Transport of terrestrial carbon through riverine systems to coastal water has a negative impact on oxygen concentration in coastal areas. However, information on seasonal variation and the impact of catchment composition on the bioavailability of allochthonous carbon is lacking. In this project we address this knowledge gap by investigating the reactivity of dissolved organic carbon (DOC) at river mouths which originate from agricultural or forested dominated catchments over a year. Using a high-capacity oxygen sensing system biological oxygen demand (BOD) was measured and converted to carbon utilization rate. This allowed a spatial and temporal resolution necessary to understand how concentrations of total nitrogen, total phosphorus, DOC, as well as carbon composition influence carbon bioavailability. Seasonality and the differing catchment compositions yielded variable results about which factors were significantly contributing to reactivity. In addition, we found that carbon utilization rate was highest during April, June, and October for most rivers. The bioavailable fraction (BFc) was significantly higher in rivers with agricultural compared to forest dominated catchments during January, April, June, and October. However, rivers with agricultural dominated catchment had a significantly higher carbon utilization rate in August. This indicate that rivers dominated by forest transport larger and more refractory pools of carbon, while rivers with agricultural dominated catchments have a higher percentage of BFc. Based on these results we suggest that management efforts, to reduce the transport of bioavailable carbon, would be most efficient during spring and autumn with equal importance on rivers with catchment areas dominated by agriculture and forest.

陆地碳通过河流系统输送到沿海水域对沿海地区的氧气浓度产生负面影响。然而，关于季节变化和流域组成对异源碳生物利用度影响的信息尚缺乏。在这个项目中，我们通过调查一年多来来自农业或森林为主的流域的河口溶解有机碳（DOC）的反应性来解决这一知识差距。使用高容量氧传感系统测量生物需氧量 (BOD) 并将其转换为碳利用率。这使得空间和时间分辨率成为了解总氮、总磷、DOC 浓度以及碳成分如何影响碳生物利用率所必需的。季节性和不同的流域组成对于哪些因素对反应性有显着贡献产生了不同的结果。此外，我们发现大多数河流的碳利用率在4月、6月和10月最高。1 月、4 月、6 月和 10 月期间，与以森林为主的流域相比，农业河流的生物可利用分数 (BFc) 显着更高。但以农业流域为主的河流8月份碳利用率明显较高。这表明以森林为主的河流输送了更大且更难处理的碳库，而以农业流域为主的河流则具有更高的 BFc 百分比。根据这些结果，我们建议采取管理措施，减少生物可利用碳的运输，