The important role of macroalgal canopies in the oceanic carbon (C) cycle is increasingly being recognized, but direct assessments of community productivity remain scarce. We conducted a seasonal study on a sublittoral Baltic Sea canopy of the brown alga
- NSF-PAR ID:
- 10321505
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 670
- ISSN:
- 0171-8630
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract Fucus vesiculosus , a prominent species in temperate and Arctic waters. We investigated community production on hourly, daily, and seasonal timescales. Aquatic eddy covariance (AEC) oxygen flux measurements integrated ~ 40 m2of the seabed surface area and documented considerable oxygen production by the canopy year‐round. High net oxygen production rates of up to 35 ± 9 mmol m−2h−1were measured under peak irradiance of ~ 1200μ mol photosynthetically active radiation (PAR) m−2s−1in summer. However, high rates > 15 mmol m−2h−1were also measured in late winter (March) under low light intensities < 250μ mol PAR m−2s−1and water temperatures of ~ 1°C. In some cases, hourly AEC fluxes documented an apparent release of oxygen by the canopy under dark conditions, which may be due to gas storage dynamics within internal air spaces ofF. vesiculosus. Daily net ecosystem metabolism (NEM ) was positive (net autotrophic) in all but one of the five measurement campaigns (December). A simple regression model predicted a net autotrophic canopy for two‐thirds of the year, and annual canopyNEM amounted to 25 mol O2m−2yr−1, approximately six‐fold higher than net phytoplankton production. Canopy C export was ~ 0.3 kg C m−2yr−1, comparable to canopy standing biomass in summer. Macroalgal canopies thus represent regions of intensified C assimilation and export in coastal waters. -
more » « less
Abstract Marine cable bacteria (
Candidatus Electrothrix ) and large colorless sulfur‐oxidizing bacteria (e.g., Beggiatoaceae) are widespread thiotrophs in coastal environments but may exert different influences on biogeochemical cycling. Yet, the factors governing their niche partitioning remain poorly understood. To map their distribution and evaluate their growth constraints in a natural setting, we examined surface sediments across seasons at two sites with contrasting levels of seasonal oxygen depletion in Chesapeake Bay using microscopy coupled with 16S rRNA gene amplicon sequencing and biogeochemical characterization. We found that cable bacteria, dominated by a single phylotype closely affiliated toCandidatus Electrothrix communis, flourished during winter and spring at a central channel site which experiences summer anoxia. Here, cable bacteria density was positively correlated with surface sediment chlorophyll, a proxy of phytodetritus sedimentation. Cable bacteria were also present with a lower areal density at an adjacent shoal site which supports bioturbating macrofauna. Beggiatoaceae were more abundant at this site, where their biomass was positively correlated with sediment respiration, but additionally potentially inhibited by sulfide accumulation which was evident during one summer. A springtime phytodetritus sedimentation event was associated with a proliferation of Beggiatoaceae and multipleCandidatus Electrothrix phylotypes, with cable bacteria reaching 1000 m length cm−2. These observations indicate the potential impact of a spring bloom in driving a hot moment of cryptic sulfur cycling. Our results suggest complex interactions between benthic thiotroph populations, with bioturbation and seasonal oscillations in bottom water dissolved oxygen, sediment sulfide, and organic matter influx as important drivers of their distribution. -
more » « less
Abstract. The trace metal iron (Fe) is an essential micronutrient that controls phytoplankton productivity, which subsequently affects organic matter cycling with feedback on the cycling of macronutrients. Along the continental margin of the US West Coast, high benthic Fe release has been documented, in particular from deep anoxic basins in the Southern California Borderland. However, the influence of this Fe release on surface primary production remains poorly understood. In the present study from the Santa Barbara Basin, in situ benthic Fe fluxes were determined along a transect from shallow to deep sites in the basin. Fluxes ranged between 0.23 and 4.9 mmol m−2 d−1, representing some of the highest benthic Fe fluxes reported to date. To investigate the influence of benthic Fe release from the oxygen-deficient deep basin on surface phytoplankton production, we combined benthic flux measurements with numerical simulations using the Regional Ocean Modeling System coupled to the Biogeochemical Elemental Cycling (ROMS-BEC) model. For this purpose, we updated the model Fe flux parameterization to include the new benthic flux measurements from the Santa Barbara Basin. Our simulations suggest that benthic Fe fluxes enhance surface primary production, supporting a positive feedback on benthic Fe release by decreasing oxygen in bottom waters. However, a reduction in phytoplankton Fe limitation by enhanced benthic fluxes near the coast may be partially compensated for by increased nitrogen limitation further offshore, limiting the efficacy of this positive feedback.
-
more » « less
Abstract Subterranean estuaries (STEs) form at the land‐sea boundary where groundwater and seawater mix. These biogeochemically reactive zones influence groundwater‐borne nutrient concentrations and speciation prior to export via submarine groundwater discharge (SGD). We examined a STE located along the York River Estuary (YRE) to determine if SGD delivers dissolved inorganic nitrogen (DIN) and phosphorus (DIP) to the overlying water. We assessed variations in STE geochemical profiles with depth across locations, times, and tidal stages, estimated N removal along the STE flow path, measured hydraulic gradients to estimate SGD, and calculated potential nutrient fluxes. Salinity, dissolved oxygen (DO), DIN, and DIP varied significantly with depth and season (
p < 0.05), but not location or tidal stage. Ammonium dominated the DIN pool deep in the STE. Moving toward the sediment surface, ammonium concentrations decreased as nitrate and DO concentrations increased, suggesting nitrification. Potential sediment N removal rates mediated by denitrification were <8 mmoles N m−2 d−1. The total groundwater discharge rate was 38 ± 11 L m−2 d−1; discharge followed tidal and seasonal patterns. Net SGD nutrient fluxes were 0.065–3.2 and 0.019–0.093 mmoles m−2 d−1for DIN and DIP, respectively. However, microbial N removal in the STE may attenuate 0.58% to >100% of groundwater DIN. SGD fluxes were on the same order of magnitude as diffusive benthic fluxes but accounted for <10% of the nutrients delivered by fluvial advection in the YRE. Our results indicate the importance of STE biogeochemical transformations to SGD flux estimations and their role in coastal eutrophication and nutrient dynamics. -
more » « less
Global change is leading to warming, acidification, and oxygen loss in the ocean. In the Southern California Bight, an eastern boundary upwelling system, these stressors are exacerbated by the localized discharge of anthropogenically enhanced nutrients from a coastal population of 23 million people. Here, we use simulations with a high-resolution, physical–biogeochemical model to quantify the link between terrestrial and atmospheric nutrients, organic matter, and carbon inputs and biogeochemical change in the coastal waters of the Southern California Bight. The model is forced by large-scale climatic drivers and a reconstruction of local inputs via rivers, wastewater outfalls, and atmospheric deposition; it captures the fine scales of ocean circulation along the shelf; and it is validated against a large collection of physical and biogeochemical observations. Local land-based and atmospheric inputs, enhanced by anthropogenic sources, drive a 79% increase in phytoplankton biomass, a 23% increase in primary production, and a nearly 44% increase in subsurface respiration rates along the coast in summer, reshaping the biogeochemistry of the Southern California Bight. Seasonal reductions in subsurface oxygen, pH, and aragonite saturation state, by up to 50 mmol m−3, 0.09, and 0.47, respectively, rival or exceed the global open-ocean oxygen loss and acidification since the preindustrial period. The biological effects of these changes on local fisheries, proliferation of harmful algal blooms, water clarity, and submerged aquatic vegetation have yet to be fully explored.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps13770
