Ecology & Environmental Biology Laboratory Manual: Quantitative Sampling, Limnology & Pedology
Experimental protocols in community phytosociological quadrat sampling (frequency, density, abundance, Shannon-Wiener diversity), mark-release-recapture population estimation (Lincoln-Petersen index), limnological dissolved oxygen and 5-day BOD assays via azide-modified Winkler titration, pedological texture and Walkley-Black soil organic carbon profiling, aquatic primary productivity via light-and-dark bottle incubations, and Secchi extinction trophic profiling aligned with B.Sc., M.Sc., CSIR-NET Unit 10, and GATE EY curricula.
Field Sampling Ethics, Chemical Hygiene & Environmental Protection Protocols
Field ecological investigations and bench limnological/pedological assays require strict compliance with field safety guidelines and chemical hygiene regulations:
- Field Sampling Ethics: When conducting quadrat sampling, minimize trampling of sensitive microhabitats. In mark-recapture exercises, use non-toxic paints (e.g., acrylic enamel or waterproof non-reactive varnishes) that do not hinder animal mobility, thermoregulation, or camouflage.
- Sample Preservation & Fixation: Dissolved oxygen samples must be fixed immediately in situ by adding Manganese Sulfate and Alkali-Iodide-Azide reagent before transport. Prevent introduction of atmospheric air bubbles when stoppering BOD bottles.
- Chemical Hygiene in Wet Oxidation: The Walkley-Black procedure utilizes concentrated Sulfuric Acid ($H_2SO_4$) and Potassium Dichromate ($K_2Cr_2O_7$), a known hexavalent chromium carcinogen. Always dispense inside a certified chemical fume hood wearing neoprene gloves and chemical splash goggles. Neutralize chromium wastes with Ferrous Sulfate before disposal in heavy-metal containers.
- Field Personal Protective Equipment (PPE): Wear high-traction waterproof boots, life jackets during limnological boat deployments, sun-protective clothing, and carry field emergency first-aid kits.
Quadrat Sampling & Phytosociological Community Attributes: Frequency, Density, Abundance, and Shannon-Wiener Diversity ($H’$)
Phytosociology provides the quantitative framework for understanding the floristic structure, dominance hierarchies, and organization of terrestrial plant communities:
- Species-Area Curve: By plotting cumulative species richness against incrementally nested quadrat sizes ($10 times 10text{ cm}$ to $2 times 2text{ m}$), a classic saturation curve emerges. The minimal representative area is identified at the inflection point where a 10% increase in area yields less than a 10% increase in newly added species.
- Raunkiaer’s Law of Frequency: Raunkiaer (1934) classified plant species into five frequency classes based on percentage occurrence: Class A ($1-20%$), Class B ($21-40%$), Class C ($41-60%$), Class D ($61-80%$), and Class E ($81-100%$). In a balanced, undisturbed climax community, species distribution conforms to the formula:
$$A > B > C gtreqless D < E$$ A pronounced spike in Class A reflects the presence of numerous rare or localized species, while Class E highlights well-adapted dominant structural species. - Shannon-Wiener Diversity Index ($H’$): Quantifies community diversity based on information theory entropy:
$$H’ = – sum_{i=1}^{S} p_i ln(p_i)$$
where $p_i = frac{n_i}{N}$ represents the proportional abundance of the $i$-th species. $H’$ incorporates both species richness ($S$) and relative equitability/evenness. - Pielou’s Species Evenness ($J’$):
$$J’ = frac{H’}{H’_{max}} = frac{H’}{ln(S)}$$
Values range from 0 (extreme dominance by a single taxon) to 1.0 (perfectly equal abundance across all species).
- Field Equipment: 1 m × 1 m collapsible wooden/PVC quadrats subdivided with nylon cord into $10 times 10text{ cm}$ grids; measuring tapes (30 m); metal survey pegs and bright flagging tape.
- Taxonomic Tools: Local regional flora keys, hand lenses ($10times$ and $20times$), botanical vasculum/plant press, botanical specimen tags, and field notebook.
- Analytical Hardware: Scientific calculator or statistical spreadsheet software (R / Excel) for matrix transformations.
