Salinity tolerance of aquatic plants indicated by monitoring data from the Netherlands

Abstract

Data on salinity tolerance of aquatic plant species are scarce, but required to better understand species’ responses in multiple stressed environments. We analyzed data from a Dutch Water board in the province of Zeeland according to the occurrence of plant taxa in relation to salinity (chloride concentration). The dataset contained 862 samples of plants (altogether 46 taxa) and chloride concentrations. The smallest range was found for Nuphar lutea occurring in sites with 43 to 140 mg l−1 Cl−. The widest range was observed for Glaux maritima occurring in sites with 710 to 22,000 mg l−1 Cl−. Two species (N. lutea and Potamogeton trichoides) had an optimum lower than 100 mg l−1 Cl−, while three taxa (G. maritima, Salicornia spp. and Ulva spp. (=non-filamentous)) had an optimum higher than 10,000 mg l−1 Cl−. Change points (CPs) were determined on salinity class level along the gradient. These CPs are defined as the class, at which the largest change in occurrence is determined. The CP of taxa that are relatively sensitive, such as Sparganium erectum and Carex riparia, were below 200 mg l−1 Cl−, while relative tolerant taxa, such as Stuckenia pectinata and Ranunculus sceleratus, had CPs at concentrations that were more than tenfold higher. The upper limit of the salinity range at which taxa occurred in the study area were generally similar to the few limits that were previously published. Implications for assigning species to water body types for implementing the Water Framework Directive in the Netherlands are discussed.