Mercury in the Cache Creek Watershed – Trends, Hot Spots and Ecosystem Services Analysis

Authors: Deseret Weeks*, Department of Geography and Environment, San Francisco State University, Leora Nanus, Department of Geography and Environment, San Francisco State University, Jason Gurdak, Department of Earth and Climate Sciences, San Francisco State University
Topics: Applied Geography, Coupled Human and Natural Systems, Natural Resources
Keywords: Mercury, Bioaccumulation, Ecosystem Services, Watersheds
Session Type: Poster
Day: 4/12/2018
Start / End Time: 8:00 AM / 9:40 AM
Room: Napoleon Foyer/Common St. Corridor, Sheraton, 3rd Floor
Presentation File: Download


The Cache Creek Watershed is one of many in California whose streams, lakes and reservoirs are on the Clean Water Act’s 303d list for mercury threshold exceedance due to historic mercury mining and use of mercury for gold mining. While the Cache Creek Watershed contains the largest natural lake in California – Clear Lake, which is known as the Bass capital of the west, is home to Native American tribes and critical habitats, it is noted to be the biggest contributing source of mercury to the San Francisco Bay Delta whose waters are also on the 303d list for mercury. Only two out of over 20 mercury mines in the Cache Creek Watershed have been fully remediated. The purpose of this project was to examine spatial trends of mercury levels in multiple sensitive indicators in the Cache Creek Watershed and to identify ecosystem services impacted. Historical mercury data from the California Environmental Data Repository and literature review was compiled and evaluated in a Geographic Information System. Mercury concentrations in fish collected from Clear Lake, Cache Creek and Bear Creek range from 0.02 to 1.91 ppm. Over 92% of fish sampled in trophic levels 3 and 4 were above the new California Environmental Protection Agency thresholds for mercury in fish for subsistence, sport fishing and wildlife, which are 0.03 ppm, 0.2 ppm and 0.05 ppm respectively. This indicates all four categories of ecosystem services are impacted while the most impacted include provisioning, habitat/supporting and cultural services.

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