Purpose

Measuring environmental capacity of total nitrogen (TN) in marine water has become an effective indicator of how much TN is entering the ocean from various sources. However, the TN environmental capacity balance is affected not only by external input but also by removal of TN from water. This removal occurs by numerous mechanisms, among which sedimentation is one that should not be ignored.

Materials and methods

The influence of sedimentation rates on the environmental capacity of TN in the water body in the northern area of Bohai Bay was studied by investigating the total nitrogen contents of both water and sediments independently. The radioactivity of lead and cesium isotopes (i.e., ²¹⁰Pb and ¹³⁷Cs) that were present in columnar sediment samples was measured for time periods ranging from 48 to 72 h using a high-purity germanium detector. A constant rate of supply model (CRS) was used to calculate sedimentation rates.

Results and discussion

The results indicate that 5.81 × 10⁶ t of sediment are removed from the water column annually through precipitation. Based on the concentration of TN in the studied sediment samples, we calculate that a total of 3.34 × 10³ t of nitrogen are removed from the water via sedimentation every year. According to the target TN concentrations for the marine environment that were adopted for the study area for 2025 and 2030, the amount of TN removed from water by sedimentation could remove 62.08% and 64.85%, respectively, of the TN introduced to the marine environment by allowable amounts of anthropogenic discharge into the northern area of Bohai Bay in 2025 and 2030.

Conclusions

The high sedimentation rate in Bohai Bay can be expected to remove half of all nitrogen currently entering the water in this area. This demonstrates that when the environmental capacity of TN in ocean water is used to determine the total amount of nitrogen that can be permissibly discharged from land sources, the capacity of the environment to “self-purify” via sedimentation should be considered.

中文翻译：

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沉积速率对渤海湾水中总氮环境容量的影响

目的

测量海水中总氮（TN）的环境容量已经成为衡量有多少总氮从各种来源进入海洋的有效指标。但是，总氮环境容量的平衡不仅受外部输入的影响，而且还受水中总氮去除的影响。这种清除是通过多种机制发生的，其中沉淀是不容忽视的一种机制。

材料和方法

通过独立研究水和沉积物的总氮含量，研究了沉积速率对渤海湾北部地区水体总氮环境容量的影响。使用高纯度锗检测器测量了柱状沉积物样品中存在的铅和铯同位素（即²¹⁰ Pb和¹³⁷ Cs）的放射性，时间范围为48至72 h。恒定供水率模型（CRS）用于计算沉降率。

结果和讨论

结果表明，每年通过降水将5.81×10 ⁶ t的沉积物从水柱中去除。根据研究的沉积物样品中TN的浓度，我们计算出每年通过沉淀从水中去除的氮总量为3.34×10 ³ t。根据研究区域在2025年和2030年采用的海洋环境目标TN浓度目标，通过沉降从水中去除的TN量可以分别去除62.08％和64.85％的氮。 2025年和2030年允许的人为排放量到渤海湾北部地区。

结论

预计渤海湾的高沉积率将清除目前进入该地区水域的所有氮的一半。这表明，当使用总氮在海水中的环境容量来确定可以从陆地源排放的氮总量时，应考虑环境通过沉降“自净”的能力。