Environmental Science: Module 2

What is the definition of a ecosystem? What are its components?

An ecosystem is the interaction of living organisms (biotic component) with their physical environment (abiotic component), facilitating the transfer of energy and minerals between them to support life.

What are the scales of studying ecosystems?

Temporal = TIME scale = the timeframe in which we study an ecosystem.

Spacial = SPACE scale = the physical size of the ecosystem in which we study.

Both these scales are relative to what we want to find out about the ecosystem, and can range from global to molecular (spacial) or billions of years to days (temporal).

What are the ecological organization levels for ecosystem.

Species < Population < Community < Ecosystem

Species: Smallest classification, a group of animals that are able to reproduce together

Population: All individuals of a species in an area

Community: Multiple species interacting with one another

Ecosystem: Biological community interacting with each other and their abiotic environment

What is a functional group?

A category of species that all perform the same role in an ecosystem.

Autotroph versus heterotroph.

Autotrophs produce their own food from abiotic components and energy from the sun. They are usually plants and called primary producers who undergo photosynthesis to convert abiotic components into organic compounds that are able to be used for energy for organisms.

Heterotrophs include both consumers and decomposers other organisms for food and energy.

Describe the energy flow through the ecosystem.

Producers tie light energy into chemical bond through photosynthesis. That energy moves up the food chain through consumption of biomass at the trophic level below, while all trophic levels die and feed into decomposers. At every level of this web, energy is lost through heat as the organism expends some of that energy for metabolism and respiration, while the rest is converted to biomass that moves up the food chain.

How does material flow through ecosystems?

The water and nutrient cycles! Nutrients enter these cycles through producers and flow between all functional groups, losing some of those nutrients at all levels (simular to energy flow).

Describe the trophic levels.

Tropic levels are positions on a food chain/web based on how an organism receives its energy. The first trophic level are primary producers that make their own energy from the sun, while each trophic level above that are consumers that consume the biomass of the trophic level below theirs for energy. All trophic levels die and decompose.

When an organism consumes another organism/undergoes photosynthesis, describe the process of how the energy is transferred and used.

Primary producers use photosynthesis to create glucose, while consumers and decomposers consume the biomass of other organisms for energy. In both cases, energy flows into the organism through ingestion/assimilation and is used for respiration and biomass production. The biomass produced is the energy available for the next trophic level (NPP = GPP - respiration), while respiration is energy lost for the organism to function, and the unusable components ingested become waste product.

What are the two components of decomposition?

Detritivores (mainly invertebrates like worms) internally break down dead matter into smaller pieces that decomposers (mainly microbes, fungi, and bacteria) can chemically alter into material that reenters the abiotic environment.

What is biomass?

The total mass of all combined organisms/producers at that trophic level, available to be consumed for energy at the next trophic level. Biomass decreases significantly while moving up each trophic level.

Gross versus net primary productivity. How to calculate.

Gross productivity is the total amount of energy brought into that trophic level, while the net primary productivity is the amount available to the next trophic level (tied up in biomass). Net productivity at the previous level is equal to the gross at the next.

Net Productivity = Gross Productivity - Respiration

Primary production vs productivity

Production is a scalar number while productivity is the rate of energy over time.

How to calculate trophic level transfer efficiency? What is the average transfer for each trophic level?

TLET = (Net productivity at CURRENT/HIGHER level)/(Net productivity at PREVIOUS/LOWER level) * 100

There is an average of 10% energy transfer per trophic level, though generally higher at lower trophic levels and lower at higher trophic levels.

How is productivity related to spacial distribution.

High productivity is found in areas with intense sunlight (high incoming energy), warm temperatures, abundant rain, and many nutrients. Thus, high productivity is found primarily around the equator and in the ascending arms of Hadley cells.

Low productivity is found in cold areas with little sunlight, rain, and nutrients. Low productivity is found in descending arms of Hadley cells and in polar regions.

How is productivity related to temporal distribution.

Productivity is highest in summer/midday - time with greater relative sunlight/energy.

Over longer time periods can be affected by conditions like drought, changing landscape, disturbances, etc.

Is the water cycle an open or closed system?

The water cycle is a closed system. The amount of water on Earth is completely finite, though it is a renewable resource because we have processes to purify and reuse water.

What is the role of the water cycle in transporting matter and energy globally?

Energy exchange: The transformation of water between states (solid, liquid, and gas) both stores and releases energy. Moving up from solid → liquid → gas corresponds with a storing of latent heat, while moving down from gas → liquid → solid corresponds with a releasing of latent heat.

• Thus, it is the energy from the SUN powering the water cycle, as it heats water and it transitions between stages and moves across the globe in the process of PGF.

Matter exchange: Nutrients can be dissolved in water/carried in runoff, which carries nutrients and matter from ecosystem to ecosystem. The physical movement of water carries matter.

What are the principle reservoirs of the water cycle, their relative inventories and fluxes?

