Data from: Pollution-tolerant invertebrates enhance greenhouse gas flux in urban wetlands

One of the goals of urban ecology is to link community structure to ecosystem function in urban habitats. Pollution-tolerant wetland invertebrates have been shown to enhance greenhouse gas (GHG) flux in controlled laboratory experiments, suggesting that they may influence urban wetland roles as sources or sinks of GHG. However, it is unclear if their effects can be detected in highly variable conditions in a field setting. Here we use an extensive dataset on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) flux in sediment cores (n = 103) collected from ten urban wetlands in Melbourne, Australia during summer and winter in order to test for invertebrate enhancement of GHG flux. We detected significant multiplicative enhancement effects of temperature, sediment carbon content, and invertebrate density on CH4 and CO2 flux. Each doubling in density of oligochaete worms or large benthic invertebrates (oligochaete worms and midge larvae) corresponded to ~42% and ~15% increases in average CH4 and CO2 flux, respectively. However, despite exceptionally high densities, invertebrates did not appear to enhance N2O flux. This was likely due to fairly high organic carbon content in sediments (range: 2.1-12.6%), and relatively low nitrate availability (median 1.96 μM NO3--N), which highlights the context-dependent nature of community structural effects on ecosystem function. The invertebrates enhancing GHG flux in this study are ubiquitous, and frequently dominate faunal communities in impaired aquatic ecosystems. Therefore, invertebrate effects on CO2 and CH4 flux may be common in wetlands impacted by urbanization, and urban wetlands may make greater contributions to the total GHG budgets of cities if the negative impacts of urbanization on wetlands are left unchecked.

城市生态学的核心目标之一，是将城市生境中的群落结构与生态系统功能建立关联。已有受控实验室实验证实，耐污染湿地无脊椎动物可提升温室气体（GHG）通量，这提示该类群可能会影响城市湿地作为温室气体源或汇的功能定位。但目前仍不清楚，在野外环境的高变异性条件下，其效应是否可被观测到。本研究依托澳大利亚墨尔本10处城市湿地在夏、冬两季采集的103份沉积物岩芯（sediment cores，n=103）所对应的二氧化碳（CO₂）、甲烷（CH₄）及一氧化二氮（N₂O）通量大规模数据集，旨在检验无脊椎动物对温室气体通量的增强效应。研究发现，温度、沉积物碳含量与无脊椎动物密度对甲烷与二氧化碳通量存在显著的倍增增强效应。寡毛类蠕虫（oligochaete worms）或大型底栖无脊椎动物（large benthic invertebrates）的密度每提升一倍，平均甲烷通量与二氧化碳通量分别提升约42%与15%；其中大型底栖无脊椎动物涵盖寡毛类蠕虫与摇蚊幼虫（midge larvae）。但尽管无脊椎动物密度极高，其并未对一氧化二氮通量产生显著增强效应。该现象或与沉积物中较高的有机碳含量（范围：2.1%~12.6%）及较低的硝酸盐可利用性（中位数为1.96 μM NO₃⁻-N）相关，这也凸显了群落结构对生态系统功能的影响具有情境依赖性。本研究中可增强温室气体通量的无脊椎动物类群分布广泛，且常为受损水生生态系统动物群落的优势类群。因此，无脊椎动物对二氧化碳与甲烷通量的影响或普遍存在于受城市化干扰的湿地中；若不对城市化对湿地的负面影响加以管控，城市湿地对城市总温室气体收支的贡献或进一步增大。