Geochemical Markers as a Tool for the Characterization of a Multi-Layer Urban Aquifer: The Case Study of Como (Northern Italy)

The analysis of geochemical markers is a known valid tool to explore the water sources and understand the main factors affecting natural water quality, which are known issues of interest in environmental science. This study reports the application of geochemical markers to characterize and understand the recharge areas of the multi-layer urban aquifer of Como city (northern Italy). This area presents a perfect case study to test geochemical markers: The hydrogeological setting is affected by a layered karst and fractured aquifer in bedrock, a phreatic aquifer hosted in Holocene sediments and connected with a large freshwater body (Lake Como); the aquifers recharge areas and the water geochemistry are unknown; the possible effect of the tectonic setting on water flow was overlooked. In total, 37 water samples were collected including water from two stacked aquifers and surface water to characterize hydrochemical features. Moreover, six sediment samples in the recent palustrine deposits of the Como subsurface were collected from cores and analyzed to understand the main geochemistry and mineralogy of the hosting material. The chemical analyses of water allow to observe a remarkable difference between the shallow and deep aquifers of the study area, highlighting different recharge areas, as well as a different permanence time in the aquifers. The sediment geochemistry, moreover, confirms the differences in trace elements derived from sediment-water interaction in the aquifers. Finally, an anomalous concentration of As in the Como deep aquifer was observed, suggesting the need of more detailed analyses to understand the origin of this element in water. This study confirms the potentials of geochemical markers to characterize main factors affecting natural water quality, as well as a tool for the reconstruction of recharge areas.

Polyarene analysis-based identification of natural and technogenic processes in underground hydrosphere

The purpose of the study is to analyze the possibility to identify the pollution genesis of the underground hydrosphere based on the data on polyarenes as geochemical markers. Their marker role is due to their toxicity, persistence and confinement to specific pollution sources and natural and technogenic processes. The main research method is the analysis of indicator ratios of polyarenes. The object of research is groundwater from different regions of the world, which are polluted by natural and anthropogenic polyarenes. The main directions of domestic and foreign researches as well as the problems of their implementation are shown. The use of indicator ratios enabled successful identification of pyro- and petrogenically polluted samples of groundwater also the examples of the study of polyarenes as geochemical markers were demonstrated. The polyarenes are shown to be an effective indicator of the pollution genesis in the underground hydrosphere. However, their analysis requires the use of modern methods of sampling, sample preparation and extraction, which significantly complicates research in practice.

Three thousand year paleo-tsunami history of the southern part of the Japan Trench

This study conducted a field survey and multiproxy analyses on sediment cores retrieved from the Kobatake-ike pond in Choshi City, Chiba Prefecture, Japan. Kobatake-ike pond is located at a high elevation (i.e., 11 m above present-day sea level) and faces the southern part of the Japan Trench. Three event sand layers were detected within the continuous mud and peat sequences of 3000 years. Based on the multi-proxy analyses, including mineralogical composition, diatom assemblages, and geochemical markers, these sedimentological events were associated with past tsunamis. The most recent event was a sandy layer and is attributed to the AD 1677 Enpo tsunami, which was reported by an earlier study conducted in the pond. Our results demonstrated that two older sand layers are associated with large tsunamis that struck the Choshi area in AD 896–1445 and in BC 488–AD 215. In addition, the age ranges of these events seem to overlap that of large earthquakes and tsunamis known from the central part of the Japan Trench. This implies a possible spatiotemporal relation of earthquake generations between the central and southern parts of the Japan Trench. However, since the error ranges of the ages of tsunami deposits at the southern and central parts of the Japan Trench are still large, further investigation is required to clarify the relations of large earthquakes in both areas.

Suitable geochemical markers to determine tsunami impact - an approach on coastal areas in Northern Japan

<p>The 2011 Tohoku-oki tsunami had a destructive effect and impact on the coast of Japan. Coinciding with the inundation of vast coastal areas, the catastrophic event released many pollutants from damaged facilities but also remobilized sediment-bound residues. These environmental and depositional variations left a distinct signature in the sediment, both sedimentologically and geochemically.</p><p>A wide variety of organic geochemical substances were detected in the sampled sediment profiles in Northern Japan (Misawa harbor, Futakawame and Oirase). Some compounds reflect the 2011 tsunami’s impact and may serve as possible indicators for further investigation of the inundation and backwash, sediment and pollutant distribution, and the preservation. For comparability, the tsunami samples and the respective over- and underlying layers (topsoil & soil) were analyzed.</p><p>The selected compound groups differentiated the tsunami layer from the non-affected layers. Natural compounds, relocated by the tsunami, revealed an enrichment of short-chained <em>n</em>-alkanes as expressed by the terrigenous/aquatic ratio (TAR) and locally accumulated <em>n</em>-aldehydes pointing to an intensive mixing of marine and terrestrial material. Petrogenic pollutants, for instance hopanes, steranes, and polycyclic aromatic hydrocarbons (PAHs), illustrate a higher load in tsunami sediments as the result of damage of harbor facilities. Sewage-related compounds, such as linear alkylbenzene (LABs) and diisopropylnaphthalene (DIPN), were also enriched in the tsunami samples in contrast to the surrounding sites. Another compound group enriched in the tsunami deposits, are chlorinated pollution burdens by the backwash, such as DDX and polychlorinated biphenyls (PCBs), remobilized by erosion dominantly.</p><p>The different environmental- and pollution-related compounds illustrate the suitability of geochemical markers as indicators to assess tsunami impact in 2011 Tohoku-oki tsunami affected sediments of Misawa harbor, Futakawame and Oirase in Northern Japan.</p>

Integration of photogrammetry from unmanned aerial vehicles, field measurements and discrete fracture network modeling to understand groundwater flow in remote settings: test and comparison with geochemical markers in an Alpine catchment

