Influence of humanity on Earth Surface Processes
Lab 13 – Influence of humanity on Earth Surface Processes
Earth System Science Lab
Lab goals and motivation
It is still a common perception among some people that the earth is such a big place that humanity could not significantly influence earth systems. In contrast, there is a large and growing body of scientific evidence that humanity is changing the global climate, warming the earth. There are also proposals to define a new geologic epoch, the Anthropocene, defined by the influence of humanity on geologic processes and the resulting distinctive geologic record we are creating. A companion idea is that traditional biomes such as grasslands, defined by the interplay of a distinctive climate, landscape and dominant organism, are no longer adequate concepts for describing the biosphere because they do not reflect the dominant role that humanity plays in shaping environments. Instead, it is argued that Anthromes, recognizing the importance of human activity, should be mapped and studied, if not designed and engineered.
In what manner, and to what extent, is humanity influencing the atmosphere, hydrosphere, biosphere and surface geologic processes? This is a very big question the breadth of which can’t possibly be covered in one lab. However, a course addressing earth system science would be significantly deficient if it did not address this question in some significant way. We will conduct a small scale student research study to begin to answer that question. First, you will learn about various classes of human landscape uses/modification and how to recognize then, then learn about the advantages of a random sampling plan, and then use Goggle Earth to assess and compile the degree of human modification of the landscape at 10 randomly selected locations with the U.S. While it would be nice to have more than 10 sites for purposes of estimating the extent of land modification in the U.S., some general conclusions can be reached in the two hours or so we have for this lab. In addition, the instructor can compile the results from the entire class to get a much more robust idea of the extent of human influence to share with the class as a whole.
Character and recognition of human landscape modifications
There are, of course, many ways humans use and modify the landscape. We will look at some of the major classes of land use. For each, we will look at three aspects: a) the basic nature of the land use, b) how this land use can be recognized in Google Earth, and c) potential influence of this activity on surface systems. Each corresponding section is labeled a, b and C respectively.
- a) In this class we include farm fields, orchards, vineyards and other land use where something is grown for human consumption. Because of the large human population it is a major land use category.
- b) Typically, farm fields are not difficult to recognize. The geometric, patchwork quilt character of fields is a give away. There is often a strong contrast with natural vegetation, which is more varied in character and more irregular in its distribution. Center pivot irrigation fields with their characteristic circular shape are particularly distinctive. Sometimes in Google Earth even the plowing pattern can be distinguished.
Right: Oblique air photo image from SW Kansas of the typical checkerboard character of farmland with a host of circular center pivot-irrigation fields. Virtually all the land use here is agricultural, with a few 5 roads and built structures. Image source: http://water.usgs.gov/ogw/gwrp/photo_gallery/
Below: Black and white air photo of Alliance, Nebraska showing how the fine grid of city blocks is immediately surrounded by the patchwork of rectangular and center pivot (circles) fields. The Ogallala aquifer lies underneath and allows irrigation fed by groundwater withdrawal. Major roads can also be seen as linear features that converge on the city. The image is about five miles across. Image from http://msrmaps.com .
- c) The potential effects of agriculture are very dependent on how it is practiced. A major distinction is between irrigated and non-irrigated land. Where land is irrigated the hydrologic cycle is being modified in order to bring water to the crops. Specifically, either water is being diverted from surface sources or being pumped out of the ground. The former can influence the riparian (river corridor related) ecosystem and the organisms involved, change the character of sedimentation, and influence groundwater recharge (e.g. where the river water seeps into its banks and feed into a underground aquifer). Most center pivot irrigation systems draw water out of the ground, and in some cases have severely depleted the aquifer. In other cases the salts left behind as the irrigation water evaporates accumulate in the soil to levels that become toxic for crops, a process known as salinization.
Where tilling occurs there is disturbance of the soil structure, which significantly changes natural soil formation processes (e.g. significantly increasing oxidation). The tilling also can allow for greater soil erosion, both by wind and water, especially where the sediment is bare for a period. Finally, a host of fertilizers, herbicides and pesticides used in modern agricultural practice disturb geochemical and biochemical systems in a variety of ways. These compounds are often picked up in run-off of water from rainfall or irrigation and end up in water bodies, including on a large scale the Gulf of Mexico, where these chemical act as microbial nutrients causing harmful algal blooms (HABs) that deplete the oxygen in the water and cause dead zones. Some more insight into these dynamics and the federal response can be found at: http://www2.epa.gov/nutrient-policy-data/gulf-mexico .
