Variability and prediction of freshwater and nitrate fluxes for the Louisiana-Texas shelf: Mississippi and Atchafalaya River source functions
Variability and prediction of freshwater and nitrate fluxes for the Louisiana-Texas shelf: Mississippi and Atchafalaya River source functions
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路易斯安那-德克萨斯陆架淡水和硝酸盐通量的变化和预测：密西西比河和阿查法拉亚河源函数
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发表时间：
1994
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影响因子：
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通讯作者：
D. Goolsby
中科院分区：
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作者：
A. Bratkovich;S. Dinnel;D. Goolsby
对密西西比河和阿查法拉亚河的河水排放、硝酸盐浓度和硝酸盐通量的时间历程进行了分析。结果表明，水流量的变化是占主导地位的年周期和较短的时间尺度的情景事件，可能与融雪径流和春季或夏季降雨。与上述情况相比，水量的年际变化相对较小。与此相反，硝酸盐浓度表现出最强的变化在十年的时间尺度。年际变化不是单调的，而是结构复杂的。弱协变性之间的水排放和硝酸盐浓度导致一个相对“嘈杂”的硝酸盐通量信号。硝酸盐通量的变化表现出低振幅，长期调制的主导年周期。预测后验分析表明，熟练的硝酸盐浓度和硝酸盐通量场的预测是可行的。由于年度水文循环的基本强度，水排放量是最可靠的后报（在季节到年际的时间尺度上）。然而，这个变量的预测工作是不太成功的后报的努力，主要是由于在我们相对较短的测试期间（18个月）在年度周期的相移。硝酸盐浓度更巧妙地预测（季节到年际的时间尺度），由于信号的十年尺度部分的相对优势。硝酸盐通量也巧妙地预测，即使历史分析似乎表明，它应该是更难以预测的水排放或硝酸盐浓度。
Time histories of riverine water discharge, nitrate concentration, and nitrate, flux have been analyzed for the Mississippi and Atchafalaya rivers. Results indicate that water discharge variability is dominated by the annual cycle and shorter-time-scale episodic events presumably associated with snowmelt runoff and spring or summer rains. Interannual variability in water discharge is relatively small compared to the above. In contrast, nitrate concentration exhibits strongest variability at decadal time scales. The interannual variability is not monotonic but more complicated in structure. Weak covariability between water discharge and nitrate concentration leads to a relatively “noisy” nitrate flux signal. Nitrate flux variations exhibit a low-amplitude, long-term modulation of a dominant annual cycle. Predictor-hindcastor analyses indicate that skilled forecasts of nitrate concentration and nitrate flux fields are feasible. Water discharge was the most reliably hindcast (on seasonal to interannual time scales) due to the fundamental strength of the annual hydrologic cycle. However, the forecasting effort for this variable was less successful than the hindcasting effort, mostly due to a phase shift in the annual cycle during our relatively short test period (18 mo). Nitrate concentration was more skillfully predicted (seasonal to interannual time scales) due to the relative dominance of the decadal-scale portion of the signal. Nitrate flux was also skillfully forecast even though historical analyses seemed to indicate that it should be more difficult to predict than either water discharge or nitrate concentration.