Nutrient Cycling

Lake Victoria Incredible

diversity of cichlid fishes. More than half of

the 500 species now endangered. Nile perch Increased

phytoplankton Cyanobacteria

Lake Victoria Algal bloom causes and increasing rate

of decomposition as algae die off. Bacteria use oxygen during

decomposition – lower DO. Lower oxygen results in increased death

for fishes.

Lake Victoria Changes including increased

phytoplankton can result from a change in the lake chemistry.

Ecology includes the study of the interaction between organisms and the physical environment. Study how nutrients cycle within an

ecosystem.

What is a Nutrient? Nutrients are chemical elements and

compounds that are essential to the health and survival of an organism. proteins, carbohydrates, cellulose, nucleic

acids, and other compounds that provide an organism's structure and physiology.

The concentrations of nutrients within an ecosystem determine which species can live there and in what abundance.

Nutrients Macronutrients are required in relative

large amounts. C, N, P, S, O, H

Micronutrients are required in smaller quantities. Zinc, Iodine, Potassium, Iron

Nutrients Nutrient availability, species-specific

nutrient requirements, and effectiveness of each plant's nutrient-capturing strategy all affect survival and competitive vigor.

Focus on Nitrogen, Phosphorous, Carbon

Lac Bleu and Lac Clair The change in the ecosystem seen in

the demo Lac Clair may have resulted in a change in lake chemistry. Change in concentration of limiting

nutrients. Nitrogen Phosphorous

The Chemistry of Lake Victoria The concentrations

of Nitrogen and Phosphorous tripled between 1960 & 1990.

Algal biomass increased.

Water clarity declined.

The Chemistry of Lake Victoria The increased nutrients in Lake Victoria

resulted from a change in the use of surrounding land. Deforestation (increased runoff) Increased agriculture (fertilizer use) Nile perch introduction may have also

contributed.

Flux Trees take up nitrogen

through their roots and use it to construct proteins and other organic compounds they need to grow.

Ecologists often describe this movement of material as a flux, measured as mass per unit time.

Pools If the magnitude of the input is greater

than zero, the tree takes up nitrogen, causing the amount stored in the tree's nitrogen pool to increase.

Simply stated: as the tree grows, it accumulates nitrogen. 

Outputs Whenever a tree sheds

leaves or drops branches, it exports nitrogen.

Collectively, these outputs can be considered a single flux represented by an arrow pointing away from the tree.

Δ Storage = Inputs - Outputs

Closed System Nitrogen cycles

between the tree pool and the soil pool. Tree takes up N

from soil for growth. Decaying leaves

return N to the soil.

Open System Ecosystems receive and lose nutrients

from and to a variety of external sources and sinks.

One of the largest potential sources of nitrogen is the atmosphere. 

Open System Through a process

called nitrogen fixation, nitrogen from the atmosphere is added to the soil nitrogen pool; thus, fixation is an input.

Conversely, denitrification is an important output that removes nitrogen from the soil pool and returns it to the atmosphere. 

Nutrient Cycling The processes involved in these

transfers are collectively known as nutrient cycling, so called because the same nutrients are constantly reused within the biosphere. 

Nutrient Cycling By physically altering the landscape

and/or changing biological communities, disturbances such as fire, floods, and crop harvesting can affect the relative sizes of various fluxes and therefore how tightly nutrients cycle.

As a result, ecosystems often gain or lose nutrients in the period following a disturbance.

Water Cycling in Terrestrial Biomes Water plays a major role in the movement

of nutrients within ecosystems. The largest pools of nitrogen and

phosphorus (N2 in the atmosphere and calcium phosphate minerals in sedimentary rock, respectively) are relatively unavailable to biota. Soluble forms of both nitrogen (e.g., nitrite

and nitrate) and phosphorus (phosphate) are readily taken up by plants and microbes.

Hydrologic Cycle Because water is such an important

vector for the movement of nutrients, it is crucial to understand the hydrologic cycle.

The average residence time of water in the atmosphere is only 9.3 days, whereas its residence time in oceans is nearly 3,100 years!

Inputs & Outputs Most essential macronutrients enter

terrestrial systems from the atmosphere.  Gaseous exchange acts as a nutrient

output as well as an input.  Physical weathering of rock and soil is

another significant nutrient input in terrestrial ecosystems. 

Inputs and Outputs Wetfall and dryfall act as nutrient

inputs in both terrestrial and aquatic ecosystems. 

Animals moving between ecosystems can act as both nutrient input and output agents.

Surface water, leaching, and groundwater flow carry nutrients out of terrestrial ecosystems.

