Concentrations of pollutants in biotic materials are usually related to dry matter. This work demonstrates with the use of heavy metal-contaminated poplar leaves (Populus nigra 'Italica'), that ash of dry matter (dry ash) obviously yields a better reference, as it eliminates the natural variations among organic substance contents.Values of heavy-metal concentrations in dry ash of leaves were generally more homogeneous and better correlated with corresponding values in air and soil than those in dry matter. It is further shown that concentrations of non-biodecomposable and non-volatile pollutants in the mineral fraction (the same as ash) of, for instance, plants and their residues (autumn leaves, mulch compost) can directly be compared with those in soil (nearly 100% mineral), and vice versa. This facilitates the setting of maximally permissible values for pollutant concentrations in plant dry matter or their residues, and in soil, which can be used in the protection of soils against pollutants accumulated in fresh or fallen leaves, mulch or compost. In this connection, the heavy-metal and lindane margins in West German regulations for issuing environmental certificates for compost products are discussed.Concentrations of pollutants in biotic materials are usually related to dry matter, rarely to fresh material. Within the framework of regional bioindication of lead-and cadmium immissions by means of leaves of the pyramidal poplar (Populus nigra 'ltalica') it was demonstrated that ashes of dry matter (dry ash) can also be used as a reference base (Claussen, 1987a;b). The leaves were sampled in the vicinity of 43 continuous measuring stations of The Institute for Protection against Immissions of North-Rhine Westfalia, which made its data available for this work. Heavy metals were determined both in ash and in dry matter.In contrast to dry substance, dry ash used as a reference medium for pollutants cannot be influence by the natural variabilities in water content and in organic substance content. One should bear in mind that the content of organic substance varies with age of the tissue and with circumstances during the growing season. Therefore these investigations in the Rhine-Ruhr region show that the measured values of lead and cadmium contents in dry ash are predominantly more homogeneous than those in dry matter. For instance, whereas the dry-matter values of these metals had coefficients of variation of 62.8% and 49.5%, respectively, those in dry ash were smaller with 57.9% and 48.1%, respectively (Claussen, 1987a).The correlations between lead and cadmium contents in dry ash and those in air or soil were
Zusammenfassung
In diesem Beitrag wird ein Schreibprojekt für angehende DaF-Lehrkräfte in Deutschland und Studierende der Auslandsgermanistik in Polen vorgestellt. Nach einer Darstellung der Rolle des Schreibens im Fremdsprachenunterricht und in der Fremdsprachenlehrerausbildung wird auf ausgewählte Online-Projekte eingegangen. Im nächsten Schritt werden die Ziele und der Ablauf des bereits erwähnten Projekts beschrieben. Im Anschluss daran wird das Projekt aus der Sicht der Lehrenden und Studierenden ausgewertet. Ziel dieses Beitrags ist es vor allem, zur Durchführung ähnlicher Projekte mit angehenden DaF-Lehrenden in den deutschsprachigen Ländern und internationalen DaF-Lernenden/-Studierenden – z. B. in der Auslandsgermanistik und in Studiengängen der Übersetzung – zu ermuntern.
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