Spatio-temporal variability in benthic mineralization processes in the eastern English Channel

Abstract

The effect of phytodetritus derived from Phaeocystis sp. bloom on benthic mineralization processes has been determined at four intertidal stations along the French coast of the eastern English Channel. Sites were chosen to offer a diversity of sediment types, from permeable sandy beach to estuarine mudflats. Sediment Oxygen Demand (SOD) as well as total fluxes of Dissolved Inorganic Nitrogen (DIN) at the sediment-water interface were determined by using whole core incubation technique and diffusive fluxes were predicted from interstitial water concentrations. In the absence of phytodetritus deposits, a marked gradient of granulometric characteristics and organic matter contents were observed, and resulted in more intensive mineralization processes in muddy sediments. Highly significant correlations (P \ 0.05) were evidenced between SOD and porosity, bacterial biomass, Organic Carbon and Organic Nitrogen, evidencing the direct link between sediment texture, organic matter accumulation and microbial activity. The spring bloom led to a massive input of organic matter in surficial sediments and mineralization rates significantly increased while higher DIN release towards the water column was observed. A modification of the mineralization pathways was evidenced but clearly depended on the sediment type. With a global view, benthic mineralization processes in the intertidal zone provided significant a part of DIN inputs in the coastal zone while water column was depleted in nutrients.

Macrobenthic diversity and sediment-water exchanges of oxygen and ammonium: Example of two subtidal communities of the eastern English Channel

“…linked, and higher F Total (O 2 ) were coupled with a more intensive ammonium release, as previously investigated in the eastern English Channel by Rauch & Denis (2008).…”

Impact of global change on coastal oxygen dynamics and risk of hypoxia

“…The sediment oxygen consumption varies, however, considerably over the year, strongly increasing in late spring due to an increased detritus supply to the bottom and increasing sediment temperature. The sediment oxygen consumption reaches its maximum at the end of September with an uptake rate of 17.5 mmol m −2 d −1 , which is slightly higher than the values measured by Neubacher et al (2011) The importance of mineralization in the sediment is also reflected in high fluxes of nitrate and ammonium across the sediment-water interface following the spring bloom (Rauch and Denis, 2008). On average the flux of nitrate and ammonium is 0.5 mmol m −2 d −1 and 0.3 mmol m −2 d −1 , respectively.…”

Influence of cyanobacteria blooms on sediment biogeochemistry and nutrient fluxes

“…Ecological effects-Although determining the cause of cyanobacteria blooms can be elusive, nutrient enrichment and ambient ratios of DIN : SRP are often critical for bloom initiation, development, and species succession (Glibert et al 2011). Sediments may act as a reservoir for phytodetritus to fuel nutrient fluxes with various time lags (Cowan and Boynton 1996;Cowan et al 1996), helping to explain the coherence between phytoplankton blooms in spring and increased nutrient release from sediments in summer (Rauch and Denis 2008). Spring-winter runoff may bring .…”