Water Resources Research Act Program

Details for Project ID 2020NC175B

Investigating the microbial culprits of taste/odor issues in City of Durham drinking water reservoir Lake Michie and algicidal mitigation tactics.

Institute: North Carolina
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $30,000 Total Non-Federal Funds: $12,762

Principal Investigators: Dr. Ryan W. Paerl

Abstract: Concentrations of the earthy/musty taste/odor compounds geosmin and MIB (2-methylisoborneol) annually exceed the threshold of human detection (~10 ng/L) in key drinking water reservoirs in Durham County, specifically Lake Michie. This causes a notable rise in customer complaints to City of Durham Water Management Department (CDWMD), especially in late Spring and Summer, and a perception that drinking water quality is poor. The microbialsource(s) of these taste & odor (T&O) compounds is assumed; thus targets for effective monitoring and mitigation are not well-established. Recent phytoplankton monitoring, via flow cytometry (FCM) and microscopy, suggests picocyanobacteria (PicoC; cyanobacteria <3 μm diameter) have a role in elevated geosmin concentrations in Spring and early Summer– an intriguing result as PicoC’s are often overlooked as geosmin sources. In summer –filamentous cyanobacteria are more prevalent and may contribute to high geosmin and MIB levels during this time of the year. CDWMD uses copper-sulfate based algicide to reduce cyanobacterial biomass and T&O but the effectiveness of the treatment and whether reduced application could better aid T&O mitigation is unknown. It is hypothesized that: (H1) high net growth of PicoC is linked to geosmin peaks in Spring, while filamentous cyanobacteria are key producers in Summer; (H2) PicoC and filamentous cyanobacteria are the most prevalent geosmin producers in LM; (H3) reduced algicide addition will have a bacteriostatic effect – where cyanobacteria are not extensively lysed and concentrations of T&O compounds in the dissolved phase are reduced. H1 will be tested via improved time-series monitoring of phytoplankton (PicoC, filamentous cyanobacteria) and concentrations of T&O earlier in the phytoplankton growth season. H2 will tested using metagenomic sequencing of Lake Michie plankton DNA to directly identify populations possessing geosmin or MIB synthase genes. Last, algicide gradient addition experiments will be performed to test H3. Expected outcomes include: (1) establishment of phytoplankton targets for future monitoring and/or prediction of elevated T&O concentrations and (2) an evaluation of reduced algicide addition as an approach for water managers to lower dissolved T&O compound levels and save on costs. An educational outcome of the project will be T&O teaching modules that convey basics of what compounds are involved and who produces them to the general public. The module will be implemented as part of an ongoing ‘mobile laboratory’ outreach program (called MAML) at Lake Johnson, Raleigh, and will include pre- and post-questionnaires to assess the effectiveness of these modules.