Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the present...Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the presented study, we investigated the controlling factors of denitrification rates within the streams of the Han River Basin, Korea, with different land-use patterns, in order to enhance the effectiveness of water resource management strategies. Ten watersheds were classified into three land-use patterns （forest, agriculture and urban） using satellite images and geographic information system techniques, and in-situ denitrification rates were determined using an acetylene blocking method. Additionally, sediment samples were collected from each stream to analyze denitrifier communities and abundance using molecular approaches. In-situ denitrification rates were found to be in the order of agricultural streams （289.6 mg N20-N m-2 d-1） 〉 urban streams （157.0 mg N20-N m-2 d-1） 〉 forested streams （41.9 mg N20-N m-2 d-l）. In contrast, the average quantity of denitrifying genes was the lowest in the urban streams. Genetic diversity of denitrifying genes was not affected by watershed land-use pattern, but exhibited stream-dependent pattern. More significance factors were involved in denitrification in the sites with higher denitrification rates. Multiple linear regression analysis revealed that clay, dissolved organic carbon and water contents were the main factors controlling denitrification rate in the agricultural streams, while dissolved organic carbon was the main controlling factor in the urban streams. In contrast, temperature appeared to be the main controlling factor in the forested streams.展开更多
Stream animals on tropical high islands have ecological counterparts among continental fauna but are confronted with highly dynamic and variable environmental conditions that can far exceed those occurring in mainland...Stream animals on tropical high islands have ecological counterparts among continental fauna but are confronted with highly dynamic and variable environmental conditions that can far exceed those occurring in mainland streams.In response to weather fronts passing through an island chain or to localized fluctuations in the formation of orographic rain,water levels in island streams can change from low flows of a few centimeters depth to sudden flash floods of several meters and back to clear shallow water within a few days.Studies of the five species of indigenous Hawaiian stream fishes have shown that the dispersal of larvae out to sea and their return several months later during their amphidromous life cycles constantly restock streams and provide a kind of ready reserve for recolonizing streams after unusually harsh disturbances,such as the recent Hurricane Iniki.Because of the predominance of amphidromy among the major species of stream fishes and macroinvertebrates on tropical Pacific high islan s,we hypothesize that maintaining biodiversity in these island streams when conditions are otherwise favorable and restoring animal life to formerly diverted streams may be no more complicated than assuring that the freshwater-marine threshold remains open and that natural fluctuations in flow are unhampered.展开更多
基金Supported by the National Research Foundation of Korea(No.2013056833)
文摘Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the presented study, we investigated the controlling factors of denitrification rates within the streams of the Han River Basin, Korea, with different land-use patterns, in order to enhance the effectiveness of water resource management strategies. Ten watersheds were classified into three land-use patterns （forest, agriculture and urban） using satellite images and geographic information system techniques, and in-situ denitrification rates were determined using an acetylene blocking method. Additionally, sediment samples were collected from each stream to analyze denitrifier communities and abundance using molecular approaches. In-situ denitrification rates were found to be in the order of agricultural streams （289.6 mg N20-N m-2 d-1） 〉 urban streams （157.0 mg N20-N m-2 d-1） 〉 forested streams （41.9 mg N20-N m-2 d-l）. In contrast, the average quantity of denitrifying genes was the lowest in the urban streams. Genetic diversity of denitrifying genes was not affected by watershed land-use pattern, but exhibited stream-dependent pattern. More significance factors were involved in denitrification in the sites with higher denitrification rates. Multiple linear regression analysis revealed that clay, dissolved organic carbon and water contents were the main factors controlling denitrification rate in the agricultural streams, while dissolved organic carbon was the main controlling factor in the urban streams. In contrast, temperature appeared to be the main controlling factor in the forested streams.
文摘Stream animals on tropical high islands have ecological counterparts among continental fauna but are confronted with highly dynamic and variable environmental conditions that can far exceed those occurring in mainland streams.In response to weather fronts passing through an island chain or to localized fluctuations in the formation of orographic rain,water levels in island streams can change from low flows of a few centimeters depth to sudden flash floods of several meters and back to clear shallow water within a few days.Studies of the five species of indigenous Hawaiian stream fishes have shown that the dispersal of larvae out to sea and their return several months later during their amphidromous life cycles constantly restock streams and provide a kind of ready reserve for recolonizing streams after unusually harsh disturbances,such as the recent Hurricane Iniki.Because of the predominance of amphidromy among the major species of stream fishes and macroinvertebrates on tropical Pacific high islan s,we hypothesize that maintaining biodiversity in these island streams when conditions are otherwise favorable and restoring animal life to formerly diverted streams may be no more complicated than assuring that the freshwater-marine threshold remains open and that natural fluctuations in flow are unhampered.
