Processing watershed‐derived nitrogen in a well‐flushed New England estuary
Processing watershed‐derived nitrogen in a well‐flushed New England estuary
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在冲洗良好的新英格兰河口处理流域产生的氮
DOI：
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发表时间：
2003
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影响因子：
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通讯作者：
Jeffrey Hughes
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文献类型：
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作者：
Craig R. Tobias;Matthew Cieri;Bruce J. Peterson;L. Deegan;Joseph Vallino;Jeffrey Hughes
采用同位素标记硝酸盐（15NO3−）在马萨诸塞州罗利河口连续添加22 d，以评估河流流量高、浮游植物活性低期间陆源氮的运输、吸收和循环。在3周的时间里，我们在3.5公里的潮汐棱柱（150,000 m3）中实现了同位素富集，这使我们能够建立河口上游的氮质量平衡模型。河口平均δ15NO3−值在300‰~ 600‰之间，其中约75% ~ 80%的δ15NO3−保守地以15NO3−的形式输出到沿海海域。在河口处理的15N中，20% ~ 25%基本上全部发生在底栖动物中，并且在直接反硝化和自养同化之间平均分配。水体15N吸收量的缺乏归因于浮游植物种群数量少和水中停留时间短（1.2-1.4 d）。底栖自养生物对水体NO3−的吸收（富集量超过100‰）是NO3−浓度的函数，分别满足底栖微藻和大藻总氮需求的15%和25%。被底栖自养生物吸收的约10%的示踪剂被矿化并以15NH4+的形式释放回水柱。研究结束时，沉积物和沼泽植物中的15N储量占河口吸收15N的50%-70%。这些隔室可以在几个月到几年的时间尺度上隔离河口流域产生的氮。
Isotopically labeled nitrate (15NO3−) was added continuously to the Rowley estuary, Massachusetts, for 22 d to assess the transport, uptake, and cycling of terrestrially derived nitrogen during a period of high river discharge and low phytoplankton activity. Isotopic enrichment of the 3.5‐km tidal prism (150,000 m3) was achieved for the 3 weeks and allowed us to construct a nitrogen mass balance model for the upper estuary. Mean δ15NO3− in the estuary ranged from 300‰ to 600‰, and approximately 75%–80% of the 15N was exported conservatively as 15NO3− to the coastal ocean. Essentially all of the 20%–25% of the 15N processed in the estuary occurred in the benthos and was evenly split between direct denitrification and autotrophic assimilation. The lack of water‐column 15N uptake was attributed to low phytoplankton stocks and short water residence times (1.2–1.4 d). Uptake of watercolumn NO3− by benthic autotrophs (enriched in excess of 100‰) was a function of NO3− concentration and satisfied up to 15% and 25% of the total nitrogen demand for benthic microalgae and macroalgae, respectively. Approximately 10% of tracer assimilated by benthic autotrophs was mineralized and released back to the water column as 15NH4+. By the end of the study, 15N storage in sediments and marsh macrophytes accounted for 50%–70% of the 15N assimilated in the estuary. These compartments may sequester watershed‐derived nitrogen in the estuary for time scales of months to years.