lec 20 Flashcards
what is a requirement for P to be limiting in a system?
all other nutrients are not limiting ie the Redfield ratio is maintained
what is nutrient spiraling? N is really important in nutrient spiraling - why? what is a problem it runs into?
nutrient spiraling is the distance that it takes for a nutrient to go through every stage in its respective cycle - for the N cycle this is particularly long. problem is that the N cycle is also fine tuned to different oxygenation levels, which arent consistent in rapidly moving waters
dissolved particles in water can be conservative or reactive. define. what are their implications for nutrient spiraling length?
conservative: no biological/chem reactivity (ex. Na, Cl) = flow downstream is uninhibited = shorter spiral length
reactive: lots of biological/chem reactivity –> flow downstream is inhibited by uptake etc = longer spiral length
what is the formula for nutrient spiraling? which is dominated in oligo- and eutrophic lakes? how can we use this formula to estimate the strength of the biotic community in the ecosystem?
nutrient spiral = Sw [transport in water] + Sp [assoc w biota]
in oligo, there are no animals around – dominated by Sw
in eu, there are animals – dominated by Sp
knowing this, we can look at the length of a nutrient spiral to estimate the strength of the community - Sw occurs either way, so longer Sp will indicate stronger comm.
ie if cycle is run through quicker, less time is being spent in biota - biotic comm is not strong
what is a hyporheic zone?
when sediments are porous enough, they can create an ‘underground’ groundwater river. this can functionally be thought of as our hypolimnion: collection of nutrients in sediment, anoxic, etc
what is darcy’s law? what is darcy’s point?
water movement through sediment = (hydraulic conductivity) * (hydraulic gradient head)
ie (resistance to flow) * (energy to overcome said resistance)
the point is to measure the flow of aq substances through porous material (think like pouring water in a bucket of rocks and water fills the space vs pouring water in a bucket of mud and it kinda just sits on top)
what is hydraulic gradient determined by?
hydraulic gradient is the energy to overcome resistance to flow
can be things like having a steeper stream slope, high pressure of incident water, etc (anything that will make water more likely to get through a sediment)
how does water look in open water vs subterr flow paths?
surface water:
- relatively turbulent: free gas exch
- algae and aq plants deplete inorganic nutrients
- food web supported by organic matter
hypor:
KEY DIFFERENCE: dark –> algae and aq plants cannot photosynth
- food web dependent on INORGANIC matter
- net draw down of O2 because decomposers dominate
- less O2 = more potential for alternate redox staircase reactions
hypor is pretty much enmeshed with the sediments. what implications does this have for chemicals and biota?
chemicals can get trapped up (recall how P and ammonia are charged and can get bound up in equally charged clays)
lots of attachment space for microbes – lots of bacterial transformation can occur (esp supported by anoxic conditions)
how do oxygen sinks occur in hypor zones? DOC sinks?
decomposers and other respiration processes can draw down oxygen quite significantly, creating an oxygen sink if there is no O2 input. this coincides w being a DOC sink, since these decomposers/respirers need DOC substrate to work on.
how do oligo- and eu- rivers compare in terms of nitrate conc?
oligo: steadily incr N but at LOW amounts since pretty much all avail N is locked up in organisms
eu: HUGE drops as organic matter is fed into the hypor zone to be decomposed - N conc falls as it is released through denitrification
the key is the presence of C in eu- hypor zones, which can allow for denitrification to occur
