USING A MULTI-PARAMETER BIOGEOLOGICAL APPROACH TO TRACK THE IMPACT OF TREATED SEWAGE DISCHARGE ON URBAN STREAMS

Assessment of sewage effluent discharge on urban streams has focused on the impact increases in nutrients has on photosynthetic autotroph productivity and subsequent river eutrophication. However, another potential tracer is shifts in microbial communities, which have the potential to specifically track human fecal sources pre- and post-plant effluent discharges. To evaluate this, grab samples were collected on two dates in May 2016 along the Wissahickon Creek, an urban stream outside Philadelphia, PA. Samples were collected above and below the discharge to the Creek of two wastewater treatment plants (WWTPs), and along one of its tributaries. These samples were chemically evaluated using IC, ICP-OES, and spectrophotography for inorganic dissolved constituents. To characterize the impact of wastewater effluent outflows on microbial communities, whole genomic DNA was extracted from these samples and subjected to real-time quantitative PCR (q-PCR) targeting human-associated bacteria and Targeted Amplicon Sequencing (TAS) on an Illumina MiSeq sequencer. Surface water below effluent discharge showed an order of magnitude increase in nitrate, up to 2.5 mg N/L, with decreases in concentration between the WWTPs indicating nutrient removal. Total dissolved P and soluble reactive PO₄ increased below WWTPs, but concentrations in the tributary are double that in the main stem, increasing from 0.15 mg P/L to 0.3 mg P/L. q-PCR results indicated that microbes associated with human fecal sources were found in higher abundance at sites immediately downstream of effluent sources, in comparison to samples collected immediately upstream. Increases of 1 to 2 orders of magnitude were observed indicating that these outflows contributed a substantial quantity of bacterial mass to the receiving stream. To complement these findings, TAS targeting bacterial 16s rRNA is currently being performed to determine the bacterial community present in the samples. Combining water chemistry with biological indicators and tools from molecular ecology reveals more clearly the impact treated sewage effluent has on water quality. The use of such multi-faceted approaches to assess water quality, and changes therein, is especially important if receiving waters are used for human recreation or have been subject to preservation efforts.