Gabriele A. Tartari

Precision and linearity of inorganic analyses by ion chromatography

Abstract The repeatability of the measurements of peak areas for calibration solutions and the precision of anion and cation determinations (3–600 μM) in freshwater are discussed on the basis of 2 years of measurements on calibration solutions and stabilized internal standards. Anion measurements show higher repeatability of the measurements of peak areas for calibration solutions (R.S.D. 2–5%) and precision (R.S.D. 2–8%) than those of cations (R.S.D. 2–10% and 2–15%, respectively). Results for the calibration technique show that multi-point (6–8 concentrations), quadratic or cubic regressions permit a correct quantification over a wide range (1.5–2 orders of magnitude) of concentrations. Thanks to the repeatability of the measurements of peak areas for calibration solutions, only two calibrations, at the beginning and end of a batch of 20–30 samples, are adequate. These conditions give better results than calibrations performed with 2–3 points and repeated every 8–10 samples.

Precision of ion chromatographic analyses compared with that of other analytical techniques through intercomparison exercises

Abstract Three intercomparison exercises on simulated rainwater were held in 1991–1993 involving 72–98 laboratories in Europe and South America. Ion chromatography was used for the determination of anions (chloride, nitrate and sulphate) by 59–72% of the participating laboratories and for the determination of cations (Na, K, Mg and Ca) by 14–22% of them. The concentration of the single ions ranged between 5 and 150 μmol l−1. The results were used to evaluate the precision of the method, and showed that it was comparable to that of spectrophotometric methods. For ammonium ion, ion chromatography was used by only 4–14% of the laboratories and the results depended on the calibration technique adopted. A general improvement in precision was observed in the course of the exercises.

A comparison between high-temperature catalytic oxidation and persulphate oxidation for the determination of total nitrogen in freshwater

Total nitrogen (TN) in freshwater samples (lakes, rivers, and atmospheric deposition) has been routinely analysed at the laboratory of the CNR Institute of Ecosystem Study in Italy by persulphate oxidation (PO) with UV determination of nitrate at 220 nm since the 1980s. In 2004, high-temperature catalytic oxidation (HTCO) with a chemiluminescence detector (CLD) began to be used for TN analysis. A mixed catalyst of cobalt–chromium and cerium oxide was selected, as this gave the best recoveries for ammonium and organic N. To assess the comparability of the new method with the reference one, almost 800 samples were analysed for TN using both methods. The average difference between paired data was low, as both absolute and relative values (0.06 mg N L−1 and 3%, respectively, in the range of 0.1–7.0 mg N L−1). The results of our study confirmed HTCO as a reliable method for TN determination in freshwater samples. Compared with PO, HTCO proved to be faster and required less sample handling. From the point of view of linearity and repeatability, the HTCO results were comparable with those with PO UV 220. The LOD of HTCO calculated in this study was lower than that of PO UV 220 (0.04 with respect to 0.09 mg N L−1).

Patagonian ostracods as indicators of climate-related hydrological variables: implications for paleoenvironmental reconstructions in Southern South America

Different precipitation regimes across Patagonia generate an environmental gradient that is expected to reflect upon the solute composition and concentration of lake water through the ensuing differences in water balance. In turn, this hydrochemical gradient could influence the occurrence and distribution of ostracods in the area. A cluster analysis on hydrochemical data of 36 Southern Patagonian waterbodies shows that low salinity, bicarbonate-dominated waters characterize Andean and ecotonal lakes, located in the wetter part of the precipitation gradient, while their steppe counterparts, which receive a much lower precipitation input, are more saline, enriched in all major anions and sodium-dominated. Kruskal–Wallis tests followed by Mann–Whitney pairwise comparisons show statistically significant differences in the ostracod species each water type hosts, with L. patagonica, E. cecryphalium, P. smaragdina and P. incae being found in the more dilute waters characteristic of Andean and ecotonal lakes and Limnocythere rionegroensis in the mesohaline, evaporatively evolved waters typical of steppe lakes. Other species studied do not appear to have such distinct distributions, having been found throughout the range of conditions studied. These findings promote the use of the aforementioned ostracods as semi-quantitative paleohydrological indicators, which could improve paleoclimatic reconstructions in Patagonia.

