Evidence is mounting that fish populations won’t necessarily recover even if overfishing stops. Fishing may be such a powerful evolutionary force that we are running up a Darwinian debt for future generations.
Darwinian Debt. That’s the elegant phrase Natasha Loder (2006) uses to describe the observation that human pressure on the environment — fishing in this particular example — has forced evolutionary changes that are not soon reversed.
Fishermen prefer to catch larger fish, depleting the population of older fish, and allowing smaller fish to successfully reproduce. Over a period of years this artificial selection — as opposed to natural selection — gives rise to new generations of fish that are permanently smaller than they used to be. And the fisheries find it hard to recover even after decades (Swain, 2007):
Populations where large fish were selectively harvested (as in most fisheries) displayed substantial declines in fecundity, egg volume, larval size at hatch, larval viability, larval growth rates, food consumption rate and conversion efficiency, vertebral number, and willingness to forage. These genetically based changes in numerous traits generally reduce the capacity for population recovery.
Shaw’s website is full of details about his adventures in foraging, as well as a lot of recipes — including some excellent photographs of the work in progress.
Jason Shankel has an article on how we could go about changing the surface of Mars into something humans can live on. He does an excellent job of condensing the not insignificant literature on terraforming the red planet.
Starting with an explanation of Mars’ geologic history, Shankel addresses Martyn Foggs’ list of critical challenges:
The surface temperature must be raised
The atmospheric pressure must be increased
The chemical composition of the atmosphere must be changed
The Martian Surface as seen by the rover Opportunity. Image Credit: NASA/JPL-Caltech/Cornell/ASU
The article is expansive in its detail, provides a wonderful primer on the red planet, and demonstrates an excellent application of planetary system science (as opposed to Earth system science) to what would be an enormous geoengineering project. For example, to warm up the planet, Shankel starts with several approaches:
so how do we warm up the Martian poles? Several approaches have been suggested, from spreading dark material on the poles to lower their albedo, to industrial ice farming to good old fashioned thermonuclear detonations.
We discussed quite a variety of topics just based on the visit to the landfill/quarry.
A single, half-day, visit to the landfill and quarry brought up quite the variety of topics, ranging from the quarry itself, to the reason for the red colors of the cliff walls, to the uses of the gases that come out of the landfill. I still have not gotten to the details about the landfill itself, but I’ve put together a page that links all my posts about the quarry and landfill so far.
Methane in a landfill. It's produced by decomposing organic material, is extracted via wells, and is then burned to produce heat (for a school and a set of greenhouses) and electricity (soon anyway).
Decomposing waste in landfills produces quite a lot of methane gas (CH4). Perhaps better known as natural gas, methane is one of the simplest hydrocarbons, and a serious atmospheric pollutant (it’s a powerful greenhouse gas). In the past the methane produced was either released into the atmosphere or just burned off.
Greenhouses that are warmed by methane produced by the landfill. It's a cheap, close source of energy.
I remember seeing the offshore oil rigs burning natural gas all night long — multiple miniature sunrises on the horizon — in the days before the oil companies realized they could capture the gas and sell it or burn it to produce energy. The landfill companies have realized the same thing. So now, wells pockmark modern landfills and the methane is captured and used.
Looking down the slope of the landfill to see the Pattonville High School, which uses natural gas from the landfill for heating.
First, of course, the hydrogen sulfide gas (H2S), is separated from the methane — H2S produces acid rain, so it’s emissions are limited by the EPA — then, the gas from the landfill we visited, is piped to:
greenhouses, where it’s burnt to produce heat;
the Pattonville High School, which is right next to the landfill and burns the gas for heating;
and (soon) to a electricity generating power plant that will burn the gas to produce heat which will boil the water that will produce the steam that will turn the turbines that will generate the electricity.
Electric power plant -- still under construction -- that's fueled by methane from the landfill.
You may have noticed the common theme of all these uses of natural gas: it has to be burned to be useful. The combustion reaction is:
CH4 (g) + 2 O2 (g) —-> CO2 (g) + 2 H2O (g)
which produces carbon dioxide (CO2) that is also a greenhouse gas, but is, at least, not nearly as powerful at greenhouse warming as is methane.
The limestone walls of the quarry were stained red with iron precipitate.
The cliffs of the quarry were stained red. Blood, seeping out from between the bedding planes between layers of rocks, might have left similar traces down the sides of the near-vertical cliffs’ faces. But these stains are actually made of iron.
Rain falling on the land above the quarry, seeps into the ground. There it moves downward through the soil, leaching out some of the minerals there, but going ever downward. Downward until it meets a layer of soil or rock that it can’t get through. Clay layers are pretty impermeable, though in this case it’s a layer of coal. The water can’t move through the near-horizontal coal seam very fast, so instead it moves sideways across, and eventually seeps out onto the cliff face.
The red on the walls of the cliffs are an oxidised iron precipitate (rust). The iron most likely was dissolved out of the pyrite in the coal seams.
The seeping water still has those minerals it dissolved in the soil. It also has more dissolved minerals from the coal it encountered too. Coal forms in swamps when trees and other plants fall into the waters and are buried before they can completely decompose. Decomposition is slow in stagnant swampy waters because most of the insects and microorganisms that do the decomposing usually need oxygen to help them with their work. Stagnant water does not circulate air very well and what little oxygen gets to the bottom of the swamp-water is used up pretty fast. You could say that conditions at the bottom of the swamp are anoxic (without oxygen), or reducing.
Coal formation. Image from the National Energy Education Development Project.A shiny pyrite crystal in a lump of coal (happy holidays). Image via USGS.
