Hydrologic effects on methane dynamics in riparian wetlands in a temperate forest catchment
Hydrologic effects on methane dynamics in riparian wetlands in a temperate forest catchment
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DOI：
10.1029/2006jg000240
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发表时间：
2007-02-27
影响因子：
3.7
通讯作者：
Tani, Makoto
中科院分区：
文献类型：
--
作者：
Itoh, Masayuki;Ohte, Nobuhito;Tani, Makoto
为了了解水文过程如何影响温带河岸湿地的生物地球化学和甲烷（CH4）循环，我们测量了CH4通量、溶解化学成分和地下水中CH4浓度，并监测了位于日本温暖湿润气候的森林水源集水区湿地的几个环境因子。地下水中溶解的氧化还原组分，包括硝酸盐（NO3-）、锰、铁和硫酸盐（SO42-）的变化取决于温度和土壤水分条件。强烈的减少条件通常发生在7月、8月和9月的高温月份。地下水中溶解CH4随氧化还原条件变化，夏季最高，冬季最低。河岸湿地CH4排放几乎全年均有观测，且具有明显的季节性。在夏季，排放率偶尔比山坡吸收率大4个数量级以上。虽然CH4排放量在夏季大部分时间内明显增加，但其排放受到以下因素的限制：(1)地下水位的波动，当地下水位下降时，地下带会向更氧化的状态转移；(2)富氧水，如降水和来自山坡的侧向地下流。这些结果表明，森林水源集水区的水文过程在向土壤提供氧气方面发挥着重要作用，从而影响生物地球化学循环，包括CH4的形成，森林流域的小湿地是CH4的大来源，特别是在夏季温暖潮湿的地区。
[1] To understand how hydrological processes affect biogeochemical and methane (CH4) cycles in temperate riparian wetlands, we measured CH4 fluxes and dissolved chemical constituents and CH4 concentrations in groundwater, and monitored several environmental factors in wetlands located within a forested headwater catchment in a warm, humid climate in Japan. Variation in redox components dissolved in groundwater, including nitrate (NO3-), Mn, Fe, and sulfate (SO42-), depended on temperature and soil-water conditions. Strongly reducing conditions usually occurred in the high-temperature months of July, August, and September. Dissolved CH4 in groundwater changed with redox conditions and was highest in summer and lowest in winter. CH4 emissions from riparian wetlands were observed almost throughout the year and displayed clear seasonality. Occasionally in summer, emission rates were more than 4 orders of magnitude greater than hillslope uptake rates. Although CH4 emissions increased markedly during most of the summer, they were constrained by (1) fluctuation of the water table, which when lowered can shift the subsurface zone to a more oxidized condition, and (2) the oxygen-rich water such as precipitation and lateral subsurface flow from the hillslope. These results suggest that hydrological processes in forest headwater catchments play an important role in supplying oxygen to soils and consequently affect biogeochemical cycles, including CH4 formation, and that small wetlands in forest watersheds function as large sources of CH4, especially in regions with warm humid summers.