Tesoriero Anthony J, Duff John H, Wolock David M, Spahr Norman E, Almendinger James E
U.S. Geological Survey, 2130 SW 5th Ave., Portland, OR 97201, USA.
J Environ Qual. 2009 Jul 23;38(5):1892-900. doi: 10.2134/jeq2008.0484. Print 2009 Sep-Oct.
Understanding nutrient pathways to streams will improve nutrient management strategies and estimates of the time lag between when changes in land use practices occur and when water quality effects that result from these changes are observed. Nitrate and orthophosphate (OP) concentrations in several environmental compartments were examined in watersheds having a range of base flow index (BFI) values across the continental United States to determine the dominant pathways for water and nutrient inputs to streams. Estimates of the proportion of stream nitrate that was derived from groundwater increased as BFI increased. Nitrate concentration gradients between groundwater and surface water further supported the groundwater source of nitrate in these high BFI streams. However, nitrate concentrations in stream-bed pore water in all settings were typically lower than stream or upland groundwater concentrations, suggesting that nitrate discharge to streams was not uniform through the bed. Rather, preferential pathways (e.g., springs, seeps) may allow high nitrate groundwater to bypass sites of high biogeochemical transformation. Rapid pathway compartments (e.g., overland flow, tile drains) had OP concentrations that were typically higher than in streams and were important OP conveyers in most of these watersheds. In contrast to nitrate, the proportion of stream OP that is derived from ground water did not systematically increase as BFI increased. While typically not the dominant source of OP, groundwater discharge was an important pathway of OP transport to streams when BFI values were very high and when geochemical conditions favored OP mobility in groundwater.
了解养分进入溪流的途径将改善养分管理策略，并有助于估计土地利用方式发生变化与观察到这些变化所导致的水质影响之间的时间滞后。在美国大陆范围内，对具有一系列基流指数（BFI）值的流域中几个环境隔室中的硝酸盐和正磷酸盐（OP）浓度进行了研究，以确定水和养分输入溪流的主要途径。随着BFI的增加，源自地下水的溪流硝酸盐比例估计值也增加。地下水与地表水之间的硝酸盐浓度梯度进一步支持了这些高BFI溪流中硝酸盐的地下水来源。然而，在所有环境中，河床孔隙水中的硝酸盐浓度通常低于溪流或高地地下水的浓度，这表明硝酸盐通过河床向溪流的排放并不均匀。相反，优先途径（如泉水、渗流）可能使高硝酸盐含量的地下水绕过生物地球化学转化强烈的区域。快速途径隔室（如坡面流、瓦管排水）中的OP浓度通常高于溪流中的浓度，并且在大多数这些流域中是重要的OP输送途径。与硝酸盐不同，源自地下水的溪流OP比例并没有随着BFI的增加而系统性地增加。虽然地下水排放通常不是OP的主要来源，但当BFI值非常高且地球化学条件有利于OP在地下水中的迁移时，地下水排放是OP输送到溪流的重要途径。
