UC Santa Cruz

In California, local stressors on water quantity and quality are pervasive. This dissertation explores questions that can improve our understanding of water quality and quantity issues in two central California systems. Chapter 1 leverages the unique dry period of California’s Mediterranean climate to better understand what water sources sustain critical low flow periods in a geologically complex watershed in central coastal California (San Lorenzo Watershed). Results from Chapter 1 show that both deep groundwater and shallow subsurface flow paths can contribute to baseflow during the summer dry down period, and that geology, specifically bedrock permeability, controls their relative contributions. This research adds to existing studies that are shifting traditional views on baseflow generation processes by showing low flow periods of hydrographs can be sustained by multiple water sources.

Chapter 2 and Chapter 3 investigate spatial and temporal variability of hydrological and biogeochemical processes in a highly altered estuary (the Sacramento-San Joaquin Delta). The Delta is comprised of over fifty peat islands that are drained for commercial agriculture. Herein we refer to this outflow from Delta islands as peat drainage (Chapter 2) and island drainage (Chapter 3). Chapter 2 examines the magnitude of lateral carbon exports from peat drainage and possible controls on carbon release. Results from Chapter 2 can be used to account for a missing term in local carbon budgets. Chapter 3 explores nutrient and trace metal inputs from island drainage and the significance of island drainage mass fluxes relative to major inflows in the system. Results from Chapter 3 suggest that island drainage is an understudied source of nutrients and trace metals, with total nitrogen loads accounting for almost 1/6 of regional inputs during dry water years. Both Chapter 2 and Chapter 3 show that exports from Delta islands are water year and season dependent, highlighting the importance of accounting for multiple time scales in future assessments of mass fluxes in this system.