Field enrichments with nitrate in two spring-fed drainage lines within the riparian zone of a small woodland stream near Toronto, Ontario showed an absence of nitrate depletion. Laboratory experiments with riparian substrates overlain with nitrate enriched solutions revealed a loss of only 5-8% of the nitrate during 48 h incubation at 12 "C. However, 22-24% of the initial nitrate was depleted between 24 and 48 h when a second set of substrate cores was incubated at 20 "C. Short-term (3 h) incubations of fresh substrates amended with acetylene were used to estimate in situ denitrification potentials which varied from 0.05 -3.19 pg N gP1 d-' for organic and sandy sediments. Denitrification potentials were highly correlated with initial nitrate content of substrate samples implying that low nitrate levels in ground water and riparian substrates may be an important factor in controlling denitrification rates. The efficiency of nitrate removal in spring-fed drainage lines is also limited by short water residence times of < 1 h within the riparian zone. These data suggest that routes of ground water movement and substrate characteristics are important in determining nitrate depletion within stream riparian areas.

Field enrichments with ammonium were conducted for periods of 4–4.5 h on two springs in the riparian zone of a small woodland stream near Toronto, Ontario. Springwater lost much of the injected ammonium as it flowed over organic and sandy riparian substrates before entering the stream. Negligible nitrate release occurred during the ammonium enrichments. Laboratory experiments revealed that riparian substrates rapidly removed ammonium from enriched springwater. Sediments covered with aerated ammonium-enriched water showed a small nitrate-N increase of 9–12 μg∙L−1 after 5 h. An absence of ammonium depletion in sterilized organic substrates and very small losses in low-temperature (1 °C) incubations suggested that microbial activity rather than adsorption was responsible for ammonium uptake. The rapid loss of ammonium from springwater overlying acetylene-treated substrates, despite the complete inhibition of nitrification, indicated that microbial immobilization was mainly responsible for ammonium depletion. We suggest that ammonium transformations in spring-fed areas of overland flow within the riparian zone may contribute significantly to the regulation of nitrogen inputs to small woodland streams.

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Die Autoren der Histoire du Canada bedienen sich einiger Brocken der indianischen Sprache und eines Französichstils, der dem Bedürfnis angepaßt ist, ein überzeugendes Bild zu liefern. Ihnen gelingt es derart, ein Lokalkolorit zu schaffen, in dem die rein sprachtheoretische Auskunft verloren geht oder sich im Pittoresken verbirgt. Man kann ihre Zwiespältigkeit (zur Schau stellen/verbergen ihrer Kompetenz) durch die Bezugnahme auf die Rivalität der religösen Qrden erklären, auf den Widerstand der «Wilden» und auf sprachtheoretische Probleme.

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