Bedrock weathering rates, reactive nitrogen influxes and effluxes, and nitrous oxide emissions rates from the Pumphouse Hillslope, East River Watershed, Colorado

Atmospheric nitrous oxide contributes directly to global warming, yet models of the nitrogen cycle do not account for bedrock, the largest pool of terrestrial nitrogen, as a source of nitrous oxide. Although it is known that release rates of nitrogen from bedrock are large, there is an incomplete understanding of the connection between bedrock-hosted nitrogen and atmospheric nitrous oxide. Here, we quantify nitrogen fluxes and mass balances at a hillslope underlain by marine shale. We found that at this site bedrock weathering contributes 78% of the subsurface reactive nitrogen, while atmospheric sources (commonly regarded as the sole sources of reactive nitrogen in pristine environments) account for only the remaining 22%. About 56% of the total subsurface reactive nitrogen denitrifies, including 14% emitted as nitrous oxide. The remaining reactive nitrogen discharges in porewaters to a floodplain where additional denitrification likely occurs. We also found that the release of bedrock nitrogen occurs primarily within the zone of the seasonally fluctuating water table and suggest that the accumulation of nitrate in the vadoes zone, often attributed to fertilization and soil leaching, may also include contributions from weathered nitrogen-rich bedrock. Our hillslope study suggests that under oxygenated and moisture-rich conditions, weathering of deep, nitrogen-rich bedrock makes an important contribution to the nitrogen cycle. The data files are in Excel, which can be accessed using Microsoft Office, and consist of many data sets from the Pumphouse Hillslope PLM (Pumphouse Lower Montane) 1, 2, 3, and 4. They include soil to rock (0-10 meters) solid phase minerals and elements compositions; time- and depth-resolved pore-water chemistry and pore-gas compositions; time- and depth-resolved water table depths and water fluxes; subsurface weathering rates; nitrogen influxes and effluxes and mass balance. The attached paper is in a Word document, which can be accessed using Microsoft Office, and in pdf format.

大气中的一氧化二氮直接加剧全球变暖，但当前氮循环模型并未将基岩——陆地最大的氮储库——作为一氧化二氮的来源纳入考量。尽管已知基岩释氮速率可观，但学界对基岩赋存氮与大气一氧化二氮之间的关联仍缺乏完整认知。本研究以海相页岩为基底的山坡为研究对象，量化了其氮通量与质量平衡。研究发现，该研究点地下活性氮的78%来自基岩风化作用，而通常被视为未受干扰自然环境中活性氮唯一来源的大气源仅占剩余22%。地下活性氮总量中约56%发生反硝化作用，其中14%以一氧化二氮形式排放。剩余活性氮通过孔隙水排放至泛滥平原，该区域大概率会发生额外的反硝化过程。本研究同时发现，基岩释氮主要发生在季节性水位波动带内；此外，通常被归因于施肥与土壤淋溶的包气带硝酸盐积累现象，或许也包含富氮基岩风化带来的贡献。本山坡研究表明，在富氧且湿度充足的条件下，深部富氮基岩的风化作用对氮循环具有重要贡献。
数据集以Excel格式存储，可通过Microsoft Office打开，包含泵室山坡PLM（Pumphouse Lower Montane）1、2、3、4号样点的多组数据。数据内容涵盖0-10米深度范围内土壤至基岩的固相矿物与元素组成、时序与深度解析的孔隙水化学及孔隙气体组成、时序与深度解析的地下水位深度与水通量、地下风化速率、氮输入输出通量及质量平衡。附带的研究论文以Word文档格式存储，可通过Microsoft Office打开，同时提供PDF版本。