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，人类显著增加了地球上矿化氮(N)的数量。在中西部和其他类似纬度的地区，早期繁殖的两栖动物在春季进入繁殖池，通常是在冰完全融化之前。此时，积雪融化和早期降雨将矿物质氮冲入地表水，但生物吸收很少。因此，两栖动物胚胎和幼虫暴露在高浓度的N中。初步证据表明，在环境中发现的浓度下，两栖动物胚胎和幼虫容易受到矿物质N的影响，远远低于人类消费的安全浓度。在这项研究中，我将解决以下研究问题：1)在实验室中，胚胎和幼虫暴露在高浓度的矿质氮中是否会减少林蛙和东虎火蜥蜴的孵化和存活，并增加变态和变形的时间；2)当两栖动物受到保护不被捕食时，田间矿质氮浓度的增加是否会减少卵孵化、幼虫存活和发育，并增加畸形的发生率。我希望证明氮在现实条件下和现实浓度下会对两栖动物胚胎和幼虫造成有害影响。我还预计，这项研究将表明，作为胚胎的矿化氮暴露，一旦两栖动物发育成幼虫，可能会对它们产生非常大的负面影响。我的结果可能会对矿物质氮对两栖动物种群和淡水生态系统的影响提供重要的见解；从而揭示出一些两栖动物种群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.