The first fish-based index to assess the ecological quality of lowland rivers in Flanders (Belgium) is based on data obtained from different fishing techniques without considering the gear specificity. As a consequence, this index could not be intercalibrated with other European indices which concentrate on one gear type only. In order to comply with the European Water Framework Directive, we developed a new fish-based index using data obtained from surveys in rivers with electric gear only. All 293 selected rivers belonged to the bream or barbel zone. An updated reference list of fish species was compiled based on previous work and recent data. Abiotic data were collected according to standard methods and habitat quality of all surveyed sites was pre-classified using pressure indicators. To develop the new index candidate metrics were selected from the literature and metric values were calculated. Linear mixed regression models selected metrics based on their response to the pre-classified habitat status. Correlation tests were performed to avoid redundancy among responsive metrics. Boundaries for metric scores were defined based on the calculated metric values. The new index of biotic integrity (IBI) was calculated by summation of the metric scores, and transformed to an ecological quality ratio (EQR), ranging between 0 and 1. Five integrity classes, ranging from bad to maximal ecological potential, were attributed and compared to the pre-classified habitat status of the site. In addition, the new index was also validated with an independent set of data. The new IBI proved to successfully assess the ecological status of the rivers.

The European Union adopted the Water Framework Directive (WFD) in the year 2000 to tackle the rapid degradation of freshwater systems. However, biological, hydromorphological, and physico-chemical water quality targets are currently not met, and identifying successful policy implementation and management actions is of key importance. We built a joint species distribution model for riverine fish in Flanders (Belgium) to better understand the response of fish communities to current environmental policy goals. Environmental covariates included physico-chemical variables and hydromorphological quality indices, while waterway distances accounted for spatial effects. We detected strong effects of physico-chemistry on fish species’ distributions. Evaluation of fish community responses to simulated policy scenarios revealed that targeting a ‘good’ status, following the WFD, increases average species richness with a fraction of species (0.13–0.69 change in accumulated occurrence probabilities). Targeting a ‘very good’ status, however, predicted an increase of 0.17–1.38 in average species richness. These simulations indicated that riverbed quality, nitrogen, and conductivity levels should be the focal point of policy. However, the weak response of species to a ‘good’ quality together with the complexity of nutrient-associated problems, suggest a challenging future for river restoration in Flanders.

in de beste omstandigheden uit te voeren,

Early nineties of previous century aquatic biodiversity was low in many West-European countries as a consequence of pollution, hydromorphological degradation and a lack of sound environmental legislation. Since the early 2000s and the implementation of the European Water Framework Directive a big step forward has been made to achieve a good ecological status of surface waters in Europe. However, to date little is known about the response of biological life in small lowland streams on improving conditions for both water quality and habitat diversity. In this study, we assessed possible relationships between chemical water quality and aquatic biodiversity of the Zwalm River basin (Belgium) using a dataset of long-term measurements of the chemical and biological water quality. Specifically, we wanted to know 1) the evolution in chemical and biological water quality over the last three decades and 2) if an improvement in chemical water quality was reflected in the macroinvertebrate and fish diversity. We found that there was indeed a significant improvement in the chemical water quality thanks to the installation of wastewater treatment plants and river basin management plans. Shortly after this improvement in chemical water quality, an increase in the number and abundance of pollution sensitive macroinvertebrate taxa was observed, which was consequently also seen in the biotic index score, based on macroinvertebrates. Despite a limited change in community composition observed for fish, no significant increase in diversity, or in the biotic index score of fish could be found. Currently, a stagnation of the improving water quality is observed. Hydromorphological restoration and free fish migration remain important key factors to improve diversity of macroinvertebrates and fish species. Based on the results of this study, we provide guidelines (for example restoration of spawning beds, decrease diffuse pollution from agriculture) to optimize the investments made in river restoration and to achieve the good ecological status by 2027 as defined by the European Water Framework Directive.

Topmouth gudgeon (Pseudorasbora parva) is one of the most invasive aquatic fish species in Europe and causes adverse effects to ecosystem structure and functioning. Knowledge and understanding of the species’ interactions with the environment and with native fish are important to stop and prevent the further spread of the species. Creating species distribution models is a useful technique to determine which factors influence the occurrence and abundance of a species. We applied three different modelling techniques: general additive models, random forests and fuzzy habitat suitability modelling (FHSM) to assess the habitat suitability of topmouth gudgeon. The former two techniques indicated that the abundance of native fish (i.e. biotic variables) was more important than environmental variables when determining the abundance of topmouth gudgeon in Flanders (Belgium). Bitterling (Rhodeus amarus), stone loach (Barbatula barbatula), three-spined stickleback (Gasterosteus aculeatus) and predator abundance were selected as the most important biotic variables and implemented in the FHSM to investigate species interactions. Depending on the preferred food source and spawning behaviour, either coexistence or interspecific competition can occur with bitterling, stone loach and three-spined stickleback. In contrast, the presence of predators clearly had a top down effect on topmouth gudgeon abundance. These findings could be applied as a biological control measure and implemented in conservation strategies in order to reduce the abundance of earlier established populations of topmouth gudgeon.

The present study investigated temporal influences on metal distribution in gudgeon (Gobio gobio) and roach (Rutilus rutilus), and its relation to condition metrics and fish community structure. Fish communities were sampled in two seasons (autumn and spring) during two successive years and the Index of Biotic Integrity (IBI) was calculated. Cadmium, Cu, Pb, Zn and As concentrations were measured in gill, liver, kidney and muscle, and condition factor (CF) and hepatosomatic index (HSI) were measured. Cadmium (max. 39.0 mu g g(-1) dw) and Zn (max 2502 mu g g(-1) dw) were most strongly stored in kidney and liver and periodical influences on metal accumulation were observed. CF appeared to be a stable metric related to accumulated metal-mixtures and was best related to hepatic levels, while the HSI was less useful. Relations between single metal accumulation and IBI were influenced by sample period, however, when taking into account multiple metals periodical influences disappeared. (C) 2014 Elsevier Ltd. All rights reserved.