Photodegradation of nitrite in lake waters: role of dissolved organic matter

Environmental context. Nitrite is an important nutrient in surface waters, a key intermediate in the interconversion of nitrate into ammonium, and a considerable photochemical source of reactive species such as the hydroxyl radical. We have found that scavengers of hydroxyl radicals such as dissolved organic matter, which are usually supposed to inhibit the photodegradation of dissolved compounds, are able on the contrary to enhance the phototransformation of nitrite. The three weeks’ lifetime of nitrite in the surface layer of lakes, derived from the results of the present work, would make photochemistry an important issue in determining the concentration of nitrite in lake water. Abstract. Here we studied the degradation rate of nitrite (NO2–), added to lake water at sub-micromolar levels, upon ultraviolet (UV) irradiation. NO2– photodegradation was considerably faster in lake water compared with ultra-pure water. A key issue was the presence in lake water of hydroxyl radical (•OH) scavengers that inhibited the reaction between NO2– and •OH. Such a reaction, while causing additional NO2– transformation, produced nitrogen dioxide (NO2•) that was subsequently involved into the regeneration of NO2– by dimerisation or the reaction with nitric oxide (NO•). The scavenging of •OH by compounds different from NO2– (mainly dissolved organic matter, DOM) prevented the regeneration reactions from taking place, and enhanced the phototransformation of NO2–. Model calculations for the direct photolysis of NO2–, applied to the lake water samples, yielded a NO2– half-life time of around three weeks in the mixing layer of the lakes because of photodegradation. Therefore, we conclude that photodegradation is a potentially important process to control the concentration of NO2– in shallow lakes, or in deeper ones under stratification conditions.

Glacier Melting Increases the Solute Concentrations of Himalayan Glacial Lakes.

Over the past two decades, we observed a substantial rise in ionic content that was mainly determined by the sulfate concentration at 20 remote high elevation lakes located in central southern Himalaya. At LCN9, which was monitored on an annual basis for the last 20 years, the sulfate concentrations increased over 4-fold. Among the main causes, we exclude a change in the composition of wet atmospheric deposition, as well as a possible influence of decrease in seasonal snow cover duration, which could have exposed larger basin surfaces to alteration processes. Glacier retreat likely was the main factor responsible for the observed increase of sulfate concentrations. We attribute this chemical changes mainly to the sulfide oxidation processes that occur in subglacial environments. Moreover, we observe that the weakened monsoon of the past two decades has only partially contributed to the lakes enrichment through runoff waters that are more concentrated in solutes or lowering the water table, resulting in more rock exposed to air and enhanced mineral oxidation.

Acidification and weathering processes in high mountain lakes in Southern Alps

About 200 lakes in Southern Alps (Italy and Switzerland) were studied in order to quantify their acidification. Although samplings were carried out in summer, long after the acid shock caused by snowmelt, some lakes were found to be acidic and 47% of them show alkalinity values of below 50 μeg 1−1. Losses in alkalinity (acidification levels) were evaluated using a titration model with variable F-factor.

pH-related variations in trace metal concentrations in Lake Orta (Italy)

Abstract The relationships between pH and trace metal concentrations in the water of Lake Orta are discussed on the basis of data collected monthly between January 1984 and March 1988 and of laboratory experiments, in which calcium carbonate was added to lake water at two different pH. The results obtained from both sets of data are in good agreement, indicating a decrease in metal concentration with increasing pH in the case of aluminium, copper, iron and chromium; zinc and nickel do not show significant variations with increasing pH, while in the case of manganese the indications are scanty and do not permit a conclusion. These results suggest that there would be a decided decrease in metal concentrations if the water underwent liming at pH > 6.0–6.5, with a substantial improvement in the water quality, given the toxic effect of some of the metals in the water of Lake Orta.

Data Quality in Laboratories: Methods and Results for Soil, Foliar, and Water Chemical Analyses

Abstract Chemical analyses are an essential part of forest ecosystem monitoring activities. Harmonized, well-defined, and documented analytical methods are an important part of a laboratory Quality Control program and are essential to maximize spatial and temporal comparability of monitoring data. Different quality and data consistency checks, plausible ranges for analytical results, use of reference materials, and control charts are described for internal laboratory Quality Control. On the other side, coordinated ring tests among participating laboratories are an integral part of external Quality Control. Organization of ring tests, evaluation, and the benchmark with tolerable limits are described and specified. Results for water, foliage, and soil ring tests and the evaluation of quality indicators within the European forest ecosystem monitoring program are reported.Chemical analyses are an essential part of forest ecosystem monitoring activities. Harmonized, well-defined, and documented analytical methods are an important part of a laboratory Quality Control program and are essential to maximize spatial and temporal comparability of monitoring data. Different quality and data consistency checks, plausible ranges for analytical results, use of reference materials, and control charts are described for internal laboratory Quality Control. On the other side, coordinated ring tests among participating laboratories are an integral part of external Quality Control. Organization of ring tests, evaluation, and the benchmark with tolerable limits are described and specified. Results for water, foliage, and soil ring tests and the evaluation of quality indicators within the European forest ecosystem monitoring program are reported.

Interlaboratory exercises to compare analytical method performances

Three intercomparison exercises on simulated rainwater were held in the period 1991–93 involving 72 to 99 laboratories in Europe and South America. The exercises required the analysis of pH, conductivity, main anions (Cl−, NO3− and SO42−) and main cations (Ca2+, K+, Mg2+, Na+ and NH4+). The concentrations of the single ions ranged between 5 and 150 μmoll−1. Results were used to evaluate and compare the precision of the analytical methods. A general improvement in precision was observed in the course of the exercises.