Hydrosphere and the Water Cycle Flashcards

The Hydrosphere and the Global Water Cycle

• The Hydrosphere Definition: The hydrosphere refers to the total amount of water on a planet. It encompasses water that is on the surface of the planet, underground, and in the air.

• The Water Cycle (Global Dynamics): As depicted in Figure $4.16$, the water cycle is the continuous movement of water throughout Earth's various spheres. Specifically, water is exchanged among the following:

  • Hydrosphere: The water bodies.

  • Atmosphere: The layer of gases surrounding the planet.

  • Geosphere: The solid parts of the Earth.

• Fundamental Drivers: The water cycle is a continuous, self-sustaining cycle driven by two primary forces:

  1. Solar Energy: Heat from the Sun provides the energy for phase changes like evaporation.

  2. Gravity: This force pulls water back to the surface and facilitates its flow from high to low elevations.

• The Three Main Processes of the Water Cycle: All water on Earth cycles through ecosystems via the interaction of three central processes:

  • Evaporation: This occurs when heat from the Sun causes water at the Earth’s surface to change state from liquid to gas (water vapor).

  • Condensation: This occurs as warm air rises, cools, and the water vapor condenses back into liquid droplets, ultimately forming clouds.

  • Precipitation: This describes water falling back to the Earth’s surface in forms such as rain or snow.

• Surface Movement (Run-off): Due to the pull of gravity, water moves over the Earth’s surface as "run-off." This water flows downhill, eventually returning to the ocean.

The Role of the Biosphere in the Water Cycle

• Transpiration Definition: This is the specific process by which water moves through the biosphere (the living component of Earth).

• Step-by-Step Process of Transpiration:

  1. Water is absorbed from the soil by the roots of plants.

  2. The water is carried upward through the structure of the plant.

  3. Water is lost to the atmosphere as water vapor through small pores in the leaves.

Global Water Distribution and Ocean Currents

• Fresh Water vs. Salt Water Distribution:

  • Salt Water: Approximately $97\%$ of Earth's total water is salty and found in the oceans.

  • Fresh Water: Only a small portion of the hydrosphere is fresh water. Examples include precipitation, rivers, streams, groundwater, and frozen glaciers.

• Functions of Ocean Currents: Oceans do not just store water; they are active in distributing resources across the globe:

  • Redistribution of thermal energy (heat).

  • Redistribution of nutrients throughout the Earth.

• Surface Currents: These are oceanic currents primarily created and driven by the wind.

• Temperature-Based Surface Currents:

  • Warm Currents: These move thermal energy from the equator toward the poles (higher, colder latitudes).

  • Cold Currents: These transport cold water from the higher, colder latitudes back toward tropical regions.

The Great Ocean Conveyor Belt: Deep-Water Dynamics

• Definition: The Great Ocean Conveyor Belt is a massive, interconnected system of deep-water currents that moves deep water, thermal energy, and nutrients around the entire planet.

• Driving Factors of Deep-Water Movement: The movement of these deep currents is determined by differences in water density, which is influenced by temperature and salinity (salt content):

  • Temperature and Density: Cold water is more dense than warm water. Consequently, cold water sinks and displaces warm water.

  • Salinity and Density: Saltier water is more dense than less salty water. Therefore, saltier water sinks and displaces less salty water.

Nutrient Cycling via the Great Ocean Conveyor Belt

• Nutrient Transport: The conveyor belt is essential for moving vital nutrients, such as Nitrogen and Phosphorus, around the world's oceans.

• The Deep-Water Nutrient Cycle:

  • Subduction of Surface Water: When surface water sinks, it typically contains very few nutrients.

  • Bacterial Action: Once the water has sunk to the deep ocean, bacteria break down organic material, which returns nutrients back into the water.

  • Upwelling/Return: When this deep water eventually returns to the surface, it possesses a very high concentration of nutrients.

Water Pollution and Environmental Persistence

• Definition of Water Pollution: Any physical, biological, or chemical change in water quality that results in an adverse effect on living organisms or renders the water unsuitable for its intended uses.

• Synthetic Chemicals: Human-made (synthetic) chemicals and pollutants can enter the environment through the air, water, and soil.

• Persistence in the Environment: These pollutants often remain in the environment for a long duration because decomposers are unable to break them down through the natural process of biodegradation.

Point and Non-Point Sources of Pollution

• Point Sources: As shown in Figure $4.18(A)$, these are localized and identifiable sources of pollution.

  • Examples: Factories, power plants, sewage treatment plants, oil wells, and industrial pipes that discharge waste.

  • Characteristics: They are relatively easy to monitor, regulate, and control.

• Non-Point Sources: As shown in Figure $4.18(B)$, these are diffuse sources where pollution originates from many different locations.

  • Examples: Run-off from farms, lawns, construction sites, logging areas, roads, and parking lots.

  • Characteristics: They are difficult to monitor, regulate, and treat because the pollution is periodic and spread over a large area.

Bioaccumulation and Biomagnification

• Bioaccumulation Definition: The gradual build-up of chemicals or pollutants within the cells and tissues of an individual organism.

• Mechanism of Accumulation: This occurs when a chemical is taken up and stored by an organism faster than it can be broken down (metabolized) and excreted.

• Pathways of Exposure: Accumulation can happen via:

  • Food intake.

  • Skin contact.

  • Respiration.

• Health Impacts of Bioaccumulation: These chemicals can cause physiological harm, including birth defects and the disruption of various body systems.

• Specific Examples of Bioaccumulation:

  • Red Tide: Algae toxins are absorbed by clams and oysters; when humans consume these, it leads to shellfish poisoning.

  • PCBs: Found in high levels in Orcas.

  • DDT: Found in high levels in Raptors (birds of prey).

• Biomagnification Definition: This is the process where the concentration of pollutants increases in the tissues of organisms at successively higher levels of a food chain or food web. As an organism eats many smaller organisms containing pollutants, the concentration of that pollutant multiplies within the consumer.