- Minimal Area Determination: In a representative grassland or forest floor plot, lay nested quadrats starting from $20 times 20text{ cm}$, expanding sequentially to $40 times 40text{ cm}$, $60 times 60text{ cm}$, $80 times 80text{ cm}$, $100 times 100text{ cm}$, and $120 times 120text{ cm}$. Record total new species discovered at each stage. Plot the species-area curve and locate the minimal area plateau (typically $1 text{ m}^2$ for grassland).
- Random Stratified Sampling: Lay at least 10 to 15 replicates of the $1text{ m} times 1text{ m}$ quadrat across the study site using random coordinate generation.
- Floristic Census: Within each quadrat, identify all angiosperm species. Count and record the exact number of individuals ($n_i$) belonging to each species.
- Attribute Calculations:
• $text{Frequency } (%) = left(frac{text{Number of quadrats in which species occurs}}{text{Total number of quadrats sampled}}right) times 100$
• $text{Density } (D) = frac{text{Total number of individuals of species across all quadrats}}{text{Total number of quadrats sampled}}$
• $text{Abundance } (A) = frac{text{Total number of individuals of species across all quadrats}}{text{Number of quadrats in which species occurs}}$ - Relative Attributes & IVI: Compute Relative Frequency ($RF$), Relative Density ($RD$), and Relative Dominance ($RDo$). Sum them to yield the Importance Value Index ($text{IVI} = RF + RD + RDo$, out of 300).
- Diversity Indices: Determine total community individuals $N = sum n_i$. Compute $p_i = n_i / N$, $ln(p_i)$, and calculate $H’$, $J’$, and Simpson’s dominance index $D_s$.
| Species | Quadrats Present (of 10) | Total Indiv ($n_i$) | Frequency (%) | $p_i$ | $ln(p_i)$ | $-p_i ln(p_i)$ |
|---|---|---|---|---|---|---|
| Cynodon dactylon (Poaceae) | 10 | 85 | 100% (Class E) | 0.472 | -0.751 | 0.354 |
| Tridax procumbens (Asteraceae) | 6 | 42 | 60% (Class C) | 0.233 | -1.457 | 0.339 |
| Parthenium hysterophorus (Asteraceae) | 4 | 28 | 40% (Class B) | 0.156 | -1.858 | 0.290 |
| Oxalis corniculata (Oxalidaceae) | 3 | 15 | 30% (Class B) | 0.083 | -2.489 | 0.207 |
| Euphorbia hirta (Euphorbiaceae) | 2 | 10 | 20% (Class A) | 0.056 | -2.882 | 0.161 |
| Total ($S=5$) | – | $N = 180$ | – | 1.000 | – | $H’ = 1.351$ |
Evenness: $J’ = frac{1.351}{ln(5)} = frac{1.351}{1.609} = 0.840$ (Indicating high community equitability).
Population Size Estimation via Mark-Release-Recapture: Lincoln-Petersen Index & Bailey’s Correction
Determining animal population density cannot rely on total censuses for vagile organisms. The mark-release-recapture (MRR) framework assumes that the proportion of marked animals in a second sample equals the proportion of marked animals in the total population:
- Lincoln-Petersen Equation:
$$frac{m}{n} = frac{M}{N} implies hat{N} = frac{M cdot n}{m}$$
where $M$ is the number of individuals marked and released in Sample 1, $n$ is the total number of individuals captured in Sample 2, and $m$ is the number of previously marked recaptures in Sample 2. - Bailey’s Correction for Small Recaptures: The standard Lincoln-Petersen estimator is positively biased when sample sizes or recapture rates are low ($m < 10$). Bailey (1951) introduced the nearly unbiased estimator: $$hat{N}_{text{Bailey}} = frac{M(n + 1)}{m + 1}$$
- Variance & Confidence Limits:
$$operatorname{Var}(hat{N}) = frac{M^2 cdot (n + 1)(n – m)}{(m + 1)^2 (m + 2)}$$
The 95% Confidence Interval is given by: $hat{N} pm 1.96 cdot sqrt{operatorname{Var}(hat{N})}$.
