ecology final

How much greater are the N and P inputs to ecosystems now versus before the advent of Modern Society and Agriculture?
Human impacts have doubled the natural background rate of nitrogen inputs and have quadrupled the phosphorus inputs.
How have these increases in N and P inputs altered the primary productivity of ecosystems, and what landscape level phenomenon might erase these gains?
The resulting increase in plant production may be large enough to affect the global carbon cycle. Human disturbances such as forest conversion, harvest, and fire increase the proportion of the nutrient pool that is available and therefore vulnerable to loss.
How has gaseous nitrogen loss increased, and what are its effects on the global ecosystem?
Gaseous losses of nitrogen influence the chemical and radiative properties of the atmosphere, causing air pollution and enhancing the greenhouse effect.
In what percentage of the worlds estuaries have dead zones become larger?
Nutrient runoff from freshwater systems to the ocean has created or intensified dead zones in 2/3 of the world’s estuaries.
Compare and contrast the movement of N and P in the ecosystem. How are they different?
Nitrogen may move either by water or air, while phosphorus, lacking a significant gaseous phase, generally moves only downhill in aqueous solution or as dust particles in the atmosphere.
Explain how human activities have made many ecosystems more open.
Human activities tend to increase inputs and outputs relative to internal transfers and make element cycles more open.
What is pelagic nutrient cycling closely coupled to?
Pelagic nutrient cycling in the open ocean is closely coupled to the flow of carbon.
What three processes control the balance of nutrient cycling in the ocean?
1) Stratification driven by surface heating restricts nutrient delivery from deep water to surface.
2) Wind-driven mixing disrupts startificaiton and deepens the mixed layer, increasing nutrient supply but reducing average light availability through mixed layer.
3) Upwelling supplements nutrient supply and keeps phytoplankton in shallow well-lighted surface waters, supporting high gross primary production.
What elements are generally limiting in the ocean?
Nitrogen and phosphorus
What primarily mediates nutrient return in pelagic systems?
Grazing accounts for most of the nutrient return from phytoplankton to the environment.
What is the primary route for nutrient loss and input in pelagic systems?
Sedimentation of zooplankton feces and phytoplankton causes a continuous nutrient loss from the pelagic zone that is replenished by nitrogen fixation, upwelling, and mixing.
What does nitrogen “mineralization” mean in the ocean?
Nitrogen is mineralized (converted from organic nitrogen to ammonium) by several processes in the ocean.
Compare and contrast nitrification to denitrification. What process predominates on the ocean bottom?
Nitrification- Ammonium absorption by nitrifying bacteria that use it as an energy source, releasing nitrate as a waste product.
Denitrification- Conversion of nitrate to gaseous forms.
In oxygen-depleted bottom water, what is the primary electron acceptor and what are the consequences of this? What are the consequences for the N:P ratio of this coastal bottom water?
Sulfate or nitrate as electron acceptor, effects of producing H2S, N2O, N2. Nitrogen trace gases deplete water of nitrogen relative to other nutrients such as phosphorus, making N Sulfur, due to the activity of anarobic autotrophs (purple sulfur fixing bacteria) sulfate acts as an electron acceptor that allows microbes to metabolize organic carbon for energy, with hydrogen sulfide as a byproduct.
Explain the process of entrainment and mixing in estuaries. How can this help explain the high productivity of estuaries?
Estuaries tend to become stratified by the inflow of low-density fresh water from rivers. This water entrains (carries with it) surface ocean water as it flows from the river mouth out into coastal ocean. Phosphorus-rich bottom water with surface water depends primarily on tidal mixing, which is greatest in long or shallow estuaries, and on surface turbulence caused by river discharge, winds, and storms.
Where does the N come from in Chesapeake Bay? How about the P.
Chesapeake Bay receives about 25% of its phosphorus from the coastal ocean but most of its nitrogen from rivers.
What processes are increasing the size and frequency of oceanic dead zones? And explain a potential positive feedback loop with one of these processes.
