Controls on Carbon, Nutrient, and Sediment Cycling in a Large, Semiarid Estuarine System; Princess Charlotte Bay, Australia
Controls on Carbon, Nutrient, and Sediment Cycling in a Large, Semiarid Estuarine System; Princess Charlotte Bay, Australia
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DOI：
10.1029/2019jg005049
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发表时间：
2020-01-01
影响因子：
3.7
通讯作者：
Steven, Andy
中科院分区：
文献类型：
--
作者：
Crosswell, Joseph R.;Carlin, Geoffrey;Steven, Andy
半干旱河口的特点是明显的季节变化，对这些系统的功能理解需要耦合生物地球化学过程和相关时空尺度的约束。在这里，我们整合了两年的空间调查和时间序列测量，以量化大堡礁地区最大河口系统的物理、化学和生物驱动因素。在雨季，淡水向河口输入的营养物和沉积物主要受洪水脉冲的影响，而碳酸盐输入也受到地下水排放的影响。这种碳酸盐输入抵消了在低盐度下会出现的最小缓冲区，从而减少了系统范围内的空气-水二氧化碳通量。沉积物再悬浮是潮汐和季节尺度上物质转化和运输的主要控制因素。在雨季，近岸混合区底栖藻类的潮汐再悬浮起到了自养过滤器的作用，从咸水羽流中去除了大部分生物可利用的营养物质。在旱季，上游运输与高盐度条件相结合，将物质困在河口上游，那里的反硝化和净异养作用很高。然而，沉积物输送的作用因潮汐不对称和密度驱动的环流而异。具有大面积潮间带的河口地区以盐滩侵蚀为主，显示出与全新世中期沼泽沉积物相关的成岩特征。这些富含有机物沉积物的潮汐再悬浮似乎是沿海水域生物地球化学循环的主要控制因素。这项研究表明，要全面了解沿海生态系统的连通性和功能，需要解决沿轴梯度和水柱梯度以及从潮汐到地质循环的一系列时间尺度。
Semiarid estuaries are characterized by pronounced seasonal variability, and a functional understanding of these systems requires constraint of coupled biogeochemical processes and relevant temporal and spatial scales. Here, we integrate 2 years of spatial surveys and time-series measurements to quantify physical, chemical, and biological drivers in the largest estuarine system in the Great Barrier Reef region. During wet season, freshwater inputs of nutrients and sediment to estuaries were dominated by flood pulses, whereas carbonate input was also influenced by groundwater discharge. This carbonate input counteracted the minimum buffering zone that would otherwise occur at low salinities, thereby decreasing system-wide air-water CO2 fluxes. Sediment resuspension was a major control on the transformation and transport of material over tidal and seasonal scales. During wet season, tidal resuspension of benthic algae in nearshore mixing zones acted as an autotrophic filter, removing most bioavailable nutrients from the brackish plume. During dry season, upstream transport combined with hypersaline conditions trapped material in upper estuaries where denitrification and net heterotrophy were high. However, the role of sediment transport varied depending on tidal asymmetry and density-driven circulation. Estuarine regions with large intertidal areas were dominated by salt flat erosion, which showed a diagenetic signature associated with mid-Holocene swamp sediments. Tidal resuspension of these organic-rich sediments appeared to be the dominant control on biogeochemical cycling in coastal waters. This study demonstrates that a holistic understanding of coastal ecosystem connectivity and function requires resolution of both along-axis and water-column gradients as well as a range of timescales from tidal to geological cycles.