| Manganese belongs to the trace metal in the ocean, mainly derives from the fluvial input, atmospheric deposition and sediment re-mineralization. Manganese can be used as the tracer of terrestrial input and mixing of different water masses. In addition, manganese is well known to be one of the essential micronutrients for biological growth, playing a key role as enzymatic cofactors in cell metabolism, e.g. N2 fixation, nitrate assimilation and photosynthesis. Manganese can be released into the seawater through physical or chemical processes, such as biological metabolism, degradation, during the settlement of particles. The biogeochemical cycle of manganese has important influence on biogeochemical cycles of carbon, nitrogen and other micronutrients. Therefore, the study of marine biogeochemical cycle of manganese attracts more and more attention of scientists all over the world these years. The Sanggou Bay is a semi-enclosed basin and open to the Yellow Sea, which is one of the most important aquaculture basements in Northern China. The Sanggou Bay is the ideal place to study the source, sink and influence of biological activities in the continental shelf region. The knowledge of biogeochemical cycles of manganese in the Sanggou Bay can help scientist to deeply understand its behavior in the ocean.The measurement methods for organic bound manganese (DOMn) by UV-digestion technique and manganese in surface sediment by two-step extraction were established in the laboratory. The precision for Geochemical Standard Reference Sample Drainage Sediment (GSD-9) analysis were 3.0% for acetic acid extraction (HAc-Mn) and 4.3% for total manganese (TMns). There was no significant difference with the certified value (P=0.95, n=7).The recovery is 99.9%. DOMn was decomposed using UV254 irradiation with an addition of hydrogen peroxide (25 μL of 30% H2O2 per 10 ml of sample) at pH= 2 for 2 h. The precision for EDTA-Mn solution analysis is better than 5%. The recovery ranges from 93.5%～95.2%.Eight cruises were carried out in 2011 and 2013 in the Sanggou Bay. Concentrations of DOMn were just measured for four cruises in 2013. The concentrations of DIMn were measured by the catalytic-kinetic spectrophotometric (NaIO4-LMG). The concentrations of DIMn in 2011-2012 ranged from 12.5-579.3 nmol/L in April,19.1-182.9 nmol/L in August,8.9～49.4 nmol/L in October and 5.4-56.0 nmol/L in January, with the annual average of 63.4 nmol/L ±71.8 nmol/L. There exists significant seasonal variation for concentrations of DIMn during the investigations (t-test, p< 0.05, n=19), with higher concentrations occurred in spring and summer than that in autumn and winter. The concentrations of DIMn in 2013-2014 ranged from 10.7～163.1 nmol/L in April,8.6～208.3 nmol/L in July,7.8 ～42.9 nmol/L in October and 3.2～38.9 nmol/L in January, with the annual average of 36.0 nmol/L±22.2 nmol/L. Similarlly, there exists significant seasonal variation for concentrations of DIMn during the investigations (t-test, p< 0.05, n=19), with higher concentrations occurred in spring and summer than that in autumn and winter. The distributions of DIMn in the study area were similar, with high concentrations always being found in the estuary and decreased from nearshore to the coastal area. Except abnormally high value in April 2011, there is no significant interannual variation for DIMn between other seasons in 2011 and 2013 (t-test, p<0.05, n=19). The negative relationship between the diurnal variation of DIMn and tide was found in the anchor stations of the Sanggou Bay in April. The concentrations of DIMn in the Sanggou Bay were higher than the Ailian Bay and the Lidao Bay in spring and summer, no significant variation in autumn and winter (t-test, p< 0.10, n=19).The concentrations of DOMn in 2013-2014 ranged from 2.0～24.2 nmol/L in April,1.5～73.8 nmol/L in July,0.2～8.8 nmol/L in October,1.3～15.3 nmol/L in January, with the annual average of 9.0 nmol/L ± 4.9 nmol/L. There exists significant seasonal variation for concentrations of DOMn during the investigations (t-test, p< 0.05, n=19), with higher concentrations occurred in spring and summer than that in autumn and winter. The distributions of DOMn decreased from nearshore to the coastal area. The concentrations of total dissolved manganese (TDMn) in 2013-2014 ranged from 16.6～177.0 nmol/L in April,11.7～276.0 nmol/L in July,9.0～44.4 nmol/L in October,4.5～50.7 nmol/L nmol/L in January, with the annual average of 45.1 nmol/L ± 25.5 nmol/L. There exists significant seasonal variation for concentrations of TDMn during the investigations (t-test, p< 0.05, n=19), with higher concentrations occurred in spring and summer than that in autumn and winter. The distributions of TDMn decreased from nearshore to the coastal area, with more significant concentration gradient change during spring and summer.The concentrations of TMns in surface sediments in 2011-2012 ranged from 363-1507 mg/kg in April,392-1742 mg/kg in August,474-760 mg/kg in October and 487～801 mg/kg in January, with the annual average of 754 mg/kg ±158 mg/kg. There exists significant seasonal variation for concentrations of TMns in surface sediments during the investigations (t-test, p< 0.05, n=8), with higher concentrations occurred in spring and summer than that in autumn and winter. The concentrations of TMns in surface sediments in 2013-2014 ranged from 527 ± 1178 mg/kg in April, 326-866 mg/kg in October and 530～739 mg/kg in January, with the annual average of 710 mg/kg ± 149 mg/kg. There exists significant seasonal variation for concentrations of TMns in surface sediments during the investigations (t-test, p< 0.05, n=8), with higher concentrations occurred in spring than that in autumn and winter. There is no significant interannual variation for TMns in surface sediments in 2011 and 2013 (t-test, p< 0.05, n=8). The concentrations of HAc-Mn in surface sediments in 2011-2012 ranged from 297～1129 mg/kg in April,177～1108 mg/kg in August, 238～450 mg/kg in October and 219～552 mg/kg in January, with the annual average of 417 mg/kg ± 97 mg/kg. There exists significant seasonal variation for concentrations of HAc-Mn in surface sediments during the investigations (t-test, p< 0.05, n=8), with higher concentrations occurred in spring and summer than that in autumn and winter. The concentrations of HAc-Mn in surface sediments in 2013-2014 ranged from 226～591 mg/kg in April,153～457 mg/kg in October and 213～ 349 mg/kg in January, with the annual average of 377 mg/kg ±115 mg/kg. There exists significant seasonal variation for concentrations of HAc-Mn in surface sediments during the investigations (t-test, p< 0.05, n=8), with higher concentrations occurred in spring than that in autumn and winter. There is no significant interannual variation for HAc-Mn in surface sediments in 2011 and 2013(t-test, p< 0.05, n=8). Seasonal variation for concentrations of manganese in surface sediments has a close relationship with biological culturing period and water power of the Sanggou Bay.The main sources of DIMn include riverine and groundwater, atmospheric wet or dry deposition and release from the sediment-water interface. Input to Yellow Sea and scavenging by biological activities may be the major sinks. The residence time (20 d ± 13 d) of DIMn in the Sanggou Bay is much lower than that in openocean. The special hydrological and aquacultural environment may be the reason for this phenomenon in the Sanggou Bay. |
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