Sampling frequency rivers

Sediment samples should be collected at an appropriate frequency, which will have to be defined on a local basis, taking into account die sedimentation rate in the studied water body and hydrological condidons (e.g. flood events). Typical sampling frequency will vary from once every 1-3 years for large rivers or estuaries that are characterised by high sedimentation rates, to once every 6 years for lakes or coastal areas with very low sedimentation rates. 

Related to the sampling frequency, the Water Framework Directive requires that surveillance monitoring shall be carried out at each monitoring site during one year in the period covered by the river basin management plan. 

Yamane et al.[13] determined cobalt in sea water and river waters with a catalytic spectrophotomeiric method after on-line preconcentration using a column packed with quinolin-8-ol immobilized on silica gel. The tartrate eluate from the preconcentraiion had to pass through a second column packed with a strongly acidic cation exchanger to remove iron(III) and manganese(II) which interfere in the catalytic reaction of oxidation of protocatechuic acid by hydrogen peroxide. An extremely low detection limit of 0.005 /ig 1 was obtained. However, the sampling frequency was less than 2 h . ... 

After an extensive comparison of different cationic dyes and extraction solvents for the FI liquid-liquid extraction spectrophotometric determination of anionic surfactants, Motomitzu et al.[27] recommended the use of Methylene Blue and 1,2-dichlorobenzene. A detection limit of 5 pg 1 was achieved with a sampling frequency of 20 h , and a precision of 0.9% r.s.d. in the analysis of river waters (for details cf. Sec. 8.8.2). 

The most ubiquitous, and also abundant, compounds in the analyzed surface waters were CO, BE, and EPH. On the other hand, HER, 6ACM, and THC were not positively identified in any of the investigated river water samples. The rest of the target analytes, except lysergic compounds, presented the lowest frequency of appearance in this aqueous matrix (see Fig. 2). The levels at which the investigated classes of illicit drugs and metabolites were detected in surface waters are shown in Fig. 6. 

The minimum, maximum, mean, and median m-cresol concentrations for 2 unremarked ambient surface water data points are 16.0, 23.0, 19.5, and 16.0 pg/L (STORET 1989). m-Cresol was detected with a frequency of occurrence of 0.9% in surface water (CLPSD 1988). In addition, m-cresol was listed as a contaminant of the St. Joseph River in the Lake Michigan Basin (Great Lakes Water Quality Board 1983). m-Cresol was detected in freshwater samples from Spirit Lake, Washington, on August 7, 1980 at unreported concentrations (McKnight et al. 1982). 

Fig. 3.14 Square-wave voltammograms of PlGEs modified with sample Cl-12 from abronze mon-tefortino helmet from the Gabriel river valley (Kehn and Ikalesken period) in the Valencian region of Requena, dating back to the Second Iron Age. Electrolyte 0.50 M potassium phosphate buffer, pH 7.0. Potential scan initiated at +650 mV in the negative direction. Potential step increment 4 mV square wave amplitude 25 mV frequency 5 Hz...

For both the Saint-Lawrence River Action Plan (Costan et al., 1993) and the Toyama Bay Japanese (Kusui and Blaise, 1999) studies, the two suites of bioassays employed represented three trophic levels (decomposers, primary producers and primary or secondary consumers), and sought to measure both acute and chronic toxicity. Toxicity tests were selected on the basis of practical and scientific criteria including low sample volume requirement, sensitivity, simplicity of undertaking the assay, ease in maintaining laboratory cultures, cost-effectiveness, procedural reliability and/or frequency of use internationally. 

Tropical storms, typhoons, or hurricanes, depending on their strength and geographical context, often deliver torrential rains. Increased river flow during such high intensity, low frequency rainfall events can transport a major portion of annual river N load to coastal systems. Historically, there has been a paucity of data on such events due to their irregular and extreme nature and the generally manual nature of water sample collection for nutrient analyses. However, with the use of in situ automatic water samplers and nutrient analysis systems, data from such events can now more readily be captured. 

The specific conductance of a water sample provides a simple method to determine the total dissolved ionic solids present in the sample. It is also an inexpensive technique, which lends itself to continuous monitoring of a river or waste stream for the total ion content (Fig. 4.1), and can be easily used to check the accuracy of analyses conducted for specific ions. Specific conductance is measured via a pair of carefully spaced platinum electrodes, which are placed either directly in the stream to be measured or in a sample withdrawn from it [22]. The water temperature should be 25 °C, or the result corrected to this temperature. Voltages in the 12 to 14 range, and frequencies of 60 to 1000 Hz AC are used, plus a Wheatstone bridge circuit to obtain a conductivity reading in xmho/cm or xS/cm (microsiemen/cm). The response obtained is linear with the total ion content over a wide range of concentrations (Fig. 4.1). Examples of the conductance ranges and seasonal variation of some typical Canadian rivers are... 

The water course of the Lippe river can be divided into the more rural upper reaches (sites 19 to 14) and the densely populated and highly industrialised lower reaches (sites 13 to 1). According to the population density, there is an increasing frequency of sewage treatment plants below sampling site 13 (see Fig. 1). Besides there are coal mines as well as numerous industrial plants located in the area of the lower reaches. 

In general, samples may be obtained from faucet outlets, at different points in pipe systems, from the surface of rivers and lake waters, and at different depths. The most important consideration is that the frequency and duration of sampling be sufficient to obtain a representative and reproducible sample. In some cases, composite samples may be used, in which individual samples taken at frequent intervals are combined. 

Levels of organochlorine pesticide found in samples tested by the food inspection authorities during 1985-1989 are summarized in Table 11.7. Samples were collected from food markets throughout the country. Levels of organochlorine pesticide and PCB in foods from markets in Zagreb (1985-1992) and from households in Karlovac along the river Kupa (1987) are listed in Table 11.8. Analysis of a small number of specimens from Karlovac did not indicate any increase in PCB levels following contamination of the river. All samples listed in Table 11.8 contained p,p -DDE and the majority also PCB. The frequency with which p,p -DDE and PCB occurred in samples listed in Tables 11.5—11.7 was not stated. 

Example 3 A fish retailer declared smoked salmon to be wild from salmon captured in a specific river. The food analyst has doubts about this declaration he thinks that the meat is from farmed salmon. In this case reference samples must be collected from salmon captured in the river and from salmon raised on aU farms. After microsatellite analysis, allele frequencies have to be determined and the likelihood has to be calculated whether the salmon can be from the river population or from one of the farm populations. 

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