Aquatic Environments: Structure, Function, and Importance

Aquatic Environments

Introduction

Aquatic environments encompass a diverse range of habitats including wetlands, lakes, streams, coastal areas, and marine systems. These ecosystems are essential for supporting life, maintaining biodiversity, and providing critical ecosystem services. Understanding their structure, function, and threats is fundamental in General Biology.

Total Water on Earth

Distribution of Water

Earth's water is distributed unevenly between saline and freshwater sources, with the vast majority found in oceans.

• Saline Water (Oceans): 97% of Earth's water

• Fresh Water: 3% of Earth's water

• Of the 3% freshwater:

  • Icecaps and Glaciers: 68.7%

  • Ground Water: 30.1%

  • Other: 0.9%

  • Surface Water: 0.3% (Lakes: 87%, Swamps: 11%, Rivers: 2%)

Example: Most accessible freshwater for human use is found in lakes and rivers.

Importance of Aquatic Ecosystems

Key Roles

Aquatic ecosystems are vital for sustaining life and supporting human activities.

• Freshwater: Essential for drinking, agriculture, and industry

• Biodiversity: Supports a wide variety of species

• Recreation: Provides opportunities for fishing, swimming, and tourism

• Food Webs: Aquatic and terrestrial food webs are closely linked

Example: Wetlands filter water and provide habitat for migratory birds.

Aquatic Habitats

Types of Aquatic Ecosystems

Aquatic habitats are classified based on their physical and biological characteristics.

• Wetlands

• Lake Ecosystems

• Stream Ecosystems

• Coastal Environments

• Marine Systems

• Linkages to Terrestrial Ecosystems

Comparison Table: Aquatic Ecosystems

Aquatic Ecosystem	Key Characteristics	Importance	Threats and Challenges
Wetlands	Saturated soils, unique hydrology, specialized vegetation	Flood control, recharge aquifers, biodiversity	Habitat loss, degradation, conversion
Lakes	Non-flowing (lentic), stratified zones, variable DO	Freshwater source, recreation, food webs	Pollution, invasive species, eutrophication, overuse
Streams	Flowing (lotic), river continuum, watershed	Biodiversity, groundwater recharge, transportation	Degradation, erosion, nonpoint pollution, dams
Coasts	Dynamic habitats (beaches, marshes, reefs)	Biodiversity, storm protection, economy	Overharvesting, pollution, habitat loss
Marine	Saline, vast, zonation (intertidal, pelagic, benthic)	Climate regulation, food, oxygen production	Overfishing, pollution, climate change

Wetlands

Definition and Characteristics

Wetlands are areas where the soil is saturated with water, either permanently or seasonally, supporting vegetation adapted to these conditions.

• Soil: Saturated, often anaerobic

• Hydrology: Water presence determines ecosystem

• Vegetation: Specialized plants (e.g., cattails, sedges)

Example: The Pantanal of Brazil is one of the world's largest wetlands.

Importance

• Flood control

• Recharge aquifers

• Biodiversity hotspot

Regulation: Wetlands are regulated by agencies such as the Army Corps of Engineers and the EPA.

Threats

• Habitat loss

• Degradation

• Wetland conversion

Lake Ecosystems

Key Characteristics

Lakes are lentic (non-flowing) systems with distinct spatial zones:

• Littoral Zone: Near shore, high light, supports photosynthesis

• Limnetic Zone: Open water, well-lit

• Profundal Zone: Deep, low light

• Benthic Zone: Bottom sediments

Physical Properties

• Stratification: Temperature layers form seasonally, affecting mixing

• Dissolved Oxygen (DO): Colder water holds more oxygen Equation: $O_2 ext{ solubility} ightarrow ext{decreases as temperature increases}$

Classification

• Oligotrophic Lakes: Clear, low nutrients, low productivity

• Eutrophic Lakes: High nutrients, high productivity, often green with algae

Eutrophication: Process where nutrient enrichment leads to excessive plant/algal growth and oxygen depletion.

Importance

• Source of freshwater

• Groundwater recharge

• Recreation and economy

• Supports food webs

Threats

• Pollution (eutrophication)

• Invasive species

• Degradation

• Overuse

Stream Ecosystems

Key Characteristics

Streams are lotic (flowing) systems, organized by the "river continuum" concept, which describes changes in ecosystem properties from headwaters to mouth.

• Functional feeding groups change

• Nutrient sources shift

• Physical and chemical properties vary

• Fish communities adapt

Watershed

• Definition: An area of land that drains into a particular drainage basin

• Watersheds are important for managing water resources and pollution

Importance

• Biodiversity

• Groundwater replenishment

• Recreation and economy

• Freshwater supply

• Transportation and hydroelectric power

Threats

• Degradation and erosion

• Nonpoint source pollution

• Channelization

• Dams (and dam removal projects)

Coastal Environments

Key Habitats

Coastal environments include a variety of habitats:

• Beaches and dunes

• Salt marshes

• Rocky coastlines and shores

• Barrier islands

• Oyster bars

• Seagrass beds

• Coral reefs

Super Habitat: These habitats are interconnected physically, biologically, and chemically.

Importance

• Biodiversity

• Recreation

• Economic value

• Protection from hurricanes and storms

Threats

• Overharvesting (e.g., blue crabs)

• Pollution

• Habitat loss

Key Concepts and Definitions

Nonpoint Source Pollution

Nonpoint source pollution refers to contamination that comes from multiple, diffuse sources rather than a single, identifiable origin. Examples include agricultural runoff and urban stormwater.

Watershed

A watershed is an area of land that drains all the streams and rainfall to a common outlet, such as a river mouth or bay.

Lake Zones

• Littoral Zone: Shallow, near shore, high light penetration, supports photosynthesis

• Limnetic Zone: Open water, well-lit

• Profundal Zone: Deep, low light

• Benthic Zone: Bottom sediments

Oligotrophic vs Eutrophic Lakes

• Oligotrophic: Clear water, low nutrients, low productivity

• Eutrophic: High nutrients, high productivity, often green with algae

Human Impacts

• Invasive Species Introduction: Disrupts native food webs and ecosystem balance

Sample Questions and Answers

• What is nonpoint source pollution? Pollution that comes from multiple, diffuse sources.

• Which zone of a lake supports photosynthesis? Littoral zone.

• Characteristic of oligotrophic lakes? Clear water with low productivity.

• Significant human impact on lake ecosystems? Invasive species introduction.

• What is a watershed? An area of land that drains into a particular drainage basin.

*Additional info: The notes expand on the original slides by providing definitions, examples, and context for each ecosystem type, as well as a synthesized comparison table for study purposes.*