Patterns of diel variation in nitrate concentrations in the Potomac River
Patterns of diel variation in nitrate concentrations in the Potomac River
复制标题
波托马克河硝酸盐浓度的昼夜变化模式
DOI：
10.1086/688777
复制
发表时间：
2015
影响因子：
1.8
通讯作者：
P. Capel
中科院分区：
文献类型：
--
作者：
D. Burns;Matthew P. Miller;B. Pellerin;P. Capel
波托马克河是切萨皮克湾的一大氮源，减少营养负荷是改善营养状况的一个重点。更好地了解NO3 -损失（部分反映在NO3 -浓度的日变化上），可以改进模型对海湾N负荷的预测。我们分析了波托马克河2年的高频NO3 -传感器数据，以量化NO3 - diel损失的幅度和时间的季节性变化。尽管NO3 -浓度有广泛的季节性和流量驱动的变化，但Diel模式明显，特别是在低流量期间。冬季变化幅度为~0.01 mg N/L，夏季变化幅度为0.02 ~ 0.03 mg N/L，春季和秋季变化幅度居中，相当于冬季NO3 -日平均浓度<1%，夏季变化幅度为~2 ~ 4%。日最大NO3 -值一般出现在上午中下旬，夏季可重复模式较多，秋冬季变化较大。Diel NO3损失在冬季和夏季分别减少了0.7%和3%的负荷。这些损失低于整个流域的总流内NO3负荷损失的估计，后者平均占每年地下水对河流贡献的33%。与光合有效辐射相比，水温和径流量对日均NO3 -变化量的影响更大。估计的日面NO3 -损失率一般为1000 mg N - m-2 - d-1，比大多数公布的值都大，因为在这条大河中测量的数据比在较小河流中测量的数据在更大的深度/单位河底面积上综合。这些diel NO3 -模式与光自养吸收和相关反硝化作用的影响是一致的，但我们不能将这些模式单独归因于同化，因为diel动力学的大小和时间受到蒸散发、瞬时储存和水动力分散等过程的影响，影响程度未知。要改善对大气损耗的估计，需要额外的高频测量，如溶解O2、溶解有机氮和NH4+，并部署2个测量站。
The Potomac River is a large source of N to Chesapeake Bay, where reducing nutrient loads is a focus of efforts to improve trophic status. Better understanding of NO3– loss, reflected in part by diel variation in NO3– concentrations, may refine model predictions of N loads to the Bay. We analyzed 2 y of high-frequency NO3– sensor data in the Potomac to quantify seasonal variation in the magnitude and timing of diel NO3– loss. Diel patterns were evident, especially during low flow, despite broad seasonal and flow-driven variation in NO3– concentrations. Diel variation was ~0.01 mg N/L in winter and 0.02 to 0.03 mg N/L in summer with intermediate values in spring and autumn, equivalent to <1% of the daily mean NO3– concentration in winter and ~2 to 4% in summer. Maximum diel NO3– values generally occurred in mid- to late morning, with more repeatable patterns in summer and wider variation in autumn and winter. Diel NO3– loss reduced loads by 0.7% in winter and 3% in summer. These losses were less than estimates of total in-stream NO3– load loss across the basin that averaged 33% of the annual groundwater contribution to the river. Water temperature and discharge had stronger relationships to the daily magnitude of diel NO3– variation than did photosynthetically active radiation. Estimated diel areal NO3– loss rates were generally >1000 mg N m–2 d–1, greater than most published values because measurements in this large river integrate over a greater depth/unit stream bottom area than do those from smaller rivers. These diel NO3– patterns are consistent with the influence of photoautotrophic uptake and related denitrification, but we cannot attribute these patterns to assimilation alone because the magnitude and timing of diel dynamics were affected to an unknown extent by processes, such as evapotranspiration, transient storage, and hydrodynamic dispersion. Improvements to diel loss estimates will require additional high-frequency measures, such as dissolved O2, dissolved organic N, and NH4+, and deployment of 2 measurement stations.
影响因子：
3.7
作者：
Lansdown, K.;Heppell, C. M.;Zhang, H.
通讯作者：
Zhang, H.