Near-Infrared Spectroscopy (NIRS)

Near-Infrared Spectroscopy (NIRS) of Epilithic Material in Streams has a Potential for Monitoring Impact from Mining

Jan Persson,^† Mats Nilsson,^‡ Christian Bigler,^† Stephen J. Brooks,^§ and Ingemar Renberg*^†

Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden, and Department of Entomology, The Natural History Museum, Cromwell Road, London SW7 5BD, England

Environ. Sci. Technol. , 2007, 41 (8), pp 2874–2880

Abstract: There is an increasing demand for cost-effective methods for environmental monitoring, and here we assess the potential of near-infrared spectroscopy (NIRS) on epilithic material from streams (material covering submerged stones) as a new method for monitoring the impact of pollution from mining and mining-related industries. NIRS, a routine technique in industry, registers the chemical properties of organic material on a molecular level and can detect minute alterations in the composition of epilithic material. Epilithic samples from 65 stream sites (42 uncontaminated and 23 contaminated) in northern Sweden were analyzed. The NIRS approach was evaluated by comparing it with the results of chemical analyses and diatom analyses of the same samples. Based on Principal Component Analysis, the NIRS data distinguished contaminated from uncontaminated sites and performed slightly better than chemical analyses and clearly better than diatom analyses. Of the streams designated a priori as contaminated, 74% were identified as contaminated by NIRS, 65% were identified by chemical analysis, and 26% were identified by diatom analysis. Unlike chemical analyses of water samples, NIRS data reflect biological impacts in the streams, and the epilithic material integrates impact over time. Given that, and the simplicity of NIRS-analyses, further studies to assess the use of NIRS of epilithic material as an inexpensive environmental monitoring method are justified.

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Initial litter properties and decay rate: a microcosm experiment on Mediterranean species

Dominique Gillon, Richard Joffre, and Adamou Ibrahima

Can. J. Bot. 72(7): 946–954 (1994) 

Abstract: Twelve leaf litters belonging to 10 Mediterranean species of coniferous and broad-leaved trees and shrubs and grass species were incubated in microcosms in the laboratory at 22 °C and constant humidity for 14 months. Samples were collected at 0.5, 1, 2, 4, 6, 10, and 14 months, the remaining dry weight being measured at each sampling time. At the end of 14 months, the litters had lost between 52 and 74% of their original mass. The comparison of regressions fitted to the various functions showed that for the species studied, the litter mass loss in relation to incubation time best fitted a double-exponential decay function. The mass loss therefore resulted from the simultaneous decomposition of two main compartments, a labile compartment that decreased rapidly (half-life of 20 – 60 days under the experimental conditions) and a resistant compartment that depending on the species, either did not decrease significantly or decreased 10 to 20 times slower than the labile compartment (half-life of 320–630 days). The litters studied could be categorized according to the relative importance of these two compartments. This was related to the initial content of water-soluble substances and of carbon in the litters. It was also strongly correlated with the spectral information of the initial litters obtained by near-infrared reflectance spectroscopy. In contrast, the rate at which the labile and resistant compartments decreased was related to the permeability of the leaves for the former and to their thickness and mass per surface area for the latter. Near-infrared reflectance spectroscopy provides new perspectives for characterizing the capacity of litters to decompose.

Key words: litter, decomposition, near infrared reflectance spectroscopy.

Résumé : Douze litières de feuilles appartenant à 10 espèces méditerranéennes, conifère, arbres et arbustes feuillus, herbacées, ont été incubées en microcosmes au laboratoire à 22 °C et à humidité constante pendant 14 mois. Les échantillons ont été prélevés à 0,5, 1, 2, 4, 6, 10 et 14 mois, et à chaque prélèvement le poids sec restant a été mesuré. Au bout de 14 mois, les litières avaient perdu entre 52 et 74% de leur masse initiale. La comparaison des ajustements à différentes fonctions a montré que, pour l'ensemble des espèces étudiées, la perte de masse des litières en fonction du temps d'incubation s'ajustait le mieux à la fonction exponentielle double. La perte en masse a donc été la résultante de la décomposition simultanée de deux compartiments principaux, l'un labile qui a diminué rapidement (demie-vie de 20 à 60 jours dans les conditions de l'expérimentation), l'autre résistant qui, selon les espèces, n'a pas diminué de façon significative ou 10 à 20 fois plus lentement que le compartiment labile (demie-vie de 320 à 630 jours). Les litières étudiées ont pu être classées selon l'importance relative de ces deux compartiments. Celle-ci est liée à la teneur initiale des litières en substances hydrosolubles et en carbone. Elle est également fortement corrélée à l'information spectrale des litières initiales, obtenue par spectrométrie de réflexion dans le proche infrarouge. Par contre, la vitesse à laquelle ont diminué les compartiments labile et résistant est liée à la perméabilité des feuilles pour le premier, et à leur épaisseur et leur masse surfacique pour le second. La spectrométrie proche infrarouge offre de nouvelles perspectives pour la caractérisation de l'aptitude des litières à décomposer.

Mots clés : litière, décomposition, spectrométrie proche infrarouge