Long-term shifts in particulate organic matter dynamics evident throughout the San Francisco Bay-Delta system

Bulk particulate organic matter (POM) composition in estuaries can be a complex mixture of sources (phytoplankton, microzooplankton, bacteria, and detritus). While challenging, identifying sources and processes that regulate the bulk POM pool is useful for understanding the broader role of organic matter in food web dynamics. To better understand if and how the dominant sources of POM have changed through time and space in the highly-altered San Francisco Bay-Delta of central California, we analyzed synoptic samples of POM C:N (at) ratios and associated 13C values, collected coeval with other water quality data (e.g., salinity, nutrients, suspended sediment concentrations) in select years spanning 2006 to 2016 and combined with historical data from the early 1990s. Broadly, we found that both the quantity and quality of detrital POM have shifted in this system at large spatial and temporal scales; detrital POM C:N ratios and detrital POM concentrations declined across nearly all sites in months with available historical data for comparison. Changes in the quantity and quality of the bulk POM pool has likely impacted food web structure in this system, both directly and indirectly through changes in OM availability for heterotrophic assimilation and remineralization.