Eutrophication and altered phytoplankton behaviour: biomass versus species-based approaches

Ted Smayda
Graduate School of Oceanography
University of Rhode Island
Kingston, RI 02881
tsmayda@gso.uri.edu

Subjective descriptions and, increasingly, mass balance approaches rooted in Redfield Ratio stoichiometry and dose-yield kinetics are usually applied to classify whether a coastal water body has become eutrophicated, and to characterise the degree of hypernutrification. From this information, water quality classification schemes have been formulated and used by regulatory agencies. The mass balance approach, which is more quantitative, is based on the interactions (relationships) that occur among plant nutrient elevation, seasonal oxygen deficiency, and increases (above long-term baseline levels) in phytoplankton biomass (usually as chlorophyll) and primary production. While powerful insights have been obtained, the linkages between altered phytoplankton behaviour and nutrient enrichment of coastal waters, and the trophic mechanisms involved, are unclear and controversial. As a result, the abatement procedures and guidelines issued by regulatory agencies are also tenuous. Inexact definition of what is a bloom; general failure to recognise that eutrophication is a process rather than a simple on/off event; disregard of species and functional group behaviour; inadequate ecophysiological extrapolations; experimental difficulties; related blooms in pristine and oligo-nutrified waters, and entrenched resistance to multiple factor regulation, demonstrated to occur, in favor of single factor and common cause theory (Liebigian) seriously compromise mass balance approaches. These issues and the need to incorporate species-specific and functional group ecophysiology in place of community biomass as the basis of the mass balance approach to quantify eutrophication and its effects will be addressed. In this, the characteristics and stages of eutrophication as a process will be described, along with the different ways in which nutrients regulate community structure, species distributions and bloom behaviour.