Ecosystem Science Division, Department of Environmental Science, Policy and Management, University of California, Berkeley, 105 Hilgard Hall, 94709, USA; Department of Geography, Institute of Ecology and Earth Sciences, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia.
Ecosystem Science Division, Department of Environmental Science, Policy and Management, University of California, Berkeley, 105 Hilgard Hall, 94709, USA.
Sci Total Environ. 2020 May 1;715:136960. doi: 10.1016/j.scitotenv.2020.136960. Epub 2020 Jan 27.
Constructed wetlands built for water treatment often need biomass harvesting to remove nutrients from the system. Usually harvesting is done during the peak growing season to maximize the amount of nutrients removed from the system. This, however, can create huge methane fluxes that escape from plant tissues to the atmosphere. We used manual chambers and eddy covariance measurements to analyze the increase in methane emissions due to the harvesting of two common wetland species, Typha spp. and Schoenoplectus spp., in two climatically different constructed wetlands in Estonia and California. In addition, we determined the biomass nutrient and carbon concentrations from harvested biomass. We found that harvesting during the summer season, e.g. June and August, resulted in a significant release of methane at both sites. At the California site, baseline median methane emissions were 217.6 nmol m s, and harvesting resulted in increases to 395.4 nmol m s that decreased to baseline emission within three days. Footprint modeling demonstrated that the emission increases measured by eddy covariance were dominated by contributions from the cut area to the total footprint signal. At the Estonian site, harvesting resulted in methane increases of 15.9 nmol m s to 110.4 nmol m s in August. However, in September and October the emission was significantly lower. Plant biomass analyses showed clear temporal dynamics in terms of nutrient concentration, being highest in summer and lowest in winter. Our experiments indicate that the optimal time for aboveground biomass harvesting is at the end of the growing season before nutrient translocation to belowground plant structures begins coinciding with lowest methane emissions. Therefore, strategic planning of the harvest timing may help reduce greenhouse gas emissions from managed wetlands and thus improve their multi-faceted ecological benefit.
用于水处理的人工湿地通常需要生物量收获来去除系统中的养分。通常在生长高峰期进行收获，以最大限度地从系统中去除养分。然而，这会产生大量甲烷通量，从植物组织逸散到大气中。我们使用手动室和涡度协方差测量来分析由于在爱沙尼亚和加利福尼亚的两个气候不同的人工湿地中收获两种常见湿地物种——香蒲属和香蒲属——而导致的甲烷排放增加。此外，我们还确定了收获生物量的生物质养分和碳浓度。我们发现，在夏季（例如 6 月和 8 月）进行收获会导致两个地点的甲烷大量释放。在加利福尼亚的地点，基线中值甲烷排放量为 217.6 nmol m s，收获导致排放量增加到 395.4 nmol m s，三天内恢复到基线排放。足迹建模表明，涡度协方差测量的排放增加主要是由切割区域对总足迹信号的贡献所致。在爱沙尼亚的地点，8 月的收获导致甲烷增加了 15.9 nmol m s 到 110.4 nmol m s。然而，在 9 月和 10 月，排放量明显较低。植物生物量分析显示出养分浓度的明显时间动态，夏季最高，冬季最低。我们的实验表明，地上生物量收获的最佳时间是在生长季节结束前，此时养分向地下植物结构的转移开始，同时甲烷排放量最低。因此，对收获时间的战略规划可能有助于减少管理湿地的温室气体排放，从而提高其多方面的生态效益。
