Geochemistry and stable isotope composition of surface waters from the Ravenna plain (Italy): implications for the management of water resources in agricultural lands

This paper examines the issues related to salinization and water quality in the complex drainage system of the historical land reclamation of Lamone basin (Ravenna coastal plain, northern Italy), with the aim of guiding ongoing agricultural-related decisions. Major and trace element concentration and O–H–B–Sr isotope-ratios were measured on surface water from a network of canals and ditches. Sampling was carried out during the winter period and in summer, to assess the effects of agricultural water management on the aquatic system. Results show widespread salinization of waters over the entire crop, due to both the direct saltwater inland flushing through the canals in proximity of the mouths, and sea salt leaching from soils. During winter, salinization is partly mitigated by rainfalls, while in summer dilution processes are due to freshwater input from outside the watershed, planned to assist the agricultural water demand. In the winter season, the concentration of some elements such as Fe, Mn, Al, and Cu in waters exceeds the maximum permissible limits imposed by the Italian regulations, while during summer the concentration of these elements is significantly reduced. A seasonal cycling is established, where the bottom sediments of canals and ditches act as sinks of harmful elements, mostly through adsorption by Fe–Mn–Al oxy-hydroxide solid phases. The irrigation practice, although improving the water quality, increases water turbidity by re-mobilization of sediments which act as transport agents of contaminants, with detrimental effects that may become significant over the years.     

Distribution of trace elements in filtered and non filtered aqueous fractions: Insights from rivers and streams of Sardinia (Italy)

The distribution of several trace elements in different aqueous fractions has been studied in running waters from Sardinia (Italy). Trace elements and major components were determined in water samples collected at high- and low-discharge from rivers (90 samples) and streams (70 samples). At selected sites, total (non filtered samples) and dissolved (0.4 μm and 0.015 μm pore-size filtered samples) amounts of trace elements were determined, and the composition of the solid matter retained on the filters was investigated for estimating the eventual interrelationship. The elements B, Li, Rb, Sr, Ba, As, Sb, Mo, Tl and U in the studied waters showed small differences between total and dissolved amounts; dissolved concentrations were higher under low flow conditions, when the contribution of rainwater to the rivers was minimum; their concentrations were often correlated with total dissolved solids (TDS), and appeared to be related to the intensity of water-rock interaction processes. The elements Al, Fe, Mn, Pb, Zn, Cd, Cu, Co, Ni, Cs, Y, REE and Th were not related to TDS and/or major ions; they showed higher concentrations under high flow conditions; marked differences occurred between total and dissolved amounts; much lower concentrations were generally observed in the water filtered through 0.015 μm than in the water filtered through 0.4 μm, especially when sampling was carried out after heavy rain events that enhanced the load of solid matter in the water. These observations indicate an aqueous transport via sorption processes on very fine particles, such as Fe-oxide/hydroxide and clay mineral particles, which have been inferred by SEM-EDX analyses of the matter retained on the filters.     

Mobility of aqueous contaminants at abandoned mining sites: insights from case studies in Sardinia with implications for remediation

Public awareness of environmental health issues has increased significantly in recent years, creating the need for detailed scientific studies that can identify potential environmental problems. This paper reports the results of hydrogeochemical surveys carried out in Sardinia, an Italian region with a long mining history. When mining operations in Sardinia ceased, actions for limiting the potential adverse effects of mine closure on the water system were not undertaken. Drainages from flooded mines and seeps from mining residues left on the ground are the main mining-related sources of contamination in Sardinia. Due to the proximity of mining sites to water resources and land that is within reach of animals and humans, the major risks to human health are associated with the direct discharge of contaminated waters into the streams and soils located down-gradient of the abandoned mines. Results of hydrogeochemical surveys carried out under different seasonal conditions showed that the dispersion of toxic and harmful elements (As, Cd, Ni, Pb, Sb and Zn) increases during the rainy season, especially under high runoff conditions. These results should help regional and national authorities to address present environmental regulations, particularly those regarding the quality of water resources. Furthermore, the results might be useful elsewhere for planning remediation actions at abandoned mining sites. Lessons learned by past mining in Sardinia indicate that correct disposal and management of mining residues should be mandatory from the beginning of exploitation and processing at each active mine. This would allow reduction of the environmental risks as well as the cost of remediation.     

