Localized climate control in the Sonoran Desert

The advent of central air conditioning is the leading factor contributing to the huge number of people moving to desert areas such as Las Vegas, NV and Phoenix, AZ. Probably also other cities in other southern states in the U.S., like Houston. Places where things are fine, until they aren't.

The house where I'm staying has the benefit that it actually has two central AC units, so when one died, the other could at least keep half of the house at a tolerable temperature. And the chances of massive, extended power outages like the one recently experienced in Houston are lower here for a number of reasons. I do not consider this sufficient reason to move to the desert, just noting the overall situation.

In any case, when central air units die, it is very expensive to replace them. But at least mildly entertaining to watch.

Shiny new unit arrives:


Craning out part of the old unit:


And old swamp cooler also got taken out at the same time since it hasn't been useable for a while now.


Whee!


Swamp coolers are far more energy-efficient than air conditioners. They are basically just giant fans that blow across water, using evaporative cooling to lower the local temperature. However, they don't work as well once the desert hits the monsoon season, so they've generally fallen out of favor. In addition to their energy efficiency, they offer the advantage that they can be used with the windows open. On the other hand, because they rely on water, they tend to rust out over time.

One of the other historic climate control methods in this area is flood irrigation. Flood irrigation is not particularly water-efficient, but it is quite nice in several different ways. For one thing, it provides deep watering that is beneficial for keeping large shade trees alive. Shade from trees is rather precious in the desert. For another thing, the evaporative cooling of flood irrigation does help keep flood-irrigated neighborhoods cooler than non-flood-irrigated neighborhoods. You can feel a noticeable temperature difference when riding a bicycle from a non-flood-irrigated area into a flood-irrigated area.

Much of the flood irrigation water travels to different neighborhoods through a network of canals. The original canal network was created by the Hohokam more than 1400 years ago, but then abandoned at around AD 1450 for unknown but likely climate-related reasons. In the recent past, many of the canals in this region were tree-lined, and served as places where people could go to swim and cool off during the summer heat. At some point that ended, I believe under the thinking that the trees were causing a lot of water loss, and maybe also the canal structure changed to the point where it no longer seemed safe or prudent for people to swim in the canals. Not sure. Some more specific history can be found here, in any case. But now the canal network forms an alternative transportation system that is tangential to the street grids, so the canals remain a great and lower-stress place for riding bikes or walking the dog. At least until a person reaches a road crossing and has to play "frogger" across 4-6 lanes of traffic traveling at speeds of 45 mph or more.

Anyway. The house where I'm staying has flood irrigation, and was scheduled to receive water yesterday. At the Farmer House, a Zanjero (just learned the term!) opened the valves, but here, the homeowner is supposed to open the valves. Except the current homeowners are down in southern Arizona, so I'm in charge.

My inner five-year-old was pleased.


12-second video of water coming out:

Watch on YouTube

The second valve:


The second of the two valves for this house, which is in the backyard, supplies the front yard, via a small "creek" that forms alongside the house.

I was trying to read papers while sitting at a desk, but got distracted by some of the small drama of the flood irrigation outside the window next to the desk, where the flood water chased a bunch of beetles out of their hiding places and onto a small rock island (center of 20-second video below):

Watch on YouTube

I didn't get this part on film, but periodically a beetle would just decide to take the plunge and would jump off the rock into the water, swimming away towards the other side. I don't know why more of them didn't just try and get closer to the house, where the ground was higher, but maybe staying in the shade was a higher priority than staying dry.

At one point, a desiccated (ornamental) orange with one side punched in floated past, looking like a small boat, and 3-4 beetles tried to jump into it, capsizing it.

Typically, the flood irrigation waters take a day or two to sink into the soil, and then it's back to desert life as usual.

Three links, unrelated

1. The NYT recently published an interview of Robert Putnam, known as author of the book Bowling Alone. He's rather pessimistic about what has happened in the US in the time since the book was published, but there are some interesting responses mixed into the interview: https://www.nytimes.com/2024/07/13/magazine/robert-putnam-interview.html

2. I appreciated this recent article about how discoveries made using ground-penetrating radar are shifting thinking about how people lived during prehistoric times: https://aeon.co/essays/an-archeological-revolution-transforms-our-image-of-human-freedoms

3. This article is a reminder to be aware of the effects of natural disasters on people who were already economically marginalized: https://www.texasobserver.org/hunger-hurricane-houston-beryl/

And now I shall close those tabs.

