PubAg

Main content area

Comparative assessment of two agriculturally-influenced estuaries: Similar pressure, different response

Author:
Lemley, Daniel A., Adams, Janine B., Taljaard, Susan
Source:
Marine pollution bulletin 2017 v.117 no.1-2 pp. 136-147
ISSN:
0025-326X
Subject:
algal blooms, anaerobic conditions, ecosystems, estuaries, hydrology, hypoxia, summer, watersheds
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 (>20Chl-aμgl−1) were persistent and seasonal in the Sundays, inducing summer bottom-water hypoxia (<2mgl−1), whilst those in the Gamtoos were episodic and flow-dependent. Of concern in the Sundays Estuary, was the magnitude (>550μgl−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.
Agid:
5623424