lec 6 Flashcards
what is the relationship bw mixing depth and strength of the metalimnion? why?
as mixing depth gets deeper, the metalimnion gets weaker, since the decline from epilimnion to hypolimnion gets smaller
are deeper or shallower lakes more likely to stratify?
deeper lakes, as mixing depth won’t go all the way to the bottom
how does mean fetch affect lakes? what about in winter?
when lakes freeze, the temp that the under-ice water stays at is largely dictated by factors such as wind
what is an amictic lake? where do we see them most often?
lake that never stratifies. we see these most often at high latitudes where ice cover never goes away
why do cold monomictic lakes appear?
mix, but they don’t warm enough to stratify in summer [???]
why do warm monomictic lakes appear?
one stratification event in summer, but lack of ice cover in winter results in continual mixing in winter (no stratification event)
why do warm polymictic lakes appear?
shallow lake + inconsistent wind patterns dictate mixing - stratification is erratic
what is the difference between mero- and holomictic lakes? why do meso- appear?
mero- mix partially while holo- mix all the way to the sediment. this has implications for nutrient distribution, where nutrients are often stored in sediment.
meso- appear bc they are either really deep, or their is saline inflow which does not mix since saline is denser than freshwater.
what type of lake is this?
https://gyazo.com/745eccce5710afa02c00aa3be9485d2d
- not stratified in summer months
- stratify all other times
–> cold monomictic
light brings about heat. does the photic zone always align with the epilimnion?
nope! things like wind can affect mixing depth, which is just as important in determining epilimnion
when zeu = zmix and zeu < zmix, the resulting productivity and biomass graphs are pretty similar. why? why is the zeu > zmix graph different?
https://gyazo.com/15d677c7cdb40b9105624e0ca71fdb14
fundamentally, we have to understand that prim prod will only occur up to the euphotic zone’s limits
when zeu = zmix, the water is mixed such that all organisms within the euphotic zone are brought to the surface at some point. this results in prod up to the zeu, and biomass slowly dropping off as some organisms are lost
when zeu < zmix, water is mixed deeper than light penetrates. a similar pattern to zeu = zmix forms since organisms are brought up for prim prod, with biomass being large within mixing depth and slowly dropping off.
zeu > zmix is different. light penetrates further than the water is mixed, so prod and biomass peaks at mixing depth. some more prim prod occurs below mixing depth, so the dropoff is not immediate. biomass slowly drops off as before.
how do rivers differ from lakes in terms of mixing?
mixing in rivers goes crazy bc they are turbid
also tend to have poor light penetration since they carry particles that reflect light
