Fluxes project at North Temperate Lakes LTER: Predicting Peat Depth in a North Temperate Lake District 2008

Peat deposits contain on the order of 1/6 of the Earth's terrestrial fixed carbon (C), but uncertainty in peat depth precludes precise estimates of peat C storage. To assess peat C in the Northern Highlands Lake District (NHLD), a approximately 7000 square km region in northern Wisconsin, United States, with 20 percent peatland by area, we sampled 21 peatlands. In each peatland, peat depth (including basal organic lake sediment, where present) was measured on a grid and interpolated to calculate mean depth. Our study addressed three questions: (1) How spatially variable is peat depth? (2) To what degree can mean peat depth be predicted from other field measurements (water chemistry, water table depth, vegetation cover, slope) and/or remotely sensed spatial data? (3) How much C is stored in NHLD peatlands? Site mean peat depth ranged from 0.1 to 5.1 m. Most of the peatlands had been formed by the in-filling of small lake basins (terrestrialization), and depths up to 15 m were observed. Mean peat depth for small peat basins could be best predicted from basin edge slope at the peatland/upland interface, either measured in the field or calculated from digital elevation (DEM) data (Adj. R2 = 0.70). Upscaling using the DEM-based regression gave a regional mean peat depth of 2.1 plus or minus 0.2 m (including approximately 0.1 to 0.4 m of organic lake sediment) and 144 plus or minus 21 Tg-C in total. As DEM data are widely available, this technique has the potential to improve C storage estimates in regions with peatlands formed primarily by terrestrialization. Number of sites: 21 Sampling Frequency: once for each site

泥炭沉积储存了约占地球陆地固定碳（C）总量1/6的碳储量，但泥炭深度的不确定性阻碍了泥炭碳储量的精准估算。为评估美国威斯康星州北部约7000平方千米、泥炭地占比20%的北高地湖区（Northern Highlands Lake District, NHLD）内的泥炭碳储量，我们对21处泥炭地开展了系统采样。在每处泥炭地中，我们以网格布点方式测量泥炭深度（若存在基底有机湖相沉积物则一并纳入测量），并通过插值法计算平均泥炭深度。本研究聚焦三个核心问题：(1) 泥炭深度的空间变异特征如何？(2) 能否通过其他野外实测数据（水化学、地下水位深度、植被覆盖度、坡度）及/或遥感空间数据对泥炭平均深度进行预测？预测精度可达何种水平？(3) NHLD泥炭地的总碳储量为多少？采样得到的单处泥炭地平均泥炭深度介于0.1~5.1米之间。多数泥炭地由小型湖盆填充演化而成（即陆地化过程），实测最大泥炭深度可达15米。小型泥炭盆的平均泥炭深度可通过泥炭地/高地交界带的盆缘坡度实现最优预测，该坡度既可通过野外实测获取，也可由数字高程模型（Digital Elevation Model, DEM）数据计算得到（校正决定系数Adj. R²=0.70）。基于DEM的回归模型进行区域尺度上推后，得到区域平均泥炭深度为2.1±0.2米（其中包含约0.1~0.4米的有机湖相沉积物），总泥炭碳储量为144±21 Tg-C。由于DEM数据可广泛获取，该方法有望为以陆地化过程形成的泥炭地分布区提供更为精准的碳储量估算结果。采样点位数量：21处 采样频率：每处点位单次采样