Water pollution

Pollution

• Pollution refers to the introduction of substances into the environment.
• This introduction results in the loss of beneficial use of resources.
• Degradation of the health of humans, wildlife, or ecosystems may occur.

Pollutants and Sources

• Pollutants enter aquatic systems via point and nonpoint sources.
• Point sources are stationary locations, like an effluent pipe.
• Nonpoint sources are diffuse sources, like land runoff and the atmosphere.

Pollutant Load

• The mass flux of a pollutant is called its load.
• Load is measured in units of mass per unit time.

Macropollutants

• Macropollutants are discharged into the world's rivers in the tens of millions of tons per year.
• Macropollutants include nitrogen, phosphorus, organic matter, and suspended solids.

Philippine Clean Water Act

• The Philippine Clean Water Act of 2004 (Republic Act No. 9275) seeks to protect Philippine water bodies.
• It focuses on pollution from land-based sources.

Environmental Protection Agency (EPA) Standards

• The Environmental Protection Agency (EPA) sets standards for water quality.
• The goal is to retain beneficial uses and protect human and ecosystem health.
• Some standards are technology-based, requiring specific treatment levels regardless of the receiving water's condition.
• Other standards are quality based, requiring additional treatment if conditions remain degraded.
• The total maximum daily load (TMDL) that can be discharged into a water body is established if controls are insufficient.
• Permits are set accordingly.

Dissolved Oxygen (DO)

• Dissolved oxygen maintains a balanced community of organisms in bodies of water.
• Oxygen is measured in its dissolved form, or dissolved oxygen (DO).
• A decline in dissolved oxygen levels occurs if more oxygen is consumed than produced.
• Sensitive animals may move away, weaken, or die if DO declines.
• DO levels fluctuate seasonally and vary with water temperature and altitude.
• Cold water holds more oxygen than warm water.
• Water holds less oxygen at higher altitudes.
• Aquatic animals are most vulnerable to lowered DO levels in the early morning on hot summer days.

Oxygen-Demanding Waste

• Adding oxygen-demanding waste (measured as BOD) to water increases oxygen consumption.
• The rate of oxygen consumption (deoxygenation) may exceed the rate of atmospheric resupply (reaeration).
• Reproduction of fish and macro invertebrates is impaired when oxygen levels drop below 4 to 5 mg O2/L.
• Severe oxygen depletion can lead to anaerobic conditions.
• Loss of biodiversity and poor aesthetics (turbidity and odor problems) can arise.

Biochemical Oxygen Demand (BOD)

• BOD (Biochemical oxygen demand) is the rate of oxygen consumption by bacteria.
• This occurs as bacteria break down organic matter in a water sample.
• The agricultural sector contributes a large percentage to global BOD and nitrogen loadings.
• Higher BOD leads to more rapid oxygen depletion.
• This translates to less oxygen available for aquatic life.
• Consequences of high BOD mirror those of low dissolved oxygen.
• Aquatic organisms become stressed, suffocate, and die.

Oxygen Saturation

• Oxygen saturation is the amount of oxygen that can dissolve in water at a given temperature.
• Its equilibrium or saturation concentration can be determined through Henry's law constant, KH.
• DOsat = KH x PO2
• DOsat represents the saturation dissolved-oxygen concentration- in moles O2/L.
• KH is Henry’s law constant (1.36 x 10-3 moles/L-atm at 20ºC).
• PO2 refers to the partial pressure of oxygen in the atmosphere (~21 percent or 2.1 atm).

Oxygen Deficit

• Oxygen deficit (D, expressed in mg O2/L) is the departure of the ambient dissolved-oxygen concentration from saturation.
• D = DOsat - DOact, where DOact is the ambient or measured dissolved-oxygen concentration (mg O2/L).
• Oversaturation occurs in lakes and rivers.
• This is under quiescent, non-turbulent conditions when algae and macrophytes are actively photosynthesizing.
• As a result, dissolved oxygen gets produced.

Hypoxia

• Hypoxia is a phenomenon in aquatic environments.
• Dissolved oxygen (DO) is reduced to a concentration detrimental to aquatic organisms that live in the system.

