Climatology and seasonal variability of satellite-derived chlorophyll a around the Shandong Peninsula

The chlorophyll a(Chl a)is an important indicator of marine ecosystems.The spatiotemporal variation of the Chl a greatly aff ects the mariculture and marine ranching in coastal waters of the Shandong Peninsula.In the current study,the climatology and seasonal variability of surface Chl-a concentration around the Shandong Peninsula are investigated based on 16 years(December 2002-November 2018)of satellite observations.The results indicate that the annual mean Chl-a concentration is greater in the Bohai Sea than in the Yellow Sea and decreases from coastal waters to off shore waters.The highest Chl-a concentrations are found in Laizhou Bay(4.2-8.0 mg/m^(3)),Haizhou Bay(4.2-5.9 mg/m^(3))and the northeast coast of the Shandong Peninsula(4.4-5.0 mg/m^(3)),resulting from the combined eff ects of the intense riverine input and long residence time caused by the concave shape of the coastline.The seasonal Chl-a concentration shows a significant spatial variation.The Chl-a concentrations in these three subregions generally exhibit an annual maximum in August/September,due to the combined eff ects of sea surface temperature,river discharge and sea surface wind.In the southeast coast region,however,the Chl-a concentration is lowest throughout the year and reaches a maximum in February with a minimum in July,forced by the seasonal evolution of the Yellow Sea Cold Water and monsoon winds.The interannual Chl-a concentration trends vary among regions and seasons.There are significant increasing trends over a large area around Haizhou Bay from winter to summer,which are mainly caused by the rising sea surface temperature and eutrophication.In other coastal areas,the Chl-a concentration shows decreasing trends,which are clearest in summer and induced by the weakening land rainfall.This study highlights the differences in the Chl-a dynamics among regions around the Shandong Peninsula and is helpful for further studies of coupled physical-ecological-human interactions at multiple scales.

The influence of water-sediment regulation on macrobenthic community structures in the Huanghe River(Yellow River)Estuary during 2012–2016

To determine if water-sediment regulation has affected macrobenthic community structure in the Huanghe River Estuary,China,macrobenthic samples were collected following regulation events from 2012 to 2016.We identify seven phyla and 138 macrobenthic species from within samples throughout the survey area,over time.Species richness and abundance in 2012 were significantly higher than in 2016.Biomass did not differ significantly during 2012–2016.Dominant species were mostly small polychaetes,with mollusks,arthropods,and echinoderms all being relatively rare.In 2016,dominant species were small polychaetes.MDS reveals macrobenthic communities at all surveyed distances from the estuary to have become the same community structure over time.Shannon-Wiener diversity and Margalef richness indexes trended down over time.CCA reveals the most dominant sediment-dwelling species to prefer lower dissolved oxygen,sulfides,and pH,and sediments with high D50 and low clay content.We speculate that water-sediment regulation has affected seabed communities,particularly Region A in our survey area.

Distribution and invasion of Spartina alterniflora within the Jiaozhou Bay monitored by remote sensing image

Spartina alterniflora as an alien invasive plant,poses a serious threat to the ecological functions of the coastal wetland of the Jiaozhou Bay.As of 2019,the distribution area of S.alterniflora in the Jiaozhou Bay has reached more than 500 hm^(2).For this reason,combined with field surveys,remote sensing monitoring of the invasion S.alterniflora in the Jiaozhou Bay has been carried out.To accurately identify S.alterniflora within the Jiaozhou Bay coastal wetland,we used a new method which is an implement of deep convolutional neural network,and by which we got a higher accuracy than the traditional method.Based on distribution of S.alterniflora extracted by the proposed method,the temporal and spatial distribution characteristics of S.alterniflora were analyzed.And then combined with environmental factors,the invasion mechanism of S.alterniflora in the Jiaozhou Bay was analyzed in detail.From the monitoring results,it can be seen that S.alterniflora in Jiaozhou Bay is mainly distributed in the beaches near the Yanghe River Estuary and its southern side,the Dagu River Estuary and the Nügukou.Spartina alterniflora first broke out near the Yanghe River Estuary and gradually spread to the tidal flats near the Nügukou.The Dagu River Estuary is dominated by S.anglica,whose area has not changed much over the years,and a small amount of S.alterniflora has invaded later.