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Base cation and nitrogen budgets for a mixed hardwood catchment in South-Central Ontario

机译：安大略中南部混合硬木集水区的基础阳离子和氮预算

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There is growing concern that available base cation pools in soil are declining in eastern North America and that some forests are approaching nitrogen (N) saturation due to the combined effects of acid deposition and harvesting. To assess these concerns, elemental mass balances for calcium (Ca), magnesium (Mg), potassium (K), and N were conducted over a 17-year period in a representative mixed hardwood forest (HP4) in the Muskoka-Haliburton region in central Ontario, Canada. On average, 76% of the N measured in bulk deposition, which is a conservative estimate of total N deposition, was retained in HP4, with tree uptake accounting for over half of the retained N. Year-to-year variations in annual NO, export were affected by climate variations, although the low annual NO3-N concentrations (80-156 mug/L) suggest that HP4 is not approaching N saturation. Losses of Ca, Mg, and K in stream export plus accumulation in trees (more than 12 cm in diameter at breast height) exceeded inputs in deposition by 296, 76.2, and 53.6 kg/ha, respectively, over the 17-year period. Inclusion of mineral weathering estimates obtained using PROFILE, zirconium (Zr) depletion, and total analysis correlation failed to balance Ca losses from HP4, and calculations indicate that between 98 and 145 kg/ha (depending on mineral weathering estimate) was lost from the soil exchangeable pool between 1983 and 1999. These losses were supported by repeated field measurements, which showed that the exchangeable Ca concentrations and soil pH decreased over the 17-year period, particularly in the upper soil horizons. When mineral weathering estimates are included, mass balance calculations generally indicated that there was no net loss of Mg and K from HP4, which was confirmed by our soil measurements. At present, there is sufficient Ca in the soil exchangeable pool to sustain forest growth at HP4; however, continued losses of Ca due to leaching and harvesting at the present rate may ultimately threaten the health and productivity of the forest within just a few decades.
机译：越来越令人担忧的是，北美东部地区土壤中可用的碱性阳离子池正在减少，并且由于酸沉降和采收的综合作用，一些森林正在接近氮（N）饱和。为了评估这些担忧，在2002年的Muskoka-Haliburton地区代表性的硬木混交林（HP4）中进行了为期17年的钙（Ca），镁（Mg），钾（K）和N元素质量平衡。加拿大安大略省中部。平均而言，在整体沉积中测得的氮的76％（这是对总氮沉积的保守估计）保留在HP4中，树木吸收占保留的N的一半以上。年NO的逐年变化，出口受到气候变化的影响，尽管每年的NO3-N浓度较低（80-156杯/升）表明HP4并未接近N饱和。在17年期间，溪流出口中钙，镁和钾的损失加上树木的堆积（胸高处直径超过12厘米）超过沉积物输入，分别为296、76.2和53.6 kg / ha。包含使用PROFILE获得的矿物风化估算，锆（Zr）耗竭以及总分析相关性无法平衡HP4造成的Ca损失，计算表明，土壤损失了98至145 kg / ha（取决于矿物风化估算） 1983年至1999年之间的可交换池。这些损失得到了反复田间测量的支持，这表明在17年内，尤其是在土壤上层，可交换的Ca浓度和土壤pH降低了。当包括矿物风化估算值时，质量平衡计算通常表明，HP4并没有Mg和K的净损失，这通过我们的土壤测量得到了证实。目前，土壤可交换池中有足够的Ca来维持HP4时森林的生长。然而，以目前的速度淋溶和收获造成的钙持续损失可能最终在短短几十年内威胁到森林的健康和生产力。

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