Estimating Organic and Inorganic Part of Suspended Solids from Sentinel 2 in Different Inland Waters

Abstract

Inland waters are very sensitive ecosystems that are mainly affected by pressures and impacts within their watersheds. One of water’s dominant constituents is the suspended particulate matter that affects the optical properties of water bodies and can be detected from remote sensors. It is important to know their composition since the ecological role they play in water bodies depends on whether they are mostly organic compounds (phytoplankton, decomposition of plant matter, etc.) or inorganic compounds (silt, clay, etc.). Nowadays, the European Space Agency Sentinel-2 mission has outstanding characteristics for measuring inland waters’ biophysical variables. This work developed algorithms that can estimate the total concentration of suspended matter (TSM), differentiating organic from inorganic fractions, through the combined use of Sentinel-2 images with an extensive database obtained from reservoirs, lakes and marshes within eastern zones of the Iberian Peninsula. For this, information from 121 georeferenced samples collected throughout 40 field campaigns over a 4-year period was used. All possible two-band combinations were obtained and correlated with the biophysical variables by fitting linear regression between the field data and bands combination. The results determined that only using bands 705 or 783 lead to the obtaining the amount of total suspended matter and their organic and inorganic fractions, with errors of 10.3%, 14.8% and 12.2%, respectively. Therefore, remote sensing provides information about total suspended matter dynamics and characteristics as well as its spatial and temporal variation, which would help to study its causes.

Towards the Combination of C2RCC Processors for Improving Water Quality Retrieval in Inland and Coastal Areas

“…For the estimation of [TSM], the optimal spectral range is located between 680 and 730 nm [46], and different studies propose to exploit the B705 band, alone or in combination with VIS bands, with which linear relationships have been observed for a wide range of TSM concentrations [41,47,48].…”

The Variability of Surface Chlorophyll-a in Rawa Pening Lake within Five-Month Observations

“…The lake surface turbidity showed a marked variation during investigation period (Figure 3). Low (high) turbidity values correspond to low (high) suspended and dissolved organic and inorganic materials (Alvado et al, 2021). We expected that the trend of turbidity will follow the trends of rainfall as well as surface chlorophylla, however, the turbidity pattern was opposite to both parameters.…”

Measurement of Turbidity and Total Suspended Matter in the Albufera of Valencia Lagoon (Spain) Using Sentinel-2 Images

“…However, as highlighted by Alvado et al [13], based on previous research [36,37], inorganic mineral particles, which have a higher refractive index than organic ones [31], would scatter light more in the NIR, contrary to particulate organic carbon (POC), which would be better estimated with algorithms that include visible bands. In this sense, the explanation that in our case study, the organic particles have obtained such high determination coefficients for the algorithms with the R783 band, so close to the NIR, is also due to the high load of particulate matter present in Albufera, which produces the saturation of the visible bands, in favor of the red-edge and NIR bands.…”

“…Within this framework, Delegido et al [9] obtained an algorithm to estimate turbidity values in nephelometric turbidity units (NTU) from S2 images in reservoirs of the Jucar basin. Subsequently, Alvado et al [13] developed algorithms to estimate [TSS], differentiating particulate inorganic matter (PIM) from organic matter (POM), for different reservoirs in the Ebro and Jucar basins, including points of the marsh surrounding Albufera, but not the lagoon. That study obtained a preliminary equation that we revised now with more data for Albufera lagoon, a hypertrophic shallow lake.…”