On the visual detection of non-natural records in streamflow time series: challenges and impacts

Large datasets of long-term streamflow measurements are widely used to infer and model hydrological processes. However, streamflow measurements may suffer from what users can consider anomalies, i.e. non-natural records that may be erroneous streamflow values or anthropogenic influences that can lead to misinterpretation of actual hydrological processes. Since identifying anomalies is time consuming for humans, no study has investigated their proportion, temporal distribution, and influence on hydrological indicators over large datasets. This study summarizes the results of a large visual inspection campaign of 674 streamflow time series in France made by 43 evaluators, who were asked to identify anomalies falling under five categories, namely, linear interpolation, drops, noise, point anomalies, and other. We examined the evaluators' individual behaviour in terms of severity and agreement with other evaluators, as well as the temporal distributions of the anomalies and their influence on commonly used hydrological indicators. We found that inter-evaluator agreement was surprisingly low, with an average of 12 % of overlapping periods reported as anomalies. These anomalies were mostly identified as linear interpolation and noise, and they were more frequently reported during the low-flow periods in summer. The impact of cleaning data from the identified anomaly values was higher on low-flow indicators than on high-flow indicators, with change rates lower than 5 % most of the time. We conclude that the identification of anomalies in streamflow time series is highly dependent on the aims and skills of each evaluator, which raises questions about the best practices to adopt for data cleaning.</p

The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats

The Mediterranean Sea is a marine biodiversity hot spot. Here we combined an extensive literature analysis with expert opinions to update publicly available estimates of major taxa in this marine ecosystem and to revise and update several species lists. We also assessed overall spatial and temporal patterns of species diversity and identified major changes and threats. Our results listed approximately 17,000 marine species occurring in the Mediterranean Sea. However, our estimates of marine diversity are still incomplete as yet—undescribed species will be added in the future. Diversity for microbes is substantially underestimated, and the deep-sea areas and portions of the southern and eastern region are still poorly known. In addition, the invasion of alien species is a crucial factor that will continue to change the biodiversity of the Mediterranean, mainly in its eastern basin that can spread rapidly northwards and westwards due to the warming of the Mediterranean Sea. Spatial patterns showed a general decrease in biodiversity from northwestern to southeastern regions following a gradient of production, with some exceptions and caution due to gaps in our knowledge of the biota along the southern and eastern rims. Biodiversity was also generally higher in coastal areas and continental shelves, and decreases with depth. Temporal trends indicated that overexploitation and habitat loss have been the main human drivers of historical changes in biodiversity. At present, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of taxonomic groups. All these impacts are expected to grow in importance in the future, especially climate change and habitat degradation. The spatial identification of hot spots highlighted the ecological importance of most of the western Mediterranean shelves (and in particular, the Strait of Gibraltar and the adjacent Alboran Sea), western African coast, the Adriatic, and the Aegean Sea, which show high concentrations of endangered, threatened, or vulnerable species. The Levantine Basin, severely impacted by the invasion of species, is endangered as well

The Messinian salt of the Mediterranean: geochemical study of the salt from the Central Sicily Basin and comparison with the Lorca basin (Spain)

