Dissolved nitrogen exports from watersheds with contrasting land uses in sub-humid cool-temperate climates

Knowledge is limited in responses of watershed dissolved nitrogen (N) export to different land uses in Baijiang soil area under sub-humid cool-temperate climates. This study provided comparisons of three adjacent sub-watersheds (SWs) with contrasting land uses (SW 1: mixed land uses of woodland, dry cropland and residen-tial area; SW 2: dry cropland dominated; and SW 3: paddy field dominated) after agricultural land use conversion (from woodland to dry cropland at SW 1 and SW 2 and from dry cropland to paddy field at SW 3) at the Abujiao River watershed, NE China. Exports of total dissolved N (TN), nitrate N (NO3-N) and ammonium N (NH4-N) in base and storm flows during the pre-growing, growing and post-growing seasons were investigated. Water discharge at the sub-watersheds mainly occurred as base flow with mean base flow index ranging within 0.62 - 0.69, while base flow and storm flow N exports were comparable. Across sub-watersheds, TN, NO3-N and NH4-N exported equally through base flow (1.36 - 3.16, 0.56 - 1.69 and 0.24 - 0.63 kg km(-2) d-1, respectively) and storm flow (1.42 - 2.95, 0.54 - 1.66 and 0.42 - 0.63 kg km-2 d-1, respectively). SW 3 presented greater N export than SW 1 and SW 2 through base flow in the pre-growing (3.49 - 3.55, 3.21 - 4.30 and 3.27 - 4.47 times for TN, NO3-N and NH4-N, respectively) and growing seasons (1.95 - 3.32, 2.34 - 2.62 and 1.94 - 2.46 times for TN, NO3-N and NH4-N, respectively) and through storm flow in the pre-growing season (2.73 - 3.97, 2.59 - 4.02 and 3.38 - 4.00 times for TN, NO3-N and NH4-N, respectively). No significant difference in N export were found between SW 1 and SW 2. This study suggested special emphasis on the increased export of dissolved N through base flow and storm flow after dry croplands were converted to paddy fields.

Automated summary

This study investigated the effects of different land uses on dissolved nitrogen export in Baijiang soil area and found increased export of dissolved nitrogen through base flow and storm flow after conversion from dry croplands to paddy fields.