Loring Pond Duckweed Abundance and Diversity Assessment Via By-Catch of Surface Skimming, and Suitability of Compost for Organic Gardens

Abstract

Duckweed are tiny aquatic plants that are part of the Lemnaceae family including five genera: Lemna, Landoltia, Spirodela, Wolffia, and Wolfiella. Previous research has shown duckweed to have strong properties of phytoremediation of heavy metals and other pollutants (Ekperusi et al., 2019). Here we examine Loring Pond, an urban pond in Minneapolis, Minnesota, that is partially covered by duckweed, and the levels of biodiversity found in the surface skimming by-catch of this wetland. We also discuss the potential of utilizing composted duckweed in agriculture. Shallow marsh sites monitored across Minnesota, by the Minnesota Department of Natural Resources, have recorded H-index ranges of 2.7 – 3.6 (MN DNR Wetland Hydrology Monitoring Report 2023, p. 21). After identifying and quantifying the specimens observed during surveys conducted, and utilizing the Shannon-Wiener index, we show that diversity in the surface skimming by-catch of Loring Pond is low with determination in June, July, and August to be H = 0.388, 0.126, and 0.212, respectively, Overall, watermeal (Wolffia spp.) dominated surveys and indicated an inverse relationship with both biodiversity and certain heavy metal levels. Elemental analysis of composted duckweed revealed a few heavy metals fell below detectable limit, including Beryllium (Be), Cadmium (Cd), Vanadium (V), and Rubidium (Rb). Lead (Pb) was found to exceed allowable limits in organic fertilizers (27 mg/kg) 4 times out of 7 samples and reaching just over 51 mg/kg at the highest level. Our results confirmed that wetlands covered by duckweed may have limited biodiversity, although surveys in this study revealed 15 genera total. Four other plant genera and eight animal phyla were observed, which suggests a variety of organisms and elements would be removed during commercial skimming of Loring Pond. Further testing is needed to confirm the ability of duckweed to inhibit diversity in the pond itself, along with the viability of utilizing composted duckweed in agriculture due to the persistence of Pb.