Effects of plant architecture and water velocity on sediment retention by submerged macrophytes

Summary Studies quantifying the content of fine particulate matter (organic and inorganic) retained in macrophyte stands are scarce. Thus, little is known about the relationship between retention of fine particulate matter and macrophyte architecture, especially in rivers. Here, we quantified the amount of organic and inorganic fine particulate matter retained by three different macrophyte species having two contrasting plant architectures (‘mesh-like’ and ‘strap-like’), to test the role of plant architecture on retention. Results showed that plant architecture and water velocity were related and their interaction was important for particle sedimentation/retention by macrophyte leaves and stems. The complexity of plant architecture appeared to be the main factor explaining variation in the amount of trapped matter. Increases in water velocity led to a decline of both the organic and the inorganic particulate matter retained by macrophytes, while a decrease in water velocity was related to an increase in macrophyte cover. The concentrations of trapped matter (both organic and inorganic) also differed significantly among seasons, indicating the existence of a seasonal cycle in the retention of fine particulate matter mainly associated with macrophyte cover (and biomass) and water velocity. Although there were seasonal and spatial variations in sediment retention in both ‘mesh-like’ and ‘strap-like’ architectures, macrophytes were effective sediment traps.