Post-Fire Watershed Nitrate Dynamics Dataset

The ecosystem services provided by forests are under threat as wildfire frequency and severity increase throughout the western US. Severe wildfire can change physical environments and biogeochemical processes in watersheds with lasting effects on watershed nutrient cycling. For example, nitrate-nitrogen (NO3-N) export often increases following wildfire and can remain elevated for decades in severely burned watersheds. In this study, we investigated the effects of wildfire on stream biotic processing and watershed nutrient balance following 2 wildfires that burned along the Colorado Front Range. We evaluated stream water chemistry, nutrient limitation, benthic biomass, and stream metabolism along stream reaches within 3 burned and 3 unburned watersheds from July 26 to August 16, 2017. Although the two high-severity wildfires occurred 5 and 15 years prior to the study, the streams draining burned watersheds still had 23-times higher NO3-N concentrations than unburned watersheds, a trend that is consistent across seasons and throughout the 15-year post-fire record. Autotrophic nitrogen (N) limitation was reduced in the nitrate-rich burned streams. Consequently, autotrophic biomass and primary productivity were 2.5 and 20-times greater, respectively, in burned relative to unburned streams. Together, these data suggest that N supply from burned uplands exceeded the increase in stream N demand and was the primary cause of chronic, elevated NO3-N export from these severely burned watersheds. Accordingly, aquatic ecosystems within or downstream of burned watersheds may be susceptible to eutrophication and harmful algal blooms until vegetation recovery and plant nutrient demand reduce N supply to streams.

Note: To learn more about the datasets, open the file titled \"Hydroshare_dataset_descriptions\".

美国西部全域野火发生频率与强度持续攀升，森林所提供的生态系统服务正面临严峻威胁。严重野火可改变流域物理环境与生物地球化学过程，对流域养分循环造成长期影响。例如，野火过后硝酸盐氮（NO3-N）的输出量通常会升高，在受严重焚烧的流域中，这种高浓度状态甚至可维持数十年。
本研究针对科罗拉多前缘地带两场野火后的情况，探究了野火对溪流生物过程及流域养分平衡的影响。研究于2017年7月26日至8月16日期间，在3个受焚烧流域与3个未受焚烧流域的溪流河段中，对水体化学性质、养分限制状况、底栖生物量以及溪流代谢情况进行了评估。
尽管这两场高烈度野火分别发生在研究开展前5年与15年，但受焚烧流域的溪流硝酸盐氮浓度仍较未受焚烧流域高出23倍，这一趋势在各季节以及野火过后15年的观测记录中均保持一致。在硝酸盐富集的受焚烧溪流中，自养生物的氮（N）限制得到缓解。因此，相较于未受焚烧的溪流，受焚烧溪流的自养生物量与初级生产力分别提升了2.5倍与20倍。
综合以上数据可知，受焚烧高地的氮供给量超出了溪流氮需求的增长幅度，这是这些严重焚烧流域长期持续高硝酸盐氮输出的主要诱因。据此，受焚烧流域内部或下游的水生生态系统可能易发生富营养化与有害藻华，直至植被恢复、植物养分需求降低溪流的氮供给水平。
注：如需了解更多数据集相关信息，请打开名为"Hydroshare_dataset_descriptions"的文件。