Energy Flows While Nutrients Cycle When nutrients move in, around, and out of

ecosystems, energy also moves. Green plants and algae and other primary

producers capture solar energy during photosynthesis.

This energy is converted into chemical energy stored in the bonds that hold molecules together.

As chemicals move around an ecosystem, the energy stored within moves with them.

Energy Flows While Nutrients Cycle While energy flows

into, through, and out of biological systems, nutrients move between the abiotic environment and living organisms, and nutrient mass is conserved throughout the process.

Nutrient Cycling and Scale When ecologists refer to

nutrient cycling, they generally do so within the context of spatial scale.

The pattern of input, internal cycling, and output discussed above occurs microscopically (even inside single-celled organisms), at the global level, and at all scales in between.

Biogeochemical Cycles This scale progression continues up to

the level of the whole planet. At the global scale, nutrients move within biogeochemical cycles.

The components of cycles at this scale are living organisms (the biosphere); rocks and soil (the lithosphere); oceans, lakes, rivers, and other water bodies (the hydrosphere); and the atmosphere.

Nitrogen Cycling in Ecosystems

Nitrogen Cycling As a nutrient moves between the

abiotic and biotic components of an ecosystem, it shifts between different inorganic and organic forms.

Nitrogen Cycling The primary reservoir for Nitrogen is the

atmosphere. 79% of air is N2. N=N Triple bond is hard to beak – it takes

lots of energy to break the bond and use each nitrogen to build other molecules.

Nitrogen Cycling Five major stages of chemical

transformation involved in the movement of nitrogen into, around, and out of an ecosystem: Nitrogen Fixation Immobilization Mineralization Nitrification Denitrification

Nitrogen Fixation Microorganisms fix atmospheric nitrogen

and convert it into forms that plants can readily utilize. 

Most of the fixed nitrogen plants draw from the soil or water is in one of three forms: ammonium (NH4

+), nitrite (NO2-)

or nitrate (NO3-). 

Nitrogen Fixation Plant life is dependent

upon microorganisms for their nitrogen and so symbiotic relationships have evolved between plants and these nitrogen fixers. Mutualism Legumes (beans,

peas)

Nitrogen Fixation Nitrogen can also be fixed by lightening

or released when we burn fossil fuels.

Immobilization After inorganic nitrogen entering

an ecosystem from the atmosphere is fixed, it is then converted into organic compounds by plants and microorganisms. 

The amount of plant-available nitrogen in the soil affects the rate of net primary productivity, the amount of nitrogen in plant tissue, and the nitrogen available to herbivores and other consumers.

Mineralization Mineralization (or

“decay”) is the opposite of immobilization.

When dead organisms and animal waste decompose, the organic forms of nitrogen contained in that material are converted back into ammonia and ammonium.

Mineralization Litter quality reflects how easily dead matter

is decomposed. It is determined by nitrogen and phosphorus

concentrations, lignin content of plant material, and the ratio of carbon to nitrogen.

Litter of higher quality is considered to have higher nitrogen, lower lignin, and a lower C:N ratio. High quality litter is easier for decomposers to

break down.

Nitrification Much of the ammonium

produced during decomposition is converted first into nitrites (NO2

-) and then into nitrates (NO3

-), which are much more soluble than ammonium and thus much more mobile.

This chemical transformation is called nitrification. 

Nitrification Many legumes convert the ammonia

formed during nitrogen fixation into nitrites and nitrates within their root systems.

However, the majority of nitrification is performed by free-living bacteria in soil or water.

Denitrification Denitrification removes

nitrogen from an ecosystem and returns it to the atmosphere.

Denitrifying bacteria are responsible for this chemical transformation. When oxygen is not

available, these bacteria use nitrate instead of O2 in order to break down organic matter.

Nitrogen Cycling in Terrestrial Ecosystems Water moving through the soil carries

free nitrites and nitrates. High rates of streamflow can therefore, lead to losses of nitrogen from the ecosystem.

The process of converting nutrients from a solid to dissolved form that leads to loss from the system is called leaching.  Decreased soil fertility Increased nitrogen in water downstream

Nitrogen Cycling in Terrestrial Ecosystems  Disturbances, whether naturally

occurring phenomena or human-caused disruptions of the ecosystem, can produce large increases in the amount of nitrogen that water carries out of the ecosystem.

Nitrogen Cycling in Aquatic Ecosystems Nutrients leaving a terrestrial ecosystem

enter a stream, river, lake, estuary, or ocean.

The amount of nutrients flowing into a water body is strongly influenced by the nutrient dynamics of the surrounding landscape or watershed. For example, large amounts of nitrogen can

come from fertilizer runoff, sewage, and animal waste.

