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Oxygen transport and reactivity within a sandy seepage face in a mesotidal lagoon ( R ia F ormosa, S outhwestern I beria)
Author(s) -
Ibánhez J. Severino P.,
Rocha Carlos
Publication year - 2016
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.1002/lno.10199
Subject(s) - benthic zone , intertidal zone , sediment , pore water pressure , seawater , advection , diagenesis , infiltration (hvac) , geology , oceanography , hydrology (agriculture) , environmental science , geomorphology , mineralogy , physics , geotechnical engineering , thermodynamics
Abstract Sandy sediments are now recognized as sites of high carbon turnover enhanced by porewater flow. However, it is unclear how coupling between porewater advection and benthic metabolism might permit O 2 ‐saturated areas and suboxic environments to coexist in close proximity. Field sampling campaigns, flow‐through reactor (FTR) experiments and diagenetic modeling were used to study benthic O 2 dynamics in surface sediments of a permeable intertidal seepage face (Ria Formosa; Southwestern Iberia). Field results demonstrated that the pressure gradient imposed by tidal oscillation at the seepage face permits seawater infiltration at high tide, and hence resupplies the benthos in O 2 and organic matter (OM). Significant aerobic respiration rates (12.1–26.8 nmol cm −3 “bulk sediment” (bs) h −1 ) were derived from vertical O 2 gradients taken from the top 28 cm of the sediment during active seepage. FTR experiments showed a vertical zonation of respiration rates following benthic OM availability (from 8.63 ± 1.88 nmol cm −3 bs h −1 at 12–32 cm depth to 53.55 ± 7.93 nmol cm −3 bs h −1 at 0–2 cm depth). Advection enhances O 2 consumption rates, but respiration is ultimately limited by OM availability at high seepage rates. Diagenetic modeling of O 2 distribution in the porewater suggests that even within a well‐oxygenated beach aquifer, local respiration is sufficiently high to lower the porewater O 2 concentration near the sediment surface during active seepage. Our results indicate that high seepage rates, OM and O 2 loading promoted by tidally‐driven seawater infiltration control the O 2 consumption at the sediment surface, thus favoring the occurrence of suboxic biogeochemical processes near the sediment surface.