The role of tidal creeks in carbon processing and export to the freshwater tidal zone at the land-estuary boundary of tropical mangrove estuaries

IF 3 3区 地球科学 Q2 CHEMISTRY, MULTIDISCIPLINARY
Claris N. Sunjo , Eliot A. Atekwana , Hendratta N. Ali , Henry M. Agbogun , Isaac K. Njilah
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Abstract

Tidal creeks are conduits for tide-driven processing and exchange of water and dissolved inorganic carbon (DIC) between the open estuary and mangrove forests. Yet, the sources of DIC, and the role of tidal creeks in the cycling of DIC and its transport to the open water of mangrove estuaries is poorly understood. This study was conducted in a tidal creek in the freshwater tidal zone at the land-estuary boundary of a tropical mangrove estuary. We made 177 measurements of salinity and 80 measurements of geogenic solutes (silica, Ca, Mg), DIC components (partial pressure of CO2 (pCO2), alkalinity and total DIC) and stable isotopes of water (δ18O and δD) and DIC (δ13CDIC). We aimed to determine the sources and the timing of water input into the tidal creek, how the different water sources control input of DIC, and how DIC is cycled through semidiurnal mixed tides and over a diel cycle. The salinity-δ18O relationship indicates two sources of water, while the relationships for salinity-DO, salinity-solute, and salinity-DIC implicated submarine groundwater discharge (SGD) as the source providing the DIC processed and transported to the open estuary. Normalized water level vs. salinity reveals that SGD sourced DIC dominates the water column during tidal ebbing and halfway through tidal flooding. In contrast, freshwater from the open estuary mainly dilutes the solutes and DIC from halfway during tidal flooding to peak high tide. The photocycle, heterotrophic and autotrophic processes are unable to explain the more than 5 times greater than atmospheric pCO2 recorded during the daytime and at low tide. These findings demonstrate that SGD is a significant DIC source in tidal creeks at the land-estuary transition zone which indicate the important role of SGD in the cycling of carbon in the freshwater tidal zones of mangrove estuaries.

Abstract Image

潮沟在热带红树林河口陆口边界淡水潮带碳加工和输出中的作用
潮沟是开放河口与红树林之间潮汐驱动水和溶解无机碳(DIC)加工交换的通道。然而,人们对DIC的来源以及潮汐溪在DIC循环及其向红树林河口开放水域运输中的作用知之甚少。本研究在热带红树林河口陆口边界淡水潮带的潮汐溪中进行。我们进行了177次盐度测量和80次地源溶质(二氧化硅、Ca、Mg)、DIC组分(CO2分压(pCO2)、碱度和总DIC)以及水的稳定同位素(δ18O和δD)和DIC (δ13CDIC)测量。我们的目的是确定水输入潮沟的来源和时间,不同的水源如何控制DIC的输入,以及DIC如何通过半日混合潮和日循环循环。盐度-δ18O关系表明水体有两个来源,而盐度- do、盐度-溶质和盐度-DIC关系暗示海底地下水排放(SGD)作为源,将DIC加工并输送到开放河口。归一化水位与盐度的关系表明,在退潮和潮汐洪水中途,SGD来源的DIC主导了水柱。而开放河口淡水对溶质和DIC的稀释作用主要在潮汐期至高潮期的一半。光循环、异养和自养过程无法解释白天和退潮时记录的比大气二氧化碳分压高5倍以上的现象。这些结果表明,SGD是陆口过渡带潮沟中重要的DIC源,表明SGD在红树林河口淡水潮带碳循环中的重要作用。
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来源期刊
Marine Chemistry
Marine Chemistry 化学-海洋学
CiteScore
6.00
自引率
3.30%
发文量
70
审稿时长
4.5 months
期刊介绍: Marine Chemistry is an international medium for the publication of original studies and occasional reviews in the field of chemistry in the marine environment, with emphasis on the dynamic approach. The journal endeavours to cover all aspects, from chemical processes to theoretical and experimental work, and, by providing a central channel of communication, to speed the flow of information in this relatively new and rapidly expanding discipline.
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