US Geological Survey, Colorado Water Science Center, Denver Federal Center, Denver, CO, 80225, USA,
Environ Monit Assess. 2013 Nov;185(11):9343-59. doi: 10.1007/s10661-013-3256-6. Epub 2013 May 29.
The Hydrologic Benchmark Network (HBN) is a long-term monitoring program established by the US Geological Survey in the 1960s to track changes in the streamflow and stream chemistry in undeveloped watersheds across the USA. Trends in stream chemistry were tested at 15 HBN stations over two periods (1970-2010 and 1990-2010) using the parametric Load Estimator (LOADEST) model and the nonparametric seasonal Kendall test. Trends in annual streamflow and precipitation chemistry also were tested to help identify likely drivers of changes in stream chemistry. At stations in the northeastern USA, there were significant declines in stream sulfate, which were consistent with declines in sulfate deposition resulting from the reductions in SO₂ emissions mandated under the Clean Air Act Amendments. Sulfate declines in stream water were smaller than declines in deposition suggesting sulfate may be accumulating in watershed soils and thereby delaying the stream response to improvements in deposition. Trends in stream chemistry at stations in other part of the country generally were attributed to climate variability or land disturbance. Despite declines in sulfate deposition, increasing stream sulfate was observed at several stations and appeared to be linked to periods of drought or declining streamflow. Falling water tables might have enhanced oxidation of organic matter in wetlands or pyrite in mineralized bedrock thereby increasing sulfate export in surface water. Increasing sulfate and nitrate at a station in the western USA were attributed to release of soluble salts and nutrients from soils following a large wildfire in the watershed.
水文基准网络（HBN）是美国地质调查局在 20 世纪 60 年代建立的一个长期监测计划，旨在追踪美国未开发流域的径流量和溪流化学变化。使用参数 Load Estimator（LOADEST）模型和非参数季节性 Kendall 检验，在 15 个 HBN 站的两个时期（1970-2010 年和 1990-2010 年）测试了溪流化学趋势。还测试了年径流量和降水化学的趋势，以帮助确定溪流化学变化的可能驱动因素。在美国东北部的站点，溪流硫酸盐有显著下降，这与《清洁空气法案修正案》要求减少 SO₂排放导致的硫酸盐沉积减少相一致。溪流水中硫酸盐的下降小于沉积量的下降，表明硫酸盐可能在流域土壤中积累，从而延迟了对沉积改善的溪流响应。该国其他地区站点的溪流化学趋势通常归因于气候变异性或土地干扰。尽管硫酸盐沉积减少，但在几个站点观察到溪流硫酸盐增加，这似乎与干旱或径流量减少时期有关。水位下降可能增强了湿地中的有机物或矿化基岩中的黄铁矿的氧化作用，从而增加了地表水的硫酸盐输出。美国西部一个站点的硫酸盐和硝酸盐增加归因于流域内的一场大型野火后土壤中可溶性盐分和养分的释放。
