human impact on the environment assignment quizlet

MS-ESS3-3   Earth and Human Activity

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3.3.5: Human Impact on the Environment

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• Melissa Ha and Rachel Schleiger
• Yuba College & Butte College via ASCCC Open Educational Resources Initiative

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The human presence and impact on this Earth has been changing with our population, technology, and affluence. In order to start understanding how these variables have an impact on Earth (in a general sense) the IPAT equation was created. As is the case for any equation, IPAT expresses a balance among interacting factors. It can be stated as:

I = P x A x T

"I" represents the impacts of a given course of action on the environment

"P" is the relevant human population for the problem at hand

"A" is the level of consumption per person

"T" is impact per unit of consumption. Impact per unit of consumption is a general term for technology, interpreted in its broadest sense as any human-created invention, system, or organization that serves to either worsen or uncouple consumption from impact

The equation is not meant to be mathematically rigorous; rather it provides a way of organizing information for a “first-order” analysis. To achieve meaningful reductions of human impact, there are intense debates on where the focus should lie. Where one group sees expensive remedies with little demonstrable return, another sees opportunities for investment in new technologies, businesses, and employment sectors, with collateral improvements in global and national well-being.

Attribution

Modified by Rachel Schleiger from Sustainability: A Comprehensive Foundation by Openstax (licensed under CC-BY )

Thumbnail: "Oil spill cleanup program" Is in the Public Domain

How to reduce human-caused environmental changes

The diversity on Earth aids the health and quality of human life. It provides the food we eat, the clothes we wear, and the air we breathe. But what do we do to serve the Earth? Human impact makes the environment less able to sustain life due to “human-induced rapid environmental changes.” There is no way to escape the effect we have, but there are ways to lessen it in order to protect the beauty of Earth and the many species that inhabit it.

Biology professor Blaine Griffen shares solutions to the five main drivers of human-induced rapid environmental changes:

1. Overexploitation of resources

Let’s take it back to the basics and reduce, reuse, and recycle. Recycling is the most familiar of the three solutions, but we should turn our focus to the other two to achieve the greatest positive impact. Learn how to reuse everyday items. DIY culture has promoted the ability to repurpose almost anything. Utilize the internet to find out what you can do. Reducing is effective economically and environmentally. One way we can reduce is by being extra cautious about the overexploitation of water. Don’t keep your water running and cut down on lawn sprinkler systems.

2. Habitat destruction

We are part of the ecosystem that we live in, so we must support it. The humans vs. nature predicament has never been a productive one and leads to a destructive mindset. Changing this mindset can lead you to be more mindful and respectful of hiking trails, your camping footprint, and nature in general. We are meant to enjoy the beauty of nature, but we should not feel entitled to abuse it.

3. Invasive species

Invasive species prove their destructive nature by causing extinctions, competing with other species, and reducing diversity in the ecosystems they invade, but they also cost the US economy approximately 120 billion dollars per year. Three easy combative measures we can take against invasive species include, never releasing pets into the environment, cleaning boats after removing them from the water, and planting native species in your yard.

4. Pollution

Whether it is trash, chemicals, or light, the whole Earth suffers from pollution, and, luckily, we can alleviate the problem through simple efforts.

Some solutions include:

• Avoiding excess use of pesticides and fertilizer. Following instructions helps to avoid infecting ground water and causing pollution. 
• Picking up litter so it isn’t ingested by animals or infecting waterways.
• Minimizing the use of outside lights. 
• Learning to enjoy nature quietly.  

5. Climate change

Broad scale problems like climate change aren’t easily solved, but simple efforts make a difference. Consider your modes of transportation, electricity use, and the benefits of buying locally. Making choices that consider the climate change problem are healthy for the planet and you.

We need to abandon the feeling of hopelessness we may feel in regards to environmental problems. We must work together to have the power to make change, otherwise nothing will get better.

INTERACTIVE

Human impacts on the environment.

Test students’ knowledge of how humans impact the environment through their human footprint, the introduction of invasive species, and the destruction of habitats.

Biology, Ecology, Geography, Physical Geography

Engage your students with this Kahoot! on human's impact on the environment. Want to play full screen? Click  here .

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Related Resources

The Anthropocene: Human Impact on the Environment

• Human Population & Impacts
• Natural Resources

Resource Type

• Click & Learn

Code to embed this content

Copy and paste this HTML into your webpage or LMS to embed a running copy of this interactive. Use the "View HTML Editor" option in your LMS to paste the HTML into a page.

