Measurement of Redox potentials in freshwater environments

Technische Universität München Measurement of Redox potentials in freshwater environments Dipl.-Biol. Marco Denic Aquatic Systems Biology Technische ...
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Technische Universität München

Measurement of Redox potentials in freshwater environments Dipl.-Biol. Marco Denic Aquatic Systems Biology Technische Universität München

Technische Universität München

Reasons for monitoring habitat quality:

• Human impacts lead to degradation of freshwater habitats: – – – – –

Water pollution Acidification Channelization River discontinuity High fine sediment input

J. Geist

Technische Universität München

Hohe Gefährdung von Süßwasser-Arten

modifiziert nach „The Nature Conservancy and NatureServe“

Technische Universität München

Definition •

The Redox potential is used to express the tendency of an environment to receive or supply electrons. (Schlesinger 1991)



Measured redox potentials are expressed as the voltage Eh, that is needed to prevent the flow of electrons between the environment and a standard electrode.

 Electric potential between Platinum tip and reference (Ag/AgCl2) is measured via a handheld voltmeter

Technische Universität München

Redox measurement in detail • When oxygen is present, it accepts electrons at the platinum probe: O2 + 4 e- + 4 H+

2 H2 O

• The elctrons are generated at the hydrogen electrode: 2 H2

4 H+ + 4 e-

Technische Universität München

• Redox potential is influenced by – Temperature – pH  Correction and reference for hydrogen electrode with activity of one at 25 °C EH(korr.) = EH – 0,198 x (T – 25) + √50230,214 – 294,67714 x T

Technische Universität München

Applications • Monitoring of industrial waste water • Swimming pool water monitoring • Soil investigation • Freshwater habitat quality

Technische Universität München

Redox potentials in natural environments Redox potential is a measure for the presence of oxygen The more oxygen the higher the redox values -Boundary value 300 mV -O2

NO3-

Mn4+

Fe3+

SO42-

Technische Universität München

Advantages • Direct measurement in free flowing and in interstitial water  No extraction of interstitial water is necessary  Difference between values indicates exchange rates • Redox potentials are more stable than oxygen concentrations • Easy to handle

Technische Universität München

Advantages • Discrimination of suitable and unsuitable pearl mussel habitats

Geist & Auerswald, 2007

Technische Universität München

Potential problems and solutions • Measuring can be time consuming  Use of salt bridge (3 M KCl agarose-gel)  Maintenance with epoxid resin • Impenetrability of hard substrates  Bending of platinum tip

Technische Universität München

Potential problems and solutions • Accretion of substances on platinum tip  Mechanical cleaning • Intoxication of reference electrode by – Sulfides – Cyanides – Ammoniac – Heavy metals

Technische Universität München

Sampling design • Representative site characterization • Search of optimum conditions

X X X

• Timing most adverse conditions

X X X X X X

Technische Universität München

Value interpretation • Low reproducibility of values due to afore mentioned constraints  Deviations of ± 25 mV are considered as normal  For statistical reasons at least 10 replicate measurements per site are recommendable

Technische Universität München

Penetration resistance Measurement of colmation status of substrates

Technische Universität München

Advantages and disadvantages • Very cheap and quick • High number of values in short time • Easy to handle • Investigator dependent

Technische Universität München

Bioindikation • Egg sandwich

Technische Universität München

a) Intact larva successful development b) Dead larva Problems in the larval phase c) Dead egg Problems during egg development d) Empty compartment Filling error / Biological decomposition

Technische Universität München

Advantages and disadvantages • Direct connection of survival rate and abiotic parameters • High flexibility of useable organisms • Reduction of infestation risk between individual eggs/specimen • Filling process is time consuming • Only suitable for stable substrates

Technische Universität München

Thank you for your attention! Contact: Dipl.-Biol. Marco Denic Aquatic Systems Biology Muehlenweg 22 D – 85354 Freising Mail: [email protected] Phone: +49 8161 71 5587