Biogeodynamics and Biodiversity Group, Center of Advanced Studies of Blanes (CEAB-CSIC), Accés a la Cala St. Francesc 14, 17300 Blanes, Girona, Spain.
Sci Total Environ. 2013 Aug 1;458-460:535-45. doi: 10.1016/j.scitotenv.2013.04.072. Epub 2013 May 22.
The aim of this study was to gain insights on the potential hydrological and biogeochemical mechanisms controlling the response of two nested Mediterranean catchments to long-term changes in atmospheric inorganic nitrogen and sulphate deposition. One catchment was steep and fully forested (TM9, 5.9 ha) and the other one had gentler slopes and heathlands in the upper part while side slopes were steep and forested (TM0, 205 ha). Both catchments were highly responsive to the 45% decline in sulphate concentration measured in atmospheric deposition during the 1980s and 1990s, with stream concentrations decreasing by 1.4 to 3.4 μeq L(-1) y(-1). Long-term changes in inorganic nitrogen in both, atmospheric deposition and stream water were small compared to sulphate. The quick response to changes in atmospheric inputs could be explained by the small residence time of water (4-5 months) in these catchments (inferred from chloride time series variance analysis), which was attributed to steep slopes and the role of macropore flow bypassing the soil matrix during wet periods. The estimated residence time for sulphate (1.5-3 months) was substantially lower than for chloride suggesting unaccounted sources of sulphate (i.e., dry deposition, or depletion of soil adsorbed sulphate). In both catchments, inorganic nitrogen concentration in stream water was strongly damped compared to precipitation and its residence time was of the order of decades, indicating that this essential nutrient was strongly retained in these catchments. Inorganic nitrogen concentration tended to be higher at TM0 than at TM9 which was attributed to the presence of nitrogen fixing species in the heathlands. Our results indicate that these Mediterranean catchments react rapidly to environmental changes, which make them especially vulnerable to changes in atmospheric deposition.
本研究旨在深入了解控制两个嵌套的地中海流域对大气无机氮和硫酸盐长期沉降变化响应的潜在水文和生物地球化学机制。一个流域陡峭且完全被森林覆盖（TM9，5.9 公顷），另一个流域上部为缓坡和石南荒地，而侧面山坡陡峭且森林覆盖（TM0，205 公顷）。这两个流域都对 20 世纪 80 年代和 90 年代大气沉降中硫酸盐浓度下降 45%做出了强烈响应，流域溪流浓度每年下降 1.4 至 3.4 μeq L(-1)。与硫酸盐相比，大气输入中无机氮的长期变化较小。大气输入变化的快速响应可以用这些流域中（通过氯离子时间序列方差分析推断）水的小停留时间（4-5 个月）来解释，这归因于陡峭的坡度和湿期大孔流绕过土壤基质的作用。硫酸盐的估计停留时间（1.5-3 个月）远低于氯离子，这表明硫酸盐有未被计算的来源（例如干沉降，或土壤吸附硫酸盐的耗尽）。在这两个流域中，溪流水中的无机氮浓度与降水相比受到强烈抑制，其停留时间为几十年，这表明这种必需营养物质在这些流域中被强烈截留。与 TM9 相比，TM0 流域溪流水中的无机氮浓度较高，这归因于石南荒地中固氮物种的存在。我们的研究结果表明，这些地中海流域对环境变化反应迅速，使它们特别容易受到大气沉降变化的影响。