Description

This interactive module explores key human impacts on the environment and how they have affected Earth’s landscape, ocean, atmosphere, and biodiversity.

Human activities are reshaping our planet in profound ways. The changes that have occurred in the last 50 to 200 years have led scientists to propose a new geologic epoch, called the Anthropocene. In this Click & Learn, students explore data on how human population growth, air pollution, agriculture, mining, water use, and other human activities have impacted the environment and will affect the fossil record.

The accompanying “Student Handout” guides students’ exploration. The “Educator Guide” contains several suggestions for implementing this Click & Learn in class, as well as discussion questions and additional background information.

The “Resource Google Folder” link directs to a Google Drive folder of resource documents in the Google Docs format. Not all downloadable documents for the resource may be available in this format. The Google Drive folder is set as “View Only”; to save a copy of a document in this folder to your Google Drive, open that document, then select File → “Make a copy.” These documents can be copied, modified, and distributed online following the Terms of Use listed in the “Details” section below, including crediting BioInteractive.

The “Poster” PDF provides an accessible version of the content in this Click & Learn.

Student Learning Targets

• Describe how different human impacts affect the ecosystem.
• Interpret and summarize data presented in graphs showing human impacts on the ecosystem.
• Describe specific types of evidence that can be used to determine whether humans are changing their local environment.
• Predict how different impacts will change over the next 100 years based on the information and data provided.

Estimated Time

atmosphere, biodiversity, biosphere, coastal habitat, farming, geologic record, invasive species, mining, ocean, water use

Terms of Use

The resource is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license . No rights are granted to use HHMI’s or BioInteractive’s names or logos independent from this Resource or in any derivative works.

Accessibility Level (WCAG compliance)

Version history, curriculum connections, ngss (2013).

HS-ESS2.A, HS-ESS3.A, HS-ESS3.B, HS-ESS3.D

AP Biology (2019)

ENE-1.N, SYI-3.F, SYI-2.B, SYI-3.G, EVO-3.H; SP6

IB Biology (2016)

Ap environmental science (2020).

Topic(s): 5.17, 8.2, 8.4, 9.10 Learning Objectives & Practices: STB-1.G, STB-3.B, STB-3.E, EIN-4.C, SP5, SP7

IB Environmental Systems and Societies (2017)

1.3, 2.3, 2.5, 3.2, 4.1

Vision and Change (2009)

Explore related content, other related resources.

Does Nature Have Rights?

A new study has found that humans' impact on the environment has grown, but slightly slower than expected. In this map, the orange places are those that face the highest pressure from humans. The blue areas face the least pressure.

• ALL OVER THE MAP

Maps Show Humans’ Growing Impact on the Planet

A new study has found a few distressing developments, but also some signs of hope.

The impact humans have on the environment has grown substantially in the last 16 years—so much so that a new study concludes three-quarters of Earth’s land surface is under pressure from human activity. But the research also shows that humanity’s footprint on the planet hasn’t grown as fast as the overall population, and that may give conservationists cause for hope.

The study, published Tuesday in the journal Nature Communications , is based on analysis of satellite imagery and other data from 1993 and 2009. Researchers sought to rigorously map our impact on the global environment—called the human footprint—and how it has changed. They found that while the human footprint has not grown in direct proportion to population or the economy, some of the most intense pressure is being felt in places with the highest diversity of plant and animal life.

It’s become clear that humans are modifying the planet on a very large geological scale , says the study’s lead author, forest conservation scientist Oscar Venter of the University of Northern British Columbia. “We thought the timing was right to get a better understanding of where the last wild places on the planet are and how those places have contracted over the last two decades and how the footprint has expanded into them,” he says.

This map shows where humans' impact on the environment increased or decreased from 1993 to 2009.

The new study is part of a growing research trend that capitalizes on improvements in satellite technology to map and monitor human activities such as deforestation , oil drilling , and movement of refugees . A recent study in Science used satellite data to map poverty . And as sensors become more sensitive, resolution improves. That, combined with more comprehensive satellite coverage, means scientists are able to map how all of these things change on finer and shorter scales, which is what Venter’s team did with the human footprint.

Building on the first comprehensive human footprint analysis published by the Wildlife Conservation Society in 2002 , Venter and his colleagues used various kinds of satellite data to analyze eight different categories of human impacts, including the extent of built environments, cropland and pasture land, population density, nighttime lights, roads, railways, and navigable waterways. They also used census data for population density and the gROADS project to track roads.

