Determining the role of benthic diatoms in ecosystem primary production in the Damariscotta River Estuary

Productivity in shallow coastal regions of the ocean on a per area basis can outweigh that of the open ocean due to high nutrient inputs from land. Within these shallow regions light can reach the sediment surface resulting in the growth of benthic diatoms. Estimates of primary productivity in coastal environments can have a significant benthic component but can vary due to physical and chemical parameters that influence the spatial and temporal distribution of biomass. Light is often the limiting factor for benthic primary producers and an understanding of the of PE (photosynthesis versus downwelling irradiance) relationship is necessary for quantifying the benthic contribution to ecosystem photosynthesis. In this work we use a combination of whole core exsitu flux incubations and microsensor oxygen profiling to determine PE curves for benthic diatoms in the Damariscotta River Estuary (DRE), a highly dynamic productive estuary in mid-coast Maine, USA. PE relationships were measured in sediments from different depths by sampling a transect across the estuary. Based on the natural range of light (6 to 63 μmol photons m^-2 s^-1) at the sampling sites, the corresponding photosynthetic rates ranged from -40 mmol O₂ m^-2d^-1 to 53 mmol O₂ m^-2d^-1. Combining these results with measurements of depth attenuation, and surface irradiance, the photosynthetic rate over an entire day light-dark cycle can be estimated. Quantifying benthic photosynthesis is needed for determining the productivity of the whole estuary. This is an important question as the DRE hosts a lucrative shellfish aquaculture industry and understanding the benthic contribution to primary productivity in the estuary is necessary for understanding how much shellfish aquaculture the estuary can support and its effect on the local ecosystem.