Aquatic Biomes: Streams, Rivers, and Ecological Investigation

Streams and Rivers

• Streams and rivers are characterized by flowing water, unlike lakes and ponds where water is generally collected in low-lying areas.
• Streams and rivers form due to liquid water entering the environment, often from precipitation in low-lying areas or snowmelt in higher elevations.
• Water flows downhill due to gravity, collecting in smaller tributaries initially.
• As water flows further downslope, more water collects from rainfall, drainage, or snowmelt, leading to larger streams and rivers.

Headwaters

• Headwaters are typically at higher elevations and have cold, clear water flowing rapidly due to the steep slopes.
• They resemble oligotrophic lakes: cold, clear, and oxygen-rich.

Downstream

• Downstream, the slope becomes less steep, and the water moves slower, becoming more turbid and less oxygenated due to increased organism activity.
• Eutrophication, similar to what affects ponds and lakes, can occur, particularly near human settlements due to fertilizer runoff.
• In very flat areas, rivers become wide and meandering with silty bottoms.
• Rivers may form estuaries at the ocean, transitioning to saltwater environments.

River Value & Ecosystem Services

• Rivers provide fresh water necessary for all living organisms.
• They supply water to lakes and streams for natural purposes and human activities like recreation.
• Rivers transport nutrients downstream, depositing them as water speed decreases.
• Faster water carries heavier particles; slower water deposits larger particles, leaving sands and silts at the end of long river systems.
• Rivers are habitats for various organisms, including anadromous fish (e.g., salmon) that live in both salt and fresh water.
• Anadromous fish, like salmon, migrate upstream to spawn, bringing nutrients from the ocean.
  • Example: Copper River salmon are valuable due to their high fat content from swimming up a long river to spawn.

Human Impact

• Dams can harness hydroelectric power but block river systems.
• Fish ladders are added to dams to allow salmon to bypass and continue upstream.
• Dam removal has led to the return of historic fish runs in some rivers.
• Rivers create breaks in riparian and forest areas, with riparian forests stabilizing riverbanks.
• Human activities cause nutrient runoff, eutrophication, and thermal pollution.
• Building near rivers removes riparian zones, leading to increased water temperatures that harm native species.

Marine Ecosystems

Factors Affecting Marine Ecosystems

• Depth: Light penetration is limited to about 200 meters, forming the photic zone where photosynthetic organisms (phytoplankton) exist.
• Nutrient Availability: Nutrient runoff from rivers and upwelling of deeper water due to ocean currents provide nutrients.
• Salinity: Organisms in freshwater environments must get rid of excess water, while those in saltwater environments must retain water and avoid excess salt.

Marine Zones

• Photic Zone: The upper layer where light penetrates, supporting phytoplankton-based ecosystems.
• Aphotic Zone: The zone below the photic zone where light does not penetrate.
• Continental Shelf: Shallow regions near the continents where plants and other organisms can live.
• Benthic Zone: The ocean floor.
• Abyssal Zone: The deepest levels of the ocean, including trenches.
• Pelagic Zone: Includes all ocean zones (photic, aphotic, abyssal) not adjacent to the continental shelf.

Ecosystem Dynamics

• Continental shelf areas are highly productive due to nutrient runoff and sunlight.
• The pelagic zone has constant mixing due to currents and wind patterns, maintaining high oxygen levels.
• Marine systems cover approximately 70% of the Earth's surface, giving them a high capacity to absorb disruption, but human activities are straining this capacity.

Impact of Human Activity on Oceans

• Human activities are threatening ocean health through pollution, including carbon dioxide and plastics.
• Increased carbon dioxide leads to ocean acidification, which affects shellfish and coral reefs.
• Ocean acidification reduces the ability of shellfish to produce shells because calcium carbonate, which is required to be secreted, is affected by it.
• Warming temperatures cause coral bleaching, where corals expel photosynthetic organisms.
• Overfishing and irresponsible harvesting diminish fish runs, potentially causing food web collapse.
• Farmed fish can help minimize overfishing but have their own issues with disease and ecosystem disruption.

Coral Reefs

• Coral reefs are diverse ecosystems in the photic zone near the continental shelf.
• They are formed from calcium carbonate skeletons of corals, which are threatened by ocean acidification.
• Corals require high oxygen concentration and a solid substrate to attach to.

Biogeography

• Biogeography studies the distribution of organisms and the reasons for their location.
• Dispersal is limited by factors such as geographic barriers and climate.

Potential vs. Actual Range

• Potential Range: The area an organism could inhabit based on environmental conditions.
• Actual Range: The area an organism actually inhabits, limited by dispersal barriers, competition, and other factors.
• Even if an organism could survive if transplanted to a new area, it might not naturally occur there.

Invasive Species

• Invasive species are transported to new areas, where they can compete with native species and disrupt ecosystems.

Factors Limiting Species Distribution

• Behavioral Habitat Selection: Animals inhabit areas they select.
• Biotic Factors:
  • Disease: Affects organisms in certain areas.
  • Herbivory: Limits plant dispersal.
  • Symbiotic Relationships: Organisms depend on other organisms for survival (e.g., Yucca plant and moth).
  • Lack of Pollinators: Plants cannot reproduce without appropriate pollinators.
  • Biotic Competition: Organisms compete for resources.
• Abiotic Factors:
  • Temperature, water, oxygen, salinity, and sunlight affect an organism's ability to survive and reproduce.

Ecological Investigation

• Ecological investigation can focus on different levels of organization:
  • Organismal Ecology: How species adapt to their environment.
  • Population Ecology: How populations vary in different areas.
  • Community Ecology: How different species interact in a particular area (community structure, competition, diversity).
  • Ecosystem Ecology: How abiotic factors (temperature, carbon dioxide levels, energy flow) influence biotic factors.
  • Global Ecology: Climate change and its effect on the biosphere.