For every square kilometer of land on Earth (excluding Antarctica), each category was scored according to its impact on the environment relative to the other categories. The researchers then combined these scores for each square kilometer for 1993 and 2009, and looked at how things changed.

Much of what they found was predictably depressing. For example, in 1993, just 27 percent of the land had no measurable human footprint. By 2009, that had grown by 9.3 percent, or 23 million square kilometers. Most of the remaining footprint-free land was in places that aren’t good for agriculture or cities, such as the Sahara, Gobi, and Australian deserts, the most remote portions of tropical rainforests in the Amazon and Congo, and the tundra. (You can explore the results online with interactive footprint maps , and the maps and data are all publicly available .) The upside of the findings is that while population increased by 23 percent, the average score for the human footprint increased by just 9 percent. Even more promising is the fact that during that same 16-year period, the global economy has grown 153 percent, 16 times the rate of footprint growth.

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Part Ape, Part Human

This is encouraging and potentially very important, says research ecologist Samuel Cushman of the U.S. Forest Service’s Rocky Mountain Research Station. “We are in an age of extinction, but the difference between a truly mass extinction and just broad-scale extinction could hinge on this linkage between how fast the human footprint grows and if it is less than population growth or more than population growth.”

But the news is not uniformly good. Human pressure on the environment is distributed unevenly, and while some wealthier regions are showing a modest decrease in human impact, other parts of the world have experienced increasingly intense pressure. The footprint more than doubled in areas such as the New Guinea mangroves and the Purus Varzea rain forest in the Amazon, and it jumped more than 1,000 percent in the Baffin coastal tundra . The Torngat Mountain tundra saw an increase of more than 10,000 percent.

Many of these areas experiencing the most pressure are also among the most biodiverse places on Earth. Among the hardest hit are areas with more than 1,500 plant species and areas with a at least 14 vertebrate species that are classified as threatened.

“When we looked at the most species-rich parts of the planet, the biodiversity hotspots, previously we thought about 15 percent of [their extent] was still natural. But our map of the human footprint showed actually only 3 percent of biodiversity hotspots are still natural,” Venter says. “This is really important because this is the most biologically valuable real estate on the planet. This is where we have unusually high concentrations of species that you just don't see anywhere else.”

Things look a little better for areas with the highest concentration of bird, mammal, and amphibian species, such as the Amazon Basin, which is still largely free from human impact. However, the researchers found that footprint-free territory within these biodiverse areas has rapidly declined since 1993.

These results suggest that the best conservation strategy may be to focus protection efforts on these species-rich areas and on remaining swaths of wilderness.

“They’re quite unique, and once they’re gone, they’re really gone,” Venter says. “I think looking at the parts of the planet that are still wild and finding ways of keeping them as they are, keeping them free of humans, should be something that we're really thinking about.”

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Middle school Earth and space science

Course: middle school earth and space science   >   unit 5, human impacts on the environment.

• Apply: human impacts on the environment

• Humans impact the environment through their activities. Examples of human activities include land and water use, deforestation, and the burning of fossil fuels.
• In many cases, the impacts of human activities are negative. For example, when humans clear forests, it causes habitat loss and puts other species at risk.
• Negative human impacts increase as the population grows. They also increase as the average person uses more natural resources.
• Science can help identify solutions to reduce our impacts on the environment. However, it is up to us—as individuals and as a society—to put these solutions into action.

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The Nitrogen Cycle: Processes, Players, and Human Impact

Introduction

Nitrogen is one of the primary nutrients critical for the survival of all living organisms. It is a necessary component of many biomolecules, including proteins, DNA, and chlorophyll. Although nitrogen is very abundant in the atmosphere as dinitrogen gas (N 2 ), it is largely inaccessible in this form to most organisms, making nitrogen a scarce resource and often limiting primary productivity in many ecosystems. Only when nitrogen is converted from dinitrogen gas into ammonia (NH 3 ) does it become available to primary producers, such as plants.

In addition to N 2 and NH 3 , nitrogen exists in many different forms, including both inorganic (e.g., ammonia, nitrate) and organic (e.g., amino and nucleic acids) forms. Thus, nitrogen undergoes many different transformations in the ecosystem, changing from one form to another as organisms use it for growth and, in some cases, energy. The major transformations of nitrogen are nitrogen fixation, nitrification, denitrification, anammox, and ammonification (Figure 1). The transformation of nitrogen into its many oxidation states is key to productivity in the biosphere and is highly dependent on the activities of a diverse assemblage of microorganisms, such as bacteria, archaea, and fungi.

