Trophic dynamics (Dissolved Inorganic Nitrogen-DIN and Dissolved Inorganic Phosphorus-DIP) in tropical urban estuarine systems during periods of high and low river discharge rates

Abstract: This paper focused on the use of the biogeochemical LOICZ (Land Ocean Interactions in the Coastal Zone) to investigate the dynamics of DIN and DIP nutrients among three highly urbanized tropical estuaries (Barra das Jangadas (BJ), Recife (RE) and Timbó (TB)), located in the northeastern region of Brazil. The input data were obtained through in situ measurements (2007) and governmental agency databases (2001-2007). The balances of the non-conservative elements showed that the RE and TB systems alternated between sources and sinks during the observation periods (0.2-0.8 mmoles DIP m-2 d-1 and 0.1-10 mmoles DIN m-2 d-1). The metabolism rates in the systems indicated that the BJ system was autotrophic during the two observation periods (10-26 mmoles C m-2 d-1), while the RE system was heterotrophic (9-12 mmoles C m-2 d-1). The river discharge rates observed during the period 2001-2007 showed averages ranging from 9.4±3.8 to 18.4±7.7 m3s-1. Measurements of the trophic status in the RE system during 2007 characterized the system as eutrophic, thereby demonstrating high levels of chlorophyll-a and inorganic nutrients. The applications of balance sheets modeling proved to be very useful toward understanding the dynamics of estuarine systems dominated by large urban centers.

摘要：本研究聚焦于运用生物地球化学方法，依托海岸带陆海相互作用（Land Ocean Interactions in the Coastal Zone, LOICZ）模型，对巴西东北部三座高度城市化的热带河口——巴拉达斯雅加达（Barra das Jangadas, BJ）、累西腓（Recife, RE）与廷博（Timbó, TB）——的溶解无机氮（Dissolved Inorganic Nitrogen, DIN）与溶解无机磷（Dissolved Inorganic Phosphorus, DIP）营养盐动力学特征展开探究。本研究的输入数据来源于2007年原位观测结果，以及2001-2007年的政府机构数据库资料。非保守组分收支分析结果显示，观测期内RE与TB河口系统会在源与汇之间动态切换，其通量范围分别为0.2~0.8毫摩尔DIP·m⁻²·d⁻¹与0.1~10毫摩尔DIN·m⁻²·d⁻¹。系统代谢速率分析表明，BJ河口系统在两次观测周期内均呈自养状态，碳代谢通量区间为10~26毫摩尔碳·m⁻²·d⁻¹；而RE河口系统则呈异养状态，碳代谢通量区间为9~12毫摩尔碳·m⁻²·d⁻¹。2001-2007年观测得到的径流量数据显示，其平均值范围为9.4±3.8至18.4±7.7 立方米·秒⁻¹。2007年对RE河口系统营养状态的测定结果表明，该系统处于富营养化状态，叶绿素a与无机营养盐含量均处于较高水平。收支模型的应用证实，其对于解析大型城市主导的河口系统动力学特征具有重要应用价值。