Spatial Heterogeneity of Denitrification in Semi-Arid Floodplains
Spatial Heterogeneity of Denitrification in Semi-Arid Floodplains
复制标题
半干旱洪泛区反硝化的空间异质性
作者：
T. Harms;E. Wentz;N. Grimm
河岸生态系统是无机氮的汇。反硝化作用是一种异养微生物过程，通常占去除氮的很大一部分。河岸土壤和水文载体的特点可能会限制反硝化作用可以发生在河岸生态系统内的位置，通过影响基质，水和合适的氧化还原条件的分布。我们采用空间显式的方法来量化半干旱河岸生态系统的土壤特性和潜在的反硝化速率的异质性。这些结果使我们能够评估的相对贡献的水文载体（水的课程，输送材料）和土壤资源（生物区系所需的材料）的反硝化作用的空间异质性。在干旱和季风季节，我们对比了一个mesic网站，其特点是浅层地下水和每年的洪水淹没，与干旱的网站，被淹没的频率较低，有一个较深的地下水位。潜在的反硝化作用，整个中潮漫滩和反硝化作用的平均速率是在中潮网站比在旱站点，表明水的可用性对反硝化作用的影响。在干旱河段，急剧下降的池的土壤资源和反硝化速率发生远离流，表明流在确定空间格局的重要性。利用地理加权回归分析，我们确定，土壤有机质和土壤硝酸盐是显着的预测反硝化作用在干旱的网站，但影响反硝化作用的因素在空间上不同。土壤中碳（C）和氮基质的空间异质性可能影响反硝化作用的空间格局，但C和N基质的分布最终由水文矢量组织。干旱将增加丰富的河段水文地貌模板类似于这里研究的干旱河段。这样的过渡的后果可能包括降低反硝化率和斑块分布的反硝化作用在洪泛区土壤，这将减少河岸生态系统的氮去除的贡献。
Riparian ecosystems are recognized as sinks for inorganic nitrogen (N). Denitrification, a heterotrophic microbial process, often accounts for a significant fraction of the N removed. Characteristics of both riparian soils and hydrologic vectors may constrain the locations where denitrification can occur within riparian ecosystems by influencing the distribution of substrates, water, and suitable redox conditions. We employed spatially explicit methods to quantify heterogeneity of soil characteristics and potential rate of denitrification in semi-arid riparian ecosystems. These results allow us to evaluate the relative contributions of hydrologic vectors (water courses that convey materials) and soil resources (materials required by biota) to spatial heterogeneity of denitrification. During dry and monsoon seasons we contrasted a mesic site, characterized by shallow groundwater and annual inundation by floods, with a xeric site that is inundated less often and has a deeper water table. Potential denitrification was detected throughout the mesic floodplain and the average rate of denitrification was greater at the mesic site than at the xeric site, indicating the influence of water availability on denitrification. At the xeric reach, sharp declines in pools of soil resources and rate of denitrification occurred away from the stream, demonstrating the importance of the stream in determining spatial patterns. Using geographically weighted regression analysis, we determined that soil organic matter and soil nitrate were significant predictors of denitrification at the xeric site, but that factors influencing denitrification varied spatially. Spatial heterogeneity of carbon (C) and N substrates in soils likely influenced spatial patterns of denitrification, but distribution of C and N substrates was ultimately organized by hydrologic vectors. Droughts will increase the abundance of reaches with hydrogeomorphic templates similar to the xeric reach studied here. Consequences of such a transition may include a reduced rate of denitrification and patchy distribution of denitrification in floodplain soils, which will decrease the contribution of riparian ecosystems to N removal.