BI 423: Dissolved Oxygen Aquatic Ecology Test 1

Why do ponds, i.e., water hazards, on golf courses almost always have clinograde DO2 profiles?

They are hypereutrophic due to fertilizer runoff

How much DO is in the atmosphere? How much in water?

21%, 1%

What do DO concentrations depend on?

Temperature, Photosynthesis, Barometric pressure, Respiration, Salinity

What increases solubility greatly?

Cold temperatures

DO is _____ in water

Sparingly soluble

When is DO highest

during the day

Where do DO2 Gains (sources) come from

Diffusion from atmosphere, mixing from wave action and wind (etc.), photosynthetic organisms

What are sources of DO2 loss

Organism respiration (i.e. fish, mollusks, insects, etc.), decomposition (utilization by bacteria and fungi)

What greatly effects the vertical profile of DO2 lakes

Thermal stratification, photosynthetic production of O2, Respiration and Decomposition of O2

When is the DO2 profile largely uniform

Fall and Spring Turnover

What percentage of saturation (DO2) are lakes during spring and fall turnover

Near 100% saturation top to bottom

What oxygenates the epilimnion

Diffusion, wave action, photosynthesis

What makes the DO2 rather uniform, throughout the epilimnion

Wave action + convective currents mix throughout epilimnion

What could contribute to high, localized DO2 levels

May have spots high in phytoplankton concentration contribute to high, localized DO2 levels

Orthograde

refers to a vertical dissolved oxygen (DO) profile in a stratified lake where oxygen concentrations remain relatively uniform from the surface down to the bottom

Clinograde

dissolved oxygen levels are high at the surface but decrease rapidly—often to near zero—at greater depths

Heterograde

a vertical distribution of dissolved oxygen (DO) in a stratified lake or reservoir where oxygen levels peak or drop significantly at an intermediate depth

What happens to the hypolimnion during summer stratification

Hypolimnion is isolated from surface epilimnion due to H2O density differences (i.e., no mixing between

hypolimnion + epilimnion)

And hypolimnion is often below _____ zone and contains the _____ zone (i.e., no net O2 production)

euphotic or trophogenic, tropholytic

Oligotrophic lakes hyoplimnion remain

relatively high in DO 2 from spring/fall turnover

during stratification

Not much organic matter produced or settling to bottom, No or little O 2 used or needed for decomposition for _____ lakes

oligotrophic

However, in summer, epilimnion DO2 levels will _____ relative to spring turnover in oligotrophic lakes

fall slightly

Warmer liquids hold ________ gas

less

In summer, epilimnion DO2 levels generally remain unchanged in ____ Lakes

eutrophic

in eutrophic lakes _____ level will decline to 0 or ~0 as _____ occurs

DO2, stratification

DO2 level will decline to 0 or ~0 as _____ occurs in eutrophic lakes

stratification

In _____, epilimnion DO 2 levels generally remain relatively unchanged or

slightly higher due to PS in eutrophic lakes

summer

Oligotrophic lakes have a ____ DO profile curve

orthograde

eutrophic lakes have a ____ DO profile curve

clinograde

DO2 in High nutrient lakes Can have a _____ Due to settling of phytoplankton to metalimnion

metalimnetic maxima

Oxidation is a _____

loss

Reduction is a ___

gain

where most of decomposing OM is located, where most of O2 is being

consumed

the redox gradient

what is the redox gradient

At the very bottom of a lake, there is a sharp transition zone where the water goes from having oxygen (oxidation) to having no oxygen (reduction). This transition is called a redox gradient.

After lake stratifies, O2 is used from

_____, Redox front progresses upward

bottom upward

Global Example- extreme eutrophication

Gulf of Mexico

What causes dead zones

excess nutrients

What is a leading cause of dead zones

Nitrogen

What about fertilizer causes dead zones

Causes algae bloom -- algae eventually die -- bacteria

decompose & use up O2; no oxygen creates an Anoxic dead zone

What are solutions to dead zones

cover crops, no-till farming, buffer strips, fence animals

from streams, timing & amount of fertilizer,

extended rotations, nitrogen management

Regarding DO and water temperature, there is generally more DO in water during the ____ and during which time of year

day time, winter

During which time of year would the uniform DO profile most likely occur? (temp profile shown is for entire lake depth, not just epilimnion)

fall

Based on the figure below, this type of temperature/oxygen profile would be found in a _____ lake during summer stratification, and is considered to be a _____ DO profile curve.

oligotrophic, orthograde

Regarding the redox boundary during summer stratification in May vs. July. Between the 2 DO profile lines in the 1st graph below, the GRAY line best represents the likely DO profile in which of those months?

july

A dead zone- or _____ zone- is an area of low oxygen that can harm fish and marine life near the bottom of the sea.

hypoxic

Dead Zones appear to be concentrated in coastal regions primarily in North America and South America (T/F)

false

how big can a dead zone get (size of this state)

NJ

In which layer of Crooked Lake is the DO level the highest?

metalimnion

is Eutrophication a natural process?

yes

Which type of Eutrophication tends to occur much more rapidly?

cultural