SPATIAL AND TEMPORAL PATTERNS OF WATER COLUMN RESPIRATION IN A SALISH SEA EMBAYMENT

Keywords: microbial respiration, carbon enrichment, eutrophication Water column respiration and carbon cycling are key drivers of ocean acidification and oxygen dynamics, yet these values and their response to carbon enrichment associated with eutrophication are poorly understood. In 2016, we began monthly monitoring of respiration rates in Padilla Bay National Estuarine Research Reserve and also developed a manipulative experiment to investigate the response of water column respiration to varying levels of carbon enrichment. Water samples were incubated at  in situ temperatures and respiration rates were determined by measuring the decline of oxygen concentration over the course of a 3-day incubation period. Values of water column respiration were generally representative of other measures within the Salish Sea and also exhibited a temporal pattern of elevated rates in the warmer summer months. Variation among sites was apparent with the lowest mean respiration rate occurring at the deep-water station and higher mean respiration rates at sample stations located within the eelgrass meadows. Carbon enrichment experiments reveal dramatic differences in the response to carbon enrichment as one moves from late fall to winter, with mean rates decreasing by as much as 85% from November to December and January. Our results reveal strong seasonal variability in the microbial response to carbon enrichment. These patterns will provide insight into our understanding of climate change and the effect of eutrophication on a warmer, carbon-rich ocean.