Rare earth elements in waters from the albitite-bearing granodiorites of Central Sardinia, Italy

With the aim of contributing to the knowledge of the geochemical behaviour and mobility of the rare earth element (REE) in the natural water systems, the ground and surface waters of the Ottana-Orani area (Central Sardinia, Italy) were sampled. The study area consists of albititic bodies included in Hercynian granodiorites. The waters have pH in the range of 6.0-8.6, total dissolved solid (TDS) of between 0.1 and 0.6 g/l, and major cation composition dominated by Ca and Na, whereas predominant anions are Cl and/or HCO₃.The pH and the major-element composition of the waters are the factors affecting the concentration of REE in solution. The concentrations of ∑REE+Y in the samples filtered at 0.4 μm vary between 140 and 1600 ng/l, with La of between 14 and 314 ng/l, and Yb of between <6 and 12 ng/l. A negative Ce anomaly, especially marked at high pH, is observed in the groundwaters. The surface waters show lower REE concentrations, which are independent of pH, and negligible Ce anomaly.Speciation calculations, carried out with the EQ3NR computer program, showed that the complexes with the CO₃²⁻ ligand are the dominant REE species at pH in the range of 6.7-8.6. The REE³⁺ ions dominate the speciation at pH <6.7 and only in the light REE (LREE).The relative concentrations of REE in water roughly reflect those in the aquifer host rocks. However, when concentrations of REE in water are normalised relative to the parent rocks, a preferential fractionation of heavy REE (HREE) into the water phase can be observed, suggesting the greater mobility and stability of HREE in aqueous solution.     

Assessment of environmental hazards at abandoned mining sites: A case study in Sardinia,Italy

In the last two centuries, several Pb–Zn mines were active in the Rio Mannu basin near Narcao (SW Sardinia, Italy), but are now abandoned. These abandoned mines pose a serious risk to the population and required an assessment of the hazard sources and the contaminant pathways in the area. The characterization plan of the Rio Mannu basin was carried out according to Italian protocols. Specifically, samples of soil, stream sediment, fine-grained ore-processing waste (from washery and flotation processes), surface water and groundwater have been analyzed in order to assess the levels of contamination in each mine area and the risks in the plains surrounding the site. Several potential chemical contaminants were considered both in solid materials and water samples. The Rosas mine was recognized as the most contaminated area in the basin, due to the presence of a large tailing pond, some fine-grained waste piles and two mine adits with concentrations of the toxic elements As, Cd, Cu, Pb, Sb and Zn exceeding Italian regulatory standards. The dispersion of contaminants occurs downstream from the small stream draining the area. In case of heavy rain the runoff into the streamlet transports the contaminated material far into the plain. The results of this study show that the characterization plan is a relatively cheap tool for establishing mitigation actions, prior to the realization of a complete, and usually expensive, remediation project at abandoned mine sites. Urgent recommended actions in the Rio Mannu basin include the treatment of the adit water prior to its discharge into the Rio Barisonis; the construction of drainage barriers on waste piles to reduce runoff and solid transport into the Rio Barisonis; the consolidation of the earthen dam containing the tailing pond of Rosas to avoid the deepening of erosion furrows that may threaten its stability.     

Findings on water quality in Upper Mustang (Nepal) from a preliminary geochemical and geological survey

