Oxygen Concentration In Sediments Research Articles

Regenerative bioturbation by intertidal burrowing crabs modifies microphytobenthic composition and enhances primary production in SW Atlantic mudflats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 632:43-57 (2019) - DOI: https://doi.org/10.3354/meps13134 Regenerative bioturbation by intertidal burrowing crabs modifies microphytobenthic composition and enhances primary production in SW Atlantic mudflats Micaela Giorgini1,*, Ana Miguez1, K. Soledad Esquius2, Clara Diaz de Astarloa1, Oscar Iribarne1, Eugenia Fanjul1, Mauricio Escapa1 1Laboratorio de Ecología, 2Laboratorio de Limnología, Instituto de Investigaciones Marinas y Costeras (IIMyC), UNMdP - CONICET, Mar del Plata, CP 7600, Argentina *Corresponding author: mikungiorgini@gmail.com ABSTRACT: In coastal systems, benthic microalgae are important primary producers that significantly contribute to global primary production. Microphytobenthic (MPB) community structure and the ecosystem functions that it mediates are modulated by biotic and abiotic factors. Through burrowing activity, different types of bioturbators can impact MPB in different ways. Through directed sampling and field experiments performed at the Mar Chiquita coastal lagoon (Argentina), we evaluated the effect of regenerative bioturbation (continuous digging and maintenance of burrows, with sediment transfer from depth to surface) by the intertidal burrowing crab Neohelice (Chasmagnatus) granulata on MPB. We compared sediment properties and MPB attributes between natural burrowed and non-burrowed areas. Moreover, we experimentally manipulated regenerative bioturbation to evaluate if MPB composition and primary production are altered by crab burrowing activity. Field sampling showed that MPB and sediment properties differed between natural burrowed and non-burrowed areas. Experimental results indicated that regenerative bioturbation by N. granulata increased sediment oxygen concentration at each measured depth and also changed MPB composition (due to the reduced total abundance of cyanobacteria), but nearly doubled primary production in comparison with plots without bioturbation. Thus, the net effects of regenerative bioturbation were positive for MPB productivity, reinforcing the idea that this kind of bioturbation is an important biological force that enhances primary production in intertidal systems. KEY WORDS: Regenerative bioturbation · Microphytobenthos · Burrowing crab · Neohelice (Chasmagnatus) granulata · Intertidal sediments Full text in pdf format PreviousNextCite this article as: Giorgini M, Miguez A, Esquius KS, Diaz de Astarloa C, Iribarne O, Fanjul E, Escapa M (2019) Regenerative bioturbation by intertidal burrowing crabs modifies microphytobenthic composition and enhances primary production in SW Atlantic mudflats. Mar Ecol Prog Ser 632:43-57. https://doi.org/10.3354/meps13134 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 632. Online publication date: December 12, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Oxygen dynamics control the burial of organic carbon in a eutrophic reservoir

AbstractOrganic carbon (OC) mineralization in freshwaters is dependent on oxygen availability near the sediments, which controls whether OC inputs will be buried or respired. However, oxygen dynamics in waterbodies are changing globally due to land use and climate, and the consequences of variable oxygen conditions for OC burial are unknown. We manipulated hypolimnetic oxygen availability in a whole‐reservoir experiment and used a mass balance OC model to quantify rates of OC burial. Throughout summer stratification, we observed that OC burial rates were tightly coupled to sediment oxygen concentrations: oxic conditions promoted the mineralization of “legacy” OC that had accumulated over years of sedimentation, resulting in negative OC burial. Moreover, our study demonstrates that fluctuating oxygen conditions can switch ecosystem‐scale OC burial in a reservoir between positive and negative rates. Consequently, changing oxygen availability in freshwaters globally will likely have large implications for the role of these ecosystems as OC sinks.

The impact of deep-tier burrow systems in sediment mixing and ecosystem engineering in early Cambrian carbonate settings

Bioturbation plays a substantial role in sediment oxygen concentration, chemical cycling, regeneration of nutrients, microbial activity, and the rate of organic matter decomposition in modern oceans. In addition, bioturbators are ecosystem engineers which promote the presence of some organisms, while precluding others. However, the impact of bioturbation in deep time remains controversial and limited sediment mixing has been indicated for early Paleozoic seas. Our understanding of the actual impact of bioturbation early in the Phanerozoic has been hampered by the lack of detailed analysis of the functional significance of specific burrow architectures. Integration of ichnologic and sedimentologic evidence from North China shows that deep-tier Thalassinoides mazes occur in lower Cambrian nearshore carbonate sediments, leading to intense disruption of the primary fabric. Comparison with modern studies suggest that some of the effects of this style of Cambrian bioturbation may have included promotion of nitrogen and ammonium fluxes across the sediment-water interface, average deepening of the redox discontinuity surface, expansion of aerobic bacteria, and increase in the rate of organic matter decomposition and the regeneration of nutrients. Our study suggests that early Cambrian sediment mixing in carbonate settings may have been more significant than assumed in previous models.

