期刊
ESTUARIES AND COASTS
卷 43, 期 2, 页码 223-239出版社
SPRINGER
DOI: 10.1007/s12237-019-00637-8
关键词
Estuary; Eutrophication; Remediation; Resilience; Benthic; Management; New Zealand
资金
- New Zealand Ministry for Business, Innovation and Employment [UOCX0902]
- NIWA SSIF [FWWQ1812]
- New Zealand Ministry of Business, Innovation & Employment (MBIE) [UOCX0902] Funding Source: New Zealand Ministry of Business, Innovation & Employment (MBIE)
Estuary ecological resilience can be gauged by response of estuary trophic state to abatement of nutrient pollution. Changes in trophic indicators were studied in the Avon-Heathcote Estuary (AHE) in Christchurch, New Zealand, over 6 years, spanning diversion of city wastewater inputs to an offshore outfall in 2010, and to temporary enrichment caused by the 2011 Christchurch earthquake. It was hypothesised that the tidally well-flushed and sandy AHE would not harbour a 'legacy' of eutrophication and would rapidly gain improved ecological function following the diversion. AHE sediments were coarse (156 mu m median grain size) with low organic matter (OM 1.2%, N 0.03%, C 0.3%), which changed little either with diversion or earthquake. Upon diversion, median water column and porewater ammonium (36, 185 mu mol) decreased by 87% and 57%, respectively, benthic microalgae (269 mg chlorophyll-a m(-2)) fell by 58%, and enrichment-affiliated polychaetes (3700-8000 m(-2)) fell by 60-80% at sites with largest benthic microalgal reductions, all within < 1-2 years. Oxygen and ammonium fluxes were usually oligotrophic and changed little upon diversion, except near the historic wastewater discharge site. Denitrification became more important for N loss, increasing from 5 to 29% of estuary N load. Responses to earthquake-driven enrichment were transient. Despite decades of heavy N loading and eutrophic growths of benthic microalgae and macroalgae, the AHE did not store a eutrophic legacy in its sediments. It reacted rapidly to improved water quality allowed by the outfall, showing that this common estuary type (sandy, well-flushed tidal lagoon) was resilient to eutrophication upon stressor removal.
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