- a) Cattle, sheep and goats are among some of the most numerous herd animals kept by humans for a variety of purposes. These livestock require large amounts of appropriate vegetation as feed. While cut and bailed hay can supplement their feed, the most efficient situation is for livestock to graze off the land. Land used for grazing is often considered as marginal for agriculture because it is too rocky or arid for planted crops.
The black and white air photo image of part of the Sand Hills some 23 km E of Alliance is one example of what a grazed landscape can look like. In the upper right is a lake. The spidery thin lines are cattle trails that are converging on what is very likely a stock pond, with a wind mill to pump water out for the livestock. One can also see a fence line just to the north of that, and a significant difference in the color of the vegetation on either side of that fence. The lighter colored areas have been more heavily grazed, and so with less vegetation the sand shows through. The image is from the http://msrmaps.com site.
- b) Ranch or grazing land use can be more difficult to recognize. Most grazing/ranching occurs in grassland dominated areas. The most obvious telltale features are fence lines and changes in vegetation appearance across fence lines due to differential grazing. The amount of difference in vegetation can be due to different grazing practices. A well managed area without overgrazing can be difficult to see as the vegetation density is similar to the surrounding area. Sometimes cattle trails can be seen. Depending on the quality of imagery, you may also be able to see stock ponds for watering purposes, or stockyards, or other ranching related infrastructure.
- c) The effects of ranching depend largely on the density of animals grazing. If the density is too high, too many animals for a given amount of pasture, overgrazing occurs, regrowth of the vegetation cannot keep up with it. This results in loss of plant cover and increased soil erosion. Plant species diversity also can be strongly influenced as most grazers are selective in what they do and do not eat. Major predators also often are eliminated by ranchers, further reducing biodiversity. In areas where the density is well below the carrying capacity, grazing and ranching can have a minimal effect, similar to that of grazing wildlife.
Logging and tree plantations
- a) In areas where the climate supports growth of forests, logging and tree farming is a very common land use. Rates of logging and logging practices differ considerably from place to place.
- b) Logged areas are typically easy to recognize by the rectangular geometries of the areas logged. If recently logged, the contrast between the forested and logged areas is typically quite striking. With time, the distinction diminishes as trees reestablish themselves in the logged area. Often the logged area is replanted, and these areas can be considered as tree plantations. Tree plantations can be recognized by an orderly distribution of the trees within the area, the homogeneity of the tree type and age, geometric outline of the boundary of the tree plantation area, and its proximity to other logged areas. Logging roads and infrastructure also often can be recognized.
USGS black and white air photo of area East of Forks Washington. The darker areas are large trees and their shadows can be seen if you look carefully. A substantial amount of this area has been logged (perhaps 60%), and the logging roads can be seen. In some areas small trees are beginning to grow back, and so logging has been done at different points in time. The Hoh National Rain Forest in Olympic National Park is nearby. The image is from the http://msrmaps.com site.
- c) Since trees are an important part of the carbon cycle, in aggregate, logging and tree plantations influence the amount of carbon dioxide in the atmosphere and therefore climate. Areas that are logged in certain ways are also prone to significantly increased top soil degradation, soil erosion, and as a result local watersheds can become choked with sediment influencing aquatic life, such as salmon spawning. Since there is less topsoil to soak up rain, the amount of run-off increases, which can lead to increased flood sizes. In addition, there is habitat destruction and a consequent loss of biodiversity. This is of special concern for deforestation in tropical areas. There are methods of logging that can reduce many of the undesirable effects such as selective and winter cutting.
- a) Roads are the obvious components of this land use class, but train tracks and associated infrastructure, bridges, airports, parking lots, port facilities, and bicycle paths can also be included.
- b) These features are typically easy to recognize in satellite and other remote imagery, by their linear and network-like geometry. In our exercise you will estimate by eye the total length of all the transportation paths.
- c) Roads often interrupt drainage patterns, and can produce wetlands (although proper engineering can reduce the effect). Pavement associated with roads and parking lots is typically impermeable, and so instead of rain water seeping into the ground, it goes into runoff. This reduces recharge to underlying aquifers, and also can increase the frequency of a given size flood event, a phenomenon especially well known for urban areas since there is so much pavement there. Roads, especially large highways, can act as barriers to the movement of organisms (e.g. turtles), inhibiting migration, and compartmentalizing the landscape. In addition, soil and water contamination can occur along roads simply because of what the vehicles release. In the days of leaded gasoline, increased lead levels were easily detectable in soils and vegetation along roads.
