Data from: Influence of natural and novel organic carbon sources on denitrification in forest, degraded urban, and restored streams

Organic carbon is important in regulating ecosystem function, and its source and abundance may be altered by urbanization. We investigated shifts in organic carbon quantity and quality associated with urbanization and ecosystem restoration, and its potential effects on denitrification at the riparian–stream interface. Field measurements of streamwater chemistry, organic carbon characterization, and laboratory-based denitrification experiments were completed at two forested, two restored, and two unrestored urban streams at the Baltimore Long-Term Ecological Research site, Maryland, USA. Dissolved organic carbon (DOC) and nitrate loads increased with runoff according to a power-law function that varied across sites. Stable isotopes and molar C:N ratios suggested that stream particulate organic matter (POM) was a mixture of periphyton, leaves, and grass that varied across site types. Stable-isotope signatures and lipid biomarker analyses of sediments showed that terrestrial organic carbon sources in streams varied as a result of riparian vegetation. Laboratory experiments indicated that organic carbon amendments significantly increased rates of denitrification (35.1 ± 9.4 ng N·[g dry sediment]−1·h−1; mean ± SE) more than nitrate amendments (10.4 ± 4.0 ng N·[g dry sediment]−1·h−1) across streamflow conditions and sites. Denitrification experiments with naturally occurring carbon sources showed that denitrification was significantly higher with grass clippings from home lawns (1244 ± 331 ng N·g dry sediment−1·h−1), and overall unrestored urban sites showed significantly higher denitrification rates than restored and forest sites. We found that urbanization influences organic carbon sources and quality in streams, which can have substantial downstream impacts on ecosystem services such as denitrification.

有机碳对于调控生态系统功能至关重要，其来源与丰度可能因城市化进程发生改变。本研究探究了与城市化及生态系统修复相关的有机碳数量与质量变化，及其在河岸-溪流界面对反硝化作用的潜在影响。研究在美国马里兰州巴尔的摩长期生态研究站点开展，对2条原生林溪流、2条生态修复后溪流及2条未修复城市溪流的河水化学特征、有机碳表征进行了野外测定，并完成了实验室反硝化实验。溶解态有机碳（Dissolved Organic Carbon, DOC）与硝酸盐负荷随径流呈幂函数形式增长，且不同样点的幂函数特征存在差异。稳定同位素与摩尔C:N比分析表明，溪流颗粒态有机质（Particulate Organic Matter, POM）由附着藻类、落叶及草本植物混合而成，其组成随样点类型不同而有所差异。沉积物的稳定同位素特征与脂类生物标志物分析显示，溪流中陆源有机碳的来源因河岸植被差异而存在变化。实验室实验结果表明，在不同径流条件与样点中，有机碳添加物对反硝化速率的提升效果显著优于硝酸盐添加物：有机碳添加组的反硝化速率为35.1 ± 9.4 ng N·(g干沉积物)⁻¹·h⁻¹（平均值±标准误），而硝酸盐添加组仅为10.4 ± 4.0 ng N·(g干沉积物)⁻¹·h⁻¹。采用天然碳源开展的反硝化实验显示，以家庭草坪剪下的草屑作为碳源时，反硝化速率显著更高（1244 ± 331 ng N·g干沉积物⁻¹·h⁻¹）；整体而言，未修复城市溪流样点的反硝化速率显著高于修复后溪流与原生林溪流样点。本研究发现，城市化会改变溪流中有机碳的来源与质量，进而对反硝化作用等生态系统服务产生显著的下游影响。