Prediction of Bioavailability of Riverine Dissolved Organic Matter from Bulk Measures of Geochemical Composition Accross Landscape and Continental Gradients

9816130土地利用的过度变化、城市发展和气候变化正在改变向世界各地沿海地带和海洋输入的有机物质和无机营养物质的大小和性质。河流输入的这种长期的、可能不可逆转的变化预计会引发全球和沿海碳收支以及沿海食物网、富营养化、缺氧和物种多样性的相应变化。要从机理上理解这些变化，就需要大幅度提高我们定量处理河流运输过程中有机物转化的能力。在我们之前的单独研究中，我们发现DOM在南方河流中的生物有效性与其平均元素组成所表明的DOM的脂肪族碳含量有关。我们进一步用生物能量学模型发现，许多简单有机底物被氧化和结合到微生物生物量中的速度和效率与这些底物的还原程度密切相关，这是从它们的元素组成推断出来的。初步的联合研究表明，这两个预测DOM生物有效性的指标具有很强的相关性(正如理论上的预期)，而且几乎同样成功。我们计划解决三个研究问题：1.河流中DOM的生物有效性是如何变化的？2.我们能否从简单的总体成分测量中预测DOM的生物有效性？3.是否可以通过简单的化学需氧量测量来预测DOM的生物有效性？利用我们的微生物生长生物能量学模型和描述不稳定和不稳定DOM池底物减少程度的技术，我们将检验不稳定和不稳定DOM池的组成和利用之间的关系。我们的目标是测试我们为已知不稳定的DOM池开发的模型，该模型通过简单测量大量DOM池的组成来预测大量有机物利用率和微生物生长的速度。这是一种成功的有机质利用模式，它提供了一种基于简单化学成分测量的因果、机械地理解微生物过程的模式。到目前为止，我们的工作是初步的，因为只从几个地点收集了DOM样本，没有采用系统的方法来调查DOM来源的光谱，当时正在开发进行实验的技术以及关于生物利用度的理论。我们现在可以对我们的模型进行严格的测试，并建议通过在特征截然不同的溪流和河流中进行实验来做到这一点。我们将测量有机物组成(脂肪族、芳香族和过量碳以及底物还原程度)和生物利用率(微生物生长、生长效率和有机物氧化)。根据我们的模型，DOM的生物利用度与DOM的脂肪族C含量和底物还原程度之间应该有很强的相关性。这项建议已提交给EGB计划，并由以下各方共同资助：1.OCE部门-(赖斯)2.DEB部门-(Firth)

9816130Perdue Land-use change, urban development, and climate change are altering the magnitude and nature of riverine inputs of organic matter and inorganic nutrients to the coastal zone and oceans throughout the world. Such long-term, and probably irreversible, changes in riverine inputs can be expected to trigger corresponding changes in both global and coastal carbon budgets and in coastal food webs, eutrophication, and anoxia and species diversity. A mechanistic understanding of these changes requires a substantial improvement in our ability to treat quantitatively the transformation of organic matter during riverine transport. In our prior separate research, we found that the bioavailability of DOM in a southern river is related to the aliphatic carbon content of the DOM, as indicated by its average elemental composition. We further found with a bioenergetic model that the rate and efficiency at which many simple organic substrates are oxidized and incorporated into microbial biomass are closely related to the degree of reduction of those substrates, as deduced from their elemental composition. Preliminary joint research showed that these two predictors of bioavailability of DOM are strongly correlated (as expected from theory) and about equally successful.We plan to address 3 research questions:1. How does the bioavailability of riverine DOM vary in stream and rivers?2. Can we predict the bioavailability of DOM from simple measures of bulk composition?3. Can bioavailability of DOM be predicted from a simple measurement of chemical oxygen demand?With the use of our bioenergetic model of microbial growth and techniques to describe the degree of substrate reduction of labile and bulk DOM pools, we will examine relationships between the composition and utilization of bulk and labile pools. Our goal is to test our model that was developed for known labile DOM pools to predict the rates of bulk organic matter utilization and microbial growth from simple measurements of the composition of the bulk DOM pool. This is a successful model of organic matter utilization that provides a causal, mechanistic understanding microbial processes on the basis of simple measures of chemical composition. Our work to date is preliminary since DOM samples were collected from only a few sites, a systematic approach to investigate a spectrum of DOM sources was not employed, and the techniques to perform the experiments as well as the theories regarding bioavailability were under development at the time. We are now in a position to rigorously test our models and propose to do so by conducting experiments in streams and rivers of greatly contrasting characteristics. We will measure organic matter composition (aliphatic, aromatic and excess carbon and degree of substrate reduction) and bioavailability (microbial growth, growth efficiency and organic matter oxidation). Based on our models, a strong correlation should be observed between DOM bioavailability and aliphatic C content and degree of substrate reduction of the DOM. This proposal was submitted to the EGB Program, and is being jointly funded by:1. Division of OCE - (Rice)2. Division of DEB - (Firth)