7.15.1 Introduction
Studies concerning diversity and abundance of hydrobiological groups and environments often indicate changes of the water quality. Very often, all groups must be monitored to understand the changes, but even single groups may indicate certain trends of its environment. Interpretation of the changes requires knowledge of species tolerance and biology.
7.15.2 Methods
A more detailed description is found in Keskitalo and Salonen, 1994. See also ICP Waters manual.
7.15.2.1 Macrozoobenthos
Local circumstances, like depth and bottom consistency, should be taken into consideration when choosing sampling sites. Macrozoobenthos samples are preferably taken from vegetation free soft bottoms of accumulation type. These are often found in the deepest parts of the lake. Distribution of individual sampling may be random or systematic. Chosen sites should be marked to ensure revisits (e.g. buoys).
For sampling macrozoobenthos on soft bottoms a bottom-sampler (of the Ekman type or of similar design) is needed. Apply a weight and a rope to the sampler. Collecting vessels of size 10 - 15 litres with lids and a sieve with 0.5 mm mesh size as well as preservation jars of size 0.5 litre with lids and preservative (96 % ethanol) are other equipments.
Zoobenthos samples are taken at least four times a year to receive a better documentation of time series. First samples in spring are taken shortly after ice breakup in areas with lake freeze-over, not later than end of May. Last samples are taken in September-November. Sampling during extreme cold is not recommended. Also times with strong winds should be avoided.
Lower the grab-sampler vertically, slowly, but steadily to ensure good bottom contact. Lock the sampler and retrieve at a steady pace. Move the sampler over the collection vessel. Take care that the sampler does not leak. Turbid water during retrieval of sampler may indicate leakage.
Record the texture, odour etc. for the sediment if sedimentological research otherwise are omitted. Pour the sample on the sieve carefully in order not to miss any material. Normally the sample is sieved at once.
Sieve with alternating vertical and horizontal movements just beneath the water surface of the vessel. One to three minutes is normally sufficient. Avoid using pressurized water. In tight sediments clumps of clay may remain in the sieved sample.
Move the sieving rest to a preservation container (e.g. a 0.5 l plastic jar) using a spraying bottle containing 96 % ethanol. Remove large animal rests with soft pincers. Wash the sieve before reuse.
7.15.2.2 Chlorophyll α (alpha)
Chlorophyll alpha is determined twice a month in summer, including sampling also in autumn and spring when the production maximum often occurs. Samples are taken with a tube sampler each covering water layers 0 - 1 m, 1 - 2 m, etc. In deep waters thicker layers may be appropriate.
Chlorophyll samples must be filtered on the sampling day. (An absolute limit is the morning of the following day, assuming that the samples have been stored at +4 ºC). The samples (normally 0.1-2 liters) are filtered through glassfibre filters (e.g.Whatman GF/F) with a vacuum < 20 kPa. The filters are dried in darkness, and stored in dark and frozen (at least -20 ºC) if the determination can not take place immediately. Maximum storage time is one month.
Chlorophyll is extracted from the algae by immersing the filter in 94% ethanol. The volume of the extractant (5 - 25 ml) must be known precisely. The extraction is carried out in glass or plastic tubes with air-tight stoppers. The sample tubes are to be placed for five minutes in a 75 ºC water bath so that the sample is completely submerged. The tubes are allowed to cool down to room temperature. If the determination cannot continue immediately, the samples can be kept overnight at +4 ºC protected from light. The absorbance of the centrifuged or filtered extract (glassfibre filters) is measured spectrophoto-metrically at 665 and 750 nm. The blanks are measured with 94% ethanol.
Calculation and expression of the results:
The chlorophyll concentration of the sample is calculated with the formula:
Chl = (A665 - A750 ) x (V1 x 103) / (V2 x L x 83.4)
where:
Chl = chlorophyll alpha concentration of the sample (mg/m3)
V1 = ethanol volume (ml)
A665 = sample absorbance at 665 nm (absorption maximum of chlorophyll α)
A750 = sample absorbance at 750 nm (turbidity) 83.4 = constant; absorption coefficient of chlorophyll α in 94% ethanol
V2 = sample volume filtered (l)
L = cuvette length (cm)
The results are expressed as (CP) mg/m3 (for each depth zone).
7.15.2.3 Planktic activity
Phytoplankton primary production is determined by the acidification and bubbling modification of the radiocarbon method. The sampling frequency should be at least twice a month in summer. Samples are collected into glass bottles with a nontoxic PFTE coated or plastic sampler. Samples are taken from five depths covering illuminated epilimnion as a geometric series, so that the sample density is highest near to the surface.
