Nutrient limitation of phytoplankton growth in Arctic lakes of the lower Mackenzie River Basin, northern Canada

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Abstract:

Water chemistry and the nutrients limiting phytoplankton growth were examined in lakes located in the Northwest Territories, Canada, along a transect from the Mackenzie River Delta south to Travaillant Lake. This 230km stretch spans gradients in vegetation types (tundra to boreal forest) and elevation (flooded by the Mackenzie River versus higher elevation lakes). Total phosphorus concentrations generally were typical of oligotrophic lakes (<10g·L–1), while nitrate and orthophosphate concentrations were below detection limits. Although some growth was noted in bioassays receiving single additions of nitrogen (N) or phosphorus (P), the greatest growth occurred in those bioassays in which nitrogen and phosphorus were added. This suggests that phytoplankton in the majority of study lakes were strongly co-limited by N and P irrespective of watershed type and Mackenzie River influence. Furthermore, it suggests that algal communities will be highly responsive to anthropogenic disturbances, which result in increased N and P loading to these lakes. Experimental results from March bioassays suggest that anthropogenic eutrophication would be exacerbated by increased temperatures (e.g., those associated with global warming).

Nous avons étudié la chimie de l’eau et les nutriments qui limitent la croissance du phytoplancton dans des lacs des Territoires du Nord-Ouest, Canada, le long d’un transect allant du delta du Mackenzie vers le sud jusqu’au lac Travaillant. Cette section de 230 km traverse des gradients de types végétaux (toundra à forêt boréale) et d’altitudes (lacs inondés par le Mackenzie à lacs de plus haute altitude). Les concentrations de phosphore total (<10g·L–1) sont généralement celles de lacs oligotrophes typiques, alors que les concentrations de nitrates et d’orthophosphore se situent sous le seuil de détection. Bien qu’il se fasse de la croissance dans certains tests biologiques ayant reçu une seule addition d’azote (N) ou de phosphore (P), la croissance la plus forte s’observe dans les tests biologiques qui ont reçu une addition d’azote et de phosphore. Cela indique que le phytoplancton dans la majorité des lacs étudiés est limité conjointement par N et P, quels que soient le type de bassin versant et les effets du Mackenzie. De plus, les résultats laissent croire que les communautés d’algues pourraient réagir fortement à des perturbations anthropiques qui augmenteraient l’apport de N et de P dans ces lacs. Les résultats expérimentaux des tests biologiques de mars indiquent que l’eutrophisation anthropique serait exacerbée par des températures plus élevées (par ex., celles associées au réchauffement global).

Document Type: Research Article

Publication date: February 1, 2009

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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