Relationship between the riverine nitrate–nitrogen concentration and the land use in the Teshio River watershed, North Japan

The present research investigated the relationship between nitrate–nitrogen (NO₃–N) in river water and the land use/land cover (hereafter, land use) in the Teshio River watershed located in northern Hokkaido island to understand the effect of human activities such as agriculture, forestry, industry, and urbanization in the drainage basin on the river ecosystem quality and services. River water was sampled at nine points seasonally during a 2-year period and the nutrients concentration was measured. Land use profiles were estimated at two spatial scales, riparian and sub-catchment, for each sampling station. The spatial pattern of water quality in the Teshio River showed increased NO₃–N levels associated with agriculture and urban expansion, and forest reduction in the watershed. Land use at the riparian scale closely reflected that at the sub-catchment scale, which masked the unique riparian buffer effect on the river water condition. The increased agricultural and reduced forest area in the riparian zone, especially in the upper middle reach, could be a possible reason for a decline of ecosystem service for the provisioning of clean water and habitat for aquatic organisms. Measures towards sustainable and more nature-friendly agricultural management are necessary in the area to protect the Teshio River ecosystem and its ecosystem services.     

Vulnerability and behavioral response to ultraviolet radiation in the components of a foliar mite prey–predator system

Ambient ultraviolet-B (UVB) radiation impacts plant-dwelling arthropods including herbivorous and predatory mites. However, the effects of UVB on prey?Cpredator systems, such as that between the herbivorous spider mite and predatory phytoseiid mite, are poorly understood. A comparative study was conducted to determine the vulnerability and behavioral responses of these mites to ultraviolet (UV) radiation. First, we analyzed dose?Cresponse (cumulative irradiance-mortality) curves for the eggs of phytoseiid mites (Neoseiulus californicus, Neoseiulus womersleyi, and Phytoseiulus persimilis) and the spider mite (Tetranychus urticae) to UVB radiation from a UV lamp. This indicated that the phytoseiid mites were more vulnerable than the spider mite, although P. persimilis was slightly more tolerant than the other two phytoseiid mites. Second, we compared the avoidance behavior of adult female N. californicus and two spider mite species (T. urticae, a lower leaf surface user; Panonychus citri, an upper leaf surface user) in response to solar UV and visible light. N. californicus actively avoided both types of radiation, whereas P. citri showed only minimal avoidance behavior. T. urticae actively avoided UV as well as N. californicus but exhibited a slow response to visible light as well as P. citri. Such variation in vulnerability and avoidance behavior accounts for differences in the species adaptations to solar UVB radiation. This may be the primary factor determining habitat use among these mites on host plant leaves, subsequently affecting accessibility by predators and also intraguild competition.     

Temporal variation of Be concentrations in atmosphere for 8 y from 2000 at Yamagata,Japan: solar influence on the Be time series

We have been continuously observing the daily ⁷Be concentrations in surface air at Yamagata, Japan (38.25° N, 140.35° E) since 2000. The yearly profile of the ⁷Be concentration indicates the variation in galactic cosmic rays owing to solar modulation. Over 8 y, the ⁷Be concentration, cosmic neutrons, and number of sunspots varied by 37.4%, 12.2%, and 92.8%, respectively. The influence of precipitation on the ⁷Be variability was approximately 5%. Hence, the yearly ⁷Be concentration was mainly varied by the solar modulation of the ⁷Be production rates. Based on the production rates found in an EXPACS simulation, the observed variability indicates ⁷Be transport from high latitudes. The daily ⁷Be concentrations have two significant periodic components of 19 d and 36 d. The 36-d component implies a relationship between the sun's rotation and the vertical transport of air masses under quiet solar activity.