APES Take Home Midterm

1. a. The purpose of this graph is to show the relationship between nitrogen fixation caused by natural processes and nitrogen fixation caused by human activities between 1960 and 1990. The graph shows that the estimated range of nitrogen fixation by natural causes has remained constant for the thirty years that the graph measures, while the amount of nitrogen fixation that is caused by human activities has increased dramatically. The three human-caused nitrogen fixation processes that the graph measures are planting legume crops, burning fossil fuels, and fertilizing plants with nitrogen-based fertilizers. The graph shows that using nitrogen fertilizer is by far the largest source of anthropogenic nitrogen fixation. The graph also shows that over the past thirty years, the amount of natural nitrogen fixation occurring has been surpassed by the amount of nitrogen fixation caused by human activities. Between 1960 and 1970, the amount of human caused nitrogen fixation was still below the amount of natural nitrogen fixation, but from about 1971 to 1990, the amount of natural nitrogen fixation is less than the amount of nitrogen fixation caused by humans. The amount of nitrogen fixation caused by humans was still increasing in 1990, so unless drastic change is made, human activities will continue to cause more and more nitrogen fixation while the amount of natural nitrogen fixation remains constant.

b. Nitrogen fixation is the process of converting molecular nitrogen (N2) into organic compounds such as ammonia (NH4+) and nitrate (NO3-2). This process is an extremely important part of the nitrogen cycle, because most organisms cannot use nitrogen when it is in its molecular form and depend on other organisms that convert it to usable, organic compounds. Because nitrogen is a relatively stable and unreactive element, nitrogen fixation depends mostly on organisms actively converting it. However, one exception to this rule is high-energy nitrogen fixation, which occurs when lightning converts atmospheric N2 into either nitrate (NO3-2) or nitrite (NO2-1). Almost all other forms of nitrogen fixation are carried out by bacteria. Sometimes, this bacteria is in a symbiotic relationship with a plant, especially plants in the legume family, where they live in nodules of the root of the plant, providing organic nitrogen compounds that the plant needs to survive and getting a safe place to live from the plant in return. Nitrogen fixing bacteria can also live in the stomachs' of animals, especially animals that have specialized stomachs with multiple chambers, such as cows and moose. When these organisms die, more bacteria in the soil turn the nitrogen that was in their bodies in other organic compounds, such as amino acids (NH3), back onto nitrogen compounds that make the soil much more nutrient-rich. Nitrogen fixation is an important process for many life forms, because nitrogen is a necessary compound for life, and cannot be used by most organisms until it has been fixed by bacteria.

c. The range of natural terrestrial nitrogen fixation in this graph is from about 90 Tg to about 140 Tg. Tg, or teragrams, is a measurement of mass that is equal to one megatonne, or ten to the twelfth grams. This wide range in values represents the amount of nitrogen fixation that would occur on earth if humans were not artificially fixing lots of nitrogen, while burning fossil fuels or through the Haber-Bosch process. One reason that this range of values is so big is that the nitrogen cycle is one of earth's natural biogeochemical cycles, and it includes a gaseous phase, which means it cycles a lot faster than other elements that do not have a gaseous phase cycle. Since nitrogen makes up about seventy eight percent of the earth's atmosphere, nitrogen is always cycling, and it makes sense that there would be a range for the amount of nitrogen that is in the stage of the cycle where it is in the soil. The amount of natural nitrogen fixation occurring Earth also depends on the amount of bacteria that are fixing it, so the more legume plants or other plants that have evolved symbiotic relationships with nitrogen fixing bacteria there are at any time, the more nitrogen fixation is probably occurring. The different phases of the nitrogen cycle are always changing, so there cannot be one value that would represent the amount of nitrogen fixation that is happening all the time.

d. The main reason that the results of this graph are of concern to environmental scientists is that the amount of nitrogen fixation because of human induced processes is much greater than the amount of natural biological nitrogen fixation that is occurring. This is a major problem for the environment partly because the excess amount of nitrogen oxide that is in the atmosphere, which is caused by the burning of fossil fuels and diesel, is a major contributor to poor air quality and smog in urban environments. Another reason that the abundance of 'fixed' nitrogen is a problem is because of eutrophication, which is what happens when an environment has access to too many nutrients, such as phosphorus or nitrogen. Since nitrogen is only usable by most organisms in non-molecular forms, it is often the limiting factor for many environments. If that environment suddenly has a huge supply of usable nitrogen, provided by nitrogen-rich fertilizers, organisms that are sensitive to the excess nitrogen and can use it more effectively are favored. These plants then spread uncontrollably and drive the plants that cannot utilize the excess nitrogen to extinction, which has negative effects on the biodiversity and balance of the ecosystem. Overall, human influence on nitrogen fixation is worrisome to environmental scientists because it fundamentally alters the nitrogen cycle, which provides many important ecosystem services for humans and other species.

