Dynamics of Nutrients and Colored Dissolved Organic Matter Absorption in a Wetland-Influenced Subarctic Coastal Region of Northeastern Japan: Contributions From Mariculture and Eelgrass Meadows
Dynamics of Nutrients and Colored Dissolved Organic Matter Absorption in a Wetland-Influenced Subarctic Coastal Region of Northeastern Japan: Contributions From Mariculture and Eelgrass Meadows
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DOI：
10.3389/fmars.2021.711832
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
Tomonori Isada;H. Abe;H. Kasai;M. Nakaoka
中科院分区：
文献类型：
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作者：
Tomonori Isada;H. Abe;H. Kasai;M. Nakaoka
沿海海洋与陆地生态系统的相互作用在生物地球化学循环中起着重要作用。因此，研究陆海相互作用对于进一步了解影响沿海地区营养动态的过程至关重要。2014年4月至2015年2月，研究了日本阿克什科河口（AKE）和阿克什湾（AB）受湿地影响的河流-大叶草草甸-滨海水体连续体中彩色溶解有机物（CDOM）、非藻颗粒（NAP）和浮游植物的养分浓度和光吸收系数的季节和空间分布。两端元预测的355 nm处CDOM吸收系数[aCDOM(355)]相对于盐度的混合稀释线显示AB中存在保守混合。除2014年12月外，AB中硅浓度与盐度和aCDOM（355）呈显著相关。这些结果表明，AB中的硅酸盐和CDOM主要来源于受湿地影响的河流排放。然而，除了2014年6月外，从发展海水养殖的AKE的大叶藻草甸采集的样本显示硅酸盐浓度和aCDOM（355）与盐度的非保守混合。在AKE的大叶藻草甸中也发现了可能从沉积物中释放的磷酸盐浓度升高，特别是在夏季。这些结果表明，海水养殖和海草生态系统的代谢活动对AKE内的养分循环和CDOM吸收以及AKE内外不同的水质量系统起着重要的作用。NAP [aNAP(443)]、浮游植物[aph(443)]和aCDOM（443）的相对吸收特性表明，CDOM是影响AKE光分布的主要因素。然而，由于春季和秋季浮游植物的大量繁殖和冬季的冰层覆盖，AB区的相对吸收特性存在季节性变化。Secchi椎间盘深度（ZSD）、aNAP（443）和aCDOM（443）之间存在显著相关性。Chl - a浓度和aph（443）不是预测研究区域ZSD的良好指标。这些结果表明，将海水养殖和海草生态系统的固有光学特性和CDOM纳入生态系统模型可以改善在光学复杂的沿海水域中沿淡水-鳗鱼-沿海水域连续体的光分布预测。
Coastal oceans interacting with terrestrial ecosystems play an important role in biogeochemical cycles. It is therefore essential to research land–ocean interactions for further understanding of the processes influencing nutrients dynamics in coastal areas. We investigated the seasonal and spatial distribution of nutrient concentrations and light absorption coefficients of colored dissolved organic matter (CDOM), non-algal particles (NAP), and phytoplankton in a wetland-influenced river–eelgrass meadows–coastal waters continuum in the protected and semi-enclosed coastal sea of Akkeshi-ko estuary (AKE) and Akkeshi Bay (AB), Japan from April 2014 to February 2015. The mixing dilution lines of the CDOM absorption coefficient at 355 nm [aCDOM(355)] relative to salinity predicted by two end-members between freshwater and coastal water showed conservative mixing in AB. Silicate concentrations were significantly correlated with salinity and aCDOM(355) in AB in each month except for December 2014. These results suggest that silicate and CDOM in AB primarily originates from wetland-influenced river discharge. However, samples collected from the eelgrass meadows of AKE, where mariculture is developed, showed non-conservative mixing of silicate concentrations and aCDOM(355) with salinity except for June 2014. Elevated phosphate concentrations, probably released from sediments, were also found in the eelgrass meadows of AKE, especially during summer. These results suggest that the metabolic activities of mariculture and seagrass ecosystem significantly contribute to the nutrient cycles and CDOM absorption in AKE and to the distinct water-mass systems inside and outside AKE. The relative absorption properties of NAP [aNAP(443)], phytoplankton [aph(443)], and aCDOM(443) showed that CDOM is the main factor affecting the light distribution in AKE. However, the relative absorption properties varied seasonally in AB because of spring and autumn phytoplankton blooms and ice cover during winter. Significant relationships were observed between the Secchi disk depth (ZSD), aNAP(443), and aCDOM(443). Chl a concentration and aph(443) were not good indicators for predicting ZSD in our study region. These results suggest that incorporating inherent optical properties and CDOM from mariculture and seagrass ecosystem into ecosystem models could improve predictions of light distribution along the freshwater–eelgrass–coastal waters continuum in optically complex coastal waters.