- a) In this classification we include buildings and other constructed features (e.g. sewage treatment plants, refineries). Everything from individual homes to factories to institutional buildings would be included. In urban areas this is a dominant land use.
- b) These are typically easily recognized in imagery since we live in and amongst them, and they have such a distinctive geometry. .
- c) Hard structures are typically impervious (green roofs represent an exception). Similar as to paved roads, this has major consequence for the local hydrologic cycle, because during each rainfall, all the impermeable surfaces, allow less water to seep into the ground, so more goes into the surface runoff. This can increase the amount of flooding as urbanization occurs. In order to protect the buildings and other features from flooding, the drainage is often highly engineered with channelization, channel armoring, and retention ponds as common elements. Where hard structures are concentrated in a city, the natural biodiversity that existed prior to the city is absent, although certain organisms adapt to urban environments (in Omaha, raccoons live in the sewer system. Cities often have their own microclimate because of the different way they reflect or absorb sunlight. Because of the concentrated human activity, chemical contamination of the air, soil, surface water and ground water is also much more prevalent.
Black and white USGS air photo of downtown Omaha along the Missouri River (the author’s home). Look carefully and those of you who live in Omaha can recognize that this is a historic image and much has changed since it was taken (look at the section along the river). Right along the Missouri River the Asarco smelting plant that used to be there resulted in significant lead contamination in the city, contributing to a Superfund site project. Image source: http://msrmaps.com .
- a) Water management structures include dams and the reservoirs they impound, irrigation canals, drainage ditches, recharge ponds, armored banks (typically channel sides lined with heavy, large rock fragments designed to prevent bank erosion), levee systems and more.
- b) These are also typically easily recognized by their regular geometry. Of course it is difficult or impossible to see some of the smaller engineered structures (such as drainage ditches) in the satellite imagery.
- c) Since water is a crucial agent to life and geological processes, this land use has significant effects on the hydrologic cycle and linked earth systems. Dams and their reservoirs act as sediment traps, and so the dynamics of the river downstream can be changed greatly, not only in terms of controlled water flow (and the attendant ability to prevent smaller flood events), but in terms of the sediment being carried by the river. The resulting erosion and deposition, in turn, changes habitat, and this is a major consideration in ongoing debates on Missouri River management at present. In addition, the reservoir created by a dam represents new lake habitat. The increased water surface area also causes increased evaporation. The chemistry of the water can be changed greatly in a lake, often becoming colder and more depleted in oxygen. This also influences aquatic organisms down stream when this water is released from the dam reservoir.
USGS black and white air photo of small dam on the North Platte River, just below the larger Kingsley Dam that forms Lake McConaughy. Note the canal connected to the lake at the lower (southern) corner of the dam. A significant percentage of the North Platter River flow can be diverted to the canal for irrigation purposes.
Other land uses: Other classes of land use and landscape modification exist. A golf course or a race course could be considered examples in the category of recreation. A land fill could fall in the category of waste management. Mining is another significant class that locally can cause significant changes to earth system processes, especially open pit mining or strip mining. There is an “other” category in your exercise where you can note these types of land uses.
You should also watch this Science for a Hungry World YouTube video on land use change at this link https://www.youtube.com/watch?v=qWbhOd4Jd68, to help reinforce some of the above material. Pay particular attention to the animations showing change in land use with time.
Above: USGS black and white air photo image of a coal mine 23 km N of Gillette, Wyoming. This is in the Powder River basin, a major source of coal for the U.S.. The dark area in the pit to the right is the coal.
This image gives a better idea of the scale of these open pit mines in the Powder River Basin of Wyoming. The “digging” machine here is many stories high. As the coal is removed the waste rock (mostly the overlying rock) is filled in behind. Image source: http://energy.usgs.gov/Coal/AssessmentsandData/CoalAssessments/tabid/372/lapg-2670/2/Default.aspx#378437-overview
Random Sampling Plan
We are exploring the question – to what extent is humanity influencing surface systems and processes and how? To say that humanity’s influence is minor, moderate or major is perhaps a starting point, but is unsatisfactory. One person’s minor can be another person’s major. The meaning of the words is quite ambiguous, vague. This is why it helps tremendously to quantify things. To say that 52% of the available land on earth has been significantly modified by human activity carries much more information. To break that down and indicate that x% of the surface is used in agriculture, y% for logging and tree plantations, and z% for urban areas begins to paint a much more detailed picture. In general quantification also allows for much better predictive models to be generated.