2. a. As far as scientists can predict now, the primary effect of adding iron to the ocean would be to increase the amount of photosynthetic algae living in the ocean's ecosystems. This is because iron is a limiting factor in many oceanic ecosystems, and algae are the ocean's main primary producers, so an increase in the amount of iron available would lead to an increase in the algae population. Proponents of this plan say that the increased amount of algae would lead to increased carbon sequestration, because when the algae die, they sink to the bottom of the ocean, with carbon still locked in their bodies. However, since scientists do not know all of the species of algae that live in the ocean, or the properties of different species of algae, they do not know whether the addition of nitrogen would have the same effects on all the different kinds of algae, or whether it would favor certain species of algae, which would take over and therefore decrease the genetic diversity in the oceanic ecosystems. Some scientists are also worried that the addition of iron to the ocean would select for species of algae that produce other gases that are even worse than carbon dioxide in terms of global warming, such as nitrous oxide and methane.

b. Some environmental groups want to increase oceanic primary productivity by adding iron to the ocean because of the fact that the increased amount of dead algae would decrease the amount of carbon dioxide that is being released into the environment, and therefore help stop global warming. When the algae die, they fall to the bottom of the ocean, and the carbon that makes up their bodies gets buried on the sea floor, becoming a carbon sink that is kept out of the atmosphere. Planktos, the company that is proposing dumping iron into the ocean, wants to measure the amount of carbon that is sequestered by the extra algal blooms and sell the carbon credits to big companies so that they can say they are carbon neutral. This proposition compromises the idea that this process would be good for global warming, because other companies could buy the carbon credits and continue to burn fossil fuels and do environmentally harmful processes. Another motivation for adding iron to the ocean is that the increased population of algae, the first trophic level in the ocean ecosystem, might possibly be able to support more consumers and predators, which would benefit fisheries that are now being depleted. This could also have negative consequences for the environment, because fisherman might think that adding iron to the ocean would lead to an unlimited supply of fish, so they might continue to practice fishing techniques that are not sustainable.

c. Because there have not been a lot of long term experiments on the effects of adding iron to the ocean, there are many possible effects, but scientists do not know which ones will occur for sure. One effect that scientists hope the addition of iron would have is that populations of algae would increase, because iron is a limiting nutrient for them. What scientists do not know is whether the addition of iron will affect all species of algae in the same way, or whether it would favor only certain types of algae. If it does favor certain types of algae, the types that are favored will take over and drive all the other kinds to extinction. This would obviously be harmful to ocean biodiversity, but it could also be bad for global warming if the species of algae that are favored are ones that emit other greenhouse gases, like nitrous oxide and methane. One possible effect of a growth in algae population would be increased carbon sequestration, because of the decaying algae on the ocean floor, which would mean less carbon dioxide in the atmosphere to cause global warming. Another possible effect is that the larger algae population would be able to support more trophic levels, which would mean more fish and other consumers to replace the ones that are being over fished n farms today. Some scientists think that adding iron to the ocean would not increase carbon sequestration because there would not be enough to greatly increase the algae population, but that it would only cause pollution in the ocean and not alleviate global warming and depleted fisheries.

3. The Klamath Mountain region of California and Oregon is important in preserving biodiversity not only because of its large number of species, but also because it has many endemic and not introduced species. The Klamath Mountains already have some areas of national forest, and so it has become one of the world’s biggest and most diverse coniferous forests. The area has thirty different species of coniferous trees, including seven species that only exist in this one forest, so the preservation of these rare species depends entirely on the preservation of this forest. In addition to coniferous forest, the Klamath Mountains also have many other plant habitats because of their varied geography and elevation, such as oak forests and alpine grasslands. Another important aspect of the Klamath Mountains' biodiversity is the plant communities that are specifically adapted to the area's serpentine soil. Serpentine soil consists of very finely ground rocks, including serpintinite, that undergo metamorphic change and hydration to form a waxy soil that is low in nutrients and minerals such as nitrogen and phosphorous. Serpentine soil is often found in areas that do not have many trees, but are surrounded by dense forests. In environments that contain serpentine soil, such as the Klamath Mountains, there are endemic plants that are specialized to live in such low nutrient soil, including many rare wildflowers such as the whiteray pygmy daisy. Protecting these communities of endemic plant species is also important for maintaining biodiversity because they have become so specialized to live in low nutrient serpentine soil that they would not be able to survive in other types of soil, and serpentine soil only covers about one percent of California's land. The Klamath Mountains are also home to many species of animals that are specially adapted to survive in that specific environment. For example, the Western Toad is adapted to blend in with the trees in the coniferous forest as a way of defending itself against predators, but its populations have been declining, mostly because of habitat loss due to human actions. Another example is the Siskiyou Mountain Salamander, which live under the shade of the coniferous forests on rock covered hillsides. They have a very small range of areas where they can survive, mostly limited to the Klamath Mountain region, and they have been severely impacted by logging of the forests, because they need their shade to survive. The rivers in the Klamath Mountain region have also been very important in maintaining fish populations and biodiversity of fish species, because many other areas are being over fished and their populations of fish are being quickly depleted. The fish in the Klamath Mountains are threatened because of logging near their spawning sites, which leads to silt and increased turbidity in the water, which keeps the fish from spawning. Although fish populations have been declining recently, the Klamath Mountains are still an important site of fish biodiversity, including nine species of salmonoid. There are also many species of mammals that live in this region, such as the northern flying squirrel and the grey fox, but some species of mammals that used to live there no longer do because of human activities, such as the Roosevelt elk and the wolf, which might be reintroduced into the region in the future. The Klamath Mountain region is one of the most important areas in the country in terms of maintaining biodiversity, because of its variety of highly specialized habitats that have coevolved with many species of plants and animals. However, the number of species and the populations of many species have already started to decline because of human uses of this land, such as logging and hunting. Making the Klamath Mountain region a national park would be an important step in preserving biodiversity in this country, especially of rare and endemic species.

