Unit 1: Environment- Aquatic Environment Notes

Almost all organisms rely on water.
The hydrologic cycle involves:
- Ascending warm air masses containing water molecules.
- Water molecules sticking together and falling as rain.
- Rainfall striking the earth.

Intercepted water: Water that doesn't reach the ground directly.
- Examples: water striking roads, roofs, or vegetation without soaking in.

Infiltrated water: Water that seeps into the soil.
- Available for plant growth.
- Plant roots absorb infiltrated water.

Percolated water: Water that seeps through the soil into bedrock and aquifers.
- Can remain underground for centuries.
- May emerge as groundwater or be accessed via wells.

Groundwater: Water that has percolated below the soil surface into the bedrock layer.
- Seeps out, often on exposed hillsides.
- Slower movement to bodies of water compared to intercepted or infiltrated water.

All water eventually flows toward larger bodies of water (rivers, streams, lakes, oceans).
Intercepted water moves fastest, followed by infiltrated water, then percolated water (as groundwater).

Evapotranspiration: Water returning to the atmosphere.
- Evaporation: Water from soil, lakes, and oceans evaporating.
- Transpiration: Water moving through plants and then released into the atmosphere.

Water is a polar molecule with positive and negative sides.
- Acts like tiny magnets, influencing its properties.

Specific heat: Energy required to raise 1 cubic centimeter of a substance by 1 degree Celsius.
Water has a high specific heat.
- Takes a lot of energy to heat up.
- Takes a long time to cool down.
Impact on local climate:
- Areas near large bodies of water have more moderate temperatures.
- Winds shift direction near large lakes and oceans due to differential heating.

Cohesion: Water molecules sticking to each other.
Adhesion: Water molecules sticking to other substances.
High surface tension results from these properties.
- Water bubbling over the top of a filled glass.
- Water forming bubbles on oily surfaces.

Surface tension is important for organisms living on or near water surfaces.
Water striders:
- Live on the surface of ponds due to surface tension.
- Cannot get underwater.
- Use modified front legs to vibrate the water surface and communicate through wave patterns.
- Territorial signals, mating signals, danger signals.
Tim Wilcox: A researcher who studied water strider communication.
- Used a water tank suspended from the ceiling to minimize vibrations.
- Used an electronic robotic arm to create vibrations and communicate with water striders.

Viscosity: Measurement of the force it takes to move through water.
Water has a relatively high viscosity.
- Requires more energy to swim through water compared to substances with lower viscosity.

Density: Mass per unit volume.
Buoyancy: Ability to float in water based on density.
Objects less dense than water float.
Fish utilize swim bladders to control buoyancy.
- Swim bladder: An air-filled chamber inside the fish.
- Relaxing muscles expands the swim bladder, decreasing density, causing the fish to float.
- Contracting muscles reduces the size of the swim bladder, increasing density, causing the fish to sink.
- Deep-water fish and swim bladder issues when rapidly brought to the surface.

Refraction: Bending of light as it moves from one medium to another.
Light bends toward the normal when moving from less dense to more dense medium (air to water).
Light bends away from the normal when moving from more dense to less dense medium (water to air).
Implications for organisms:
- Objects underwater appear higher and closer than they actually are.
- Great blue herons and kingfishers must compensate for refraction when hunting.
- Archer fish spits water at insects, compensating for the refraction of light.

Pure water absorbs sunlight.
Absorption increases with depth.
Infrared and ultraviolet light are absorbed rapidly.
Red light is absorbed within 5-7.5 meters.
Blue light penetrates deepest.
Plants can't grow very deep because of light limitations.
75% of light is absorbed in the first 10 meters.
Shallow coral reefs have a variety of colors, while deeper waters become monochromatic.

Littoral zone: Area where plants grow attached to the bottom.
Limnetic zone: Open water area where plants don't grow at the bottom.
Vertical layers:
- Epilimnion: Upper layer, warm with most oxygen during summer.
- Thermocline: Layer of rapid temperature transition.
- Hypolimnion: Coldest layer at the bottom.
Stratification: Layers don't mix during summer.
Turnover: Mixing of layers in fall and spring.
- Fall: Surface water cools, thermocline disappears, nutrients cycle up, oxygen cycles down.
- Spring: Ice melts, surface water reaches 4 degrees Celsius, another turnover occurs.
Late spring: Ice covers the lake longer than average, can lead to fish die-offs due to lack of oxygen.

Intertidal zone: Area between high and low tide.
Neritic zone: Extends out to the continental shelf.
Oceanic zone: Rest of the ocean.
Plants grow in the intertidal and shallow neritic zones.
Organisms classified as benthic (living on the substrate) or pelagic (living in the water column).
Stratification: Layers stratified by temperature and salt.
- Colder water sinks.
- Warmer water rises.
- Saltwater is denser than freshwater.
- Ocean currents are affected by these factors.
- Melting glaciers release freshwater, slowing the descent of cold, dense saltwater, affecting climate.

Water dissolves various substances, primarily salt in oceans.
Dead Sea: High salt concentrations allow for easy floating.
Adaptations for osmoregulation:
- Freshwater organisms prevent water from diluting their internal salt concentrations.
- Saltwater organisms prevent salt from entering their bodies.
Euryhaline species: Fish that can live in both freshwater and saltwater (e.g., Pacific and Atlantic salmon).
Estuaries: Areas where freshwater meets saltwater, require adaptations to handle both conditions.

Water has a pH of 7.
Organisms have varying tolerances for pH levels.
- Bacteria, plants, and algae have broader tolerances than fish.
Acid rain: Can lower pH levels, leading to die-offs of sensitive organisms.
Runoff from land can carry various substances into the water, impacting aquatic environments.