Factors controlling the distribution of aquatic macrophyte communities with special reference to the rapid expansion of a semi-emergent Phalaris arundinacea L. in Bibi River, Hokkaido, northern Japan

Abstract

To identify the causes of the rapid expansion of the semi-emergent Phalaris arundinacea L. community in a nutrient-loaded river, we investigated the factors that determine the distribution of the Phalaris and other aquatic macrophyte communities and the shoot growth of P. arundinacea. The Phalaris community was distributed through areas with high organic nitrogen (Org-N), total phosphorus (T-P), PO 4 -P and suspended solids (SS) concentrations and low dissolved oxygen (DO). P. arundinacea shoots grow better in deep mud and high SS and T-P, all of which were strongly correlated with slower stream currents. Accordingly, although the concentration of total nitrogen constantly increased from 1985 to 1998, the determining nutrient for the expansion of the Phalaris community and P. arundinacea shoot growth stimulation was phosphorus rather than nitrogen. The Phalaris community increased rapidly between 1991 and 1996, when brief but prominent loadings of phosphorus were observed. We concluded that the Phalaris community was restricted due to phosphorus deficiency under nitrogen excess until 1991 and subsequently rapidly expanded over the channel due to the temporary excess phosphorus present during this period. Thereafter, the rapid expansion of the Phalaris community was maintained by the clogging effect of the floating mats formed by shoots and their remains of P. arundinacea, which results in slower currents. A slower current resulted in low DO, the sedimentation of degraded plant remains (high Org-N), and the adsorption of phosphorus by suspended matter (high SS and T-P). The anaerobic conditions caused by low oxygen and the accumulation of decomposable organic matter ensure the continuous development of the Phalaris community through the release of soluble phosphorus from the sediment.

Unique habitat and macroinvertebrate assemblage structures in spring-fed stream: a comparison among clastic lowland tributaries and mainstreams in northern Japan

“…In contrast to our results, previous studies have reported that spring-fed streams often have lush macrophytes (e.g., Sherwood et al 2000;Katagiri et al 2011) and are accordingly dominated by herbivorous invertebrates (Takemon 2010).…”

Unique habitat and macroinvertebrate assemblage structures in spring-fed stream: a comparison among clastic lowland tributaries and mainstreams in northern Japan

“…In contrast to our results, previous studies have reported that spring-fed streams often have lush macrophytes (e.g., Sherwood et al 2000; Katagiri et al 2011) and are accordingly dominated by herbivorous invertebrates (Takemon 2010). Although obligate herbivores feeding on macrophytes are generally rare, macrophytes may supplement food resources for grazers that usually consume algal masses and provide spatially complex habitats.…”

Sediment composition mediates the invasibility of aquatic ecosystems by a non-native Poaceae species

“…Our results also supported the conclusion that the effects of sediment composition, in terms of the percentage of mud, are most likely mediated by the OM, N and P concentrations because these variables are highly correlated with the sediment mud content. This result was also found in other macrophytes studies (e.g., Boeger, 1992;Katagiri et al, 2011). We highlight that our data was obtained under controlled experimental conditions and thus, direct extrapolation to nature conditions should be carefully taken.…”