Using the Modified Redfield Ratio to estimate Harmful Algal Blooms

Abstract

Many waterbodies across Nova Scotia (Canada) have been experiencing algal blooms occurring in large numbers and diversity, without knowledge or understanding about their causes and effects. Algal blooms have appeared in Mattatall Lake (ML) and other lakes of the province in recent years. ML experienced severe algal blooms in 2013. During the fall of 2014, massive algal blooms appeared in ML, and persisted until late December 2014. The blooms have a pattern of being nontoxic in the summer and potentially toxic in the fall-winter season, with nutrients increasing on a monthly basis. This phenomenon is unusual as algal blooms have not been known to last until the winter season or coexist with icy conditions. The dominant species in this bloom was identified to be Anabaena planctonica (Dolicospermum planctonicum) with a cell count around 250 000 cells/mL, which may produce the neurotoxin Anatoxin-a. This cell count is approximately two and a half times higher than the alert level 2 guideline from World Health Organization’s drinking water standards (WHO, 2003). The goal of this paper is to use an index (Modified Redfield Ratio, hereafter called MRR) to estimate the HAB occurrence the Mattatall lake (Nova Scotia, Canada), served as a pilot site for our pioneering systematic study in order to evaluate the recent bloom phenomena in the entire province of Nova Scotia.