Evidence of infaunal effects on porewater advection and biogeochemistry in permeable sediments: A proposed infaunal functional group framework

Bioturbating infauna significantly modify reaction and transport processes in permeable sediments, though most studies to date are limited in the scope of species examined. We conducted a comparative field study measuring density-dependent effects of six common bioturbating species on porewater advection and biogeochemistry, across three intertidal permeable sediment habitats. The species in this study are; head-down like deposit feeders (Abarenicola pacifica and Balanoglossus aurantiacus), surface deposit feeders (Diopatra cuprea and Onuphis jenneri) and gallery diffusers (Upogebia pugettensis and Neotrypaea californiensis). Tracer loss from gel diffusers was used to assess relative differences in porewater advection among sites, and porewater peepers were used to measure solute concentrations of carbon, nitrogen, phosphate, and silicate in experimental plots. Characteristic surface features of different infauna were counted and used as a proxy for infaunal density. Density of surface features was then used in regression analyses as an explanatory variable affecting porewater transport and chemistry. Significant infaunal density effects on porewater transport or biogeochemistry were found in all but one species, D. cuprea. The species-specific attributes and mechanisms by which these infauna affect permeable sediment processes are explored. A process based functional group framework is presented for permeable sediments. Bulk granulometric properties also were assessed. There were little to no within-site effects of porosity, hydraulic conductivity, or organic matter on porewater transport and biogeochemistry. However, significant across-site differences in granulometry and site properties were found and these are addressed in relation to infaunal effects on porewater transport and chemistry

Omega Oracle: forecasting estuarine carbonate weather

There are serious concerns about ecological, social, and economic impacts in the Pacific Northwest due to Ocean Acidification (OA). We built a system to predict aragonite saturation state (Ω) of seawater in Netarts Bay, Oregon based on large scale forcing parameters. An artificial neural network – trained against a continuous, multiyear monitoring record of carbonate chemistry – learns a regression estimate of Ω based on seasonality, tides, and wind conditions. This approach is agnostic to the details of the underlying chemical and biological processes offering a distinct modelling perspective. The result is a conceptually simpler and more strictly empirical parameterization and a model that is flexible in application due to dependence on only easily obtainable parameters. Forecast validation by a cross validation method indicates good prediction performance, particularly for the high frequency content of the Ω time series, over periods of stable wind forecasting. Our forecast model demonstrates that the complex temporal dynamics of carbonate chemistry within an estuary can emerge from forcing operating on longer timescales. This further elucidates the management and commercial value of this model; experimental work with calcifiers suggests the details of these high frequency chemical dynamics are critical to the magnitude of stress imposed. Lastly, these forecasts, deployed as a web application, can facilitate OA mitigation strategies by providing aquaculturists with real-time predictions for consideration in operational decisions. Numerous sites, including on the Salish Sea, are poised to soon have viable training data for application of this method. Broader deployment promises to enable comparison between sites and expansion of direct aquaculture and management applications. Expansion to other sites is expected to require altered explanatory variables but this exercise may itself yield insight. Relatedly, we note the potential of this approach to help constrain timescales and sources (natural and anthropogenic) of contributions to physiological OA stress

Evidence of infaunal effects on porewater advection and biogeochemistry in permeable sediments: A proposed infaunal functional group framework

Bioturbating infauna significantly modify reaction and transport processes in permeable sediments, though most studies to date are limited in the scope of species examined. We conducted a comparative field study measuring density-dependent effects of six common bioturbating species on porewater advection and biogeochemistry, across three intertidal permeable sediment habitats. The species in this study are; head-down like deposit feeders (Abarenicola pacifica and Balanoglossus aurantiacus), surface deposit feeders (Diopatra cuprea and Onuphis jenneri) and gallery diffusers (Upogebia pugettensis and Neotrypaea californiensis). Tracer loss from gel diffusers was used to assess relative differences in porewater advection among sites, and porewater peepers were used to measure solute concentrations of carbon, nitrogen, phosphate, and silicate in experimental plots. Characteristic surface features of different infauna were counted and used as a proxy for infaunal density. Density of surface features was then used in regression analyses as an explanatory variable affecting porewater transport and chemistry. Significant infaunal density effects on porewater transport or biogeochemistry were found in all but one species, D. cuprea. The species-specific attributes and mechanisms by which these infauna affect permeable sediment processes are explored. A process based functional group framework is presented for permeable sediments. Bulk granulometric properties also were assessed. There were little to no within-site effects of porosity, hydraulic conductivity, or organic matter on porewater transport and biogeochemistry. However, significant across-site differences in granulometry and site properties were found and these are addressed in relation to infaunal effects on porewater transport and chemistry

Mechanistic understanding of ocean acidification impacts on larval feeding physiology and energy budgets of the mussel M. californianus

