Sampling and Data Treatment Methods 1 Sampling Methods in Surface Waters
Sampling Methods in Surface Waters
Munro Mortimer, Jochen F Müller, and Matthias Liess
1.2 General Aspects of Sampling and Sample Handling 5
1.2.6.5 Quality Control in Water Sampling 16
1.3 Sampling Strategies for Different Ecosystems 16
1.3.2.1 Location of Sampling within the Stream 17
1.3.2.2 Description of the Longitudinal Gradient 18
1.3.2.3 Temporal Changes of Water Quality 18
1.3.2.4 Using Sediments to Integrate over Time 19
1.4.2.1 Simple Sampler for Shallow Water 22
1.4.2.2 Sampler for Large Quantities in Shallow Water 22
1.4.2.4 Deepwater Sampler (Not Adding Air to the Sample) 23
1.4.2.5 Deepwater Sampler for Trace Elements (Allowing Air to Mix with the Sample) 23
1.4.3 Systems for Sampling the Benthic Boundary Layer at Different Depths 26
1.4.4.2 Sampling Average Concentrations: Sampling Buoy 26
1.4.4.3 Event-Controlled Sampling of Industrial Short-Term Contamination 27
A U.S Environmental Protection Agency (USEPA) handbook on wastewater sampling, published three decades ago, identifies four critical factors influencing environmental data quality: sample collection, preservation, analysis, and recording It cautions that any misstep in these areas can lead to unreliable data and flawed judgments This guidance remains pertinent today, highlighting that the overall quality of an environmental sampling project is constrained by its weakest link, whether during the sampling or analysis phases.
Advancements in analytical protocols have made sample collection the crucial step in water quality assessment Laboratory results can be rendered invalid if the initial sampling is flawed, as poor design or handling during sampling leads to irreparable errors A recent review highlighted that less than 5% of studies adhered to recognized guidelines for monitoring experimental design, particularly in variable sources of flow and contaminant concentrations This raises concerns about whether observed variations are genuine or merely artifacts of sampling Despite the importance of proper sampling protocols for obtaining reliable data, most research papers devote extensive detail to analytical methods while only briefly addressing sampling methodology, often lacking explicit justification for their chosen protocols.
This chapter aims to explore methods for environmental sampling in surface waters, including lakes, rivers, and marine environments, highlighting its significance amid rising concerns over environmental contamination While conventional solid material sampling methods are not the focus here, a brief discussion on sampling suspended particulates, such as mineral or organic sediments, is included These suspended solids play a crucial role in the behavior of less water-soluble chemicals, like many insecticides, as these substances are dynamically distributed between the suspended particles and the water phase.
Environmental water analysis often relies on selected water samples to infer the overall quality of the water source While consistent quality would simplify this process, such stability is rarely found in reality, as water quality typically varies both spatially and temporally Therefore, careful consideration of the timing and location for sampling is crucial Additionally, since increasing the number of sampling sites and occasions can raise costs, it is essential to determine the minimum number of sampling points needed to obtain the necessary information effectively.
1.4.4.5 Event-Controlled Sampling: Surface Water Runoff from Agricultural
1.4.4.6 Other Considerations Regarding Automatic Sampling Equipment 30
1.4.5.1 Liquid–Liquid Extraction of Large Volumes 32
1.4.6 Concentration of Contaminants in Suspensions and Sediment 39
1.4.6.1 Suspended-Particle Sampler for Small Streams 39
Analyzing a material involves multiple steps, including sampling, storage, preparation, measurement, evaluation, and comparison with standards This chapter focuses on the crucial aspects of sampling strategy, sample storage, and equipment Section 1.2 discusses general sampling design and the characteristics of substances that may impact results, such as degradation and sorption post-collection Section 1.3 provides an overview of sampling strategies tailored to various ecosystems, highlighting the importance of temporal and spatial scaling based on the study's objectives Lastly, Section 1.4 outlines different types of sampling equipment, covering both general and specific methods like deepwater sampling, event-controlled sampling, large-volume sampling, and time-integrated passive sampling techniques.
1.2 General Aspects of Sampling and Sample Handling
Sampling approaches are as varied as chess moves, necessitating a precise definition of the situation to be assessed Choosing an appropriate sampling design based on the temporal and spatial dynamics of the ecosystem is crucial to ensure that samples accurately represent the system This is essential for generating meaningful analytical results Additionally, the handling, preservation, and storage of samples must align with the properties of the chemicals involved, optimizing efforts to gather necessary information within available resources Key considerations for achieving these objectives are outlined in Figure 1.1.
Define time and frequency of sampling
Define objectives and accuracy required
Choose analytical methods, sampling volume
Define sample stabilization and transport
Interpretation on the basis of –assessed accuracy –sampling design (arrows)
FIgure 1.1 Initial considerations for planning and carrying out sampling procedures.
Sampling for quality control in the metal and food industries typically employs statistical methods to ensure that small subsamples accurately represent the entire material In contrast, environmental sampling faces greater spatial variation, particularly due to factors like water currents in marine ecosystems Stratification significantly influences the distribution of contaminants, especially in lakes Therefore, sampling locations must be strategically chosen based on expected contamination sources, such as varying distances from sewage discharge points A comprehensive understanding of the sampling site— including locational coordinates, gradients, depth, water level, and proximity to contamination sources—is essential for designing an effective sampling program.
The timing of environmental sampling is crucial when changes occur rapidly, such as in river systems, which can fluctuate within minutes or hours, or lakes that may change over days or weeks The sampling schedule should align with the anticipated frequency of these environmental changes In governmental wastewater treatment monitoring programs, continuous sampling may be necessary to ensure that regulatory limits are adhered to.
A single sample provides a limited view of the situation, resulting in low reliability and power of the findings, which heavily rely on the available background data and additional information However, a key benefit is that the equipment needed for this type of sampling is typically straightforward and cost-effective.
To effectively monitor environmental changes, it's crucial to align the sampling rate with the expected variation patterns Event-controlled samplers are particularly beneficial for detecting peak concentrations during short-term water quality fluctuations For accurately quantifying contaminant loads, discontinuous sampling systems may be necessary Various discontinuous sampling types, essential for quality control and automatic wastewater sampling in compliance with international standards (ISO 5667-10), are illustrated in Figure 1.2 In time-proportional sampling, identical volume samples are collected at consistent time intervals.
In discharge-proportional sampling, the time intervals are constant but the volume of each sample is
Different types of discontinuous sampling include quantity-proportional sampling, where the volume of each sample remains constant while the temporal resolution is based on the discharge volume Additionally, event-controlled sampling relies on a trigger signal, such as a discharge threshold, to determine sampling intervals These methods ensure that sampling is effectively aligned with varying discharge conditions.
Continuous sampling and analysis are essential for managing complex effluents with unpredictable composition changes that aren't tied to specific variables like discharge or temperature In such cases, automatic sampling and analysis units can be beneficial However, the time and financial investment required for continuous sampling is typically much greater and may not always be justifiable.
A composite sample is created by combining multiple single samples or by aggregating samples collected during an automatic sampling program This type of sample can also be formed by mixing discontinuous samples gathered through various methods previously mentioned and illustrated in Figure 1.2.
The required number of samples varies based on the specific problem being addressed To calculate the necessary sample size for obtaining an average concentration from multiple samples, one can use a general equation to determine the value of N.
The estimate of the standard deviation of the arithmetic mean from all individual samples is represented by S, while x denotes the estimated arithmetic mean of these samples Additionally, d signifies the tolerable uncertainty of the result, which can be exemplified as 20% (d = 0.2).
If peak concentrations are to be quantified, the number of samples depends on the specific problem.