The major ion and trace element chemistry of water samples, including springs, rivers and irrigation ditches, collected during a survey on August 2016 in the Upper Mustang region of the Mustang District of Dhawalagiri Zone (Nepal) has been investigated. The Upper Mustang region, a cold desert, represents a hot-spot for climate change: indeed, violent hailstorms and rainstorms have been recently observed, consequently exposing land to erosion. Results of this study indicate that waters in the region belong to the Ca–HCO₃, Ca–Mg–Cl–SO₄ and Na–K–Cl-types, reflecting different hydrochemical regimes. Uranium is widespread in waters, with concentrations up to 19 µg/L recorded in a potable water supply. Locally, anoxic conditions affect uranium mobility due to the low solubility of U(IV) minerals. Highly toxic thallium was detected in a thermal spring at an elevated concentration (45 µg/L Tl). The association of thallium with high concentrations of iron suggests that these elements are derived from pyrite oxidation. Detectable levels of thallium were also measured in the water of an irrigation ditch. Lithium concentrations ranged from 7 µg/L to 12 mg/L in the thermal water and showed a strong association with chloride ions. Arsenic concentrations up to 4.7 µg/L were measured in tributaries of the Kali Gandaki river. The data provide evidence that solutes in water have originated from an array of input sources, including carbonate dissolution, the dissolution of soluble salts, silicate weathering and localized sulfide oxidation. In particular, chemical weathering of granitic rocks is likely the primary source for metals and metalloids in waters. Since the erosion rate is a factor affecting lithological weathering, high-intensity rainfalls due to climate change are expected to influence the release and fate of potentially harmful elements in the in the Upper Mustang Valley.     

Acid drainage from sulfides hosting gold mineralization (Furtei, Sardinia)

 The past mining activity for kaolin minerals left several abandoned quarries in the area of Furtei (southern Sardinia). Recently, gold mineralization has been found in association with intensely altered andesitic rocks, and an open-pit gold mine is expected to open in the near future. Twenty-one water samples were analyzed for a wide range of major and trace elements, in order to define the present hydrochemical situation before exploitation starts. Waters interacting with the altered andesitic rocks had higher salinity and metal concentrations than waters in contact with nonaltered rocks. Acid drainage and high concentrations of metals (Al, Fe, Mn, Zn, Cu, As) in solution were observed in waters leaching the mineral deposit. An environmental impact study is urgently called for since the waste material derived from the exploitation is expected to enhance acidification and metal-releasing processes, due to the increase in the specific yield, which favors the oxidation of sufide minerals. Received: 15 February 1995 · Accepted: 10 October 1995     

Transport of trace elements under different seasonal conditions: Effects on the quality of river water in a Mediterranean area

Concentrations of total and dissolved elements were determined in 35 water samples collected from rivers in Sardinia, a Mediterranean island in Italy. The overall composition did not change for waters sampled in both winter and summer (i.e., January at high-flow condition and June at low-flow condition), but the salinity and concentrations of the major ions increased in summer. Concentrations of elements such as Li, B, Mn, Rb, Sr, Mo, Ba and U were higher in summer with only small differences between total and dissolved (i.e., in the fraction <0.4 μm) concentrations. The fact that these elements are mostly dissolved during low flow periods appears to be related to the intensity of water–rock interaction processes that are enhanced when the contribution of rainwater to the rivers is low, that is during low-flow conditions. In contrast, the concentrations of Al and Fe were higher in winter during high flow with total concentrations significantly higher than dissolved concentrations, indicating that the total amount depends on the amount of suspended matter. In waters filtered through 0.015 μm pore-size filters, the concentrations of Al and Fe were much lower than in waters filtered through 0.4 μm pore-size filters, indicating that the dissolved fraction comprises very fine particles or colloids. Also, Co, Ni, Cu, Zn, Cd and Pb were generally higher in waters collected during the high-flow condition, with much lower concentrations in 0.015 μm pore-size filtered waters; this suggests aqueous transport via adsorption onto very fine particles. The rare earth elements (REE) and Th dissolved in the river waters display a wide range in concentrations (∑REE: 0.1–23 μg/L; Th: <0.005–0.58 μg/L). Higher REE and Th concentrations occurred at high flow. The positive correlation between ∑REE and Fe suggests that the REE are associated with very fine particles (>0.015 and <0.4 μm); the abundance of these particles in the river controls the partitioning of REE between solution and solid phases.Twenty percent of the water samples had dissolved Pb and total Hg concentrations that exceeded the Italian guidelines for drinking water (>10 μg/L Pb and >1 μg/L Hg). The highest concentrations of these heavy metals were observed at high-flow conditions and they were likely due to the weathering of mine wastes and to uncontrolled urban wastes discharged into the rivers.