4. a. The Hawaiian Islands are the most isolated chain of islands in the world. Because Hawaii is a chain of islands in the middle of the Pacific Ocean, all of the species that live there arrived from somewhere else at one point, so in a way they are all introduced species. However, another effect of Hawaii's geographical isolation is that the species that are there normally do not have any interaction with species from the mainland. The result of this isolation is that the species that came to the islands a long time ago undergo adaptive radiation, meaning that they specialize to fill specific ecological niches based on the conditions of their habitats, and eventually become separate species. The plant and animal species coevolve with each other and with their environment, so that they become highly specialized to Hawaii's climate and environment. Although the islands that make up the Hawaiian archipelago today have only been above water for less than ten million years, species that live there have had longer than that to evolve to fit specific niches in that environment. This is because the area is a geological hotspot, meaning there are active volcanoes underneath it, so there were islands of similar altitudes with similar conditions in the same area that the Hawaiian Islands are now. Hawaii now has approximately 10,000 endemic species that do not live anywhere else in the world. So although Hawaii's distance from the mainland means that the rate of species entering from other environments is relatively small, the isolating location of the islands actually increases the biodiversity and rate of endemic species because of adaptive radiation, when species evolve to fit a specific niche in their specific environment.

b. Because Hawaii is such an isolated chain of islands, it is especially vulnerable to introduced and invasive species. All of the species that have been living and evolving in Hawaii for a long time have had no contact with species from any other part of the world, so they have not needed to evolve any defenses against pests or microbes that do not live in Hawaii. When new species enter Hawaii, transported intentionally or by accident, native Hawaiian species will be at a disadvantage because they have not evolved defenses against them the way that species that have been exposed to them for long periods of time have. The introduced species that come to Hawaii might also have no natural predators in the Hawaiian environment, which would let them grow uncontrollably and drive native species to extinction. The part of Hawaii that has been the most affected by invasive plant species is the low elevation parts of Hawaii. This is partially because the low elevation areas of Hawaii are where most of the plant species are originally introduced, and partially because the high incidence of disturbances, such as fire and development, in these areas create good conditions for weeds to spread. One example of a plant starting as an introduced species and spreading to become an invasive weed is the nasturtium, which was introduced into the volcano national park, and then grew out of control. Another plant species that has become a major pest in Hawaii is the strawberry guava, or waiawi. It grows in tropical rain forest environments, and it becomes so dense that it blocks out native species that used to grow there. It also is a food source to another pest, the fruit fly, and costs a lot of money in damages to agricultural areas. Invasive species are one of the biggest threats facing Hawaii's native species today.

c. Many of Hawaii's native species are also endemic, which means that they do not live in any other place in the world. If these species go extinct in Hawaii, they are gone forever, because there are no other species like them in the world. It is important that they do not go extinct because they are all interconnected in their ecosystems, and we do not know what the effect on the ecosystem as a whole would be if any of them went extinct. We have no way of knowing which of the species might be a keystone species, one that would cause a trophic cascade and effect all of the organisms in the ecosystem, until it is gone, and it would be too late to de anything about it. So it is safer if we do not let any of the species go extinct, and the ecosystem will stay intact. Another reason that it is important for species in Hawaii not to go extinct is that we have not identified or studied many of them, and we do not know whether any of them contain chemicals that might be effective drugs against cancer or other diseases. In the past, some plant species have been found to fight cancer in ways that we did not predict, and if we let plant species in Hawaii go extinct, we might be missing an important chemical that could be made into a drug that could save millions of lives. In addition to all of these reasons, the rich biodiversity contributes to the beauty and uniqueness of Hawaii, which is valuable because of its effect on people. It is also valuable as an attraction of tourists to Hawaii, which is extremely important for Hawaii's economy. Preserving biodiversity is important in all parts of the world, but it is especially important in Hawaii. Take Home Test