Nitrogen Cycle EVR3021

Nitrogen majorly __________, especially in temperate forests and marine ecosystems.

Limits primary production

Primary producers depend on ___ N.

Soluble

__ comprises 79% of the atmosphere, is not bioavailable, and is very stable. Answer with chemical formula and full name.

N2 (Dinitrogen)

Describe the Haber-Bosch process

Hydrogen gas reacts with a catalyst to produce bioavailable ammonia (NH3) from the unavailable N2 (dinitrogen)

N cascade

Nitrogen’s ability to transition between forms and indefinitely pass through numerous biotic pathways.

Eutrophication

An increase in the rate of supply of organic matter to a system (Nitrogen causes eutrophication by accelerating primary production). Primarily refers to aquatic ecosystems and leads to excess growth of algae.

Eutrophication can ______ to create ____ conditions that can kill organisms, leading to a decrease in biodiversity.

Decrease available oxygen | hypoxic

N saturation

When an ecosystem has more N than it can use, may lead to eutrophication.

Excess nitrogen can exist in the atmosphere as precursors to ____ and ___, or as ____ (GHG).

Ozone and particulate matter | N2O (Nitrous oxide)

N fixation

Conversion of dinitrogen (N2) to ammonia (NH3) or other forms of reactive N. Resulting forms are reffered to as NOy.

Non-biologic N fixation can occur naturally through ___.

Lightning strikes

Biological N fixation occurs via _____. List examples.

Nitrogen-fixing organisms | microbes, cyanobacteria, N-fixing plants, and archaea.

____ is only possible because of the nitrogenase enzyme.

Biological N-fixation

N fixation has a high energy cost, so it usually only occurs naturally as ____. Finish the sentence.

A symbiotic relationship, where a primary producer supplies the N-fixing organism with energy to fix N.

List species that can fix nitrogen

Legume family and genus Alnus plants, when in synchrony with Rhizobia and Frankia bacteria. Aquatic cyanobacteria, aquatic sulfate-reducing bacteria.

NO (what is it, what is its importance?)

Nitric oxide. Toxic precursor to ozone.

N2O

Nitrous oxide. Greenhouse gas, destroys stratospheric ozone.

NH3

Ammonia, soluble (plant available), can be toxic, rapidly deposited

NOy

Diverse, reactive forms of N in the atmosphere, produced by combustion of fossil fuels and/or atmospheric chemical reactions. Plant available, component of acid rain, rapidly deposited.

NH4+

Ammonium, available to plants

NO2-

Nitrite, toxic, rarely found at high levels in nature

NO3-

Nitrate, available to plants, highly leachable

DON

Dissolved organic N, mixture of many different chemical forms

N mineralization

Organic N is converted into inorganic NH4+ (ammonium), thus becoming available to plants.

N immobilization

The reverse process of mineralization. Ammonium (NH4+) is converted to organic nitrogen, decreasing the soluble N pool and the amount of N available to plants.

When Imm > Minn, the soluble pool ___.

Decreases

Materials with a greater ratio of carbon to nitrogen (C:N) are likely to lead to ___ because microbes experience a ____ of nitrogen and thus ____.

Immobilization | lack of nitrogen | absorb available nitrogen

Nitrification refers to two processes. Describe those two processes.

1) The conversion of ammonium (NH4+) to nitrite (NO2-), 2) the conversion of nitrite (NO2-) to nitrate (NO3-).

The main product of nitrification is ___. Nitrification is what makes N a(n) ___.

Nitrate | Limiting factor

Oligotrophic

Refers to water bodies that are low in N and Phosphorus, opposite of eutrophic. Water is typically clear compared to the green water of a eutrophic water body.

Nitrogen deposition

Occurs when oxidized nitrogen is formed, creating reactive NOx/NOy particles that are reactive and considered pollutants. Human activity causes deposition through the combustion of fossil fuels and the use of industrial fertilizers.

How does excess Nitrogen enter aquatic ecosystems?

Runoff

Nitrogen fixing plants are most successful in environments with __ C:N ratios.

Low

What is responsible for BNF in aquatic ecosystems?