Since the mid-1900s, humans have been exerting an ever-increasing impact on the global nitrogen cycle. Human activities, such as making fertilizers and burning fossil fuels, have significantly altered the amount of fixed nitrogen in the Earth's ecosystems. In fact, some predict that by 2030, the amount of nitrogen fixed by human activities will exceed that fixed by microbial processes (Vitousek 1997). Increases in available nitrogen can alter ecosystems by increasing primary productivity and impacting carbon storage (Galloway et al . 1994). Because of the importance of nitrogen in all ecosystems and the significant impact from human activities, nitrogen and its transformations have received a great deal of attention from ecologists.

Nitrogen Fixation

Nitrogen gas (N 2 ) makes up nearly 80% of the Earth's atmosphere, yet nitrogen is often the nutrient that limits primary production in many ecosystems. Why is this so? Because plants and animals are not able to use nitrogen gas in that form. For nitrogen to be available to make proteins, DNA, and other biologically important compounds, it must first be converted into a different chemical form. The process of converting N 2 into biologically available nitrogen is called nitrogen fixation. N 2 gas is a very stable compound due to the strength of the triple bond between the nitrogen atoms, and it requires a large amount of energy to break this bond. The whole process requires eight electrons and at least sixteen ATP molecules (Figure 2). As a result, only a select group of prokaryotes are able to carry out this energetically demanding process. Although most nitrogen fixation is carried out by prokaryotes, some nitrogen can be fixed abiotically by lightning or certain industrial processes, including the combustion of fossil fuels.

Some of these bacteria are aerobic, others are anaerobic; some are phototrophic, others are chemotrophic (i.e., they use chemicals as their energy source instead of light) (Table 1). Although there is great physiological and phylogenetic diversity among the organisms that carry out nitrogen fixation, they all have a similar enzyme complex called nitrogenase that catalyzes the reduction of N 2 to NH 3 (ammonia), which can be used as a genetic marker to identify the potential for nitrogen fixation. One of the characteristics of nitrogenase is that the enzyme complex is very sensitive to oxygen and is deactivated in its presence. This presents an interesting dilemma for aerobic nitrogen-fixers and particularly for aerobic nitrogen-fixers that are also photosynthetic since they actually produce oxygen. Over time, nitrogen-fixers have evolved different ways to protect their nitrogenase from oxygen. For example, some cyanobacteria have structures called heterocysts that provide a low-oxygen environment for the enzyme and serves as the site where all the nitrogen fixation occurs in these organisms. Other photosynthetic nitrogen-fixers fix nitrogen only at night when their photosystems are dormant and are not producing oxygen.

Genes for nitrogenase are globally distributed and have been found in many aerobic habitats (e.g., oceans, lakes, soils) and also in habitats that may be anaerobic or microaerophilic (e.g., termite guts, sediments, hypersaline lakes, microbial mats, planktonic crustaceans) (Zehr et al . 2003). The broad distribution of nitrogen-fixing genes suggests that nitrogen-fixing organisms display a very broad range of environmental conditions, as might be expected for a process that is critical to the survival of all life on Earth.

Table 1: Representative prokaryotes known to carry out nitrogen fixation © 2010 Nature Education .

Nitrification

Nitrification is the process that converts ammonia to nitrite and then to nitrate and is another important step in the global nitrogen cycle. Most nitrification occurs aerobically and is carried out exclusively by prokaryotes. There are two distinct steps of nitrification that are carried out by distinct types of microorganisms. The first step is the oxidation of ammonia to nitrite, which is carried out by microbes known as ammonia-oxidizers. Aerobic ammonia oxidizers convert ammonia to nitrite via the intermediate hydroxylamine, a process that requires two different enzymes, ammonia monooxygenase and hydroxylamine oxidoreductase (Figure 4). The process generates a very small amount of energy relative to many other types of metabolism; as a result, nitrosofiers are notoriously very slow growers. Additionally, aerobic ammonia oxidizers are also autotrophs, fixing carbon dioxide to produce organic carbon, much like photosynthetic organisms, but using ammonia as the energy source instead of light.

