Hydrologic Cycle

Vocabulary flashcards summarizing the main processes in the hydrologic cycle.

Evaporation

• Definition: Water changes from liquid to vapor, driven by solar heat.

• Relevance: Removes heat from surfaces, increases atmospheric moisture, and initiates cloud formation.

Condensation

• Definition: Water vapor cools and turns back into liquid droplets.

• Relevance: Forms clouds and fog; releases latent heat that powers storms.

Precipitation

• Definition: Water falls from the atmosphere as rain, snow, sleet, or hail.

• Relevance: Recharges freshwater supplies and influences estuary salinity.

Infiltration

• Definition: Water soaks into soil and permeates down through pores.

• Relevance: Recharges groundwater and naturally filters pollutants.

Runoff

• Definition: Water flows across the surface into rivers, lakes, and oceans.

• Relevance: Main source of erosion, sediment transport, and surface pollution.

Transpiration

• Definition: Water vapor is released from plant leaves (stomata).

• Relevance: Adds atmospheric moisture and helps regulate local humidity.

Evapotranspiration

• Definition: Combined loss of water through evaporation and plant transpiration.

• Relevance: Represents total water loss from landscapes; important for agriculture and drought studies.

Groundwater Recharge

• Definition: Water from infiltration that percolates deep into aquifers.

• Relevance: Maintains wells, springs, and river baseflows during dry periods.

Watershed

• Definition: Land area that drains all precipitation and runoff to a single water body.

• Relevance: Determines nutrient and pollutant inputs into rivers, lakes, and estuaries.

Estuary

• Definition: Zone where freshwater meets saltwater, often at river mouths.

• Relevance: Maintains unique ecosystems, filters nutrients, and regulates coastal salinity.

Percolation

• Definition: Downward movement of water through soil layers into groundwater.

• Relevance: Critical for aquifer replenishment and natural water purification.

Surface Water

• Definition: Water on Earth’s surface (rivers, lakes, reservoirs).

• Relevance: Main sources for drinking water, agriculture, and hydroelectric power.

Groundwater

• Definition: Water stored in soil pores and rock layers below ground.

• Relevance: Key water supply during droughts and for wells.

Cloud Formation

• Definition: The accumulation of condensed water droplets or ice in the atmosphere.

• Relevance: Precursor to precipitation and weather patterns.

Snowmelt

• Definition: Melting of snow and ice, feeding rivers and lakes.

• Relevance: Significant seasonal contributor to runoff and freshwater flow.

Latent Heat

• Definition: Heat absorbed or released during phase changes (e.g., evaporation/condensation).

• Relevance: Drives energy transfer in weather systems.

Sublimation

• Definition: Water changes directly from ice to vapor without becoming liquid.

• Relevance: Occurs in high mountains and polar regions, contributing to atmospheric moisture.

Deposition

• Definition: Water vapor turns directly into ice (e.g., frost formation).

• Relevance: Forms snow crystals in clouds and frost on surfaces.

Polarity

• Definition: Unequal sharing of electrons in H₂O; oxygen (δ–) pulls electrons more strongly than hydrogen (δ⁺), creating partial charges.

• Importance: Enables hydrogen bonding and water’s ability to dissolve salts and polar molecules.

Hydrogen Bonding

• Definition: Weak attraction between the hydrogen atom (δ⁺) of one molecule and the oxygen atom (δ–) of another.

• Importance: Causes surface tension, cohesion, high boiling point, and stabilizes biological molecules like DNA.

Cohesion

• Definition: Water molecules sticking together due to hydrogen bonds.

• Importance: Creates surface tension, allows droplet formation, and supports phenomena like water striders walking on water.

Adhesion

• Definition: Water molecules sticking to other surfaces (e.g., glass, soil, leaves).

• Importance: Enables water to cling to plant cell walls and soil particles, aiding nutrient transport.

Capillary Action

• Definition: Water rises in narrow tubes due to combined cohesion and adhesion.

• Importance: Explains xylem flow in plants, water movement in soil, and ink flow in paper or fabric.

Specific Heat

• Definition: Amount of heat needed to raise 1g of water by 1°C (4.18 J/g°C), which is very high compared to most liquids.

• Importance: Stabilizes climate, buffers temperature changes in estuaries, and maintains stable environments for life.

High Heat of Vaporization

• Definition: Large amount of energy required for water to change from liquid to gas.

• Importance: Enables cooling through evaporation (sweating, transpiration) and moderates weather patterns.

Surface Tension

• Definition: The “skin” on water’s surface caused by cohesive hydrogen bonding.

• Importance: Allows insects to walk on water and causes water to bead on surfaces.

Universal Solvent

• Definition: Water dissolves many polar and ionic substances due to its polarity and ability to form hydration shells.

