本研究在实验室条件下对2017年夏季（8月）和秋季（11月）采集于牟平海洋牧场及其邻近海域6个站位的表层沉积物样品进行了模拟培养，测定了沉积物-水界面NO₂-N、NO₃-N、NH₄-N、PO₄-P、SiO₃-Si的交换通量，估算了其对上覆水初级生产力的贡献，分析探讨了沉积物-水界面各营养盐交换通量的影响因素，获得如下结果和认识：

    （1）夏季NO₂-N（S8站除外）、NH₄-N、PO₄-P和SiO₃-Si均由沉积物向上覆水释放，NO₃-N则相反；秋季沉积物对NO₃-N（S4站除外）、NH₄-N和PO₄-P表现为汇，对SiO₃-Si表现为源，对NO₂-N而言则有的表现为源有的表现为汇，但整体上为NO₂-N的源。夏季沉积物-水界面NO₂-N、NO₃-N、NH₄-N、PO₄-P和SiO₃-Si的交换通量分别为-7.0 ~ 13.0（平均值为5.7±7.0）、-173.8 ~ -318.6（平均值为-236.0±44.6）、215.6 ~ 347.0（平均值为265.2±45.7）、20.8 ~ 97.4（平均值为59.7±26.5）和922.8 ~ 1435.1（平均值为1154.3±177.1）μmol/(m² d)；秋季NO₂-N、NO₃-N、NH₄-N、PO₄-P和SiO₃-Si交换通量分别为-13.7 ~ 15.6（平均值为1.0±13.2）、-303.6 ~ 34.3（平均值为-182.0±111.8）、-172.3 ~ -356.0（平均值为-268.4±67.5）、-21.5 ~ -51.4（平均值为-45.7±10.1）和802.7 ~ 1219.0（平均值为1013.6±142.9）μmol/(m² d)。

    夏季沉积物-水界面溶解无机氮（DIN；[DIN] = [NO₂-N] + [NO₃-N] + [NH₄-N]）交换通量仅可提供(0.1 ~ 1.0)%（平均值为(0.4±0.3)%）的上覆水体初级生产力需求；PO₄-P和SiO₃-Si通量可分别提供(3.3 ~ 15.6)%（平均值为(9.5±4.2)%）、(9.2 ~ 14.4)%（平均值为(11.5±1.8)%）的上覆水体初级生产力需求。秋季沉积物是DIN和PO₄-P的汇，因此对上覆水体初级生产力无促进作用；沉积物释放的SiO₃-Si可提供初级生产力需求的(11.6 ~ 17.7)%（平均值为(14.9±2.1)%）。

   （2）无机氮的交换通量主要受扩散过程及硝化、反硝化作用的控制。NO₂-N与所研究的各个参数的关系不明显。夏季沉积物颗粒越细、TOC含量越高、沉积物含水率越高，越利于NO₃-N和NH₄-N的交换。上覆水盐度、pH、沉积物C/N等对各形态DIN的通量整体影响程度不大。夏季沉积物TN含量越高、间隙水NH₄-N浓度越大，NH₄-N交换通量越大。夏季NO₃-N交换通量与间隙水NO₃-N浓度、秋季NO₃-N通量与上覆水NH₄-N浓度均呈现负相关关系。沉积物间隙水及上覆水中无机氮的浓度梯度可能是控制DIN扩散的关键因素。

    采用连续浸取法对各站位表层沉积物中P的地球化学形态进行了分析，结果表明：夏季各形态P的含量顺序为碎屑磷（De-P）> 自生钙结合态磷（ACa-P）> 有机磷（OP）> 铁结合态磷（Fe-P）> 可交换与弱结合磷（Ex-P），秋季为De-P > ACa-P > Fe-P > OP > Ex-P。沉积物中含量较多的P形态为De-P和ACa-P。Ex-P和Fe-P影响上覆水及沉积物之间PO₄-P的交换，尤其是Fe-P可通过吸附-解吸过程影响PO₄-P的交换通量。夏季OP的净含量较大可能与较高的初级生产力有关，而占TP比例相对较小的原因可能是相对较快的分解速率。PO₄-P交换通量与个别站位细颗粒沉积物、含水率、有机质含量、间隙水PO₄-P浓度有一定的正相关性，盐度和pH对PO₄-P交换的影响不明显。该海域沉积物-水界面PO₄-P的扩散过程对于PO₄-P交换通量的影响可能不及吸附-解吸过程。

