Monte Lago polje, a case study regarding the influence of geologic structure and degree of karstfication on groundwater drainage in the Central Apennines (Italy)

Research on the cave and karst water in the area of Monte Lago polje (Central Apennines) has revealed an articulate drainage pathway, influenced by the karstfication degree and geological setting. A fast drainage occurs from the ponor in the polje to the main temporary resurgence in the valley of San Giovanni, impeding the karst water in achieving thermal equilibrium with the rock. The water temperature in the resurgence decreases to very low values (~3 °C) during the winter, and the daily thermal cycles are clearly recognizable. These inputs of vadose water from the ponor have only a minor influence on the chemo-physical characteristics of San Giovanni spring, the largest emergence in the area, located a few hundred meters downstream in the same valley and fed by the main basal aquifer. The two nearby springs are recharged by different hydrostructures divided by low permeability levels in the Jurassic carbonate succession. This reduces the cross-formational communication mainly for the descending vadose fluxes. The fast drainage of karst water in the transfer vadose zone is due to a high karstfication, confirmed by the typology and distribution of the karst caves. A more regular discharge in the springs fed by the basal aquifer is probably related to a minor karstfication in the lower part of the limestone massifs.Key words: Monte Lago, Central Apennines, Karst, Groundwater monitoring.Kraško polje Monte Lago, študija vpliva geološke zgradbe in stopnje zakraselosti na tok podzemne vode v Centralnih Apeninih (Italija)Raziskave jam in kraške vode na območju kraškega polja Monte Lago (Centralni Apenini) so razkrile obstoj drenažne mreže, na katero vplivata stopnja zakraselosti in geološka zgradba. Med ponorom na polju in glavnim občasnim izvirom v dolini San Giovanni se pojavlja hiter tok, ki preprečuje uravnoteženje temperature vode s temperaturo kamnine. Pozimi ima voda v izviru zelo nizko temperaturo (~3 °C), jasno so vidni dnevni temperaturni cikli. Ti dotoki vadozne vode iz ponora imajo le majhen vpliv na fizikalno-kemijske značilnosti izvira San Giovanni, največjega izvira na tem območju, ki je lociran nekaj sto metrov dolvodno v isti dolini in se napaja iz glavnega spodnjega vodonosnika. Dva sosednja izvira se napajata iz različnih hidrostruktur, ločenih s plastmi slabše prepustnosti v jurskem karbonatnem zaporedju. To zmanjšuje prehajanje predvsem navzdol tekočih vadoznih vod skozi formacije. Hitro pretakanje kraške vode v vadozni coni je posledica dobre zakraselosti, ki jo potrjujeta tipologija in razpored kraških jam. Bolj enakomeren pretok izvirov, ki se napajajo iz spodnjega vodonosnika, je verjetno povezan z manjšo zakraselostjo v spodnjem delu apnenčastega masiva.Ključne besede: Monte Lago, Centralni Apenini, kras, monitoring podzemne vode.

Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications

Richard Joseph-Etienne. Résumé du rapport de Richard sur les gestes de l'armée de la Moselle et des lettres des envoyés en mission qui racontent de la prise du fort de Rheinfeld, lors de la séance du 18 brumaire an III (8 novembre 1794). In: Archives Parlementaires de 1787 à 1860 - Première série (1787-1799) Tome C - Du 3 au 18 brumaire an III (24 octobre au 8 novembre 1794) Paris : CNRS éditions, 2000. p. 549

An overview of the Italian forest biodiversity and its conservation level, based on the first outcomes of the 4th Habitat Report ex-Art. 17

