TOPIC 3: THE AQUATIC ENVIRONMENT

Question 1

Why is water important?

Answer 1

• Aquatic ecosystems cover 75% of the planet making them the most dominant habitats
* lot more aquatic environments then terrestrial

• All living things contain a large percentage of water and most physiological process depend on water

• Almost all living phyla of animals evolved in an aquatic environment.
*life started in aquatic environment

Question 2

Properties of Water

Answer 2

Water is a polar molecule that acts as a universal solvent

Water molecules become less dense when moving from a liquid to a solid state
* most substances lose energy shrink water does opposite
Pure water does become denser as it is cooled to 4°C, but if cooled further, its density decreases

Question 3

Water molecules become less dense when moving from a liquid to a solid state What does this allow for?

Answer 3

This property allows freshwater organisms to live below the surface of ice formed in the winter.
* surface ice helps insulate the water below and helps it from feezing solid

Question 4

Cohesion

Answer 4

result of h bonding they stick together and Resists external forces that would break its bonds

Question 5

Viscosity

Answer 5

result of cohesion; A fluid medium’s resistance to flow (ie. fluid friction). Water being forced downwards will exert pressure upwards.* a fluid stops a force from separating its molecules which would cause it to flow or let an object pass thru

Viscosity and buoyancy can operate together to force a moving object in the water closer to the surface

high cohesion and viscosity of water allow plants and animals to be buoyant

water has high viscosity; anything living thru the water column allow living things to push thru and move

Question 6

Aquatic Environments

Answer 6

Despite being the dominant habitat on Earth has low microclimate variability

Question 7

how can aquatic environments be divided?

Answer 7

Divided by depth:
Divided by salinity

Question 8

Divided by depth:

Answer 8

Mean ocean depth is 3.7km (Max ~11km)

Question 9

Divided by salinity:

Answer 9

Saltwater (Oceans – 97%)
Freshwater (Lakes, Rivers, Etc. – 1%)

Question 10

Freshwater:

Answer 10

• are divided by ph rather than salinity
• each unit of ph is a 10 fold increase in the concentration of H+
  on a scale from 0-14
  7 is neutral
  below 7 is acidic (worse for most organisms)
  above 7 alkaline (basic); tolerated by some organisms

Question 11

what is ocean salinity affected by?

Answer 11

ocean salinity affected by evaporation and precipitation
generally higher salinity at equator lower at poles

Question 12

Light

Answer 12

75% of the ocean is 3-6km deep

Solar radiation is:
1. Reflected back into atmosphere
2. Absorbed or reflected by suspended particles (alive & dead)
3. Absorbed by water

Question 13

What does solar radiation decline with?

Answer 13

declines exponentially with depth
→ Distinct vertical profiles of light, temperature, oxygen, pressure, etc.
* higher pressure as you go deeper down in ocean

Question 14

What does the decline of solar radiation have an impact on?

Answer 14

Direct impact: plants
Plants require sunlight for photosynthesis
Plants are restricted to top 100 m

Indirect impact: animals
Herbivores are restricted to depths where plants reside

Animals inhabiting deep water (> 200 m) have adaptations:
Lack pigment
Large eyes (maximum light-gathering ability)
Organs that produce light (bioluminescence)
Organisms undergo chemosynthesis in the ocean depths

Question 15

How does depth impact temperature

Answer 15

Exponential decline in solar radiation with depth → decline in temperature with depth
anything in the depths can’t be lower then 0 (freezing point) will rise to surface

Question 16

• Thermocline

Answer 16

region with most rapid decline in temperature
• After temperature continues to decline with depth but at a slower rate

anything above generally warm ( lower density)

below= cold temp (high density)

Question 17

Fall Turnover

Answer 17

The mixing of the thermal stratification of a water column due to the seasonal change of surface temperatures
Water grows more dense as it cools to 40C
However, it grows less dense as it cools further from 4-00C
Denser water sinks and less dense water floats to the surface (such that ice floats)

n fall, as radiation and air temperature decrease, surface waters cool, become denser, and sink, displacing warmer water below to the surface, where it cools in turn (
the density difference between the epilimnion and the hypolim- nion decreases, winds mix the profile to greater depths. This mixing continues until the temperature is uniform, allowing water to circulate throughout the pond or lake. This vertical cir- culation, called fall turnover, is important for nutrient dynam- ics in open-water systems. Stirred by wind, vertical mixing continues until ice forms at the surface.

Then comes winter. If the surface water cools below 4°C, it becomes lighter again and remains on the surface. If the winter is cold enough, the surface water freezes; otherwise, it remains close to 0°C. Now the warmest place in the water body is on the bottom

Answer 18

in the fall turn over begins
surface temps cool and wind action allows mixing between layers
stratification ends
imp. for nutreint and o2 dynamics
winter ends turnover as the surface freezes and deeper h20 become the warmest

Question 19

Oxygen

Answer 19

Oxygen diffuses from the atmosphere into aquatic environments
* higher atmospheric oxygen= go towards low concentration

Question 20

Oxygen produced by plants during photosynthesis

Answer 20

• Restricts high concentrations of oxygen to surface waters
• Limits respiration and metabolic activity of animals
• Mixing of the water column can break down this gradient

Question 21

List advantages and disadvantages of living in an aquatic environment?

Answer 21

access to light o2 and nutrients
2. constant osmostic pressure
3. low variabilty in microclimate

major advantage of living in water; acess to lots of water

Question 22

Despite being the dominant habitat on Earth, aquatic environments have a ___________

Answer 22

Low microclimate variability

Question 23

surface tension

Answer 23

water exhibits High surface tension caused by stronger attraction of water molecules to each rather than air

polar nature of molecules allow it to form h bonds; give it a high surface tension

• allows water striders to walk across

Question 24

buoyancy

Answer 24

density= mass/ volume

when an objects specific density is lower than the fluid medium in which it sits it will float to the surface

Question 25

where is thermocline a permanent feature?

Answer 25

tropics
the relatively constant radiation year-round makes the thermocline a permanent feature,

Question 26

Explain what is meant by thermal stratification?

Answer 26

occurs when the surface layer of water, warmed by the sun, becomes less dense than the water underneath it.

The surface layer remains on top and the lower layer, deprived of surface contact and insulated from the sun, continues to get colder. This increases the difference in density between the two layers and makes it even more difficult for them to mix together

• lakes divided into different layers with different temps
• SOME FORM OF THIS OCCURS IN ALL OPEN BODIES OF WATER
• Permanent stratification occurs in the tropics, no mixing can take place

Question 27

What does fall turnover do to oxygen in the lake?

Answer 27

Oxygen from the surface mixes with the bottom. Nutrients and decomposing organic matter from the bottom is mixed up and throughout the lake. This is why some lakes will have an unpleasant smell in the fall. If the turnover happens too quickly, oxygen level can drop low enough to result in a fish kill.

Lake turnover is extremely important in freshwater lakes, as it is the event that is responsible for replenishing dissolved oxygen levels in the deepest lake waters. When the lakes are a uniform temperature and density, it takes relatively little wind energy to mix water deep into the lake. Wind moves highly oxygenated surface water to the lake bottom, forcing low oxygen water from the lake bottom up to the surface where it becomes saturated with oxygen. This is critical for aquatic organisms, as once the lakes freeze over for the winter, no new oxygen gets mixed into the lake from the atmosphere, and what is in the lake must last until ice goes off in the spring.

Question 28

what is water density dependent on?

Answer 28

temp; The warmer the water, the less dense it becomes.