Fiddler crab (Uca spp.) burrows have little effect on surrounding sediment oxygen concentrations

In the literature, it is commonly stated that Uca spp. (fiddler crab) burrows aerate marsh sediment. However, to date few studies have attempted to determine the pore water oxygen (O2) concentrations associated with Uca spp. burrows; instead most studies have looked at redox potential, a measure of oxidation and not of O2. In an in situ study conducted in salt marshes on the Atlantic coast of Virginia, USA, O2 concentrations surrounding individual burrows were measured to assess the potential of burrows to aerate bulk sediment. Using an O2 microelectrode, concentration profiles were measured at depth intervals of 500μm to a depth of 10mm. The O2 profiles were measured at distances of 2, 4, 6, 8, and 10mm from the burrow wall. Measurements were made surrounding natural and artificial burrows as well as where burrows were absent as a control.Contrary to convictions in the literature, this study determined that, within poorly drained muddy sediments, oxygen penetration depth only had a significant increase out to a distance of 2mm from the burrow wall, and the increase in oxygen depth penetration was only 0.5mm compared to areas not affected by the presence of the burrow. In typical muddy sediments of salt marshes along the mid-Atlantic coast, USA, the presence of Uca pugnax burrows increased the oxic zone little, but may have had an effect on the extent of the suboxic zone. Therefore, generalizations should not be made concerning the ability of burrows to aerate surrounding bulk sediments. In addition, the capacity of sediments to drain is an important factor in determining the potential for increased sediment aeration due to the presence of Uca spp. burrows.

Meiofauna Metabolism in Suboxic Sediments: Currently Overestimated

Oxygen is recognized as a structuring factor of metazoan communities in marine sediments. The importance of oxygen as a controlling factor on meiofauna (32 µm-1 mm in size) respiration rates is however less clear. Typically, respiration rates are measured under oxic conditions, after which these rates are used in food web studies to quantify the role of meiofauna in sediment carbon turnover. Sediment oxygen concentration ([O2]) is generally far from saturated, implying that (1) current estimates of the role of meiofauna in carbon cycling may be biased and (2) meiofaunal organisms need strategies to survive in oxygen-stressed environments. Two main survival strategies are often hypothesized: 1) frequent migration to oxic layers and 2) morphological adaptation. To evaluate these hypotheses, we (1) used a model of oxygen turnover in the meiofauna body as a function of ambient [O2], and (2) performed respiration measurements at a range of [O2] conditions. The oxygen turnover model predicts a tight coupling between ambient [O2] and meiofauna body [O2] with oxygen within the body being consumed in seconds. This fast turnover favors long and slender organisms in sediments with low ambient [O2] but even then frequent migration between suboxic and oxic layers is for most organisms not a viable strategy to alleviate oxygen limitation. Respiration rates of all measured meiofauna organisms slowed down in response to decreasing ambient [O2], with Nematoda displaying the highest metabolic sensitivity for declining [O2] followed by Foraminifera and juvenile Gastropoda. Ostracoda showed a behavioral stress response when ambient [O2] reached a critical level. Reduced respiration at low ambient [O2] implies that meiofauna in natural, i.e. suboxic, sediments must have a lower metabolism than inferred from earlier respiration rates conducted under oxic conditions. The implications of these findings are discussed for the contribution of meiofauna to carbon cycling in marine sediments.

Oxygen penetration deep into the sediment of the South Pacific gyre

Abstract. Sediment oxygen concentration profiles and benthic microbial oxygen consumption rates were investigated during an IODP site survey in the South Pacific Gyre. Primary production, particle fluxes and sedimentation rates are extremely low in this ultra-oligotrophic oceanic region. We derived O2 consumption rates from vertical oxygen profiles in sediments obtained on different spatial scales ex situ (in piston cores and multi cores), and in situ (using a benthic lander equipped with a microelectrode profiler). Along a transect in the area 24 to 46° S and 165 to 117° W, cores from 10 out of 11 sites were oxygenated over their entire length (as much as 8 m below seafloor), with deep O2 concentrations >150 μmol L−1. This represents the deepest oxygen penetration ever measured in marine sediments. High-resolution microprofiles from the surface sediment layer revealed a diffusive oxygen uptake between 0.1 and 1.3 mmol m−2 d−1, equal to a carbon mineralization rate of ~0.4–4.5 gC m−2 yr−1. This is in the lower range of previously reported fluxes for oligotrophic sediments but corresponds well to the low surface water primary production. Half of the pool of reactive organic matter was consumed in the top 1.5–6 mm of the sediment. Because of the inert nature of the deeper sediment, oxygen that is not consumed within the top centimeters diffuses downward to much greater depth. In deeper zones, a small O2 flux between 0.05 and 0.3 μmol m−2 d−1 was still present. This flux was nearly constant with depth, indicating extremely low O2 consumption rates. Modeling of the oxygen profiles suggests that the sediment is probably oxygenated down to the basalt, suggesting an oxygen flux from the sediment into the basaltic basement.

