藻华暴发是局部的藻类扩散,发生于藻类*佳的生长条件及来自捕食的压力减轻的情况下。当特定的微藻类(特别是蓝藻细菌)在暴发中达到很高的富集量时,这种暴发就会呈现出有害特征(图1)。尽管这些微藻类物种只占自然界很小的一部分,但是它们能够产生造成各种不利影响的有害或有毒物质,包括食物链的破坏、动物死亡以及严重的人类健康危害等(百度百科)。或许大家没有想过这小小的藻类会给人类社会带来如此巨大的影响,仅在美国,每年淡水水体中有害藻华的现象就造成大约40亿美元的经济损失。图1 中俄边境兴凯湖(左)和美加边境St. Clair湖(右)不同程度藻华现象 近年来,有关湖泊等水体有害藻华的相关报道和研究正在逐年增加,但学术界关于全球范围内湖泊藻华的程度,并没有明确的研究数据,同时关于人类活动和气候变化对藻华的影响关系尚不清楚。近日,就该问题来自美国卡内基研究院和NASA的研究者,在国际**期刊Nature发表文章,**对全球数十个大型淡水湖泊进行系统调查分析(图2),结果表明过去30年中,夏季藻类爆发的强度的确有所增加。图2 1980年以来研究点藻华程度变化程度图虽然大家早已经注意到有害藻华巨大的影响,但是长期以来科学家对淡水藻华的研究,要么集中在单个湖泊或特定区域,要么所研究的时期相对较短。迄今为止,学术界尚未对淡水藻华进行长时间尺度、全球范围的研究。有鉴于此,研究者通过美国Landsat 5近地卫星获取近30年高分辨率(30m)卫星数据,选取全球六大洲33个国家/地区的71个大湖进行长时间序列的对比分析,获取了720亿个数据点,在Google Earth Engine帮助下,*终揭示了夏季藻类大量繁殖的长期趋势。结果表明,超过三分之二的湖泊夏季藻华的峰值强度明显增加,仅仅只有6个湖泊具有下降趋势(图3),这指示了藻华实际上正在变得越来越普遍和强烈。另一方面,尽管全球湖泊藻华恶化的趋势十分明显,但是这造成藻华恶化的原因似乎在各个湖泊之间各不相同。研究者在充分考虑化肥使用、降雨或温度等因素的情况下发现,藻华恶化在不同湖泊之间并没有一致的规律。图3 研究点藻华现象的时空分布图研究者同时也指出气候变化对湖泊藻华的影响很明显,气候变暖在某种程度上阻碍了湖泊藻华自我修复的速度。上述研究成果发表在*新一期的Nature上,详情请点击文章底部阅读原文,查阅文章。参考资料1、J. C. Ho, A. M. Michalak, N. Pahlevan. Widespread global increase in intense lake phytoplankton blooms since the 1980s. Nature, 2019; DOI: 10.1038/s41586-019-1648-72、Carnegie Institution for Science. "Lakes worldwide are experiencing more severe algal blooms: Climate change is likely hampering recovery efforts."Phys.org. https://phys.org/news/2019-10-lakes-worldwide-experiencing-severe-algal.html(accessed October 18, 2019).

