Smith R L, Baumgartner L K, Miller D N, Repert D A, Böhlke J K
U.S. Geological Survey, 3215 Marine St., Boulder, CO, USA.
Microb Ecol. 2006 Jan;51(1):22-35. doi: 10.1007/s00248-004-0159-7. Epub 2006 Jan 1.
Nitrification was measured within a sand and gravel aquifer on Cape Cod, MA, using a series of single-well injection tests. The aquifer contained a wastewater-derived contaminant plume, the core of which was anoxic and contained ammonium. The study was conducted near the downgradient end of the ammonium zone, which was characterized by inversely trending vertical gradients of oxygen (270 to 0 microM) and ammonium (19 to 625 microM) and appeared to be a potentially active zone for nitrification. The tests were conducted by injecting a tracer solution (ambient ground water + added constituents) into selected locations within the gradients using multilevel samplers. After injection, the tracers moved by natural ground water flow and were sampled with time from the injection port. Rates of nitrification were determined from changes in nitrate and nitrite concentration relative to bromide. Initial tests were conducted with (15)N-enriched ammonium; subsequent tests examined the effect of adding ammonium, nitrite, or oxygen above background concentrations and of adding difluoromethane, a nitrification inhibitor. In situ net nitrate production exceeded net nitrite production by 3- to 6- fold and production rates of both decreased in the presence of difluoromethane. Nitrification rates were 0.02-0.28 mumol (L aquifer)(-1) h(-1) with in situ oxygen concentrations and up to 0.81 mumol (L aquifer)(-1) h(-1) with non-limiting substrate concentrations. Geochemical considerations indicate that the rates derived from single-well injection tests yielded overestimates of in situ rates, possibly because the injections promoted small-scale mixing within a transport-limited reaction zone. Nonetheless, these tests were useful for characterizing ground water nitrification in situ and for comparing potential rates of activity when the tracer cloud included non-limiting ammonium and oxygen concentrations.
在马萨诸塞州科德角的一个砂石含水层中，通过一系列单井注入试验对硝化作用进行了测量。该含水层含有一个源自废水的污染物羽流，其核心区域缺氧且含有铵。研究在铵带的下游末端附近进行，该区域的特征是氧气（270至0微摩尔）和铵（19至625微摩尔）的垂直梯度呈反向变化，似乎是一个潜在的硝化作用活跃区域。试验通过使用多级采样器将示踪剂溶液（环境地下水 + 添加成分）注入梯度范围内的选定位置来进行。注入后，示踪剂随自然地下水流移动，并在不同时间从注入端口进行采样。根据硝酸盐和亚硝酸盐浓度相对于溴化物的变化来确定硝化速率。最初的试验使用了富含（15）N的铵；后续试验研究了添加高于背景浓度的铵、亚硝酸盐或氧气以及添加硝化抑制剂二氟甲烷的影响。原位净硝酸盐产量比净亚硝酸盐产量高出3至6倍，并且在二氟甲烷存在的情况下两者的产量速率均下降。在原位氧气浓度下，硝化速率为0.02 - 0.28微摩尔/（升含水层）·小时，在底物浓度无限制的情况下高达0.81微摩尔/（升含水层）·小时。地球化学方面的考虑表明，单井注入试验得出的速率高估了原位速率，可能是因为注入促进了传输受限反应区内的小规模混合。尽管如此，这些试验对于原位表征地下水硝化作用以及在示踪剂云包含无限制铵和氧气浓度时比较潜在的活性速率是有用的。
