Characterization of pigments in photosynthetic benthic biomass on the river bed of the Upper Clark Fork River (Montana, USA) during the algal growing season of 2020

The Upper Clark Fork River (UCFR) Long Term Research in Environmental Biology (LTREB) umbrella monitoring project generating these data is conducted separately and complementarily to the 200-million-dollar (USD) superfund project for ecological restoration of the UCFR, associated tributaries, and head water streams including Silver Bow and Warm Springs Creeks. Restoration along the UCFR in western Montana includes removal of metal-laden floodplain soils, lowering of the floodplain to its original elevation, and re-vegetation of over 70 km of the river’s floodplain closest to contaminant sources. The UCFR LTREB project includes bi-weekly water quality monitoring across the first 200 km of the river and its major tributaries along a gradient of heavy metal contamination associated with historic mining. Monitoring includes inorganic phosphorus and nitrogen concentrations, biotic standing stocks, and dissolved and whole-water heavy metal concentrations. The monitoring program began in 2017 with funding likely to be extended through 2028. The original analytical intent for data in this product was to assess the response of the river algal community to the floodplain restoration. Data are measurements of benthic biomass organic matter standing stocks and pigments associated with primary producers. Benthic biomass data were collected on the UCFR (USGS HUC 17010201) at seven monitoring sites distributed from Warm Springs (near Anaconda, MT) to Bonita (east of Missoula, MT). Data from the Deer Lodge and Garrison sites were obtained from the River Algal Succession Study, a project funded by the Montana Consortium for Research on Environmental Water Systems. Data from Bonita were obtained from the Nitrogen Fixation Algal Study, a Research Experience for Undergraduates project. Benthic samples were obtained using a cylindrical benthic sampler isolating a known area of the river bed. Five samples were obtained at each site. Estimates of organic matter in biomass were obtained from area-normalized ash-free dry mass. Algal pigment concentrations for chlorophyll and phaeophytin were obtained through the use of extraction in acetone followed by spectroscopy. Phycocyanin concentrations were measured in aqueous suspension (in-vivo) with a fluorometer. Biomass compartments were discriminated between epilithon on river bed substrate, epiphyton on filamentous algae, terrestrial coarse particulate organic carbon, deposited fine benthic organic matter, and macrophytes. Data are from the 2020 algal growing season.