Does iron availability determine the trophic state of freshwater lakes?

Ecohydrology seminar

Dr. Diane Orihel
Department of Biological Sciences, University of Alberta Freshwater Institute, Winnipeg

Everyone welcome

Refreshments provided

Abstract:

Eutrophication of freshwaters is generally attributed to excessive nutrient inputs, but sulphur pollution may be exacerbating this global problem by stimulating internal phosphorous loading in lakes. Because sulphur forms insoluble complexes with iron, sulphur may render lakes deficient in the element that sequesters phosphorous in sediments. However, the role of iron in controlling the trophic state of freshwaters is poorly elucidated due to its antagonistic effects on primary productivity. Iron is an essential micronutrient that stimulated algal growth, if other nutrients are in adequate supply. In contrast, iron increases the phosphorous-binding capacity of sediments which may inhibit algal growth, if phosphorous is in short supply. We tested these competing hypotheses by adding different amounts of iron to fifteen mesocosms in an iron-deficient hypereutrophic Canadian lake. Iron reduced phosphorous levels, decreased algal biomass, and suppressed cyanobacterial dominance. This research suggests that iron may act as a master variable controlling lake trophic state, and that the consequences of sulphur pollution on iron availability- and hence water quality –in freshwaters needs to be considered.