Radiocarbon solution is injected into the light and dark bottles which are then incubated at the depths of sampling. Two control samples killed in 1 % formaldehyde are incubated near to the surface and at the greatest depth. After 24 h the bottles are taken away and biological activity is stopped by adding 40 % unbuffered formaldehyde to 1 % final concentration in each bottle. Particular care should be taken to minimise the exposure of dark bottles to the light.
Determination of dissolved inorganic carbon is necessary for the calculation of the primary production results. It should be determined with a carbon analyzer on the sampling day.
In the laboratory appropriate subsamples in liquid scintillation vials are acidified with phosphoric acid and put into a vaacum hood for 2 days to exchange inorganic radiocarbon with carbon dioxide in the air. Formaldehyde poisoned control samples are treated similarly. The radioactivity is measured with liquid scintillation counter, using appropriate scintillation liquid/sample water ratio. In the calculation of primary production dark results are substracted from the light ones.
Respiration of plankton is determined by measuring either oxygen consumption or carbon dioxide accumulation in dark bottles. The choice between the methods depends on the methods available and carbon dioxide concentration. Select the method yielding the best sensitivity. Samples are taken as described above, but particular care should be taken to ascertain that the determinations of initial and final concentrations, from which the respiration is calculated as a difference, are made of the same water. This is done by letting water flow from the sampler tube into the bottles through a Y-shaped divider.
Carbon calculations:
- Assimilated inorganic carbon at each sample depth is calculated using the formula:
C = (1.05 x C1) x (Rv_ Rp) / (Rt_ Rk)
where:
C = concentration of assimilated inorganic carbon (mg/m3)
1.05 = rejection coefficient for radiocarbon
C1 = concentration of inorganic carbon in the sample (mg/m3) Rv = radioactivity of the light sample (average of two determinations, dpm or Bq) Rp = activity of the dark sample (dpm or Bq) Rt = radioactivity added to the sample (dpm or Bq) (average of two determinations, calculated to the same volume as Rv, Rp and Rk)
Rk = mean activity of the two control samples (surface, deepest sample) (dpm or Bq)
The results are expressed as assimilated carbon (CINOA) mg C/m3/d (for each analysed depth).
- Carbon dark fixation at each sample depth is calculated using the formula:
Cp = (1.05 x C1) x (Rp - Rk) / (Rt - Rk)
where:
Cp = carbon dark fixation (mg C/m3)
1.05 = rejection coefficient for radiocarbon
C1 = inorganic carbon concentration of the sample (mg/m3)
Rp = radioactivity of the darkened sample (dpm or Bq)
Rk = mean activity of the two control samples (at surface and lowermost depth)(dpm or Bq)
Rt = radioactivity added to the sample (dpm or Bq) (average of two determinations, calculated to the same sample volume as Rp and Rk)
The results are expressed as (CINOD) mg C/m3/d (for each analysed depth).
7.15.3 Data reporting
Chlorophyll α and planktic activity parameters can be reported using the common format for chemical subprogrammes, see Chapter 4, for an example see e.g. subprogramme Lake chemistry, LC.
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Parameters
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list
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unit
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CP
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DB
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chlorophyll alpha
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mg /m3
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CINOA
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IM
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inorganic assimilated carbon
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mg C/m3/d
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CINOD
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IM
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carbon dark fixation
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mg C/m3/d
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O2R
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IM
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respiration
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mg O2/m3/d
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Profundal benthos
Due to the specific nature of the Macrozoobenthos data, these data are recommended to be stored at the National Focal Points, this is partly due to problems in coding the species and the local expertice needed in evaluation of the data. The assessment of these data will be carried out periodically and a special request will be made for the NFPs prior to the assessment.
The data should cover the characteristics of the sampling site and sampling information, species names with specimen density (ind/m2) and biomass (g/m2), and also the Shannon-Wiener diversity index (for calculation, see Annex 7).
7.15.4 References
Keskitalo, J., Salonen, K. Manual for Integrated Monitoring Subprogramme Hydrobiology of Lakes. Publications of the National Board of Waters and the Environment. Series B. Finland, 1994.
ICP Waters Programme manual. Compiled by the the Programme Centre, Norwegian Institute for Water Research. Revised edition, Oslo.
ISO standards: ISO 9391: 1993 (E), ISO 7828-1985 (E)