Ocean acidification (OA) - a process describing the ocean’s increase in dissolved carbon dioxide (PCO2) and a reduction in pH and aragonite saturation state (Ωar) due to higher concentrations of atmospheric CO2 – is considered a threat to bivalve mollusks and other marine calcifiers. While many studies have focused on the effects of OA on shell formation and growth, we present findings on the separate effects of PCO2, Ωar, and pH on larval feeding physiology (initiation of feeding, gut fullness, and ingestion rates) of the California mussel Mytilus californianus. We found elevated PCO2 delays initiation of feeding, while gut fullness and ingestion rates were best predicted by Ωar; however, pH was not found to have a significant effect on these feeding processes under the range of OA conditions tested. We also modeled how OA impacts on initial shell development and feeding physiology might subsequently affect larval energy budget components (e.g. scope for growth) and developmental rate to 260 µm shell length, a size at which larvae typically become pediveligers. Our model predicted that Ωar impacts on larval shell size and ingestion rates over the initial 48 h period of development would result in a developmental delay to the pediveliger stage of \u3e 4 days, compared with larvae initially developing in supersaturated conditions (Ωar \u3e 1). Collectively, these results suggest that predicted increases in PCO2 and reduced Ωar values may negatively impact feeding activity and energy balances of bivalve larvae, reducing their overall fitness and recruitment success

Ocean acidification stress index for shellfish (OASIS): Linking Pacific oyster larval survival and exposure to variable carbonate chemistry regimes

Understanding larval bivalve responses to variable regimes of seawater carbonate chemistry requires realistic quantification of physiological stress. Based on a degree-day modeling approach, we developed a new metric, the ocean acidification stress index for shellfish (OASIS), for this purpose. OASIS integrates over the entire larval period the instantaneous stress associated with deviations from published sensitivity thresholds to aragonite saturation state (ΩAr) while experiencing variable carbonate chemistry. We measured survival to D-hinge and pre-settlement stage of four Pacific oyster (Crassostrea gigas) cohorts with different histories of carbonate chemistry exposure at the Whiskey Creek Hatchery, Netarts Bay, OR, to test the utility of OASIS as a stress metric and document the effects of buffering seawater in mitigating acute and chronic exposure to ocean acidification. Each cohort was divided into four groups and reared under the following conditions: 1) stable, buffered seawater for the entire larval period; 2) stable, buffered seawater for the first 48 hours, then naturally variable, unbuffered seawater; 3) stable, unbuffered seawater for the first 48 hours, then buffered seawater; and 4) stable, unbuffered seawater for the first 48 hours, then naturally variable, unbuffered seawater. Patterns in Netarts Bay carbonate chemistry were dominated by seasonal upwelling at the time of the experimental work, resulting in naturally highly variable ΩAr for the larvae raised in the unbuffered treatments. Two of the four cohorts showed strongly positive responses to buffering in survival to 48 hours; three of the four, in survival to pre-settlement. OASIS accurately predicted survival for two of the three cohorts tested (the fourth excluded due to other environmental factors), suggesting that this new metric could be used to better understand larval bivalve survival in naturally variable environments. OASIS may also be useful to an array of diverse stakeholders with increasing access to highly resolved temporal measurements of carbonate chemistry

Seasonal patterns of estuarine acidification in seagrass beds of the Snohomish Estuary, WA

Recent studies have begun to explore physical and biogeochemical mechanisms of carbonate chemistry variability in a variety of coastal habitats, including coral reefs, upwelling margins, and inland seas. To our knowledge, there have been limited mechanistic studies of annual carbonate chemistry variability in nearshore estuarine environments. Here, we present autonomous sensor and grab sample data of carbonate chemistry covering a 10 month period from two subtidal seagrass bed sites in Possession Sound, WA. Simple mass balance stoichiometric models are used to evaluate seasonal drivers of carbonate system parameters in the seagrass beds. Simulations of increasing anthropogenic carbon (Canth) burdens in the habitats reveal seasonal differences in the magnitude of carbonate system responses. The addition of Canth alters the thermodynamic buffer factors (e.g. the Revelle factor) of the carbonate system, decreasing the system’s ability to buffer natural variability in the seagrass habitat on high-frequency (e.g. tidal, diel) and seasonal timescales. As a result, the most harmful carbonate system indices for many estuarine organisms (minimum pHT, minimum Ωarag, and maximum pCO2(s.w.)) change most rapidly with increasing Canth. We highlight how the observed seasonal climatology and non-linear response of the carbonate system to increasing Canth drive the timing of the crossing of established physiological stress thresholds for endemic organisms, as well as thresholds relevant for water quality management. In this system, the relative benefits of the seagrass beds in locally mitigating ocean acidification during the growing season increase with the higher atmospheric CO2 levels predicted toward 2100. Presently however, these mitigating effects are mixed due to intense diel cycling of CO2 driven by community metabolism

Death by dissolution : sediment saturation state as a mortality factor for juvenile bivalves

