Suspended matter concentrations in coastal waters: Methodological improvements to quantify individual measurement uncertainty

Abstract

Measurements of total suspended matter (TSM) concentration and the discrimination of the particulate inorganic (PIM) and organic matter fraction by the loss on ignition methods are susceptible to significant and contradictory bias errors by: (a) retention of sea salt in the filter (despite washing with deionized water), and (b) filter material loss during washing and combustion procedures. Several methodological procedures are described to avoid or correct errors associated with these biases but no analysis of the final uncertainty for the overall mass concentration determination has yet been performed. Typically, the exact values of these errors are unknown and can only be estimated. Measurements were performed in coastal and estuarine waters of the German Bight that allowed the individual error for each sample to be determined with respect to a systematic mass offset. This was achieved by using different volumes of the sample and analyzing the mass over volume relationship by linear regression. The results showed that the variation in the mass offset is much larger than expected (mean mass offset: 0.85±0.84 mg, range: -2.4 -7.5 mg) and that it often leads to rather large relative errors even when TSM concentrations were high. Similarly large variations were found for the mass offset for PIM measurements. Correction with a mean offset determined with procedural control filters reduced the maximum error to <60%. The determination errors for the TSM concentration was <40% when three different volume were used, and for the majority of the samples the error was <10%. When six different volumes were used and outliers removed, the error was always <25%, very often errors of only a few percent were obtained. The approach proposed here can determine the individual determination error for each sample, is independent of bias errors, can be used for TSM and PIM determination, and allows individual quality control for samples from coastal and estuarine waters. It should be possible to use the approach in oceanic or fresh water environments as well. The possibility of individual quality control will allow mass-specific optical properties to be determined with better resolved uncertainties and, hence, lower statistical variability, greatly improving our capability to model inherent optical properties of natural particles and its natural variability, e.g. dependence on particle size and the complex refractive index.

Water Constituents and Water Depth Retrieval from Sentinel-2A—A First Evaluation in an Oligotrophic Lake

“…Arriving at an identical match, however, would be credited to mere coincidence rather than a flawless model. We compared two different methods of SPM estimation: in situ data from a gravimetric measurement of a 1 L water sample, and SPM from S2-A radiance values of selected pixels at varying spatial resolutions, i.e., 10-60 m. Gravimetric analyses of SPM contain a variety of uncertainties, such as loss of filter or sample material [86]. Thus, SPM concentrations retrieved from water samples should not be considered absolute.…”

Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany)

“…In addition to absorption, total suspended matter concentration, , was determined in four sets of four filters following the approach of Röttgers et al [35] by filtering different volumes (0.5, 1, 1.5 and 2 l) of lake water through pre-combusted and weighted GF/F filters (Whatman). After drying the filters at 65 °C (1 set of filters) and 105 °C (3 set of filters), their dry weight was measured and filter weights of the empty filters were subtracted.…”

Towards Cost-Effective Operational Monitoring Systems for Complex Waters: Analyzing Small-Scale Coastal Processes with Optical Transmissometry

“…(2014) [44] to reject potential errors associated with salt retention in the filters and loss of materials during washing and combustion [44–45]. Thereby, four different volumes of each water sample (within the range from 0.6 to 2.2 liters) were filtered immediately after collection through pre-weighed Whatman GF/F filters (ø 47 mm).…”

“…Afterwards, the gained mass of each filter was determined by subtracting the weight of the filter from the final weight. A linear regression analysis was performed for filtered volume versus the gained mass, and the regression slope was taken as the TSM concentration value [44]. …”