    对于该海域沉积物-水界面SiO₃-Si的交换通量而言，所研究的各个参数对其影响均不明显，仅粘土含量及上覆水、间隙水中SiO₃-Si浓度与其呈一定相关性，TOC、盐度、pH与SiO₃-Si通量之间的相关性更弱，说明单因素变化对沉积物-水界面SiO₃-Si交换通量的影响较小，推测生源硅的沉淀-溶解过程可能发挥着较大作用。

    （3）通过改变培养体系的温度（T = 10和20 °C）和溶解氧（DO）浓度（贫氧：DO < 2 mg/L、富氧：DO > 8 mg/L），考察了二者对营养盐交换通量的影响。

    温度变化对NO₂-N的交换通量影响情况比较复杂，而对NO₃-N和NH₄-N均表现为温度高，交换通量大。溶解氧浓度变化改变了沉积物-水界面氧化还原电位，进而影响了硝化、反硝化过程。对于NO₂-N交换的影响未体现一定的规律。贫氧条件下间隙水中NO₃-N浓度减小，NH₄-N浓度增大，在夏季利于NO₃-N和NH₄-N的迁移，在秋季则利于NO₃-N的迁移而不利于NH₄-N的交换。

    对于夏季采集的沉积物，升温有利于PO₄-P向水体释放，而对于秋季沉积物则不利于PO₄-P从上覆水迁出，其迁移受到分子热运动及金属结合态P的吸附-解吸过程双重控制。夏季贫氧环境下PO₄-P的释放速率更快，秋季反之，且其迁移方向甚至发生了转变，说明溶解氧浓度对PO₄-P交换的影响可能与铁锰氧化物与P的吸附-解吸过程有关。

    相比于低温（T = 10 °C），高温条件（T = 20 °C）对沉积物-水界面SiO₃-Si的释放起促进作用。温度升高一方面使间隙水中溶解态Si的扩散速率增大，另一方面加快了沉积物中颗粒态Si的溶解过程，使其转化为SiO₃-Si。溶解氧变化对SiO₃-Si交换通量的影响效果不明显，无论是贫氧还是富氧环境，夏秋两季沉积物-水界面SiO₃-Si交换通量的变化均较小。

    In this research, the exchange fluxes of NO₂-N, NO₃-N, NH₄-N, PO₄-P and SiO₃-Si across the sediment-water interface were measured by a laboratory incubation method on the surface sediment samples collected from 6 sites in the Muping Marine Ranch and its adjacent area in summer (August) and autumn (November) 2017. The key environmental factors that could influence the nutrient fluxes across the sediment-water interface were analyzed and discussed. The results and understanding were as follows:

    (1) NO₂-N (except for Station S8), NH₄-N, PO₄-P and SiO₃-Si were released from sediments to overlying water in summer, while NO₃-N was the opposite. In autumn, sediments acted as a sink of NO₃-N (except for Station S4), NH₄-N and PO₄-P, but a source of SiO₃-Si. For NO₂-N, some sediments acted as a sink while the others were a source, but as a whole they acted as a source of NO₂-N. In summer, the exchange fluxes of NO₂-N, NO₃-N, NH₄-N, PO₄-P and SiO₃-Si across the sediment-water interface were -7.0 ~ 13.0, -173.8 ~ -318.6, 215.6 ~ 347.0, 20.8 ~ 97.4, 922.8 ~ 1435.1 μmol/(m² d) with the average values of 5.7±7.0, -236.0±44.6, 265.2±45.7, 59.7±26.5, 1154.3±177.1 μmol/(m² d), respectively. In autumn, the corresponding exchange fluxes were -13.7 ~ 15.6, -303.6 ~ 34.3, -172.3 ~ -356.0, -21.5 ~ -51.4, 802.7 ~ 1219.0 μmol/(m² d) with the average values of 1.0±13.2, -182.0±111.8, -268.4±67.5, -45.7±10.1, 1013.6±142.9 μmol/(m² d), respectively.

    In summer, the exchange fluxes of dissolved inorganic nitrogen (DIN; [DIN] = [NO₂-N] + [NO₃-N] + [NH₄-N]) could provide only (0.1 ~ 1.0)% of primary productivity of overlying water, with the average value of (0.4±0.3)%. PO₄-P and SiO₃-Si could provide (3.3 ~ 15.6)% and (9.2 ~ 14.4)% of primary productivity, with the average value of (9.5±4.2)% and (11.5±1.8)%, respectively. In autumn, sediments acted as sink of DIN and PO₄-P, so theirs fluxes could not contribute to the primary productivity of overlying water. Fluxes of SiO₃-Si could provide (11.6 ~ 17.7)% of primary productivity，with the average value of (14.9±2.1)%.

