Spaulding, S. | Search bioRxiv

bioRxiv2018

Enhancing Percolation in Phosphatic Clay Using Diatoms under Laboratory Conditions

Clay settling areas are large impoundments brought about by phosphate mining with water-holding capacity that renders it very poor for agriculture and crop production. This study aims to enhance water percolation in phosphatic clay using porous diatom frustules under laboratory conditions. Phosphatic clay collected from settling areas was brought to the laboratory for the experiment. Diatom frustules were purchased commercially and dry samples of the diatom, Didymosphenia were provided by the University of Colorado-Boulder. Oven-dried clay was mixed with diatom frustules into 125 mL centrifuge tubes following a 1:1 volume ratio as experimental set-ups while pure phosphatic clay was used as control. Deionized water was poured into each set-up and the percentage of unpercolated water overlying the sediment, water retained in the sediment particles, water that percolated and passed through the hole of the centrifuge tube were monitored for 48 hours. Results showed that the addition of diatom frustules enhances the percolation of water in the sediment mixture especially those with Didymosphenia frustules. However, this mixture also showed higher percentage of water retained in the sediment particles which could be attributed to the high carbon and organic content brought about by the presence of stalks which is a major component of this species morphology. Considering how Didymosphenia disturbs freshwater habitats, proper management may render it useful for the mitigation of clay settling areas in the land environment. The implication of this on crop production remains to be explored and further in situ experimentations need to be conducted.\n\nIMPORTANCEClay settling areas abound in places where phosphate mining is conducted. The very fine particles and the chemical property of this phosphatic clay allows it to hold water more than normal clay sediments making the area unstable and less suitable for agricultural use. Studies show that mitigative measures to enhance surface drainage is very costly leaving most areas barren and unused. Diatoms are unicellular algae in various size and shapes with silicified cell walls that are porous and are ubiquitous in aquatic environments. The significance of our research is being able to demonstrate the potential use of diatoms, most especially the genus Didymosphenia which is regarded as an environmental threat to some habitats, in mitigating the drainage problem in clay settling areas by mixing phosphatic clay with diatom frustules. This process is cost-effective and more importantly provides utilization of a resource that is regarded as nuisance in freshwater environments.

ecology↗

bioRxiv2018

Environmental DNA reveals the structure of phytoplankton assemblages along a 2900-km transect in the Mississippi River

The environmental health of aquatic ecosystems is critical to society, yet traditional assessments of water quality have limited utility for some bodies of water such as large rivers. Sequencing of environmental DNA (eDNA) has the potential to complement if not replace traditional sampling of biotic assemblages for the purposes of reconstructing aquatic assemblages and, by proxy, assessing water quality. Despite this potential, there has been little testing of the ability of eDNA to reconstruct assemblages and their absolute and relative utility to infer water quality metrics. Here, we reconstruct phytoplankton communities by amplifying and sequencing DNA from a portion of the 23S rRNA region from filtered water samples along a 2900-km transect in the Mississippi River. Across the entire length, diatoms dominated the assemblage (72.6%) followed by cryptophytes (8.7%) and cyanobacteria (7.0%). There were no general trends in the abundances of these major taxa along the length of the river, but individual taxon abundance peaked in different regions. For example, the abundance of taxa genetically similar to Melosira tropica peaked at approximately 60% of all reads 2750 km upstream from the Gulf of Mexico, while taxa similar to Skeletonema marinoi began to increase below the confluence with the Missouri River until it reached approximately 30% of the reads at the Gulf of Mexico. There were four main clusters of samples based on phytoplankton abundance, two above the confluence with the Missouri and two below. Phytoplankton abundance was a poor predictor of NH4 + concentrations in the water, but predicted 61% and 80% of the variation in observed NO3 -and PO4 3-concentrations, respectively. Phytoplankton richness increased with increasing distance along the river, but was best explained by phosphate concentrations and water clarity. Along the Mississippi transect, there was similar structure to phytoplankton and bacterial assemblages, indicating that the two sets of organisms are responding to similar environmental factors. In all, the research here demonstrates the potential utility of metabarcoding for reconstructing aquatic assemblages, which might aid in conducting water quality assessments.

ecology↗