Seawater carbonate chemistry and benthic primary production and inorganic nitrogen fluxes in two coastal sediments

• Main Authors: Vopel, Kay, Del-Río, Vopel, Pilditch, Conrad A
• Format: Dataset
• Language: English
• Published: PANGAEA 2018
• Subjects: Alkalinity; total; standard deviation; Ammonium; flux; Aragonite saturation state; Benthos; Bicarbonate ion; Calcite saturation state; Calculated using CO2calc; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; Containers and aquaria (20-1000 L or < 1 m**2); Difference; Entire community; Event label; EXP; Experiment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Hauraki_Gulf; Identification; Laboratory experiment; Light mode; Nitrate and Nitrite; Nitrite and nitrate; OA-ICC; Ocean Acidification International Coordination Centre; Other studied parameter or process; Oxygen uptake; Partial pressure of carbon dioxide; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.887792; https://doi.org/10.1594/PANGAEA.887792

Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NOX- (nitrite/nitrate), NH4+ and O2, we incubated estuarine sand and subtidal silt in recirculating seawater with a CO2-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NOX- content but the seawater kept at pH 7.9 lost only 18%. Excess CO2 increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NOX- efflux into influx. The estuarine sand sustained its initial NOX- influx but, by the end of the incubation, released more NH4+ at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO2 increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH4+ and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO2 may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication.