lec 18 Flashcards
with acid precipitation, sometimes there are larger bursts of algal biomass. why is this?
benthic grazers are killed off by acidity, so while acid is a sel pressure on algae, it’s not stronger than the pressure that the grazers exerted
what are the main problems of toxic cyanobacteria attributed to?
microcystins, which are the toxins that are most common
loch leven had eutrophication concerns, so efforts were made to reduce external loading. P conc were noticed to decrease in spring and winter, but not summer - P conc stayed the same, and even increased towards the end of summer. why?
external loading switched to internal loading - ie the effects were so profound, it just became a way of life for the organisms in the lake.
what we should take from this is that external loading can be a great source of nutrients, but it should not be all we think about
the following are methods of lake management. explain them:
- dredging
- aeration
- iron addition
dredging: the removal of sediments, which may contain nutrients that are just settling down
aeration: manually oxygenating the bottom of the water column (can fuck up stratification)
iron addition: so yk how iron is necessary in controlling P levels through locking it up as FePO4. adding iron in low iron lakes has shown to be good at bringing cyanobacteria levels down n stuff
what is the difference between a point source and a nonpoint source input?
point source can be thought of as a direct input (ie an action that directly puts nutrients into an ecosystem) while nonpoint source can be thought of as an indirect input (ex. fertilizer runoff reaching lakes, incr N and P)
what is one problem with adding N and P with respect to other elements, such as silicon
N and P promote all sorts of growth. organisms such as diatoms use up silicon, so when diatom growth is promoted silicon conc goes down. the problem is silicon is not readily available since it comes off weathering, and no human inputs put a lot of silicon in the water – silicon gets pretty readily used up
copper inputs. purpose? problems (3)?
+ good for immediately killing off cyanobacteria
- in hard water, copper precipitates w carbonates
- copper can be toxic to other aquatic life
- when copper kills cyanobacteria, the toxins may get released anyways
what is alum? benefits? problems?
alum is just a chemical idk
+ good at binding phosphorus
- can be toxic at high levels
- expensive
hydrologic methods
take nutrient-rich water out of hypolimnion without causing destratification
what happened in lake washington? did management work? how was this illustrated ecologically?
historically oligotrophic, sewage was causing eutrophication –> diverted sewage caused oligotroph to return
cyanobact when down and daphnia went up!
what happened in lake trummen? did management work?
sewage inputs etc
solved by dredging soil, and it went pretty well - P trapped in soil was removed and no longer available for cycling
what does lake tahoe demonstrate? specifically, give me two factors that changed how lake tahoe looks
super oligotrophic, but tending toward eutrophic due to nearby anthro inputs
nearby sewage + removal of trees
