Ecosystems: Material and Energy Flow

Ecosystems

• Includes all organisms in a specific location
• Includes the abiotic environment, and their interactions

Materials Flow

• Also known as biogeochemical cycles
• Chemicals move through the ecosystem, including carbon, nitrogen, and water
• Involves both biotic and abiotic processes

Energy Flow

• Governed by the laws of thermodynamics
• Involves producers and consumers at different trophic levels

Carbon Cycle

• Carbon is a major component of organisms
• Carbon Fixation: Metabolic reactions create non-gaseous compounds, such as photosynthesis, from gaseous ones
• Cellular respiration releases CO2

Carbon Reservoirs

• Carbon exists in reservoirs or pools and moves between them (flux)
• The graphic provided is from 2007, and in 2019 the average atmospheric CO2 was 410 ppm or 875 Petagrams

Water

• All life requires water
• Water accounts for over 60% of adult human body weight
• The amount of water influences nature and abundance of organisms
• Synthesized during cellular respiration and broken down during photosynthesis
• Exists as freshwater and saltwater

Water Cycling

• Includes precipitation to water (0.320) to ice (29.2), runoff (0.030) to oceans (1320)

Changes in Water Capacity & Flux

• Deforestation disrupts the local water cycle
• Surface modification causes water to drain as rain
• Aquifer use results in higher discharge
• Climate Change causes ice, glacier melt, temperature, and is also linked to evaporation

Groundwater

• Groundwater is found underground
• Aquifers- Permeable, underground layers of rock, sand, and gravel saturated with water
• 95% of fresh water used in the United States is from this import reservoir

Nitrogen Cycle

• Nitrogen is a component of all proteins and nucleic acids
• Usually the element in shortest supply
• Atmosphere is made up of 78% nitrogen
• Most plants and animals cannot use N2 (gas)
• Plants and animals instead use NH3 (ammonia) and NO3 (nitrate)

Nitrogen Fixation

• Synthesis of nitrogen-containing compounds from N2
• Nitrification: N2 converts to NH3 then to NO3
• Denitrification: NO3 converts to N2
• Microbes carry out both processes
• Nitrogenous wastes and fertilizers radically alter the global nitrogen cycle
• Humans have doubled the rate of transfer of N₂ in usable forms into soils and water

Phosphorus

• Required by all organisms
• Occurs in nucleic acids, membranes, and ATP
• Phosphorus has no significant gas form
• Exists as PO4 in ecosystems
• Plants and algae use free inorganic phosphorus
• Animals eat plants to obtain their phosphorus

Thermodynamics

• First Law of Thermodynamics: Energy is neither created nor destroyed; it changes forms and can take the form of light, chemical-bond energy, motion, and heat
• Second Law of Thermodynamics: Entropy measures disorder in a system and all systems increase in disorder over time, it takes energy to maintain order
• Earth is an open system, energy arrives to, and is released from, Earth
• Earths incoming and outgoing flows of radiant energy must be equal for global temperatures to stay constant

Incoming and Outgoing Energy

• Human activities may be changing the composition of the atmosphere
• Greenhouse effect: heat accumulating on Earth

Trophic Levels

• This is the level at which an organism "feeds"
• Autotrophs: Synthesize the organic compounds from inorganic
• Photo autotrophs: light as energy source
• Chemoautotrophs: energy from inorganic oxidation reactions (prokaryotic)
• Heterotrophs: Cannot synthesize organic compounds from inorganic precursors
• Animals that eat plants and other animals

Producers and Consumers

• Primary producers are autotrophs
• Consumers are heterotrophs
• Herbivores on the first consumer level
• Primary carnivores eat herbivores
• Secondary carnivores eat primary carnivores or herbivores
• Detritivores eat decaying matter, such as earthworms, millipedes, and flies
• Decomposers break down dead matter and include bacteria and fungi

Trophic Cascade

• Food web indirect interactions result in a change of population size in one level affecting others

Trophic Cascade: Food Web of Flathead Lake

• Emphasizing three of the trophic levels: piscivores, planktivores, and herbivores
• Altered by the introduction of nonnative fishes and an opossum shrimp, M. diluviana

Productivity

• The rate at which organisms in the trophic level collectively synthesize new organic matter
• Primary productivity the productivity of the primary produces
• Respiration is the rate at which primary producers break down organic compounds
• Gross Primary Productivity (GPP): the raw rate at which primary producers synthesize new organic matter
• Net Primary Productivity (NPP) GPP less the respiration of the primary producers
• Secondary Productivity: is the productivity of a heterotroph trophic level