Fast and cost-effective techniques for hydrogeological modeling are of broad interest for water resources exploitation, especially in remote settings, where hydrogeological measurements are difficult to perform. Unmanned aerial vehicles (UAV)-based techniques are potentially useful for these aims, but their application is still limited. In this study, a field-based approach and UAV-based approach are integrated for the computation of a discrete fracture network model of a fractured aquifer in the Central Alps. Then, calculated directions of the hydraulic conductivity components were compared with a geostatistical analysis of geochemical markers from sampled spring waters, to infer a conceptual model of groundwater flow. The comparison of field-based and UAV-based fracture measurements confirmed a good matching for fracture orientations and recognized a more reliable estimation of fracture dimensions for the UAV-based dataset. Nonetheless, an important variable for hydrogeological modeling—fracture aperture—is not measurable using UAV, as this requires field measurements. The calculated directions of the main conductivities fit well with the analyzed geochemical markers, indicating the presence of two partially separated fractured aquifers and describing their possible groundwater flow paths. The adopted integrated approach confirms UAV-based measurements as a potential tool for characterization of fracture sets as the input for hydrogeological modeling and for a fast and effective surveying tool, reducing time and cost for other following measurements.

Fractionation of polycyclic aromatic hydrocarbons at geochemical barriers

The purpose of the study was to identify patterns of fractionation at geochemical barriers (GCB) of associations of marker compounds - polycyclic aromatic hydrocarbons (PAHs). Based on thermodynamic parameters, the throughput of GCB in geochemical systems (GCS) in relation to organic substances at the molecular level is analyzed. PAHs are very informative indicators of the properties of GCB (up to singular surfaces). The processes of migration and selective penetration through GCB of 15 PAHs from the list of priority pollutants recommended by the US Environmental Protection Agency (widely used in the world EPA list): Naphthalene (Naph), acenaphthene (Ace), Fluorene (Flourene), Phenanthrene (Phen), Anthracene (An), Fluoranthene (Flu), Pyrene (Py), Benzo(a)Anthracene (BaA), Chrysene (Chr), Benzo(b)Fluoranthene (BbFlu), Benzo(k)fluoranthhene (BkFlu), Benzo(a)pyrene (BaP), benzo(ghi)perylene (Bghi), Dibenzo(a, h) anthracene (DbA), Indeno(1,2-cd)pyrene (Ip). Being geochemical markers, these compounds can accumulate on barriers and selectively penetrate through them, making them especially important objects of study. Despite numerous studies, these mechanisms of mass transfer have not been sufficiently studied. The types of GCB have been identified in terms of their permeability to PAHs. It is shown that the functions of GCB in systems are much more significant and consist not only in the separation of systems from the external environment and the regulation of mass transfer. The above models of migration and accumulation are based on quantitative estimates, which makes the results more reasonable in comparison with the “conceptual” representations of the behavior of substances on GCB in most studies. The most important point - the influence of the medium contact time for establishing a stable state (stability by the migration of compounds) on GCB has been demonstrated.

Assessment of the pyrogenic pollution of the soil-plant system on the base of geochemical markers for a local model of transport pressure

The choice of informative indicators for local estimates of the transport pressure on urban soil-plant systems is a serious problem of preserving green spaces. The spatial variations of the characteristics of the flows of marker compounds (polycyclic aromatic hydrocarbons (PAHs) acting as geochemical markers), the integral characteristics of the toxicity of soil pollutants, roots and aerial parts of plants TEQ, as well as the values of indicator ratios based on the concentrations of PAHs in the media are considered. The object of local research is the RUDN University campus (Moscow, Russia) with an adjacent forest park area. The territory is located in the zone of influence of heavy traffic flows and is experiencing an intense load from emissions. The state of the territory is monitored at 33 points according to a unique monitoring program. Pollution indicators showed different informativeness for constructing transport pressure models. Various modes of pollution in 3 functional zones of the territory are revealed; the zones of influence of the main sources of pollution are justified. The indicator ratios confirmed the leading source of pollution –pyrogenic emissions of transport, but they are to varying degrees sensitive to the activity of local pollution sources. Priority routes of PAH intake and accumulation in the components of the soil and plant system were identified. For the first time, a correlation between a number of ratios and indicators of polyarene contamination toxicity (TEQ) was established.

Three thousand year paleo-tsunami history of the southern part of the Japan Trench

This study conducted a field survey and multiproxy analyses on sediment cores retrieved from the Kobatake-ike pond in Choshi City, Chiba prefecture, Japan. Kobatake-ike pond is located at a high elevation (i.e., 11 m above present-day sea level) and faces the southern part of the Japan Trench. Three sedimentological events were detected within the continuous mud and peat sequences of three thousand years. Based on the multi-proxy analyses, including mineralogical composition, diatom assemblages, and geochemical markers, these sedimentological events were associated with past tsunamis. The most recent event was a sandy layer from the AD 1677 Enpo tsunami, reported by an earlier study conducted in the pond. The estimated recurrence interval for tsunamis was approximately 700 years, comparable to that of the central part of the Japan Trench. The timing of at least two of three sedimentological events seems to have been close (i.e., intervals of few tens of years) before or after the occurrence of large earthquakes and tsunamis along the central part of the Japan Trench. This implies a possible spatiotemporal relation of earthquake generations between the central and southern parts of the Japan Trench, which can be associated with drastic changes in stress fields in the neighborhood of the rupture area. The risk of future large earthquakes and tsunamis along the southern part of the Japan Trench seems exceptionally high, considering the stress change caused by Tohoku-oki earthquake with 9.0 Mw in 2011. This study necessitates the need to investigate the spatiotemporal relationship of large earthquakes from the perspectives of geology, seismology, and history.