Lab Session 2: Water Quality Analysis
Lab Session 2: Water Quality - A Detective Exercise
Introduction to the Lab Session
Lab Session 2 on Water Quality is designed as a detective exercise where students will analyze unknown water samples. The objective is to match these samples to four distinct water bodies based on prior knowledge of their environmental conditions. This hands-on session, termed "CSI gets wet," is a practical application of environmental science principles.
Rationale for the Exercise
This laboratory session offers multiple benefits:
Practical Experience: Students gain hands-on experience using equipment and techniques commonly employed in water quality analysis within the environmental workforce.
Real-World Data Analysis: The water samples analyzed are authentic, sourced directly from local wetlands, providing a realistic data set.
First-Hand Understanding: It fosters a direct understanding of how human activities and the broader environment impact the wetlands that are part of the local ecosystem.
Ecological Insight: The exercise helps students discover "How wetlands work" by observing various physical, chemical, and biological parameters.
The "Suspect" Water Bodies
Four distinct water bodies serve as the potential sources for the unknown water samples, each with unique environmental characteristics:
Melaleuca Swamp:
A natural wetland located on campus.
Characterized by dense vegetation.
Bibra Lake:
A natural lake that has experienced degradation.
Degradation is due to surrounding urban land-use, including vegetation removal.
Receives nutrient-rich runoff from urban areas.
Recent Issues (as of 2024): The lake often dries in summer due to multiple stressors, including urbanization, invasive species, and climate change. A 6-month drought (October to June) resulted in the lakebed becoming dry enough to walk on, causing mass turtle deaths (approximately 100 turtles). Turtles typically aestivate (go dormant) when wetlands dry, but severe conditions can be lethal.
Frederick Baldwin Lake:
A created wetland, functioning as a drainage basin within an urban park.
Periodically flushed, indicating a system designed for water management.
Subject to human impacts due to its urban setting.
Grey Water:
This sample is a chemical approximation of discharge from an environmentally unfriendly household kitchen sink.
It is not actual household grey water; it is sterile, containing no bacteria or food particles, to ensure safety for laboratory analysis.
Water Quality Variables for Analysis
The lab session involves analyzing several key water quality parameters, each providing insights into the wetland's health and functioning:
Colour
Description: The visual appearance of the water, which can be derived from suspended particles (e.g., algae causing yellow/green hues, soil particles causing red/brown) or dissolved molecules (e.g., tea-brown staining from dissolved organic material).
Wetland Component: Primarily tannins and humic acids.
Process: These organic acids leach from native vegetation (which produces tannins for protection against bacterial/fungal attacks) when plants die and decompose in the water. This process reduces light penetration.
Wetland Characteristics: High colour is typical in wetlands with abundant vegetation, soils incapable of binding organic materials (e.g., Bassendean Sands vs. limestone), and low pH due to humic acid presence.
High/Low Indicator: Dark brown indicates high colour; clear/pale indicates low colour.
Measurement: Ideally using a spectrophotometer to measure absorbance at 440 ext{ nm}, but for this lab, observation and description suffice.
Impact: Elevated colour reduces light penetration into the water column, consequently diminishing photosynthesis with depth and limiting algal growth at lower depths.
Turbidity
Description: The cloudiness or haziness of a fluid caused by fine particles held suspended in the water, which reduces the amount of light that can pass through.
Wetland Component: Can be inorganic (e.g., silt or clay) or organic (e.g., algal cells).
Process: Occurs when rains wash sediments from catchments into wetlands, where silt and clay can remain suspended. Alternatively, high nutrient levels can trigger algal blooms, increasing turbidity due to a high concentration of algal cells.
Wetland Characteristics: Found in catchments prone to erosion (e.g., bare soil) or in wetlands experiencing algal blooms.
High/Low Indicator: Turbidity greater than 10 ext{ NTU} (Nephelometric Turbidity Units) is considered high.
Measurement: Measured using a turbidity meter.
Impact: Suspended solids reduce light penetration, hindering photosynthesis, and can clog the filtering mechanisms of aquatic organisms.
Conductivity / Salinity
Description: Conductivity measures the water's ability to conduct an electrical charge, which is directly related to the concentration of dissolved salts (ions). Higher salt concentration leads to higher conductivity. In Western Australian wetlands, salinity is primarily due to sodium chloride (NaCl).
Wetland Component: Salinity, referring to dissolved salts in the water.
