Habitat modeling in high‐gradient streams: the mesoscale approach and application

Abstract

This study aimed to set out a new methodology for habitat modeling in high-gradient streams. The methodology is based on the mesoscale approach of the MesoHABSIM simulation system and can support the definition and assessment of environmental flow and habitat restoration measures. Data from 40 study sites located within the mountainous areas of the Valle d'Aosta, Piemonte and Liguria regions (Northwest Italy) were used in the analysis. To adapt MesoHABSIM to high-gradient streams, we first modified the data collection strategy to address the challenging conditions of surveys by using GIS and mobile mapping techniques. Secondly, we built habitat suitability models at a regional scale to enable their transferability among different streams with different morphologies. Thirdly, due to the absence of stream gauges in headwaters, we proposed a possible way to simulate flow time series and, therefore, generate habitat time series. The resulting method was evaluated in terms of time expenditure for field data collection and habitat-modeling potentials, and it represents a specific improvement of the MesoHABSIM system for habitat modeling in high-gradient streams, where other commonly used methodologies can be unsuitable. Through its application at several study sites, the proposed methodology adapted well to high-gradient streams and allowed the: (1) definition of fish habitat requirements for many streams simultaneously, (2) modeling of habitat variation over a range of discharges, and (3) determination of environmental standards for mountainous watercourses.

Random forests to evaluate biotic interactions in fish distribution models

“…RF can be seen as a promising tool for the ecological management of Mediterranean rivers and predictive models can be implemented in the context of hydraulic-habitat simulation systems (Vezza et al, 2014b). Species distribution models should include the effects of interspecific interactions (Elith and Leathwick, 2009) and many conservation actions could benefit from modelling approaches that include both abiotic and biotic habitat variables (Guisan and Thuiller, 2005).…”

Modelling Tools to Analyze and Assess the Ecological Impact of Hydropower Dams

“…For dams with a considerable storage reservoir, the hydropower generation interruptions could be replaced with temporal increases of flow release. This offers more protection to the most vulnerable stream sections, while maintaining the natural flow paradigm in rivers affected by hydropeaking [96]. In addition, the impacts can be mitigated by river restoration actions such as removing migration barriers and then restocking rivers [97,98].…”

“…In the next step, the output from the flow simulation was used as an input variable for a habitat suitability model to quantify biodiversity loss under several pulsed flow scenarios. A major advantage of model simulations is that they can detect specific adverse effects on the aquatic biota, allowing restoration strategies to be focused [96]. Habitat modelling is a suitable tool to explore the impacts of for example hydropeaking flows on habitat availability, thus improving the understanding of long-term effects of hydropeaking on different life-stages of organisms and their abundance [47].…”

“…Furthermore, they simplified the calculations of invertebrate production by assuming that the entire invertebrate community can be represented by a single species. Moreover, Vezza et al [96] did not take into account the effect of biotic interactions. Knowledge of these assumptions provides caution to the model users.…”

Hierarchical Object-Based Mapping of Riverscape Units and in-Stream Mesohabitats Using LiDAR and VHR Imagery

“…These spatial units represent specific combinations of hydrodynamic and morphological conditions, which can be linked to distinctive habitats and ecological niches [23]. In the habitat classification of Frissell et al [24], they are related to the concept of functional river habitat.…”