Benthic diatom diversity and eutrophication in temporarily closed estuaries
In: Estuaries and Coasts. Estuarine Research Federation: Port Republic, Md.. ISSN 1559-2723; e-ISSN 1559-2731, more
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| Keywords |
Halamphora coffeiformis (C.Agardh) Levkov, 2009 [WoRMS]
Brackish water; Fresh water |
| Authors | | Top |
- Nunes, M.
- Lemley, D.A.
- Adams, J.B.
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| Abstract |
Low-inflow estuaries are naturally more susceptible to anthropogenic stressors, compared to well flushed systems, with excessive nutrient loading posing a particular threat. This study investigated the benthic diatom community structure of two eutrophic, microtidal estuaries impacted by daily wastewater effluent discharges. It was hypothesised that the community structure would be similar between the warm-temperate Hartenbos and subtropical uThongathi estuaries due to disproportionally high dissolved inorganic nitrogen (H: 38 kg DIN d−1; uT: 67.5 kg DIN d−1) and phosphorus (H: 22 kg DIP d−1; uT: 29.7 kg DIP d−1) inputs from wastewater treatment works (WWTWs). Taxa tolerant of high nutrient conditions proliferated in both systems. However, the dominant taxa differed with the brackish Halamphora coffeaeformis species occurring in the Hartenbos Estuary and the freshwater Navicula rostellata, Sellaphora pupula and Navicula gregaria species in the uThongathi Estuary. The overall benthic diatom diversity in both systems was low (H’ > 0 but ≤ 1.5) and indicative of a degraded health state. Temporal differentiation driven by salinity was evident in the Hartenbos Estuary, while changes in community structure were limited to periods of increased river inflow in the uThongathi Estuary. Therefore, while the trophic status of the dominant taxa was determined by the nutrient stress (primary stressor), changes in salinity and river inflow (secondary stressors) shaped the distinct community assemblages observed in each estuary. This study provides insight into the impact of similar anthropogenic-induced pressures in different biogeographical regions and the importance of managing towards a natural dynamic state of microtidal, low-inflow estuaries. |
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