U.S. Environmental Protection Agency, National Risk Management Research Lab., Ground Water and Ecosystems Restoration Division, Ada, OK 74820, USA.
J Environ Qual. 2010 Apr 13;39(3):810-23. doi: 10.2134/jeq2009.0012. Print 2010 May-Jun.
Few studies have quantified the impact of urbanization on the biogeochemistry of streams at the groundwater-surface water interface, a zone that may be critical for managing nitrogen transformations. We investigated the groundwater ecosystem of Minebank Run, a geomorphically degraded urban stream near Baltimore, Maryland in the Chesapeake Bay watershed. Our objectives were to identify the spatial and temporal extent of chemical, microbial, and hydrological factors known to influence denitrification, a microbial process that removes nitrate nitrogen (NO(3)(-)). Measurements of denitrification enzyme activity confirmed that subsurface sediments at Minebank Run, especially those with high concentrations of organic carbon, have the capacity to denitrify NO(3)(-). Levels of NO(3)(-) in groundwater were lower where more dissolved organic carbon (DOC) was available, suggesting that denitrification and removal of NO(3)(-) in groundwater were limited by DOC availability. Groundwater NO(3)(-) was highest when groundwater levels were highest, which, in turn, corresponded to high oxidation-reduction potential (ORP), indicative of high groundwater-surface water exchange. Stream flow patterns controlled stream bank and bed infiltration and, subsequently, dictated groundwater levels. Declines in water levels likely increased subsurface mixing, which led to low ORP conditions that sustained NO(3)(-) removal via denitrification. The groundwater-surface water interface is a zone of active nitrogen transformation. Management efforts that increase DOC availability to denitrifiers, reduce stream-flow velocity and flashiness, and increase groundwater residence time will likely improve the nitrogen removal capacity of urban stream channels.
很少有研究量化城市化对地下水-地表水界面溪流生物地球化学的影响，而该界面区域可能是管理氮转化的关键区域。我们研究了马里兰州切萨皮克湾流域巴尔的摩附近地形退化的城市溪流 Minebank Run 的地下水生态系统。我们的目标是确定已知会影响反硝化作用（一种去除硝酸盐氮（NO3(-)）的微生物过程）的化学、微生物和水文因素的时空范围。反硝化酶活性的测量证实，Minebank Run 的地下沉积物，尤其是那些含有高浓度有机碳的沉积物，具有反硝化作用去除 NO3(-)的能力。当有更多溶解有机碳（DOC）时，地下水中的 NO3(-)水平较低，这表明地下水中的反硝化作用和 NO3(-)去除受到 DOC 供应的限制。当地下水位最高时，地下水中的 NO3(-)最高，而地下水位最高又对应着高氧化还原电位（ORP），表明地下水-地表水交换频繁。溪流流动模式控制着溪岸和床渗透，进而决定了地下水位。地下水位的下降可能增加了地下混合，导致低 ORP 条件，从而维持通过反硝化作用去除 NO3(-)。地下水-地表水界面是一个活跃的氮转化区。增加反硝化菌可利用的 DOC、降低水流速度和波动性以及增加地下水停留时间的管理措施，可能会提高城市溪流渠道的氮去除能力。
