DISSERTATION RESEARCH: Amphibians and Mineralized Nitrogen: Hidden Jeopardy?

在过去的30年里，研究人员已经意识到两栖动物数量的长期下降，通常从本世纪初开始。在同一时期，人类极大地增加了地球上矿化氮(N)的数量。在中西部和类似纬度的其他地区，早期繁殖的两栖动物通常在春天冰完全融化之前进入繁殖池塘。在这个时候，融雪和早雨将矿物氮冲入地表水，但生物吸收很少。因此，两栖动物胚胎和幼体暴露于高浓度的氮中。初步证据表明，两栖动物胚胎和幼体对环境中矿物质氮的浓度很敏感，这些浓度远低于人类食用的安全水平。在本研究中，我将解决以下研究问题：1)在实验室中，升高的矿物氮浓度是否会降低林蛙和东部虎蝾螈的孵化和存活率，并增加其蜕变和畸形的时间；2)在实验中，野外矿物氮浓度升高是否会降低两栖动物的卵孵化、幼虫的存活和发育，并增加其畸形的频率。我希望证明氮在现实条件下和现实浓度下对两栖动物胚胎和幼虫有不利影响。我还希望这项研究能表明，在胚胎时期接触矿化氮会对两栖动物发育成幼虫产生非常大的负面影响。我的研究结果可能会对矿物氮对两栖动物种群和淡水生态系统的影响提供重要见解；因此，揭示了一些两栖动物种群数量下降的一个以前未被认识到的因素。

Over the past 30 years researchers have become aware of long-term declines in amphibian populations, often starting earlier in this century. Over this same time period, humans have dramatically increased the amount of mineralized nitrogen (N) across the planet. In the Midwest and other areas of similar latitude, early breeding amphibians enter breeding ponds in spring often before ice has completely melted. At this time snowmelt and early rains flush mineral N into surface waters, but there is very little biological uptake. Hence, amphibian embryos and young larvae are exposed to elevated concentrations of N. Preliminary evidence suggests that amphibian embryos and larvae are susceptible to mineral N at concentrations found in the environment, concentrations well below those considered safe for human consumption. In this study I will address the following research questions: 1) does exposure to elevated concentrations of mineral N as embryos and larvae in the laboratory decrease hatching and survival, and increase the time to metamorphosis and deformities in the wood frog and eastern tiger salamander, and 2) do experimentally increased concentrations of mineral N in the field decrease egg hatching, larval survival and development, and increase the frequency of deformities when amphibians are protected from predation. I expect to demonstrate that nitrogen can detrimentally affect amphibian embryos and larvae under realistic conditions and at realistic concentrations. I also expect that this research will show that exposure to mineralized nitrogen as embryos can have very large negative implications for the amphibians once they develop into larvae. My results will potentially provide major insights into the effects of mineral N on amphibian populations and freshwater ecosystems; thus, revealing a previously unrecognized factor in the declines of some amphibian populations.