Daily benthic Photosynthetically Active Radiation (PAR) at seagrass sites in Cleveland Bay (NESP TWQ 3.2.1, TropWATER, James Cook University)

This dataset summarises daily integrals of photosynthetically active radiation (PAR) at six sites in Cleveland Bay from March 2017 to October 2018. PAR was measured every 15 minutes (as µmol m-2 s-1), and converted to daily light integrals (mol m-2 d-1).

Seagrasses are dependent on light for photosynthetic carbon fixation, growth and biomass production. Within the Great Barrier Reef, seagrasses occupy sediment-rich banks in relatively shallow water in order access light and where nutrients are abundant to support growth to depths of ~60m. These habitats are at risk from terrestrial discharge and from coastal development. Benthic light is affected by water clarity, water depth and incoming solar radiation. Benthic light levels within seagrass habitat of the GBR follow clear seasonal, but with interannual variability particularly associated with periods of high river discharge.

There has been considerable research into seagrass light requirements, with a focus on short-term (weeks-months) light requirements that resemble typical durations of dredging within ports for channel maintenance and periods of elevated suspended sediment/low light from wet season run-off. Light requirements for the most common species occurring in areas of high risk were used to model sediment load reduction targets for the Reef 2050 WQIP (Brodie et al. 2017). In NESP TWQ project 3.2.1, sediment loads from rivers influencing Cleveland Bay were connected to seagrass condition indicators. Benthic light levels were measured at six sites as a component of project 3.2.1 linking sediment loads to seagrass condition, and to validate spatially explicit benthic light predictions. Light loggers were deployed at six sites within the Bay.

In making this data publicly available for management, the authors from the TropWATER Seagrass Group request being contacted before using this data to ensure it is fully understood.

Methods:
The sampling methods used to measure photosynthetically active radiation (PAR), are described in a number of reports (e.g. Chartrand et al. 2012, Bryant and Tasker 2014, Chartrand et al. 2016). Submersible OdysseyTM photosynthetic irradiance autonomous loggers (light loggers) were deployed with automatic wiper units which clean the optical surface of the sensor every 15 minutes to prevent marine organisms fouling the sensors. At each location, two independent light loggers and wiper units were deployed on the seabed and affixed to a metal stake or a frame. The presence of dual loggers reduces the risk of data loss through unit malfunction, fouling or disturbance during the three months between equipment exchange and download. Odyssey PAR loggers log a cumulative reading at 15-minute intervals, which is calibrated and summed to gain total daily PAR (mol m-2 day-1). The raw data captured by the loggers requires calibrating to a known light value. Sensors were calibrated against a certified reference irradiance sensor (LI-CORTM LI-192SB Underwater Quantum Sensor) in controlled laboratory conditions. A custom-built calibration device held the light loggers a consistent distance from the source light and excluded all external light. Because the light loggers are calibrated in air, a multiplication factor of 1.33 was applied to data to allow for the differences in light absorption properties between air (calibration medium) and water (deployment media). These adjustments were also applied to data during submersion periods based on the tide record (supplied by MSQ) and the depth of each logger. If both loggers were collected free of fouling, then the average value of both loggers was taken as the true value.

Limitations of the data:
Due to tampering with deployed equipment, not all data sets are continuous.

Format:
This dataset consists of one csv file including daily PAR values as mol photons m-2 d-1 for each day and site that data were collected.

References:
Lambert, V. M., K. O’Brien, C. J. Collier, J. Brodie, M. P. Adams, M. Baird, Z. T. Bainbridge, A. Carter, S. Lewis, M. Rasheed and M. Saunders (2020). Connecting Sediment Load Targets to Ecological Outcomes for Seagrass. Report to the National Environmental Science Program. Cairns, Reef and Rainforest Research Centre Limited: 153pp.

