Biol 1110- Ecosystems and Nutrient Cycling

What are gross primary production (GPP), net primary production (NPP), and secondary production?

GPP: Total light energy converted into chemical energy by autotrophs.

NPP: Energy remaining in organic molecules after autotrophs use energy for cellular respiration.

Secondary production: Energy that consumers convert into new biomass over a given period.

What is chemical cycling, and how does carbon cycle through an ecosystem?

Elements move between biotic and abiotic components. Plants absorb atmospheric CO₂, consumers eat plants, and waste and decomposition return carbon to the environment.

How do mineral nutrients enter forest ecosystems, and how is nitrogen supplied?

Mineral nutrients enter through dust and solutes dissolved in rainwater. Nitrogen is supplied through nitrogen fixation

What is a limiting nutrient? Give an example.

An essential chemical element or compound that is in shortest supply relative to an organism demand, restricting growth, reproduction and biological production in ecosystems.

In marine ecosystems, nitrogen or phosphorus may be limiting.

The water cycle: What are evaporation and transpiration?

Evaporation: Solar heat converts liquid water into water vapour.

Transpiration: Plants absorb soil water through roots and release vapour through leaf pores.

What are condensation and precipitation?

Condensation: Water vapour cools into liquid droplets, forming clouds and fog.

Precipitation: Water falls to Earth as rain, snow, sleet, or hail.

What are runoff, collection, infiltration and sublimation?

Runoff: Water flows across land.

Collection: Water gathers in oceans, lakes, and rivers.

Infiltration: Water soaks into soil and moves underground or feeds streams.

Sublimation: Frozen water changes directly into water vapour without first becoming liquid.

How does carbon move between plants, animals, and the atmosphere?

Photosynthesis: plants, algae, and cyanobacteria absorb CO2 from the atmosphere or water to make sugars

Consumption: Animals and other consumers eat plants or other animals, passing carbon through the food web

Cellular respiration: Plants, animals, and microbes break down food for energy, releasing CO2 back into the atmosphere or water

Decomposition: Fungi and bacteria break down dead organic material returning carbon to the soil and air

Fossilization and combustion: Over many years, buried organic matter turns into fossil fuels. Burning of these releases CO2 back into the atmosphere

What are the major nitrogen reservoirs and key process in the nitrogen cycle?

Major reservoir: Atmospheric N₂.

Key process: Nitrogen fixation, which converts atmospheric nitrogen into usable forms.

What are the steps of the nitrogen cycle?

Nitrogen fixation: Atmospheric N2 is converted into ammonia or ammonium by nitrogen fixing bacteria (in soil or plant roots)

Nitrification: Nitrifying bacteria in the soil convert ammonia into nitrites and then nitrates,which plants absorb

Assimilation: Plants absorb nitrates through their roots to build proteins and DNA; animals eat plants to obtain nitrogen

Decomposition: when plants and animals die or produce waste, decomposers convert organic nitrogen back into ammonia

Denitrification: Denitrifying bacteria convert nitrates back into N2 releasing it back into the atmosphere

What are the steps of the phosphorus cycle?

Weathering: Rain and natural weathering break down phosphate-containing rocks, releasing inorganic phosphate ions into soil and water

Absoprotion: Plants and fungi absorb dissolved phosphates from the soil or water

Consumption: Herbivores and carnivores obtain phosphorus by eating plants or other animals

Decomposition and excretion: Plants and animals release waste or die; decomposers return inorganic phosphorus to the soil or water

Sedimentation: Phosphorus washes into rivers and oceans, settling into marine sediments over long periods, which eventually uplift to form new phosphate rocks

Why is phosphorus often less available to organisms, and what are its major reservoirs?

Phosphorus salts are relatively insoluble and less readily available. Its major reservoirs are rocks and soils, and weathering is a key process in its cycle.

How can human activities disrupt nutrient cycling?

Humans increase nutrient mobilization through activities such as agriculture, land clearing, and fossil-fuel combustion, potentially creating nutrient imbalances in ecosystems.

How does temperature affect decomposition?

Low temperatures slow metabolism and decomposition in both aquatic and terrestrial ecosystems.

How do nutrient availability, oxygen, and water affect decomposition?

Nutrients: Nitrogen or other resource shortages slow biological processes.

Oxygen: Low oxygen in deeper aquatic environments slows decomposition.

Water: Dry conditions slow decomposition.

What roles does vegetation play in terrestrial nutrient cycling and microclimates?

Vegetation absorbs and retains nutrients, controls how much light reaches the ground, and provides shade that affects ground-dwelling organisms.

What is eutrophication, and what causes it?

Excessive nutrient enrichment of a body of water, promoting increased growth of algae and bacteria. Agricultural runoff and waste inputs can contribute to it.

Why can eutrophic lakes experience oxygen depletion?

High biomass produces abundant organic matter. Decomposition consumes oxygen, creating oxygen-poor areas; where oxygen is absent, aerobic decomposition cannot proceed.

How does clearing land and harvesting crops affect soil nutrients?

Clearing removes natural vegetation that retains nutrients. Harvesting removes nitrogen and other nutrients absorbed by crops, depleting soil reserves.

How do humans increase nitrogen availability in agricultural ecosystems?

By adding organic amendments, cultivating nitrogen-fixing legumes, and burning fossil fuels, which releases nitrogen compounds that can enter ecosystems through rainfall as nitrate.

What is a critical load, and what can happen when nutrient inputs exceed ecosystem capacity?

A critical load is the level of nutrient input an ecosystem can tolerate without harmful effects. Excess inputs can cause environmental damage, including nitrate contamination of groundwater to unsafe drinking levels.

What are aquatic dead zones, and how can their size be reduced?

Dead zones are low-oxygen coastal areas where decomposition of dead phytoplankton consumes oxygen. More efficient fertilizer use can reduce nutrient runoff and help shrink dead zones.

What is biological magnification, and why are top-level carnivores often most affected?

Toxic compounds can accumulate and become more concentrated at higher trophic levels. Top-level carnivores are often most severely affected because they consume organisms containing these compounds.

How can pharmaceutical drugs enter aquatic ecosystems?

Drugs that are not adequately broken down can pass through sewage treatment plants and enter rivers and lakes.

How does fossil-fuel combustion contribute to climate change?

It releases carbon dioxide into the atmosphere faster, increasing atmospheric CO₂ and strengthening the greenhouse effect.

How have human activities altered atmospheric ozone?

CFCs used in refrigeration and manufacturing accumulate in the atmosphere and contribute to ozone depletion.

What are the ecological consequences of ozone depletion?

More intense ultraviolet radiation reaches Earth's surface, harming plants, animals, and microorganisms.

How do human impacts on nutrient cycling differ from their impacts on atmospheric composition?

Nutrient cycling: Fertilizers, land clearing, and combustion alter nutrient availability, potentially causing eutrophication and dead zones.

Atmospheric composition: Fossil-fuel emissions increase greenhouse gases, while CFCs contribute to ozone depletion.