Cyanobacteria

What processes refer to Nitrogen that is already present in an ecosystem?

Immobilization and Mineralization

Describe what happens in high C:N scenarios.

Microbes are limited by N, so no N is released after they are done with decomposition. Immobilization dominates because the microbes are removing the available Nitrogen.

Describe what happens in perfect ratio C:N scenarios.

All of the Nitrogen is used by microbes, so none is released.

Describe what happens in low C:N ratios.

The microbes have excess N left over after decomposition, which they release into the environment for plants to use. Mineralization.

Why is organic Nitrogen unavailable to plants?

Organic nitrogen means that it is currently composing organic matter, such as the body of a living organism. Can only be used once the organism decomposes and the nitrogen is turned into inorganic nitrogen.

Denitrification

Nitrate (NO3) is converted back into atmospheric N2. Allows nitrogen to leave an ecosystem. It is an anaerobic process carried out by microbes in zero-oxygen conditions.

Nitrification

The breakdown of NH4 (ammonium) into nitrate (NO3). Aerobic process, can only occur where there is oxygen. Needs to happen before denitrification can happen.

How do aquatic systems act as a sink for Nitrogen, returning it to the atmosphere?

Nitrification occurs at the top of the system (epilimnion), turning ammonium into nitrate. That nitrate may settle to the bottom of the system (hypolimnion), where there is very low oxygen due to the respiration of organisms and no production. These nitrates that make it into the anaerobic layer can be used for denitrification, thus creating N2 and returning it to the atmosphere.

What happens when natural events cause mixing in water bodies?

An intense event, like a storm, mixes up the nitrogen sediment at the bottom of the ecosystem. This introduces a lot of nitrogen to the epilimnion, where it is available to plants, and may cause algae blooms. However, this also drives production in the ecosystem such as fish production. Not always bad.

Epilimnion

The warmer, less dense water that rests at the top of a water body. High light levels, high levels of photosynthesis, high levels of Nitrogen uptake and nitrification.

Hypolimnion

The colder, denser layer of water that rests at the bottom of a water body. Low light, low productivity, low levels of Nitrogen uptake, high levels of denitrification.

Rank the 3 main greenhouse gases by their heat-trapping strength and describe the strength of each. How long do they last?

Carbon (base value of 1), methane (30 x carbon), nitrous oxide (273 x carbon). Carbon exists in much higher concentrations and lasts for thousands of years, methane lasts about 12 years, and nitrous oxide lasts about 100 years.

Rank the pools of Nitrogen in terrestrial ecosystems by their relative size.

Largest pool - Soil organic matter, Second largest pool - Plant biomass, Third largest pool - Inorganic N in soil

How does adding Phosphorus increase the risk of eutrophication?

Introducing more Phosphorus allows for more primary production, leading to more sedimentation of decaying organic matter. The decomposing organic matter lowers the level of oxygen in the water above the sediment, causing the sediment to release even more Phosphorus. Also, increasing P allows for cyanobacteria to fix more N and bloom.

Phosphates are the ___ form of Phosphorus and include…

Oxidized | Fertilizers, feed additives, detergent additives

Phosphorus primarily exists in terrestrial ecosystem in its most oxidized state, _.

Phosphate (PO4)

Phosphorus is trapped in soil and sediment because it reacts to bind with chemicals like __.

iron oxides

Natural terrestrial ecosystems have limited Phosphorus because it is primarily available depending on…

The amount in nearby rock formations that must be weathered down

Phosphorus limits production in many ___ ecosystems. Many ecosystems are __ by N and P. In others, only N is the limiting factor.

Freshwater | Colimited

Low P levels in inland waters can also lead to lower ___.

Grazer abundance

A harmful algae bloom is the ____ as the result of ___.

Growth of microscopic algae or plankton | an increase of a limiting nutrient.

What is the limiting nutrient in freshwater systems and why?

Phosphorus because it gets trapped in sediment

What is the limiting nutrient in saltwater systems and why?

Nitrogen because salt makes phosphorus available and nitrogen fixation happens more slowly

____ temperatures increase algae blooms.

Warmer

What are the effects of droughts in freshwater systems?

