Sources of nitrate contamination and age of water in large karstic springs of Florida
Sources of nitrate contamination and age of water in large karstic springs of Florida
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DOI：
10.1007/s00254-004-1061-9
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发表时间：
2004-10-01
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影响因子：
--
通讯作者：
Katz, BG
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作者：
Katz, BG
在过去的几十年里，在佛罗里达的许多第一级泉水沃茨（流量大于或等于2.8 m（3）/s）中，硝酸盐浓度稳步增加，为了应对这一问题，对12个大泉水的水样进行了多种同位素和其他化学示踪剂的分析，以评估硝酸盐污染的来源和时间尺度。春季沃茨中硝态氮浓度范围为0.50 ~ 4.2 mg/L，春季沃茨中硝态氮的δ（15）N值范围为2.6 ~ 7.9/mil，大多数δ（15）N值低于6/mil，表明无机肥料是这些沃茨中氮的主要来源。根据多种示踪剂分析（CFC-12、CFC-113、SF6、H-3/He-3）和活塞流假设，泉水排出地下水的表观年龄从5年到35年不等;然而，表观示踪剂年龄一般不一致。最可靠的泉水年龄似乎是基于氚和He-3的数据，因为在几个泉水沃茨中CFCs和SF6的浓度远远高于与现代大气浓度平衡的预期。所有示踪剂的数据是最一致的输出曲线的指数和二元混合模型，代表自20世纪60年代初以来，在上弗洛里丹含水层补给的水的混合物。鉴于地下水过境时间是几十年的顺序，并从多个来源的含水层的氮的长期输入有关，硝酸盐可能会持续几十年的地下水流向泉水，由于缓慢的运输溶质通过含水层矩阵。
In response to concerns about the steady increase in nitrate concentrations over the past several decades in many of Florida's first magnitude spring waters (discharge greater than or equal to2.8 m(3)/s), multiple isotopic and other chemical tracers were analyzed in water samples from 12 large springs to assess sources and timescales of nitrate contamination. Nitrate-N concentrations in spring waters ranged from 0.50 to 4.2 mg/L, and delta(15)N values of nitrate in spring waters ranged from 2.6 to 7.9 per mil. Most delta(15)N values were below 6 per mil indicating that inorganic fertilizers were the dominant source of nitrogen in these waters. Apparent ages of groundwater discharging from springs ranged from 5 to about 35-years, based on multi-tracer analyses (CFC-12, CFC-113, SF6, H-3/He-3) and a piston flow assumption; however, apparent tracer ages generally were not concordant. The most reliable spring-water ages appear to be based on tritium and He-3 data, because concentrations of CFCs and SF6 in several spring waters were much higher than would be expected from equilibration with modern atmospheric concentrations. Data for all tracers were most consistent with output curves for exponential and binary mixing models that represent mixtures of water in the Upper Floridan aquifer recharged since the early 1960s. Given that groundwater transit times are on the order of decades and are related to the prolonged input of nitrogen from multiple sources to the aquifer, nitrate could persist in groundwater that flows toward springs for several decades due to slow transport of solutes through the aquifer matrix.