Using Simple Dilution Models to Predict New Zealand Estuarine Water Quality

Plew, David R.; Zeldis, John; Shankar, Ude; Elliott, Alexander H.

doi:10.1007/s12237-018-0387-6

Cited by 27 publications

(35 citation statements)

References 27 publications

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“…It is also common among NZ estuaries in having a sandy sediment, with low %OM (Robertson et al (2015). Several of these estuaries are currently receiving heavy diffuse-source catchment loading of nutrients and are eutrophic (Plew et al 2018;Robertson and Savage 2018). The present study has shown that this common estuary type is sensitive to eutrophication via water column forcing but is also amenable to remediation, suggesting that such estuaries could respond similarly to the AHE, if water quality of their loading was improved.…”

Section: Resultsmentioning

confidence: 57%

“…The time frame for recovery of eutrophic estuaries is of high interest to stakeholders including regulators and the public involved in remediation efforts. This study informs this issue and is particularly relevant because this estuary type, well-flushed tidal lagoon (Hume et al 2007(Hume et al , 2016, is a common one in NZ (Plew et al 2018). It is also common among NZ estuaries in having a sandy sediment, with low %OM (Robertson et al (2015).…”

Section: Resultsmentioning

confidence: 57%

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Trophic Indicators of Ecological Resilience in a Tidal Lagoon Estuary Following Wastewater Diversion and Earthquake Disturbance

Zeldis

Depree

Gongol

et al. 2019

Estuaries and Coasts

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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 μm 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 μmol) 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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Section: Resultsmentioning

confidence: 57%

Section: Resultsmentioning

confidence: 57%

Trophic Indicators of Ecological Resilience in a Tidal Lagoon Estuary Following Wastewater Diversion and Earthquake Disturbance

Zeldis

Depree

Gongol

et al. 2019

Estuaries and Coasts

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“…There are no published residence times for Golden Bay. For the Firth, the methods of Plew et al (2018), based on the modified tidal prism modelling of Luketina (1998), were used to estimate residence time, yielding a time of 12 days. This is a shorter time than we estimated (annual averages of 24 day in 2000-2001 and 21 days in 2012-2013).…”

Section: Residence Timesmentioning

confidence: 99%

Balance of Catchment and Offshore Nutrient Loading and Biogeochemical Response in Four New Zealand Coastal Systems: Implications for Resource Management

Zeldis

Swaney

2018

Estuaries and Coasts

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Nutrient mass balance analyses are a way of obtaining 'whole system' viewpoints on coastal biogeochemical functions and their forcing. Seasonal mass balances are presented for four large bay systems in New Zealand (NZ), with the aim of showing how they can inform coastal management. Freshwater volumes, and surface and groundwater, wastewater and atmospheric inorganic and organic nitrogen (N) and phosphorus (P) were balanced with levels of salinity, N and P from ocean surveys, used to determine non-conservative N and P fluxes and, via stoichiometry, carbon (C) fluxes. For Golden and Tasman Bays and Hauraki Gulf, exchange with adjacent shelf waters usually dominated total N supply (80-85%). In contrast, for the Firth of Thames, 51% of total N and 85% of dissolved inorganic N supply originated from its agricultural catchment. Net ecosystem metabolism (NEM; balance of autotrophy and heterotrophy) of Golden and Tasman Bays and Hauraki Gulf was usually nearly balanced. In contrast, Firth NEM was highly seasonally variable, often exhibiting strong heterotrophy coincident with expression of respiration-related stressors (low O 2 and high DIC/low pH). Denitrification accounted for about 51% of total N export across the four systems, signifying its importance as a eutrophication-regulating ecosystem service. Budgets made 12 years apart in the Firth showed decreased denitrification efficiency, coincident with large increases in system N and phytoplankton. The findings for land-ocean nutrient balance, NEM and denitrification showed how mass balance budgeting can inform coastal management, including inventories of nutrient inputs, balances of oceanic and terrestrial nutrient loading, and potential for risk associated with biogeochemical responses.

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“…However, eutrophic conditions in New Zealand estuaries are rare and highly localized (Thrush et al, ). Of the estuaries studied, nitrate levels are greatest at Shag River Mouth, followed by Blueskin Bay and Purakaunui Inlet (Plew, Zeldis, Shankar, & Elliott, ), which are not eutrophic, and so if nitrate enrichment were driving the observed trends, we would expect to see increased rates of growth at these sites through time, which was not the case.…”

Section: Discussionmentioning

confidence: 93%

Historical changes in bivalve growth rates indicate ecological consequences of human occupation in estuaries

Wells

Chan

Smith

et al. 2019

Aquatic Conservation

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1. Only 800 years ago, New Zealand became the last major land mass to be settled by humans, leading to environmental degradation and precipitating a decline in indigenous fauna. Such ecological downgrading can alter ecosystem processes and drive down the capacity for remnant ecosystems to withstand the anthropogenic pressures of today.2. In New Zealand, these impacts are chronicled in a concise and remarkably complete archaeological record and are distinguishable from natural changes due to changing climate.3. Estuaries are subject to strong environmental gradients that drive productivity and contain critical habitats for key life-history phases for marine and terrestrial species. Linking land to sea, they host abundant, accessible human resources and are sensitive to anthropogenic environmental modification. 4. Austrovenus stutchburyi is a common filter feeding bivalve in New Zealand estuar-ies. An important food source for Māori, their shells are abundant in middens.Growth rates of A. stutchburyi are affected by multiple environmental factors, including temperature, salinity, nutrients, and sediment, and are recorded through time as easily measurable annual shell bands. Measuring spatial and temporal variation in growth rate of A. stutchburyi can be used to identify the timing of changes in estuarine conditions. Growth bands were measured in archaeological and modern (AD 1300-present)A. stutchburyi shells from six sites around New Zealand with varying occupational histories. There were no increases in growth rate, and rates declined measurably over time at three sites (up to a 50% reduction in growth per year). This decline was greater at estuaries that had experienced greater catchment modification, indicating that sediment loading due to land clearance was a likely driver of this change.6. New Zealand's coastline and marine resources are often perceived as wild and pristine. We propose that fundamental changes have occurred in the functioning of coastal marine ecosystems, which constrain its future.

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Using Simple Dilution Models to Predict New Zealand Estuarine Water Quality

Cited by 27 publications

References 27 publications

Trophic Indicators of Ecological Resilience in a Tidal Lagoon Estuary Following Wastewater Diversion and Earthquake Disturbance

Trophic Indicators of Ecological Resilience in a Tidal Lagoon Estuary Following Wastewater Diversion and Earthquake Disturbance

Balance of Catchment and Offshore Nutrient Loading and Biogeochemical Response in Four New Zealand Coastal Systems: Implications for Resource Management

Historical changes in bivalve growth rates indicate ecological consequences of human occupation in estuaries

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