🌿Intro to Environmental Science Unit 7 – Freshwater Resources & Water Pollution

Water Cycle and Freshwater Distribution

• Water cycle, also known as the hydrologic cycle, involves the continuous movement and recycling of water on Earth
  • Driven by solar energy and gravity
  • Main processes include evaporation, transpiration, condensation, precipitation, infiltration, and surface runoff
• Freshwater represents only a small fraction (~2.5%) of the total water on Earth
  • Majority of freshwater is locked up in glaciers, ice caps, and groundwater
  • Surface freshwater sources (rivers, lakes) account for a tiny portion (~0.3%) of total freshwater
• Uneven distribution of freshwater resources across the globe
  • Influenced by factors such as climate, geography, and geology
  • Some regions experience water scarcity while others have abundant freshwater supplies
• Groundwater, water stored in aquifers and porous rock formations, constitutes a significant portion of accessible freshwater
  • Recharged through infiltration of precipitation and surface water
  • Extraction rates often exceed recharge rates, leading to groundwater depletion
• Climate change impacts the water cycle and freshwater availability
  • Altering precipitation patterns, increasing evaporation rates, and causing more frequent and severe droughts and floods

Types of Freshwater Resources

• Surface water resources include rivers, lakes, and wetlands
  • Rivers transport water from high elevations to the oceans, providing water for various uses along the way
  • Lakes store large volumes of freshwater and support aquatic ecosystems
  • Wetlands, such as marshes and swamps, filter water, regulate water flow, and provide habitat for diverse species
• Groundwater is water stored in underground aquifers and porous rock formations
  • Accessed through wells and springs
  • Provides a reliable water source, especially in areas with limited surface water
  • Aquifers can be confined (bounded by impermeable layers) or unconfined (connected to the surface)
• Glaciers and ice caps store a significant portion of Earth's freshwater
  • Glacial meltwater contributes to river flow and groundwater recharge
  • Retreating glaciers due to climate change can impact long-term water availability
• Artificial reservoirs, created by damming rivers, store water for various purposes
  • Irrigation, hydropower generation, flood control, and water supply
  • Can have ecological and social impacts, such as altered river flow and displacement of communities
• Desalination, the process of removing salt from seawater or brackish water, is an emerging freshwater resource
  • Requires significant energy input and can have environmental impacts (brine disposal)

Water Usage and Demand

• Agriculture is the largest consumer of freshwater globally
  • Irrigation accounts for ~70% of total water withdrawals
  • Inefficient irrigation practices and water-intensive crops contribute to high water usage
• Industrial water use includes manufacturing, power generation, and mining
  • Cooling, processing, and cleaning require significant amounts of water
  • Industrial water consumption is expected to increase with economic growth
• Domestic water use encompasses household activities (drinking, cooking, sanitation)
  • Per capita water consumption varies widely across countries and regions
  • Urbanization and population growth drive increased domestic water demand
• Ecosystem water requirements, often overlooked, are crucial for maintaining healthy aquatic habitats
  • Sufficient water flow and quality are necessary to support biodiversity and ecosystem services
• Water scarcity occurs when water demand exceeds available water resources
  • Physical water scarcity results from insufficient water quantity
  • Economic water scarcity arises from inadequate infrastructure and management
• Virtual water trade refers to the hidden flow of water in food and goods produced in one region and consumed in another
  • Allows water-scarce regions to import water-intensive products and conserve local water resources

Major Sources of Water Pollution

• Agricultural runoff carries excess nutrients (nitrogen and phosphorus), pesticides, and sediment into water bodies
  • Nutrients from fertilizers cause eutrophication, leading to algal blooms and oxygen depletion
  • Pesticides can be toxic to aquatic life and accumulate in food chains
• Industrial effluents contain a wide range of pollutants (heavy metals, chemicals, organic compounds)
  • Inadequate treatment and improper disposal of industrial waste threaten water quality
  • Accidental spills and leaks from industrial sites can contaminate water sources
• Domestic sewage and wastewater introduce pathogens, nutrients, and organic matter into water bodies
  • Inadequate sanitation and wastewater treatment infrastructure exacerbate the problem
  • Combined sewer overflows during heavy rainfall events can release untreated sewage into the environment
• Urban and stormwater runoff carries pollutants from streets, parking lots, and rooftops
  • Pollutants include oil, grease, heavy metals, and litter
  • Impervious surfaces in urban areas increase the volume and velocity of runoff, causing erosion and habitat degradation
• Atmospheric deposition of pollutants, such as acid rain and mercury, can contaminate water bodies
  • Emissions from fossil fuel combustion and industrial processes are the main sources
  • Acid rain lowers the pH of water bodies, harming aquatic life and leaching metals from soils
• Marine debris, particularly plastic waste, poses a growing threat to aquatic ecosystems
  • Microplastics, tiny plastic fragments, can be ingested by marine organisms and enter food chains
  • Larger debris (fishing nets, plastic bags) can entangle and suffocate marine life

