3/5/2023 0 Comments Morro notsu![]() ![]() ![]() For the same reason, the total CO 2 output was estimated based on both methodologies (GSA and sGs) in order to compare the results and to estimate the total CO 2 flux for the lakes that did not show spatial structure. Therefore, the deterministic method of inverse distance weighting (IDW) was used to interpolate the data and consequently generate CO 2 flux distribution maps for the Patos and Branca lakes’ surveys, considering four and ten neighboring points, respectively. ![]() In addition, their experimental variograms also did not show a spatial structure, thus excluding the use of kriging as an interpolation method. In these latter lakes, the sGs method was excluded considering that (1) the original data did not follow a normal distribution, (2) each survey had less than 100 measurements, and (3) it was not possible to calculate the normal scores. The sGs was applied in the surveys from all the lakes, with the exception of Patos and Branca lakes. All the isotopic analyses were carried out at the Stable Isotope Laboratory of the Estación Biológica Doñana (CSIC) in Spain, using a continuous-flow isotope-ratio mass spectrometry system (Thermo Electron) with a Flash HT Plus elemental analyzer interfaced with a Delta V Advantage mass spectrometer for the determination of δ 13C and a laser spectrometer CRDS (cavity ring down spectroscopy) Picarro L2130-i for the determination of δ 18O and δ 2H. For the analysis of dissolved inorganic carbon (DIC) δ 13C, water samples were collected using the sampling procedure proposed by the International Atomic Energy Agency, while for the samples for δ 18O and δ 2H analyses, the standard procedure described by Clark and Fritz (1997) was followed, and the samples were kept in high-density polyethylene (HDPE) bottles. The presence of a dense macrophyte mass in a few of the lakes appears to enhance the CO 2 flux in these lakes.ĭuring the second survey, which was carried out in three lakes on Flores Island, a collection of samples for isotopic determinations (δ 13C, δ 18O, and δ 2H) was made at the same location as the vertical profiles (P), when the lakes were not under the effect of the thermal stratification process ( Figure 2F–H). CO 2 emissions ranged between 0.18 t d −1 (CE1) and 0.50 t d −1 (CW1) for the Corvo lakes and between 0.03 t d −1 (P1) and 0.32 t d −1 (R2) for the seven lakes studied on Flores Island. Significant differences in the final CO 2 output values were verified between surveys (e.g., 0.16 t d −1 in R1 0.32 t d −1 in R2), and these differences are probably associated with the monomictic character of the lakes. ![]() The results seem to indicate that there is a single source of CO 2 (a biogenic source), which is also supported by the waters’ δ 13C isotopic signatures. In this study, diffuse CO 2 flux measurements were taken using the accumulation chamber method, and statistical analyses utilizing the graphical statistical approach (GSA) and sequential Gaussian simulation (sGs) were conducted on the CO 2 flux data, showing that the CO 2 flux values measured in these lakes were relatively low (0.0–18.6 g m −2 d −1). The lake waters on Corvo and Flores islands are mainly of the Na–Cl type, which is likely caused by the lakes’ sea salt signatures, arising from nearby seawater spraying however, a few samples show evidence of slight alkali earth metal and bicarbonate enrichments in the lake waters, suggesting a contribution of water–rock interaction. This research is of interest in order to determine (1) the overall CO 2 emission from such lakes, as volcanic lakes are often underrepresented in the databases of these water bodies, and (2) the diffuse CO 2 degassing estimates in active volcanic areas such as the Azores. Here, we present the first detailed study on diffuse CO 2 degassing in the lakes in the Western Group (Corvo and Flores islands) of the Azores archipelago. ![]()
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