ch 21 : movement of elements in ecosystems Flashcards
are chemical elements reused constantly?
yes; they cycle between biologically usable and un-usable states (organic and inorganic)
what happens to energy during transformations?
it’s either gained or lost
- oxidation—gives up electrons (loses energy)
- reduction—accepts electrons (gains energy)
assimilatory processes
- inorganic –> organic
- requires energy (photosynthesis)
dissimilatory processes
- organic –> inorganic
- releases energy (respiration)
an ecosystem may be viewed as a set of _________ among which elements are cycled at various rates:
compartments
the movement of water through ecosystems and the atmosphere; including evaporation, transpiration, and precipitation.
hydrologic cycle
97% of water is found where?
in the oceans; the remaining water is in lakes, streams, rivers, wetlands, underground aquifers, and soil
the amount of ________ must balance the amount of _________ or all water would accumulate in one part of the cycle
evaporation; precipitation
what is the relationship between precipitation and evaporation on a global scale?
on a global scale, precipitation exceeds evaporation in terrestrial ecosystems; evaporation exceeds precipitation in aquatic systems.
what is the relationship between precipitation and evaporation on a global scale?
on a global scale, precipitation exceeds evaporation in terrestrial ecosystems; evaporation exceeds precipitation in aquatic systems.
what happens to excess water that falls on land?
it’s transported in runoff and groundwater into aquatic systems
what are some of the ways that humans impact the hydrologic cycle?
- creation of impervious surfaces (e.g., roofing, pavement) reduces the water that enters the soil and increases runoff.
- removing plant biomass (e.g., cutting down a forest) decreases evapotranspiration and also increases runoff.
- increased runoff causes soil erosion and flooding
- humans often use water from the ground (e.g., for irrigation) before it can be replenished.
- climate change may increase temperatures and evaporation rates, leading to increased intensity of rain and snowstorms.
what is used for respiration in oxygen-poor habitats?
carbon is used for respiration instead of oxygen
which is more effective: CO2 or CH4 (methane)?
methane is 72 times more effective as a greenhouse gas than CO2
what does the precipitation of calcium carbonate lead to?
the development of rock known as dolomite and limestone
describe the rate of carbon burial
it’s slow and is offset by rates of carbon release from limestone weathering and volcanic eruptions
what are the human impacts on the carbon cycle?
- over the past two centuries, extraction and combustion of fossil fuels (e.g., coal, oil, natural gas) has increased to meet energy demands.
- combustion of fossil fuels releases CO2 into the atmosphere.
- measurements atop Mauna Loa on the island of Hawaii indicate a 25% increase in atmospheric CO2 between 1958 and 2012.
- researchers use ice cores to measure CO2 concentrations that were in the atmosphere hundreds of thousands of years ago.
- in very cold regions (e.g., Greenland), snowfall compresses into ice over thousands of years, trapping tiny bubbles of air.
- researchers date the layers of ice in a core sample, melt the layers, and sample CO2 concentrations of the air inside trapped bubbles.
- such studies indicate that current CO2 levels in our atmosphere fluctuate greatly, but are currently 31% higher than
the maximum
concentration
during the past
400,000 years.
what does CO2 absorb? Too much of CO2 could cause the planet to what?
- CO2 is a greenhouse gas that absorbs infrared radiation.
- excessive amounts of CO2 could cause our planet to become much warmer than it has been in a very long time.
what does warming in the high latitude regions cause?
peat, which is the mixture of dead sphagnum moss and other plants, to thaw and begin decomposing
decomposing peat releases methane gas, which exacerbates the problems of excessive greenhouse gases and global warming
what is the most limiting nutrient on earth?
nitrogen
what are some other characteristics of nitrogen?
- more complex (C)
- ammonification
- organic nitrogen(proteins) ->NH3 ->NH4+ - de/nitrification
- nitrifying bacteria: NH4+ -> NO2-
- denitrification: NO2- -> N2 - nitrogen-fixing bacteria:N2 NH3 NH4+
important bacteria for nitrogen fixing
- rhizobium (in legumes, other plants) - azobacter (free-living)
important bacteria for nitrification
- nitrosomonas (soil) - nitrosococcus (ocean)
important bacteria for denitrification
pseudomonas (soil)
what are the human impacts on the nitrogen cycle?
- human activities (e.g., fuel combustion, fertilizer production, planting nitrogen-fixing crops) have doubled the amount of nitrogen put into terrestrial ecosystems.
- nitric oxide in the air reacts with water to form nitrates, which fall to the ground during precipitation.
- data collection across many North American sites reveals that the precipitation of nitrates fertilizes ecosystems, increases productivity, and decreases species richness.
what is smtn special about phosphorus?
