Calibrating lake sediment records as proxies of environmental change in East Africa: integrating lacustrine, climatic and epidemiological archives

气候变化是21世纪全球社会关注的一个问题，因为温度和降水（降雨）的变化将影响环境和社会的许多方面。计算机模型预测，气候变化将在全球范围内对农业、水资源、海洋和陆地生态系统、生物多样性产生重大影响，而且也会对人类健康产生重大影响。疾病的分布可能发生变化，特别是那些由昆虫或其他载体（病媒）传播的疾病，因为昆虫（及其携带的致病生物体）对温度、湿度和植被条件很敏感。在缺乏过去气候和疾病如何变化的信息的情况下，很难预测可能发生的事情，也很难检验做出这些预测的模型。我们从（气候和疾病）监测项目中获得的信息通常只涵盖过去几十年，在这段时间里，人类活动的影响一直在影响自然系统本身的行为。在东非，许多湖泊通过其水文（水平衡）的变化（通常就湖泊水位而言）对区域气候（例如降雨）作出反应。在湖泊表面没有出水口的地方（封闭的盆地），湖泊水位的波动与水化学的变化密切相关，尤其是盐度的变化（因为水蒸发后留下了盐）。这些湖泊的生物反过来又与湖水的盐度密切相关，因此湖泊生物、盐度、湖泊水位和气候之间存在联系。在乌干达西部发现了许多小的、封闭的盆地火山口湖。湖底聚集的泥（沉积物）往往包含着湖泊及其局部地区历史的连续记录，这些记录既存在于生活在湖中及其周围陆地上的动植物的生物遗骸中，也存在于沉积物本身的化学和物理特征中。通过研究湖泊沉积物中保存的生物遗迹和物理或化学特征，有可能发现过去气候是如何变化的。这项研究的目的是提供东非乌干达气候和植被的长期历史，我们知道这个地区对区域气候事件很敏感，比如厄尔尼诺-南方涛动现象，来自火山口湖的湖泊沉积物。这些系统被认为对小规模和短期的变化有反应，这与东非大湖形成了对比。我们将比较来自乌干达西部的气候历史记录（降水、温度），使用气象站的数据和未发表的欧洲传教士和探险家的记录，与这些沉积记录。另外，我们将为乌干达西部的三种疾病（昏睡病、鼠疫和回归热）编制一个时间序列，涵盖20世纪（或者更早的文献档案）。如果我们能够证明湖泊沉积物中的这些生物、化学或物理信号已经对该地区有记录的气候变化做出了反应，我们就可以应用这些方法在湖泊沉积物档案中回溯到更早的时间，以观察没有书面记录的时期的气候，并为该地区提供长期的环境变化历史及其可变性。我们还可以比较该地区三种疾病的历史，并检查湖泊沉积物代用物与疾病发病率之间是否存在关系，例如，这可能与气候或植被有关。通过这种方式，湖泊沉积物也可能在提供对该地区疾病的长期看法方面发挥作用。因此，关于过去环境变化及其与气候、植被、疾病和人类社会之间联系的证据，可能与关于未来环境变化如何影响自然系统和人类社会的辩论极为相关。

Climate change is a cause for concern in the 21st century to societies around the world, as changes in temperature and precipitation (rainfall) will affect many aspects of the environment and society. Computer models predict climate change will have major consequences across the globe for agriculture, water resources, marine and terrestrial ecosystems, biodiversity - but also for human health. The distribution of diseases may alter, particularly those spread by insects or other carriers (vectors), as insects (and the disease-causing organisms that they carry) are sensitive to conditions of temperature, moisture and vegetation. In the absence of information on how climate and diseases have altered in the past, it is very difficult to predict what may happen, or test the models that make these predictions. What information we have from monitoring programmes (of both climate and disease) generally only covers the last few decades, during which time the impacts of human activity have been affecting the behaviour of natural systems themselves. In East Africa, many lakes respond to regional climate (for example, rainfall) through changes in their hydrology (water balance), often in terms of lake level. Where lakes have no outlet stream at the surface (closed basins), this lake level fluctuation is closely linked to changes in water chemistry, and especially salinity (as water evaporates leaving the salts behind). The biology of these lakes is in turn strongly linked to the salinity of the lake water, and so a link exists between lake organisms, salinity, lake level and climate. Many small, closed basin crater lakes are found in western Uganda. The mud (sediment) that collects in the bottom of lakes often contains a continuous record of the history of the lake and its local area, both in the biological remains of plants and animals living in the lake and on the land surrounding it, and also from chemical and physical characteristics of the sediments themselves. The possibility exists to discover how climate has changed in the past by studying the biological remains and physical or chemical signatures that are preserved in lake sediments. This research aims to provide a long-term history of climate and vegetation in Uganda, East Africa, an area that we know is sensitive to regional climate events such as the El Nino-Southern Oscillation phenomenon, from lake sediments from crater lakes. These systems are thought to respond to small scale and shorter term changes, in contrast to the great lakes of East Africa. We will compare the historical record of climate (precipitation, temperature) from the western part of Uganda, using both data from meteorological stations and unpublished accounts of European missionaries and explorers, with this sedimentary record. Separately, we will compile a time series for three diseases (sleeping sickness, plague and relapsing fever) covering the 20th century (and perhaps earlier from documentary archives) for western Uganda. If we can show that these biological, chemical or physical signals in lake sediments have responded to changes in climate in the region that have been documented, we can apply these methods to go back further in time within the lake sediment archive to look at climate in periods where there are no written records, and provide a long-term history of environmental change, and its variability, for this region. We can also compare the history of the three diseases in the region and examine if there are relationships between lake sediment proxies and disease incidence, that may be related to climate, or vegetation, for example. In this way, lake sediments may also have a role in providing a long-term perspective on diseases in the region. Evidence of past environmental change and its links to climate, vegetation, disease and human society may therefore be extremely relevant to debates on how natural systems, and human societies, may be affected by environmental change in the future.