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|Title: ||Export of Dissolved Inorganic Nitrogen in a Partially Cultivated Subtropical Mountainous Watershed in Taiwan|
|Authors: ||Kao ShuhJi|
Owen, Jeffrey S.
|Issue Date: ||2017-02-08T06:09:24Z
|Publisher: || Water Air and Soil Pollution|
|Abstract: ||Abstract: A spatial and temporal investigation of dissolved inorganic nitrogen (DIN; NO3, NO2 and NH4) was conducted under various water discharge conditions in Lanyang-Hsi, a subtropical mountainous stream, which drains through distinct degrees of agriculture-influenced sub-watersheds. In both the cultivated and non-cultivated sub-watersheds, NO3 was the most abundant species accounting for >80% of total DIN, while NH4 and NO2 accounted for 3 concentrations (13–246 M) and DIN yields (1300–3800 kg N km–2 yr–1) in main channel when compared to those of non-cultivated tributaries (9–38 M for NO3 and 550–740 kg N km–2 yr–1 for yield). The much lower and less variable DIN yields observed in tributary stations (mean = 660 120 kg N km–2 yr–1) are considered as the present day background of DIN yield, which is significantly higher than those of most natural watersheds in other regions. Elevated atmospheric DIN deposition is likely the cause for the high background DIN yield. Human activity within the watershed results in additional DIN yield, which accounted for 49% of total N export. However, the reported atmospheric DIN input in northern Taiwan (1800 kg N km–2 yr–1) is much higher than the background DIN yield implying that a major fraction (70%) of atmospheric inputs are retained or processed within the watershed. A dilution pattern occurred in the main channel where high NO3 concentrations from the upstream sources decreased significantly in downstream direction due to inputs of NO3-diluted water from non-cultivated areas. We adopted a two-source mixing model to predict the NO3 dilution pattern. This model revealed a third yet not recognized N source in the lower part of watershed. Model results also indicated the importance of water discharge rate in regulating the relative contribution to total DIN export among these sources.|
|Appears in Collections:||[海洋環境與生態研究所] 期刊論文|
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