Writing progress: nonlinear [work, status, manuscript of doom, writing]

So about a week after getting to Arizona, I finally finished a reasonably thorough draft revision to a manuscript I'll call the 2018 seed-harvester ant paper, and sent it over to my hosts, who are coauthors on it, for their review and feedback.

Then, while in the transition phase between that and the next writing project, I had one of those thinking-out-loud conversations that went, "Oh yeah, of course the next writing project I should work on is the next paper that's closest to being ready to submit."

...That would be a leafcutter manuscript rather than the next seed-harvester paper (the "2021 seed-harvester ant paper").

...the only major downside being that switching from seed-harvesters to leafcutter ants is kind of a big intellectual shift, for me, at least. To wit, I spent a bunch of time last week just trying to get my leafcutter ant annotated bibliographies better organized (yes, that's bibliographies, plural), to identify where I need to brush up on the literature, and since then I've been spending a bunch of time trying to find and read any information I can about how fungi might respond to excess nitrogen (protein).

Half of the challenge tends to be just figuring out how to dial in on what my question actually is, to figure out how to search for sufficiently specific information related to my question. "All fungi" is FAR too broad; I really just want to learn about saprotrophs - and soil saprotrophs rather than wood saprotrophs, but often they get studied in the context of "soil microbiota," which will also always include ectomycorrhizal fungi and bacteria, okay, rightly so. But the thing is, the context of other microbes might actually be really important, seeing as most leafcutter ants grow their fungus gardens underground. They do keep their gardens immaculately clean, but there are still bacteria in the mix.

Out of the papers I found, I only finished reading the best of them yesterday and today - a review article from 2014 that basically laid out a great framework for thinking mechanistically about how soil microbial communities could and do respond to C, N, or P limitation (so interesting and cool*), and a fun paper from 2024 that helps to clarify that there are some systematic patterns to fungal fruiting body element content, related to both fungal evolutionary history and ecology. The latter is important for being able to assert that fungi regulate their body element composition homeostatically.

Things I'm still not entirely clear about: in soil microbial communities, when there's an abundance of nitrogen around, it sounds like basically "microbes" (presumably mostly bacteria rather than fungi) produce and excrete "mineralized" nitrogen (ammonium) - a form of nitrogen readily available to plants. This basically means plants will renege on their deal with ectomycorrhizal fungi and just get their nitrogen directly. In contrast, when nitrogen is limited, microbes are said to "immobilize" it, which basically means they hold onto it and put it to use in forms that are not directly accessible to plants. (that would lead plants to barter with fungi for nitrogen in exchange for some sweet photosynthesized sugar).

But: do fungi also mineralize nitrogen? If there's too much nitrogen around and not enough carbon, are fungi more likely to die by way of simply running out of energy (can't get to enough organic carbon), or from some form of nitrogen toxicity, perhaps related to having lower tolerance to high nitrogen and getting outcompeted by microbes with higher nitrogen tolerance?

That's what I still don't really know and can't fully conjecture about.

This line of speculative thinking will probably only contribute to 1-2 sentences in the Discussion section of the leafcutter ant manuscript, but on the other hand, it's fun and interesting to think about.

...And so only eventually have I been able to get back to working on a coauthor's feedback on the 2018 seed-harvester ant manuscript.

I wasn't quite expecting so much of this time to get devoted to the writing step of reading papers and learning things, but here I am.




*Responses differ depending on the limiting element/nutrient (out of C, N, and P), because the extracellular enzymes that these organisms secrete in order to obtain nutrients require nitrogen and energy (but not phosphorus!) to synthesize. Fungi and microbes don't appear to store appreciable amounts of nitrogen, but they DO stockpile phosphorus! If nitrogen is limiting, that will then favor organisms that can burn a bunch of energy to get N (consider N fixation, for instance). If C (energy) is limiting, that will favor more energetically-thrifty organisms. P limitation will favor organisms that can store and transport phosphorus from one place to another (fungal hyphae FTW!).