in a watershed, or planting buffer zones around waterbodies, which help trap nutrients and organic matter before it enters waterbodies. Ensuring waste water is treated properly is another important thing that can be done locally to regionally.

How can citizen scientists help you to improve or extend your dataset?

Citizen scientists and lake associations are really important! Many individuals play a key role in collecting data, including data used in our study. However, measuring dissolved oxygen can be expensive. Sensors are about $1000 USD each. But measuring temperature and water clarity are pretty cheap and easy.

We published our dataset, so folks can see what data we already have: https://portal.edirepository.org/nis/mapbrowse?scope=edi&identifier=698&revision=3

In terms of adding new lakes or starting collecting new data, the best way to go about it would be to contact a lake association. These organizations often care very much for their nearby waterbodies and engage in routine monitoring. Statement management agencies (e.g., your State DNR) also often play a coordinating role, and sometimes have equipment to lend out.

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Not sure I follow...can you explain what you mean?