Composition of algae assemblages in middle Tennessee streams and correlations of composition to trophic state

Abstract

Evaluations of the composition and biomass of photoautotrophic periphyton, nutrient concentrations of water, and concentrations of total phosphorous of benthic organic matter at eight stream sites in Middle Tennessee were used to: (1) document the composition of soft-algae and diatom assemblages, (2) assess the trophic state of the stream sites, (3) correlate trophic state to percent composition of soft-algae taxa, and (4) construct biotic indices using soft-algae taxa to help monitor trophic state. The concentration of total phosphorous of benthic organic matter was a more accurate indicator of the trophic state of the stream sites we studied relative to nutrient concentrations of water as demonstrated by correlation coefficients for nutrient concentrations to benthic concentrations of chlorophyll a, ash-free dry mass of benthic organic matter, and biotic indices which denote trophic state using diatom and soft-algae taxa. The algae trophic index developed using soft-algae taxa abundance-weighted averages of benthic concentrations of chlorophyll a correlates significantly to all of the benthic characteristics used to denote trophic state. This index is the first to utilize periphyton characteristics, as opposed to nutrient concentrations of water, to assign trophic-indicator values to soft-algae taxa in lotic systems and does not require a computer program to compute.

Photoautotrophic-Periphyton Composition in Reaches with Differing Nutrient Concentrations in the Harpeth River of Middle Tennessee

“…Taxa not identified to species were excluded from index calculations and included less than 10% of the algae observed. The algae trophic index of soft-algae assemblages values for stream reaches studied by Grimmett and Lebkuecher (2017) were very similar to and significantly correlated with concentrations of benthic chl a (mg . m À2 ).…”

“…All sites had AFDM values >10 g . m À2 , a threshold value indicative of eutrophic environments based on earlier studies (O'Brien and Wehr 2010, Lebkuecher et al 2015, Grimmett and Lebkuecher 2017. The eutrophic concentrations of TP at the sites upstream of the Franklin Wastewater Treatment Facility likely reflect the heavy anthropogenic activities in the watershed and naturally high concentrations of P in the limestone bedrock (TDEC 2005).…”

“…Periphyton pigment concentrations and ash-free dry mass. Methods to determine periphyton pigment concentrations and AFDM followed those described in Lebkuecher et al (2015) and Grimmett and Lebkuecher (2017). One cobble was placed in a glass pan containing 0.1 L of 90% acetone and the periphyton was removed with a single-edged razor blade and scrub brush.…”

“…where: n j ¼ number of taxon units j sampled at a site, ti j ¼ trophic-indicator value for taxon j, and N ¼ total number of taxon units at the sampling site used to calculate the index (Grimmett and Lebkuecher 2017). The trophic-indicator values are the abundance-weighted average of the concentration of benthic chl a, listed in Grimmett and Lebkuecher (2017). Taxa not identified to species were excluded from index calculations and included less than 10% of the algae observed.…”

“…Algae are a major component of the trophic base of most shallow lotic systems and assemblage composition may reflect periphyton habitat quality (Stancheva and Sheath 2016). The composition of algae assemblages of the majority of streams in the Interior Plateau Level III Ecoregion that extends from southern Indiana and Ohio to northern Alabama is unknown (Grimmett and Lebkuecher 2017). This lack of knowledge limits the ability of watershed managers to monitor changes of habitat quality.…”