In 2019 the 4th Report ex-Art. 17 on the conservation status (CS) of Annex I Habitats of the 92/43/EEC Directive was expected by every EU/28 country, with reference to the period 2013-18. In Italy, the process was in charge to the Italian Institute for Environmental Protection and Research (ISPRA), on behalf of the Ministry for Environment, Land and Sea Protection (MATTM), with the scientific support of the Italian Botanical Society (SBI). A large group of thematic and territorial experts elaborated the available data concerning the 124 types of terrestrial and inland water Habitats present in Italy, 39 of which are represented by Forest Habitats (Group 9),. The main aim of the work was the evaluation of the overall CS of each Habitat by Biogeographic Region (Mediterranean, Continental and Alpine), for a total amount of 294 assessments. A high proportion of these (92, corresponding to 31% of the total) referred to Forest Habitats, including 20 marginal types for which the CS was not requested. The analysis was carried out at different scales: a) administrative territory, through the data contained in the ISPRA database, whose compilation was in charge to the Regions and Autonomous Provinces; b) Natura 2000 site, with the latest updates available (Standard Data Forms updated to 2018); c) national scale, implementing the distribution maps for each Habitat based on the European grid ETRS89-LAEA5210 (10x10 km2 mesh); d) Biogeographic Region, scale of the final assessment. Cartographic outcomes, associated databases and additional data used for the assessments will be available online on the ISPRA Portal as soon as the validation process by the European Commission will be completed. A dedicated archive named "HAB_IT" has been created in the national database "VegItaly" (1), managed by the Italian Society of Vegetation Science, where the phytosociological relevés representative of the various Annex I Habitats in Italy will be archived and freely accessible. An overview of the results regarding the Forest habitats is here provided, including a comparison with the outcomes of the former reporting cycle, the 3rd Report ex-Art. 17 (2). In several cases (e.g. 9120, 91L0), the distribution maps have been remarkably improved due to better knowledge and more fitful interpretation. The conservation status resulted as Favourable (FV) for 6,7%, Inadequate (U1) for 58,7% and Bad (U1) for 32,0% of the 72 assessed forest Habitat types. In no case there was an improvement of the conservation status, while in 6 cases a worsening of the conditions resulted from the data analysis, pointing out the Habitats types with a higher need of action. Similarly to other projects carried out as a team by the network of Annex I Habitat experts of the Italian Botanical Society and the Italian Society for Vegetation Science (e.g. 3, 4), this is another step in the direction of supporting the implementation of the 92/43/EEC "Habitat" Directive in Italy and Europe. On this ground, the high biodiversity of the Italian forest Habitats could be emphasized, however results pointed out that some rare or endemic types (e.g. Alnus cordata or Betula aetnensis-dominated forests) are still scarcely acknowledged by the most prominent EU conservation tools such as the Annex I to the "Habitat" Directive. 1) F. Landucci et al. (2012) Plant Biosyst., 146(4), 756-763 2) P. Genovesi et al. (2014) ISPRA, Serie Rapporti, 194/2014 3) E. Biondi et al. (2009) Società Botanica Italiana, MATTM, D.P.N., http://vnr.unipg.it/habitat/ 4) D. Gigante et al. (2016) Plant Sociology, 53(2), 77-8

Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications

The measurement of the weight loss in limestone tablets placed in the Grotta del Fiume (Frasassi, Italy) provided data on the rate of limestone dissolution due to the sulfidic water and on the influence of local environmental conditions. A linear average corrosion rate of 24 mm ka-1 was measured in stagnant water, while the values were higher (68-119 mm ka-1) where the hydrologic conditions facilitate water movement and gas exchanges. In these zones the increase in water aggressivity is due to mixing with descending, O2-rich, seepage water and is also favored by easier gas exchange between ground-water and the cave atmosphere. Very intense corrosion was due to weakly turbulent flow, which caused evident changes in the tablets shape in few months. A comparison between the measured corrosion rates and the cave features showed that the values measured in the pools with stagnant water are too low to account for the largest solutional cave development, while the average values measured in the zones with moving water are compatible with the dimension of the cave rooms in the main cave levels, that must have developed when the base level was stable and hydrologic conditions favored the increase of water aggressivity

Barite replacement boxwork in the Frasassi caves (Italy)

The Frasassi caves, located in the Sentino River Gorge in Ancona Province (Marche, Italy), contains boxwork in a small zone in the inner part of the cave system where it is closely associated with subaqueous corrosion produced by sulfuric acid speleogenesis. The boxwork consists of barite that replaces calcite spar-filled veins and limestone porosity and projects from the corroded cave walls. The replacement involved only the calcite that protrudes from the rock surfaces, indicating that the process took place in the cave environment, and therefore the boxwork is not simply a product of differential corrosion. I hypothesize that the boxwork formed in nearly stagnant bodies of sulfidic water as a consequence of lateral recharge of O2-rich bicarbonate water moving upward along the walls because of its lower density. The acidity produced by the oxidation of H2S enhanced limestone corrosion and incision of rills and channels, while also releasing sulfate ions that induced the precipitation of barite. This sulfuric acid process was sufficiently slow to dissolve the micritic bedrock and replace spar with barite, preserving the shape of the network of fissures and pores formerly filled by calcite

Barite replacement boxwork in the Frasassi caves (Italy)

The Frasassi caves, located in the Sentino River Gorge in Ancona Province (Marche, Italy), contains boxwork in a small zone in the inner part of the cave system where it is closely associated with subaqueous corrosion produced by sulfuric acid speleogenesis. The boxwork consists of barite that replaces calcite spar-filled veins and limestone porosity and projects from the corroded cave walls. The replacement involved only the calcite that protrudes from the rock surfaces, indicating that the process took place in the cave environment, and therefore the boxwork is not simply a product of differential corrosion. I hypothesize that the boxwork formed in nearly stagnant bodies of sulfidic water as a consequence of lateral recharge of O2-rich bicarbonate water moving upward along the walls because of its lower density. The acidity produced by the oxidation of H2S enhanced limestone corrosion and incision of rills and channels, while also releasing sulfate ions that induced the precipitation of barite. This sulfuric acid process was sufficiently slow to dissolve the micritic bedrock and replace spar with barite, preserving the shape of the network of fissures and pores formerly filled by calcite

La circolazione carsica nel fianco di anticlinali dell’Appennino Marchigiano: l’esempio della grotta Sasso Pozzo (Gagliole), Sandro Galdenzi, Alfredo Campagnoli

