Visible Derivative Spectroscopic Monitoring of the Old Woman Creek National Estuary During a Historically Dry Year and a Wet Year

Abstract

Visible derivative spectroscopy was used to interpret the sediment and phytoplankton assemblages within the old woman creek natural estuarine reserve during the summers of 2016 and 2017. A Varimax-rotated Principal Component Analysis (VPCA) of reflectance data collected from four sampling sites in 2016 identified three Varimax-rotated Principal Components (VPCs): Diatom + Illite (2016-VPC 1), Dinoflagellate Algae + Cyanobacteria + Cryptophytes (2016-VPC 2) and Cyanobacteria + Illite + Dinoflagellate Algae (2016-VPC 3). Four leading components were identified from the VPCA of 2017 data collected from six sampling sites. These include a diatom + green algae + cyanobacteria (2017-VPC 1), suspended clay (2017-VPC 2) and two dinoflagellate algae communities, each of which was associated with sediments and cyanobacteria (2017-VPC 3 and 4). Significant correlations between chlorophyll-a versus 2017-VPC 1 and 2017-VPC 2 versus total suspended solids confirm these PCs' applicability as proxies for algal abundance and suspended material/sediments, respectively. During the wet 2017 sampling period, when the mouth bar controlling the flow from the estuary to Lake Erie was open; diatom, cyanobacteria and green algae abundance in the estuary declined immediately after rainfall and increased within two to three days as the estuary recolonized with phytoplankton transported from upstream. The inflow of storm water increased the concentration of insoluble clay minerals within the estuary but declined within two to three days. Suspended sediments were transported into the lake through the estuary when the mouth bar was open. As the mouth bar progressively narrowed towards the end of the 2017 sampling period, the amount of algae and suspended material transported into the lake declined and was more concentrated in the upstream sampling sites. Observed temporal and spatial variation of sediments demonstrates the significance of the estuary environments as natural sediment retention structures.