Nitrogen Cycling in Aquatic Ecosystems Aquatic plants and algae can use nitrites,

nitrates and ammonium dissolved in the surrounding water.

Cyanobacteria fix atmospheric nitrogen and convert it into ammonium, and aquatic nitrifying bacteria convert it into nitrites and nitrates.

Nitrogen is immobilized and stored in aquatic sediments in a similar way as it is in soil.

Nitrogen Cycling in Aquatic Ecosystems Aquatic ecologists often to refer to

"nutrient spiraling": an atom of a nutrient travels through a cycle, but is displaced downstream by the current as it goes. The faster the current, the more elongated the spiral.

Impacts of Disturbance The movement of

water and cycling of nutrients in ecosystems can be greatly affected by disturbance.

In forestry plantations, a repeated disturbance occurs when timber is harvested.

The Hubbard Brook Experiment The Hubbard Brook

experiment was designed to investigate how a forest and its vegetation affects the loss of nutrients from the ecosystem.

They studied two adjacent tracts of land for 3 years to gather baseline data, and then clearcut one of them.

The Hubbard Brook Experiment The clearcut and undisturbed forest areas were

compared through time to see how nutrient dynamics differed between the two.

They discovered that the loss of nitrates in streamflow from the clearcut area was 40 to 50 times greater than from the intact forest.

Impact of Human Activity

Impacts of Human Activity Humans significantly impact how

nutrients move around the planet. Our agricultural, forestry, and industrial

pursuits all affect the cycling of carbon, nitrogen, phosphorus, sulfur, and water. For example, human activities have at

least doubled the rate fixed nitrogen is being added to terrestrial ecosystems. 

Impacts of Human Activity Disturbing these biogeochemical cycles

causes phenomena such as acid rain, the greenhouse effect, and eutrophication.

Humans are Nitrogen Fixers Anthropogenic sources of nitrogen are

estimated to add the same amount of nitrogen to the atmosphere as natural processes.

Industrial nitrogen fixation greatly increases crop yields, but also produces large amounts of nitrous oxide, a greenhouse gas, and nitric oxide, an important contributor to smog and acid rain.

Humans are Nitrogen Fixers The production of synthetic nitrogen

fertilizer adds nitrate or ammonium directly to the soil, bypassing part of the natural nitrogen cycle.

The denitrification systems in many ecosystems are not able to keep up with the high rates of artificial nitrogen fixation occurring with fertilizer use in agriculture and forestry, widespread planting of legumes, and burning fossil fuels.

Humans are Nitrogen Fixers Primary production in estuaries is

typically considered nitrogen limited and excess nitrogen inputs into oceans cause algal blooms in marine waters.

Acid Rain The term "acid rain" refers to rain

water that has been mixed with pollutants, decreasing its pH to 4.5 or lower.

Burning fossil fuels, smelting ore, and other industrial processes release large amounts of SO2 into the atmosphere. Nitrous oxides are primarily produced by fuel combustion in vehicles and power plants. When these gases enter the atmosphere, they react with water vapor to form sulfuric and nitric acids and other secondary pollutants.

Effects of Acid Rain - Aquatic Acid deposition directly impacts the biota living

in freshwater aquatic systems. If the pH of freshwater falls below 6.0, many

aquatic invertebrates die and fish species decline.

Once pH drops below 5.0, fish cannot survive, decomposers can no longer break down dead organic matter, and the ecosystem becomes severely denuded.

As fish stocks dwindle and water quality declines, waterbirds, amphibians, and mammals also suffer.

Effects of Acid Rain - Terrestrial Any significant change in soil pH will

affect plants growing in that soil. Because plant species have different pH

tolerances, shifts in soil pH can alter competitive dynamics and thus the composition of local plant communities.

Effects of Acid Rain - Terrestrial Although acid rain does not immediately

kill trees directly, it reduces their vitality and ability to regenerate.

Prolonged exposure to acid rain significantly impacts nutrient cycling in forest ecosystems. Over the long run, this indirect effect is

especially harmful to trees.

Impacts of Acid Rain on Nutrient Cycling Acidic water dissolves nutrients in the

soil and washes them out via streamflow. Trees are subjected to a double

whammy: their supply of nutrients declines, and their ability to use remaining nutrients is impeded. 

A forest's capacity to withstand these effects depends on how well its soil buffers acidification.

Phosphorous Cycling The Phosphorous cycle does not include

a significant atmospheric component. Most phosphorous is found in sediments

and mineral deposits.

Phosphorous Cycling Weathering of rocks slowly releases

phosphorus into terrestrial and aquatic ecosystems.

Since rock weathering is a slow process, most undisturbed terrestrial ecosystems are normally phosphorus-limited.