The three principle water reservoirs are the ocean, land, and atmosphere. The ocean is the biggest by far, with the land being the second greatest (ice caps and groundwater), while the atmosphere carries very little water relatively.

Water fluxes from the ocean to the atmosphere through evaporation, moving through atmospheric circulation to more ocean/land where it precipitates. Runoff is the primary method of movement of water over land/to the ocean. There is also evaporation and transpiration over land as a flux into the atmosphere.

****Over ocean: evaporation > precipitation

****Over land: precipitation > evaporation

What are the two horizontal transport fluxes?

Atmospheric transport and runoff.

How is global precipitation distributed?

Precipitation is highest at the equator where more energy is entering the system, allowing more water to be evaporated and also for warmer air to hold more water. Precipitation is lowest at the poles for the opposite reasons. Natural variability across seasons and years.

How to calculate residence time?

Inventory of reservoir / flux out

***when the reservoir is in steady state, flux in = flux out

How are humans altering the water cycle?

Agriculture: Irrigation and groundwater pumping moves water from runoff/groundwater transport into the atmosphere through evapotranspiration. Moving massive amounts of water for crop and livestock.

Industrial and domestic appropriation: Redirecting from ecosystems.

Pollution: To deal with pollution we have to dilute it with water.

Deforestation and urban development: changes the way that the environment holds water

What are examples of organic carbon? What types of molecules are organic carbon.

Carbon molecules connected with covalent bonds are organic (C-C or C-H).

Some examples: Carbohydrates, sugars, methane, fossil fuels.

Energy versus matter in the carbon cycle.

Energy can only be used once before the organic carbon is transferred back to inorganic (respiration of organisms). The physical carbon molecule can be used as many times as needed as long as its fixed back into organic form!

What are the major reservoirs of carbon? What are their relative sizes?

Lithosphere > oceans > soil > atmosphere > biosphere

Describe the carbon cycle and its fluxes.

Inorganic carbon in the atmosphere is uptaken by plants undergoing photosynthesis and fixed into organic carbon tied in glucose sugars, from there is can move up terrestrial food webs. Inorganic carbon is also absorbed into the oceans, where a simular process is found through photosynthesis fixing organic molecules that travel up the aquatic ecosystems.

Organic carbon is transferred from land to aquatic ecosystems through runoff (surface) and leeching (subsurface). Organic carbon can sink down into the sediment of the ocean and turn into rock holding organic carbon, which is very slowly cycled through the lithosphere and can be weathered into ecosystems.

All animals respire inorganic carbon back into the atmosphere, and combustion of fossil fuels also releases inorganic carbon back into the atmosphere.

Non-steady state since humans started mining fossil fuels after the industrial revolution.

What are the two deep ocean vertical transports of organic carbon.

Upwelling and sedimentation.

What are the two sources of carbon in the lithosphere?

Fossil fuels are buried organic carbon that has sedimented in rock. Sedimentary rock carries inorganic carbon through shells, CACO₃, and other sediments.

Why is the carbon cycle important?

Organic carbon is required for all life, it determines atmosphere GHG concentrations, ocean pH depends on the CO₂ concentrations in the water, and global systems depend on carbon to carry energy.

What are the seasonal CO₂ changes in the biosphere and atmosphere and why do they occur?

Carbon is sucked out of the atmosphere by plants during springtime! In contrast, atmospheric CO₂ levels are at an extreme high in the winter when plants lose their leaves and go dormant.

Where do carbon emissions end up?

¼ of carbon emissions are sunk by vegetation, ¼ is sunk by the oceans (contributing to ocean acidification, and the remaining ½ remains in the atmospheric resovoir.

What are two ways that humans are impacting the carbon cycle?

Burning of fossil fuels: Adds a major source of CO₂ emissions.

Deforestation: Removes a major sink of carbon.

What are the two ways that nitrogen is fixed from the atmosphere?

Through lightning strikes that provide enough energy in the atmosphere to break the triple bond of N₂ in the atmosphere to create nitrate, OR through microbes that fix nitrogen into ammonium.

• Of the microbes, there are N fixing bacteria in the soil OR in root nodules of legumes.

This fixed nitrogen is NOT organic, these are types of nitrogen that can be assimilated by plants to form organic nitrogen that moves up the food chain.

How does nitrogen get out of its organic cycle?

Ammonium can be nitrified by nitrifying bacteria into Nitrite, then must be nitrified again into Nitrate, which can either be DEnitrified by bacteria into N₂ N₂O and N₂x or be uptaken by bacteria again to undergo ammonification.

What are anthropogenic agricultural and industrial processes that have altered the nitrogen cycle?

1. An agricultural process is the planting of legume crops that have N fixing bacteria in their root nodules.

2. An industrial process is the mass production of synthetic fertilizer, which inputs massive amounts of N into ecosystems.

   1. Combustion from the process increases NO_x into the atmosphere.

What is an atmospheric