Description of Analysis
In this section you will find a brief definition of the Types of Analysis performed in the NMWSC Sediment Lab, as well as any acronyms associated with each analysis.
Suspended-Sediment Concentration (C, CC): The two methods utilized at the NWSC are evaporation and filtration. Filtration is faster than evaporation if the amount of sediment in each sample is not too large. The evaporation method consists of allowing the sediment to settle to the bottom of the sample bottle, decanting the supernatant liquid, washing the sediment into an evaporating dish, and drying it in the oven. The filtration method consists of filtering a decanted sample or the sample in its entirety through a Whatman 934-AH glass microfiber filter. These filters have a nominal particle retention of 1.5 µm. The filtration analysis is not recommended for samples high in clays and typically reserved for lower concentrations. For samples with a low concentration of sediment and high dissolved solids content, a dissolved solids correction may need to be applied at the discretion of the lab.
Sand (SA): If requesting a sand analysis (SA), there are two methods that can be utilized: sieve or VA. Size breakdown for the SA analysis includes % finer at 31.5mm, 16mm, 8mm, 4mm, 2mm, 1mm, 0.5mm, 0.25mm, 0.125mm, 0.0625mm.
VA Tube: The visual accumulation tube method is a fast, economical, and reasonably accurate means of determining the size distribution of a sediment sample in terms of the fundamental hydraulic properties of the particles and the fall velocity or fall diameter. This method is best suited for samples which are primarily composed of sand. Fine material less than 0.053 mm is removed via sieve and can be evaporated, filtered, or analyzed by pipet. Sand in the 1mm and 2mm size class is also sieved prior to using the settling tube. This method is usually applied only when the customer needs a breakdown of sand sizes only (SA), but can be employed in a total size (Z,CZ) request. Breakdown of the following sand sizes are available with the VA method: 0.700mm, 0.500mm, 0.350mm, 0.250mm, 0.175mm, 0.125mm, 0.088mm, 0.0625mm.
Full Size (Z, CZ); pipet: The pipet method is considered the most reliable indirect method for determining particle size gradation of fine material. A pipet is used to withdraw fine sediment at known depths over a period of time. These withdrawals are used to determine the concentration of the cylinder at the predetermined depths as a function of settling time. If full size is requested, sand larger than 0.0625mm is sieved from the sample and further sieved to their respective size classes. If requesting VA sand analysis in place of sieve, please indicate that on the sediment lab analysis request form. We offer the following sizes for sand for full size sieve analysis: 31.5mm, 16mm, 8mm, 4mm, 2mm, 1mm, 0.5mm, 0.25mm, 0.125mm, 0.0625mm. Fine analysis includes the following sizes: 0.031mm, 0.016mm, 0.008mm, 0.004mm, 0.002mm.
Dissolved Solids (DS): A dissolved solids correction may be required when the conductivity as measured in the lab is high and the amount of sediment in the sample makes it impossible to filter. An aliquot of the sample is taken before decanting and dried, then the weight of the dried aliquot is used in a formula to correct the concentration based on the calculated total mass of dissolved solids in the sample. Will be performed as needed and at the discretion of the lab personnel.
Bed and Bank Material Samples (SA or Z): Bed Material samples are dried and ran through a nest of 9-inch sieves. The sieves are run through a ROTAP machine and then they are weighed to provide a size distribution. If the sample have a high content of clay or fine material, a wet sieve may be necessary initially to prevent hardening when dried. If total size is requested for a bank material sample, a wet sieve is usually performed initially. Sand (SA) analysis is typically requested with bed material samples, and the following sizes are provided: 31.5 mm, 16 mm, 8 mm, 4 mm, 2 mm, 1 mm, 0.5 mm, 0.25 mm, 0.125 mm, and 0.063 mm. We can provide a total size breakdown (CZ) to include fines if requested. We are equipped to handle larger samples (up to 5-gallons) if it is primarily sand. If the sample has a high content of fines, we request that the sample be roughly tennis ball sized.
Loss of Ignition (LOI): This type of analysis provides a rapid estimation for the content of water, organic material, carbonate minerals, and siliciclastics & diatoms. Sequential loss on ignition (LOI) is a common and widely used method to estimate the organic and carbonate content of sediments. In a first reaction, organic matter is oxidized at 500-550° C to carbon dioxide and ash. In a second reaction, carbon dioxide is evolved from carbonate at 900-1000° C, leaving oxide. The weight loss during these reactions is easily measured by weighting the samples before and after heating and is closely correlated to the organic matter and carbonate content of the sediment.
Bulk Density: According to the USDA, bulk density is an indicator of soil compaction. It is calculated as the dry weight of the soil divided by its volume. We currently utilize the pycnometer method and results are provided in g/cm3.
Water Potential: Our lab is equipped with a WP4C Water Dewpoint PotentiaMeter. It is a fast, accurate, and reliable way to measure water potential using the chilled-mirror dew point technique.
*The lab offers other types of services which include, but are not limited to quantitative determination, removal of organic matter, and soil moisture content. Please contact us to inquire about any non-typical samples.
The lab is purchasing a laser diffraction analyzer (Beckman Coulter LS 13 320 XR) and has a PARIO+ (digital hydrometer) that we will be performing method verification and validation to add these to standard lab methods, contact us with any questions.