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<p>Agricultural carbon export is an important driver of aquatic carbon cycling. As the key linkage between croplands and river systems, the regulation of drainage channels on dissolved organic matter (DOM) turnover remains unclear. Here, we investigated water quality, dissolved organic carbon (DOC), bioavailable DOC (BDOC) and DOM optical properties in inlet and outlet waters of paddy drainage channels along an urban-mountain gradient in southeastern China, using UV–Vis and fluorescent spectroscopy coupled with PARAFAC. Urban paddy showed significantly higher DOC, BDOC and optical component values than mountain paddy due to stronger anthropogenic sewage inputs and nutrient stimulated algal production. In contrast, mountain paddy showed lower DOM abundance but a higher photochemically degraded humic-like component and aromaticity due to weaker tillage intensity and higher elevation. DOC decreased along 76% of the drainage channels, whereas DOM aromaticity increased due to the microbial degradation of bio-labile DOM, leading to increased export of recalcitrant DOM. However, a net increase in DOC was observed in the remaining drainage channels, suggesting that enhanced in-channel production under high nutrient loading exceeded the removal effect. Our findings provide new insight into the influence of tillage intensity and landscape change on agricultural carbon cycling and water management.</p>

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Paddy drainage channels regulate dissolved organic matter transport and transformation across contrasting agricultural landscapes

  • 期刊论文

  • 发表日期：

    2026年7月10日

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  • Lei Ding,
  • Liyin Qu,
  • Ting Wang

摘要

Agricultural carbon export is an important driver of aquatic carbon cycling. As the key linkage between croplands and river systems, the regulation of drainage channels on dissolved organic matter (DOM) turnover remains unclear. Here, we investigated water quality, dissolved organic carbon (DOC), bioavailable DOC (BDOC) and DOM optical properties in inlet and outlet waters of paddy drainage channels along an urban-mountain gradient in southeastern China, using UV–Vis and fluorescent spectroscopy coupled with PARAFAC. Urban paddy showed significantly higher DOC, BDOC and optical component values than mountain paddy due to stronger anthropogenic sewage inputs and nutrient stimulated algal production. In contrast, mountain paddy showed lower DOM abundance but a higher photochemically degraded humic-like component and aromaticity due to weaker tillage intensity and higher elevation. DOC decreased along 76% of the drainage channels, whereas DOM aromaticity increased due to the microbial degradation of bio-labile DOM, leading to increased export of recalcitrant DOM. However, a net increase in DOC was observed in the remaining drainage channels, suggesting that enhanced in-channel production under high nutrient loading exceeded the removal effect. Our findings provide new insight into the influence of tillage intensity and landscape change on agricultural carbon cycling and water management.