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Using the 10AU for Ammonium Measurements

Parameters: Ammonium

Rebecca North is a doctoral student under the supervision of Dr. Stephanie Guildford and Dr. Ralph Smith at the University of Waterloo. She was awarded an International Development Research Centre (IDRC, Ottawa, Canada) doctoral research grant to continue her studies on nutrient limitation in African Great Lakes by visiting Lake Tanganyika and Lake Victoria in the fall of 2004. The goal of her thesis project is to understand the relationships between phosphorus (P), nitrogen (N), iron (Fe) and light in controlling algal biomass in temperate and tropical Great Lakes: Lake Erie, Lake Malawi, Lake Victoria and Lake Tanganyika. Her research has identified which nutrients, P, N, or Fe, are limiting to the phytoplankton communities in the pelagic and littoral zones of the lakes. These issues are important as changing nutrient regimes can affect all freshwater systems and it is critical to understand which type of nutrient inputs can have the most impact. She investigated the nutrient status of the Lake Tanganyika phytoplankton and the role of iron in mediating nutrient uptake and interactions. The Lake Tanganyika data will be incorporated into her Ph.D. thesis entitled “The influence of Fe bioavailability on the nutrient status of phytoplankton communities in temperate and tropical Great lakes” as well as in primary scientific journals. Her hypothesis is that the bioavailability of Fe affects N and P limitation of phytoplankton communities in Great Lakes. Lake Tanganyika is a N limited system where Fe appears to influence the availability and species of N and P utilized by the phytoplankton communities. Ammonium assimilation is the only means of meeting N demands of the phytoplankton communities that does not require Fe.

Using the 10-AU Field Fluorometer and employing a new sensitive fluorometric technique for the detection of low concentrations of ammonium [Holmes et al. 1999] has allowed her to measure the extremely low ammonium concentrations in Lake Tanganyika. Her research will build upon previous studies of Lake Tanganyika and its phytoplankton by Dr. Piet Verburg and Dr. Robert Hecky at the University of Waterloo [Verburg et al. 2003]. Verburg’s research published in 2003 has established that the nutrient regime of the lake may be changing due to a warming climate and this may be increasing the probability of iron limitation of algal growth. Her specific program for Lake Tanganyika was to measure a variety of nutrient status indicators for the nutrients N, P, and Fe and incorporate this data into a summary of the phytoplankton nutrient status of Lake Tanganyika. Her research will greatly expand on the understanding of phytoplankton-nutrient relationships on the lake to support ongoing efforts to manage the lake’s productivity and in particular, its valuable fishery.

References Holmes, R. M., Aminot, A., Kerouel, R., Hooker, B. A., and Peterson, B. J. A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Canadian Journal of Fisheries and Aquatic Sciences 56, 1801-1808. 1999. Verburg, P., Hecky, R. E., and Kling, H. Ecological consequences of a century of warming in Lake Tanganyika. Science 301, 505-507. 2003.

Author: Rebecca North Institution: University of Waterloo

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