Geography 2412 Lecture Notes

Sept. 30

Thanks to the TAs and to you students for tolerating my absence from class. I traveled with CU Pres. Betsy Hoffman to meet prospective students and donors on the west slope and I attended and gave a talk at a Hewlett Foundation meeting in Montana on environmental issues in the American West. I will miss one more class in Nov. to attend a land use planning conference in Arizona.

I reviewed the material on how humans interact with ecosystems.

We discuss both biotic and a-biotic ecosystems. The terms presented in the text about “Basic Units” of ecosystems (see Table p. 13; make an overhead),

Organism

Species

Population

Community

Ecosystem

Biome

refer to terrestrial biotic ecosystems,. But we also need to think in terms of the flows of matter and energy in the global system, so we talk also about bio-geochemical cycles, like the carbon cycle and the hydrological cycle.

Secondly, our focus is always on human influences and interventions. They are of two main types:

Purposeful: meant to serve a specific human goal, like getting rid of nuisance species (wolves, etc.), or cutting forests for timber and for farmland, or damming to river to store runoff.

Inadvertant: These are the accidental or unintended consequences of human interventions, like the fact that damming a river causes the downstream river ecology to change dramatically. Humans intervene in the carbon cycle by burning fossil fuels. Their goal was to use energy, not to increase the carbon storage in the atmosphere.

The difference between Purposeful and Inadvertant impacts gets fuzzied a bit where, for example, humans introduced a species to an ecosystem that then became a pest or problem. We purposefully brought Russian Olive trees and tumbleweed (Russian Thistle) to the West, but found after getting them here that they ran amuck in the ecosystem. Russian Olive trees are “phreatophytes” (you don’t need to memorize this word) that are great at transpiring soil water, thus they tend to dry out wetlands—a big problem in a semi-arid region with few wetlands.

Other purposefully introduced species that then caused problems include: gypsy moths; kudzu; rabbits in Australia. Of course, there are also cases of inadvertant introductions: as a student mentioned in class, zebra mussels have been introduced around the world by ships, and cause problems in, say, the Great Lakes, where they didn’t naturally exists.

The CABON CYCLE

[see p. 15]

The cycling of carbon through the earth system. We will speak of as SOURCES and SINKS because, as Harper points out, carbon is neither created or destroyed, but rather cycled. There are also STORAGES of carbon, in standing biomass (vegetation), in the atmosphere, in the earth’s crust (as fossil fuels) and in the oceans. Carbon is released into the atmosphere from biomass thru burning and deforestation (which allows decay of the wood, say), and from the crust as humans dig up and burn fossil fuels. This carbon is stored as carbon dioxide (it has been oxidized) in the atmosphere. This CO2 may be re-absorbed back into the biomass (now acting as sink instead of a source) if that biomass is growing (photosynthesizing), and it may be absorbed into the oceans. Part of what gets it into the oceans is again photosynthesis by plankton and other chlorophyll-rich organisms which live in to the photo-zone (top few meters of ocean where sunlight penetrates). Over long periods of time this material in the ocean, falling to the ocean floor, may be re-absorbed into geological deposits.

Key issue here is the balance of sources and sinks. The human source right now is causing a net increase is storage in the atmosphere. The sinks (biomass and oceans) are not taking it up as fast as it is being released, so the amount in the atmosphere is increasing.

The HYDROLOGICAL CYCLE

You know this one from grade school. Note that the text does not describe it in detail, but do learn the basic components and processes:

Evaporation (E): from oceans, standing water on continents (e.g., lakes)

Transpiration (T): release of water vapor by plants as they photosynthesize

Precipitation (P): from condensation of vapor into drop or snowflakes and they fall back to surface.

Runoff (R): flow of water over the surface

Percolation (also know as Infiltration = I): movement of water into the soil, down into

Groundwater flow: movement of water under the surface

Humans intervene in this system in several ways at several points:

Purposeful: cloud seeding to increase Precipitation; damming to collect and store Runoff..

Inadvertant: paving that reduces Infiltration (or percolation); timber cutting that then increases Runoff from the former forest.

I showed slides of human-transformed ecosystems:

Forests cleared for crops and grazing (forest ecosystems changed into crop and grassland ecosystems); Rivers dammed to store runoff. I illustrated this with a photo of a fisherman holding a brown trout caught on the green River in Utah. The baseline conditions of this desert river are that it ran relatively warm and muddy (turbid with silt). The dam makes it run clear and cold. Native fish species, like the humpback chub and pikeminow, which were adapted to warmer, muddy water, have been replaced with cold-water fish like trout. We’ll talk more about such effects as we discuss water resources Wed and next Monday.