Aquatic Environments Overview

Aquatic Environments

• Freshwater Environments: rivers, streams, ponds, lakes, reservoirs, ice (icebergs, snows), wetlands, and groundwater.
• Brackish Water Environments: estuaries, mangroves, brackish seas & lakes, brackish marsh.
• Marine Environments: seas and oceans.
  • Oceans: Pacific, Atlantic, Indian, Southern, Arctic. Oceans cover ~71% of the Earth's surface.
  • Salinity: measured as parts per thousand (ppt), (‰), [g/kg] and ratio (no unit-often written as S=37).
    • 'Normal' Salinity range: 32 – 37 ppt.
• Seawater Salinity:
  • Why is the sea salty?
    • Decaying biological matter
    • Weathering and erosion processes
    • Rains and streams transport minerals to the sea
    • Dissolved rocks and sediments from the ocean floor
    • Solid and gas material from hydrothermal vents
  • The proportion of salt + its content in ALL the oceans remains the same!
• Dissolved Gases in Seawater:
  • Dissolved gases are very important in the oceans.
  • Involved in biogeochemical cycling e.g.CO₂ used in photosynthesis to produce O₂, O₂ used in respiration to produce CO₂, N used in the nutrient cycle.
• Density of Seawater:
  • Pure water density: 1.000 g/cm³ at 4°C
  • Seawater is usually more dense: 1.022-1.030 g/cm³
  • Difference in Seawater densities create deep ocean currents.
• Freshwater vs. Saltwater Properties:

  Property	Freshwater	Seawater
  Odour	Odourless	Distinctly marine
  Taste	Tasteless	Salty
  pH	7.0 (neutral)	8.1 (alkaline)
  Density (4°C)	1.000 g/cm³	1.028 g/cm³
  Freezing point	0 °C	-1.9 °C
  Boiling Point	100 °C	100.6 °C

Watersheds

• Geographic boundaries of a water body, its ecosystem and the land that drains to it.
• Includes groundwater that receives discharges from streams, wetlands, ponds, and lakes.
• Can be as small as a backyard or as large as the land that drains into the Great Lakes.

Hydrological Cycle

• Continual exchange of water between the Earth and the atmosphere.
• Pathways of water movement and distribution.
• Components:
  • Precipitation (amount, frequency, intensity, type)
  • Evapotranspiration (evaporation plus transpiration from plants)
  • Soil moisture
  • Runoff, streamflow and river discharge into the oceans
  • Atmospheric moisture flows (e.g. by wind) and divergence
  • Atmospheric moisture storage
• Related issues:
  • Co-variability of temperature and precipitation
  • Forcings of the hydrological cycle, such as solar energy.

Impacts of Human Activities on the Water Cycle

• Deforestation: Run-off discharge increases.
• Land Clearing: Soil evaporation is high, transpiration is low.
• Urbanization: Retain run-off, inland evaporation increases, groundwater input decreases, wetland areas dry out.
• Man-Made Reservoirs: Withdrawal for human usage & irrigation
  • Lowering the groundwater table
  • Reduction of water in streams and lakes
  • Land subsidence
  • Saltwater intrusion

Sustainability

• Consider how daily water usage may not be sustainable.

Explore the diverse types of aquatic environments, including freshwater, brackish, and marine ecosystems. Learn about the significance of salinity, the factors contributing to seawater's saltiness, and the importance of dissolved gases in ocean environments. This quiz will enhance your understanding of the complex interactions within aquatic habitats.