r-IPT_(ra)与r-IPT_V在淡水沉积物脱氮速率研究中的对比分析

The Comparison of the Application r-IPT_(ra) and r-IPT_V in the Research of Nitrogen Loss Rates in Freshwater Sediments

正确评估淡水环境中沉积物脱氮效应对理解淡水系统氮循环过程具有重要的科学意义,修正^(15)N同位素配对技术(revised ^(15)N isotope pairing techniques,r-IPT)可同时评估沉积物柱样中反硝化与厌氧氨氧化速率及其脱氮贡献。本文利用流动柱样培养实验,首次在淡水系统中对比了利用泥浆实验提供参数的r-IPT_(ra)与由柱样培养实验本身提供参数的r-IPT_V计算沉积物脱氮速率的差异性,并评估了秋季太湖不同沉积环境脱氮速率。研究表明:(1)泥浆实验结果表明,太湖梅梁湾与胥湖沉积物中均存在反硝化与厌氧氨氧化作用。(2)r-IPT方法的基本假设在研究区域均成立。其中,r-IPT_V得到的两湖区沉积物原位脱氮速率均与添加15NO-3浓度无关,表明r-IPT_V对沉积物脱氮速率评估具有更好的计算精度。(3)r-IPT_V计算结果表明,梅梁湾与胥湖沉积物反硝化、厌氧氨氧化、脱氮速率分别为3.09、1.47、4.56μmol/(m2·h)与0.69、0.02、0.71μmol/(m^2·h),厌氧氨氧化对两湖区沉积物脱氮贡献率(ra)分别为32.2%与3.3%。(4)对比r-IPT_(ra)与r-IPT_V在两个湖区的计算结果,当ra较低时(3.3%),r-IPT_(ra)与r-IPT_V计算的沉积物脱氮速率及厌氧氨氧化速率接近;而当ra较高时(32.2%),r-IPT_(ra)显著高估沉积物脱氮速率,低估厌氧氨氧化贡献率。

Correctly estimating nitrogen loss in the sediments is of great significance for our understanding of the nitrogen cycle in the freshwater ecosystems. The revised 15 N isotope pairing techniques （r-IPT） can simultaneously estimate the denitrification and anammox rates and their contributions to the nitrogen loss in intact core sediments. In the present study, we compared the applicability of the r-IPTra whose parameter was related to the slurry incubations, and the r-IPTv whose parameter was derived directly from the intact core incubations, and estimated nitrogen loss rates of different sedimentary environments in Lake Taihu in autumn using the continuousflow intact core incubation instrument. The main results were as follows. （ 1 ） The occurrence of denitrification and anammox in Meiliang Bay and Xuhu Bay was proved using the slurry incubations. （2） The basic assumptions of the r-IPT were hold. And the r-IPTv was of higher accuracy because of the independency between the in situ nitrogen loss rates estimated using the r-IPT and the addition of 15NO3 in both Meiliang and Xuhu Bays. （3） Based on the r-IPTv, the denitrification, anammox, and nitrogen loss rates were estimated as 3.09, 1.47, and 4.56 μmol/（m2 . h） in Meiliang Bay, while those rates were 0.69, 0.02, and 0.71 Ixmol/（m2 ~ h） in Xuhu Bay. （4） Compared with the r-IPTv, the r-IPTra provided a nitrogen loss rate approximating to that from r-IPTv in sediments where the ra was low （3.3%）, while the r-IPTra would overestimate the nitrogen loss rates and underestimate the anammox contribution in sediments where the ra was high （32.2%）.