14C as a tool to trace terrestrial carbon in a complex lake: implications for food-web structure and carbon cycling

许多人通过垂钓的直接经历或自然纪录片对淡水中的生活很熟悉。大多数人可能意识到水生栖息地的食物链与陆地上的食物链不同。然而，并不是所有人都知道湖泊中复杂生态系统的细节，也不是所有人都知道湖泊与其陆地集水区之间的联系。湖泊污染的问题众所周知，因为肥料中的营养物质可以从农田进入水中，导致植物生命接管湖泊（富营养化）-这一问题经常在媒体上突出。然而，陆地碳流入湖泊和随后湖泊中这种资源的利用是出乎意料的。众所周知，鱼类以水生昆虫和植物为食——没有多少人会把泥炭沼泽或土壤列为褐鳟的食物群！我们已经证明，这些陆地物质实际上确实进入了食物链，因此使用了一种被称为稳定同位素分析的技术。我们还使用放射性碳——一种更熟悉的测年方法——来澄清爱尔兰湖泊鱼类饮食中陆生物质的重要性。利用放射性碳或14C，我们可以证明鱼正在消耗水生植物产生的碳。这种“湖内”碳部分来自风化的石灰岩，并溶解在水中。这种岩石风化的碳不含14C放射性同位素，因此人为地看起来有几千年的历史。另一方面，大多数陆地碳与地球大气处于平衡状态，并且含有较高水平的放射性碳——这种碳是“现代的”，可以与“湖内的”碳区分开来。储存在泥炭中的其他碳可能是“古老的”；这也可以在湖泊中发现，我们还不知道湖泊中的植物和动物使用了“死亡”、“现代”和“古老”碳的比例。我们可以分离溶解在水中的碳成分，这些碳成分被湖中的植物、动物和细菌所利用。我们可以测量这些碳成分中的稳定同位素以及它们的14C水平，并找出进入湖泊的陆地碳的去向。我们还可以测量湖中动植物的“放射性碳年龄”和稳定同位素值，这可以显示它们是在消耗“湖内”碳还是从周围土地进入的陆地（“现代”或“古老”）碳。这项研究很重要，因为进入湖泊的陆地物质数量会受到气候变化和土地管理措施的影响。湖泊中物种对陆地碳的消耗也会受到入侵物种的影响，比如斑马贻贝，它们贪婪地消耗“湖内碳”，并迅速蔓延到爱尔兰和英国的湖泊，导致鱼类更多地依赖陆地物质。我们在贝尔法斯特女王大学提出的将稳定同位素与放射性碳的使用结合起来的建议，将调查这一重要的新研究领域，以揭示淡水湖泊中复杂的食物网。

Many people are familiar with life in freshwater either from direct experience with angling or from nature documentaries. Most are probably aware that food chains in aquatic habitats differ from those on the ground. However not all are aware of the details of the complex ecosystems found in lakes, or indeed of the links between the lake and its terrestrial catchment. The problems of pollution in lakes are well known as nutrients from fertilisers can enter the water from agricultural land causing plant life to take over the lake (eutrophication) - this issue is regularly highlighted in the media. However the influx of terrestrial carbon into the lake and subsequent utilisation of this resource in lakes is unexpected. Fish are known to eat aquatic insects and plant life - not many people would name peat bog or soil amongst the food groups of the brown trout! We have shown that such terrestrial material does in fact make it's way into the foodchain and therefore fish diet using a technique known as stable isotope analysis. We have also used radiocarbon - more familiar as a dating method - to clarify the importance of terrestrial material in the diet of fish in Irish lakes. Using radiocarbon, or 14C, we can show that a fish is consuming carbon produced by aquatic plants. This 'within-lake' carbon is partly sourced from weathered limestone and is dissolved in the water. This rock weathered carbon does not contain the 14C radio-isotope and as a result artificially appears to be thousands of years old. Most terrestrial carbon on the other hand is in equilibrium with the earth's atmosphere and contains higher levels of radiocarbon - this carbon is 'modern' and can be distinguished from 'within-lake' carbon. Other carbon stored in peat can be 'old'; this can also be found in lakes and we don't yet know what proportions of 'dead', 'modern' and 'old' carbon are used by plants and animals in lakes. We can separate carbon components dissolved in the water which are used by plants, animals and bacteria in the lake. We can measure the stable isotopes in these carbon components as well as their 14C levels and find out where the terrestrial carbon entering the lake goes. We can also measure the 'radiocarbon age' and stable isotope values of the animals and plants living in the lake can show whether they are consuming 'within-lake' carbon or terrestrial ('modern' or 'old') carbon entering from surrounding land. This research is important as the amount of terrestrial material entering a lake can be affected by climate change and land management practices. The consumption of terrestrial carbon by species in the lake can also be affected by invasive species such as the zebra mussel which voraciously consumes 'within-lake carbon' and is rapidly spreading through Irish and U.K. lakes, causing fish to rely more on terrestrial material. Our proposal to combine the use of stable isotopes with radiocarbon in Queen's University Belfast will investigate this important new field of research to shed light on the complicated food webs in freshwater lakes.