Aquatic Environments: Structure, Function, and Human Impacts

Aquatic Environments

Introduction

Aquatic environments encompass a diverse range of habitats including wetlands, lakes, streams, coastal, and marine systems. These ecosystems are critical for supporting biodiversity, regulating Earth's water cycle, and providing essential resources for human societies.

Total Water on Earth

Distribution of Water

• 97% of Earth's water is saline, found in oceans.

• 3% is freshwater, with the majority locked in icecaps and glaciers (68.7%), followed by groundwater (30.1%), and a small fraction as surface water (0.3%).

• Surface freshwater is further divided among lakes (87%), rivers (2%), and other sources.

Example: The limited availability of accessible freshwater highlights the importance of conserving aquatic ecosystems.

Importance of Aquatic Ecosystems

• Freshwater is essential for all life forms.

• Biodiversity: Aquatic habitats support a wide variety of species.

• Recreation: Lakes, rivers, and coasts provide opportunities for human recreation and tourism.

• Food Webs: Aquatic and terrestrial food webs are closely linked, with energy and nutrients cycling between them.

Types of Aquatic Habitats

• Wetlands

• Lake ecosystems

• Stream ecosystems

• Coastal environments

• Marine systems

• Linkages to terrestrial ecosystems

Summary 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	Lentic (non-flowing), stratified zones, variable oxygen	Freshwater source, recreation, food webs	Pollution, invasive species, eutrophication, overuse
Streams	Lotic (flowing), river continuum, watershed-based	Biodiversity, groundwater recharge, hydroelectric power	Degradation, erosion, dams, nonpoint source pollution
Coasts	Dynamic, tidal influence, diverse habitats (marshes, reefs)	Biodiversity, storm protection, economy	Development, pollution, overharvesting
Marine	Saline, vast, zoned by depth and light	Climate regulation, food, oxygen production	Overfishing, acidification, pollution

Wetlands

Definition and Characteristics

• Areas inundated or saturated by surface or groundwater, supporting vegetation adapted to saturated soil conditions.

• Three key characteristics: soil, hydrology, and vegetation.

Importance

• Flood control

• Recharge of aquifers

• Biodiversity hotspots

Regulation

• Regulated by agencies such as the Army Corps of Engineers, EPA, and state agencies.

• Classified by hydrology and vegetation (e.g., marsh, bog, fen, swamp).

Threats

• Habitat loss

• Degradation

• Conversion to other land uses

Lake Ecosystems

Key Characteristics

• Lentic (non-flowing) systems

• Defined by spatial zones: littoral, limnetic, profundal, benthic

Physical Properties

• Stratification: Temperature layers form in lakes, affecting oxygen distribution.

• Dissolved Oxygen (DO): Colder water holds more oxygen.

Classification

• Oligotrophic lakes: Clear, deep, low nutrients, low productivity.

• Eutrophic lakes: High nutrients, high productivity, often murky.

Eutrophication

• Process where nutrient enrichment leads to excessive plant and algal growth, followed by oxygen depletion.

Importance

• Source of freshwater

• Recreation and economy

• Support complex food webs

Threats

• Pollution (especially eutrophication)

• Invasive species

• Degradation and overuse

Stream Ecosystems

Key Characteristics

• Lotic (flowing) systems

• River continuum concept: changes in physical, chemical, and biological properties from headwaters to mouth

Watersheds

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

• Important for delineating aquatic systems and managing water resources.

Importance

• Biodiversity

• Groundwater recharge

• Recreation and economy

• Hydroelectric power and transportation

Threats

• Degradation and erosion

• Nonpoint source pollution

• Channelization and dams

• Habitat fragmentation

Coastal Environments

Key Habitats

• Beaches and dunes

• Salt marshes

• Rocky coastlines and shores

• Barrier islands

• Oyster bars

• Seagrass beds

• Coral reefs

Super Habitat Concept

• Coastal habitats are interconnected physically, biologically, and chemically, forming a 'super habitat' that supports high biodiversity and ecosystem services.

Importance

• Biodiversity

• Recreation and economy

• Protection from hurricanes and storms

Threats

• Development and habitat loss

• Pollution

• Overharvesting of resources (e.g., blue crabs)

Key Terms and Concepts

• Nonpoint Source Pollution: Pollution that comes from multiple, diffuse sources rather than a single, identifiable source.

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

• Littoral Zone: The area of a lake with high light penetration, supporting photosynthesis.

• Oligotrophic Lake: A lake with clear water, low productivity, and low nutrient levels.

• Eutrophication: The process by which a body of water becomes enriched in dissolved nutrients, often leading to plant growth and oxygen depletion.

Sample Questions and Answers

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

• Which zone of a lake is known for high light penetration and supports photosynthesis? Littoral zone.

• Which of the following is a characteristic of oligotrophic lakes? Clear water with low productivity.

• What is a 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:

• Decomposers in aquatic systems break down dead organic matter, recycling nutrients back into the ecosystem.

• Riparian zones (areas adjacent to streams) filter pollutants, stabilize banks, and provide wildlife habitat.