2.6 Water quality and chemistry

Water quality is crucial for fish populations and aquatic ecosystems. It encompasses physical, chemical, and biological factors that determine habitat suitability, affecting fish reproduction, growth, and survival.

Understanding water chemistry is key to effective fisheries management. pH levels, dissolved oxygen, salinity, and pollutants all impact fish health. Monitoring these parameters helps identify threats and informs conservation strategies to protect aquatic environments.

Basics of water quality

• Water quality fundamentally impacts aquatic ecosystems and fish populations in freshwater and marine environments
• Understanding water quality parameters enables effective fisheries management and conservation efforts
• Monitoring water quality helps identify potential threats to fish habitats and informs conservation strategies

Components of water quality

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• Physical characteristics include temperature, turbidity, and color
• Chemical properties encompass dissolved oxygen, pH, nutrients, and contaminants
• Biological factors involve presence of microorganisms, algae, and aquatic plants
• Hydrological aspects consider water flow, depth, and circulation patterns

Importance for aquatic life

• Determines habitat suitability for different fish species and their prey
• Influences fish reproduction, growth rates, and overall population dynamics
• Affects oxygen availability, essential for fish respiration and metabolism
• Impacts the availability of food sources and the entire aquatic food web

Chemical properties of water

pH levels in aquatic environments

• Measure of water's acidity or alkalinity on a scale of 0 to 14
• Most freshwater fish thrive in pH range of 6.5 to 8.5
• Affects fish osmoregulation and toxicity of certain pollutants
• Influenced by factors like geological composition and aquatic vegetation
• Extreme pH levels can cause direct mortality or reduced reproductive success

Dissolved oxygen content

• Critical for fish respiration and overall aquatic ecosystem health
• Measured in parts per million (ppm) or milligrams per liter (mg/L)
• Influenced by temperature, atmospheric pressure, and biological activity
• Cold water holds more dissolved oxygen than warm water
• Fish species have varying oxygen requirements (cold-water species generally need higher levels)

Salinity and conductivity

• Salinity measures dissolved salt content in water
• Conductivity indicates the water's ability to conduct electrical current
• Both parameters affect osmoregulation in fish and distribution of species
• Salinity influences fish metabolism, growth, and reproduction
• Conductivity can serve as an indicator of pollution or changes in water chemistry

Water pollutants

Types of water pollutants

• Organic pollutants include sewage, agricultural runoff, and industrial waste
• Inorganic pollutants encompass heavy metals, acids, and synthetic chemicals
• Thermal pollution results from discharge of heated water into water bodies
• Radioactive contaminants from nuclear power plants or medical facilities
• Microplastics and other emerging pollutants pose new threats to aquatic life

Sources of pollution

• Point sources originate from specific, identifiable locations (industrial discharges)
• Non-point sources come from diffuse areas (agricultural runoff, urban stormwater)
• Atmospheric deposition of pollutants through rainfall or dust particles
• Groundwater contamination from leaking underground storage tanks or landfills
• Accidental spills or illegal dumping of hazardous materials

Effects on fish populations

• Direct mortality from acute toxicity or reduced oxygen levels
• Chronic health issues leading to decreased growth and reproductive success
• Bioaccumulation of pollutants in fish tissues, affecting entire food chains
• Habitat degradation and loss of spawning grounds
• Altered behavior patterns and migration routes due to chemical cues disruption

Nutrient cycles in water

Nitrogen cycle

• Essential for protein synthesis and growth in aquatic organisms
• Involves processes of nitrogen fixation, nitrification, and denitrification
• Excess nitrogen can lead to eutrophication and harmful algal blooms
• Sources include agricultural runoff, sewage, and atmospheric deposition
• Nitrogen-fixing bacteria play a crucial role in making nitrogen available to plants

Phosphorus cycle

• Vital for energy transfer and cell structure in aquatic life
• Often the limiting nutrient in freshwater ecosystems
• Sediments act as both source and sink for phosphorus
• Excessive phosphorus can cause algal blooms and oxygen depletion
• Phosphorus enters water bodies through erosion, fertilizers, and detergents

Carbon cycle

• Regulates pH and carbonate availability in aquatic systems
• Involves processes of photosynthesis, respiration, and decomposition
• Dissolved organic carbon supports microbial food webs
• Carbon dioxide absorption affects water acidity and carbonate shell formation
• Climate change alters carbon cycling in aquatic ecosystems

Water temperature

Thermal stratification

• Process of water column layering based on temperature differences
• Occurs in lakes and reservoirs, creating distinct thermal zones (epilimnion, metalimnion, hypolimnion)
• Affects nutrient cycling, dissolved oxygen distribution, and fish habitat selection
• Can lead to fish kills if mixing of layers occurs too rapidly
• Climate change may alter stratification patterns in water bodies

Effects on fish metabolism

• Directly influences metabolic rates and energy requirements of fish
• Warmer temperatures generally increase metabolism, feeding, and growth rates
• Extreme temperatures can cause stress, reduced feeding, and mortality
• Different fish species have optimal temperature ranges for various life stages
• Temperature changes can alter timing of spawning and migration patterns

