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Hydraulic control of pore water geochemistry within the oxic‐suboxic zone of a permeable sediment
Author(s) -
Falter James L.,
Sansone Francis J.
Publication year - 2000
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 - 10.4319/lo.2000.45.3.0550
Subject(s) - pore water pressure , sediment , geology , sediment–water interface , reef , hydrology (agriculture) , oceanography , soil science , geomorphology , geotechnical engineering
The geochemical behavior of the top 70 cm of permeable reef flat sediments on Checker Reef, Oahu, Hawai'i was examined using spatial and temporal changes in pore water O 2 , NO 3 − , NO 2 − , NH 4 + , and N 2 O concentrations. The shallow depth of the sediment‐water interface relative to the height of waves propagating across the reef creates an environment in which pore water mixing and transport are dominated by wave‐induced mechanisms. Dissolved oxygen penetrated 15–50 cm in the four sites studied. The depth‐integrated concentration of dissolved oxygen was greater under larger wave conditions and in more permeable sediments, which suggests that dissolved oxygen may be a good indicator of the relationship between sediment metabolism and the physical nature of the sediment environment. The absence of any subsurface N 2 O maxima, limited temporal variability in pore water N 2 O concentrations, and vertically coherent profiles of O 2 , NO 3 − , NO 2 − , and N 2 O suggest that suboxic processes are typically restricted to spatial scales that are smaller than for oxic processes in these sediments. The geochemical response of the sediments to a natural perturbation was monitored by examining the composition of pore waters immediately following a large wave event and for several weeks thereafter. Significant changes in the depth‐integrated concentrations of O 2 , NO 3 − , NO 2 − and NH 4 + were observed following the perturbation; however, only changes in NO 3 − lasted for several weeks after the event, whereas most other species returned to previous conditions within two weeks or less.