PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal

Food web stable isotopes and organic contaminants in the Truckee River, Nevada, USA.

Saito, Laurel^*,1, Rosen, Michael², Fritsen, Christian³, Fay, Christa¹, Chandra, Sudeep¹, ¹ University of Nevada, Reno, Reno, NV, USA² United States Geological Survey, Carson City, NV, USA³ Desert Research Institute, Reno, NV, USA

ABSTRACT- Stable carbon and nitrogen isotopes to detect anthropogenic influences on the aquatic food web of the Truckee River in Nevada, and semipermeable membrane devices (SPMDs) were used to simultaneously assess the effect of organic contaminants from urban runoff on toxicity to aquatic organisms. The Truckee River originates in Lake Tahoe and traverses 187 km (116 miles) to its terminus in Pyramid Lake in the Great Basin. The river provides hydropower, most of the water supply for the cities of Reno and Sparks, and irrigation water to the Lahontan Valley. Fish, macroinvertebrate, and periphyton samples and toxicity data were collected during high and low flow periods for 2 years at seven sites on the river. Average nitrogen signatures (¹⁵N) have a general decreasing trend (~ -0.1‰ per km) in the downstream direction, but an abrupt increase of ~6‰ in ¹⁵N and a corresponding decrease of ~6‰ in carbon signatures (¹³C) exists throughout the food web at the site just downstream of the Reno-Sparks urban area. The site is below the confluence of a major nutrient-loading tributary (Steamboat Creek) that also receives tertiary treated sewage effluent and this location is also downstream of the confluence of an irrigation ditch (North Truckee Drain) that receives urban runoff and irrigation return flows. The SPMDs sample lipophilic organic contaminants and these toxicity data indicate similar patterns to the stable isotope data. Measured potential toxicity increases 3-4 times through the urban area and is greatest downstream of the confluence of the tributaries. However, SPMD data indicate that higher toxicity also is influenced by diffuse urban runoff from the North Truckee Drain and Steamboat Creek. The conjunctive use of stable isotope and organic-contaminant data is being used to further develop and assess the Truckee River’s food web, and assess material transport and the influence of organic contaminants from urban runoff and other sources along the river.

Key words: stable isotopes, passive organic samplers, aquatic food web, Truckee River