• Importance: Essential for biochemical reactions, nutrient transport, and cellular function.

Density Anomaly of Ice

• Definition: Ice is less dense than liquid water because of its open hexagonal hydrogen-bond lattice.

• Importance: Ice floats, insulating liquid water below and allowing aquatic life to survive in winter.

Heat Capacity Buffering

• Definition: Water’s resistance to temperature change due to hydrogen bonding.

• Importance: Stabilizes ecosystems, regulates body temperature, and moderates coastal climates.

Latent Heat

• Definition: Heat absorbed or released during a phase change (e.g., evaporation/condensation) without a temperature change.

• Importance: Powers storms, regulates energy transfer, and maintains thermal balance in the environment.

Autoionization of Water

• Definition: A small fraction of water molecules split into H⁺ (as H₃O⁺) and OH⁻ ions.

• Importance: Establishes the basis for pH and acid-base chemistry in living systems.

Meniscus

• Definition: The curved water surface in a container due to adhesion (concave) or cohesion (convex).

• Importance: Evidence of adhesive forces; used in accurate volume measurements.

Cohesion-Tension Theory

• Definition: Explains how water moves up plants through xylem via cohesion (molecule-to-molecule) and tension created by evaporation.

• Importance: Critical for the survival of tall plants and trees.

Dielectric Constant

• Definition: Water’s ability to reduce electrostatic attraction between charged particles.

• Importance: Allows salts and ionic compounds to dissolve readily.

Ice Lattice

• Definition: Hexagonal structure formed by hydrogen bonds when water freezes.

• Importance: Creates lower density and allows ice to float.

Universal Solvent

• Definition: Water’s polarity allows it to dissolve more substances than any other liquid.

• Example/Importance: Salt (NaCl), sugar, and ammonia dissolve easily, enabling nutrient transport in living organisms.

Polarity

• Definition: Oxygen pulls electrons more strongly than hydrogen, creating partial charges (δ– on O, δ⁺ on H).

• Example/Importance: Polarity allows water to attract and separate ions, forming hydration shells around Na⁺ and Cl⁻.

Hydration Shell

• Definition: The sphere of water molecules surrounding and stabilizing dissolved ions or molecules.

• Example/Importance: When NaCl dissolves, water molecules form shells around Na⁺ and Cl⁻ to prevent them from rejoining.

Ionic Solubility

• Definition: Water dissolves ionic compounds by separating their positive and negative ions.

• Example/Importance: Road salt dissolves into runoff, changing river salinity.

Non-Ionic (Polar) Solubility

• Definition: Water dissolves polar, non-ionic molecules via hydrogen bonding.

• Example/Importance: Sugar (C₆H₁₂O₆) dissolves because its OH groups form hydrogen bonds with water.

Nonpolar Molecules

• Definition: Molecules with no charge or polarity that water cannot dissolve.

• Example/Importance: Oils and fats are hydrophobic and form separate layers in water.

Nutrient Transport

• Definition: Water dissolves and carries nutrients needed for plant and algae growth.

• Example/Importance: Nitrates (NO₃⁻) and phosphates (PO₄³⁻) travel in water, supporting aquatic food webs.

Eutrophication

• Definition: Excess nutrient buildup in water causes algae blooms and oxygen depletion.

• Example/Importance: Runoff with dissolved fertilizers leads to fish kills in lakes and rivers.

Pollutant Transport

• Definition: Water dissolves and spreads contaminants through runoff and groundwater.

• Example/Importance: Mercury and pesticides enter rivers and bioaccumulate in fish.

Dissolved Gases

• Definition: Gases like O₂ and CO₂ dissolve in water depending on temperature and salinity.

• Example/Importance: Dissolved O₂ supports fish respiration; CO₂ drives photosynthesis in algae.

Temperature Effect on Gas Solubility

• Definition: Cold water holds more dissolved gases than warm water.

• Example/Importance: Fish thrive better in cooler, oxygen-rich streams.

Salinity Effect on Gas Solubility

• Definition: Saltwater holds less O₂ and CO₂ compared to freshwater.

• Example/Importance: Marine organisms have special adaptations to lower gas levels.

Runoff

• Definition: Water flowing over land that can carry dissolved nutrients and pollutants.

• Example/Importance: Rainwater runoff spreads pesticides into streams.

Hydrophilic

• Definition: Molecules or surfaces that attract and dissolve in water due to polarity.

• Example/Importance: Sugars, salts, and amino acids are hydrophilic.

Hydrophobic

• Definition: Molecules that repel water and do not dissolve due to lack of polarity.

• Example/Importance: Oils and waxes are hydrophobic and float on water surfaces.