Modeling Historical Trends in Lake Superior Total Nitrogen Concentrations
Modeling Historical Trends in Lake Superior Total Nitrogen Concentrations
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模拟苏必利尔湖总氮浓度的历史趋势
DOI：
10.1016/j.jglr.2010.07.008
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发表时间：
2010
期刊：
影响因子：
2.4
通讯作者：
Colin M. Casey
中科院分区：
文献类型：
--
作者：
C. McDonald;N. Urban;Colin M. Casey
1900 年至 1980 年间，苏必利尔湖的硝酸盐浓度增加了五倍，并且自那时以来几乎保持不变。在水力停留时间较长（约 190 年）的湖泊中，浓度变化如此之快令人惊讶。我们开发了一个模型，以更好地了解历史变化的原因并预测硝酸盐浓度的未来变化。历史负荷是根据全国平均氮氧化物排放估计、最近（过去~30年）大气氮沉降数据、最近支流浓度数据和全流域径流估计来重建的。仅大气氮沉降的增加不足以导致观察到的趋势。然而，将大气沉降增加与支流氮负荷增加和/或本世纪中叶埋藏+反硝化减少相结合的模型运行再现了观测到的氮积累。由于内部氮通量比外部通量大一个数量级，因此湖泊内部氮循环相对较小的变化可能会导致总氮浓度发生相对较大的变化。流域土地利用的变化，特别是伐木活动的增加，可能改变了河流的氮输入。不管导致硝酸盐浓度上升的历史机制如何，系统目前似乎处于或接近峰值氮含量。
Nitrate concentrations in Lake Superior increased fivefold between 1900 and 1980, and have remained nearly constant since that time. Such rapid changes in concentration in a lake with a long hydraulic residence time (~190years) are surprising. We developed a model to better understand the causes of the historical changes and to predict future changes in nitrate concentrations. Historical loadings were reconstructed based on average national NOxemissions estimates, recent (past ~30years) atmospheric N deposition data, recent tributary concentration data, and basin-wide runoff estimates. Increases in atmospheric N deposition alone were insufficient to have resulted in the observed trends. However, model runs combining increased atmospheric deposition with increased tributary N loading and/or decreased burial+denitrification mid-century reproduced the observed accumulation of N. Because internal N fluxes are an order of magnitude greater than external fluxes, relatively small changes in the lake's internal N cycle may produce relatively large changes in total N concentrations. Land-use changes in the watershed, particularly increases in logging activity, may have altered riverine N inputs. Regardless of the historical mechanisms leading to the rise in nitrate concentrations, it appears as though the system is currently at or is approaching peak N content.