River Water Quality

• River water quality treatment focuses on managing dissolved oxygen (DO) levels.
• Deals with the discharge of oxygen-demanding wastes.
• Issuance of discharge permits and setting total maximum daily loads for receiving waters are classic issues of interest.

Dissolved-Oxygen Sag Curve

• Oxygen-demanding wastes discharged to a river causes a typical response in oxygen levels.
• The location of the critical point and the oxygen concentration are of principal interest.
• This pinpoints where water quality conditions are at their worst.

Lake and Reservoir Water Quality

• Water quality conditions are linked to biogeochemical cycles.
• The magnitude and routing of chemical and energy fluxes influence these lakes.
• Cultural perturbations, specifically in phosphorus and nitrogen cycles, result in eutrophication.

Thermal Stratification

• The major difference between lakes and rivers is the means of mass transport.
• Rivers are completely mixed.
• Lakes undergo thermal stratification in temperature latitudes.
• Thermal stratification divides the system into layers and restricts mass transport.
• This restriction impacts the cycling of chemical species like iron, oxygen, and phosphorus.
• Thermal stratification is driven by the relationship between water temperature and density.
• Lake stratification separates lakes into three layers: epilimnion, Metalimnion, and hypolimnion.
• Epilimnion is the top layer of the lake.
• Metalimnion (or thermocline) is the middle layer and may change depth throughout the day.
• Hypolimnion is the bottom layer.

Stratification and Destratification

• Stratification and destratification follow a predictable seasonal pattern.
• Spring turnover is a mixing process involving convection and wind energy.
• It circulates the water column, leading to an isothermal condition.
• Surface waters are warmer and less dense than lower waters during summer stratification.
• Fall turnover occurs as surface waters cool and become denser: sink and promote circulation aided by wind.
• As the lake cools further, cold, low-density waters gather at the surface.
• The lake reenters winter stratification.

Organic Matter, Thermal Stratification, and Oxygen Depletion

• Internal production of organic matter in lakes comes from algal and macrophyte growth.
• This growth is stimulated by discharges of growth-limiting nutrients (nitrogen & phosphorus).
• Organic matter in well-lit upper waters settles, decomposes, and consumes oxygen.
• Oxygen depletion accelerates the cycling of chemicals in lake sediments.
• Undesired and hazardous chemical species (NH3, H2S, CH4) get generated.
• Fish and macroinvertebrates become extirpated.

Wetlands

• Historically, wetlands were considered nuisances.
• They were seen as breeding grounds for disease and obstacles to agriculture, navigation, and urbanization.
• Compensatory mitigation is the creation or restoration of wetlands to compensate for damage to other wetlands when unavoidable.

Types of Wetlands

• Wetlands represent an ecotone.
• They are a transition between terrestrial and aquatic environments.
• Types of wetlands can be identified by looking at variations in the source of water (direct rainfall or groundwater).
• The position of the water table, the hydroperiod, and levels of productivity and enrichment matter too.

Four Types of Wetlands

• Marshes are frequently or continually inundated with water and characterized by emergent, soft-stemmed vegetation.
• Swamps are dominated by woody (as opposed to soft-stemmed) vegetation.
• Bogs are peat-forming wetlands that receive all water and nutrient inputs from atmospheric deposition.
• Bogs are typically acidic and nutrient-poor.
• Fens receive nutrients by drainage from mineral soils and groundwater input.
• Fens are typically less acidic and more nutrient-rich than bogs.

Additional Wetland Characteristics

• Wetlands are also characterized by their proximity to other habitats.
• Riparian wetlands are close to rivers, while coastal wetlands are near oceans and large lakes.
• A site is further characterized as a wetland if it's inundated or saturated with water for at least part of the year.
• Hydric soils and support of predominantly hydrophytic plants are also considered.

Hydric Soils and Hydrophytic Plants

• Hydric soils exist under waterlogged, anaerobic conditions with specific chemical and physical characteristics.
• Hydrophytic plants have developed adaptations that allow them to grow in oxygen-deficient soils.

