United States Geological Survey , Reston, Virginia 20192, United States.
Environ Sci Technol. 2013;47(23):13330-8. doi: 10.1021/es401334k. Epub 2013 Nov 12.
A study has been undertaken to determine the time required for the effects of nitrogen-reducing best management practices (BMPs) implemented at the land surface to reach the Chesapeake Bay via groundwater transport to streams. To accomplish this, a nitrogen mass-balance regression (NMBR) model was developed and applied to seven watersheds on the Delmarva Peninsula. The model included the distribution of groundwater return times obtained from a regional groundwater-flow (GWF) model, the history of nitrogen application at the land surface over the last century, and parameters that account for denitrification. The model was (1) able to reproduce nitrate concentrations in streams and wells over time, including a recent decline in the rate at which concentrations have been increasing, and (2) used to forecast future nitrogen delivery from the Delmarva Peninsula to the Bay given different scenarios of nitrogen load reduction to the water table. The relatively deep porous aquifers of the Delmarva yield longer groundwater return times than those reported earlier for western parts of the Bay watershed. Accordingly, several decades will be required to see the full effects of current and future BMPs. The magnitude of this time lag is critical information for Chesapeake Bay watershed managers and stakeholders.
一项研究旨在确定通过地下水输送到达切萨皮克湾的陆地表面实施的减少氮素最佳管理措施（BMPs）的影响所需的时间。为了实现这一目标，开发并应用了一个氮质量平衡回归（NMBR）模型，该模型涵盖了从区域地下水流动（GWF）模型获得的地下水回流时间分布、过去一个世纪土地表面氮素应用的历史以及考虑反硝化作用的参数。该模型（1）能够再现溪流和井中硝酸盐浓度随时间的变化，包括浓度增加速度最近的下降，以及（2）用于预测在不同的地下水表氮负荷减少情景下，从特拉华半岛向海湾输送的未来氮素。与海湾流域西部的报告相比，特拉华相对较深的多孔含水层产生的地下水回流时间更长。因此，需要几十年的时间才能看到当前和未来 BMP 的全部效果。这种时滞的大小是切萨皮克湾流域管理者和利益相关者的关键信息。
