Small-scale heterogeneity in the geochemistry of seagrass vegetated and non-vegetated estuarine sediments: causes and consequences |
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Authors: | Andrew B Hebert John W Morse Peter M Eldridge |
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Institution: | (1) Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Rd. MSB 505, Honolulu, HI 96822, USA;(2) Department of Oceanography, Texas A&M University, 3146 TAMU, College Station, TX 77843, USA;(3) USEPA, Coastal Ecology Branch, Western Ecology Division, 2111 SE Marine Science Center Drive, Newport, OR 97365, USA |
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Abstract: | In addition to nutrient and light availability, sedimentary biogeochemical processes can play an essential role in seagrass
productivity. Previous investigations of the interactions between seagrasses and their underlying sediments have failed to
clearly identify the spatio-temporal variability of the major geochemical parameters involved. Dissolved and solid phase chemical
parameters in eelgrass vegetated and nearby non-vegetated sediments were investigated in this study to determine their vertical,
lateral, and temporal distributions. Solid-state microelectrodes were used to investigate dissolved O2, ΣH2S, Fe2+, and Mn2+ on mm space scales. In this study, spatial heterogeneity was assessed and diurnal “ventilation” by seagrass productivity
(i.e., the translocation of photosynthetically produced oxygen to the anoxic sedimentary environment) was not observed probably
because benthic infaunal activity (bioturabation and bioirrigation) and microzones established by microbial processes led
to highly heterogeneous sediment geochemistry where temporal variability was obscured by small-scale spatial variability.
Non-vegetated sediments were less geochemically variable laterally than vegetated sediments, however, in some cases, they
had similar vertical variability, possibly because they had been vegetated at an earlier time. This study demonstrates that
in vegetated sediments where there is also substantial benthic macrofaunal activity it is difficult to separate the impacts
of the two types of biota on sediment geochemistry and their spatial patterns, and it also raises the question of the applicability
of traditional one-dimensional diagenetic models for such spatially–temporally complex sediments. |
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Keywords: | Seagrass Sulfide Light Heterogeneity Nutrients Carbon Voltammetry |
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