Wetland Functions

• Water storage and flood mitigation are wetland functions.
• Wetlands are important in the filtration of water and removal of suspended solids and bacteria.
• They can remove nutrients and toxic substances.
• Wetlands provide wildlife habitats and biogeochemical cycling of materials on local to global scales.

Building Wetlands

• Banking creates wetlands to offset future destruction, turning banked wetlands into mitigation wetlands.
• Created wetlands refer to those built for mitigation purposes.
• Constructed wetlands are designed for pollutant removal, like municipal wastewater treatment

Low-Impact Development

• Low-impact development mimics pre-development natural hydrology.
• It reduces the peak flow rate and considers the timing of discharge.
• It also thinks about retention of stormwater, principles of biodiversity, green space, water storage, and groundwater recharge.

Built Environment

• A major problem of the built environment is the impact of nonpermeable surfaces on the hydrologic cycle and water quality.
• Covering surfaces with buildings, roofs, roads, and parking lots reduces precipitation infiltration.
• Urbanization also affects a city's ability to store freshwater.
• Traditional stormwater management utilizes concrete catch basins and pipes transporting stormwater to larger detention basins.
• Water discharges by an orifice or discharge pipe at a specific peak rate.

Green Roofs

• A living or green roof is partially or completely covered with vegetation and a growing medium over a waterproofing membrane.
• These may include root barriers, drainage, and irrigation systems.
• Rooftop runoff is a major contributor to municipal storm sewer systems.
• Green roofs provide many private and public benefits compared to traditional roofs.

Benefits

• Enhanced stormwater management and a reduction in building energy costs are benefits.
• Increase of green space and habitat, and a reduction in the urban heat island are also benefits.

Three Types of Green Roofs

• Intensive green roofs have thicker soil layers (150-400mm), weigh more, and need more structural support.
• These work well with concrete roofs.
• Extensive green roofs have thinner soil layers (60-200mm): they need less structural support.
• Semi-intensive green roofs have some components of both extensive and the intensive options.

Permeable Pavements

• Permeable (or porous) pavement allows for the vertical passage of water.
• Examples include grass, gravel/crushed stone, grid, paver stones, and porous concrete/asphalt.
• Permeable concrete consists of conventional material.
• It is characterized by coarse aggregate limited in its range sizes, with fine aggregates being minimal or nonexistent.
• Porous asphalt is also known as open-graded coarse aggregate.
• It is bonded together by asphalt cement with sufficient interconnected voids to make it permeable to water.

Bioretention Cells

• These cells are shallow depressions in the soil.
• Stormwater is directed here for storage and to maximize infiltration.
• Bioretention cells may also be called bioinfiltration cells, vegetated biofilters, and rain gardens.
• As vegetation grows, bioretention cells gain capacity to accept water.
• This occurs as the plant network evolves and increases transpiration.

Groundwater Quality

• Groundwater contaminants originate from natural and anthropogenic sources.
• Sources exhibit different areal and temporal characteristics.
• Groundwater contaminants include pathogens, inorganic chemicals, radionuclides, anthropogenic inorganic chemicals, and organic chemicals.

Sources of Groundwater Contamination

-Septic tanks, leaking storage tanks and agricultural activities are sources.

• Some additional sources are industrial activities, domestic and hazardous landfills.
• Other sources include mining activities, chemical spills, and improper waste disposal and home lawn care.
• Nonaqueous phase liquids (NAPLs) are a specialized class of organic contaminants.
• NAPLs do not mix readily with water.

Pollutant Fate and Transport

• Groundwater contaminants are transported via advection and dispersion.
• Advection occurs when the contaminant moves with the bulk flow of groundwater.
• Dispersion occurs when contaminants tend to spread as they are advected with groundwater.

Groundwater Remediation

• Contaminated groundwater is expensive and time-consuming to clean.
• Groundwater remediation occurs through physical, biological, and chemical means.
• Natural attenuation implies that as the contaminant plume moves, biological and chemical degradation processes reduce concentrations.