limno_prof

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.

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.

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.

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! ;-)

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