Author(s): F.G. Wortelboer

Linked Author(s):

Keywords: Aquatic plants; River IJssel; Environmental key factors; Macrophytes; Water Framework Directive

Abstract: The spatial pattern of aquatic plants in the river IJssel is predicted on the basis of environmental key factors. The European Water Framework Directive (WFD) aims at good ecological status for surface waters to be reached by 2027. Measures are proposed to improve ecological status for waters that have not reached this state yet. Ecological status is defined for the ecological quality elements fytoplankton, fytobenthos, macrophytes, macrofauna and fish. Macrophytes are especially interesting in riverine ecosystems as they define habitat structure both by their presence and by interacting with fluvial processes such as sedimentation and flow (Van Oorschot, 2017). For a large number of species of macrofauna and fish, the presence of submerged macrophytes in river ecosystems is essential in providing food, hiding spots and habitat for reproduction. The Water Framework Directive Explorer (WFD Explorer) is a general framework for the calculation of water quality and the assessment of the ecological status for the WFD. It consists of a number of modules for the calculation of flow, nutrient fluxes and a neural network model linking nutrient concentrations and environmental characteristics directly to Ecological Quality Ratios (EQR’s) for the WFD. For large rivers and lakes a new method is developed to improve the prediction of future EQR values as a result of measures planned. This paper describes the first results for the River IJssel and discusses the lessons learned. Tolerance ranges of macrophytes for environmental factors are confronted with the spatial distribution of the values of these environmental factors. If all the environmental factors fall within the tolerance boundaries of a species, that species can occur under these conditions. Thus the potential occurrence is calculated. Tolerance ranges of macrophytes species were derived from a data set of 600 Dutch surface waters which were monitored for macrophytes and physico-chemical characteristics of surface water and sediment in the period 1980-1983. Additionally, environmental factors were added from literature. Water depth and stream velocity were derived from results of a WAQUA 2D model of the river. Values for environmental factors were estimated from the ambient national water monitoring programme (MWTL), modelling results and literature. The water body of the river IJssel was subdivided into spatial units from coarse (subunits) to fine (ecotopes). Values of environmental variables were assigned to every spatial unit. Translation of units between tolerance data and environmental data was taken into account.

DOI: https://doi.org/10.3850/978-981-11-2731-1_176-cd

Year: 2018