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

许多人都熟悉淡水生活，无论是从直接经验与钓鱼或从自然纪录片。大多数人可能意识到水生栖息地的食物链与地面上的食物链不同。然而，并不是所有人都知道湖泊中复杂生态系统的细节，或者湖泊与其陆地集水区之间的联系。湖泊污染的问题是众所周知的，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）-这个问题经常在媒体上突出。然而，陆地碳流入湖泊和随后在湖泊中利用这种资源是出乎意料的。众所周知，鱼吃水生昆虫和植物-没有多少人会在褐鳟鱼的食物群中命名泥炭沼泽或土壤！我们已经证明，这种陆地材料实际上使它的方式进入食物链，因此鱼类饮食使用一种技术称为稳定同位素分析。我们还使用了放射性碳-更熟悉的一种测年方法-来阐明陆地物质在爱尔兰湖泊鱼类饮食中的重要性。使用放射性碳或14 C，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石，并溶解在水中。这种岩石风化的碳不包含14 C放射性同位素，因此人为地看起来有数千年的历史。另一方面，大多数陆地碳与地球大气平衡，含有较高水平的放射性碳-这种碳是“现代”的，可以与“湖泊内”的碳区分开来。泥炭中储存的其他碳可能是“旧”的;这也可以在湖泊中找到，我们还不知道湖泊中的植物和动物使用的“死”，“现代”和“旧”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14 C水平，并找出进入湖泊的陆地碳的去向。我们还可以测量生活在湖中的动物和植物的“放射性碳年龄”和稳定同位素值，可以显示它们是否消耗“湖中”碳或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的数量会受到气候变化和土地管理做法的影响。湖中物种对陆地碳的消耗也会受到入侵物种的影响，如斑马贻贝，它贪婪地消耗“湖中碳”，并迅速蔓延到爱尔兰和英国。湖泊，导致鱼类更多地依赖陆地物质。我们的建议，联合收割机的使用稳定同位素与放射性碳在女王大学贝尔法斯特将调查这一重要的新的研究领域，揭示在淡水湖泊复杂的食物网。

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.