Controls upon dissolved organic matter export from glaciers

NERC: Rory Burford: NE/ r011524 /1研究简单描述：我们正在调查加拿大两条冰川河流（一条在落基山脉，一条在北极）中溶解有机物（DOM）的来源，DOM是一种已知的水生生态系统的营养物质。DOM是一组非常多样化的不同分子，其中一些分子比其他分子更适合细菌（异养生物）。在我们的实验中，我们将观察水样中DOM的分子组成，并测量这种DOM有多少能够被细菌消耗（其生物利用度）。通过比较不同的水样，我们应该能够找出哪一组分子（往往是一起出现的）对下游生态系统最重要。我们还将测量样品中的某些同位素（稀有形式的化学元素）。当化学物质发生某些转化时（例如在细胞内），含有这些稀有同位素的化学物质可能比含有常见同位素的化学物质更容易或更不容易发生转化。这意味着，例如，如果我们从一组化学物质开始，其中1%是稀有同位素，其中一半转化为新化学物质，那么这些新化学物质中稀有同位素的比例可能大于或小于最初的1%。因此，我们可以使用同位素比率来了解一组特定的分子经过了哪些过程才能形成这种形式。在这种情况下，我们可以使用碳和氮的同位素来了解生物可利用的溶解有机物的来源。然后，我们将使用一种放射性碳定年法来测量当细菌消耗样品中的DOM时呼出（释放）的二氧化碳的年龄。这将告诉我们生物可利用的DOM分子在被细菌消耗之前的年龄。在试图找出生物可利用DOM的来源时，了解这些信息也很有用。例如，如果DOM来自燃烧化石燃料（煤、石油和天然气）释放的空气中的微小颗粒，那么我们就会认为它非常古老（因为化石燃料是由史前植物形成的）。此外，我们的计划中还有生物因素。我们将分析一种特殊的遗传物质（16S核糖体RNA）在我们的自然样本和我们的孵化实验。这种rRNA存在于所有活细胞中，并且由于其重要性而非常保守（即在密切相关的物种中非常相似）。通过分析天然样本中的所有rRNA，我们可以了解整个水生微生物群落。如果一些样本中含有对一组细胞比另一组更有利的DOM，那么我们应该能够在水的16S rRNA组成中看到这一点。这使我们能够将水化学——DOM的数量和质量——与有形的生物影响联系起来。最后，我们将把结果与来自不同地区（例如喜马拉雅和安第斯山脉）的结果进行比较，看看是否在世界各地发现了相同的关键分子群；如果没有，这表明不同地区生物可利用DOM的主要来源不同。

NERC : Rory Burford : NE/R011524/1Simple description of research:We are investigating the source of dissolved organic matter (or DOM) - a class of nutrients known to fertilise aquatic ecosystems - in two glacial rivers in Canada (one in the Rockies and one in the Arctic). DOM is a very diverse group of different molecules, and some of these molecules are better food for bacteria (heterotrophs) than others. In our experiments, we will look at the molecular composition of DOM in water samples and we will measure how much of this DOM is able to be consumed by bacteria (its bioavailability). By comparing different water samples, we should be able to work out which groups of molecules (that tend to appear together) are most important to downstream ecosystems.We will also measure certain isotopes (rare forms of chemical elements) in our samples. When chemicals undergo certain transformations (e.g. inside of cells), chemicals containing these rare isotopes may be more or less likely to be transformed than chemicals containing common isotopes. This means, for instance, that if we start with a group of chemicals where 1% are rare isotopes, and half of them are transformed into new chemicals, then the proportion of rare isotopes in these new chemicals may be more or less than the original 1%. We can therefore use isotopic ratios to understand which processes a particular group of molecules has been through in order to reach that form. In this case, we can use isotopes of carbon and nitrogen to understand where the bioavailable dissolved organic matter is coming from.We will then use a form of radiocarbon dating to measure the age of carbon dioxide that is respired (given out) when bacteria consume DOM in our samples. This will tell us how old the bioavailable DOM molecules were before they were consumed by bacteria. This information is again useful to know when trying to work out the source of bioavailable DOM. For instance, if the DOM comes from tiny particles in the air released by burning fossil fuels (coal, oil and gas), then we would expect it to be very old (because fossil fuels are formed from prehistoric plants).In addition, there is a biological component to our plans. We will analyse a particular kind of genetic material (16S ribosomal RNA) in our natural samples and our incubation experiments. This rRNA is present in all living cells and is very conserved (i.e. it's very similar in closely related species) because of its importance. By analysing all of the rRNA in a natural sample, we can get an idea of the entire community of aquatic microbes. If some samples contain DOM that favours one group of cells over another, then we should be able to see this in the 16S rRNA composition of the water. This allows us to link water chemistry - the quantity and quality of DOM - with tangible biological impacts.Lastly, we will compare the results with those from different regions (e.g. the Himalaya and the Andes) to see whether or not the same key groups of molecules are found across the world; if not, this indicates that the main source of bioavailable DOM varies between different regions.