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Impact of Climate Variability and Change on Nitrogen Delivery from Watersheds to Waterbodies.

机译：气候变化和变化对从流域到水体的氮输送的影响。

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摘要

Excess nitrogen in waterbodies is responsible for water pollution, eutrophication, and ecological deterioration around the world. Recent anthropogenic activities have greatly enhanced the release of fixed nitrogen to the environment. The nitrogen cycle has been altered even more than the carbon cycle due to the recent anthropogenic activities. Nitrogen export through streams and waterbodies depends on watershed nitrogen sources and transport mechanisms. Watershed attributes and hydrologic conditions affect nitrogen transport over the landscape to waterbodies. The goal of this work is to better understand these hydrologic transport mechanisms of nitrogen and, more specifically, how variability in hydrologic/climatic conditions affect past, present, and future nitrogen export to waterbodies. This dissertation includes three independent but related studies that target this overarching research goal.;The objective of the first study was to quantify the relative effects in nitrogen export due to changes in hydrology/climate conditions compared to changes in nitrogen source contributions over a decade for the contiguous United States using the USGS SPARROW model. The conclusion was that large-scale watershed nitrogen export can be heavily driven by hydrologic conditions so that, even without changes in source input, drier hydrologic conditions can result in an overall reduction of nitrogen export.;The second study aimed to answer the question of how future climate conditions might affect nitrogen export in the contiguous United States, given the importance of climatic conditions to nitrogen export from watersheds. An ensemble of downscaled Global Circulation Model (GCM) outputs of future temperature and precipitation were used within a SPARROW model to estimate changes in nitrogen export rates. Results of the study show an overall decrease in nitrogen export due mainly to increases in air temperature, which is responsible for increased denitrification in landscapes and shallow waters.;The third study applied a physically-based watershed model (SWAT), rather than a statistical hybrid model (SPARROW) that was applied in the second study for the contiguous United States, to address the potential impact of future climate conditions on streamflow and nitrogen export. Results of this study are in line with the second study also indicating an overall decrease in nitrogen export in future climatic conditions. This study also suggests seasonal patterns in change in nitrogen export with increases in fall and winter months and decreases in spring and summer months over the next century.;Ultimately this work contributes to the understanding of weather and climate variability and its impact on regional-scale nitrogen exported from watersheds. Through analysis of the past conditions, this research shows that climate and weather conditions are a major driver for nitrogen export through hydrologic transport, and that weather and climate variability attributes for more of the observed changes in nitrogen export rates than variability in nitrogen sources over the period of analysis. Given this finding, future climatic conditions will have significant impact on nitrogen export. This research found that, for most of the contiguous United States, future climatic conditions will lessen nitrogen yield, although there are some regions where yield is projected to increase. This finding was verified for a smaller forested watershed using a physically-based model. For water resources management, special attention should be paid to regions where future climatic conditions will be more favorable for increased nitrogen export and the associated water quality problems that result from excess nitrogen.
机译：水体中过量的氮是造成世界范围内水污染，富营养化和生态恶化的原因。最近的人为活动大大增加了固定氮向环境的释放。由于最近的人为活动，氮循环的变化甚至比碳循环的变化大。通过河流和水体的氮出口取决于流域的氮源和运输机制。流域的属性和水文条件影响了氮素从景观向水体的迁移。这项工作的目的是更好地了解氮的这些水文传输机制，更具体地说，是水文/气候条件的变化如何影响过去，现在和将来向水体输出的氮。本论文包括针对这一总体研究目标的三项独立但相关的研究。第一项研究的目的是量化与十年来氮素贡献变化相比，水文/气候条件变化对氮输出的相对影响。使用USGS SPARROW模型的连续美国。结论是大规模流域氮的输出受水文条件的严重驱动，因此，即使在不改变源头输入的情况下，较干燥的水文条件也可导致氮输出的总体减少。考虑到气候条件对流域氮出口的重要性，未来的气候条件将如何影响美国连续的氮出口。在SPARROW模型中，使用了一组按比例缩小的未来温度和降水的全球循环模型（GCM）输出，以估算氮出口速率的变化。研究结果表明，氮的总体出口量下降主要是由于气温升高所致，这导致景观和浅水区反硝化作用增强。第三项研究采用了基于物理的分水岭模型（SWAT），而不是统计学方法混合模型（SPARROW）在美国的第二个研究中应用，以解决未来气候条件对河流流量和氮出口的潜在影响。这项研究的结果与第二项研究相吻合，也表明未来气候条件下氮素出口总体下降。这项研究还提出了氮素出口变化的季节性模式，该变化在下一世纪的秋季和冬季月份增加，而在春季和夏季月份减少;最终，这项工作有助于人们了解天气和气候的变化及其对区域规模的影响。流域输出的氮。通过对过去条件的分析，这项研究表明，气候和天气条件是通过水文运输输出氮的主要驱动力，而且天气和气候的可变性是导致观测到的氮输出速率变化的主要原因，而不是氮源在整个氮源的变化。分析期。根据这一发现，未来的气候条件将对氮的出口产生重大影响。这项研究发现，尽管在某些地区，单产预计会增加，但在美国大部分连续地区，未来的气候条件都会降低氮的产量。使用基于物理的模型对较小的森林流域进行了验证。对于水资源管理，应特别注意那些未来的气候条件将更有利于增加氮的出口以及因氮过多而引起的相关水质问题的地区。

著录项

  • 作者

    Alam, Md. Jahangir.;

  • 作者单位

    University of South Carolina.;

  • 授予单位 University of South Carolina.;
  • 学科 Water resources management.;Climate change.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 144 p.
  • 总页数 144
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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