Statistical Modeling of Variability in Sediment-Water Nutrient and Oxygen Fluxes

Abstract

Mineralisation of organic detritus in the marine surficial sediments generates a flux of dissolved inorganic nutrient between the sediment and overlying water column. This is a key process in the marine ecosystem, which links the food webs of the sea-floor and the overlying water-column, and is potentially affected by a range of interacting environmental and sedimentary factors. Here, we use General Additive Models (GAM) to statistically disentangle some of the factors controlling the seasonal and spatial variability in nutrients and oxygen fluxes in a field dataset collected in the North Sea off the northeast coast of Scotland. We show that sediment grain size, turbidity due to sediment re-suspension, temperature, and sediment chlorophyll content were the key factors affecting oxygen, ammonia, and silicate fluxes. However, phosphate fluxes were only related to suspended sediment concentrations, whilst nitrate fluxes showed no clear relationship to any of the expected drivers of change, probably due to the effects of denitrification. Our analyses show that the stoichiometry of nutrient regeneration in the ecosystem is not necessarily constant and may be affected by combinations of processes.

A synthetic map of the north-west European Shelf sedimentary environment for applications in marine science

“…Significant wave height, mean wave period and mean wave direction were downloaded from the ECMWF website at http://www.ecmwf.int/en/research/ climate-reanalysis/. The ERA-Interim reanalysis has a spatial resolution of approximately 79 km and a temporal resolution of 6 h. Orbital velocities at the seabed were calculated using the equations of Soulsby (2006), and the relevant equations are given in this paper's Appendix. Bathymetry for the wave and tidal model runs was attained from the high-resolution (30 arcsec) General Bathymetric Chart of the Oceans (GEBCO).…”

“…To our knowledge the best dataset available on the relationship between whole-sediment permeability and median grain size is that of Serpetti et al (2016). This dataset covered muddy sand, sand and mixed sediments sampled at approximately monthly intervals over 1 year at seven sites off the east coast of Scotland.…”

“…The bed shear stress and sediment dislocation rates were calculated by combining the equations of Soulsby and Clarke (2005), Soulsby (2006) and Wilcock et al (2009).…”

“…We calculate the wave orbital velocities using the equations of Soulsby (2006). All waves are assumed to be irregular (spectral).…”

Oxygen dynamics in shelf seas sediments incorporating seasonal variability

“…The ability to sequester organic carbon is influenced by the presence and activity of macrofauna and meiofauna (Woulds et al 2007), and the type of sediment (cohesive vs permeable (Fuchsman et al 2015;Glud 2008)). The efficiency of organic carbon burial has been directly linked to the pore water oxygen concentration and exposure time (Hartnett et al 1998), and the availability of oxygen regulates different benthic biogeochemical processes (Glud 2008;Klar et al 2017;Scholz et al 2014;Serpetti et al 2016). Oxygen distribution in sediments influences denitrification, trace metal speciation and release of iron in pore waters (Kitidis et al 2017;Klar et al 2017;Rabouille et al 2003; Thompson et al submitted, this issue).…”