Marine nutrient subsidies promote biogeochemical hotspots in undisturbed, highly humic estuaries
Marine nutrient subsidies promote biogeochemical hotspots in undisturbed, highly humic estuaries
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DOI：
10.1002/lno.12387
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发表时间：
2023-06-13
影响因子：
4.5
通讯作者：
Mayor，Daniel J.
中科院分区：
文献类型：
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作者：
Evans，Chris D.;Felgate，Stacey L.;Mayor，Daniel J.
陆地-海洋溶解有机碳（DOC）通量在全球碳收支中是一个重要的术语，泥炭地占主导地位的地区是陆地DOC输出最强烈的来源。作为淡水和海洋系统之间的界面，河口有可能充当陆地-海洋碳通量的过滤器，通过物理化学和生物过程的结合，去除海洋中低浓度的陆源DOC。然而，河口泥炭源DOC的命运仍然缺乏量化，部分原因是异质性土壤、土地利用、点源和上游有机质改性的复杂影响。为了尽量减少这些修饰因素，我们研究了四个小的、泥炭为主的、最小干扰的、少营养的福克兰群岛河口的DOC和无机营养物质。与预期相反，我们发现物理化学去除河口DOC的证据有限，相反，我们观察到明显的生物地球化学活动“热区”，在那里，陆地衍生的硅酸盐与无机氮和磷混合从营养丰富的海洋生态系统进入河口。在两个河口，这与明显的原位DOC产量相吻合。我们认为，观测到的海洋营养补贴河口生产力的现象，以及在低营养系统内多种营养物质的灵活利用，可能曾经在温带河口广泛存在。然而，由于农业和城市发展造成的流域富营养化，这一功能在许多生态系统中已经丧失。我们得出结论，福克兰群岛的河口为温带河口接收高有机质输入的自然生物地球化学功能提供了有价值的干扰前模拟。
The land‐ocean dissolved organic carbon (DOC) flux represents a significant term within the global carbon budget, with peatland‐dominated regions representing the most intense sources of terrestrial DOC export. As the interface between freshwater and marine systems, estuaries have the potential to act as a filter of the land‐ocean carbon flux, removing terrestrially derived DOC, which is present at low concentrations in the oceans, via a combination of physicochemical and biological processes. However, the fate of peat‐derived DOC within estuaries remains poorly quantified, partly due to the complicating influences of heterogeneous soils, land‐use, point sources, and upstream modification of organic matter. To minimize these modifying factors, we studied DOC and inorganic nutrients in four small, peat‐dominated, minimally disturbed, and oligotrophic Falkland Island estuaries. Contrary to expectations, we found limited evidence of physicochemical estuarine DOC removal, and instead observed apparent “hot zones” of biogeochemical activity, where terrestrially‐derived silicate mixed with inorganic nitrogen and phosphorus entering the estuaries from the nutrient‐rich marine ecosystem. In two estuaries, this coincided with apparent in situ DOC production. We suggest that the observed phenomena of marine nutrient subsidy of estuarine productivity, and flexible utilization of multiple nutrients within the oligotrophic system, may once have been widespread in temperate estuaries. However, this function has been lost in many ecosystems due to catchment eutrophication by agricultural and urban development. We conclude that the estuaries of the Falkland Islands provide a valuable pre‐disturbance analogue for natural biogeochemical functioning in temperate estuaries receiving high organic matter inputs.