The Water Cycle, Pollution & Sustainability of Aquatic Resources

Posted on Aug 25, 2024 in Geology

The Water Cycle

  • Renewable: atmosphere, rivers (circular process)
  • Middle ground: groundwater aquifers
  • Non-renewable: oceans, icecaps

Transfers are: advection, flooding, surface run-off.

Storages: oceans, soils, groundwater, lakes

Human Impact on the Water Cycle

  • Withdrawals: domestic use, irrigation in agriculture and industry
  • Discharges: adding pollutants to water
  • Diverting rivers or sections of rivers

Urbanization and Flash Floods

Ocean Currents and Energy Distribution

  • Ocean currents: movements of water vertically and horizontally; they play an important role in global energy distribution.
  • Surface currents: moved by the wind.
  • Deep water currents: constitute 90% of ocean currents and drive the oceanic conveyor belt.
    • Caused by differences in water density due to salt and temperature
    • Warm water: holds less salt, making it less dense, so it rises; cold water rises from depth to replace it (upwellings).
    • Cold water: holds more salt, making it denser, so it sinks.
    • When cold water rises, it must be replaced by warm water (downwellings).
    • Warm currents flow from the equator to the poles.

Access to Freshwater

Water scarcity: the imbalance between water use and available water resources.

Sustainability of Freshwater Resource Usage

Using water cautiously ensures its sustainability and allows for replenishment. We extract freshwater from surface and groundwater sources (aquifers).

Aquifers are underground water reservoirs between rock layers, recharged through slow filtration.

Fossil aquifers: aquifers that will never be replenished.

Issues Regarding Freshwater Use

  • Unequal rainfall distribution throughout the year leads to supply inequalities.
  • Low water levels in rivers and streams
  • Freshwater contamination
  • Salinization: excessive irrigation leads to mineral buildup in the soil. When water is added, these minerals dissolve, increasing salinity.

Solutions

  • Increase freshwater supplies
  • Grey-water recycling: reuse water from showers and baths for other purposes.
  • Regulate maximum temperatures of released cooling water.
  • Implement water treatment plants in industries

Aquatic Food Production Systems

Marine Ecosystems and Food Webs

Marine ecosystems: highly biodiverse with high stability and resilience.

Continental shelf: comprises 15% of ocean water but accounts for 50% of ocean productivity due to abundant light, which supports photosynthesis.

Phytoplankton: the primary producers in the ocean; zooplankton feed on phytoplankton.

Classification of Marine Organisms

  • Benthic: species living on the seabed
  • Pelagic: organisms living in the water column above the seabed

Fisheries – Industrial Farming and Hunting

  • Target shellfish and some vertebrates
  • According to the FAO, over 70% of the world’s fisheries are fully exploited or in decline.

Aquaculture

As demand for seafood increases, aquaculture, or fish farming, is becoming more prevalent and is steadily improving in sustainability.

Impacts of Fish Farms

  • Pollution
  • Habitat loss
  • Spread of diseases (high fish density increases disease susceptibility)

Unsustainable Wild Fishing Industry

  • Conflicts over fishing grounds and rights have arisen.
  • Fish provide 15% of the protein consumed by humans.

The Tragedy of the Commons: the overexploitation of shared resources, like oceans, for individual gain, ultimately harming everyone. Legislation is often necessary to address this issue.

Maximum Sustainable Yield: the highest amount of a resource that can be harvested without depleting the stock.

Types of Water Pollution

  • Anthropogenic (human-caused) or natural
  • Point source or non-point source
  • Organic or inorganic
  • Direct or indirect

Sources of freshwater pollution: agricultural runoff, sewage, industrial discharge, and solid domestic waste.

Sources of marine pollution: rivers, pipelines, atmosphere, and human activities.

Measuring Water Pollution

Biochemical Oxygen Demand (BOD): measures the amount of oxygen consumed by microorganisms during the decomposition of organic matter in water.

