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

Abstract

Four sites of the Harpeth River, two upstream and two downstream of the Franklin Wastewater Treatment Facility in Franklin, Tennessee, were sampled to assess the impact of nutrient enrichment on the integrity of photoautotrophic periphyton. Concentrations of total phosphorus of water samples ranged from 310 μg.L-1 at the uppermost site to 1035 μg.L-1 at the site immediately downstream of the wastewater treatment facility. Concentrations of total nitrogen of water samples ranged from 687 μg.L-1 at the uppermost site to 1,434 μg.L-1 at the site immediately downstream of the wastewater treatment facility. Concentrations of benthic chlorophyll a did not differ significantly among the sites and ranged from 103 ± 11 mg.m-2 at the site immediately upstream of the wastewater treatment facility to 151 ± 13 mg.m-2 at the site immediately downstream. Percent composition of 186 algae taxa were documented: 92 taxa of soft-bodied algae and 94 taxa of diatoms. Values for the algae trophic index for soft-bodied algal assemblages increased from 71 at the site immediately upstream of the wastewater treatment facility to 107 at the site immediately downstream. Values for the pollution tolerance index for diatom assemblages decreased from 2.55 at the site immediately upstream of the wastewater treatment facility to 2.20 at the site immediately downstream. These index values demonstrate that the assemblages of soft-bodied algae and diatoms immediately downstream the wastewater treatment facility had a greater relative abundance of taxa tolerant of eutrophic conditions compared to the assemblages at the site immediately upstream.