Water–Sediment Exchanges Control Microbial Processes Associated with Leaf Litter Degradation in the Hyporheic Zone: a Microcosm Study
Water–Sediment Exchanges Control Microbial Processes Associated with Leaf Litter Degradation in the Hyporheic Zone: a Microcosm Study
复制标题
水-沉积物交换控制与潜流区落叶退化相关的微生物过程：一项微观研究
作者：
S. Navel;F. Mermillod‐Blondin;B. Montuelle;É. Chauvet;L. Simon;P. Marmonier
本研究旨在通过实验量化地表沉积物渗透性降低对潜流带（即地表水和地下水之间的沉积界面）微生物特征和生态过程（呼吸和落叶分解）的影响。水-沉积物界面的物理结构通过在填充有异质砾石/砂沉积基质的慢滤柱的沉积物表面添加2 cm厚的粗砂（未堵塞系统）或细砂（堵塞系统）来操纵。堵塞的影响进行了量化，通过测量的水力传导性，水化学，微生物丰度和活动和相关的过程（分解的桤木叶凋落物插入在9厘米的深度沉积物，氧气和硝酸盐的微生物消耗）。细砂沉积物大大降低了水力传导率（与粗砂覆盖的未堵塞系统相比，约为8倍）和相关的水流，导致氧气（在3 cm深度达到不到1 mg L−1）和沉积物中硝酸盐浓度随深度急剧下降。在堵塞的系统中，从好氧条件向厌氧条件的转变有利于在沉积物上生活的微生物细菌的建立。对掩埋的落叶进行的分析表明，减少了30%的有机物分解堵塞系统相比，畅通的系统。这种减少与堵塞对叶相关微生物的活动和丰度的负面影响有关。最后，我们的研究清楚地表明，微生物参与有机物分解过程是依赖于在潜流区的水力传导率和氧气的可用性。
The present study aimed to experimentally quantify the influence of a reduction of surface sediment permeability on microbial characteristics and ecological processes (respiration and leaf litter decomposition) occurring in the hyporheic zone (i.e. the sedimentary interface between surface water and groundwater). The physical structure of the water–sediment interface was manipulated by adding a 2-cm layer of coarse sand (unclogged systems) or fine sand (clogged systems) at the sediment surface of slow filtration columns filled with a heterogeneous gravel/sand sedimentary matrix. The influence of clogging was quantified through measurements of hydraulic conductivity, water chemistry, microbial abundances and activities and associated processes (decomposition of alder leaf litter inserted at a depth of 9 cm in sediments, oxygen and nitrate consumption by microorganisms). Fine sand deposits drastically reduced hydraulic conductivity (by around 8-fold in comparison with unclogged systems topped by coarse sand) and associated water flow, leading to a sharp decrease in oxygen (reaching less than 1 mg L−1 at 3 cm depth) and nitrate concentrations with depth in sediments. The shift from aerobic to anaerobic conditions in clogged systems favoured the establishment of denitrifying bacteria living on sediments. Analyses performed on buried leaf litter showed a reduction by 30% of organic matter decomposition in clogged systems in comparison with unclogged systems. This reduction was linked to a negative influence of clogging on the activities and abundances of leaf-associated microorganisms. Finally, our study clearly demonstrated that microbial processes involved in organic matter decomposition were dependent on hydraulic conductivity and oxygen availability in the hyporheic zone.