We show that death by dissolution is an important size-dependent mortality Utilizing a new experimental design, we were able to replicate saturation states frequently encountered by Mercenaria mercenaria in coastal deposits mercenaria were reared in sediments at Ωaragonite = 0.4 and 0.6, significant occurred (14.0% and 14.4% d⁻¹, respectively), relative to supersaturated-control mm M. mercenaria, significant mortality occurred under the most mortality = 9.6% d⁻¹), although mortality at Ωaragonite = 0.6 was not significant (mortality = 2.7% d⁻¹; control-saturated mortality = 0.2% d⁻¹). For the largest size- clams under the most undersaturated sediments (Ωaragonite = 0.4, 2.8% d⁻¹). To increase survivorship of juvenile bivalves during periods of recruitment, we saturation state by adding crushed Mya arenaria shell to a mud flat in West Bath, increased the average sediment saturation state within retrieved cores from Ω = numbers of live M. arenaria in buffered sediment increased almost three-fold in the metabolic acids that cause lowered saturation states may represent a strategy to decrease dissolution mortality.Keywords: Sediment saturation state, Dissolution, Mortality factors, Juvenile bivalve

The effects of infaunal biodiversity on biogeochemistry of coastal marine sediments

We tested the role of benthic infaunal functional diversity in regulating the biogeochemistry of nearshore sediments using laboratory microcosms. Single and multispecies assemblages of deposit-feeding polychaetes (Clymenella torquata, Spio setosa, and Leitoscoloplos fragilis) were used, and fluxes of oxygen and phosphate, as well as profiles of oxygen and pH in the sediment pore water, were measured. Significant differences in flux rates were found among treatments that were unrelated to polychaete abundance or biomass alone. Multispecies assemblages had lower flux rates of both oxygen and phosphate than rates calculated from the single-species treatments. Depthintegrated oxygen and pH profiles also showed significant differences between multispecies assemblages and selected single-species treatments. These differences were most likely from species-specific feeding and burrowing behavior and species-related interactions. Coefficients of variance for both oxygen and pH were highest for microcosms with no polychaetes and lowest for the assemblages, indicating a dampening effect of multispecies assemblages on porewater heterogeneity. When oxygen flux data was incorporated into a model of oxygen dynamics in Long Island Sound, results indicated that shifts in the benthic community composition could change sediment oxygen consumption rates sufficiently to disrupt the balance between the physical supply of oxygenated water and biological oxygen demand. The results of this study confirm the importance of benthic functional biodiversity to nearshore sedimentary processes and suggest that losses of functional diversity can have significant effects on ecosystem function

Quantifying the combined impacts of anthropogenic CO2 emissions and watershed alteration on estuary acidification at biologically-relevant time scales: a case study from Tillamook Bay, OR, USA

The impacts of ocean acidification (OA) on coastal water quality have been subject to intensive research in the past decade, but how emissions-driven OA combines with human modifications of coastal river inputs to affect estuarine acidification dynamics is less well understood. This study presents a methodology for quantifying the synergistic water quality impacts of OA and riverine acidification on biologically-relevant timescales through a case study from a small, temperate estuary influenced by coastal upwelling and watershed development. We characterized the dynamics and drivers of carbonate chemistry in Tillamook Bay, OR (USA), along with its coastal ocean and riverine end-members, through a series of synoptic samplings and continuous water quality monitoring from July 2017 to July 2018. Synoptic river sampling showed acidification and increased CO2 content in areas with higher proportions of watershed anthropogenic land use. We propagated the impacts of 1). the observed riverine acidification, and 2). modeled OA changes to incoming coastal ocean waters across the full estuarine salinity spectrum and quantified changes in estuarine carbonate chemistry at a 15-minute temporal resolution. The largest magnitude of acidification (-1.4 pHT units) was found in oligo- and mesohaline portions of the estuary due to the poor buffering characteristics of these waters, and was primarily driven by acidified riverine inputs. Despite this, emissions-driven OA is responsible for over 94% of anthropogenic carbon loading to Tillamook Bay and the dominant driver of acidification across most of the estuary due to its large tidal prism and relatively small river discharges. This dominance of ocean-sourced anthropogenic carbon challenges the efficacy of local management actions to ameliorate estuarine acidification impacts. Despite the relatively large acidification effects experienced in Tillamook Bay (-0.16 to -0.23 pHT units) as compared with typical open ocean change (approximately -0.1 pHT units), observations of estuarine pHT would meet existing state standards for pHT. Our analytical framework addresses pressing needs for water quality assessment and coastal resilience strategies to differentiate the impacts of anthropogenic acidification from natural variability in dynamic estuarine systems

Redox reactions and weak buffering capacity lead to acidification in the Chesapeake Bay

The combined effects of anthropogenic and biological CO2 inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would contribute to acidification. Here we report estuarine acidification dynamics based on oxygen, hydrogen sulfide (H2S), pH, dissolved inorganic carbon and total alkalinity data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia, and low pH. We show that a pH minimum occurs in mid-depths where acids are generated as a result of H2S oxidation in waters mixed upward from the anoxic depths. Our analyses also suggest a large synergistic effect from river-ocean mixing, global and local atmospheric CO2 uptake, and CO2 and acid production from respiration and other redox reactions. Together they lead to a poor acid buffering capacity, severe acidification and increased carbonate mineral dissolution in the USA\u27s largest estuary