Dissolved inorganic nitrogen uptake by intertidal microphytobenthos: nutrient concentrations, light availability and migration

Abstract

The importance of intertidal flats as areas of nitrogen filtering has become increasingly apparent in recent times. To understand fully the cycling of this nutrient in these areas of high metabolic activity, it is necessary to elucidate the influence of microphytobenthos (MPB) on stocks of ammonium and nitrate in surface areas. In this study, we aimed to quantify nitrogen uptake and relate it to the in situ concentrations and environmental conditions to which MPB are exposed. In an estuarine system on the Korean Peninsula, we conducted kinetic experiments using 15 N stable isotopes and core sampling over the tidal cycle to determine the temporal evolution of porewater nutrient concentrations and the migration of MPB. The results revealed a range of K s values between 1.5 and 11.8 μmol l -1 for ammonium and 19.2 μmol l -1 for nitrate. Thus MPB communities vary their affinity for dissolved inorganic nitrogen (DIN), which may be related to the substrate conditions to which they are exposed. Uptake of ammonium under experimentally darkened or natural night conditions was, on average, 50% lower than during light periods. The range of porewater DIN concentrations was large and appeared to be primarily determined by tidal influences. This oscillation, coupled to the vertical migration of the MPB in sediments, is likely to have a substantial effect on uptake over the short term (hours). The results indicate that, contrary to our conceptual model, the MPB largely incorporates DIN at the sediment surface during low tide periods when ammonium concentrations are at their highest. As a result, our representation of the MPB in coastal and estuarine models needs to be reassessed.

Ammonium cycling in the rocky intertidal: Remineralization, removal, and retention

“…5b cycling likely mediated by primary production-Tidepool NH z 4 removal rates were highest during daylight (Fig. 5), consistent with previously noted diurnal activities of phytoplankton (Goering et al 1964), macroalgae (McGlathery et al 1997, and microphytobenthic communities (Longphuirt et al 2009) and emphasizing the importance of photosynthesis in this system. Similarly, tidepool NH z 4 remineralization rates in MC pools were, on average, 5.29 mmol L 21 h 21 greater during the day, while those in MR pools were 0.71 mmol L 21 h 21 greater, possibly a consequence of the linkage between primary production and food supply to mussels and other macrofauna.…”

The influence of pore‐water advection, benthic photosynthesis, and respiration on calcium carbonate dynamics in reef sands

“…The influence of advective pore-water exchange on benthic primary production is further supported by the observation of higher O 2 fluxes (NPP; (Longphuirt et al 2009). However, it has been shown that under nutrient-limiting conditions, photosynthesis by benthic diatoms continues unbalanced, with overflow metabolism shunted to exopolysaccharide (EPS) excretion (Alcoverro et al 2000).…”

“…The difference between benthic photosynthesis rates measured in advective conditions with in situ flux chambers and ex situ rates under diffusive conditions indicates that pore-water advection relieves an important limitation of microphytobenthic productivity. (Longphuirt et al 2009). However, it has been shown that under nutrient-limiting conditions, photosynthesis by benthic diatoms continues unbalanced, with overflow metabolism shunted to exopolysaccharide (EPS) excretion (Alcoverro et al 2000).…”

The role of microphytobenthos in soft‐sediment ecological networks and their contribution to the delivery of multiple ecosystem services

“…Single‐celled, photosynthesizing organisms are quantitatively important for estuarine and shelf primary productivity, benthopelagic exchange of sediment, the cycling of nutrients and oxygen production (Chen et al, ; Jones et al, ; Longphuirt et al, ; Pinckney, ). MPB productivity also supports energy transfer to higher organisms (MacIntyre et al, ) with compositional changes in the MPB taxa altering the nutritional quality of this primary food source (Müller‐Navarra, Brett, Liston, & Goldman, ).…”