Like the case with nitrogen, phosphorus cycles between inorganic and organic forms within an ecosystem, and some is lost via leaching and streamflow.

Human Impact on Phosphorous Cycle Phosphate rock is mined for use in

fertilizers, industrial processes, and the manufacture of detergents. Globally, the artificial transfer of phosphorus from rocks to soil is about five times faster than natural weathering. 

Agricultural and human sewage, even after being treated, still contains high concentrations of phosphorus, which also flows into aquatic ecosystems.

Eutrophication Eutrophication takes place when water

bodies receive large inputs of nutrients, stimulating plant growth, particularly algae.

The increased plant growth in turn increases inputs into decomposer systems (with more plants present, there are more plants dying) which leads to deoxygenation of the water.

Deoxygenation can cause aquatic animals to die, thus causing significant change to the local community.

Eutrophication Phosphorus

enrichment of aquatic systems can lead to sudden blooms of phytoplankton and aquatic vegetation. Indeed, phosphorus has long been thought the main culprit responsible for the eutrophication of lakes.

Eutrophication Although we now recognize that limiting

both phosphorus and nitrogen pollution is critical for maintaining healthy aquatic ecosystems, how best to accomplish this goal remains the focus of much current research.

Lake Washington In the 1940s and

1950s, the local human population grew rapidly and huge amounts of phosphorus-rich sewage effluent (20 million gallons per day at one stage!) were deposited into the lake.

Lake Washington In the 1950s, local residents noticed

that the lake water was becoming progressively cloudier and smellier, fish were dying, and phytoplankton were blooming every summer. These are classic symptoms of

phosphorus enrichment.

Carbon Cycling More than 99% of Earth's carbon is tied

up in rocks, particularly limestone, and cycles very slowly.

So the major fluxes of carbon involve less than 1% of the total carbon on Earth, and of that, most involve carbon dioxide (CO2).

Carbon Cycling Because oceans are

so huge, the biggest pool of CO2 is actually in the deeper ocean waters, and, on the timescale of decades to millennia, oceans are the primary regulator of atmospheric CO2.

Carbon Cycling Carbon dioxide that diffuses into the surface

waters of oceans from the atmosphere is used by photosynthesizing plankton and macrophytes.

This carbon moves through the food web of the marine community from lower to higher trophic levels.

Marine organisms such as clams, oysters, coral, and some algae store carbon in their shells and cells as calcium carbonate.

Carbon Cycling When these organisms die, their bodies

and shells drop to the ocean floor where they accumulate as carbon-rich deposits.

Over long periods of time, these deposits form the sedimentary rocks like limestone where most of the Earth's carbon is stored.

But over shorter time periods (decades to centuries) this is an important flux of carbon from the surface to deep ocean.

Terrestrial Carbon Cycling The CO2 in the atmosphere cycles not

only with that in the ocean's surface, but also with living matter on land.

The terrestrial fluxes of CO2 are closely linked to energy flow. Plants take up atmospheric CO2 during

photosynthesis, as they capture solar energy, and virtually all organisms release CO2 during respiration, as they consume stored energy.

Terrestrial Carbon Cycling After organisms die, decomposers

release carbon that was tied up in their bodies.

Fires can also release carbon.

Terrestrial Carbon Cycling The two major carbon pools on

land are in the aboveground biomass (for example, the wood of trees holds much of the carbon in an old-growth forest) and in the soils, where carbon is stored in dead material that has not fully decayed.

Given enough time and the right conditions, carbon stored in the soil can be transformed into fossil fuels like coal, oil, and natural gas.

Human Effects on the Carbon Cycle The exchanges of carbon

among land, sea and atmosphere have been disturbed by the rapid release of atmospheric CO2 from fossil fuel burning, deforestation and other land use changes, and by the release of methane (CH4) from agriculture and industry.

Human Effects on the Carbon Cycle This plot represents continuous data for atmospheric

CO2, which show regular seasonal fluctuations, and mean CO2 levels per year, depicted as the smooth line superimposed on the seasonal variation.

Climate Change Increases in atmospheric CO2 have alarmed

scientists because of probable effects on Earth's climate.

Climate Change Increased emissions of carbon dioxide,

methane, and other greenhouse gases are thought to be increasing annual mean temperatures around the world.

Greenhouse gases trap radiation emitted from the Earth's surface, warming the atmosphere.

Climate Change With continued increase in atmospheric carbon,

scientists predict that weather patterns will become more erratic and unpredictable, Northern Hemisphere winters will become warmer and wetter, and sea levels will rise around the world due to the melting of polar ice and thermal expansion of oceans.