Laboratório de Pesquisa em Monitoramento Ambiental Marinho (LAPMAR), Universidade Federal do Pará, Belém, PA, Brazil.
Laboratório de Oceanografia Física Estuarina e Costeira (LOFEC), Departamento de Oceanografia da Universidade Federal de Pernambuco (DOCEAN/UFPE), Recife, PE, Brazil; Brazilian Research network on Global Climate Change (Rede CLIMA), São José dos Campos, SP, Brazil.
Sci Total Environ. 2022 Dec 20;853:158432. doi: 10.1016/j.scitotenv.2022.158432. Epub 2022 Aug 31.
The Amazon Continental Shelf (ACS) has a coastline of ∼1000 km and is situated in a humid equatorial region with two distinct seasons, wet and dry, and two transitional climatic periods. A total of eight oceanographic cruises were conducted to investigate the dynamics of the inorganic nutrients dissolved in the surface layer of the water column of the ACS and their associations with Sargassum blooms. An excess of nitrogen-N* (NH = 0.01-9.30 μmol l) was verified through the salinity gradient from the continent to the ACS, mainly during the period of maximum discharge of the Amazon and Tocantins-Pará rivers. The highest NH concentrations coincided with the occurrence of macrophyte (Sargassum sp.) blooms in the mesohaline and oceanic regions. During this period the high values of NH accompany the low values of Sea Surface Salinity (SSS), indicating the advection of the Amazonian plume towards the Caribbean Sea. In the Sargassum belts we observed a N:P ratio = 60:1 during wet period, while outside this region, the N:P ratio was 34:1. According to DIN vs. AOU ratio, we observed that heterotrophic processes prevail over productive processes, mainly in the mesohaline and low salinity regions. Nitrogen concentrations from runoff, mainly from hydrographic basins, showed significant increases in the last decade, mainly due to anthropogenic factors such as agriculture, deforestation, livestock, urban sewage (domestic and industrial), and demographic growth of the population in the Tocantins-Pará Basin. Additionally, associations of diatoms and cyanobacteria provide more nitrogen in the mesohaline and oceanic regions that nourishes Sargassum blooms. Seasonal comparisons (October and April) of Sargassum belts with other studies, indicated that currents play a fundamental role in the transport of these macrophytes from the east edge (Africa) to the west edge (Brazil and French Guiana) towards the Caribbean Sea in the tropical Atlantic.
亚马逊大陆架（ACS）拥有约 1000 公里的海岸线，地处湿润的赤道地区，具有明显的干湿两季和两个过渡性气候期。共进行了 8 次海洋学考察，以研究 ACS 水柱表层溶解无机物营养元素的动力学及其与马尾藻海草床爆发的关系。通过从大陆到 ACS 的盐度梯度，验证了氮素的过剩（N*：NH=0.01-9.30μmol/L），主要是在亚马逊河和托坎廷斯-帕拉河的最大径流量时期。NH 的最高浓度与中盐度和海洋区域大型海藻（马尾藻属）爆发同时出现。在此期间，高 NH 值伴随着低海面盐度（SSS），表明亚马逊羽流向加勒比海的输送。在马尾藻带，我们在雨季观察到 N:P 比值=60:1，而在该区域之外，N:P 比值为 34:1。根据 DIN 与 AOU 比值，我们观察到，异养过程主要在中盐度和低盐度区域超过了生产过程。主要来自流域的径流水（主要来自水文盆地）的氮浓度在过去十年中显著增加，主要是由于农业、森林砍伐、畜牧业、城市污水（生活和工业）和托坎廷斯-帕拉流域人口增长等人为因素造成的。此外，硅藻和蓝藻的共生关系为中盐度和海洋区域提供了更多的氮，滋养了马尾藻海草床的生长。与其他研究的季节性比较（10 月和 4 月）表明，海流在这些大型藻类从东边缘（非洲）向西边缘（巴西和法属圭亚那）向热带大西洋的加勒比海的运输中起着至关重要的作用。
