The role of groundwater as a driver of spatial and temporal heterogeneity of ecological conditions in streams is not well understood, particularly at larger spatial scales. To evaluate the association between groundwater and ecological communities and processes, we assessed stream biofilm communities (biomass and diatom assemblage composition) and cellulose decomposition over four seasons in 19 reaches with varying amounts of groundwater input in a headwater stream network in southern Ontario, Canada. Seasonal variation was found to drive diatom assemblage composition and cellulose decomposition among seasons. Moreover, there were clear seasonal patterns in taxa succession in the diatom assemblages where the dominant taxa shifted in accordance with ecological preferences of the taxa. Within season assessments of stream biofilms among individual reaches showed that biomass, diatom assemblage composition, and cellulose decomposition were not associated with amount of groundwater input. The lack of concordance between groundwater influence and stream biofilm condition suggests that the groundwater signal may have been overwhelmed by surface water influences, such as nutrients and thermal effects, at the reach scale. Our findings also demonstrate the importance of assessing stream biofilm communities and cellulose decomposition in multiple seasons to identify and understand discrete shifts in ecosystem conditions of temperate streams.

地下水作为河流生态条件时空异质性驱动因素的作用尚不清楚，特别是在较大的空间尺度上。为了评估地下水与生态群落和过程之间的关联，我们评估了加拿大安大略省南部源头河流网络中 19 个河段四个季节的河流生物膜群落（生物量和硅藻组合成分）和纤维素分解，其中地下水输入量不同。研究发现季节变化会驱动硅藻组合成分和纤维素分解。此外，硅藻组合中的类群演替存在明显的季节性模式，其中优势类群根据类群的生态偏好而变化。在季节内，对各个河段的河流生物膜进行的评估表明，生物量、硅藻组合成分和纤维素分解与地下水输入量无关。地下水影响和河流生物膜状况之间缺乏一致性表明，在河段范围内，地下水信号可能已被地表水影响（例如营养物和热效应）所淹没。我们的研究结果还证明了评估多个季节河流生物膜群落和纤维素分解的重要性，以识别和了解温带河流生态系统条件的离散变化。地下水影响和河流生物膜状况之间缺乏一致性表明，在河段范围内，地下水信号可能已被地表水影响（例如营养物和热效应）所淹没。我们的研究结果还证明了评估多个季节河流生物膜群落和纤维素分解的重要性，以识别和了解温带河流生态系统条件的离散变化。地下水影响和河流生物膜状况之间缺乏一致性表明，在河段范围内，地下水信号可能已被地表水影响（例如营养物和热效应）所淹没。我们的研究结果还证明了评估多个季节河流生物膜群落和纤维素分解的重要性，以识别和了解温带河流生态系统条件的离散变化。