Crawford John T, Stanley Emily H
U.S. Geological Survey, National Research Program, 3215 Marine Street, Boulder, Colorado, 80303, USA.
Center for Limnology, University of Wisconsin-Madison, 680 North Park Street, Madison, Wisconsin, 53706, USA.
Ecol Appl. 2016 Jul;26(5):1581-1591. doi: 10.1890/15-1330.
Streams and rivers are active processors of carbon, leading to significant emissions of CO and possibly CH to the atmosphere. Patterns and controls of CH in fluvial ecosystems remain relatively poorly understood. Furthermore, little is known regarding how major human impacts to fluvial ecosystems may be transforming their role as CH producers and emitters. Here, we examine the consequences of two distinct ecosystem changes as a result of human land use: increased nutrient loading (primarily as nitrate), and increased sediment loading and deposition of fine particles in the benthic zone. We did not find support for the hypothesis that enhanced nitrate loading down-regulates methane production via thermodynamic or toxic effects. We did find strong evidence that increased sedimentation and enhanced organic matter content of the benthos lead to greater methane production (diffusive + ebullitive flux) relative to pristine fluvial systems in northern Wisconsin (upper Midwest, USA). Overall, streams in a human-dominated landscape of southern Wisconsin were major regional sources of CH to the atmosphere, equivalent to ~20% of dairy cattle emissions, or ~50% of a landfill's annual emissions. We suggest that restoration of the benthic environment (reduced fine deposits) could lead to reduced CH emissions, while decreasing nutrient loading is likely to have limited impacts to this ecosystem process.
溪流和河流是碳的活跃处理器，会导致大量的一氧化碳以及可能的甲烷排放到大气中。河流生态系统中甲烷的模式和控制机制仍相对鲜为人知。此外，对于人类对河流生态系统的重大影响如何改变其作为甲烷生产者和排放者的角色，人们了解甚少。在这里，我们研究了由于人类土地利用导致的两种不同生态系统变化的后果：营养物质负荷增加（主要是硝酸盐），以及底栖带细颗粒沉积物负荷增加和沉积。我们没有找到证据支持以下假设：即增加硝酸盐负荷会通过热力学或毒性效应下调甲烷生成。我们确实发现有力证据表明，与美国威斯康星州北部（中西部上游地区）的原始河流系统相比，底栖生物的沉积增加和有机物质含量提高会导致更多的甲烷生成（扩散通量+冒泡通量）。总体而言，在威斯康星州南部以人类为主导的景观中的溪流是该地区大气甲烷的主要来源，相当于奶牛排放量的约20%，或垃圾填埋场年排放量的约50%。我们建议恢复底栖环境（减少细颗粒沉积物）可能会导致甲烷排放量减少，而减少营养物质负荷可能对这一生态系统过程影响有限。