本文章转自:https://www.oala.ca/ground_articles/research/Research:Experimental lakes areaAn experiment from the 1970s at IISD Experimental Lakes Area showing that phosphorus is the key driver of algal blooms. IMAGE/ IISD Experimental Lakes AreaThe Experimental Lakes Area (ELA), a research station east of Kenora, Ontario, recently celebrated its 50th year of monitoring and manipulating lakes—50 years during which scientific and government focus has changed enough to imperil the research station and open exciting new directions.The field station is deliberately isolated from human activity, at the end of an unpaved road off the Trans Canada Highway. It has been protected by special legislation since 1968, when the need to investigate pressing freshwater issues prompted the Fisheries Research Board to establish the research station. The legislation reserved 58 small lakes and their watersheds for the study of human impacts on freshwater. Fundamental to the ELA mandate has been finding solutions to anthropogenic impacts, and informing policy, such as the landmark work on algal blooms that illustrated the effects of phosphates in detergents in the 1960s and 1970s.Dr. Michael Paterson has worked at the ELA for more than 20 years, and served as the section leader (or chief scientist) from 2004 to 2010 and 2014 to 2017. As he says, “The thing that’s unique about the ELA is that we apply experimental methods at the environmental scale, and it is at the environmental scale that we as a society primarily interact. And that’s where the problems arise.”He elaborates further: “The Great Lakes have been impacted by nutrients, new species, fishing pressure, contaminants, and climate change. All of these things are happening simultaneously so it makes it very hard to partition the effects of all of these various insults that are occurring to the lakes. What we can do at the ELA is manipulate one factor at a time in a care- fully controlled fashion, following what happened to the lake before and after the manipulation. We also have the ability to compare what’s going on in our manipulated lakes with a set of unmanipulated lakes, analogous to controls in a laboratory experiment. So, we have a comparison to see what kind of natural variation in lakes might also occur in these lakes.”Researchers at IISD Experimental Lakes Area use a seine to capture fish for monitoring. IMAGE/ IISD Experimental Lakes AreaThis approach has led to a body of work that has been cited in more than 1,000 peer-reviewed publications, covering topics from cattail bio-platforms to climate change and mercury contamination. The longest running experiment has been in progress for almost 50 years and relates to the addition of nutrients to and subsequent eutrophication of Lake 227.A graduate student handles a turtle at the IISD Experimental Lakes Area. IMAGE/ IISD Experimental Lakes AreaThe longevity of the ELA has also proved to be valuable in some unexpected ways as climate change becomes a more important area of research. For limnologist and ELA research scientist Scott Higgins, five reference lakes have provided opportunities to look back at the history of climate change. Higgins notes: “We talk about climate change like it is something that is going on in the future, but the climate has been changing since human industrialization. If we look back over the last 50 years of data from the reference lakes, we can ask how climate change has happened without the impact of other stressors like fishing pressure or impact from cities or development. As the data sets get longer, they get to be really valuable. There are a few other places in the world where you get these really long data sets, but typically not with data this comprehensive.”As just one example, Higgins points to a meteorological station at the ELA that has been jointly operating with Environment Canada since 1968. “We’ve got data on hydrology, how much water is flowing over land, and the chemistry of that water. We can start to ask and answer some really good questions about climate change.”In 2012, the Harper government announced its intention to stop funding the ELA. This move proved to be wildly unpopular with the Canadian public, the international scientific community, and non-profit organizations. Negotiations between provincial governments resulted in a joint solution, with ownership shared between the Ontario government and the Winnipeg-based non-profit International Institute for Sustainable Development (IISD). According to Dr. Paterson, the transfer to the IISD has come with a broader mandate to do science in the public interest, beyond fish and lakes to terrestrial ecology and new research into oil spill remediation.Researchers track and process individual fish at IISD Experimental Lakes Area. IMAGE/ IISD Experimental Lakes Area“Ultimately, lakes are a reflection of every- thing that happens around them. Lakes are really just holes in the ground that collect water, and all of that water is very strongly affected by any of the activities that happen on the land,” says Dr. Paterson. “One of the things that I have looked forward to working on now that we are a part of IISD is to try to get more terrestrial ecologists involved, so we can link what we are doing right now to the surrounding land,” Dr. Paterson notes.The land around the ELA is significant as it consists of boreal forest, the world’s largest intact forest and an important global carbon sink. As Scott Higgins describes it, the black spruce and pine burn on an approximately 100-year cycle, sending their carbon back into the atmosphere. However, the carbon in the sediment of the wetlands, lakes, and peat bogs is stored for long periods of time under water, potentially dating back to the last ice age. This makes the ELA a particularly valuable and potent data point in global climate change research.A newt is processed and analyzed in the chemical laboratory at IISD Experimental Lakes Area. IMAGE/ IISD Experimental Lakes Area“We get a lot of data requests every year from external organizations asking for our data to answer questions about global change. And then we become one site of many sites around the world. It makes our site even more valuable that we aren’t just collecting data for ourselves and our research questions; we freely provide the data to anyone who asks for it,” says Higgins.According to Dr. Paterson, there are unique challenges when working on an ecosystem scale: “Ecosystems are complicated things, and our understanding of ecosystem responses is still very imperfect. I think part of the problem comes from the fact that historically not that many people have looked at ecosystem responses. We tend to have a lot of specialists that have looked at isolated slices and we have lacked the tools to integrate all the parts to come up with effective predictions. I definitely believe that the accumulation of data and the development of more synthetic tools for putting that data together and understanding it will lead to improvements in policy and best practices.”A researcher looks out over a lake at IISD Experimental Lakes Area. IMAGE/ IISD Experimental Lakes AreaThis entry was posted in . Bookmark the permalink.

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