Tracking Land-Based Nutrient and Bacteria Inputs to Tillamook Estuary - Oregon (USA)

Tillamook Bay, located in Oregon (USA), experiences water quality impairments including low oxygen levels and elevated fecal bacteria levels. Addressing these issues is challenging due to the presence of multiple nutrient and bacterial sources including run-off from dairy operations, and human waste associated point source inputs and septic systems; hence, methods are needed to track fecal and nutrient sources to the system. Water samples were collected monthly (Jul 2016 - May 2017) at 16 tributary sites above and below potential anthropogenic pollution sources. Paired measurements were recorded for host-associated qPCR genetic markers targeting human, ruminant, cattle, canine, and avian fecal sources along with nutrient and E. coli levels and nitrate isotope (δ15N). Elevated nitrate isotopic ratios suggest anthropogenic sourcing of nitrate, but do not discriminate between human and other animal pollution sources. In 3 rivers (Kilchis, Wilson and Trask), nitrate and E. coli levels increased with downstream distance as the watershed transitioned from forested to agricultural/developed land use. During the wet season, ruminant marker (Rum2Bac) levels were highly correlated with E. coli (r2 = 0.89) and nitrate isotope (r2 = 0.83). Nitrogen load estimates from SPARROW demonstrate that manure and fertilizer explains >80% of the variation in ruminant marker, E. coli, and nitrate isotope levels. We demonstrate that additional discrimination of sources can be obtained by combining microbial source tracking, stable isotopes, and watershed models.

Impact/Purpose

Nutrients often enter water bodies with other co-pollutants such as bacteria. Tools are needed to identify pollutant sources within particular water bodies so that remediation efforts can be directed to the appropriate source to maximize the effectiveness of remediation efforts. Water samples were collected monthly (Jul 2016 - May 2017) at 16 tributary sites of the Tillamook Estuary, a system that has point source inputs associated with wastewater treatment facilities, and nonpoint source inputs associated with agricultural operations and on-site septic systems. We demonstrate that additional discrimination of sources can be obtained by combining microbial source tracking, stable isotopes, and watershed models of nitrogen inputs. Through this approach we were able to identify which sites are influenced by agricultural inputs, point source inputs, as well as unexpected contributions from birds.

Citation

Brown, C., A. Zimmer-Faust, J. Kaldy, T Chris Mochon Collura, S. Pacella, P. Clinton, W. Rugh, AND D. Wise. Tracking Land-Based Nutrient and Bacteria Inputs to Tillamook Estuary - Oregon (USA). American Geophysical Union Fall 2019 Meeting, San Francisco, California, December 09 - 13, 2019.