Droughts can concentrate nutrients in less water, and make the lake shallower and more vulnerable to mixing

What makes an algae bloom harmful?

Excessive levels of algae have a negative impact on the ecosystem, species of algae may be inedible and thus uncontrollable and useless, the decomposition of algae causes hypoxic dead zones (because bacteria respire almost all of the oxygen), and the production of toxic chemicals (some species, red tide and brown tide)

What is a dead zone?

A hypoxic area where algae has bloomed to the extent that it’s decomposition uses almost all of the oxygen in the water, killing other species

What are the characteristics of red tide?

Red tide produces a neurotoxin that kills marine animals and harms humans. Creates dead zones by killing so many organisms that hypoxic conditions arise. Gulf coast of FL

What are the management strategies for harmful algae blooms?

Reduce fertilizer use, reduce runoff through shoreline management (utilizing ecosystems), treat wastewater better, stop using septic tanks, manually remove excess nutrient stocks from systems like lakes, better large-scale water management

Lake Okeechobee and it’s limiting nutrient (s)

Humans disrupted flow of water to the Everglades and changed it into two rivers that flow to the East and West coasts. So many nutrients from agriculture around the Lake flow through these rivers that algal blooms and red tides result. Needs to be controlled for BOTH Nitrogen and Phosphorus because the saltwater mixes with freshwater.

What different scales can biodiversity be applied to?

Genetic diversity (inbreeding), species diversity (typical scale, number and distribution of species), and ecosystem diversity (diversity of different ecosystems)

Precautionary principle

If there is uncertainty involved, air on the side of caution!

Biodiversity as a stock

Inflow: Speciation (very slow process), Outflow: Extinction (very rapid process)

What is background extinction?

Some extinction that occurs naturally and is not the result of mass extinction, around 7-5 families per millions of years

How many mass extinctions have there been?

Five, and we are at the beginning of the 6th mass extinction caused by humans

HIPPCO

Six main drivers of biodiversity loss: Habitat loss, Invasive species, Population growth, Pollution, Climate change, Over-exploitation

What is the single greatest threat to species on Earth?

Habitat loss (destruction, fragmentation, degradation)

What is the problem with plentiful small wilderness areas?

Compared to a single larger wilderness area, many smaller areas result in more edges (species on the edge vary from those in the inner portions, species with large ranges die trying to travel). Fragmentation.

Exotic vs. Invasive species

Exotic species have evolved elsewhere and now exist in a new ecosystem, typically due to humans. Invasive species are exotic species that become a problem and cause significant negative economic or ecological impacts. Technically, a native species can become invasive if it starts to harm the ecosystem (e.g. uncontrolled deer).

What is meant by “weedy species”?

Invasive species that became invasive because of several advantages, such as rapid reproduction, wide dispersion (population spreading), and generalists (wide diets or adapted to many conditions). Aggressive, versatile, prolific, and ready to travel.

Why does the population of rodents increase when invasive pythons are increased in FL?

Population dynamics- Pythons are apex predators that hunt other predators, such as foxes, which were controlling the rodent population

Point source vs. non-point source pollution

Point source pollution comes from a very specific single source (e.g. one factory), while non-point source comes from multiple sources (e.g. lawn runoff, cars)

Non-point source pollution and tragedy of the commons

Because non-point source pollution comes from many people contributing a little, it is difficult to convince people to change their behavior compared to a problem caused by a single entity

Why did the Newfoundland Cod Fishery collapse?

Technology allowed us to catch fish faster than they could reproduce

What are the three main management approaches to biodiversity conservation?

Species focused, ecosystem focused, and resilience focused

Species focused approach to biodiversity conservation

Endangered species act- Identify endangered species on the brink of extinction and provide it with extra protection. Restoration is often neglected, often is not successful. Awards protection to critical habitat (any habitat that the endangered species resides in). May focus on protecting keystone species (e.g. wolves).

What are the three phases of the species focused approach to conservation?

Phase 1: Identify species that is about to go extinct, Phase 2: Award the species extra protection, Phase 3: Restore the species and (importantly) its habitat.

