ABSTRACT

Excess nitrogen (N) is one of the most widespread and serious pollutants in the environment, but wetlands can reduce N loads, ameliorating its damaging effects downstream. Tropical wetlands are highly productive and experience high temperatures year-round, resulting in potentially high denitrification rates. However, few measurements of denitrification have been reported for tropical wetlands. In this study, we measured denitrification within stands of macrophytes at the edge of a tropical lake (900 m length, 4 m deep) in Australia. We compared denitrification rates among sediments under emergent grass (giant bulrush, Actinoscirpus grossus), sediments under floating waterlilies (Nymphae spp.), and sediments from the deeper sections of the lagoon with no macrophytes. We also measured the denitrification and primary productivity of the epiphyton on macrophytes and compared the rates with those from the sediment. Denitrification in the sediment was higher (D_t = 3.3–52 mg m⁻²h⁻¹) than denitrification of the epiphyton (D_t = 1.9–3.6 mg m⁻²h⁻¹) and was mostly coupled with nitrification (D_n). Denitrification was highest in sediments rich in organic carbon (32.3%) and N (1.4%), and during times of the year when nitrates (NO_x⁻-N = NO₂⁻-N + NO₃⁻-N) concentrations were relatively high (>0.10 mg L⁻¹). Denitrification was lowest in sediments with no macrophytes, which comprised most of the lake area. Denitrification rates of sediments under these macrophyte stands were among the highest values measured for natural wetlands and highlight the potential role of this process in ameliorating N pollution in tropical catchments.

摘要

过量的氮 (N) 是环境中最普遍和最严重的污染物之一，但湿地可以减少氮负荷，减轻其对下游的破坏作用。热带湿地生产力高，常年高温，导致潜在的高反硝化率。然而，很少有关于热带湿地反硝化作用的测量报告。在这项研究中，我们测量了澳大利亚热带湖泊（900 m 长，4 m 深）边缘大型植物群内的反硝化作用。我们比较了挺水草（巨型芦苇，Actinoscirpusgrossus）下沉积物和漂浮睡莲下沉积物（睡莲）下沉积物的反硝化率spp.)，以及来自没有大型植物的泻湖较深部分的沉积物。我们还测量了大型植物上附生生物的反硝化作用和初级生产力，并将其速率与沉积物中的速率进行了比较。沉积物中的反硝化作用（D _t  = 3.3-52 mg m ^-2 h ^-1）高于附生生物的反硝化作用（D _t  = 1.9-3.6 mg m ^-2 h ^-1），并且主要与硝化作用（D _n）。在富含有机碳 (32.3%) 和 N (1.4%) 的沉积物中，以及在一年中硝酸盐 (NO _x ^- -N = NO ₂ ^- -N + NO ₃ ^--N) 浓度相对较高（>0.10 mg L ^-1）。在没有大型植物的沉积物中反硝化作用最低，这些沉积物构成了大部分湖区。这些大型植物林分下沉积物的反硝化率是天然湿地测量的最高值之​​一，突出了这一过程在改善热带集水区氮污染方面的潜在作用。