Date of Award


Degree Name

MS in Environmental Sciences and Management


Natural Resources Management


College of Agriculture, Food, and Environmental Sciences


Bwalya Malama

Advisor Department

Natural Resources Management

Advisor College

College of Agriculture, Food, and Environmental Sciences


The endemic eelgrass (Zostera marina) community of Morro Bay Estuary, located on the central coast of California, has experienced an estimated decline of 95% in occupied area (reduction of 344 acres to 20 acres) from 2008 to 2017 for reasons that are not yet definitively clear. One possible driver of degradation, that has yet to be investigated is the role of herbicides from agricultural fields in the watershed that feeds into the estuary. Thus, the primary research goal of this project was to better understand temporal and spatial trends of herbicide use within the context of San Luis Obispo (SLO) County and Morro Bay Watershed by analyzing data of application by mass, area, and intensity to identify herbicides with the highest potential for impacting marine seagrass. California Pesticide Use Annual Summary Reports (PUASR) from the years 2000 to 2017 were used to obtain data for conducting a meta-analysis to estimate total herbicide application by weight within every township, range, and section for each of eight selected chemicals: oxyfluorfen, glyphosate, diuron, chlorthal-dimethyl, simazine, napropamide, trifluralin, and oryzalin. A second goal was to select an analytical laboratory that would be best suited for herbicide analysis of estuary sediments to determine the presence, or lack thereof, of the eight selected herbicides. Criteria of consideration in v laboratory selection included herbicides detection capabilities, detection /reporting limits, testing prices, chain of custody protocols, turnaround times, and laboratory site locations The meta-analysis yielded results showing high herbicide application rates in SLO County, with glyphosate, oxyfluorfen and chlorthal-dimethyl being identified as three chemicals of elevated risk for local environmental contamination due high rates of use by mass, by area, and/or intensity during the study timeframe. Additionally, Morro Bay Watershed exhibited moderate rates of herbicide application, with chlorthal-dimethyl and glyphosate being of highest risk for contamination and accumulation within the estuary because of high application rates by mass, by area, and/or intensity. Finally, Environmental Micro Analysis (EMA) and Primus Group, Inc. (PrimusLabs) were identified as the top candidates for analytical laboratory testing of Morro Bay Estuary sediment samples to be taken to detect the selected herbicides. These laboratories provide superior analytical capabilities of the eight herbicides, accurate reporting limits or lower detection limits, reasonable testing prices for detecting multiple constituents in multiple samples, robust chain of custody protocols, options for quick turnaround times, and laboratory site locations within California.

Included in

Hydrology Commons