Unlike nitrogen fixation that is carried out by many different kinds of microbes, ammonia oxidation is less broadly distributed among prokaryotes. Until recently, it was thought that all ammonia oxidation was carried out by only a few types of bacteria in the genera Nitrosomonas , Nitrosospira , and Nitrosococcus . However, in 2005 an archaeon was discovered that could also oxidize ammonia (Koenneke et al . 2005). Since their discovery, ammonia-oxidizing Archaea have often been found to outnumber the ammonia-oxidizing Bacteria in many habitats. In the past several years, ammonia-oxidizing Archaea have been found to be abundant in oceans, soils, and salt marshes, suggesting an important role in the nitrogen cycle for these newly-discovered organisms. Currently, only one ammonia-oxidizing archaeon has been grown in pure culture, Nitrosopumilus maritimus , so our understanding of their physiological diversity is limited.

The second step in nitrification is the oxidation of nitrite (NO 2 - ) to nitrate (NO 3 - ) (Figure 5). This step is carried out by a completely separate group of prokaryotes, known as nitrite-oxidizing Bacteria. Some of the genera involved in nitrite oxidation include Nitrospira , Nitrobacter , Nitrococcus , and Nitrospina . Similar to ammonia oxidizers, the energy generated from the oxidation of nitrite to nitrate is very small, and thus growth yields are very low. In fact, ammonia- and nitrite-oxidizers must oxidize many molecules of ammonia or nitrite in order to fix a single molecule of CO 2 . For complete nitrification, both ammonia oxidation and nitrite oxidation must occur.

Ammonia-oxidizers and nitrite-oxidizers are ubiquitous in aerobic environments. They have been extensively studied in natural environments such as soils, estuaries, lakes, and open-ocean environments. However, ammonia- and nitrite-oxidizers also play a very important role in wastewater treatment facilities by removing potentially harmful levels of ammonium that could lead to the pollution of the receiving waters. Much research has focused on how to maintain stable populations of these important microbes in wastewater treatment plants. Additionally, ammonia- and nitrite-oxidizers help to maintain healthy aquaria by facilitating the removal of potentially toxic ammonium excreted in fish urine.

Traditionally, all nitrification was thought to be carried out under aerobic conditions, but recently a new type of ammonia oxidation occurring under anoxic conditions was discovered (Strous et al . 1999). Anammox (anaerobic ammonia oxidation) is carried out by prokaryotes belonging to the Planctomycetes phylum of Bacteria. The first described anammox bacterium was Brocadia anammoxidans . Anammox bacteria oxidize ammonia by using nitrite as the electron acceptor to produce gaseous nitrogen (Figure 6). Anammox bacteria were first discovered in anoxic bioreactors of wasterwater treatment plants but have since been found in a variety of aquatic systems, including low-oxygen zones of the ocean, coastal and estuarine sediments, mangroves, and freshwater lakes. In some areas of the ocean, the anammox process is considered to be responsible for a significant loss of nitrogen (Kuypers et al . 2005). However, Ward et al . (2009) argue that denitrification rather than anammox is responsible for most nitrogen loss in other areas. Whether anammox or denitrification is responsible for most nitrogen loss in the ocean, it is clear that anammox represents an important process in the global nitrogen cycle.

Denitrification

Denitrification is the process that converts nitrate to nitrogen gas, thus removing bioavailable nitrogen and returning it to the atmosphere. Dinitrogen gas (N 2 ) is the ultimate end product of denitrification, but other intermediate gaseous forms of nitrogen exist (Figure 7). Some of these gases, such as nitrous oxide (N 2 O), are considered greenhouse gasses, reacting with ozone and contributing to air pollution.

Unlike nitrification, denitrification is an anaerobic process, occurring mostly in soils and sediments and anoxic zones in lakes and oceans. Similar to nitrogen fixation, denitrification is carried out by a diverse group of prokaryotes, and there is recent evidence that some eukaryotes are also capable of denitrification (Risgaard-Petersen et al . 2006). Some denitrifying bacteria include species in the genera Bacillus , Paracoccus , and Pseudomonas . Denitrifiers are chemoorganotrophs and thus must also be supplied with some form of organic carbon.

Denitrification is important in that it removes fixed nitrogen (i.e., nitrate) from the ecosystem and returns it to the atmosphere in a biologically inert form (N 2 ). This is particularly important in agriculture where the loss of nitrates in fertilizer is detrimental and costly. However, denitrification in wastewater treatment plays a very beneficial role by removing unwanted nitrates from the wastewater effluent, thereby reducing the chances that the water discharged from the treatment plants will cause undesirable consequences (e.g., algal blooms).