Sasso Pozzo è la più importante grotta conosciuta negli acquiferi minori presenti sui fianchi delle anticlinali dell’Appennino Marchigiano, ed è stata studiata insieme alla vicina sorgente di Mignano (Gagliole, MC) per acquisire dirette informazioni sulle modalità di drenaggio in questo tipo di acquiferi. La grotta si sviluppa in un’unità calcarea compresa entro orizzonti marnosi al letto e al tetto, la cui giacitura ha condizionato il drenaggio e la struttura in grande della grotta, che si sviluppa parallelamente al versante, secondo l’andamento della stratificazione, mantenendosi circa 130 m sotto la superficie topografica per lo più sotto coperture marnose. La grotta, di origine freatica, si comporta attualmente da emergenza di troppo pieno ed è formata da un’angusta galleria lunga 500 m, dalla quale si dipartono poche diramazioni laterali. La grotta ha andamento discendente e profilo longitudinale irregolare, con tratti sifonanti e frequenti contropendenze. Raggiunge la superficie dell’acquifero a -29 m rispetto all’ingresso. Una livellazione di dettaglio ed il monitoraggio idrologico continuo protrattosi per un anno, con tre stazioni interne ed una presso la sorgente, hanno consentito di definire la geometria delle grotta e di seguire le variazioni assolute dei livelli idrici in risposta agli eventi meteorologici superficiali. La temperatura e la conducibilità delle acque nella grotta e alla sorgente sono molto simili e seguono lo stesso trend stagionale. L’alta permeabilità dell’ammasso roccioso nella zona vadosa causa risposte molto rapide agli eventi meteorici di superficie, mentre una riduzione di permeabilità nelle zone più profonde nell’acquifero giustifica l’elevato gradiente piezometrico misurato tra la grotta e la sorgente. In occasione di importanti eventi meteorici si verifica una rapida risalita dei livelli piezometrici, fino a 16 m/h, per un totale di +45 m rispetto al livello di magra. In queste situazioni la risalita di acqua dal lago sifone terminale determina la riattivazione della grotta che viene totalmente invasa dalle acque fino a defluire dall’ingresso.In the Umbria-Marche Apennines small aquifers, often perched above the main base level, are present in the limestones interbedded with marls. Many small caves related to this type of aquifers are known in the limbs of anticlines. Sasso Pozzo is the most important cave in a similar setting, and it was studied together with the nearby Mignano Spring to define the conditions of karst caves development and the characteristics of groundwater drainage. The cave is a temporary karst emergence, consists of a main tube 500 m long, with few lateral branches for a total length of ~ 600 m, and reaches the piezometric surface in its termination, -29 m below the entrance. It exhibits typical phreatic features, with prevailing inclined passages and common siphoning zones. The passages have a small size (diameter 1-2 m) and their walls are covered by scallops. The marl Formation underlying limestone has an important role in concentrating the seepage water from the ridge to the limb of the anticline, where the limestone is sandwiched between poorly permeable beds. The cave formed in this geologic setting due to the ground-water flow parallel to bedding in the saturated zone. During the Middle and Upper Pleistocene, the deepening of the surface streams eroded the marl cover and caused the drop of the water table, so that the cave was abandoned by the ground-water. After this event, the invasion of ground-water became occasional and the cave evolved mainly in vadose conditions. The ground-water monitoring and a detailed survey in the cave clarified the hydraulic behaviour of the cave. A high hydraulic gradient exists between the spring and the ground-water in the cave, probably due to the low permeability of the limestone in the phreatic zone of the aquifer. The water characteristics and the hydrodynamic are similar in the cave and in the spring, and are influenced by the fast recharge of infiltration water from the karst surface. The meteoric water reaches the saturated zone in a few hours through a network of fractures and small karst passages existing in the vadose zone. This fast recharge of infiltration water is not drained through the normal pathway due to the low karstfication rate in the phreatic zone, and the flooding events causes important and fast rises (up to 16 m/h) of the ground-water. The piezometric level increases over 45 m and the cave is completely flo-oded by water that rises from the terminal lake and reaches the surface. In the remaining periods, the cave remains dry, excluding some siphons that can be filled by the seepage water descending in the vadose zone

Gypsum deposits in the Frasassi Caves, Central Italy

The Frasassi Caves are hypogenic caves in central Italy, where H2S-rich groundwater flows in the lowest cave level. Near the water table, the H2S is converted to sulfuric acid by biotic and abiotic processes, which have enhanced cave development. The sulfate generally deposits above the water table as a replacement gypsum crust coating limestone walls or as large gypsum crystals. Although the oxidation of sulfide also occurs below the water table, sulfate saturation is not achieved, therefore, sulfate does not precipitate below the water table. In the upper dry levels of the cave, three main types of ancient gypsum deposits occurs: (1) replacement crusts, similar to the presently forming deposits of the active zone, (2) microcrystalline large and thick floor deposits, and (3) euhedral crystals inside mud. The study of the depositional setting and the analysis of sulfur isotopes in the gypsum and groundwater clearly demonstrate that all the sampled gypsum in the cave formed by H2S oxidation above the water table. Some fraction of small sulfur isotopic differences between H2S in the water and gypsum can be explained by isotopic fractionation during abiotic and/or biotic oxidation of H2S