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Differential effects of chronic and acute simulated seawater intrusion on tidal freshwater marsh carbon cycling

机译:慢性和急性模拟海水入侵对潮汐淡水沼泽碳循环的差异影响

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摘要

Tidal freshwater ecosystems experience acute seawater intrusion associated with periodic droughts, but are expected to become chronically salinized as sea level rises. Here we report the results from an experimental manipulation in a tidal freshwater Zizaniopsis miliacea marsh on the Altamaha River, GA where diluted seawater was added to replicate marsh plots on either a press (constant) or pulse (2 months per year) basis. We measured changes in porewater chemistry (SO42−, Cl, organic C, inorganic nitrogen and phosphorus), ecosystem CO2 and CH4 exchange, and microbial extracellular enzyme activity. We found that press (chronic) seawater additions increased porewater chloride and sulfate almost immediately, and ammonium and phosphate after 2–4 months. Chronic increases in salinity also decreased net ecosystem exchange, resulting in reduced CO2 and CH4 emissions from press plots. Our pulse treatment, designed to mimic natural salinity incursion in the Altamaha River (September and October), temporarily increased porewater ammonium concentrations but had few lasting effects on porewater chemistry or ecosystem carbon balance. Our findings suggest that long-term, chronic saltwater intrusion will lead to reduced C fixation and the potential for increased nutrient (N, P) export while acute pulses of saltwater will have temporary effects.
机译:潮汐淡水生态系统会经历与周期性干旱相关的急性海水入侵,但随着海平面上升,预计将逐渐变成盐渍化。在这里,我们报告了在佐治亚州Altamaha河上的潮汐淡水Zizaniopsis miliacea沼泽中进行实验操作的结果,在这里,按压力(恒定)或脉动(每年2个月)添加了稀释的海水以复制沼泽地。我们测量了孔隙水化学变化(SO4 2--sup>,Cl -,有机碳,无机氮和磷),生态系统中的CO2和CH4交换以及微生物细胞外酶活性的变化。我们发现,按(长期)添加海水几乎立即增加了孔隙水中的氯化物和硫酸盐,并在2-4个月后增加了铵盐和磷酸盐。盐度的长期增加也减少了生态系统的净交换,从而导致压榨地块的CO2和CH4排放量减少。我们的脉冲处理旨在模拟阿尔塔马哈河(9月和10月)的自然盐度入侵,暂时增加了孔隙水铵的浓度,但对孔隙水化学或生态系统碳平衡几乎没有持久的影响。我们的发现表明,长期,长期的盐水入侵将导致C固定减少,并可能增加养分(N,P)的出口,而盐水的剧烈波动将产生暂时性影响。

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