Direct measurement of nutrient concentrations in freshwaters with a miniaturized analytical probe: evaluation and validation.

This work deals with the evaluation of the aqueous concentrations of dissolved reactive phosphorus (DRP), total phosphorus (TP), and ammonium nitrogen (N-NH4) in surface water by means of direct online instrumentation. A portable, submersible, and automated analyzer designed to measure dissolved and total nutrient concentrations characterized by miniaturization of the entire analytical process was tested against laboratory methods. A total number of 36 water samples of different origin (i.e., rain, river, lake, and sewage waters) were analyzed and used in the comparison of DRP, TP, and N-NH4 data. Raw data were distributed in a broad range of concentrations: 5-299 µg P/L for DRP, 7-97 µg P/L for TP, and 11-332 µg N/L for N-NH4. Regression analysis underlined a high significant correlation between the measures of the probe and those of the laboratory (0.6 < R 2 < 0.9; p < 0.001) and pointed out the effectiveness of the new instrument in representing a broad range of nutrient concentrations.

Decadal trends in water chemistry of Alpine lakes in calcareous catchments driven by climate change.

High mountain lakes are considered sensitive indicators of the effects of natural and anthropogenic drivers, including atmospheric deposition and climate change. In this study, we assess long-term trends in the chemistry of a group of high altitude lakes in the Western Alps, Italy, lying in bedrock with a relevant presence of basic, soluble rocks. An in-depth investigation was performed on two key-sites (Lakes Boden Inferiore and Superiore) for which continuous chemical data are available for a period of 30 years. A group of 10 additional lakes in the same area was also considered; these lakes were sampled at the end of the ice-free period during irregular surveys in the period 1980-2017. Water samples were analysed for the main chemical variables, including pH, electrical conductivity, major ions (Ca2+, Mg2+, Na+, K+, HCO3-, Cl-, SO42-, NO3-) and algal nutrients (phosphorus and nitrogen compounds, reactive silica). A steep increase in conductivity and ion concentrations was detected at the key-sites: conductivity increased from 40-45 to 60-70 µS cm-1 over the period 1984-2017; sulphate concentrations more than doubled over the same period (from 50-60 to 120-180 µeq L-1) and base cations increased from 400-500 to 600-750 µeq L-1. An increase in the solute content was also detected in the survey lakes (average conductivity from 39 ± 20 to 57 ± 23 µS cm-1). The analysis of meteorological data revealed a significant increase of air temperature (0.019 °C y-1 over the period 1950-2017), mainly in spring and summer (0.033 °C y-1), and a decrease of snow cover depth and duration. Meteo-climatic drivers were identified as the responsible for the chemical changes occurred in the lakes. Climate-driven effects on weathering rates were mainly indirect and occurred by affecting the flow paths of water at both surface and subsurface level. Cryosphere modification (reduced snow cover and permafrost thawing) also played a role.

Influence of permafrost, rock and ice glaciers on chemistry of high-elevation ponds (NW Italian Alps).

Permafrost degradation, rock-glacier thawing, and glacier retreat are influencing surface water quality at high elevations. However, there is a lack of knowledge on the dominant geochemical reactions occurring in different cryospheric conditions and how these reactions change during the ice-free season. In the Col d'Olen area (LTER site, NW Italian Alps), four ponds with similar sizes, located in basins with different cryospheric features (glacier, permafrost, rock glacier, none of these), are present in a geographically limited area. All ponds were sampled weekly in 2015 and partially in 2014. Major ions, selected trace elements, and biotic parameters (dissolved organic carbon-DOC, fluorescence index-FI, and nitrate) are examined to evidence the effect of different cryospheric features on water characteristics. Where cryospheric conditions occur chemical weathering is more intensive, with strong seasonal increase of major ions. Sulphide oxidation dominates in glacier and permafrost lying on acid rocks, probably driven by enhanced weathering of freshly exposed rocks in subglacial environment and recently deglaciated areas, and active layer thickness increase. Differently, carbonation dominates for the rock glacier lying on ultramafic rocks. There, high Ni concentrations originate from dissolution of Mg-bearing rocks in the landform. In all settings, pH neutralisation occurs because of the presence of secondary carbonate lithology and ultramafic rocks. Nitrate highest concentrations and changes occur in cryospheric settings while DOC and FI do not show strong differences and seasonal variations. The establishment of more frequent monitoring for water quality in high-elevated surface waters is necessary to provide greater statistical power to detect changes on longer time scales.

Toxicity identification evaluation of Lake Orta (Northern Italy) sediments using the Microtox system.

Pore waters extracted by centrifugation from Lake Orta (Northern Italy) sediments were studied with a modified Toxicity Identification Evaluation (TIE) procedure using the Microtox bacterial luminescence toxicity test system. The most toxic pore water samples were from stations near a rayon factory, known as a source of copper and ammonium discharges. The TIE manipulations used were filtration, EDTA chelation, and C18 solid-phase resin adsorption. The most effective treatments to remove toxicity were the EDTA and C18, indicating that both metals and nonpolar organic compounds contribute to the observed toxicity.