U. Scherer

A parsimonious approach to estimate PAH concentrations in river sediments of anthropogenically impacted watersheds

The contamination of riverine sediments and suspended matter with hydrophobic pollutants is typically associated with urban land use. However, it is rarely related to the sediment supply of the watershed, because sediment yield data are often missing. We show for a suite of watersheds in two regions of Germany with contrasting land use and geology that the contamination of suspended particles with polycyclic aromatic hydrocarbons (PAH) can be explained by the ratio of inhabitants residing within the watershed and the watersheds sediment yield. The modeling of sediment yields is based on the Revised Universal Soil Loss Equation (RUSLE2015, Panagos et al., 2015) and the sediment delivery ratio (SDR). The applicability of this approach is demonstrated for watersheds ranging in size from 1.4 to 3000km2. The approach implies that the loading of particles with PAH can be assumed as time invariant. This is indicated by additional long-term measurements from sub-watersheds of the upper River Neckar basin, Germany. The parsimonious conceptual approach allows for reasonable predictions of the PAH loading of suspended sediments especially at larger scales. Our findings may easily be used to estimate the vulnerability of river systems to particle-associated urban pollutants with similar input pathways as the PAH or to indicate if contaminant point sources such as sites of legacy pollution exist in a river basin.

Earth system dynamics as the consequence of the second law: Maximum power limits, dissipative structures, and planetary interactions

Planet Earth is a thermodynamic system far from equilibrium and its functioning—obviously—obeys the second law of thermodynamics, at the detailed level of processes, but also at the planetary scale of the whole system. Here, we describe the dynamics of the Earth system as the consequence of sequences of energy conversions that are constrained by thermodynamics. We first describe the well-established Carnot limit and show how it results in a maximum power limit when interactions with the boundary conditions are being allowed for. To understand how the dynamics within a system can achieve this limit, we then explore with a simple model how different configurations of flow structures are associated with different intensities of dissipation. When the generation of power and these different configuration of flow structures are combined, one can associate the dynamics towards the maximum power limit with a fast, positive and a slow, negative feedback that compensate each other at the maximum power state. We close with a discussion of the importance of a planetary, thermodynamic view of the whole Earth system, in which thermodynamics limits the intensity of the dynamics, interactions strongly shape these limits, and the spatial organization of flow represents the means to reach these limits.