Effect of Transient Hydrologic Events on Biogeochemical Processes

瞬态水文事件对生物地球化学过程的影响

• 批准号: 0208386
• 负责人: Aaron Mills
• 金额: --
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-01 至 2008-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0208386&HistoricalAwards=false
• 关键词: Effect; Transient; Hydrologic; Events; Biogeochemical

0208386MillsIn field studies of groundwater in a range of hydrogeological settings, the rates of microbially mediated geochemical reactions have been shown to be far faster than hydrological transport rates. These relative rates lead to large changes in concentration of a variety of redox-sensitive chemical species over short distances within aquifers. In some systems, however, transient hydrological events (e.g., heavy precipitation on dry soil or floods in streams) can rapidly alter the geochemical environment in which the microbes exist. In that circumstance, the time constants associated with the physical events approach those of the microbially mediated processes. The proposed research addresses the question: How do hydrological processes and biogeochemical processes interact in the riparian-hyporheic zone of streams where time scales of the various processes are on the same order - hours to weeks? The proposed research will examine the effect of bank-storage events on reductive microbiological processes occurring in the riparian-hyporheic zone of a low-relief coastal plain stream. In particular, the concentration of nitrate-N in the groundwater feeding the stream is about 15 mg/liter, but the stream-water concentrations average only 1.6 mg/liter, suggesting high denitrification activity in the riparian- hyporheic zone. We envision the disruption of anaerobic processes during rain events in which rapid infiltration raises the water table and "flushes" chemicals (viz., nitrate) in the pore water out into the stream and perfuses the area with oxygenated water. We expect a similar disruption without flushing during storms in which a rapid rise in stream level pushes oxygenated water into the stream banks, thereby transiently extending the hyporheic zone. We will also examine the effect of flushing or bank-storage events on the denitrification and will document the rate of return of the functional abilities of the microbial communities to the pre-disturbance levels. Because these transient events have the potential to affect release of chemicals like nitrate from the groundwater into the surrounding surface waters, we will investigate how transient conditions in riparian soils affect the overall budget of biologically active chemicals. The proposed work includes detailed field observations, field manipulation experiments, laboratory batch and "mesocosm" experiments and mathematical modeling. We anticipate that we will learn how microbially mediated geochemical reactions and transient hydrological processes with time scales on the same order are linked. We will develop quantitative descriptions of these processes and investigate how frequently biogeochemical processes are "reset" by different hydrological events the synoptic data that we will examine how the transient effects of local processes influence regional nutrient fluxes.

0208386 Mills在一系列水文地质背景下对地下水进行的实地研究中，微生物介导的地球化学反应速率已被证明远远快于水文输运速率。这些相对速率导致含水层内短距离内各种氧化还原敏感化学物质浓度的巨大变化。然而，在某些系统中，瞬时水文事件（例如，干旱土壤上的强降水或河流中的洪水）可以迅速改变微生物存在的地球化学环境。在这种情况下，与物理事件相关的时间常数接近微生物介导过程的时间常数。拟议的研究解决了这个问题：水文过程和地球化学过程如何相互作用的河岸流，其中各种过程的时间尺度是相同的顺序-小时到星期？拟议的研究将检查银行存储事件还原微生物过程发生在河岸潜流带的低浮雕沿海平原流的影响。特别是，在地下水中的硝酸盐-N的浓度为约15毫克/升，但流水浓度平均只有1.6毫克/升，这表明在河岸-潜流区的高反硝化活性。我们设想在降雨过程中厌氧过程的破坏，其中快速渗透提高了地下水位和“冲洗”化学物质（即，硝酸盐）排出到溪流中，并用含氧水灌注该区域。 我们预计，在风暴期间，河流水位的迅速上升将含氧水推入河岸，从而短暂地延长了潜流区，但不会发生类似的破坏。 我们还将研究冲洗或银行存储事件对反硝化作用的影响，并将记录返回的微生物群落的功能能力的干扰前的水平的速率。 由于这些瞬态事件有可能影响硝酸盐等化学物质从地下水释放到周围的地表沃茨中，我们将研究河岸土壤中的瞬态条件如何影响生物活性化学物质的总体预算。拟议的工作包括详细的现场观察，现场操作实验，实验室批次和“围隔”实验和数学建模。 我们预计，我们将了解微生物介导的地球化学反应和瞬态水文过程的时间尺度上相同的顺序是如何联系在一起的。我们将开发这些过程的定量描述，并调查如何频繁的地球化学过程是“重置”不同的水文事件的天气数据，我们将研究如何当地过程的瞬变效应影响区域养分通量。