Process: Salts are washed into wetlands from catchments by rainfall. In seasonally drying wetlands, evaporation concentrates salts. Older wetlands can accumulate salinity over time. Wetlands with exit drains (flushed systems) tend not to build up salts.
Wetland Characteristics: High salinity is common in seasonal wetlands, those lacking flushing, and areas subject to secondary salinity (like the Wheatbelt in WA).
High/Low Indicator: Refer to specific slide for detailed ranges.
Measurement: Conducted using a conductivity meter, measured in microSiemens per centimeter ( ext{µS/cm}) or milliSiemens per centimeter ( ext{mS/cm}). To convert conductivity to salinity: ext{mS/cm} imes 0.64 = ext{ppt} (parts per thousand).
Salinity Ranges:
Freshwater: 0 ext{ ppt} (parts per thousand)
Brackish: 2 ext{ ppt}
Marine: 35 ext{ ppt}
Salt lakes/estuaries: >40-60 ext{ ppt}
Impact: Organisms are adapted to a specific range of salinity. Changes in salinity can severely stress or kill organisms. For example, increased salinity in a freshwater environment causes dehydration in freshwater animals as osmosis drives water out of their bodies to equalize the salt concentration inside and outside their cells.
Dissolved Oxygen (DO)
Description: The concentration of oxygen gas dissolved in the water, essential for aerobic organisms to respire. Air contains 21% oxygen, while water typically contains only about 0.6% oxygen.
Factors Affecting DO:
Temperature: Hot water holds less DO, cold water holds more DO.
Salinity: Saline water holds less DO, fresh water holds more DO.
Wetland Component: Dissolved oxygen in the water.
Process:
Oxygen Input: Physical mixing of air and water (e.g., turbulence, currents, wind mixing) and photosynthesis by algae, which produces oxygen ( ext{CO}2 + ext{H}2 ext{O} = ext{sugars} + ext{O}_2).
Oxygen Removal: Respiration by aquatic organisms and especially by bacteria decomposing high organic loads.
Wetland Characteristics: High DO is found in systems open to wind, flushed, or equipped with fountains, or those with high algal concentrations. Shelter from wind or light (e.g., tree canopy) reduces mixing and photosynthesis, leading to lower DO.
High/Low Indicator:
Very High: >100% saturation or ext{ ~} 10 ext{ mg/L}.
Good: 100% saturation, or 8-10 ext{ mg/L}.
Very Low: <50% saturation, or ext{ ~} 5 ext{ mg/L} (aerobic organisms may die).
Measurement: Must be performed in the field using an oxygen meter, as oxygen concentrations can change rapidly after sample collection.
Photosynthesis and Wind: Wind can lead to 100% oxygen saturation, while active photosynthesis can result in super-saturation, potentially reaching 140% saturation. Conversely, bacterial decay and respiration by other organisms reduce DO levels.
Temperature
Description: The thermal energy content of the water.
Wetland Component: Water temperature.
Process: Water is heated by the sun and cooled by shade or wind. As wetlands are typically shallow, their temperature often reflects the diurnal temperature cycle of the environment.
Wetland Characteristics: Specific temperature depends on wind exposure and shading by tree canopies (warmer or cooler).
High/Low Indicator: Relative to other wetlands. Most aquatic organisms prefer a temperature range of 15-25^ ext{o} ext{C}. Temperatures outside this range are considered high or low.
Measurement: Using a thermometer. The pH meter also often provides temperature readings. Measurement must be done in the field for accuracy.
pH
Description: A measure of the concentration of ext{H}^+ ions on a logarithmic scale, indicating how acidic or alkaline the water is. Like salinity, organisms are generally adapted to a specific pH range (acidic, neutral, or alkaline).
Wetland Component: The acid, neutral, or alkaline nature of the water.
Process: Primarily determined by the soil type of the wetland's basin (e.g., Bassendean sands typically lead to acidic conditions, while limestone results in alkaline conditions). Photosynthesis can also influence pH.
Wetland Characteristics: Directly influenced by the underlying soil type.
High/Low Indicator:
High/Alkaline: 8-10
Neutral: 7
Low/Acid: 4-6
Measurement: Measured using a pH meter.
pH Scale: An example scale: pH 4 (Acid, associated with humic acids), pH 7 (Neutral), pH 10 (Alkaline, associated with limestone).
Nutrients: Nitrogen (N)
Description: Nitrogen is one of two major inorganic nutrients (the other being phosphorus) that limit plant growth, forming the base of the food chain. Algae utilize inorganic nitrogen forms for growth.