Seasonal temperature variations

• Influence fish distribution, behavior, and life cycle events
• Trigger spawning migrations and determine egg incubation periods
• Affect prey availability and predator-prey interactions
• Can cause fish kills during extreme heat waves or cold snaps
• Climate change may lead to shifts in seasonal temperature patterns

Turbidity and clarity

Causes of turbidity

• Suspended sediments from erosion or runoff
• Algal blooms resulting from excess nutrients
• Organic matter from decomposing plants and animals
• Industrial discharges or construction activities
• Resuspension of bottom sediments by wind, waves, or boat traffic

Measuring water clarity

• Secchi disk method measures light penetration depth
• Turbidity meters quantify suspended particles in nephelometric turbidity units (NTU)
• Transparency tubes provide quick field assessments of water clarity
• Satellite imagery and remote sensing for large-scale monitoring
• Continuous monitoring systems for real-time turbidity data collection

Impact on fish behavior

• Reduced visibility affects predator-prey interactions and feeding efficiency
• High turbidity can impair gill function and cause respiratory stress
• Influences habitat selection and distribution of fish species
• Alters light penetration, affecting aquatic plant growth and fish habitat
• Can disrupt spawning behavior and egg development in some species

Dissolved solids

Total dissolved solids (TDS)

• Measure of all inorganic and organic substances dissolved in water
• Expressed in milligrams per liter (mg/L) or parts per million (ppm)
• Affects water density, conductivity, and osmotic pressure
• High TDS levels can stress fish osmoregulation and reduce dissolved oxygen
• Sources include natural mineral dissolution, agricultural runoff, and wastewater

Suspended vs dissolved solids

• Suspended solids remain in suspension and contribute to turbidity
• Dissolved solids pass through filters and affect water chemistry
• Suspended solids can settle out, forming sediment layers
• Dissolved solids include ions, nutrients, and trace elements
• Both types impact aquatic ecosystems but through different mechanisms

Biological indicators

Macroinvertebrates as indicators

• Organisms visible to the naked eye, living on or in sediments
• Include insects, crustaceans, mollusks, and worms
• Vary in sensitivity to pollution and environmental changes
• Used to assess long-term water quality and ecosystem health
• Sampling methods include kick nets, artificial substrates, and sediment cores

Algae and aquatic plants

• Respond quickly to changes in nutrient levels and water quality
• Serve as primary producers in aquatic food webs
• Excessive growth can lead to eutrophication and oxygen depletion
• Some species indicate specific water quality conditions (diatoms for pH)
• Monitoring includes species composition, biomass, and chlorophyll levels

Water quality testing

Field testing methods

• Portable meters for pH, dissolved oxygen, and conductivity measurements
• Test kits for nutrient levels, hardness, and alkalinity
• Colorimetric methods for rapid assessment of various parameters
• In-situ sensors for continuous monitoring of key variables
• Sampling techniques for collecting water, sediment, and biological specimens

Laboratory analysis techniques

• Spectrophotometry for precise measurement of nutrients and metals
• Gas chromatography and mass spectrometry for organic pollutant detection
• Atomic absorption spectroscopy for heavy metal analysis
• Microbiological tests for fecal coliform and other pathogens
• Advanced techniques like PCR for detecting specific organisms or contaminants

Water quality management

Best practices for conservation

• Implementing riparian buffers to reduce runoff and erosion
• Proper management of agricultural fertilizers and pesticides
• Upgrading wastewater treatment facilities to remove more pollutants
• Controlling invasive species that can alter water quality
• Educating the public on responsible water use and pollution prevention

Restoration of degraded waters

• Removing contaminated sediments through dredging or capping
• Reintroducing native aquatic plants to improve habitat and water quality
• Implementing erosion control measures to reduce sediment input
• Restoring natural flow regimes in regulated rivers and streams
• Addressing point and non-point sources of pollution in the watershed

Regulations and standards

Clean Water Act overview

• Establishes the basic structure for regulating water pollution in the U.S.
• Sets water quality standards for surface waters
• Requires permits for point source discharges (National Pollutant Discharge Elimination System)
• Addresses non-point source pollution through management programs
• Provides funding for wastewater treatment plant construction and upgrades

State vs federal water quality standards

• Federal standards set minimum requirements for all states
• States can adopt more stringent standards based on local conditions
• State agencies responsible for monitoring and enforcing water quality
• Federal oversight ensures consistency and compliance across states
• Tribal governments can also set standards for waters within their jurisdictions

Climate change impacts

Effects on water chemistry

• Increased water temperatures affect dissolved oxygen levels and stratification
• Changes in precipitation patterns alter runoff and nutrient loading
• Ocean acidification from increased atmospheric CO2 absorption
• Altered dissolved organic carbon dynamics in freshwater systems
• Potential release of legacy pollutants from melting glaciers and permafrost

Adaptation strategies for fisheries

• Developing thermal refugia to protect cold-water fish species
• Enhancing habitat connectivity to allow for species range shifts
• Implementing adaptive harvest management based on changing conditions
• Restoring and protecting coastal wetlands as buffers against sea-level rise
• Investing in research and monitoring to understand and predict ecosystem responses