Tidal export of particulate organic matter from Coral Creek, Hinchinbrook Island, north Queensland

Water sampling was carried out at the channel mouth of Coral Creek, Missionary Bay, Hinchinbrook Island to determine the transport and exchange of carbon and nitrogen in particulate organic carbon (POC), the component of particulate organic matter consisting of finely divided materials which range in size from 10 µm to 2 mm. Samples were taken during 13 tidal cycles over a 2-year period. Beginning at low tide, water samples were collected from three depths (surface, mid-depth (4-5 m) and at 0.5 m above the creek bed) at half-hour intervals during the complete 12 hour tidal cycle. Initially, samples were taken at three different points across the channel and later only from a single central station, which was adequate to monitor exchanges.Analysis of POC was carried out using the wet digestion method. On two runs, concurrent samples were filtered through 25-mm GFC filters and analysed with a Perkin Elmer analyser to obtain the C : N ratio of the material and to verify the wet digestion method for POC analysis. Concurrent sampling for ATP and chlorophyll analyses was also carried out on two tidal cycle sampling runs, to obtain information on the character of the particulate matter.During each sampling run, regular measurements of tidal depth at the mouth of the channel were made. The volume of water entering or leaving the basin during any time period was calculated from the tide height measurements and the survey data. The average POC concentration during the same time period was interpolated from the graphs of the average POC (average of the three depths) versus time and the amount of POC passing through the mouth of the creek during that time period was calculated. Summation of the individual fluxes for the entire cycle gives the net import or export of POC for that tidal cycle. To check the accuracy of the calculated volume-time data, a bank of Salvonius-type current meters, with automated data logging, were placed in a 3 X 3 matrix across the channel mouth. These meters measured the current flow every 5 min during a continuous series of tidal cycles for 4 days and the average current was determined as a function of time. This research was undertaken to establish carbon and nitrogen budgets for a mangrove system for which litter fall statistics were available. The mangrove forests surrounding Coral Creek have been extensively surveyed to provide detailed information on topography, and to allow estimation of areas inundated at various tidal heights, and the corresponding volumes of water contained in the basin. Except during infrequent tidal runs greater than 3·2 m, all of the water entering and leaving the basin flows through the mouth of Coral Creek and hence all of the observations of the tidal water were monitored at this point.

本研究于欣钦布鲁克岛传教湾珊瑚溪河道口开展水样采集工作，旨在测定颗粒有机碳（Particulate Organic Carbon，POC）中碳与氮的运移与交换过程——颗粒有机碳是由粒径10μm至2mm的细碎物质组成的颗粒有机质组分。采样工作在为期2年的周期内覆盖13个潮汐周期：采样始于低潮时段，在完整的12小时潮汐周期内，每半小时从表层、中层（4~5米）以及距溪床0.5米处三个深度采集水样。最初在河道的三个不同点位开展采样，后续仅在单个中心站位采样即可满足交换过程监测需求。颗粒有机碳采用湿消解法开展分析。在两次采样运行中，同步使用25mm GFC滤膜过滤样品，并通过珀金埃尔默（Perkin Elmer）分析仪开展分析，以获取物料的碳氮比，并验证湿消解法用于颗粒有机碳分析的可靠性。另有两次潮汐周期采样过程中同步开展了三磷酸腺苷（Adenosine Triphosphate，ATP）与叶绿素（chlorophyll）分析，以获取颗粒物性质相关信息。每次采样运行期间，均定期测量河道口的潮汐水深。基于潮高测量数据与勘测数据，可计算出任意时间段内进出该流域的水体体积。同期平均颗粒有机碳浓度可通过"三个深度的平均颗粒有机碳浓度随时间变化"的曲线插值得到，据此可计算该时段内通过溪口的颗粒有机碳总量。对整个潮汐周期内的各单次通量求和，即可得到该潮汐周期内颗粒有机碳的净输入或输出量。为验证计算得到的体积-时间数据的准确性，将一组搭载自动化数据记录功能的Salvonius型流速计以3×3矩阵布设在河道口：这些仪器在连续4天的多个潮汐周期中每5分钟测量一次流速，进而得到平均流速随时间的变化函数。本研究旨在建立已有枯落物沉降统计数据的红树林生态系统的碳氮收支模型。环绕珊瑚溪的红树林已被全面勘测，以获取详细地形信息，并可估算不同潮汐高度下的淹没区域及流域内相应水体体积。除罕见的潮高超过3.2米的潮汐过程外，所有进出该流域的水流均需经过珊瑚溪河口，因此所有潮汐水体观测均在此点位开展。