Ecosystem focused approach to conservation

Since we cannot preserve all ecosystems, focus conservation efforts on biodiversity hotspots. Not related to climate, only the degree of biodiversity (

Nas et al. biodiversity goals

Protect 50% of habitat in a region, maintain corridors across large landscapes, focus on habitat loss over climate change, demonstrate the value of nature to humans (non-material value), and convince people that it can be achieved. Set targets as high as scientifically necessary.

Resilience focused approach to biodiversity conservaiton

Kill all the native animals because they are inferior, what even is their purpose? introduce 100% exotics, all animals are replaceable anyways. Kill all the seals right now!!! (species triage).

What is a sustainable food system?

Food security and nutrition for all, with environmental and economic bases for future generations are not compromised. (Three legs of sustainability). Focus on nutrition, not calories.

What are the two challenges for future generations (larger population) producing sustainable food?

Increasing food production to meet the growing population without destroying the environment

Food scarcity

Number of people globally suffering from malnutrition (should be minimized)

Agricultural intensification

Agricultural techniques that increase the amount of food grown per acre (in industrial agriculture, involves synthetic fertilizer, pesticides, heavily criticized issues, but can be vertical farming and other harmless techniques)

Compared to 1900, ___ US citizens were working on farms. What are the negatives and positives.

Way more, allowing us to focus on other things (like art and science). However, now most of us have no idea how food is produced and we do not pay attention to the processes behind where our food comes from (social and environmental problems).

There are ___ small farms now, and they are worked by ___ adults.

Far less, much older (more than 50% over the age of 55).

What is the green revolution?

Essentially the development of industrial agriculture. Techniques designed to increase agricultural intensity (amount of food per acre). Not focused on environmental impacts, only on greater food production (environmentalists do not like it). Began because people were concerned that food production could not keep up with population growth.

What are the key shifts of the green revolution?

Industrial fertilizer using industrial nitrogen fixation, larger farms replacing smaller farms, advanced technology (heavy mechanization), heavy pesticide use, larger capital inputs (financial) and energy inputs (powering machines, using fossil fuels to fix nitrogen in the HB process). Decreased labor input (less workers needed) and cheaper food prices (don’t need to pay those people).

Criticisms of pesticides

All pesticides do not have a narrow spectrum (kill and impact other species besides target), do not break down quickly, spread rapidly into aquatic ecosystems, open up niche for other pests, biomagnify in fat cells (increase in concentration as moving up trophic levels, impact apex predator birds the most like ospreys and bald eagles). Even low concentrations can increase rapidly. Increase resistance of species (think of weeds).

Benefits of reliance on pesticides

Can save lives (eradicating malaria, such as DDT which killed birds and is still killing them), effective

High-yield plant varieties / Monocultures

Bioengineered plants that use more energy to produce more parts that we consume (e.g. less energy into stalks and more into grain of rice). As long as it does one thing well, we can accommodate for all the other serious problems caused to the species by our artificial altering. These species are not resilient to the effects of climate change because they are so sensitive. Cause less biodiversity and genetic diversity in agricultural ecosystems and make them more vulnerable to environmental issues.

What is the reinforcing feedback loop that occurs with monoculture?

Selling natural varieties of monocultured foods is not feasible because people are only familiar with one variety of these species, so we won’t buy them. Makes them harder to become part of our agricultural system.

Why is industrial agriculture inefficient?

We use 35 calories of fossil fuels to produce 1 calorie of food (not counting the packaging and processing of that food), food travels 1500 miles on average, 18% of global GHGs come from animal agriculture (CAFOs alone)

CAFO

Concentrated animal feeding operation (factory system instead of a farm, industrial animal agriculture).

If everyone in the U.S. did not eat meet on Mondays alone, it would be equivalent to not driving ___ miles.

91 billion

Genetically modified crops

Taking the piece of one organism’s DNA and entering it into another species. Artificial selection is NOT equivalent (slower, does not control genetics). Sometimes improve nutrition, production rates, and may require less pesticides. But may potentially harm humans and environments, require more herbicide (Roundup).