Humphries Georgie E, Espinosa Jessica I, Ambrosone Mariapaola, Ayala Zabdiel Roldan, Tzortziou Maria, Goes Joaquim I, Greenfield Dianne I
School of Earth and Environmental Sciences, Queens College, Queens, NY 11367 USA.
Advanced Science Research Center at the Graduate Center, New York, NY 10031 USA.
Biogeochemistry. 2023;163(2):219-243. doi: 10.1007/s10533-023-01021-2. Epub 2023 Feb 25.
Nitrogen (N) inputs to developed coastlines are linked with multiple ecosystem and socio-economic impacts worldwide such as algal blooms, habitat/resource deterioration, and hypoxia. This study investigated the microbial and biogeochemical processes associated with recurrent, seasonal bottom-water hypoxia in an urban estuary, western Long Island Sound (WLIS), that receives high N inputs. A 2-year (2020-2021) field study spanned two hypoxia events and entailed surface and bottom depth water sampling for dissolved nutrients as inorganic N (DIN; ammonia-N and nitrite + nitrate (N + N)), organic N, orthophosphate, organic carbon (DOC), as well as chlorophyll and bacterial abundances. Physical water quality data were obtained from concurrent conductivity, temperature, and depth casts. Results showed that dissolved organic matter was highest at the most-hypoxic locations, DOC was negatively and significantly correlated with bottom-water dissolved oxygen (Pearson's = -0.53, = 0.05), and ammonia-N was the dominant DIN form pre-hypoxia before declining throughout hypoxia. N + N concentrations showed the reverse, being minimal pre-hypoxia then increasing during and following hypoxia, indicating that ammonia oxidation likely contributed to the switch in dominant DIN forms and is a key pathway in WLIS water column nitrification. Similarly, at the most hypoxic sampling site, bottom depth bacteria concentrations ranged ~ 1.8 × 10-1.1 × 10 cells ml pre-hypoxia, declined throughout hypoxia, and were positively and significantly correlated (Pearson's = 0.57; = 0.03) with ammonia-N, confirming that hypoxia influences N-cycling within LIS. These findings provide novel insight to feedbacks between major biogeochemical (N and C) cycles and hypoxia in urban estuaries.
The online version contains supplementary material available at 10.1007/s10533-023-01021-2.
全球范围内，发达海岸线的氮（N）输入与多种生态系统和社会经济影响相关，如藻华、栖息地/资源退化和缺氧。本研究调查了纽约州长岛湾西部（WLIS）一个城市河口反复出现的季节性底层水缺氧相关的微生物和生物地球化学过程，该河口接收大量的氮输入。一项为期两年（2020 - 2021年）的实地研究跨越了两次缺氧事件，涉及对表层和底层深度水进行采样，以分析溶解养分，包括无机氮（DIN；氨氮和亚硝酸盐 + 硝酸盐（N + N））、有机氮、正磷酸盐、有机碳（DOC）以及叶绿素和细菌丰度。同时获取了电导率、温度和深度测量的物理水质数据。结果表明，溶解有机物在缺氧程度最高的位置含量最高，DOC与底层水溶解氧呈显著负相关（皮尔逊相关系数 = -0.53， = 0.05），并且氨氮是缺氧前占主导的DIN形式，在整个缺氧过程中下降。N + N浓度则相反，在缺氧前最低，在缺氧期间及之后增加，这表明氨氧化可能导致了主导DIN形式的转变，并且是WLIS水柱硝化作用的关键途径。同样，在缺氧程度最高的采样点，底层细菌浓度在缺氧前范围约为1.8×10 - 1.1×10个细胞/毫升，在整个缺氧过程中下降，并且与氨氮呈显著正相关（皮尔逊相关系数 = 0.57； = 0.03），证实了缺氧影响长岛湾内的氮循环。这些发现为城市河口主要生物地球化学（氮和碳）循环与缺氧之间的反馈提供了新的见解。
在线版本包含可在10.1007/s10533 - 023 - 01021 - 2获取的补充材料。
