Lemley Daniel A, Adams Janine B, Taljaard Susan
Botany Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa.
Botany Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa.
Mar Pollut Bull. 2017 Apr 15;117(1-2):136-147. doi: 10.1016/j.marpolbul.2017.01.059. Epub 2017 Feb 1.
This study compared the spatio-temporal dynamics in two agriculturally-influenced South African estuaries - Gamtoos and Sundays - to investigate how contrasting hydrological alterations influence physical, chemical and biological responses. With the Gamtoos Estuary experiencing regular high flow conditions, a key difference between the two systems is the propensity for natural flushing events to occur; a mechanism largely eliminated from the highly-regulated Sundays Catchment. Phytoplankton blooms (>20Chl-aμgl) were persistent and seasonal in the Sundays, inducing summer bottom-water hypoxia (<2mgl), whilst those in the Gamtoos were episodic and flow-dependent. Of concern in the Sundays Estuary, was the magnitude (>550μgl) and recurrent nature of two harmful algal bloom (HAB) species. This study provides the first account of HAB persistence and seasonal hypoxia in a South African estuary, demonstrating the possible consequences of shifting an ecosystem into a new stable state.
本研究比较了受农业影响的两个南非河口——甘托斯河和桑迪河——的时空动态，以调查截然不同的水文变化如何影响物理、化学和生物响应。甘托斯河河口经常出现高流量情况，这两个系统的一个关键差异在于自然冲刷事件发生的可能性；而在高度调控的桑迪河流域，这种机制在很大程度上已被消除。浮游植物水华（>20微克/升叶绿素a）在桑迪河中持续存在且具有季节性，导致夏季底层水缺氧（<2毫克/升），而在甘托斯河中则是偶发性的且依赖于流量。桑迪河河口令人担忧的是两种有害藻华（HAB）物种的规模（>550微克/升）和反复出现的特性。本研究首次描述了南非河口有害藻华的持续存在和季节性缺氧情况，证明了将生态系统转变为新的稳定状态可能产生的后果。
