Natural nutrient enrichment and algal responses in near pristine micro-estuaries and micro-outlets.

Autor: Human LRD; Department of Botany, Institute for Coastal and Marine Research, Nelson Mandela University, Summerstrand South Campus, Port Elizabeth 6031, South Africa; South African Environmental Observation Network, Elwandle Coastal Node, Ocean Science Campus, Nelson Mandela University, Port Elizabeth 6031, South Africa. Electronic address: lucienne.human@saeon.ac.za., Magoro ML; SARChI Chair: Shallow Water Ecosystems, Nelson Mandela University, Summerstrand South Campus, Port Elizabeth 6031, South Africa; South African Institute for Aquatic Biodiversity, Grahamstown 6139, South Africa., Dalu T; South African Institute for Aquatic Biodiversity, Grahamstown 6139, South Africa; Department of Ecology and Resource Management, University of Venda, Thohoyandou, Limpopo, South Africa., Perissinotto R; SARChI Chair: Shallow Water Ecosystems, Nelson Mandela University, Summerstrand South Campus, Port Elizabeth 6031, South Africa., Whitfield AK; South African Institute for Aquatic Biodiversity, Grahamstown 6139, South Africa., Adams JB; Department of Botany, Institute for Coastal and Marine Research, Nelson Mandela University, Summerstrand South Campus, Port Elizabeth 6031, South Africa., Deyzel SHP; South African Environmental Observation Network, Elwandle Coastal Node, Ocean Science Campus, Nelson Mandela University, Port Elizabeth 6031, South Africa; Department of Zoology, Institute for Coastal and Marine Research, Nelson Mandela University, Summerstrand South Campus, Port Elizabeth 6031, South Africa., Rishworth GM; SARChI Chair: Shallow Water Ecosystems, Nelson Mandela University, Summerstrand South Campus, Port Elizabeth 6031, South Africa.
Jazyk: angličtina
Zdroj: The Science of the total environment [Sci Total Environ] 2018 May 15; Vol. 624, pp. 945-954. Date of Electronic Publication: 2017 Dec 27.
DOI: 10.1016/j.scitotenv.2017.12.184
Abstrakt: Naturally-occurring pristine estuarine ecosystems are rare in modern environments due to anthropogenic encroachment. There are more than 100 outlets around the South African coast arising from streams flowing from small catchments close to the sea. Eight near natural systems were sampled seasonally over the period of a year to acquire baseline information on water quality and chlorophyll a status across a variety of algal guilds (benthic microalgae, phytoplankton and macroalgal cover). Albeit on a much smaller-scale, these systems represent natural surrogates of larger temporarily open/closed estuaries (TOCEs). Inorganic nutrients (ammonium, total oxidized nitrogen and soluble reactive phosphate), phytoplankton and microphytobenthos chlorophyll a, as well as macroagal percentage cover, were measured using standard methods. Algae showed a seasonal trend, with blooms of both micro- and macro-algae occurring during summer, with a dieback recorded in autumn. During summer, only one system had a phytoplankton peak in chlorophyll a above 20μgL -1 , while the microphytobenthos concentrations in three of the systems were above 100mgm -2 . Summer blooms of green filamentous macroalgae occurred in all four micro-outlets and in one micro-estuary. Using a linear mixed-effects modelling approach, significant drivers for algal growth related to temperature, nutrient conditions, light availability and water residence time, all of which are known to stimulate primary production. The results show that enrichment from natural sources display similar responses from primary producers to mesotrophic and/or eutrophic water bodies, with the exception that they revert to a natural state rather than continue into a degraded state as is the case in artificially enriched systems. This importantly demonstrates how larger temporarily/open closed estuaries, most of which are anthropogenically degraded, might have functioned under a former more balanced state. Some of these larger systems now respond to nutrient enrichment by exhibiting permanent cultural eutrophication.
(Copyright © 2017 Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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