Comparative assessment of two agriculturally-influenced estuaries: Similar pressure, different response. Issue 1 (15th April 2017)

• Record Type: Journal Article
• Authors: Lemley, Daniel A.; Adams, Janine B.; Taljaard, Susan
• Is Part Of: Marine pollution bulletin. Volume 117:Issue 1/2(2017)
• Page Start: 136
• Page End: 147
• Publication Date: 2017-04-15
• Subjects: Phytoplankton -- Heterosigma akashiwo -- Heterocapsa rotundata -- Hypoxia -- Eutrophication -- Ecohydrodynamics; Marine pollution -- Periodicals; Marine Biology -- Periodicals; Water Pollution -- Periodicals; Mer -- Pollution -- Périodiques; Publications périodiques; Pollution des mers; Lutte antipollution; Electronic journals; 363.7394
• DOI: 10.1016/j.marpolbul.2017.01.059
• Languages: English
• ISSNs: 0025-326X

Abstract

Abstract: 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 (> 20 Chl- a μg l − 1 ) were persistent and seasonal in the Sundays, inducing summer bottom-water hypoxia (< 2 mg l − 1 ), whilst those in the Gamtoos were episodic and flow-dependent. Of concern in the Sundays Estuary, was the magnitude (> 550 μg l − 1 ) 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. Highlights: Natural flow variability results in episodic and event-dependent in situ responses. Removal of natural system dynamism causes persistent and undesirable disturbances. Red-tide events were comprised of Heterosigma akashiwo and Heterocapsa rotundata . Exceptional phytoplankton blooms (> 550 μg l − 1 ) recorded in the Sundays Estuary. First record of seasonal bottom-water hypoxia in a South African estuary.