Algal Preservation and Enumeration Techniques for use in Micro- and Mesocosms Studies
Standard, lower tier, testing strategies for the effects of Plant Protection Products (PPP’s) on algae are focused on single species studies and may not provide adequate protection for these important communities. Higher tier approaches, such as micro/mesocosm studies are designed to represent edge of field water bodies by creating a habitat that will support communities of aquatic macrophytes, algae, zooplankton and macroinvertebrates in a contained system. Therefore, these experimental systems offer a more comprehensive analysis of the effects of PPPs on these communities. Whilst definitively more representative of natural systems, this increase in complexity brings further challenges.
Freshwater algal communities are very diverse, the taxonomic identification of these species is difficult, and requires trained taxonomists. When designing these studies, consideration needs to be given to the methods employed for sampling, preservation and enumeration to ensure all steps are fit for purpose. The sampling processes need to offer a true representation of the algal assemblages present. One of the major difficulties in sampling freshwater alage is preservation. The need for preservation at all should be considered as they will damage algal morphology over time, however this step is often a necessity in larger, long-term studies. Following sample collection, enumeration is necessary to collect the data needed to derive ecotoxicological endpoints, e.g. MDD’s, ECx and NOEC’s. As with the sampling procedures, this process needs to use sub-samples that accurately reflect the whole test system. Here we present and assess different methods that can be used for the sampling preservation and enumeration of freshwater phytoplankton and periphyton. We discuss the pro’s and cons of these approaches and present methods for the analysis of microcosm and mesocosm algal samples that have provided the most reliable and robust statistical data from studies conducted at CEA.
For further information about this work please contact Zoe Parker-Crosse.