Studies On The Seasonal And Spatial Distributions Of Biogenic Elements In The Jiaozhou Bay

In recent years, a significant increase in red tides and giant jellyfish blooms hasbeen observed in the Jiaozhou Bay. In addition, the continually increasing dischargeof waste water as well as the rapid enlarging urban construction areas of Qingdao hadcaused a series of environmental problems to the Jiaozhou Bay, drawing growingpublic concerns. In this study, we examined the seasonal and spatial variability on theconcentrations of dissolved and colloidal biogenic elements during a whole yearstarting from May2012to August2013, providing comprehensive scientific basis forthe coastal ecosystem improvement. The main results in the thesis were drawn asfollows:(1) In the surface water of the Jiaozhou bay, NH4-N ranged from anundetectable low value to52.4μmol·L-1with an average of8.03μmol·L-1, whileNO3-N concentrations were0.70to81.8μmol·L-1(averaged in11.5μmol·L-1).Compared with NH4-N and NO3-N, NO2-N was much lower, ranging from anundetectable low value to6.40μmol·L-1with an average of1.36μmol·L-1. DIN wasthe sum of NH4-N, NO3-N and NO2-N, varying from2.30to132.7μmol·L-1(averaged in21.6μmol·L-1). As for PO4-P and SiO3-Si, they were0.10to2.50μmol·L-1(averaged in0.29μmol·L-1), and an undetectable low value to48.3μmol·L-1(averaged in7.04μmol·L-1), respectively.(2) The nutrients concentrations of the surface water inside Jiaozhou bay werehigher than that outside Jiaozhou bay. The concentrations of all dissolved inorganicnutrients in the bay presented a gradually decreasing trend from the inside part to theoutside part of the bay. The high values were mainly found in the near shore area ofthe northeast and northwest part of the bay. The horizontal distributions of nutrientswere largely controlled by their sources. The maximum value of NH4-N was in thenortheast of inner bay, with a high concentration of NH4-N all the year round. Theconcentrations of NO3-N and NO2-N in the northeast and northwest of the inner bay were much higher than that in the mouth and outside of the bay. The maximum valueof PO4-P was found in the northeast of inner bay during the sampling time in2012,April2013and July2013. While during the rest of the sampling time in2013，PO4-Pwere quite low and exhibited a uniform horizontal distribution. The maximum valueof SiO3-Si was mainly in the northeast of the inner bay between May and December2012. The SiO3-Si concentrations were low and showed a uniform horizontaldistribution during the sampling time of2013(except July). Whereas SiO3-Si had amaximum value in the northwest and decreased from northwest to southeast in July2013. In the vertical direction, dissolved inorganic nutrients in the bay have beenmixed uniformly without obvious stratification.(3) Dissolved inorganic nutrients in the surface water of the bay have exhibitednotable seasonal variation effected by terrigenous input. In the inner bay, theconcentrations of NO3-N were higher in the late summer and autumn; while there wasa lower value of NO3-N in spring. In the mouth and outside of the bay, theconcentrations of NO3-N were quite low (except in July,2013). The highconcentrations of NH4-N in the inner bay were found in the late summer and autumnand low in spring. There was no seasonal variation of NH4-N in the mouth and outsideof the bay due to quite low values. The content of NO2-N had increased since summerand reached a high value in autumn, followed by a decrease in winter and had a lowcontent in spring. The concentration of PO4-P in the inner bay was low in winter andspring and high in summer and autumn. There was no seasonal variation in the mouthand outside of the bay. The concentration of SiO3-Si was high in summer and autumnand low in winter and spring with a minimum value in the late winter and thebeginning of spring.(4) In recent years, the composition of dissolved inorganic nitrogen (DIN) hassignificantly changed effected by terrigenous input and zooplankton. The proportionof NO3-N in DIN has increased and became the dominant fraction of DIN, especiallyin the surface water. The proportion of NO2-N in DIN was about10%with a smallvariation. The proportion of nitrogen forms in DIN exhibited obvious seasonalvariability. NH4-N was the main fraction of DIN in spring with the percentage of60% and lowest in winter with30.4%.(5) The proportion of dissolved inorganic nutrients in the bay greatly deviatedfrom the Redfield ratio, especially for the ratio of DIN/P. As a whole, limitation ofPO4-P and moderate nutrition occurred in the bay. The potential eutrophication withthe limitation of PO4-P occurred in the near shore area of the bay.(6) The percentage of ultra-filtered organic carbon (UOC) in the dissolvedorganic carbon (DOC) had increased and UOC accounted for the dominant fraction ofDOC in the bay. The colloidal organic carbon (COC) only accounted for a minorfraction of DOC and had decreased. Dissolved organic phosphorus (DOP) was thedominant fraction of the dissolved total phosphorus (DTP) and accounted nearly ahalf of DTP. The percentages of colloidal organic phosphorus (COP) in DOP andcolloidal organic nitrogen (CON) in DON were low and decreased gradually.