Groundwater-surface water interactions and flux of organic matter and nutrients in an urban, Mediterranean stream.

The chemical quality of dissolved organic matter (DOM) and the speciation of nitrogen exported from urban catchments is of great importance to biogeochemical cycling in riverine and coastal receiving waters. Many urban streams in Mediterranean climates have a flashy hydrologic regime, which would suggest a rapid pulsing and shunting of solutes downstream. However, the role of these systems both as passive pipes for solute transport or as reactors for DOM and nutrient transformation is still an open question for urban, Mediterranean streams. To address this question, we evaluated changes in concentrations of inorganic and organic solutes and DOM optical properties in Alvarado Creek, a perennially-flowing, urban, first-order tributary of the San Diego River in San Diego, CA, USA, during dry weather (baseflow) conditions and during four storm events in 2016-2018. Chloride and sulfate concentrations corroborate the supposed saline groundwater supply that maintains perennial flow and brackish nature in this urban stream. During dry weather, high proportions of protein-like fluorescent component (AC4) and downstream decreases in total dissolved nitrogen (TDN) and nitrate imply in-stream processing (nitrification and denitrification). By contrast, storm hysteresis curves indicate that the supply of DOM and TDN was not exhausted over the duration of a storm event, whereas nitrate was eventually depleted, presumably because nitrification could not keep up with the export of nitrate from source areas. Rapid decreases in chloride during the storm hydrograph coincided with a shift in specific ultraviolet absorbance (SUVA) and fluorescence index (FI) to more terrestrially-derived and aromatic carbon sources, most likely from interflow of stormwater through vadose zone soils. On an annual basis, the export of microbially-derived DOM during dry weather was higher than the export of terrestrially-derived DOM during storm events; both represent important carbon inputs to coastal waters.

Scaling of SARS-CoV-2 RNA in Settled Solids from Multiple Wastewater Treatment Plants to Compare Incidence Rates of Laboratory-Confirmed COVID-19 in Their Sewersheds.

Published and unpublished reports show that SARS-CoV-2 RNA in publicly owned treatment work (POTW) wastewater influent and solids is associated with new COVID-19 cases or incidence in associated sewersheds, but methods for comparing data collected from diverse POTWs to infer information about the relative incidence of laboratory-confirmed COVID-19 cases, and scaling to allow such comparisons, have not been previously established. Here, we show that SARS-CoV-2 N1 and N2 concentrations in solids normalized by concentrations of PMMoV RNA in solids can be used to compare incidence of laboratory confirmed new COVID-19 cases across POTWs. Using data collected at seven POTWs along the United States West Coast, Midwest, and East Coast serving ∼3% of the U.S. population (9 million people), we show that a 1 log change in N gene/PMMoV is associated with a 0.24 (range 0.19 to 0.29) log10 change in incidence of laboratory confirmed COVID-19. Scaling of N1 and N2 by PMMoV is consistent, conceptually, with a mass balance model relating SARS-CoV-2 RNA to the number of infected individuals shedding virus in their stool. This information should support the application of wastewater-based epidemiology to inform the response to the COVID-19 pandemic and potentially future viral pandemics.

SARS-CoV-2 in wastewater settled solids is associated with COVID-19 cases in a large urban sewershed

Wastewater-based epidemiology (WBE) may be useful for informing public health response to viral diseases like COVID-19 caused by SARS-CoV-2. We quantified SARS-CoV-2 RNA in wastewater influent and primary settled solids in two wastewater treatment plants to inform the pre-analytical and analytical approaches, and to assess whether influent or solids harbored more viral targets. The primary settled solids samples resulted in higher SARS-CoV-2 detection frequencies than the corresponding influent samples. Likewise, SARS-CoV-2 RNA was more readily detected in solids using one-step digital droplet (dd)RT-PCR than with two-step RT-QPCR and two-step ddRT-PCR, likely owing to reduced inhibition with the one-step ddRT-PCR assay. We subsequently analyzed a longitudinal time series of 89 settled solids samples from a single plant for SARS-CoV-2 RNA as well as coronavirus recovery (bovine coronavirus) and fecal strength (pepper mild mottle virus, PMMoV) controls. SARS-CoV-2 RNA targets N1 and N2 concentrations correlate positively and significantly with COVID-19 clinical confirmed case counts in the sewershed. Together, the results demonstrate that measuring SARS-CoV-2 RNA concentrations in settled solids may be a more sensitive approach than measuring SARs-CoV-2 in influent.