- Field Trial (e.g., Tenebrionid Beetles / Snails): Pitfall traps with non-toxic collection funnels; quick-drying, waterproof, non-odorous cellulose paint markers (white or fluorescent red); fine point brushes; sorting trays.
- Bench Simulation Alternative: Large opaque mixing bin containing 500-1000 identical white plastic beads/beans representing the unknown population; permanent colored marking pens; sampling scoop.
- Sample 1 Capture & Tagging: Draw a random sample of $M$ individuals (e.g., $M = 50$ beetles from pitfall traps or beads from the container). Apply a discrete dot of waterproof paint onto the dorsal elytron or bead surface. Record the exact number $M$.
- Release & Random Mixing: Release all marked individuals back into their habitat/bin. Allow sufficient time ($Delta t = 24-48text{ h}$ in the field, or thorough hand-stirring in simulation) to ensure completely homogeneous random redistribution throughout the population.
- Sample 2 Recapture: Take a second random sample without replacement. Count the total number of individuals captured ($n$, e.g., $n = 45$).
- Recapture Tally: Inspect each individual in Sample 2 for paint marks. Record the number of marked recaptures ($m$).
- Statistical Calculation: Compute $hat{N}$ using both the standard Lincoln-Petersen formula and Bailey’s modification. Calculate variance and 95% confidence intervals.
Given Data: $M = 60$, $n = 50$, $m = 12$.
Lincoln-Petersen Estimate: $hat{N} = frac{60 times 50}{12} = 250text{ individuals}$.
Bailey’s Corrected Estimate: $hat{N}_{text{Bailey}} = frac{60 times (50 + 1)}{12 + 1} = frac{60 times 51}{13} = 235.4 approx 235text{ individuals}$.
Variance: $operatorname{Var}(hat{N}) = frac{3600 times 51 times 38}{169 times 14} = frac{6,976,800}{2366} approx 2948.7$.
Standard Error: $text{SE} = sqrt{2948.7} = 54.3$.
95% CI: $235 pm (1.96 times 54.3) = [128.6, 341.4]$.
Limnological Analysis: Dissolved Oxygen (DO) & Biological Oxygen Demand ($text{BOD}_5$) via Azide-Modified Winkler Titration
Dissolved oxygen is the master limnological variable governing aquatic aerobic metabolism. The azide modification suppresses interference from nitrites ($NO_2^-$), which otherwise catalyze false iodine liberation:
- Oxygen Fixation: Manganese Sulfate ($MnSO_4$) reacts with Sodium Hydroxide ($NaOH$) in the presence of dissolved $O_2$ to form an oxidized brown basic manganic oxide precipitate:
$$2MnSO_4 + 4NaOH + O_2 longrightarrow 2MnO(OH)_2downarrow + 2Na_2SO_4$$
In the absence of oxygen, a white precipitate of pure manganous hydroxide ($Mn(OH)_2$) forms. - Acidification & Iodine Liberation: Adding concentrated $H_2SO_4$ dissolves the precipitate, reducing $Mn^{4+}$ back to $Mn^{2+}$ while quantitatively oxidizing iodide ($I^-$) to free elemental iodine ($I_2$):
$$MnO(OH)_2 + 2KI + 2H_2SO_4 longrightarrow MnSO_4 + I_2 + K_2SO_4 + 3H_2O$$ - Thiosulfate Titration: The liberated iodine is titrated against standard Sodium Thiosulfate ($0.025text{ N } Na_2S_2O_3$) with a starch indicator (turning from intense blue-black to crystal clear):
$$2Na_2S_2O_3 + I_2 longrightarrow Na_2S_4O_6 + 2NaI$$
Because $1text{ mL of } 0.025text{ N } Na_2S_2O_3 equiv 0.2text{ mg } O_2$, titrating a $200text{ mL}$ aliquot gives:
$$text{DO (mg/L)} = frac{V_{text{titrant}} times N_{text{thiosulfate}} times 8 times 1000}{V_{text{sample aliquot}}}$$ - Biochemical Oxygen Demand ($text{BOD}_5$): Reflects the amount of oxygen utilized by heterotrophic microorganisms to aerobically decompose organic matter over 5 days at 20°C in total darkness:
$$text{BOD}_5text{ (mg/L)} = (text{DO}_{text{initial}} – text{DO}_{text{day 5}}) times text{Dilution Factor}$$
- Reagents: Manganese Sulfate solution ($480text{ g } MnSO_4cdot 4H_2O / text{L}$); Alkali-Iodide-Azide reagent ($500text{ g } NaOH + 150text{ g } KI + 10text{ g } NaN_3 / text{L}$); Concentrated Sulfuric Acid ($H_2SO_4$, sp. gr. 1.84); $0.025text{ N}$ Standard Sodium Thiosulfate ($Na_2S_2O_3cdot 5H_2O$); freshly prepared 1% soluble starch indicator solution.
