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