A comparison of phytoplankton quantifying techniques to assess nutrient limitation of
communities
John Whalen, Mike Vanni, Beth Mette, Nicole Hayes
Phytoplankton growth is limited by the availability of solar radiation and limiting nutrients.
Nutrient limitation assays are commonly used to determine whether phytoplankton are
individually or co-limited by nitrogen and/or phosphorus. The degree of nutrient limitation of
phytoplankton is traditionally assessed using a fluorometer, which measures chlorophyll-a as an
indicator of phytoplankton biomass. There is little research that utilizes a spectrofluoroprobe for
nutrient limitation assays. The spectrofluoroprobe is unique in that it not only estimates
phytoplankton biomass, but also the concentration of major phytoplankton taxonomic groups,
Nutrient limitation assays were conducted on phytoplankton samples from two sites in Lake
Acton using both the fluorometer and spectrofluoroprobe techniques. This allowed us to 1.
compare the two techniques for quantifying phytoplankton biomass and the degree of nutrient
limitation of the whole community and 2. assess the variations in the degree of nutrient limitation
of four major phytoplankton taxonomic groups (chlorophytes, cyanobacteria, diatoms,
cryptophyta).
The data show that the two methods are strongly and positively correlated when looking at the
two sites, both together and independently (p < 0.0001). The two methods are strongly and
positively correlated with each type of limitation, while independently evaluating both sites (p <
0.005). This study suggests that the phytoplankton community composition impacts the response
of the whole community to nutrient limitation, as the taxonomic groups had differential
responses to nutrient limitation.
This suggests that the spectrofluoroprobe technique is a promising method for assessing nutrient
limitation of the whole phytoplankton community and within individual taxonomic groups.