- Apparatus: 300 mL ground-glass stoppered BOD bottles; automatic burette (50 mL, 0.1 mL precision); volumetric pipettes (1 mL, 2 mL); BOD refrigerated incubator calibrated at $20 pm 1^circtext{C}$.
- Sample Collection & Initial Fixation: Fill a 300 mL BOD bottle underwater without creating turbulence or bubbles. Immediately insert pipette below liquid surface and add $2text{ mL}$ Manganese Sulfate followed by $2text{ mL}$ Alkali-Iodide-Azide. Stopper securely, avoiding trapped air bubbles, and invert 15 times. Allow brown flocculent precipitate to settle past the upper third.
- Acidification: Add $2text{ mL}$ concentrated $H_2SO_4$ down the neck of the bottle. Re-stopper and invert vigorously until all precipitate completely dissolves into a clear golden-brown iodine solution.
- Titration: Transfer exactly $203text{ mL}$ (accounting for $4text{ mL}$ reagent displacement in a $300text{ mL}$ bottle, giving an effective $200text{ mL}$ sample) into an Erlenmeyer flask. Titrate with $0.025text{ N } Na_2S_2O_3$ until pale straw-yellow. Add $1-2text{ mL}$ starch indicator (turns deep blue-black). Continue dropwise titration to the persistent colorless endpoint. Record $V_1$.
- BOD5 Setup: Prepare a duplicate BOD bottle with the sample (or diluted sample if treating wastewater). Incubate in the dark at $20^circtext{C}$ for exactly 5 days. On Day 5, fix and titrate to determine $text{DO}_{text{day 5}}$.
Unpolluted Lake Sample: Initial DO = $8.2text{ mg/L}$, Day 5 DO = $6.8text{ mg/L}$ (No dilution).
$text{BOD}_5 = 8.2 – 6.8 = 1.4text{ mg/L}$ (Prisinte, oligotrophic / Class A standard).
Municipal Drain Outfall: 1:20 dilution ($15text{ mL}$ effluent in $300text{ mL}$ aerated blank).
Initial DO = $8.0text{ mg/L}$, Day 5 DO = $2.4text{ mg/L}$.
$text{BOD}_5 = (8.0 – 2.4) times 20 = 112text{ mg/L}$ (Heavy organic sewage pollution, requiring wastewater treatment).
Pedological Analysis: Soil Texture by Sieve/Hydrometer & Walkley-Black Wet Oxidation for Soil Organic Matter
Soil physics and biogeochemistry determine primary productivity, microbial respiration, cation exchange capacity (CEC), and water retention in terrestrial ecosystems:
- Soil Textural Fractions: The USDA separates mineral soil particles into Sand ($0.05 – 2.0text{ mm}$), Silt ($0.002 – 0.05text{ mm}$), and Clay ($< 0.002text{ mm}$). Settling velocity in an aqueous suspension follows Stokes' Law: $$v = frac{2}{9} frac{(rho_s - rho_f) g r^2}{eta}$$ where coarse sand particles settle within 40 seconds, silt within 2 hours, and colloidal clay remains suspended.