    (2) The exchange fluxes of inorganic nitrogen were mainly controlled by diffusion process, nitrification and denitrification process. The influences of each environmental factors on the exchange fluxes of NO₂-N were not obvious. The tinier sediment particles, the more TOC contents, and the higher moisture contents in sediments resulted in higher exchange fluxes of NO₃-N and NH₄-N. Salinity and pH of overlying water and C/N ratio of sediments had little effect on the fluxes of DIN. In Summer, the more TN contents, the higher NH₄-N concentrations in interstitial water brought about higher exchange fluxes of NH₄-N. In summer, there was a negative correlation between NO₃-N exchange fluxes and NO₃-N concentrations in interstitial water. In autumn, it also had a negative correlation between NO₃-N exchange fluxes and NH₄-N concentrations in overlying water. These phenomena indicated that the concentration gradients of inorganic nitrogen in interstitial and overlying water may be the key factor to the diffusion of DIN.

    The geochemical forms of P in surface sediments were extracted by a sequential extraction method. And the contents of varied forms of P changed with the season: De-P > ACa-P > OP > Fe-P > Ex-P in summer, and De-P > ACa-P > Fe-P > OP > Ex-P in autumn. De-P and ACa-P were the most abundant forms of P in surface sediments. Ex-P and Fe-P affected the exchange fluxes of PO₄-P, especially for Fe-P, which affected the fluxes through the adsorption-desorption process. The higher net OP contents in summer may be related to higher primary productivity, and the smaller proportions may be due to the relatively vigorous mineralization and disslotion rates. Tinier sediment particles at individual stations, moisture contents, organic matter contents, PO₄-P concentrations in interstitial water had a certain positive correlation with the fluxes of PO₄-P, but the effects of salinity and pH on the fluxes were not obvious. The diffusion process may have less effect than the adsorption-desorption process on the exchange fluxes of PO₄-P.

    The influences of each environmental factors on the exchange fluxes of SiO₃-Si in this area were not obvious. The correlations were only found with the contents of clay and the concentrations of SiO₃-Si in overlying and interstitial water. There was a worse correlation between another factors (TOC, salinity, and pH) and fluxes of SiO₃-Si. It indicated that the change of single factor has less effect on the exchange fluxes of SiO₃-Si, and the precipitation-dissolution process of biogenic silica may play an important role.

    (3) The effects of temperature and dissolved oxygen concentrations on exchange fluxes were discussed by setting the temperature to T = 10 and 20 °C, the dissolved oxygen (DO) concentrations to anoxic (DO < 2 mg/L), and aerobic (DO > 8 mg/L) conditions.

     The influences of temperature change on fluxes of NO₂-N were complex. High temperature led to high exchange fluxes of NO₃-N and NH₄-N. The variation of DO concentrations changed the oxidation-reduction potential across the sediment-water interface, which affected the nitrification and denitrification process. The effects of DO concentrations changes on NO₂-N fluxes did not reflect certain rules. In anoxic conditions, the concentrations of NO₃-N in the interstitial water decreased, and the concentrations of NH₄-N in the interstitial water increased, which were beneficial to the migration of NO₃-N and NH₄-N in summer, conducive to the migration of NO₃-N but not to the exchange of NH₄-N in autumn.

    In summer, high temperature promoted the release of PO₄-P from sediment to water. However, the high temperature was not conducive to the migration of PO₄-P in autumn. Its migration was controlled by both molecular thermal movements and adsorption-desorption of metal-bound P. In summer, the release rates of PO₄-P were faster in anoxic conditions. While in autumn was the opposite, the migration direction even changed under anoxic conditions. The phenomena demonstrated that the concentrations of DO may affectd the adsorption-desorption process of iron-manganese oxides with P.

    Compared with low temperature (T = 10 °C), high temperature (T = 20 °C) promoted to the exchange of SiO₃-Si. It not only increased the diffusion rate of dissolved Si from interstitial water to overlying water, but also accelerated the dissolution process of particulate Si. Those processes would produce more SiO₃-Si. The effect of DO changes on fluxes of SiO₃-Si were not obvious in anoxic and aerobic conditions, and the changes of SiO₃-Si fluxes across the sediment-water interface were tiny.