Periphyton (aufwuchs) as an indicator of water quality
Dr G.Dussart Canterbury Christ Church University College, Canterbury, Kent CT1 1QU |
Introduction
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What is the periphyton ? (peri = on top of…………phyton = plant).
epipelic | silt and sediment habitats usually in depositional areas with slow current. Algae may form a thin mat that loosely adheres to the surface of the epipelon | suck material from the mud-water interface using an eye-dropper bulb and a disposable pasteur pipette or gently lift algal mat from the surface of the sediment using a knife. |
episammic | sand habitats. | as above |
epilithic | rock or other hard surface habitats including dams, bridge abutments, boat ramps, etc. | scrape or hand-pick material from epilithon in riffles, pools, and runs. |
epidendric | woody habitats. | scrape or hand-pick material from submerged logs, tree roots, drifts, etc. |
epiphytic | usually associated with aquatic mosses, macrophytes, and filamentous algae. | scrape, wring out, hand-pick, or collect the entire substratum. |
epizooic | animal habitats including turtle shells, snail shells, and other macroinvertebrates. | scrape, hand-pick, or collect the entire substratum |
In the river, it is best to focus on the whole community (aufwuchs) on submerged surfaces, including
diatoms | Tabellaria |
desmids | Pediastrum |
dinoflagellates | Xiphophoridium |
filamentous green algae
left Tribonema
right Oedogonium |
………… |
flagellate protista
left Euglena right Chlamydomonas |
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filamentous bacteria | Sphaerotilus |
fungi | Tetracladium |
blue-green algae | Oscillatoria |
protoctistans | Chaos (Amoeba) |
microfauna eg. rotifers | Brachnionis |
Why use the aufwuchs?
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present all year and in most localities
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present even when macroinvertebrates are difficult to find
- taxonomy easy to family level
- sampling is not expensive and easy assessment can be done in the field with a portable microscope
- taxa respond quickly
- community response times are commensurate with needs of monitoring (cf chemistry)
Methods
Sampling
- method depends on purpose
- is there an impact ? – qualitative
- how strong is the impact ? – quantitative or semi quantitative
Auchwuss are in clumped distributions. Therefore, either
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Gomphonema |
From a representative substratum, standard sample is removed from its surface.
Sample preparation
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For diatoms,
- dissolve protoplasm with potassium dichromate (K2CrO4)and 30% hydrogen peroxide (H2O2) to leave frustules
- dry on a glass slide and mounted in Naphrax
- observe under oil immersion
but not usually justified because
- modern diatom taxonomy to species level requires electron microscopy and molecular genetics
- family and genus level is adequate for most monitoring purposes
- dissolving other components such as desmids removes important information
Qualitative approaches
Valency issues (Kolkwitz and Marsson, 1908)
- taxa are given a value
- mathematically manipulated eg. average score per taxon
Palmer (1969) 80 most tolerant algae valencies value to each. Top nine (1= most polluted) are….
- Euglena viridis (95)…green single celled flagellate
- Nizschia palaea (60) …diatom
- Oscillatoria limosa (42) …blue green algae
- Scenedesmus quadricauda (41) …green one-celled
- Oscillatoria tenuis (40) …blue green algae
- Stigeocloneum tenue (34) ..green filamentous
- Synedra ulna (33) …diatom
- Ankistrodesmus falcatus (32) …green one-celled
- Pandorina morum (30) …green multicellular flagellate
Quantitative approaches
- direct analyses by diatometer
- floating artificial substrata (glass slides or plastic bottle) observe directly under a microscope at x400.
- strip-off and homogenise before counting.
- indirect analyses
- chlorophyll; preserve or analyse quickly as chlorophyll degrades to phaeophytin
Data handling
Archibald (1972) compared a range of diversity indices
- Simpson – Margalef – Brillouin
- Menhinick
- Cairns & Dickson
- simple index may not be appropriate. Dussart (1982) used subjective measures of diversity, contamination and productivity on scales of 1-10 to describe water quality status of rivers
- Battarbee et al. (1988) and Dussart (1984) used multivariate techniques to study auchwuss.