- Walkley-Black Wet Dichromate Oxidation: Readily oxidizable organic carbon in dry soil is digested by Potassium Dichromate ($K_2Cr_2O_7$) in concentrated $H_2SO_4$:
$$2Cr_2O_7^{2-} + 3C^0 + 16H^+ longrightarrow 4Cr^{3+} + 3CO_2uparrow + 8H_2O$$
Unreacted excess dichromate ($Cr_2O_7^{2-}$, orange) is back-titrated against standard Ferrous Ammonium Sulfate (FAS, $0.5text{ N } Fe(NH_4)_2(SO_4)_2cdot 6H_2O$) using ferroin (1,10-phenanthroline ferrous sulfate) indicator:
$$Cr_2O_7^{2-} + 6Fe^{2+} + 14H^+ longrightarrow 2Cr^{3+} + 6Fe^{3+} + 7H_2O$$
The endpoint transition is sharp: from bluish-green ($Cr^{3+}$) to chocolate/wine-red. - Van Bemmelen Factor: Because soil organic matter contains on average 58% organic carbon, % SOM is derived via the conversion factor $1.724$:
$$% text{SOM} = % text{SOC} times 1.724$$
- Texture Analysis: Set of calibrated standard soil test sieves ($2.0text{ mm}$, $0.5text{ mm}$, $0.25text{ mm}$, $0.05text{ mm}$); Bouyoucos hydrometer ($152text{ H}$); sodium hexametaphosphate dispersing agent ($5%$).
- Walkley-Black Reagents: $1text{ N Potassium Dichromate } (K_2Cr_2O_7)$; concentrated Sulfuric Acid ($H_2SO_4$, $98%$); $0.5text{ N Ferrous Ammonium Sulfate } (FAS)$; Orthophosphoric acid ($85% H_3PO_4$); Ferroin indicator ($1.485text{ g 1,10-phenanthroline monohydrate} + 0.695text{ g } FeSO_4cdot 7H_2O / 100text{ mL}$).
- Soil Sample Preparation: Air-dry freshly collected surface soil ($0-15text{ cm}$ core) for 48 hours. Crush peds with a wooden pestle and pass through a 2 mm stainless steel sieve to remove gravel and root fragments. For Walkley-Black analysis, grind a sub-sample to pass a 0.2 mm (100-mesh) sieve.
- Hydrometer Texture Sinking: Disperse 50 g dry soil in 100 mL of 5% sodium hexametaphosphate for 10 minutes in a high-speed mixer. Transfer to a 1000 mL cylinder, fill to the mark with distilled water. Invert 30 times. Take hydrometer and temperature readings at 40 seconds (sand settled) and 2 hours (silt settled). Calculate percentages of Sand, Silt, and Clay. Plot on the USDA triangle.
- Walkley-Black Digestion: Weigh accurately $1.00text{ g}$ of 0.2 mm sieved soil into a 500 mL Erlenmeyer flask. Add exactly $10.0text{ mL}$ of $1text{ N } K_2Cr_2O_7$ via volumetric pipette. Swirl gently. Rapidly add $20.0text{ mL}$ of concentrated $H_2SO_4$. Swirl for 1 minute and allow the flask to stand undisturbed on an asbestos mat for 30 minutes to complete spontaneous exothermic oxidation.
- Titration: Dilute with $200text{ mL}$ distilled water. Add $10text{ mL}$ of $85% H_3PO_4$ (to complex $Fe^{3+}$ ions and sharpen the color change) and $1text{ mL}$ ferroin indicator. Titrate with $0.5text{ N FAS}$ until the greenish cast flashes suddenly to a bright wine-red. Run a blank without soil simultaneously.
Textural Fractions: Sand = 42%, Silt = 36%, Clay = 22%.
USDA Classification:Loam (Ideal agricultural soil with optimal water holding capacity and aeration).
Walkley-Black Titration Data:
$V_{text{blank}} = 21.4text{ mL FAS}$, $V_{text{sample}} = 14.8text{ mL FAS}$, Normality of FAS = $0.512text{ N}$, Soil Weight = $1.00text{ g}$.
$$% text{SOC} = frac{(21.4 – 14.8) times 0.512 times 0.003 times 100 times 1.3}{1.00} = 1.318%$$
$$% text{SOM} = 1.318% times 1.724 = 2.27%$$
Ecological Assessment: Moderately fertile grassland soil capable of sustaining active microbial decomposition and nitrogen mineralization.
