Crop-livestock production systems are the largest cause of human alteration of the global nitrogen (N) and phosphorus (P) cycles. Our comprehensive spatially explicit inventory of N and P budgets in livestock and crop production systems shows that in the beginning of the 20th century, nutrient budgets were either balanced or surpluses were small; between 1900 and 1950, global soil N surplus almost doubled to 36 trillion grams (Tg)·y−1 and P surplus increased by a factor of 8 to 2 Tg·y−1. Between 1950 and 2000, the global surplus increased to 138 Tg·y−1 of N and 11 Tg·y−1 of P. Most surplus N is an environmental loss; surplus P is lost by runoff or accumulates as residual soil P. The International Assessment of Agricultural Knowledge, Science, and Technology for Development scenario portrays a world with a further increasing global crop (+82% for 2000–2050) and livestock production (+115%); despite rapidly increasing recovery in crop (+35% N recovery and +6% P recovery) and livestock (+35% N and P recovery) production, global nutrient surpluses continue to increase (+23% N and +54% P), and in this period, surpluses also increase in Africa (+49% N and +236% P) and Latin America (+75% N and +120% P). Alternative management of livestock production systems shows that combinations of intensification, better integration of animal manure in crop production, and matching N and P supply to livestock requirements can effectively reduce nutrient flows. A shift in human diets, with poultry or pork replacing beef, can reduce nutrient flows in countries with intensive ruminant production.

https://www.pnas.org/content/pnas/110/52/20882.full.pdf

Exploring global changes in nitrogen and phosphorus cycles in agriculture induced by livestock production over the 1900–2050 period

Riparian vegetation strips are widely used by river managers to increase streambank stability, among other purposes. However, though the effects of vegetation on bank stability are widely discussed they are rarely quantified, and generally underemphasize the importance of hydrologic processes, some of which may be detrimental. This paper presents results from an experiment in which the hydrologic and mechanical effects of four riparian tree species and two erosion-control grasses were quantified in relation to bank stability. Geotechnical and pore-water pressure data from streambank plots under three riparian covers (mature trees, clump grasses and bare/cropped turf grass) were used to drive the ARS bank stability model, and the resulting factor of safety (Fs) was broken down into its constituent parts to assess the contribution (beneficial or detrimental) of individual hydrologic and mechanical effects (soil moisture modification, root reinforcement and surcharge). Tree roots were found to increase soil strength by 2–8 kPa depending on species, while grass roots contributed 6–18 kPa. Slope stability analysis based on data collected during bank failures in spring 2000 (following a very dry antecedent period) shows that the mechanical effects of the tree cover increased Fs by 32 per cent, while the hydrologic effects increased Fs by 71 per cent. For grasses the figures were 70 per cent for mechanical effects and a reduction of Fs by 10 per cent for the hydrologic effects. However, analysis based on bank failures in spring 2001 (following a wetter than average antecedent period) showed the mechanical effects of the tree cover to increase Fs by 46 per cent, while hydrologic effects added 29 per cent. For grasses the figures were 49 per cent and −15 per cent respectively. During several periods in spring 2001 the hydrologic effects of the tree cover reduced bank stability, though this was always offset by the stabilizing mechanical effects. The results demonstrate the importance of hydrologic processes in controlling streambank stability, and highlight the need to select riparian vegetation based on hydrologic as well as mechanical and ecological criteria. Published in 2002 by John Wiley & Sons, Ltd.

Quantifying the mechanical and hydrologic effects of riparian vegetation on streambank stability

Bank and near-bank processes in an incised channel

https://www.engr.colostate.edu/~bbledsoe/pubs/2006/Poff_etal_2006_Binghamton.pdf

Hydrologic variation with land use across the contiguous United States: Geomorphic and ecological consequences for stream ecosystems

Bank erosion is integral to the functioning of river ecosystems. It is a geomorphic process that promotes riparian vegetation succession and creates dynamic habitats crucial for aquatic and riparian plants and animals. River managers and policymakers, however, generally regard bank erosion as a process to be halted or minimized in order to create landscape and economic stability. Here, we recognize bank erosion as a desirable attribute of rivers. Recent advances in our understanding of bank erosion processes and of associated ecological functions, as well as of the effects and failure of channel bank infrastructure for erosion control, suggest that alternatives to current management approaches are greatly needed. In this article, we develop a conceptual framework for alternatives that address bank erosion issues. The alternatives conserve riparian linkages at appropriate temporal and spatial scales, consider integral relationships between physical bank processes and ecological functions, and avoi...

https://www.jstor.org/stable/10.1641/B580608

Bank Erosion as a Desirable Attribute of Rivers

Pore Pressure and Bank Stability: The Influence of Matric Suction

The entrainment and erosion of cohesive bed material, is partly controlled by the magnitude and distributionof positive and negative pore-water pressures. Upward-directed seepage forces within cohesive streambedsprovide a mechanism of entrainment for flocculated aggregates. In contrast, suction caused by negative pore-waterpressures is found to increase the shear strength of unsaturated cohesive bed and bank materials.A hypothesis for detachment and erosion of chips or blocks of cohesive bed material is proposed: (1) Large(5 m), rapid rises in stage increase pore pressures and decrease matric suction dramatically in the region justbelow the bed surface; (2) A relatively rapid decrease in stage causing a loss of downward water pressurecombined with low-rates of pore-pressure dissipation result in steepened hydraulic gradients just below the bedsurface; and (3) A resulting net upward seepage force is great enough to contribute to detachment andentrainment of cohesive bed material.

Andrea Curini

Papers

Bank and near-bank processes in an incised channel

Pore Pressure and Bank Stability: The Influence of Matric Suction

The Role of Pore-Water Pressures and Upward-Directed Seepage Forces in the Erosion of Cohesive Streambeds