One adult White-breasted WaterhenAmaurornis phoenicurus was observed in Lake Izunuma, Miyagi Prefecture, on 3 June 2010. This is the first report on the occurrence of the species in Lake Izunuma.

Yellow floatingheart, Nymphoides peltata ( S. G. Gmel.) Kuntze (Menyanthaceae) is a floating-leaved plant that has been designated as an endangered species in various regions of Japan. We investigated the flower visitor fauna of N. peltata in Lake Izunuma to reveal organismal interactions in the sexual reproduction of the plant. As the results of observations in 2009 and 2010, we recorded 5 species of insects belonging to 2 orders. All but one of these species, Artageia rapae crucivora (Boisduval), was considered to be pollinators. Main flower visitors were bees; a bumblebee, Bombus ignitus Panfilov, and a honeybee, Apis mellifera (L.). Except for the lack of dipteran insects such as syrphid flies, the results of our investigations were similar to those conducted in Europe yet tended to differ from the studies conducted in the Kanto district, eastern Japan. The discrepancy in flower visitor fauna between the Tohoku and Kanto districts was determined to be the result of the difference in the temporal abundance of insect groups and the flowering time of N. peltata.

In a pond located around Lake Izunuma-Uchinuma in Miyagi Pref., Japan, aquatic plants were monitored during the month of August from 2006 to 2010. Vallisneria denseserrulata grew well (60-80 cm in leaf length) in the pond from 2006 to 2009. After lotus, Nelumbo nucifera, was first observed at the pond in 2008, the lotus community spread and covered more than 80% of the water surface by 2010. Once the distributional area of V. denseserrulata was covered by the lotus, the V. denseserrulata community disappeared in 2010. At that time, three stunted and uprooted V. denseserrulata floated on the water surface. The stunted plants had short roots which may have allowed them to be easily uprooted by fish or wave action. These results indicated that limited light conditions caused by the lotus community caused the growth suppression and subsequent disappearance of V. denseserrulata.

Dietary components of larval chironomid species, Chironomus plumosus, in Lake Izunuma were investigated using carbon stable isotope ratios and fatty acid composition. Carbon stable isotope ratios (δ¹³C) of the potential foods for the larval chironomids, particulate organic matter (POM) and sediment, were –27.8±1.3‰ and –27.8±0.1‰, respectively. The larval chironomids showed large inter-individual δ¹³C variation; –50.9 to –27.5‰. Some larvae, which showed similar δ¹³C values to POM and sediment, were considered to assimilate carbon derived from POM and/or sediment, while others which showed dramatically lower δ¹³C than POM or sediment were considered to assimilate carbon derived from biogenic methane sources by feeding on methane-oxidizing bacteria (MOB). Fatty acid composition of 4 larval individuals which showed different δ¹³C levels (–50.9‰, –47.5‰, –36.4‰, –31.7‰) were analyzed. All larvae contained a higher ratio of bacterial fatty acid biomarker i17:0 than did diatoms, green algae, and cyanobacteria. This indicated that bacteria are an important food source for larval chironomids. The content of i17:0 was correlated with larval δ¹³C. This result suggested that i17:0 was derived from methane-utilizing bacteria such as MOB.