Aquatic Primary Productivity via Light and Dark Bottle Technique (Gaarder & Gran)
Autotrophic aquatic organisms (phytoplankton, periphyton, and cyanobacteria) drive energy flow in lakes and oceans. Gaarder and Gran developed the light and dark bottle method to isolate photosynthetic oxygen evolution from community respiratory demand:
- Light Bottle (LB): Transmits ambient solar photosynthetically active radiation (PAR, $400-700text{ nm}$). Within this bottle, simultaneous photosynthesis ($P$) and community respiration ($R$) occur. The change in DO relative to initial concentration reflects Net Primary Productivity:
$$text{NPP} = frac{text{DO}_{text{light}} – text{DO}_{text{initial}}}{Delta t}$$ - Dark Bottle (DB): Coated with opaque black enamel or wrapped in thick light-impenetrable aluminum foil. In complete darkness, photosynthesis is zero ($P = 0$), so oxygen decline measures total community respiration ($R$):
$$R = frac{text{DO}_{text{initial}} – text{DO}_{text{dark}}}{Delta t}$$ - Gross Primary Productivity (GPP): Represents the total photochemical rate of photosynthetic oxygen production before respiratory losses:
$$text{GPP} = text{NPP} + R = frac{text{DO}_{text{light}} – text{DO}_{text{dark}}}{Delta t}$$ - Compensation Depth ($Z_c$): The depth in the water column where photosynthetic carbon assimilation equals respiratory expenditure ($text{GPP} = R implies text{NPP} = 0$). Occurs typically where irradiance falls to $sim 1%$ of subsurface intensity.
- Incubation Vessels: Triplicate sets of 300 mL clear glass BOD bottles (Light Bottles) and light-shielded opaque black bottles (Dark Bottles).
- Suspension Apparatus: Calibrated depth lines with cross-arms and float buoys to suspend bottles horizontally at depths of $0.2text{ m}$, $0.5text{ m}$, $1.0text{ m}$, and $2.0text{ m}$.
- Analytical Equipment: Winkler titration reagents or optical dissolved oxygen meter with submersible polarographic/luminescent sensor.
- Water Sampling: Collect an integrated water sample from the limnetic zone using a Kemmerer or Van Dorn sampler. Fill three identical 300 mL BOD bottles: Initial Bottle (IB), Light Bottle (LB), and Dark Bottle (DB), taking precautions to avoid aeration.
- Immediate Initial Fixation: Fix the Initial Bottle immediately on the boat with Winkler reagents and place in the dark.
- In Situ Incubation: Suspend the Light Bottle and Dark Bottle horizontally at the sampling depth for an incubation period of $Delta t = 4-6text{ hours}$ over peak daylight (10:00 AM to 3:00 PM).
- Termination & Titration: Retrieve the bottles. Immediately fix the contents with Winkler reagents. Titrate IB, LB, and DB aliquots against $0.025text{ N Sodium Thiosulfate}$.
- Mathematical Computation: Calculate NPP, $R$, and GPP in $text{mg } O_2/text{L/hr}$. Convert to carbon assimilation using the photosynthetic quotient ($PQ approx 1.2$):
$$text{mg C/m}^3text{/hr} = text{GPP (mg } O_2text{/L/hr)} times left(frac{12}{32}right) times left(frac{1}{1.2}right) times 1000$$
Incubation Parameters: Depth = $0.5text{ m}$, Incubation Duration = 4.0 hours.
• Initial Bottle DO ($text{DO}_{text{initial}}$) = $7.40text{ mg/L}$
• Light Bottle DO ($text{DO}_{text{light}}$) = $9.60text{ mg/L}$
• Dark Bottle DO ($text{DO}_{text{dark}}$) = $6.20text{ mg/L}$
Results:
• $text{NPP} = frac{9.60 – 7.40}{4.0} = 0.550text{ mg } O_2text{/L/hr}$
• $R = frac{7.40 – 6.20}{4.0} = 0.300text{ mg } O_2text{/L/hr}$
• $text{GPP} = frac{9.60 – 6.20}{4.0} = 0.850text{ mg } O_2text{/L/hr}$
• Carbon Fixed: $0.850 times 0.375 times 0.833 times 1000 = 265.5text{ mg C/m}^3text{/hr}$ (Typical mesotrophic lake productivity).
