Purpose

The quality of organic matter influencing sediment nitrate (NO₃⁻) reduction processes in estuarine zones is not well understood. This study aimed to assess the denitrification (DNF), anaerobic ammonium oxidation (ANA), and dissimilatory reduction of nitrate to ammonium (DNRA) in estuarine zones of South Africa, and to understand the effects of organic matter fractions and degradation states on anaerobic NO₃⁻ reduction processes.

Materials and methods

We measured the anaerobic NO₃⁻ reduction process rates using ¹⁵N isotope-tracing techniques in Knysna Estuary, South Africa. Total hydrolyzable amino acids and fractions and geochemical parameters were also measured. The correlation analysis and structural equation model were used to evaluate the key environmental factors driving NO₃⁻ reduction processes.

Results and discussion

Potential DNF, ANA, and DNRA rates in Knysna Estuary varied from 3.59 to 16.62, 0.28 to 1.16, and 1.52 to 8.38 nmol g⁻¹ h⁻¹, respectively, with a large spatial variation. The variations in NO₃⁻ reduction process rates can largely be explained by sediment water content, dissolved organic carbon, and amino acid–based degradation index, while the total organic carbon and inorganic nitrogen contents were not related to the NO₃⁻ reduction processes. The DNF process contributed 47.28–79.34% total NO₃⁻ reduction, as compared to 17.59–47.58% for DNRA and 2.53–5.76% for ANA. The retention of reactive nitrogen (N) attributed to the DNRA process was approximately 42 t N km⁻² year⁻¹.

Conclusions

This study reported the first simultaneous investigation of the anaerobic NO₃⁻ reduction processes in estuarine areas of South Africa, implying that the qualities of substrate were more important in regulating NO₃⁻ reduction processes than substrate quantities and highlighting that DNRA played an important role in reactive N retention.

中文翻译：

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有机物降解状态影响南非克尼斯纳河口沉积物中异化硝酸盐还原过程

目的

的影响沉积物硝酸盐有机物的质量（NO ₃ ^- ）在河口区还原过程不能很好地理解。这项研究旨在评估南非河口区的反硝化（DNF），厌氧铵氧化（ANA）和硝酸盐异化还原成铵（DNRA），并了解有机物组分和降解状态对厌氧NO的影响。₃ ^-还原过程。

材料和方法

我们没有测量厌氧₃ ^-使用还原过程率¹⁵克尼斯纳河口，南非ñ同位素示踪技术。还测量了总可水解氨基酸和馏分以及地球化学参数。相关分析和结构方程模型被用来评估驱动NO关键环境因素₃ ^-还原过程。

结果与讨论

克尼斯纳河口的潜在DNF，ANA和DNRA速率分别在3.59至16.62、0.28至1.16和1.52至8.38 nmol g ^-1 h ^-1之间变化，并具有较大的空间变化。在NO的变化₃ ^-还原处理速率可以在很大程度上被沉积物的水含量，溶解的有机碳，以及基于氨基酸的退化指标进行说明，而总的有机碳和无机氮内容物不相关的NO ₃ ^-还原过程。在DNF过程贡献NO 47.28-79.34％的总₃ ^-还原相比，17.59-47.58％为DNRA和ANA 2.53-5.76％。归因于DNRA过程的活性氮（N）保留量约为42 t N km^－2年^－1。

结论

该研究报告的厌氧的第一同时调查NO ₃ ^-南非河口地区减少的过程，这意味着衬底的品质是在调节NO更重要的₃ ^-还原过程比基板数量和突出显示DNRA中发挥了重要作用反应性氮保留。