Soil Respiration Along a Hydrological Gradient at Harvard Forest EMS Tower 2003-2006

Soil respiration is an important component of the terrestrial carbon budget. Spatial variation of organic matter and plant cover induce temperature and moisture gradations that obscure direct response of soil respiration to radiative forcing. Separation of spatial patterns from microclimate and substrate availability is vital to predict the response to global change. We are measuring temporal and spatial patterns of soil CO2 flux across a hydrological gradient from wetland to upland soils. A system of 8 automated opaque chambers were installed in 2003 along a hydrological gradient on the northeast margin of the "Beaver Swamp" north of the EMS tower (+42.537755,-72.171478). Two additional clear chambers were installed in the wetland in 2006. Each automated chamber closes for a measurement every four hours. The resulting semi-continuous data has been providing a high-temporal density characterization of soil flux during the growing season since 2003. Soil temperature and moisture were recorded in the litter, organic, and mineral soils during 2004 at three locations along the slope. These structures will provide a database of soil respiration flux, temperature, and soil moisture with both high spatial and temporal resolution, across multiple cover types and ground water levels. The analysis will seek to determine the appropriate spatial scale of soil respiration measurement in eastern hardwood forests.土壤呼吸（soil respiration）是陆地碳收支（terrestrial carbon budget）的重要组成部分。有机质与植被覆盖的空间异质性会形成温度与湿度梯度，进而掩盖土壤呼吸对辐射强迫（radiative forcing）的直接响应。区分土壤呼吸的空间格局与微气候、底物可获得性的影响，对预测其对全球变化的响应至关重要。本研究针对湿地至旱地的水文梯度样带，测定土壤CO₂通量的时空分布格局。2003年，研究团队在EMS观测塔（EMS tower，北纬42.537755°，西经72.171478°）北侧的“海狸沼泽（Beaver Swamp）”东北缘沿水文梯度布设了8台自动不透明箱（automated opaque chambers）组成的监测系统。2006年，研究团队在该湿地增设了2台透明箱（clear chambers）。每台自动箱每4小时完成一次密闭测量。自2003年起，这套系统获取的半连续数据已实现生长季内土壤通量的高时间分辨率表征。2004年，研究团队沿坡地设置的3个监测点同步记录了枯落物层、有机质层与矿质土壤层的温度与湿度数据。本数据集将形成覆盖多种植被覆盖类型与地下水位梯度、兼具高空间与时间分辨率的土壤呼吸通量、温度及土壤湿度数据库。后续分析将旨在明确东部硬木林区土壤呼吸监测的适宜空间尺度。