Ecosystem Physicochemical Profiling: Water Transparency (Secchi Disc Depth & Carlson’s TSI), pH, Conductivity & TDS
Water transparency integrates suspended mineral particulates, organic detritus, and phytoplankton biomass:
- Secchi Depth ($Z_{sd}$): The vanishing depth of a 20 cm circular plate divided into alternating black and white quadrants. Reflects the diffuse attenuation of visible solar radiation.
- Euphotic Zone Depth ($Z_{eu}$): The photic depth where downwelling irradiance drops to 1% of surface values. Empirically related to Secchi depth by:
$$Z_{eu} approx 2.7 times Z_{sd} quad (text{or } 2.5 – 3.0 times Z_{sd})$$ - Poole-Atkins Extinction Coefficient ($k$):
$$k = frac{1.7}{Z_{sd}}$$ - Carlson’s Trophic State Index (TSI): Carlson (1977) formulated a continuous numerical scale (0 to 100) based on algal biomass:
$$text{TSI(SD)} = 60 – 14.41 ln(Z_{sd} text{ in meters})$$
• $text{TSI} < 40$: Oligotrophic (Clear water, deep photic zone, low productivity).
• $text{TSI } 40 – 50$: Mesotrophic (Moderately clear, intermediate nutrient load).
• $text{TSI } 50 – 70$: Eutrophic (Frequent cyanobacterial blooms, shallow Secchi depth).
• $text{TSI} > 70$: Hypereutrophic (Severe scum, nocturnal anoxia, low biodiversity).
- Optical Tools: Standard 20 cm alternating black/white Secchi disc with non-stretch calibrated nylon lanyard marked at 0.1 m intervals and brass sounding weight; viewing tube (aquascope) to eliminate surface glare.
- Electronic Probes: Portable multi-parameter digital meter calibrated with pH 4.01, 7.00, and 9.21 buffers, and conductivity standards ($1413 mutext{S/cm}$ KCl).
- Secchi Disc Deployment: Lower the Secchi disc vertically on the shaded (leeward) side of the boat between 10:00 AM and 2:00 PM without wearing polarized sunglasses.
- Vanishing & Reappearance Depths: Note the exact depth $d_1$ at which the disc just disappears from view. Lower an additional 0.5 m, then slowly raise it until the white quadrants just reappear ($d_2$). The true Secchi depth is: $Z_{sd} = frac{d_1 + d_2}{2}$.
- Calculations: Compute euphotic zone depth $Z_{eu}$, extinction coefficient $k$, and Carlson’s $text{TSI(SD)}$.
- Physicochemical Profiling: Immerse calibrated probe sensors at $0.5text{ m}$ depth. Record temperature, pH, electrical conductivity ($mutext{S/cm}$), and Total Dissolved Solids ($text{mg/L}$).
| Parameter | Oligotrophic Lake Site | Urban Eutrophic Pond Site |
|---|---|---|
| Secchi Depth ($Z_{sd}$) | $4.50text{ m}$ | $0.65text{ m}$ |
| Euphotic Zone Depth ($Z_{eu}$) | $12.15text{ m}$ | $1.75text{ m}$ |
| Attenuation Coeff ($k$) | $0.378text{ m}^{-1}$ | $2.615text{ m}^{-1}$ |
| Carlson’s $text{TSI(SD)}$ | $mathbf{38.3}text{ (Oligotrophic)}$ | $mathbf{66.2}text{ (Eutrophic)}$ |
| Field pH | 7.42 | 8.85 (High photosynthetic $CO_2$ drawdown) |
| Conductivity / TDS | $115 mutext{S/cm}$ ($75text{ mg/L}$) | $680 mutext{S/cm}$ ($442text{ mg/L}$) |
Comprehensive Practical Viva-Voce Examination & Ecological Assessment Bank
Essential questions testing conceptual understanding of community phytosociology, population demography, limnological DO/BOD stoichiometry, pedological wet oxidation, bioenergetics, and trophic index profiling:
Ans: The smallest plot area that adequately represents the floristic composition and species richness of a community. It is determined using a species-area curve at the point of flattening where additional area yields minimal new species.