River Water Quality Model no. 1 (RWQM1): Case study I. Compartmentalisation approach applied to oxygen balances in the River Lahn (Germany)

A case study on the application of the River Water Quality Model No. 1 (RWQM1) is presented in order to illustrate the importance of modelling a sediment compartment for an ecologically meaningful assessment of the impact of wastewater effluents and combined sewer overflows. The focus of this case study is on the compartmentalisation approach of the RWQM1 that makes such a description possible. In contrast to this, a strongly simplified biochemical submodel is used that considers only oxygen and dissolved substrate. The object of the case study is the River Lahn, a moderately polluted 5th order stream in Germany, for which the connectivity of surface/subsurface flows and mass fluxes within river sediments have been intensively investigated. The hyporheic flow between a downwelling and upwelling zone of a riffle-pool sequence has been studied with the aid of tracer experiments and continuous records of water constituents. High diurnal fluctuations of oxygen travelled to considerable depth of the sediment and oxygen in the interstitial water decreased considerably while travelling through the riffle. Starting with the implementation of a strongly simplified version of the biochemical part of the RWQM1, but with the consideration of a sediment pore water compartment in addition to the water column compartment, a calibration procedure is performed using tracer data from the water column and the sediment. The calibrated model is then used to study the system response to wastewater treatment plant effluent and combined sewer overflow emissions. The modelling approach makes it possible to quantify the sediment oxygen demand and the spatial and temporal extent of sediment zones with oxygen depletion. However, the spatially averaged approach does not account for inhomogeneities in the sediment. It is shown that for this river with its alluvial coarse sediments even moderate emissions from sewerage systems may be high enough to drop sediment oxygen concentrations to low levels while those in the surface flow remain close to saturation. Similarly, it is demonstrated that combined sewer overflows may cause anoxic sediment oxygen conditions for extended time periods. The implications for ecologically sound river water quality modelling and for specific quality objectives are discussed.

Nematode distribution in ocean margin sediments of the Goban Spur (northeast Atlantic) in relation to sediment geochemistry

Nematode density along a depth gradient (206–2760 m) in the northeastern Atlantic (Goban Spur) is linearly and positively related to organic matter mineralization in the sediment. It is estimated that nematodes contribute at most 13% to total carbon turnover, and this contribution decreases with water depth. The vertical distribution of nematodes in the sediment closely follows concentration vs depth profiles of total nitrogen in the sediment. Both nematodes and total nitrogen tend to be more concentrated towards the surface with increasing water depth. There is no indication that nematode vertical distribution is directly influenced by the oxygen penetration in the sediment. However, it is hypothesized that the sediment oxygen concentration can explain the relatively greater importance of smaller organisms in benthic communities with increasing water depth. The nitrogen vs sediment depth profiles are consistent with a greater impact of larger organisms on sediments at the shallow stations and decreased sediment mixing with increasing water depth.

Oxygen limitations and aging as explanations for the field persistence of naphthalene in coal tar-contaminated surface sediments

Naphthalene has been transported approx. 400 m via groundwater flow from buried subsurface coal tar to an organic matter-rich seep area where the water emerges at the foot of a hill in a field study site. We have tested several hypotheses for explaining why naphthalene persists in seep sediments. In aerobic laboratory flask assays, conversion of 14C-naphthalene to 14CO2 occurred and was not stimulated by amendments with vitamins or inorganic nutrients. Thus, neither toxicity nor nutrient limitation were the cause of naphthalene persistence. At the site, in situ sediment oxygen concentrations were below detection. Oxygen-limited naphthalene biodegradation was demonstrated both by measuring no conversion of 14C-naphthalene to 14CO2 in samples of seep sediments prepared anaerobically and by measuring naphthalene loss from anaerobic nitrate-amended slurry-phase incubations of the sediment only after O2 was added. However, when H2O2 was added as an O2 source to site sediments in situ in a randomized block design, no discernible naphthalene loss occurred. The possibility that decreased bioavailability might contribute to naphthalene persistence was investigated by monitoring 14CO2 evolved by microorganisms added to γ-ray sterilized sediments that had been exposed under aseptic conditions to 14C-labeled naphthalene for periods ranging from 0 to 28 d. Resulting patterns in the extent and rate of naphthalene mineralization revealed an inverse relationship to the duration of contact with the sediment, but only when the mixed microbial inoculum had been enriched on aqueous-phase naphthalene. We conclude that oxygen limitation is the most probable cause for lack of naphthalene biodegradation at our field study site. However, diffusion or sorption reactions may also play a role.