Evaluating Patterns of Nitrogen Supply UsingMacroalgal Tissue Content and Stable IsotopicSignatures in Tomales Bay CA

摘要

Through bioassay techniques and field collections of red macroalgae (Gracilariopsissp.) and eelgrass (Zostera marina), we evaluated growth, tissue %Nitrogen (N) and Nstable isotopic signatures as bioindicators of potential changes in N supply to TomalesBay, CA ( USA). Gracilariopsis sp. collected, cultured, and outplanted across a spatialgradient in Tomales Bay showed pronounced changes in N patterns from past studiesin this system, and was superior to field collections in detecting spatial N signals.Rather than a single peak in N concentration near the oceanic source found in previouswork, we detected two N peaks, one near the bay head and one near the bay mouth.This spatial pattern suggests two sources account for these discrete regions ofincreased N supply. The temporal N patterns showed marked seasonality, with greatertissue N concentration during the wet season and reduced N concentrations during thedry season. The spatial patterns presented here suggest shifting nutrient dynamicswithin Tomales Bay, with increased N supply detected near the major watershedinflow. Nitrogen isotopic values suggest an enriched wastewater source, but additionalwork is needed to confirm the source of this newly reported N signal.