- it doesn’t have a gas phase; it can only enter the atmosphere in the form of dust
- it rarely changes its chemical form and commonly moves as a phosphate ion
how do animals excrete excess phosphorus?
by excreting urine with PO43– or other phosphorus compounds that are converted to PO43– ions by phosphatizing bacteria.
what happens to phosphorus in oxygenated waters?
phosphorus precipitates after binding with calcium and iron (e.g., calcium phosphate, Ca(H2PO4)2).
what happens with phosphorus in low-oxygen conditions?
under oxygen-low conditions, iron binds with sulfur instead of phosphorus, making phosphorus more available
what are the human impacts on phosphorus cycling?
- phosphorus is a limiting nutrient in terrestrial and aquatic systems; adding phosphorus to these systems can have harmful effects.
- phosphorus, in combination with excess nitrates, can contribute to algal blooms in aquatic ecosystems.
an increase in productivity of aquatic ecosystems
eutrophication
cultural eutrophication
an increase in the productivity of aquatic ecosystems caused by human activities
what is the nutrient loss from leaching and water transport balanced with?
by inputs of nutrients from the air (e.g., nitrogen) and from weathering of bedrock beneath the soil (e.g., phosphorus).
acids from rainwater and decomposition react with minerals in bedrock to do what??
release elements essential to plant growth.
how can weathering rates be determined?
by measuring nutrients entering a system from rainfall and leaving a system by leaching
ecologists often measure rates of nutrient regeneration in a watershed. what is a watershed?
an area of land draining into a single stream or river
because weathering is a slow process, primary production relies on what?
regeneration of nutrients from the breakdown of detritus
the process that breaks down organic matter into smaller and simpler chemical compounds
decomposition
what is decomposition primarily conducted by?
bacteria and fungi
breakdown of organic matter: in terrestrial ecosystems, 90% of all plant matter produced in a year is not _______ by herbivores, but is ultimately __________
consumed; decomposed
breakdown of organic matter: what does leaching remove?
10–30% of soluble substances from organic matter; larger organic compounds are left behind (e.g., lignin)
breakdown of organic matter: what happens to lignin and other decay-resistant compounds?
may never break down and will be buried
breakdown of organic matter: how do large detritivores consume the energy in leaf litter?
large detritivores can consume 30–45% of energy in leaf litter; they also increase breakdown rates by macerating litter, which provides more surface area for microbial growth
breakdown of organic matter: what do bacteria and fungi do for the breakdown of organic matter?
bacteria and fungi convert organic matter into inorganic nutrients; hyphae of some fungi (e.g., shelf fungi) can penetrate wood and break down lignin and cellulose.
why would detritus in the tropics decompose more rapidly?
because of warmer temperatures and higher amounts of precipitation
proportion of dead plant matter to total plant matter in …
- temperate coniferous forests
- temperate hardwood forests
- tropical rainforests
- temperate coniferous forests: 20%
- temperate hardwood forests: 5%
- tropical rainforests: 1-2%
t/f tropical forests have a larger proportion of total organic matter in living vegetation than in soil and detritus
true
what happens when vegetation in tropical forests is cleared and burned for agriculture?
nutrients are rapidly mineralized and taken up by crops
what happens after 2-3 years of crop harvesting?
soil fertility degrades and cleared fields must be allowed to undergo natural succession
are the chemical and biochemical processes of decomposition similar in terrestrial and aquatic ecosystems?
yes
what happens to decomposition processes in terrestrial ecosystems compared to aquatic ecosystems?
- in terrestrial ecosystems, nutrients regenerate close to the location where they are taken up by producers.
- in aquatic ecosystems, nutrients regenerate in the sediments, which are often far from the surface waters where producers (e.g., phytoplankton) live.
- terrestrial ecosystems commonly experience aerobic decomposition, whereas aquatic ecosystems commonly experience much slower anaerobic decomposition.
forested streams and wetlands receive energy in the form of what?
dead leaves from terrestrial plants
what do decomposition rates depend on?
water temperature and leaf traits
when does decomposition occur?
- leaching
- shredding by invertebrates (e.g., amphipods, isopods)
- consumption by fungi and bacteria.
what happens to most decomposed organic matter in most rivers, lakes, and oceans?
sinks to the bottom; nutrients accumulate in the sediments
productivity __________ when sediments are far from the site of algal primary production (e.g., surface waters).
decreases
________ are the least productive aquatic ecosystems because the benthos is far from the surface waters.
deep oceans
____________ are more productive because sediments are closer to surface waters
shallow oceans
in some regions (e.g., the western coast of South America), upwelling of nutrients from deep sediments generates _____________
high productivity