Forms of Nitrogen: Nitrate ( ext{NO}3 ext{-N} ) and Ammonium ( ext{NH}4 ext{-N} ).
Wetland Component: Nitrogen in its nitrate or ammonium form.
Process:
Nitrate ( ext{NO}_3 ext{-N} ): Typically found in aerobic water and often originates from fertilizers, commonly through urban runoff.
Ammonium ( ext{NH}_4 ext{-N} ): Forms in low-oxygen, anaerobic conditions from the breakdown of organic matter (decay).
Wetland Characteristics:
Nitrate ( ext{NO}_3 ext{-N} ): Suggests runoff from gardens or agriculture.
Ammonium ( ext{NH}_4 ext{-N} ): Indicates the presence of significant organic matter (e.g., dead vegetation), low dissolved oxygen, or animal waste.
High/Low Indicator: Relative concentrations are important. Anything greater than 1 ext{ mg/L} is considered high.
Measurement: Using HACH kits, which involve a spectrophotometer to quantify a color change reaction. Note: Nessler's Reagent used in ammonium analysis is toxic, so gloves must be worn.
Nutrients: Phosphorus (P)
Description: Phosphorus is the other major inorganic nutrient limiting plant (and algal) growth. It is primarily utilized by algae in the form of soluble reactive phosphate or orthophosphate ( ext{PO}_4 ext{-P} ).
Wetland Component: Phosphorus.
Process: Phosphate ( ext{PO}_4 ext{-P} ) typically originates from fertilizers, entering water bodies via urban runoff.
Wetland Characteristics: Suggests runoff from gardens or agriculture.
High/Low Indicator: Relative concentrations are important. Anything greater than 1 ext{ mg/L} is considered high.
Measurement: Using HACH kits, involving a spectrophotometer to quantify a color change reaction.
Chlorophyll a
Description: Chlorophyll a is the primary photosynthetic pigment found in plant cells. Its concentration is used to measure the amount of algae present in the water column. It does not measure aquatic plants or fringing vegetation.
Wetland Component: Algae.
Process: High chlorophyll a indicates an algal bloom. This generally occurs due to high nutrient availability (e.g., from fertilizer runoff) combined with high light levels, which promote photosynthesis.
Wetland Characteristics: Found in systems with high nutrient concentrations and ample light.
High/Low Indicator:
0-8 ext{ } ext{µg/L} : Background levels in a natural system.
10-20 ext{ } ext{µg/L} : An algal bloom typical of a natural system.
>100 ext{ } ext{µg/L} : A severe algal bloom ("pea soup"), which rarely occurs without anthropogenic (human-caused) input.
Measurement: Involves extracting chlorophyll a from algal cells using acetone, followed by spectrophotometric measurement of the color. This process requires 24 hours for extraction, so this analysis will be pre-done for the lab session.
Data Sheet and Reasoning for Wetland Choice
Students are required to:
Complete the Data Sheet: Use provided equipment to analyze water samples and ensure every cell on the data sheet is filled before making a decision on the wetland source for each sample.
Provide Reasoning: For each sample, justify the choice of wetland by detailing:
Variable Measured: Specify the water quality variable (e.g., colour, turbidity, conductivity, DO, pH, phosphorus, ammonium-nitrogen, nitrate-nitrogen, or chlorophyll a).
Wetland Component: Describe the ecological aspect of the wetland that the variable represents (e.g., colour = humic substances (tannins and humic acids), turbidity = particulate material, conductivity = salinity).
Characteristic of Wetland: Explain what ecological characteristic of the wetland would result in the observed high or low value for that variable. Relevant characteristics include:
Age and size of the wetland
Location
Exposure (open or sheltered from wind)
Natural or artificial status
Surrounding land use
Runoff and drainage patterns
Soil type
Amount of vegetation and organic matter
Water regime (e.g., dries out seasonally or is flushed)
Human infrastructure (e.g., presence of fountains, taps)
And other relevant factors.
Process: Describe the action or mechanism by which the water quality variable reached its observed state. Examples include photosynthesis, wind-mixing, respiration (especially from bacterial decomposition of organic matter) for dissolved oxygen. This also includes direct human impacts, management actions within the wetland, or changes in land use within its catchment that influenced the outcome.
This structured approach ensures a comprehensive analysis and understanding of the factors influencing water quality in different wetland environments.