Clark Heidi, Kremer James N
Yale School of Forestry and Environmental Studies, New Haven, CT 06524, USA.
Mar Environ Res. 2005 May;59(4):349-66. doi: 10.1016/j.marenvres.2004.06.001.
Direct deposition of atmospheric nitrogen to shallow coastal embayments is usually estimated, since insufficient field measurements are available. Using Waquoit Bay (Cape Cod, MA. USA) as a case study, and a recent review of literature, we determined reasonable bounds on wet and dry inputs of inorganic and organic N. Since precipitation and wind vary daily, we explored the potential of episodic events to stimulate phytoplankton blooms. Many coastal waterbodies like Waquoit Bay are small relative to their watersheds. Nevertheless, direct deposition of NH(3), NO(3)(-), and HNO(3) is significant in the loading budget. For Waquoit Bay, direct deposition was calculated to be 7-15.5 kg total N ha(-1)yr(-1), representing 70-150% of the atmospheric N reported to reach the bay via the watershed, and 20-45% of the total N reaching the bay from all land-based sources. Episodic events were estimated to deliver up to 65 mg N m(-2)day(-1), representing a phytoplankton stock of 12.3 mg Chl m(-2), an amount unlikely to stimulate dense blooms in shallow coastal waters in the northeastern United States.
由于缺乏足够的实地测量数据，通常采用估算的方法来计算大气氮向浅海沿岸海湾的直接沉降量。以美国马萨诸塞州科德角的瓦夸特湾为例，并结合近期的文献综述，我们确定了无机氮和有机氮干湿沉降的合理范围。由于降水和风力每天都在变化，我们探讨了偶发事件刺激浮游植物大量繁殖的可能性。许多像瓦夸特湾这样的沿海水体相对于其流域来说面积较小。然而，氨（NH₃）、硝酸根（NO₃⁻）和硝酸（HNO₃）的直接沉降在负荷预算中占比很大。对于瓦夸特湾，计算得出直接沉降的总氮量为7 - 15.5千克每公顷每年（kg N ha⁻¹yr⁻¹），占通过流域进入该湾的大气氮的70 - 150%，占从所有陆源进入该湾的总氮的20 - 45%。据估计，偶发事件的氮沉降量可达65毫克每平方米每天（mg N m⁻²day⁻¹），这相当于叶绿素含量为12.3毫克每平方米（mg Chl m⁻²）的浮游植物量，在美国东北部浅海沿岸水域，这个量不太可能刺激形成密集的水华。