Nutrient pollution in estuaries causes extremely high productivity and generates large quantities of organic matter that sinks to depth. This stimulates bacterial activity depletes oxygen in the lower 20 m of the water column, creating zones of hypoxia and anoxia (low and no oxygen)
increased land-use change, intensification of agriculture, and warming ocean temperatures have increases the frequency of dead zones
Dead zones have created a new climate feedback, in which climate warming intensifies stratification that augments the low-oxygen, high nitrate conditions that favor denitrification and the production of N2O, a powerful greenhouse gas that contributes to warming climate.
Why is nutrient concentration so low in unpolluted freshwater lakes?
Active absorption of N and P by phytoplankton often maintains extremely low nutrient concentrations in the surface waters of unpolluted lakes.
What % of the worlds land surface area is occupied by lakes?
What is the N:P ratio of an oligotrophic lake compared to a eutrophic lake and what causes that change?
N:P of oligotrophic lakes are high, suggesting P limitation, and N:P ratio decreases in waters of more nutrient-rich lakes.
What are CPOM and FPOM?
CPOM- Course particulate organic matter
FPOM- Fine particulate organic matter
What is the spiraling length of a stream and what are the differences between the turnover length and the uptake length?
Spiraling Length – the average horizontal distance between successive uptake events.
turnover length – the downstream distance moved while an element is in organic form
uptake length – the average distance an atom moves from the time it is released until it is absorbed again
Is invertebrate drift an important flux for nutrients in streams? Why or why not.
It is not very important, because most of the invertebrates are stuck to the rocks, which causes minimal cycling.
What is the N:P ratio of water entering the Ocean compared to water entering a river?
The N:P ration of water entering the ocean is typically much lower than that which enters the river.
What is the primary pathway for Nitrogen input in unpolluted terrestrial ecosystems?
Biological nitrogen fixation is the main pathway by which new nitrogen enters unpolluted terrestrial ecosystems.
What enzyme carries out nitrogen fixation and what organisms have it?
Only nitrogen-fixing bacteria have the capacity to break triple bonds of N2 and reduce it to ammonium. The enzyme is called nitrogenase.
What environmental conditions are necessary for this enzyme to work?
The reduction of N2 has a large energy requirement and therefore occurs only where the bacterium has an abundant carbohydrate supply and adequate phosphorus. The enzyme is denatured in the presence of oxygen, so organisms must protect the enzyme from contact. Temperature often constrains the carbon supply and activity of nitrogenase enzymes, so nitrogen fixation is most prominent in tropical environments and constrained at high latitudes
What was the cost of N absorption from symbiotic sources compared to inorganic absorption from soils in laboratory conditions? Who’s winning?
The energetic requirement for nitrogen fixation can be about 25% of GPP under laboratory conditions, two to four times higher than the cost of absorbing inorganic nitrogen from soils.
Which has a higher rate of Nitrogen fixation, a free living or symbiotic N fixer and why?
free living nitrogen-fixing bacteria typically have the lowest rates of nitrogen fixation. most active in soils or sediments that have high concentrations of organic matter to provide the carbon substrate that fuels nitrogen reduction.
What makes a lichen and do they fix nitrogen?
Lichens are composed of green algae or cyanobacteria as the symbiont, cyanobacteria that fix nitrogen, and fungi that provide physical protection. Yes they do fix nitrogen.
Why aren’t all plant Nitrogen fixers? Provide three plausible reasons
Because only nitrogen fixing bacteria have the capacity to break the triple bonds of N2 and reduce it to ammonium
What are the anthropogenic sources of N and N deposition?
The application of urea or ammonia fertilizer leads to volatilization of NH3, which is converted to NH4 in the atmosphere and deposited in rainfall. Domestic animal husbandry has increased NH3 emissions to the atmosphere. Emission of nitric oxides from fossil fuel combustibles, biomass burning.
What are the three pathways for deposition of N.
1. Wet deposition delivers nutrients dissolved in precipitation
2. Dry deposition delivers compounds as dust or aerosols by sedimentation or impaction.
3. Cloud-water deposition delivers nutrients in water droplets onto plant surfaces immersed in fog.
What role does weathering play in the N cycle?
In some watersheds underlain by high-nitrogen sedimentary rocks, rock weathering contributes.

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