Separation Efficiency Studies

Much attention has recently been given to the occurrence of harmful algal blooms (HABS) and the need for enhanced regulation through the U.S. EPA Water Quality Standards Program. Many studies have been conducted to further our understanding of the complex dynamics of cyanobacterial abundance and community composition as they are affected by water temperature, solar irradiance, hydrology, nutrient supply and meteorological conditions. A recent report (Lopez et al 2008) outlines current and future efforts that would support and expand our understanding of cyanobacteria, the cyanotoxins they produce, ecological impacts, human health effects and management techniques.

The regulatory community may require data on the weight specific toxicity of the phytoplankton and zooplankton to implement future regulatory programs. The toxigenicity of the cyanobacterial community could be assessed with a rapid, cost effective method to obtain samples that yield precise measures of phytoplankton biomass and weight specific toxicity. This information could be used to determine trends in the ecological integrity of the aquatic systems and support the decision making process regarding use attainment. Ecological risk assessments of bioaccumulation in zooplankton (i.e. bulk zooplankton, dominant grazers) could be simplified and improved with a rapid, cost effective method to obtain samples that yield precise measures of zooplankton biomass and weight specific toxicity.

Currently several methods are commonly used to obtain these samples, including particle size fractioning using mesh filters, and physical separation using pipettes and stereomicroscopes. The particle size fractioning method can be conducted quickly, however resultant sample purity for both the phytoplankton and zooplankton fractions is questionable. Physical separation using pipettes and stereomicroscopes can provide a completely pure zooplankton sample, however this is a costly, labor intensive process. Our method relies upon the phenomenon of phototaxis to physically separate the zooplankton from the phytoplankton. We have developed a device that provides the conditions necessary to initiate and direct the movement of zooplankton. Studies were conducted over two years (2013-2014) in freshwater systems (Figure 1 and Figure 2) to evaluate separation efficiency for zooplankton and phytoplankton as measured by zooplankton biomass, microcystis equivants and chlorophyll(a). These studies revealed that a net plankton sample could be successfully separated into a zooplankton sample containing dominant grazers (80% or greater biomass) with minimal contamination of phytoplankton (<5% biomass) in 30 minutes. The evaluation included the original prototype (2013) and an improved design (2014). There was no significant difference in zooplankton separation efficiencies for either lake between sampling years. As can be seen from Figure 1 and Figure 2, significant reductions in amount and variability of microcystis equivalents and chlorophyll(a) were observed in 2014 with the improved design.

WEB_Fig1_LakeCochichewick_20132014 WEB_Fig2_WillandPond_20132014
Figure 1
Figure 2


Additional studies were conducted in 2014 to determine whether similar results would be obtained in marine systems. Net plankton samples were obtained from a near shore estuarine site.As shown in Figure 3, the separation efficiency was similar to that observed for Lake Cochichewick and Willand Pond.

 Figure 3 JELPier_2014
Figure 3

These results suggest there may be several factors which will influence the separation efficiency that can be achieved including trophic status, community composition and body length. The 2014 data from Lake Cochichewick was used to evaluate the influence of body length on separation efficiency. The regression analysis, as shown in Figure 4, revealed a significant relationship between the two variables. Additional analysis (Figure 5) indicated that community composition and body length both influenced the separation efficiency that could be achieved. A more complete data set will be needed to conduct more robust analysis of the variables that influence separation efficiency. These preliminary findings suggest that separation efficiency could be estimated based upon an initial identification, enumeration and measurement of the zooplankton in a sample.

WEB_Fig4_LakeCochichewick_2014_regression WEB_Fig5_LakeCochichewick_2014_ordertime
Figure 4
Figure 5