EXAM 1: Carbon in Lakes

Many northeastern U.S lakes are in areas with granite as the primary underlying bedrocks. These lakes are very vulnerable to acid rain. Why?

the soils do not have a good buffering capacity

How much of earth's surface is lakes?

less than 2%

Do lakes or oceans store more carbon in sediments?

lakes store more carbon in sediments.

Do lakes release or store more carbon?

they tend to release more CO2 to the atmosphere than they absorb (they release almost as much CO2 as all oceans)

Why do lakes release more carbon?

they obtain a lot of carbon. they drain large landscapes so they get carbon from forests, fields, lawns

Is CO2 in lakes high or low?

often high and varies widely

What are the sources of carbon in a lake?

atmosphere, respiration, H2O percolates through soil

-surrounding vegetation and life dies and is washed into lake

The amount of CO2 in a lake is based on?

lake and watershed sizes, watershed ecosystem, land use (agriculture), precipitation amount, types of soils and rocks

Is CO2 soluble in water?

CO2 is very soluble (about 200 times more than O2)

What are the forms of CO2 in a lake?

free form, carbonic acid, bicarb, carbonate

What is CO2 tied to?

pH

-Adding CO2 causes pH to go down (carbonic acid is made)

-Removing CO2 causes pH to go up (carbonic acid is removed)

What form of carbon is high when entering a lake?

carbonates

What is hard water?

when the H2CO3 formed dissolves CaCO3 and MgCO3

-Comes from alkaline earth materials (bicarb, carbonates, sulfates, and chlorides)

Where does hard water come from?

usually from deposits with high levels of Ca and/or Mg

-Ca(HCO3)2 and Mg(HCO3)2 are primary contributors around here

What is total hardness?

the measure of levels of Ca2+ and Mg2+ in waters

What is the primary buffering system in freshwater?

bicarbonate

-also the most important buffering system in the human body.

What is alkalinity?

sum total of all things contributing to a pH shift towards alkaline

What is acid neutralizing capacity (ANC)?

measured as quantity of acid needed to neutralize all Oh-, HCO3-, and CO3 -2

In freshwater ecology, what is alkalinity a measure of?

a lake's buffering capacity

When alkalinity is up to 200 mg/L CaCO3 what does this mean?

very common in freshwater, means the water is very stable

When alkalinity is 100 to 200 what does this mean?

CaCO3 is well-buffered and pH is fairly stable

When alkalinity is below 10-20 what does this mean?

CaCO3 is poorly buffered and pH is variable

What are two factors affecting the sum CO2 in lakes?

photosynthesis (consumes CO2)

decomposition and respiration (release CO2)

During fall and spring turnover, what does the sum CO2 curve look like?

very uniform, mixed top to bottom

During summer stratification in a oligotrophic lake, what does the sum CO2 curve look like?

orthograde.

pH can be uniform or inverse orthograde

During summer stratification in an eutrophic lake, what does the sum CO2 curve look like?

the lake has a clinograde O2 curve so the CO2 curve is inverse of that.

CO2 is lower in the epilimnion due to photosynthesis being higher than decomposition

In a eutrophic lake, if the water is hard what does the pH curve look like?

-high alkalinity

-pH is essentially uniform top to bottom

In a eutrophic lake, is the water is soft, what does the pH curve look like?

-likely low alkalinity

-pH is essentially opposite of sum CO2 curve