Abstract The potential of biocrusts (biological soil crusts) to generate runoff is a matter of great controversy, especially in arid and semiarid regions. Most authors maintain that runoff in the presence of biocrusts is generated as a result of hydrophobicity, crust structure, texture or surface roughness. Hypothesizing that runoff over biocrusts may result from partial pore clogging, brought on by extracellular polymeric substances (EPS), we compare two crust types from Nizzana in the northwestern Negev, Israel (NIZID, NIZPON) that readily generate runoff under natural field conditions to a crust type from Nizzanim in the southern coast of Israel (NIMID) that fails to generate runoff. We hypothesize that biocrust-induced EPS of the NIZ crusts will have different biochemical and viscoelastic properties than that of NIM. We conducted sprinkling experiments on the crusts, measured the biochemical properties (thickness, water repellency, compressive strength, water-holding capacity, silt and clay content, roughness) and the adhesion and viscoelastic properties of the crust EPS using quartz crystal microbalance with dissipation monitoring (QCM-D). Both crusts were not water repellent and were characterized by a relatively smooth surface. The NIZ crusts were however characterized by higher water-holding capacity and compressive strength. As far as the EPS is concerned, higher shear viscosity and shear modulus characterized the NIZ crusts, indicating higher crust integrity and rigidity and the formation of durable mineral grain-EPS matrix of the NIZ crusts. The findings point to a possible link between crust rigidity and runoff coefficients providing supporting evident for the role played by EPS in crust formation and runoff generation. Knowledge regarding the potentiality of runoff and hence water redistribution may assist in ecosystem management and agroforestry practices.

中文翻译：

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胞外多糖可能会增加生物地壳硬度并诱导径流产生

摘要 生物结皮（生物土壤结皮）产生径流的潜力是一个有很大争议的问题，特别是在干旱和半干旱地区。大多数作者认为，生物结壳存在时的径流是由于疏水性、结壳结构、质地或表面粗糙度而产生的。假设生物地壳上的径流可能是由细胞外聚合物 (EPS) 引起的部分孔隙堵塞造成的，我们比较了以色列内盖夫西北部 Nizzana 的两种地壳类型 (NIZID，NIZPON)，它们在自然田间条件下很容易产生径流来自以色列南部海岸 Nizzanim (NIMID) 无法产生径流的地壳类型。我们假设 NIZ 地壳的生物地壳诱导 EPS 将具有与 NIM 不同的生化和粘弹性特性。我们对地壳进行了洒水实验，使用石英晶体微天平和耗散监测测量了地壳 EPS 的生化特性（厚度、拒水性、抗压强度、持水能力、粉砂和粘土含量、粗糙度）以及附着力和粘弹性。 (QCM-D)。两种外壳都不防水，并且具有相对光滑的表面。然而，NIZ 地壳的特点是具有更高的持水能力和抗压强度。就 EPS 而言，较高的剪切粘度和剪切模量表征 NIZ 地壳，表明更高的地壳完整性和刚度以及 NIZ 地壳的耐用矿物颗粒-EPS 基质的形成。研究结果指出地壳刚度和径流系数之间可能存在联系，为 EPS 在地壳形成和径流生成中的作用提供了证据。关于径流潜力和水资源再分配的知识可能有助于生态系统管理和农林业实践。