Fv/Fm as an Indicator of Phytoplankton Nutrient Status in Lake Malawi

Session: 27. - Emerging Partnerships, Research, and Capacity in the African Great Lakes

Stephanie Guildford, Large Lakes Observatory, University of Minnesota Duluth, [email protected]
Robert Hecky, Editor, Journal of Great Lakes Research, [email protected]
Greg Silsbe, University of Maryland Center for Environmental Science, [email protected]
Geoffrey House, [email protected]
Maxon Ngochera, Monkey Bay Fisheries Research Station, [email protected]

Abstract

Previously, using a suite of nutrient status indicators we demonstrated that phytoplankton in oligotrophic Lake Malawi is nutrient limited in the stratified season. Both nitrogen (N) and/or phosphorus (P) were limiting and the lake appeared to be in approximate balance for these two nutrients. Fluorometric methods are being increasingly utilized to evaluate nutrient status and estimate primary productivity. In particular the quantity Fv/Fm (as a measure of the quantum efficiency of photosystem II) has been investigated in cultures and natural systems. We used a Pulse Amplitude Modulated fluorometer to measure the dark adapted yields of photosystem II (Fv/Fm) at two stations in Lake Malawi. To determine if Fv/Fm can be used to identify limitation by a specific nutrient, we measured Fv/Fm in samples from an offshore and near shore station before and after amendment with N, P or Fe. Statistically significant differences in amendments and depth were observed at both stations. Fv/Fm appears to be a sensitive indicator for N deficiency. The method is a promising rapid assessment technique for investigating spatio-temporal variability in nutrient status in large lakes.

1. Keyword
Africa

2. Keyword
Lake Malawi

3. Keyword
photosynthesis

4. Additional Keyword
Fv/Fm

5. Additional Keyword
nutrient status