Multiscale Impacts of Cyanobacterial Crusts on Landscape Stability

大多数土壤是无机（矿物）和有机（如植物）物质的混合物。在沙漠中，通常没有足够的雨水供大型植物生长，但藻类和地衣等生物可以生存。我们的研究重点是生活在土壤表面或土壤表面附近的蓝藻，当它们生长时产生糖，称为多糖，它可以将小颗粒（如沙粒）粘在一起。这将土壤结合在一起，形成一种“蓝藻土壤外壳”，这对景观有帮助，因为它使土壤侵蚀更难发生。蓝藻土壤结皮是自然发生的，但也可以人工制造，作为土地管理计划的一部分。在沙漠中，土壤侵蚀通常是由风引起的，但有时降雨会引起水土流失，降雨的数量和强度会影响地壳。小雨会导致蓝藻生长，并有助于变厚和加强外壳，但大雨会破坏外壳，使其保护土壤免受侵蚀的能力下降。我们对不同的降雨强度和地壳保护土壤免受风和水侵蚀的能力之间的关系知之甚少，但是这样做是有用的，因为我们可以更好地计划活动，比如牛在哪里吃草（蹄子打破薄弱的地壳），以及什么时候让田地裸露。这个项目是令人兴奋的，因为它研究降雨，径流（地表流量）和风蚀对不同尺度的蓝藻外壳的影响。首先，我们通过在降雨模拟器下的人工土壤床上种植结壳来控制条件，让我们选择降雨量和持续时间。我们还可以选择土壤床是平坦的还是倾斜的，并且可以控制径流速率。在模拟降雨后，我们将在土床顶部使用风洞来模拟风蚀-同样，我们选择风速，可以测量多少土壤被吹走。通过这样做，我们可以测试蓝藻土壤结皮对不同降雨事件的反应(结皮变厚了吗？是被破坏了还是被冲走了？)，我们就可以测量地壳在防止风蚀方面的效果。我们的方法不同寻常，因为它观察的是一组过程（降雨和径流）如何影响另一组过程（风蚀）。由此，我们将开发一个模型来解释和预测降雨/径流对土壤结皮生长和风蚀敏感性的影响。然后，该模型将在现场使用自然土壤和蓝藻结壳进行测试。为了保证一系列降雨和风力事件，现场试验将使用便携式现场降雨模拟器和风洞进行部分控制。最后，控制实验是在小尺度上进行的，但我们将把项目的时空范围扩大到更适用于理解景观稳定性的区域尺度。我们将使用遥感来做这件事，因为蓝藻外壳生长和发育的各个方面可以使用卫星数据来检测。我们将使用这些数据在区域尺度上检查蓝藻外壳对降雨和径流（也可以从太空中检测到）的响应，并监测这些水文输入与沙尘暴之间的时滞，以便在更大的时空尺度上进一步测试该模型。蓝藻出现在许多环境中，例如，它们形成的保护性外壳在温带气候中很重要，它们保护作物之间的土壤免受水分侵蚀，它们在沿海沙丘上形成，在那里它们减少风吹沙。在开发和校准了用于预测水对旱地地壳保护作用的影响的模型之后，我们可以在其他土壤和其他降雨模式（例如温带或热带）下测试该模型。科学家预测，未来许多地区的降雨量和强度将发生变化；也有可能使用我们的模型来尝试和预测这将如何影响蓝藻外壳。

Most soils are a mixture of inorganic (mineral) and organic (e.g. plant) material. In deserts, often there is not enough rain for large plants to grow, but organisms such as algae and lichens can survive. Our research focuses on cyanobacteria which live on or near the soil surface and produce sugars as they grow, called polysaccharides, which can stick small particles (e.g. sand grains), together. This binds the soil forming a 'cyanobacterial soil crust' that is helpful in the landscape because it makes it harder for soil erosion to take place. Cyanobacterial soil crusts occur naturally, but can also be made artificially as part of a land management plan. In deserts often soil erosion is caused by wind, however sometimes it rains causing water erosion, and the amount and intensity of rainfall affects crusts. Light rain causes cyanobacterial growth and helps to thicken and strengthen the crusts, but heavy rain can break up crusts, making them less able to protect soil from erosion. We know little about the relationship between different rainfall intensities and the ability of crusts to protect soil from wind and water erosion but it would be useful to do so because we could better plan activities such as where cattle graze (hooves break up weak crusts) and when to leave fields bare.This project is exciting because it studies the impact of rainfall, runoff (surface flow) and wind erosion on cyanobacterial crusts at different scales. To begin, we control conditions by growing crusts on an artificial soil bed under a rainfall simulator that lets us choose how much rainfall occurs, and how long it lasts. We also choose whether the soil bed is flat or sloping, and can control runoff rate. After the simulated rainfall, we will use a wind tunnel on top of the soil bed to simulate wind erosion - again we choose the wind speed and can measure how much soil is blown away. By doing this, we can test the response of cyanobacterial soil crust to different rainfall events (does the crust get thicker? is it broken up and washed away?) and we can measure how good the crust is at preventing wind erosion. Our approach is unusual because it looks at how one set of processes (rainfall and runoff) affects a second process (wind erosion). From this we will develop a model to explain and predict the impact of rainfall/runoff on soil crust growth and susceptibility to wind erosion. The model will then be tested in the field using natural soils and cyanobacterial crusts. To guarantee a range of rainfall and wind events, the field tests will be partially controlled using a portable field rainfall simulator and wind tunnel.Finally, the controlled experiments are conducted at a small scale but we will broaden the spatial and temporal scope of the project to the regional scale which is more applicable to understanding landscape stability. We will do this using remote sensing because aspects of cyanobacterial crust growth and development can be detected using satellite data. We will use these data to examine cyanobacterial crust response to rainfall and runoff (both also detectable from space) at the regional scale and monitor the time-lag between these hydrological inputs and dust storms to further test the model at larger spatial and temporal scales.Cyanobacteria occur in many environments, e.g. the protective crusts they form are important in temperate climates where they protect soil between crops from water erosion, and they form on coastal dunes, where they reduce sand transport by wind. Having developed and calibrated a model for predicting the impact of water on the protective role of crusts in drylands, we can test the model on other soils and under alternative rainfall patterns (e.g. temperate or tropical). Scientists have predicted that the amount and intensity of rainfall in many areas will change in the future; it will also be possible to use our model to try and predict how this will affect cyanobacterial crusts.