The estimated total number of diatom valves recovered after each extraction technique is shown in Fig. 1. A greater number of diatom particulates were recorded in the stream control sample when compared to the pond and Greenland sites which was reflected in the experimental samples. Over 12,000 valves per cm2 of t-shirt were observed in all experimental stream samples,
compared to fewer than 1000 valves in the majority of the pond and Greenland sites. A greater proportion of diatoms were recovered after H2O2 extraction in all samples (Fig. 2). The diatom yield from RE and RW extraction varied amongst sites, with a higher proportion of diatoms recovered after ethanol rinsing in Greenland samples (RE [383%]) and water in pond samples (RW [206%]). The majority of diatoms observed in all t-shirt samples were extracted following 3 h of submersion (Fig. 3). Though still relatively high, diatom counts after 24h decreased marginally. Counts were lower after shorter submersion intervals.
Species richness (the total number of diatom taxa identified in a sample) was higher in stream and Greenland sites when compared to the pond. All control samples identified distinctive assemblages, composed of both abundant species and exotic markers. For example in the stream control site, Melosira varians was observed in abundance whereas Gomphonema truncatum was relatively sparse. Composition data for the t-shirt samples reflected this trend. Correspondence analysis plots highlight the similarity of experimental and control samples in their species assemblage. The closer sample points are in proximity displays greater similarity
than to those samples further apart (Fig. 4). In the stream samples, all extraction methods exhibit affinity to the control site although greater similarity is observed in all four of the H2O2 samples. The Greenland and pond t-shirt samples display greater variation amongst experimental samples, with greater similarity witnessed in the species composition of diatoms extracted by H2O2 submersion. This is an important finding as it suggests that H2O2 samples consistently resemble the greatest similarity to the relevant control site.