由于人类活动,沿海海洋的环境发生了变化,富营养化成为全球关注的问题。然而,局部发生寡养并减少鱼类产量。历史上,塞奇深度已被用作初级生产力的指标。我们分析了在相模湾和东京湾进行的超过半个世纪的常规观测的结果,以根据在大东京地区附近的温带沿海地区的Secchi深度观测来验证富营养化/寡营养化趋势,受到人类活动的高度影响。
本研究使用了1963年至2018年在神奈川县记录的数据。质量控制后,观测区被划分为东京湾,浦加海峡(东京湾外部),相模湾(北部),和SagamiNada(SagamiBay的南部)基于10m深度的温度和盐度。由于环境参数显示出自相关,使用带有Prais-Winsten估计器的广义最小二乘(GLS)模型进行时间序列和相关性分析。
Secchi的深度是东京湾最浅的,接下来是Uraga频道,相模湾,和SagamiNada,在冬天(12月和1月)很深,在所有地区的夏季(7月)都很浅。使用GLS模型的相关分析表明,Secchi深度的变浅与温度的降低显着相关。盐度,和磷酸盐浓度。然而,使用GLS模型的时间序列分析表明,Secchi深度明显较浅,除了在东京湾,地表温度显着变暖,表面磷酸盐和亚硝酸盐浓度到处都在下降。在限光季节(1月至3月)主要观察到Secchi深度的显着变浅趋势。
相关分析表明水平对流运输的重要性,特别是来自东京湾,它有寒冷和较少的盐水富营养化水。然而,塞奇深度的长期变浅与变暖有关,当Secchi深度趋势显着时,大多数月份的盐度变化不明显。因此,水平平流不是长期富营养化的主要原因。因为富营养化趋势主要在冬季观察到,当光是初级生产的主要限制因素时,我们得出结论,变暖为浮游植物的生长提供了更好的光环境,并导致富营养化。据报道,调查地区在1990年代后人为营养输入有所下降,长期的富营养化趋势很可能是由于全球变暖引起的,这是人类活动造成的另一个令人震惊的影响。
The coastal ocean\'s environment has changed owing to human activity, with eutrophication becoming a global concern. However, oligotrophication occurs locally and decreases fish production. Historically, the Secchi depth has been used as an index of primary productivity. We analyzed the results of over-a-half-century routine observations conducted in Sagami Bay and Tokyo Bay to verify the eutrophication/oligotrophication trend based on Secchi depth observations in a temperate coastal region near the Greater Tokyo area, which is highly affected by human activities.
Data recorded in the Kanagawa Prefecture from 1963 to 2018 were used in this study. After quality control, the observation area was divided into Tokyo Bay, the Uraga Channel (outer part of Tokyo Bay), Sagami Bay (northern part), and Sagami Nada (southern part of Sagami Bay) based on temperature and salinity at a depth of 10 m. Because the environmental parameters showed autocorrelation, time-series and correlation analyses were conducted using generalized least squares (GLS) models with a Prais-Winsten estimator.
The Secchi depth was the shallowest in Tokyo Bay, followed by the Uraga Channel, Sagami Bay, and Sagami Nada, and was deep in winter (December and January), and shallow in summer (July) in all regions. The correlated analyses using the GLS model indicated that the shallowing of Secchi depth was significantly associated with decreases in temperature, salinity, and phosphate concentration. However, time-series analyses using GLS models indicated that the Secchi depth was significantly shallower, except in Tokyo Bay, where the surface temperature was significantly warming and the surface phosphate and nitrite concentrations decreased everywhere. A significant shallowing trend of the Secchi depth was mostly observed during the light-limiting season (January-March).
Correlation analyses suggested the importance of horizontal advective transport, particularly from Tokyo Bay, which has cold and less saline eutrophic water. However, long-term shallowing of the Secchi depth was associated with warming, and changes in salinity were not significant in most months when the Secchi depth trend was significant. Thus, horizontal advection is not the primary cause of long-term eutrophication. Because the eutrophication trend was primarily observed in winter, when light is the major limiting factor of primary production, we concluded that warming provides a better photoenvironment for phytoplankton growth and induces eutrophication. As a decline in anthropogenic nutrient input after 1990s was reported in the investigated area, the long-term eutrophication trend was most likely caused due to global warming, which is another alarming impact resulting from human activities.