Role of forests in headwater control with changing environment and society

Forest practices in headwater catchments are related to environmental and social contexts.The aim of this study is to analyse the changing protective functions of forests in the upper plain of the Jizera Mts.(North Bohemia,Czech Republic)since the second half of the 19th century.With time,forests have gradually changed from native stands to spruce plantations(Picea abies),introducing exotic conifers(more resistant to air pollution),and,recently,back to more diverse mixed stands.The priority in pro-tective forest functions there shifted from flood protection to integrated control of water resources(quantity and quality).In the 1980s,forest-water interactions were degraded by consequences of extreme acid atmospheric deposition,forest die-back,and extensive clear-cut.In the Jizerka catchment,first signs of recovery were observed in the early 1990s.but.stream waters there are still affected by prolonged acidification.While reconstruction of stream water chemistry at Jizerka follows the drop of the acid deposition in some 5 years,the revival of stream biota takes 10-15 years.In 2071-2100,the pro-jected climate change shows rising annual air temperatures by 3.0-4.6℃,decreasing water yield by 65-123 mm,60%drop in'minimum residual discharge',and 20-30%rise in peak-flows.However,these projected environmental changes cannot substantially decline the high potential in water resource recharge,or,start reverse processes in recent recovery from acidification and radically affect the exis-tence of planned mixed forests in the upper plain of the Jizera Mts.

NitroMAC：An instrument for the measurement of HONO and intercomparison with a long-path absorption photometer

Nitro MAC（French acronym for continuous atmospheric measurements of nitrogenous compounds） is an instrument which has been developed for the semi-continuous measurement of atmospheric nitrous acid（HONO）. This instrument relies on wet chemical sampling and detection using high performance liquid chromatography（HPLC）-visible absorption at540 nm. Sampling proceeds by dissolution of gaseous HONO in a phosphate buffer solution followed by derivatization with sulfanilamide/N-（1-naphthyl）-ethylenediamine. The performance of this instrument was found to be as follows： a detection limit of around 3 ppt with measurement uncertainty of 10% over an analysis time of 10 min. Intercomparison was made between the instrument and a long-path absorption photometer（LOPAP） during two experiments in different environments. First, air was sampled in a smog chamber with concentrations up to 18 ppb of nitrous acid. Nitro MAC and LOPAP measurements showed very good agreement. Then, in a second experiment, ambient air with HONO concentrations below250 ppt was sampled. While Nitro MAC showed its capability of measuring HONO in moderate and highly polluted environments, the intercomparison results in ambient air highlighted that corrections must be made for minor interferences when low concentrations are measured.