Data_Sheet_1_Hydromorphologic Control of Streambed Fine Particle Standing Stocks Influences In-stream Aerobic Respiration.docx

Fine particulate organic matter (FPOM) accumulated in streambeds is a major component of organic matter budgets in headwater streams and greatly affects productivity and metabolism of stream communities. The spatiotemporal distribution of benthic FPOM in the stream, as well as its quantity and quality, depend on inputs from different source types. These can be natural such as soils, streambanks and riparian vegetation, or anthropogenic such as effluents from wastewater treatment plants (WWTP). In addition, stream flow is a key driver of FPOM dynamics, which influences the balance between its transport and accumulation in the streambed. Yet, the link between FPOM dynamics and its effects on stream metabolism is still largely unknown. The aim of this study was to investigate the influence of stream channel hydromorphology on water transport and streambed accumulation of fine particulate matter (FPM) (mineral and organic fractions), FPOM (organic fraction) and its quality (characterized by %OM, %C, %N and the C:N molar ratio). In addition, we quantified the metabolic activity associated with FPM at the habitat scale, and its potential contribution to whole-reach ecosystem respiration using the resazurin-resorufin bioreactive tracer as a proxy for aerobic respiration. We also characterized water transport and metabolic activity with combined additions of hydrological and bioreactive tracers at the reach scale. The study was conducted in the Cànoves stream (Catalonia, NE Spain) downstream of a WWTP that contains three reaches that were hydromorphologically modified using bioengineering techniques. Slower local velocities at the habitat scale increased accumulation of FPM, but did not influence the spatial variability of its quality. Instead, FPM quality declined further downstream from the WWTP. Accumulation of FPM did not increase metabolic activity, but higher %OM of FPM and lower C:N ratios favored the microbial metabolic activity efficiency (normalized by the gram of FPM). Reach-scale metabolic activity was higher in reaches with higher water exchange rate and longer relative travel times, highlighting hydromorphology as an important driver of microbial metabolic activity at the reach-scale. This demonstrates that the interplay of hydrologic exchange and residence time in streambed sediments associated with the microbial metabolic activity of FPOM can ultimately influence reach-scale metabolic activity.

细颗粒有机物质（fine particulate organic matter, FPOM）在河床中的沉积是源头溪流有机质收支的重要组成部分，对溪流群落的生产力与代谢活动具有显著影响。溪流底栖FPOM的时空分布、丰度与质量，取决于不同来源的物质输入：自然来源包括土壤、河岸带与河岸植被，人为来源则包括污水处理厂（wastewater treatment plant, WWTP）的出水。此外，水流是调控FPOM动态的关键因子，其影响FPOM在河床中的输运与沉积之间的平衡。然而，目前学界对FPOM动态及其对溪流代谢活动的影响之间的关联仍知之甚少。
本研究旨在探究河道水文形态学对细颗粒物质（fine particulate matter, FPM，包含矿物与有机质组分）、FPOM（仅有机质组分）及其质量（以有机质占比%OM、碳占比%C、氮占比%N以及碳氮摩尔比C:N表征）的河床沉积与水输运过程的影响。此外，本研究以刃天青-试卤灵生物反应示踪剂作为有氧呼吸的替代指标，量化了栖息地尺度下与FPM相关的代谢活动，及其对整条河段生态系统呼吸的潜在贡献。同时，本研究还通过在河段尺度联合添加水文与生物反应示踪剂，表征了水输运过程与代谢活动。
本研究在西班牙东北部加泰罗尼亚地区某污水处理厂下游的卡诺韦斯溪（Cànoves stream）开展，该溪流包含3个经生物工程技术改造了水文形态学特征的河段。研究结果显示：栖息地尺度下更低的局部流速会提升FPM的沉积量，但不会影响其质量的空间异质性；与之相反，FPM的质量随其距离污水处理厂下游越远而逐渐降低。FPM的沉积量并未提升代谢活动，但FPM更高的有机质占比与更低的碳氮比，会提升以单位克FPM归一化后的微生物代谢活动效率。水文交换速率更高、相对停留时间更长的河段，其河段尺度代谢活动也更强，这表明水文形态学是河段尺度微生物代谢活动的关键驱动因子。本研究结果表明，FPOM的微生物代谢活动与河床沉积物中的水文交换过程及停留时间之间的相互作用，最终会影响河段尺度的代谢活动。