Curvature distribution within hillslopes and catchments and its effect on the hydrological response

Topographic convergence and divergence are first order controls on the hillslope and catchment hydrological response, as evidenced by similarity parameter analyses. Hydrological models often do not take convergence as measured by contour curvature directly into account; instead they use comparable measures like the topographic index, or the hillslope width function. This paper focuses on the question how hillslope width functions and contour curvature are related within the Plynlimon catchments, Wales. It is shown that the total width function of all hillslopes combined suggest that the catchments are divergent in overall shape, which is in contrast to the perception that catchments should be overall convergent. This so-called convergence paradox is explained by the effect of skewed curvature distributions and extreme curvatures near the channel network. The hillslope-storage Bossiness (hsB) model is used to asses the effect of within-hillslope convergence variability on the hydrological response. It is concluded that this effect is small, even when the soil saturation threshold is exceeded. Also described in this paper is a novel algorithm to compute flow path lengths on hillslopes towards the drainage network, using the multidirectional flow redistribution method

New modelling technique for aperiodic-sampling linear systems

A general input-output modelling technique for aperiodic-sampling linear systems has been developed. The procedure describes the dynamics of the system and includes the sequence of sampling periods among the variables to be handled. Some restrictive conditions on the sampling sequence are imposed in order to guarantee the validity of the model. The particularization to the periodic case represents an alternative to the classic methods of discretization of continuous systems without using the Z-transform. This kind of representation can be used largely for identification and control purposes.Comment: 19 pages, 0 figure

Effecten van landgebruiksveranderingen op gemiddelde en extreme afvoer in het Rijnstroomgebied

Recentelijk heeft veel onderzoek plaatsgevonden om de invloed van klimaatverandering te kwantificeren. Dit kan op verschillende manieren gebeuren, bijvoorbeeld kan er op basis van gemeten data een extreme-waardenverdeling worden geëxtrapoleerd. Een dergelijke aanpak heeft als nadeel dat de aanpak gebaseerd is op statistische kenmerken van het huidige klimaat, terwijl die juist waarschijnlijk veranderen. Een andere mogelijkheid is daarom het doorberekenen van klimaatscenario's zoals die worden gegenereerd met klimaatmodellen. Het landoppervlaktemodel dat in deze studie is gebruikt, namelijk het Variable Infiltration Capacity (VIC) model maakt gebruik van statistische parameters voor de invloed van verzadigde bodems. Het gebied betreft de substroomgebieden van Ruhr, Lahn, Mosel, Main en Necka

Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis

Permafrost thawing is likely to change the flow pathways taken by water as it moves through arctic and sub-arctic landscapes. The location and distribution of these pathways directly influence the carbon and other biogeochemical cycling in northern latitude catchments. While permafrost thawing due to climate change has been observed in the arctic and sub-arctic, direct observations of permafrost depth are difficult to perform at scales larger than a local scale. Using recession flow analysis, it may be possible to detect and estimate the rate of permafrost thawing based on a long-term streamflow record. We demonstrate the application of this approach to the sub-arctic Abiskojokken catchment in northern Sweden. Based on recession flow analysis, we estimate that permafrost in this catchment may be thawing at an average rate of about 0.9 cm/yr during the past 90 years. This estimated thawing rate is consistent with direct observations of permafrost thawing rates, ranging from 0.7 to 1.3 cm/yr over the past 30 years in the region

Assessing Microbial Community Patterns During Incipient Soil Formation From Basalt

Microbial dynamics drive the biotic machinery of early soil evolution. However, integrated knowledge of microbial community establishment, functional associations, and community assembly processes in incipient soil is lacking. This study presents a novel approach of combining microbial phylogenetic profiling, functional predictions, and community assembly processes to analyze drivers of microbial community establishment in an emerging soil system. Rigorous submeter sampling of a basalt-soil lysimeter after 2 years of irrigation revealed that microbial community colonization patterns and associated soil parameters were depth dependent. Phylogenetic analysis of 16S rRNA gene sequences indicated the presence of diverse bacterial and archaeal phyla, with high relative abundance of Actinomyceles on the surface and a consistently high abundance of Proteobacteria (Alpha, Beta, Gamma, and Delta) at all depths. Despite depth-dependent variation in community diversity, predicted functional gene analysis suggested that microbial metabolisms did not differ with depth, thereby suggesting redundancy in functional potential throughout the system. Null modeling revealed that microbial community assembly patterns were predominantly governed by variable selection. The relative influence of variable selection decreased with depth, indicating unique and relatively harsh environmental conditions near the surface and more benign conditions with depth. Additionally, community composition near the center of the domain was influenced by high levels of dispersal, suggesting that spatial processes interact with deterministic selection imposed by the environment. These results suggest that for oligotrophic systems, there are major differences in the length scales of variation between vertical and horizontal dimensions with the vertical dimension dominating variation in physical, chemical, and biological features.NSF [EAR-1344552, EAR-1340912, EAR-1417097]; Philecology Foundation of Fort Worth Texas; Water, Environmental, and Energy Solutions (WEES) initiative at the University of Arizona; office of Research, Discovery and Innovation's Accelerate for Success Grant at the University of Arizona; U.S. Department of Energy (DOE), Office of Biological and Environmental Research (BER), as part of Subsurface Biogeochemical Research Program's Scientific Focus Area (SFA) at Pacific Northwest National Laboratory (PNNL); DOE [DE-AC06-76RLO 1830]6 month embargo; first published 28 March 2019.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The taste of diatoms: the role of diatom growth phase characteristics and associated bacteria for benthic copepod grazing

The interactions between primary producers and their consumers are of particular interest for the overall functioning of marine ecosystems. The biochemical composition of the organisms involved affects the efficiency of energy transfer in marine food webs. In addition to top-down control by grazers, bottom-up control of these interactions by primary producers and associated bacteria has recently received more attention. Planktonic copepods selectively feed on older diatom cells, a behaviour regulated by changes in exometabolites around diatoms. To test whether this also applies to benthic copepods, Seminavis robusta cells in lag, exponential and stationary growth phases were biochemically screened, and the diversity of associated bacteria was assessed. The diatoms were subsequently 13C prelabelled and offered to the harpacticoid copepod Microarthridion littorale in a grazing experiment. Harpacticoid copepods incorporated more carbon from younger diatom cells in the lag growth phase, which might be based on (1) biochemical differences of diatom cells in different growth phases and (2) the bacteria associated with the diatoms. The younger diatom cells were characterised by a higher C:N ratio and more extracellular polymer secretions but a lower fatty acid content. The bacterial community on these cells differed from those on cells in the later growth phases. Our results thus suggest that the feeding strategies of benthic harpacticoid copepods differ from those of calanoid copepods. This outcome can be explained by the tight contact between benthic copepods and the typical carbon and bacteria-rich biofilm on sediments