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Natural nutrient enrichment and algal responses in near pristine micro-estuaries and micro-outlets
- Source :
- Science of The Total Environment. 624:945-954
- Publication Year :
- 2018
- Publisher :
- Elsevier BV, 2018.
-
Abstract
- 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 20 μg L− 1, while the microphytobenthos concentrations in three of the systems were above 100 mg m− 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.
- Subjects :
- Chlorophyll
0106 biological sciences
Chlorophyll a
Environmental Engineering
010504 meteorology & atmospheric sciences
Nitrogen
01 natural sciences
Phosphates
South Africa
chemistry.chemical_compound
Nutrient
Water Quality
Ammonium Compounds
Phytoplankton
Microalgae
Environmental Chemistry
Waste Management and Disposal
0105 earth and related environmental sciences
geography
geography.geographical_feature_category
Primary producers
Ecology
Chlorophyll A
010604 marine biology & hydrobiology
Estuary
Eutrophication
Pollution
chemistry
Benthic zone
Linear Models
Environmental science
Seasons
Water quality
Estuaries
Subjects
Details
- ISSN :
- 00489697
- Volume :
- 624
- Database :
- OpenAIRE
- Journal :
- Science of The Total Environment
- Accession number :
- edsair.doi.dedup.....40cfbc60fdd6088e017ccb1a091b01cd