Ans: Raunkiaer stated that in a normal undisturbed plant community: A > B > C >= D < E. Class A consists of numerous rare species, while Class E contains widespread dominant climax species.
Ans: Shannon-Wiener (H’) is an information-theoretic index sensitive to species richness and rare taxa. Simpson’s Index emphasizes dominance and common species.
Ans: IVI reflects the overall ecological importance and structural contribution of a plant species in a community. It is calculated by summing Relative Frequency (RF), Relative Density (RD), and Relative Dominance (RDo) (Total IVI = 300).
Ans: 1. Closed population (no births, deaths, immigration, emigration); 2. Equal catchability of marked and unmarked animals; 3. Marks are permanent and do not affect survival or recapture probability; 4. Sufficient time for random mixing.
Ans: The standard Lincoln-Petersen index exhibits severe positive bias when recaptures (m) are small (m < 10). Bailey's correction provides an unbiased estimator: N = M(n + 1) / (m + 1).
Ans: Sodium azide destroys nitrites (NO2-), preventing them from reacting with iodide to produce false positive iodine release in wastewater or polluted streams.
Ans: Manganic basic oxide, MnO(OH)2 (or MnO2·H2O), formed when dissolved oxygen oxidizes manganous hydroxide under alkaline conditions.
Ans: To prevent photosynthetic oxygen evolution by autotrophic algae, ensuring that only heterotrophic microbial respiratory consumption of oxygen is measured.
Ans: A mathematical model describing the balance between microbial deoxygenation (BOD exertion) and atmospheric reaeration downstream of an organic sewage discharge, showing an initial DO drop to a critical deficit followed by gradual recovery.
Ans: Sand: 0.05 to 2.0 mm; Silt: 0.002 to 0.05 mm; Clay: < 0.002 mm (< 2 micrometers).
Ans: The rapid addition generates intense exothermic heat of dilution (reaching ~120°C), which provides the thermal activation energy required to oxidize organic carbon without external heating.
Ans: It complexes ferric ions (Fe3+) formed during oxidation, removing their yellowish coloration and decreasing the redox potential of the Fe3+/Fe2+ system, resulting in a razor-sharp ferroin endpoint.
Ans: The factor 1.724 is used to convert Soil Organic Carbon (SOC) to Soil Organic Matter (SOM) based on the empirical observation that soil organic matter contains approximately 58% organic carbon (100 / 58 = 1.724).
Ans: In the Light bottle, photosynthesis produces O2 while respiration consumes O2 (Net = P – R). In the Dark bottle, only respiration consumes O2 (-R). Adding the two changes cancels out respiration, yielding total photochemical Gross Primary Productivity.
Ans: The depth in the water column where gross photosynthetic rate equals the community respiration rate (GPP = R), resulting in zero net primary production (NPP = 0).
Ans: Euphotic zone depth (Zeu) is approximately 2.7 times the Secchi disc transparency depth (Zsd), representing the depth where downwelling irradiance is 1% of surface irradiance.
Ans: A continuous numerical scale (0 to 100) classifying lake trophic status based on Secchi depth, chlorophyll-a, and total phosphorus. Values > 50 denote eutrophic conditions with high nutrient loading and frequent algal blooms.
Ans: Intense phytoplankton photosynthesis rapidly consumes dissolved carbon dioxide (CO2) and carbonic acid, shifting bicarbonate/carbonate equilibria and driving pH alkaline (often > 8.5-9.0).
Ans: Oligotrophic lakes maintain high dissolved oxygen throughout the hypolimnion due to low organic sedimentation. Eutrophic lakes experience severe hypolimnetic anoxia/hypoxia due to massive microbial decomposition of settling algal blooms.
Explore Theoretical Ecology & Environmental Systems
Connect quantitative sampling findings, limnological bioenergetics, and pedological dynamics with population dynamics, community succession, and biogeochemistry modules.