Biotic Indices and Indicator Species

Indicator species are highly sensitive to environmental changes and serve as early warning signs of pollution.

Biotic index: a scale that assesses the quality of an ecosystem based on the presence and abundance of indicator species.

  • Invertebrates are commonly used to estimate pollution levels due to their sensitivity to oxygen depletion in water.
  • BOD provides a snapshot of pollution at the time of sampling, while indicator species offer insights into the recent history of pollution.

Eutrophication

Eutrophication occurs when excess nutrients, primarily nitrates and phosphates, enter aquatic ecosystems. This process can be natural but is often accelerated by human activities. Eutrophication can lead to the formation of”dead zone” in oceans and freshwater bodies due to oxygen depletion.

In severe cases, the decomposition of organic matter consumes large amounts of oxygen, creating anoxic (oxygen-depleted) conditions that favor anaerobic decomposition. This process releases toxic gases such as methane, hydrogen sulfide, and ammonia.

Impacts of Eutrophication

  • Unsightly algal blooms and duckweed cover rivers, ponds, and lakes.
  • Release of foul-smelling gases like hydrogen sulfide
  • Oxygen depletion in water
  • Loss of biodiversity and shortened food chains
  • Death of higher plants and aerobic organisms
  • Increased water turbidity

Excess nutrients often originate from point sources such as:

  • Detergents containing phosphates
  • Fertilizers
  • Drainage from intensive livestock farming
  • Sewage
  • Increased erosion of topsoil into water bodies

Process of Eutrophication

  1. Fertilizers rich in nitrates and phosphates are carried into rivers or lakes through runoff.
  2. High phosphate levels, in particular, promote rapid algal growth.
  3. Algal blooms form, blocking sunlight from reaching underwater plants, leading to their death.
  4. Increased algae provide more food for zooplankton and small animals, which in turn support a larger fish population. This disrupts the balance, as fewer zooplankton are available to consume the excess algae.
  5. As algae die, they are decomposed by aerobic bacteria, consuming large amounts of oxygen.
  6. Oxygen levels plummet, leading to the death of fish and other aquatic organisms, causing a collapse of the food chain.
  7. Oxygen depletion worsens, and dead organic matter accumulates as sediment on the lake or riverbed, increasing turbidity.
  8. In extreme cases, all life is extinguished, leaving behind a clear but lifeless body of water.

Possible Solutions

Nutrient Trading: A proposed solution for the Gulf of Mexico, nutrient trading is a voluntary market-based approach to reduce nutrient runoff. It identifies cost-effective methods for nutrient reduction in both industrial and agricultural sectors. This system allows entities that can reduce nutrient pollution at a lower cost to sell credits to those facing higher costs for similar reductions. Nutrient trading offers a flexible and economically viable solution for managing nutrient pollution.

Red Tides

In coastal waters, algal blooms, sometimes called red tides, can be triggered by an excess of nutrients. These blooms are caused by specific types of phytoplankton called dinoflagellates. Red tides pose a serious threat to marine life because the algae produce toxins that can kill fish and accumulate in shellfish, making them unsafe for human consumption.

Impact of Water Flow on Eutrophication

Slow-moving water: Eutrophication leads to significant and lasting damage, reducing biodiversity.

Fast-moving water: Eutrophication may cause a temporary decline in biodiversity downstream, but recovery and restoration of clean water are more likely.

Management Strategies

:

  • Altering the human activity producing pollution: limit detergents with phosphates, new technology in washing machines, plant buffer zones between the fields and water courses to absorb the excess nutrients, stop leaching of slurry, educate farmers about effective timing for fertilizer.
  • Regulating and reducing the pollutants at the point of emission: treat washwater before release to remove phosphates and nitrates, divert or treat sewage waste effectively and minimize fertilizer dosage on agricultural lands or use organic matter instead.
  • Clean up and restoration: pumping air through the lakes, dredging sediments with high nutrients level from the river and lake beds, remove excess weeds, restock ponds or water bodies with appropriate organisms.