Abstract
Oysters enhance benthic-pelagic coupling in coastal systems by moving large quantities of suspended particulates to the sediments, stimulating biogeochemical processes. Recent research efforts have focused on quantifying the impact of oysters on coastal biogeochemical cycling, yet there is little consensus on how oysters influence processes across systems. A potential driver of this variance is availability of organic material suspended in the water column and subsequent loading to sediment by oysters. Here, we measured fluxes of sediment di-nitrogen (N2-N), ammonium (NH4+), combined nitrate-nitrite (NOx), and phosphate (PO43-) in spring, summer, and fall at 2 oyster reefs and 1 farm in a temperate estuary (Narragansett Bay, Rhode Island). We then linked these fluxes with patterns of water column primary production. Nitrogen removal from the system was highest in spring, when we detected net sediment denitrification (48.8 µmol N2-N m-2 h-1) following a winter-spring diatom bloom. In contrast, we measured sediment N2 fixation in fall (-44.8 µmol N2-N m-2 h-1) at rates nearly equivalent to spring denitrification. In the summer, we measured a nearly net zero sediment N2-N flux (-2.7 µmol N2-N m-2 h-1). Recycling of nitrogen to the water column was consistent across seasons, composed almost exclusively of NH4+. These results demonstrate that sediment nitrogen cycling in oyster habitats is dynamic and can change rapidly based on seasonal patterns of productivity. At carrying capacity, the impact of oysters on nitrogen cycling is large and should be considered during efforts to increase oyster populations through aquaculture or reef restoration.
Highlights
Large oyster populations characterized many estuaries on the Atlantic Coast of North America prior to European colonization (Nixon 1997, Beck et al 2011, Zu Ermgassen et al 2013, Rick et al 2016)
We found that N2-N, NH4+, and PO43− fluxes were best described by normal distributions, ΣN and O2 fluxes best fit gamma distributions, and NOx fluxes were log normal
The high rate of N2 fixation we found in fall (−44.8 μmol N2-N m−2 h−1) is the highest mean N2 fixation rate ever reported for oyster habitats
Summary
Large oyster populations characterized many estuaries on the Atlantic Coast of North America prior to European colonization (Nixon 1997, Beck et al 2011, Zu Ermgassen et al 2013, Rick et al 2016). Some studies report enhanced denitrification in sediments beneath oysters in reef and aquaculture systems (Kellogg et al 2013, Smyth et al 2015, Humphries et al 2016, Lunstrum et al 2018), while others have found no difference (Higgins et al 2013, Testa et al 2015, Westbrook et al 2019). Perhaps the reason for this disparity is the assumption that oysters will enhance sediment denitrification regardless of the properties of the system they are in (e.g. dissolved nutrient concentrations, temperature, turbidity, etc.). Another reason for this disparity could rest in the complexity of the N cycle
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
