André Frédéric, Jonard Mathieu, Ponette Quentin
Université catholique de Louvain, Faculté d'Ingénierie Biologique, Agronomique et Environnementale, Unité des Eaux et Forêts, Croix du Sud 2/009, 1348 Louvain-la-Neuve, Belgium.
Sci Total Environ. 2008 Jul 1;397(1-3):215-28. doi: 10.1016/j.scitotenv.2008.02.043. Epub 2008 Apr 10.
The effects of meteorological variables and local canopy characteristics on throughfall chemistry were investigated within a mixed oak-beech stand during the leafed and the leafless seasons. Throughfall was collected after each rain event in 12 structural units delimited by three neighbouring trees each. For each investigated ion (H+, Mg2+, Ca2+, K+, NH4+, Na+, Cl(-), NO3(-) and SO4(2-)), mixed linear models were used to analyse the effects of the rain volume (R) and of the length of the preceding dry period (ADP) on net throughfall ion fluxes and to evaluate the influence of canopy density and tree species composition on these relationships. The models explained more than 70% of the total variability. Canopy characteristics accounted for most of the spatial variability while a large part of the temporal variability was not explained by R and ADP, suggesting an influence of other variables such as wind force and direction. For each season, net throughfall ion fluxes generally increased with increasing R and ADP, whose coefficients were interpreted as leaching capacity and dry deposition rate, respectively; H+ is an exception with negative exchange capacity (i.e. absorption) during the leafed season. Dry deposition rate and exchange capacity estimates were generally lower for the leafless canopies compared with the leafed season. For a given density level, exchange capacities were either higher for oak than for beech or similar for both species while dry deposition tended to increase with increasing beech proportion. The enhancing effect of canopy density on dry deposition was particularly marked for the mixed leafed canopies. For the pure canopies, the effect of canopy density on dry deposition rate and exchange capacity tended to be more pronounced during the leafless period compared with the leafed season, while it was generally limited compared with the species effect.
在一个混合的橡树 - 山毛榉林分中，研究了气象变量和当地冠层特征在有叶和无叶季节对穿透雨化学性质的影响。在每次降雨事件后，在由相邻三棵树划定的12个结构单元中收集穿透雨。对于每个研究的离子（H⁺、Mg²⁺、Ca²⁺、K⁺、NH₄⁺、Na⁺、Cl⁻、NO₃⁻和SO₄²⁻），使用混合线性模型分析降雨量（R）和前一个干旱期长度（ADP）对净穿透雨离子通量的影响，并评估冠层密度和树种组成对这些关系的影响。这些模型解释了总变异性的70%以上。冠层特征占大部分空间变异性，而大部分时间变异性不能由R和ADP解释，这表明其他变量如风力和风向有影响。对于每个季节，净穿透雨离子通量通常随着R和ADP的增加而增加，其系数分别解释为淋溶能力和干沉降速率；H⁺是一个例外，在有叶季节具有负交换容量（即吸收）。与有叶季节相比，无叶冠层的干沉降速率和交换容量估计值通常较低。对于给定的密度水平，橡树的交换容量要么高于山毛榉，要么两种树种相似，而干沉降往往随着山毛榉比例的增加而增加。冠层密度对干沉降的增强作用在混合有叶冠层中尤为明显。对于纯冠层，与有叶季节相比，冠层密度对干沉降速率和交换容量的影响在无叶期往往更明显，而与树种效应相比通常有限。