A geochemical study has been performed on Messinian halite deposits fi om the Central Sicily Basin and the results compared with those published for the Lorca Basin (Spain), in order to provide a depositional model for these marine salt formations and to improve our understanding of the Messinian evaporitic event. Halite samples from boreholes and mine galleries from the Salt Member of the Gessoso Solfifera Formation of the Caltanissetta Basin (Sicily) were studied petrographically and geochemically. The bromine content of halite increases from the base of the Salt Member to the horizons containing kainite (layer B) up to 150 ppm. Upwards, the bromine content decreases and at the top of the member it drops down below 13 ppm. thus reflecting a marked dilution of the mother brine, which resulted in the precipitation of almost bromine-free salt. This dilution has been attributed to the inflow of continental waters in the literature. Fluid inclusion compositions at the top of the unit demonstrate the SO4-rich character of the brine, which is only slightly depleted in SO4 with respect to normal evaporated seawater and shows a significantly Mg and K content, indicating the marine origin of the brine which controlled the final precipitation. This is in agreement with the petrographically well-established primary origin of kainite. In the case of the Saline Unit from the Lorca Basin (SE Spain), bromine profiles are essentially similar to those described above, whereas fluid inclusion compositions at the top of the unit reveal the Mg, K and SO4-poor character of the brine and reflect an inflow of continental waters into the basin which were responsible for final dilution and bromine-free salt precipitation. Thus, in the Lorca basin, which occupied a marginal position in the Mediterranean Basin, dilution and salt reprecipitation at the top of the salt unit occurred when the basin was cut off from the sea and became completely isolated and desiccated. In the Caltanissetta basin, which occupied a relatively more central position, similar saline sediments were formed al the top of the Salt Member as a result of fresh marine waters inputs. Accordingly, in the Sicilian basin, the existing unconformity at the top of the Lower Evaporite Unit does not imply subaerial exposure or complete desiccation of the marine basin. Local tectonism probably controlled the different hydrochemical evolutions of these basins

Anaerobic oxidation of methane in hypersaline Messinian environments revealed by ¹³C-depleted molecular fossils

International audienc

Lithostratigraphic correlation of Messinian evaporites in Lorca and Fortuna basins (Murcia, SE Spain)

The Messinian evaporite formations of Lorca and Fortuna basins may be linked along the exposures developed in the Guadelentín depression. Accordingly, the La Serrata Gypsum unit of the Lorca basin correlates with the "lower evaporite init" of the Fortuna basi

Two modes of gypsum replacement by carbonate and native sulfur in the Lorca Basin, SE Spain

International audienceOrganoclastic sulfate reduction and bacterial sulfide oxidation have been suggested to explain the formation of authigenic carbonate and native sulfur replacing gypsum in the Lorca Basin, Spain. To gain more insight into the nature of this replacement, two types of sulfur-bearing carbonate (laminated and brecciated) from the late Miocene Lorca Basin were studied. Petrographic observations revealed that a sulfur-bearing laminated carbonate consists of clay-rich and dolomite-rich laminae with carbonate and native sulfur pseudomorphs after gypsum. Positive δ 18 O carbonate values in the laminae (δ 18 O = 2.6‰) and lipid biomarkers of halophilic archaea (e.g., extended archaeol) suggest formation under hypersaline conditions. Bacterial sulfate reduction, evidenced by biomarkers such as iso -C 15 , iso -C 16 , and iso -C 17 fatty acids, produced hydrogen sulfide inducing the abiotic formation of organic sulfur compounds. Gypsum in the laminated carbonate likely dissolved due to undersaturation as evidenced by a low content of carbonate-associated sulfate (3,668 ppm) and 34 S-enriched native sulfur (δ 34 S = 22.4‰), reflecting sulfate limitation. Such 34 S-enrichment implies limited fluid flow, which probably restricted the supply of molecular oxygen required for native sulfur formation through oxidation of hydrogen sulfide. Alternatively, sulfate-reducing bacteria may have mediated native sulfur formation directly as a stress response to environmental conditions. The formation of sulfur-bearing calcite in brecciated carbonates is due to post-depositional alteration. Negative δ 18 O values of the calcite (δ 18 O = −1.5‰) and a tenfold decrease in carbonate-associated sulfate content (752 ppm) suggest gypsum dissolution and subsequent calcite precipitation from meteoric water. Relatively 34 S-depleted native sulfur (δ 34 S = 13.1‰) leaves it ambiguous whether meteoric water influx could have supplied sufficient molecular oxygen for oxidation of hydrogen sulfide. In case of the brecciated carbonate, methanogenesis, anaerobic oxidation of methane, and bacterial sulfate reduction apparently mediated the formation of secondary minerals as indicated by 13 C-depleted lipid biomarkers representative for the respective metabolisms. This study reveals that the conditions and timing of gypsum replacement are variable–taking place 1) during or shortly after gypsum deposition or 2) significantly after sedimentation–and suggests that methanogens in addition to anaerobic methanotrophic archaea and sulfate-reducing bacteria may be involved in the mineral-forming processes in the sedimentary subsurface