In the present study, long-term changes in the first bloom date of shrub and tree species in Seoul (126.56°E, 37.34°N), Korea were examined using historical observational data for the period 1922-2004 (83 years). The study focused on two shrub species, golden-bell (Forsythia koreana) and azalea (Rhododendron mucronulatum), and three tree species, cherry (Prunus yedoensis), peach (Prunus persica), and American locust (Robinia pseudoacacia). The annual-mean temperature has increased by about 2°C in Seoul over the 83 years analyzed. The temperature increase is significant during the winter and early spring and becomes less significant during late spring. As a result of this regional warming, all five species showed an advance in the first bloom date over this time period. The advanced date is particularly apparent in early-spring flowering species like golden-bell (−2.4 days 10-year −1 ), azalea (−2.4 days 10-year −1 ), cherry (−1.4 days 10-year −1 ), and peach (−1.4 days 10-year −1 ) as compared to late-spring flowering species like American locust (−0.5 days 10-year −1 ). The present results have demonstrated that the major factor for the determination of flower blooming is heat accumulation, i.e. a certain threshold of growing degree-days (GDD) index. In particular, early spring flowers were sensitive to the accumulation of warm temperature than late-spring flowers.

Abstract. Optical measurements using ultraviolet-visible (UV-VIS) spectrophotometric sensors and fluorescent dissolved organic matter (FDOM) sensors have recently been used as proxies of dissolved organic carbon (DOC) concentrations in streams and rivers at a high temporal resolution. Despite the merits of the sensors, temperature changes and particulate matter in water can interfere with the sensor readings, over-or underestimating DOC concentrations. However, little efforts have been made to compare responses of the two types of the sensors to critical interferences such as temperature and turbidity. The performance of a UV-VIS sensor and an FDOM sensor was compared in both laboratory experiments and in situ monitoring in a forest stream in Korea during three storm events. Although the UV-VIS sensor did not require temperature correction in laboratory experiments using the forest stream water, the deviations of its values from the DOC concentrations measured with a TOC analyzer increased linearly as turbidity increased. In contrast, the FDOM sensor outputs decreased significantly as temperature or turbidity increased, requiring temperature and turbidity correction for in situ monitoring of DOC concentrations. The results suggest that temperature correction is relatively straightforward but turbidity correction may not be simple because the attenuation of light by particles can significantly reduce the sensitivity of the sensors in highly turbid waters. Shifts in composition of fluorophores also need to be carefully tracked using periodically collected samples since light absorbance and fluorescence can vary as the concentrations of dominant fluorophores change.