Effects of environmental factors on <i>Sparganium emersum</i> and <i>Sparganium erectum</i> colonization in two drainage ditches with different maintenance

Abstract

In the Niheishimizu and Ooshimizu sections of the town of Misato in the Akita Prefecture, Northern Japan, there are many abundant spring water areas. Sparganium ( Sparganium emersum and Sparganium erectum ) species are widely distributed in the irrigation water that fed by spring water. The irrigation waters were divided the natural type ditch and the maintained ditch that connect with nearby natural ditch to promote environmentally friendly agriculture. This study was conducted in both sections to support the maintenance of the irrigation water fed by the abundant spring water. A vegetation survey was conducted in September of 2005. The survey collected data on the amount of vegetation cover and the stem lengths of the plant species found in selected locations of the study area. The water depths and the flow velocities were also measured in these locations. As for the growth situation of S. emersum and S. erectum , the submerged form of S. emersum was found in water approximately 15 cm deep with a surface flow velocity of approximately 7 cm/s. This species was characterised by a relatively fast flow and relatively shallow water. The emergent and submerged growth forms of S. emersum were found in waters having flow velocities faster than those associated with S. erectum . The emergent form of S. emersum grew in relatively deep water. S. emersum is more capable of adjusting to the conditions of stream habitats than S. erectum .