Environmental Impacts of Water Pollution

• Eutrophication, caused by excess nutrients, leads to algal blooms and oxygen depletion (hypoxia)
  • Algal blooms can produce toxins harmful to aquatic life and humans
  • Hypoxic conditions stress and kill fish and other aquatic organisms
• Biodiversity loss occurs when pollution alters aquatic habitats and disrupts ecosystem balance
  • Sensitive species may disappear, while pollution-tolerant species thrive
  • Reduced biodiversity diminishes ecosystem resilience and functioning
• Bioaccumulation and biomagnification of persistent pollutants in aquatic food chains
  • Pollutants (mercury, PCBs) accumulate in the tissues of organisms and become more concentrated at higher trophic levels
  • Poses health risks to top predators, including humans who consume contaminated fish
• Degradation of ecosystem services provided by healthy water bodies
  • Water purification, nutrient cycling, flood regulation, and recreational opportunities are compromised
  • Economic losses in sectors such as fisheries, tourism, and water-dependent industries
• Human health impacts from exposure to contaminated water and seafood
  • Waterborne diseases (cholera, typhoid) spread through untreated sewage and contaminated drinking water
  • Long-term exposure to pollutants can cause chronic health problems (cancer, neurological disorders)
• Groundwater contamination, often difficult to detect and remediate
  • Pollutants can seep into aquifers from landfills, septic systems, and agricultural activities
  • Contaminated groundwater can remain polluted for decades, affecting drinking water supplies

Water Treatment and Conservation Methods

• Wastewater treatment removes contaminants from domestic and industrial sewage
  • Primary treatment: physical removal of solids through screening and sedimentation
  • Secondary treatment: biological degradation of organic matter using microorganisms
  • Tertiary treatment: advanced processes (filtration, disinfection) to further purify water for reuse or discharge
• Drinking water treatment ensures the safety and quality of water for human consumption
  • Processes include coagulation, flocculation, sedimentation, filtration, and disinfection (chlorination, UV irradiation)
  • Regular monitoring and testing to meet drinking water standards
• Water conservation measures aim to reduce water consumption and improve efficiency
  • Fix leaks in distribution systems and households
  • Promote water-saving appliances and fixtures (low-flow toilets, showerheads)
  • Encourage behavioral changes (shorter showers, turning off taps)
• Agricultural water management practices optimize irrigation efficiency and reduce water waste
  • Drip irrigation delivers water directly to plant roots, minimizing evaporation and runoff
  • Precision agriculture uses sensors and data to apply water and nutrients based on crop needs
• Stormwater management techniques mitigate the impacts of urban runoff
  • Green infrastructure (permeable pavements, rain gardens) allows water to infiltrate and recharge groundwater
  • Retention and detention basins store and slowly release stormwater, reducing peak flows and flooding
• Water reuse and recycling conserve freshwater resources and reduce wastewater discharge
  • Greywater (from sinks, showers) can be treated and reused for non-potable purposes (irrigation, toilet flushing)
  • Reclaimed wastewater can be used for industrial processes, landscape irrigation, and groundwater recharge

Case Studies and Current Issues

• Flint, Michigan water crisis (2014-2019)
  • Switching water sources and inadequate treatment led to lead contamination in drinking water
  • Exposed thousands of residents, particularly children, to elevated lead levels
  • Highlighted issues of environmental injustice and the need for infrastructure upgrades
• Aral Sea shrinkage in Central Asia
  • Diversion of rivers for irrigation caused the Aral Sea to lose 90% of its volume since the 1960s
  • Resulted in biodiversity loss, climate change, and economic hardship for local communities
  • Demonstrates the unsustainable use of water resources and the long-term consequences
• Gulf of Mexico dead zone
  • Nutrient pollution from agricultural runoff in the Mississippi River Basin creates a large hypoxic zone
  • Seasonal occurrence disrupts marine ecosystems and fisheries
  • Emphasizes the need for improved agricultural practices and nutrient management
• Cape Town, South Africa water crisis (2015-2018)
  • Severe drought and rapid population growth brought the city close to "Day Zero" (taps running dry)
  • Implemented strict water rationing and conservation measures to avert the crisis
  • Highlights the vulnerability of cities to water scarcity and the importance of resilient water management
• Microplastics pollution in aquatic environments
  • Tiny plastic particles (< 5 mm) originate from the breakdown of larger plastic debris and microbeads in personal care products
  • Ingested by aquatic organisms, potentially transferring up the food chain to humans
  • Raises concerns about the long-term effects on marine life and human health
• Sustainable Development Goal 6 (SDG 6): Clean Water and Sanitation
  • One of the 17 UN Sustainable Development Goals, aiming to ensure availability and sustainable management of water and sanitation for all by 2030
  • Targets include achieving universal access to safe drinking water, improving water quality, and increasing water-use efficiency
  • Emphasizes the importance of integrated water resources management and protecting water-related ecosystems