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首页> 外文期刊>Ecosystems >Effects of holocene Alnus expansion on aquatic productivity, nitrogencycling, and soil development in southwestern Alaska
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Effects of holocene Alnus expansion on aquatic productivity, nitrogencycling, and soil development in southwestern Alaska

机译：全新世Al木扩张对阿拉斯加西南部水生生产力，氮循环和土壤发育的影响

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Numerous pollen records provide evidence for the widespread range expansion of Alnus throughout Alaska and adjacent Canada during the middle Holocene. Because Alnus can fix atmospheric N-2, this vegetational change probably had a profound effect on N availability and cycling. To assess this effect, we analyzed a sediment core from Grandfather Lake in southwestern Alaska for a suite of geochemical indicators, including elemental composition, biogenic silica (BSi) content, and carbon (C) and nitrogen (N) isotopes of organic matter. These data, in conjunction with a pollen record from the same site, are used to infer biogeochemical processes associated with the mid-Holocene Alnus expansion. The increase in Alnus pollen percentages from 10% to 70% circa 8000-7000 BP (C-14 years before present) suggests the rapid spread of Alnus shrub thickets on mountain slopes and riparian zones in the Grandfather Lake region. Coincident with this vegetational change, the mean value of the sediment BSi content increases from 20.4 to 106.2 mg/g, reflecting increased diatom productivity within the lake as a result of Alnus N-2 fixation in the watershed soils and the associated N flux to the lake. Elevated aquatic productivity at this time is also supported by increased percentages of organic C and N, decreased C:N ratios, and decreased values of delta C-13. Furthermore, the delta N-15 values of sediments increase substantially with the establishment of Alnus shrub thickets, suggesting enhanced N availability and accelerated N cycling within the lake and its watershed. Superimposed on a general trend of soil acidification throughout the postglacial period, soil acidity probably increased as a result of the Alnus expansion, as can be inferred from decreasing ratios of authigenic base cations to allogenic silica (Si) and increasing ratios of authigenic aluminum (Al) to allogenic Si. The ultimate cause of these mid-Holocene ecosystem changes was an increase in effective moisture in the region.
机译：许多花粉记录提供证据，表明全新世中期阿尔努斯在整个阿拉斯加及邻近加拿大广泛分布。因为Al木能够固定大气中的N-2，所以这种植被变化可能会对氮的有效性和循环产生深远的影响。为了评估这种影响，我们分析了阿拉斯加西南部祖父湖的沉积物核心，提供了一系列地球化学指标，包括元素组成，生物硅（BSi）含量以及有机物的碳（C）和氮（N）同位素。这些数据与来自同一地点的花粉记录一起，用于推断与全新世中型Al蛇扩张相关的生物地球化学过程。大约8000-7000 BP（现今的C-14年）之前，Alnus花粉的百分比从10％增加到70％，这表明Alnus灌木丛在祖父湖地区的山坡和河岸带迅速蔓延。与此植被变化相吻合的是，沉积物中BSi含量的平均值从20.4增加到106.2 mg / g，这反映了由于Alnus N-2固定在流域土壤中以及与此相关的N通量的作用，湖中硅藻的生产率提高了。湖。同时，有机碳和氮的百分比增加，碳氮比降低以及C-13值降低也支持了水生生产力的提高。此外，随着Alnus灌木灌丛的建立，沉积物的δN-15值显着增加，这表明氮的可利用性增加，湖泊及其流域内的氮循环加快。与整个冰川期后土壤酸化的总体趋势相叠加，由于阿尔努斯膨胀，土壤酸度可能会增加，这可以从自生碱阳离子与异源二氧化硅（Si）的比例降低和自生铝（Al ）异源硅。这些全新世中期生态系统变化的最终原因是该地区有效水分的增加。

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