Abstract Eddy-covariance based carbon flux datasets spanning decades are becoming available worldwide due to the effort of associated scientists. Tall tower based monitoring stations are relatively rare, but provide important information about the carbon balance of a larger region surrounding the tower. In this study we report and analyze the 21-year-long dataset provided by the Hungarian tall tower site, Hegyhatsal. The daily and annual cycles of net ecosystem exchange (NEE), gross primary production, and total ecosystem respiration are presented. Footprint analysis reveals that the fluxes mostly originate from the surrounding arable lands; the main source region is located within 1 km around the tower. Long-term, mean NEE was -0.467 gC m-2 day-1, or -170 gC m-2 year-1, revealing that the complex region was a net carbon sink from the atmospheric perspective. Trend analysis indicates that overall, NEE decreased (i.e. became more negative, which means stronger sink) by 12 gC m-2 year-1, a trend that is explained by improved agrotechnology and climate change. Net biome production (NBP) was estimated using crop census data and assumptions about the management practices that affect lateral carbon flux. Long term mean NBP was -30 gC m-2 year-1, which indicates that the soils may be losing carbon, though this loss is within the range of uncertainty of the measurements (~50 gC m-2 year-1). Analysis of county-scale yield statistics suggested that the results can be representative to at least county scale (1651 km2). Interannual variability was analyzed by using environmental variables such as maximum and minimum temperature, precipitation, vapor pressure deficit, soil water content, and satellite based vegetation index aggregated at monthly and longer time intervals. The results indicate that environmental conditions in spring have a major role in the annual carbon balance. Moreover, water availability represented by soil water content rather than by precipitation is a major driver of the interannual variability of NEE. The statistical analysis suggested that the large positive NEE anomaly during 2001–2003 was caused by interplay among the environmental drivers, in particular maximum temperature, vapor pressure deficit and radiation in April, followed by a soil water content deficit during the growing season. This novel statistical analysis provides insight into the drivers of the carbon balance of a mixed agricultural region.

中文翻译：

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对来自中欧高塔场地的 21 年二氧化碳通量数据集的分析

摘要 由于相关科学家的努力，跨越数十年的基于涡度协方差的碳通量数据集正在全球范围内可用。基于高塔的监测站相对较少，但提供有关塔周围更大区域碳平衡的重要信息。在这项研究中，我们报告并分析了由匈牙利高塔遗址 Hegyhatsal 提供的长达 21 年的数据集。呈现了净生态系统交换 (NEE)、初级生产总值和总生态系统呼吸的每日和年度周期。足迹分析表明，通量主要来自周围的耕地；主要源区位于塔周围 1 公里范围内。长期，平均 NEE 为 -0.467 gC m-2 day-1，或 -170 gC m-2 year-1，揭示了从大气的角度来看，该复杂区域是一个净碳汇。趋势分析表明，总体而言，NEE 下降（即变得更负，意味着汇更强）12 gC m-2 year-1，这一趋势可以通过改进的农业技术和气候变化来解释。净生物群落产量 (NBP) 是使用作物普查数据和关于影响横向碳通量的管理实践的假设来估计的。长期平均 NBP 为 -30 gC m-2 year-1，这表明土壤可能正在失去碳，尽管这种损失在测量的不确定性范围内（~50 gC m-2 year-1）。对县级产量统计数据的分析表明，结果至少可以代表县级（1651 平方公里）。通过使用环境变量（如最高和最低温度、降水、蒸气压亏缺、土壤含水量和卫星植被指数，按月和更长的时间间隔汇总）分析年际变化。结果表明，春季环境条件在年度碳平衡中起主要作用。此外，以土壤含水量而非降水量表示的可用水量是 NEE 年际变化的主要驱动因素。统计分析表明，2001-2003 年期间 NEE 的大正异常是由环境驱动因素之间的相互作用引起的，特别是 4 月的最高温度、蒸气压不足和辐射，其次是生长季节的土壤含水量不足。