A new device to follow temporal variations of oxygen demand in deltaic sediments: the LSCE benthic station

Abstract

A new benthic station equipped with oxygen microelectrodes and environmental sensors was developed by Laboratoire des Sciences du Climat et de L'Environnement (LSCE) and Division Technique of the Institut National des Sciences de L'Univers (DT‐ INSU) to perform in situ time series monitoring of sediment oxygen demand, linked to the mineralization of organic matter. The time series typically cover periods of 2‐ 3 months, with a base frequency of 1 set of oxygen profiles per day. The profiling head assessed the lateral heterogeneity of the sediment oxygen demand at the beginning of the time series over a 0.8‐ m long rectangle to discriminate spatial and temporal variability. A continuous recalibration is performed using a moored oxygen optode anchored to the benthic station together with a set of environmental sensors. These sensors (turbidity, temperature, salinity, and oxygen) can trigger a high‐ frequency profiling mode to investigate the fate of particulate organic matter delivered during floods, resuspension, and deposition events. Deployments of the benthic station were performed in the Rhone River subaqueous delta (Mediterranean Sea). We show that “stable” periods (when neither floods nor storms occur) were characterized by a stable oxygen demand. In the case of resuspension events, an increase of the sediment oxygen demand by a factor of 2‐ 3 with a relaxation time of 1 day was observed, indicating that the new benthic station can adequately capture the impact of resuspension events on the oxygen demand in deltaic sediments.

The roles of resuspension, diffusion and biogeochemical processes on oxygen dynamics offshore of the Rhône River, France: a numerical modeling study

“…1), accumulation rates at this site are ∼ 10 cm yr −1 for sediment and 657 g m −2 yr −1 of carbon (Radakovitch et al, 1999;Pastor et al, 2011a), although deposition varies in response to seasonal and episodic changes in river discharge and wave energy (Pont, 1997;Miralles et al, 2006;Ulses et al, 2008;Cathalot et al, 2010). Deposition is punctuated by erosional events, and our study period, April-May 2012, included three instances when wave energy resuspended 1-2 cm of material from the seabed (Toussaint et al, 2014). At this site, erosion and deposition are the main sources of seabed disturbance; little bioturbation has been observed (Pastor et al, 2011b).…”

“…Our study is co-located with the site from Toussaint et al (2014) at the "Mesurho" station (Pairaud et al, 2016) and is only a few kilometers away from Site A in Pastor et al (2011a); both locations are at ∼ 25 m water depth and are characterized by similar biogeochemical characteristics (e.g., Rassmann et al, 2016), and so data from both sites were used for model input, validation, and evaluation. Importantly, data from Toussaint et al (2014) included a time series of oxygen profiles with submillimeter-scale resolution within the seabed and bottom centimeter of the water column. By resolving changes that occurred during resuspension events, Toussaint et al (2014) showed that diffusion of oxygen into the seabed increased during resuspension events.…”

“…Importantly, data from Toussaint et al (2014) included a time series of oxygen profiles with submillimeter-scale resolution within the seabed and bottom centimeter of the water column. By resolving changes that occurred during resuspension events, Toussaint et al (2014) showed that diffusion of oxygen into the seabed increased during resuspension events.…”

“…For example, Abril et al (1999) observed that oxygen concentrations were inversely correlated with tidal fluctuations of suspended particulate matter concentrations in the Gironde Estuary, France. Recently, Toussaint et al (2014) collected high-resolution time series of microelectrode oxygen profiles on the Rhône River subaqueous delta that showed resuspension may also increase oxygen consumption in the seabed. This experiment revealed increases in diffusive fluxes of oxygen from the water column to the seabed during erosional events.…”

Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea Loch: An Integrative In Situ Study

“…While laboratory-based investigations can provide valuable insight on diagenetic processes, measurements of benthic solute exchange using cores and microcosms can be compromised by disturbances during sediment recovery and challenges in re-establishing natural environmental conditions in the laboratory. However, while there for some time has been considerable awareness on the necessity of in situ investigation for quantifying microbial processing in deep-sea sediments (Reimers et al 1986;Jahnke et al 1990;Glud et al 1994;Smith et al 1997) only more recently has the requirement for in situ investigations of coastal sediments been acknowledged (Jahnke and Jahnke 2008;Toussaint et al 2014).…”