How can such estimates be made? One could get an expert to map it all out, and a tremendous amount of this work has been done for some areas, but it is also very time consuming and expensive approach. Another approach would be to take a representative sample, and from a sufficient number of samples be able to say what the relative proportion of one land use is to another with a certain degree of confidence. Sampling of this sort is what polling is all about.
How you choose your samples is known as your sampling plan, a very crucial part of doing science. You could imagine a grid superimposed on the area of interest, and sample an area of fixed size by noting the different land use categories that occur at every grid line intersection . However, it turns out that there is a more efficient sampling plan that is commonly used. If you use a random sampling plan, in which you choose the location of your sample randomly each time you sample, then you get a more accurate estimate of percentage proportion than with other geometries of spatial sampling (this may seem counterintuitive, but it is so). This is the approach we will use. Because of time constraints you will only take 10 samples each of a consistent size (we will use a 1 km by 1 km square or a 1 km-squared area). This is not enough samples to have much precision in your estimates of the extent of different land use/modification classes described above, but it will give you a good idea of how one conducts this type of research and some very preliminary results. In addition, since the entire class is doing the same exercise, but each of you will end up with different sampling points, we can aggregate the class effort to get a much more precise measure of land use. As you probably realize, the accuracy with which your sample represents reality increases as you increase your sample size. You are of course free to sample more than 10 times if you wish to do so.
This week’s Exercise
Please open up the companion Excel file and navigate to the training sheet. For the purposes of this lab you will be making quick visual estimates of what percentage a particular land use/modification category covers in a Google Earth image in a sample site that is 1 kilometer square. There are much more precise ways to make such percentage estimate, but they are much too time consuming for our purposes. It is therefore useful to train yourself and see how accurate you can be in making such visual estimates, and this Excel sheet is intended to do that. Detailed explanations can be found in that sheet. Basically, you will make an estimate of the relative percentage of 0s in a grid, and then compare that with the actual percentage. Your final result will be a record of 10 trials where you do this and a measure of the average difference (a crude measure of your accuracy in making visual estimates). If you wish, you can train your eye more by doing an additional 10 trials (or as many as you like). Experience suggests that the average difference can be 10% or less.
Question 1: Average difference for 10 trials? _____________
After you have trained your eye to your satisfaction, navigate to the second sheet entitled “data sheet”. Read through the explanation and familiarize yourself with the structure of the sheet. When you are ready, use the randomly produced sampling point from the Excel Sheet in Google Earth to navigate to that part of the U.S. Resize the window so that you are seeing a bit more than a 1 km by 1 km area in the window. Remember that under the view option in the top horizontal menu you can select so that a scale is shown in the image. Then, using the line and or path tool draw a rectangle that is 1 by 1 km (or fairly close to it). Save that image and paste into this document below as your sample 1 area. Fill out the sample 1 row in the Excel sheet with the requested visual estimates and other information. Repeat this procedure and sampling 10 times. Use “Save As” to save a copy of your results when you are done and rename the file with your last name. The Excel sheet will be submitted as part of this exercise.
Question 2: Sample 1 area image:
Question 3: Sample 2 area image:
Question 4: Sample 3 area image:
Question 5: Sample 4 area image:
Question 6: Sample 5 area image:
Question 7: Sample 6 area image:
Question 8: Sample 7 area image:
Question 9: Sample 8 area image :
Question 10: Sample 9 area image:
Question 11: Sample 10 area image:
Question 12: Consider your results and then write a paragraph below that addresses the question: In the mainland U.S.A., to what extent is humanity influencing surface systems and processes and how?
Additional reading for those interested:
NASA Space Observatory World of Change Web Site – This provides a series of case histories of major landscape changes and their environmental consequences. http://earthobservatory.nasa.gov/Features/WorldOfChange/
Description of the proposal for the Anthropocene Epoch – http://en.wikipedia.org/wiki/Anthropocene
For a global view of the distribution of same land use you can explore the maps for free site at http://www.maps-for-free.com/ . In the layers section you can chose and see the extent of cropland, and road networks. Another data site on land use can be found at http://www.sage.wisc.edu/iamdata/ .