Ammonification

When an organism excretes waste or dies, the nitrogen in its tissues is in the form of organic nitrogen (e.g. amino acids, DNA). Various fungi and prokaryotes then decompose the tissue and release inorganic nitrogen back into the ecosystem as ammonia in the process known as ammonification. The ammonia then becomes available for uptake by plants and other microorganisms for growth.

Ecological Implications of Human Alterations to the Nitrogen Cycle

Many human activities have a significant impact on the nitrogen cycle. Burning fossil fuels, application of nitrogen-based fertilizers, and other activities can dramatically increase the amount of biologically available nitrogen in an ecosystem. And because nitrogen availability often limits the primary productivity of many ecosystems, large changes in the availability of nitrogen can lead to severe alterations of the nitrogen cycle in both aquatic and terrestrial ecosystems. Industrial nitrogen fixation has increased exponentially since the 1940s, and human activity has doubled the amount of global nitrogen fixation (Vitousek et al . 1997).

In terrestrial ecosystems, the addition of nitrogen can lead to nutrient imbalance in trees, changes in forest health, and declines in biodiversity. With increased nitrogen availability there is often a change in carbon storage, thus impacting more processes than just the nitrogen cycle. In agricultural systems, fertilizers are used extensively to increase plant production, but unused nitrogen, usually in the form of nitrate, can leach out of the soil, enter streams and rivers, and ultimately make its way into our drinking water. The process of making synthetic fertilizers for use in agriculture by causing N 2 to react with H 2 , known as the Haber-Bosch process, has increased significantly over the past several decades. In fact, today, nearly 80% of the nitrogen found in human tissues originated from the Haber-Bosch process (Howarth 2008).

Much of the nitrogen applied to agricultural and urban areas ultimately enters rivers and nearshore coastal systems. In nearshore marine systems, increases in nitrogen can often lead to anoxia (no oxygen) or hypoxia (low oxygen), altered biodiversity, changes in food-web structure, and general habitat degradation. One common consequence of increased nitrogen is an increase in harmful algal blooms (Howarth 2008). Toxic blooms of certain types of dinoflagellates have been associated with high fish and shellfish mortality in some areas. Even without such economically catastrophic effects, the addition of nitrogen can lead to changes in biodiversity and species composition that may lead to changes in overall ecosystem function. Some have even suggested that alterations to the nitrogen cycle may lead to an increased risk of parasitic and infectious diseases among humans and wildlife (Johnson et al . 2010). Additionally, increases in nitrogen in aquatic systems can lead to increased acidification in freshwater ecosystems.

Nitrogen is arguably the most important nutrient in regulating primary productivity and species diversity in both aquatic and terrestrial ecosystems (Vitousek et al . 2002). Microbially-driven processes such as nitrogen fixation, nitrification, and denitrification, constitute the bulk of nitrogen transformations, and play a critical role in the fate of nitrogen in the Earth's ecosystems. However, as human populations continue to increase, the consequences of human activities continue to threaten our resources and have already significantly altered the global nitrogen cycle.

References and Recommended Reading

Galloway, J. N. et al . Year 2020: Consequences of population growth and development on deposition of oxidized nitrogen. Ambio 23 , 120–123 (1994).

Howarth, R. W. Coastal nitrogen pollution: a review of sources and trends globally and regionally. Harmful Algae 8 , 14–20. (2008).

Johnson, P. T. J. et al. Linking environmental nutrient enrichment and disease emergence in humans and wildlife. Ecological Applications 20 , 16–29 (2010).

Koenneke, M. et al. Isolation of an autotrophic ammonia-oxidizing marine archaeon. Nature 437 , 543–546 (2005).

Kuypers, M. M. M. et al. Massive nitrogen loss from the Benguela upwelling system through anaerobic ammonium oxidation. Proceedings of the National Academy of Sciences of the United States of America 102 , 6478–6483 (2005).

Risgaard-Petersen, N. et al. Evidence for complete denitrification in a benthic foraminifer. Nature 443 , 93–96 (2006).

Strous, M. et al. Missing lithotroph identified as new planctomycete. Nature 400 , 446–449 (1999).

Vitousek, P. M. et al. Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications 7 , 737–750 (1997).

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