Model-Based Evaluation of Urban River Restoration: Conflicts between Sensitive Fish Species and Recreational Users

Abstract

Urban rivers are socioecological systems, and restored habitats may be attractive to both sensitive species and recreationists. Understanding the potential conflicts between ecological and recreational values is a critical issue for the development of a sustainable river-management plan. Habitat models are very promising tools for the ecological evaluation of river restoration projects that are already concluded, ongoing, or even to be planned. With our paper, we make a first attempt at integrating recreational user pressure into habitat modeling. The objective of this study was to analyze whether human impact is likely to hinder the re-establishment of a target species despite the successful restoration of physical habitat structures in the case of the restoration of the Isar River in Munich (Germany) and the target fish species Chondostroma nasus L. Our analysis combined high-resolution 2D hydrodynamic modeling with mapping of recreational pressure and used an expert-based procedure for modeling habitat suitability. The results are twofold: (1) the restored river contains suitable physical habitats for population conservation but has low suitability for recruitment; (2) densely used areas match highly suitable habitats for C. nasus. In the future, the integrated modeling procedure presented here may allow ecological refuge for sensitive target species to be included in the design of restoration and may help in the development of visitor-management plans to safeguard biodiversity and recreational ecosystem services.

Model-Based Evaluation of the Effects of River Discharge Modulations on Physical Fish Habitat Quality

“…Several parameters, such as sediment characteristics, the timing of the discharge variation, extreme events, and historical trends should be considered in greater detail to better understand the quality, quantity, and distribution of suitable habitats. Other site-specific aspects, including the limited accessibility to spawning sites in tributaries, limitations of the river restoration potential due to urbanization and hydroelectric power plants, or the unsuitability of habitats due to recreational pressure [81] are beyond the scope of physical habitat modeling but need to be considered for successful restoration. If they were included, the use of the modeling procedure could help to design restoration trajectories that combine technical and political solutions in order to maximize ecosystem integrity with an adequate and non-destructive use of the natural resources [111][112][113].…”

“…The common nase historically occurred in the investigated urban section of the Isar, but currently, no C. nasus can be found [52]. Six habitats have been identified [49,[77][78][79][80][81] and were labeled CNS (Habitat for spawning), CNL (Habitat for larval development), CNJ (Habitat for Juveniles), CNR (Habitat for Adults during the pre-reproduction period), CNAS (Habitat for Adults during the summer), and CNAW (Habitat for Adults during the winter) in this study (Table 1). …”

“…The fuzzy logic approach is an excellent modeling technique to overcome the problems of dealing with uncertain and unprecise information, which commonly occur in ecological investigations [82]. The influence of the interactions between the three physical variables on habitat suitability have been elaborated based on the literature and in collaboration with a fish biology expert from the Bavarian State Research Center for Agriculture (Bayerische Landesanstalt für Landwirtschaft) during a personal interview (Table 3) [81]. Table 3.…”

Urban River Transformation and the Landscape Garden City Movement in China

“…After a century in which industrial cities in the West turned their backs on their rivers and during which urban rivers underwent adjustments in response to altered flow, sediment loads, and pollutant loads [9], the late 20th and early 21st centuries have seen a resurgence of interest in reconnecting cities with their rivers [71,73]. While some of these projects have emphasized ecological restoration [77], most have focused on social and economic benefits. Our research has for the first time documented the extent of urban rivers projects in China.…”

Nature-Based Solutions (NBSs) Application for Hydro-Environment Enhancement. A Case Study of the Isar River (DE)

“…The main risk to the urban areas considered in the Isar River (DE) concept case is thus the propagation of flash floods caused by intense summer rainfall events in the Alps and snow melting [16]. The Bavarian Water Agency recorded flow rates of the river in Munich varying from 8 to 1.050 m 3 /s (http://www.hnd.bayern.de), forecasting a further increase of about 25% due to CC [17]. The implemented NBSs, as depicted in Figure 1, were mainly devoted to: (a) increasing the water retention capacity; (b) improving the natural riverine morphological processes; (c) settling the longitudinal continuity and replacing the steep embankments.…”