Element fluxes and landscape position in a northern hardwood forest watershed ecosystem
Element fluxes and landscape position in a northern hardwood forest watershed ecosystem
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DOI：
10.1007/s100210000017
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发表时间：
2000-03-01
期刊：
影响因子：
3.7
通讯作者：
Likens, GE
中科院分区：
文献类型：
--
作者：
Johnson, CE;Driscoll, CT;Likens, GE
新罕布什尔州哈伯德溪实验森林（Hubbard Brook Experimental Forest）上游河流的化学变化表明，在小流域生态系统中，沿着海拔梯度存在着重要的生物地球化学循环差异。利用1982年至1992年期间收集的数据，我们构建了流域6（一个森林流域）内三个子流域的元素预算[Ca、Mg、It、Na、Si、Al、溶解有机碳（DOC）、S和N]。高海拔云杉-冷杉-白桦亚集水区的生物地球化学以自然发生的有机化合物过程为主。与低海拔地区相比，该地区的溪流和土壤溶液的有机酸度、狗和有机结合单体铝（Al,）浓度较高。以硬木植被为主的中高程小流域，无机单体铝（Al）的净产量最大，且表现出DOC和Al的净固定化。同样以落叶植被为特征的低海拔子流域，其碱离子（Ca2+、Mg2+、K+、Na+）的净生产量在各子流域中最高。在研究期间，云杉-白桦亚集水区树木生物量略有下降，中高程保持不变，低高程增加5%。将生物量营养库的相应变化与地球化学模式相结合，我们观察到在这个13.2 ha的流域内，三个子流域土壤中Ca、Mg、K、Na和Si的净产量差异高达15倍。Ca， Na和溶解Si在海拔最高的亚流域的释放可以用185 mol ha(-1) y（-1）的斜长石的一致溶解来解释。根据Na的净输出，斜长石的风化速率在中高程亚流域和低高程亚流域分别增加到189和435 mol ha(-1) y（-1）。然而，长石在硬木亚集水区的溶解度仅占观测到的净Ca输出的26%-37%。钙从土壤交换点和有机质中流失是最可能的原因。此外，这种枯竭似乎在分水岭的下半部分发生得最快。哈伯德溪实验森林的小流域具有土壤链，土壤深度和土壤-水接触时间在下坡增加。这些因素通过影响水文路径和酸中和过程，对小流域生物地球化学通量产生重要影响，但对森林活力的影响不太清楚。我们的研究结果说明了流域水位研究对空间尺度的敏感性。然而，元素通量的大部分变化似乎发生在前10-20公顷的流域区域。
Chemical changes along headwater streams at the Hubbard Brook Experimental Forest in New Hampshire suggest that important differences exist in biogeochemical cycles along an altitudinal gradient within small watershed ecosystems. Using data collected during the period 1982-92, we have constructed element budgets [Ca, Mg, It, Na, Si, Al, dissolved organic carbon (DOC), S, and N] for three subcatchments within watershed 6, a forested watershed last logged around 1917-20. The biogeochemistry of the high-elevation spruce-fir-white birch subcatchment was dominated by processes involving naturally occuring organic compounds. Stream water and soil solutions in this zone had elevated concentrations of organic acidity, DOG, and organically bound monomeric aluminum (Al,), relative to lower-elevation sites. The middle-elevation subcatchment, dominated by hardwood vegetation, had the greatest net production of inorganic-monomeric aluminum (Al,), and exhibited net immobilization of DOC and Al,. The low-elevation subcatchment, also characterized by deciduous vegetation, had the highest rates of net production of base cations (Ca2+, Mg2+, K+, Na+) among the subcatchments. Living biomass of trees declined slightly in the spruce-fir-white birch subcatchment during the study period, remained constant in the middle-elevation zone, and increased by 5% in the low-elevation subcatchment. Coupling the correspending changes in biomass nutrient pools with the geochemical patterns, we observed up to 15-fold differences in the net production of Ca, Mg, K, Na, and Si in soils of the three subcatchments within this 13.2-ha watershed. Release of Ca, Na, and dissolved Si in the highest-elevation subcatchment could be explained by the congruent dissolution of 185 mol ha(-1) y(-1) of plagioclase feldspar. The rate of plagioclase weathering, based on the net output of Na, increased downslope to 189 and 435 mol ha(-1) y(-1) in the middle-elevation and low-elevation subcatchments, respectively. However, the dissolution of feldspar in the hardwood subcatchments could account for only 26%-37% of the observed net Ca output. The loss of Ca from soil exchange sites and organic matter is the most likely source of the unexplained net export. Furthermore, this depletion appears to be occurring most rapidly in the lower half of watershed 6. The small watersheds at the Hubbard Brook Experimental Forest occupy a soil catena in which soil depth and soil-water contact time increase downslope. By influencing hydrologic flowpaths and acid neutralization processes, these factors exert an important influence on biogeochemical fluxes within small watersheds, but their influence on forest vigor is less clear. Our results illustrate the sensitivity of watershed-level studies to spatial scale. However, it appears that much of the variation in element fluxes occurs in the first 10-20 ha of drainage area.