Iron in air will rust as it reacts with water and oxygen — rust is the red mineral hematite (Fe2O3) that you see on the walls of the quarry. Iron in a reducing environment, on the other hand, will form minerals like pyrite (FeS2). According to our guide, the thin coal seam in the quarry has a fair bit of pyrite. In fact, because of the pyrite, the coal has too much sulfur for it to be economical to burn. Like the landfill gas, hydrogen sulfide, burned sulfur turns into sulfur dioxide, which reacts with water droplets in the air to create acid rain so sulfur emissions are regulated.
The water that seeps along and through the coal seam will dissolve some of the pyrite, putting iron into solution. However, the iron will only stay dissolved as long as the water remains anoxic. As soon as the high-iron water is exposed to air, the iron will react with oxygen to create rust. Thus the long stains of rust on the cliff walls show where the water emerges from underground and drips down the cliff face.
Diagram showing the coal seam, and the seeping water that creates the iron (rust) staining.
Iron precipitate in other environments
On our Natchez Trace hike we found it quite easy to stick fingers into the red precipitate at the bottom of the stream.
We’ve seen the precipitation of iron (rust) as a result of changes in redox (oxidizing vs reducing) conditions before: on the sandbar on Deer Island in the Gulf of Mexico; in the slow streams along the Natchez Trace Park‘s hiking trails in Tennessee. Iron precipitation is an extremely common process in natural environments, and it’s easily noticeable. Just look for the red.
The rich black of decaying organic matter, sits just beneath the rusty-orange surface sediment. The red is from hematite (rust) and shows that the surface is oxidizing, while the black shows that just a few centimeters beneath the surface, there is no oxygen to decompose the organic matter (a reducing environment). This image was taken on Deer Island on the Gulf Coast.
Diagram of the hydrogen sulfide system in a landfill.
Although it makes up less than 1% of the gases produced by landfills, hydrogen sulfide (H2S) is the major reason landfills smell as bad as they do. H2S is produced by decomposition in the landfill, and if it’s not captured it not only produces a terrible, rotten-egg smell, but also produces acid rain, and, in high enough concentrations, it can be harmful to your health (OSHA, 2005; Ohio Dept. Health, 2010).
Decomposition
A wall partially covered with drywall. Image via FEMA via Wikimedia Commons (Nauman, 2007).
Some hydrogen sulfide is produced when organic matter decays, but for big landfills like the one we visited, construction materials, especially gypsum wallboard (drywall), are probably the biggest source.
Gypsum is a calcium sulphate mineral, that’s made into sheets of drywall that are used cover the walls in most houses because it’s easy to work with and retards fire. The U.S. used 17 million tons of gypsum for drywall in 2010 according to the USGS’s Mineral Commodity Summary (USGS, 2011 (pdf)).
Gypsum:
CaSO4•2(H2O)
As you can see from the chemical formula, each gypsum molecule has two water molecules attached. In a fire, the heat required to evaporate the water keeps the temperature of the walls down to only 100 degrees Celcius until the water has evaporated out of the gypsum board.
A number of landfills have banned drywall because it produces so much hydrogen sulfide, but the one we visited still takes it. It’s big enough that they capture the landfill gasses, including the hydrogen sulfide, and then separate it from the other, more useful gasses, like methane, which can be burned to produce heat energy. H2S can also be burned, but they you end up contributing to acid rain.
H2S and Acid Rain
When hydrogen sulfide reacts with oxygen in the atmosphere it produces sulfur dioxide.
2 H2S (g) + 3 O2 (g) —-> 2 SO2 (g) + 2 H2O (g)
Sulfur dioxide, in turn, reacts with water droplets in clouds to create sulfuric acid.
SO2 (g) + H2O (g) —-> H2SO4 (aq)
Acid rain accelerates the dissolution of statues. (Image by Daniele Muscetta)
When those droplets eventually coalesce into raindrops, they will be what we call acid rain.
Acid rain damages ecosystems and dissolves statues. It used to be a major problem in the midwestern and eastern United States, but in 1995 the EPA started a cap and trade program for sulfur dioxide emissions (remember sulfur dioxide is produced by burning hydrogen sulfide) that has made a huge difference.
The head (top) of a well (vertical metal pipe) that captures the gas from inside the landfill.
Capturing H2S
Probably because of the EPA’s restrictions, the landfill company pipes all the gases it collects through scrubbers to extract the hydrogen sulfide. There are a few ways to capture H2S, they all involve running the gas through a tank of some sort of scavenging system that holds a chemical that will react with hydrogen sulfide and not the other landfill gases. At the landfill we visited the remaining landfill gas, which consisted of mostly methane, was used for its energy.
A thermostat that adapts, is connected, saves money, saves energy (and the environment), and looks good too? (Image from the Nest Labs website).
There is a lot of potential for the new Nestthermostat to bring modern technology into some of the the essential but mundane devices that surround us. Its importance is not in the addition of new technology (which usually means new complexity), but in how that technology can actually make life easier, help save money, and reduce our impact on the environment by saving energy. Steven Levy has an excellent article in Wired about the project.
A key thing that students should note is the large range of expertise that went into creating this device: engineers, computer scientists, venture capitalists, and artistic designers to name a few. The ability to collaborate with diverse groups is an essential skill to master.
Just because of the large savings that can be gained, thermostats have been long overdue for an overhaul. Most buildings are heated by burning fossil fuels, like natural gas or coal, or with electricity that is produced by the burning of of fossil fuels. Similarly, cooling is also usually powered by electricity. Thus every savings in energy that results from this thermostat reduces the human impact on global warming. Because the energy savings means that you pay less for energy, saving the environment in this way means that you’re also saving money.
It’s good to see projects like this one come to fruition. We can only hope that they did a good job, that this is actually a good product, and that it is successful so similar projects will follow.
