Schutten J, Davy A J
ARISE, Department of Aquatic Ecology and Ecotoxicology, University of Amsterdam, Kruislaan 320, 1098 SM, Amsterdam, The Netherlands, , , , , , NL.
School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK e-mail:
Oecologia. 2000 Jun;123(4):445-452. doi: 10.1007/s004420000348.
Aquatic macrophytes are important in stabilising moderately eutrophic, shallow freshwater lakes in the clear-water state. The failure of macrophyte recovery in lakes with very soft, highly organic sediments that have been restored to clear water by biomanipulation (e.g. in the Norfolk Broads, UK) has suggested that the physical stability of the sediment may limit plant establishment. Hydraulic forces from water currents may be sufficient to break or remove plants. Our aim was to develop a simple model that could predict these forces from plant biomass, current velocity and plant form. We used an experimental flume to measure the hydraulic forces acting on shoots of 18 species of aquatic macrophyte of varying size and morphology. The hydraulic drag on the shoots was regressed on a theoretically derived predictor (shoot biomass × current velocity). Such linear regressions proved to be highly significant for most species. The slopes of these lines represent species-specific, hydraulic roughness factors that are analogous to classical drag coefficients. Shoot architecture parameters describing leaf and shoot shape had significant effects on the hydraulic roughness factor. Leaf width and shoot stiffness individually did not have a significant influence, but in combination with shoot shape they were significant. This hydraulic model was validated for a subset of species using measurements from an independent set of shoots. When measured and predicted hydraulic forces were compared, the fit was generally very good, except for two species with morphological variations. This simple model, together with the plant-specific factors, provides a basis for predicting the hydraulic forces acting on the root systems of macrophytes under field conditions. This information should allow prediction of the physical stability of individual plants, as an aid to shallow-lake management.
水生大型植物对于稳定处于清水状态的中度富营养浅水湖泊至关重要。在通过生物操纵恢复为清水状态的、具有非常松软且高有机沉积物的湖泊中，大型植物恢复失败（例如在英国诺福克湖区），这表明沉积物的物理稳定性可能会限制植物的定植。水流产生的水力可能足以折断或冲走植物。我们的目标是开发一个简单的模型，该模型可以根据植物生物量、流速和植物形态来预测这些力。我们使用实验水槽来测量作用在18种不同大小和形态的水生大型植物茎枝上的水力。茎枝上的水力阻力与一个理论推导的预测因子（茎枝生物量×流速）进行回归分析。结果表明，这种线性回归对大多数物种都具有高度显著性。这些直线的斜率代表物种特异性的水力粗糙度因子，类似于经典的阻力系数。描述叶片和茎枝形状的茎枝结构参数对水力粗糙度因子有显著影响。叶片宽度和茎枝刚度单独作用时没有显著影响，但与茎枝形状结合时则具有显著性。使用来自另一组独立茎枝的测量数据对该水力模型的一部分物种进行了验证。当比较测量的和预测的水力时，除了两个具有形态变异的物种外，拟合效果通常非常好。这个简单的模型，连同特定于植物的因子，为预测野外条件下水生大型植物根系上的水力提供了基础。这些信息应该有助于预测单株植物的物理稳定性，以辅助浅水湖泊的管理。
