Paolo Perona

Modelling river and riparian vegetation interactions and related importance for sustainable ecosystem management

Abstract.We discuss the importance of modelling riparian vegetation and river flow interactions under differing hydrologic regimes. Modelling tools have notable implications with regard to the understanding of riverine ecosystem functioning and to promote sustainable management of water resources. We present both deterministic and stochastic approaches with different levels of simplification, and discuss their use in relation to river and vegetation dynamics at the related scale of interest. We apply such models to both meandering and braided rivers, in particular focusing on the floodplain dynamics of an alpine braided river affected by water impoundment. For this specific case we show what the expected changes in riparian vegetation may be in a ‘controlled release’ scenario for the postdam river Maggia, Switzerland. Finally, the use of these models is discussed in the context of current research efforts devoted to river restoration practice.

An observation‐based stochastic model for sediment and vegetation dynamics in the floodplain of an Alpine braided river

Riparian vegetation dynamics in Alpine rivers are to a large extent driven by the timing and magnitude of floods which inundate the floodplain, transport sediment, erode the river bed, and create and destroy suitable germination sites. Here we present a stochastic approach for studying sediment-vegetation dynamics lumped at the floodplain scale and driven by stochastic flood disturbances. The premise of the model is that floods erode riparian vegetation in the inundated part of the floodplain and expose bare sediment surfaces. In the absence of subsequent flooding these surfaces are gradually recolonized. The stochastic nature of the disturbance process and the deterministic rate of vegetation colonization are described by a Poisson arrival of floods and a process equation which treats the floodplain erosion and vegetation colonization processes, respectively. An analytical solution is developed to obtain the probability density function of the exposed sediment area. The model is applied to the Maggia River in Switzerland, where it reproduces the changes in riparian vegetation cover observed from aerial photographs with an absolute error less than 5%. The model has potential as a tool to study the impacts of changes in the disturbance regime on sediment and vegetation dynamics Copyright 2009 by the American Geophysical Union.

Impact of virus aggregation on inactivation by peracetic acid and implications for other disinfectants

Viruses in wastewater and natural environments are often present as aggregates. The disinfectant dose required for their inactivation, however, is typically determined with dispersed viruses. This study investigates how aggregation affects virus inactivation by chemical disinfectants. Bacteriophage MS2 was aggregated by lowering the solution pH, and aggregates were inactivated by peracetic acid (PAA). Aggregates were redispersed before enumeration to obtain the residual number of individual infectious viruses. In contrast to enumerating whole aggregates, this approach allowed an assessment of disinfection efficiency which remains applicable even if the aggregates disperse in post-treatment environments. Inactivation kinetics were determined as a function of aggregate size (dispersed, 0.55 and 0.90 μm radius) and PAA concentration (5-103 mg/L). Aggregation reduced the apparent inactivation rate constants 2-6 fold. The larger the aggregate and the higher the PAA concentration, the more pronounced the inhibitory effect of aggregation on disinfection. A reaction-diffusion based model was developed to interpret the experimental results, and to predict inactivation rates for additional aggregate sizes and disinfectants. The model showed that the inhibitory effect of aggregation arises from consumption of the disinfectant within the aggregate, but that diffusion of the disinfectant into the aggregates is not a rate-limiting factor. Aggregation therefore has a large inhibitory effect if highly reactive disinfectants are used, whereas inactivation by mild disinfectants is less affected. Our results suggest that mild disinfectants should be used for the treatment of water containing viral aggregates.

Integrating river cross section measurements with digital terrain models for improved flow modelling applications

An important element in hydraulic modelling is the topography data of the riverbed and the floodplain area. The latter can be obtained directly from digital terrain models (DTM), but the measurement of the riverbed topography is not straightforward. Since in the aerial survey only the elevation of the water surface is recorded, information about the riverbed topography cannot be obtained from the DTM. Therefore a method for the integration of river topography data in a DTM was developed. While the DTM contains in most cases regularly spaced data points, the resolution of the cross section profiles is generally much higher in the lateral than in the longitudinal direction of the river. An algorithm was developed which combines lateral river profiles with a DTM to produce a grid that can be used for flow modelling. The cross section data are interpolated to the grid points of the DTM that are part of the channel by using a bilinear technique with bounding breaklines, which can be obtained from the river cross section profiles. Additionally the algorithm can be adapted so that only the submerged part of the riverbed is subject to interpolation. It preserves the original DTM in the exposed part of the gravel bars. The algorithm was applied to a restored reach of the river Thur in Switzerland. The corrected grid represents well the complex morphological features of the river such as gravel bars and widenings. The accuracy of the algorithm was tested by comparing the interpolated elevation of the exposed part of the gravel bar to measurements obtained from an aerial survey. The mean height difference is in the order of about 9cm. Further the interpolated grid was used for a two dimensional flow simulation and the resulting water level was compared to the one recorded in the original DTM.

Transient response of Salix cuttings to changing water level regimes

Sustainable water management requires an understanding of the effects of flow regulation on riparian ecomorphological processes. We investigated the transient response of Salix viminalis by examining the effect of water-level regimes on its above-ground and below-ground biomass. Four sets of Salix cuttings, three juveniles (in the first growing season) and one mature (1 year old), were planted and initially grown under the same water-level regime for 1 month. We imposed three different water-level regime treatments representing natural variability, a seasonal trend with no peaks, and minimal flow (characteristic of hydropower) consisting of a constant water level and natural flood peaks. We measured sap flux, stem water potential, photosynthesis, growth parameters, and final root architecture. The mature cuttings were not affected by water table dynamics, but the juveniles displayed causal relationships between the changing water regime, plant growth, and root distribution during a 2 month transient period. For example, a 50% drop in mean sap flux corresponded with a -1.5 Mpa decrease in leaf water potential during the first day after the water regime was changed. In agreement with published field observations, the cuttings concentrated their roots close to the mean water table of the corresponding treatment, allowing survival under altered conditions and resilience to successive stress events. Juvenile development was strongly impacted by the minimum flow regime, leading to more than 60% reduction of both above-ground and below-ground biomass, with respect to the other treatments. Hence, we suggest avoiding minimum flow regimes where Salix restoration is prioritized.

An experimental comparison of silica gel and quartz sand grains as sediment media for growing vegetation at the laboratory scale

Abstract.In this technical note we compare silica gel grains and quartz sand as sediment media for vegetation root growth in laboratory experiments for ecohydrology and ecohydraulics. Silica gel grains become quite transparent when saturated with water. This would be useful in order to non-invasively observe the rate of growth of plant roots and plan parallel laboratory experiments made in more typical sand sediments. In this work, we compare the results of preliminary tests conducted using quartz sand with the same grain size distribution of silica gel grains. We show that the complex microstructure of silica gel grains seems to influence the evaporation and, in turn, plant growth dynamics. The potential and limitations of the use of silica grains are accordingly discussed in light of more detailed experiments.

DAPNA: An Architectural Framework for Data Processing Networks

A data processing network is as a set of (software) components connected through communication channels to apply a series of operations on data. Realization and maintenance of large-scale data processing networks necessitate an architectural approach that supports analysis, verification, implementation and reuse. However, existing tools and architectural styles fall short to support all these features. In this paper, we introduce an architectural style and framework for documenting and realizing data processing networks. Our framework employs reusable and composable data filters. These filters are annotated with their deployment information. The overall architecture is specified with an XML-based architecture description language. The specification is processed by a toolset for analysis and code generation. The framework has been utilized for defining and realizing an environmental monitoring application.