Data Location:

This dataset is filed in the eAtlas enduring data repository at: data\NESP3\3.2.1-Eco-load-targests-seagrass

本数据集汇总了2017年3月至2018年10月期间，克利夫兰湾六个站点的光合有效辐射（Photosynthetically Active Radiation, PAR）日积分值。研究以15分钟为间隔测量PAR（单位：μmol·m⁻²·s⁻¹），并将其转换为日光积分（单位：mol·m⁻²·d⁻¹）。

海草依赖光照完成光合碳固定、生长及生物量生产。在大堡礁（Great Barrier Reef, GBR）海域，海草栖息于沉积物富集的浅水区，以获取充足光照与营养物质，其分布水深可达约60米。此类生境面临陆地径流与沿海开发的双重威胁。底栖光照水平受水体透明度、水深及入射太阳辐射调控。大堡礁海草生境的底栖光照呈现显著季节性变化，但同时存在年际变异，尤其与高河流径流量时期密切相关。

现有大量针对海草光照需求的研究，多聚焦于短期（数周至数月）光照需求，此类时长与港口航道维护疏浚的典型周期，以及雨季径流引发的悬浮泥沙升高、光照减弱的时期相符。针对高风险区域常见海草物种的光照需求，被用于为《大堡礁2050水质行动计划（Reef 2050 WQIP）》制定沉积物负荷削减目标（Brodie等，2017）。在NESP TWQ项目3.2.1中，研究人员将影响克利夫兰湾的河流沉积物负荷与海草健康指标建立关联。作为该项目中连接沉积物负荷与海草健康、并验证空间显式底栖光照预测模型的组成部分，研究团队在湾内六个站点部署了光照记录仪，开展底栖光照测量工作。

本数据集面向管理需求公开发布，TropWATER海草研究组的作者恳请使用者在使用数据前先行联系，以确保数据被充分理解与正确应用。

## 采样方法
光合有效辐射（PAR）的测量采样方法已在多篇报告中详述（如Chartrand等，2012；Bryant与Tasker，2014；Chartrand等，2016）。研究使用可水下部署的Odyssey™光合辐照度自主记录仪（光照记录仪），配套自动刮拭装置，每15分钟清洁传感器光学表面，防止海洋生物附着污损。每个测点部署两台独立的光照记录仪与刮拭装置，固定于海底的金属桩或框架上。双记录仪部署可降低设备在设备更换与数据下载间隔的三个月内发生故障、污损或受扰动导致数据丢失的风险。Odyssey PAR记录仪以15分钟为间隔记录累积辐照度读数，经校准后求和得到每日总PAR（单位：mol·m⁻²·d⁻¹）。记录仪采集的原始数据需校准至已知光照标准值。研究人员在受控实验室环境中，使用经认证的参考辐照度传感器（LI-COR™ LI-192SB水下量子传感器）对记录仪进行校准。定制校准装置将光照记录仪固定在距光源恒定距离处，并屏蔽所有外部光线。由于记录仪在空气中完成校准，需乘以1.33的修正系数，以补偿校准介质（空气）与部署介质（海水）之间的光吸收特性差异。基于MSQ提供的潮汐数据与各记录仪的部署水深，针对水下部署时段的数据应用上述修正。若两台记录仪均未发生污损，则取二者平均值作为实测值。

## 数据局限性
由于部署设备曾遭人为干扰，并非所有数据集均为连续完整的。

## 数据格式
本数据集包含一个CSV文件，收录了各采样日期与站点对应的日PAR值，单位为摩尔光子每平方米每天（mol photons·m⁻²·d⁻¹）。

## 参考文献
Lambert, V. M., K. O’Brien, C. J. Collier, J. Brodie, M. P. Adams, M. Baird, Z. T. Bainbridge, A. Carter, S. Lewis, M. Rasheed 与 M. Saunders (2020). 《将沉积物负荷目标与海草生态效益挂钩》。提交给国家环境科学计划的报告。凯恩斯：大堡礁与雨林研究中心有限公司，153页。

## 数据存储位置
本数据集存储于eAtlas永久数据仓库中，路径为：dataNESP33.2.1-Eco-load-targests-seagrass