Welcome to Estuary Trophic Index (ETI) Tools

Although nutrient enrichment threatens many New Zealand estuaries, guidance on how to assess the extent of eutrophication (including indices and indicators that are useful for management) is limited. As a result, it has been difficult to:

  • Determine the current state of estuaries with regard to eutrophication;
  • Assess the effects of the recent landuse intensification and change on estuaries;
  • Gauge the consequences for estuaries of nutrient limits for freshwater (e.g., the National Policy Statement for Freshwater Management, NPSFM, 2014); and
  • Set nutrient load limits to achieve estuarine objectives.

In response, regional council coastal scientists sought advice via the coastal Special Interest Group (cSIG), with funding through Envirolink Tools Grant (Contract No. C01X1420), on the development of a nationally consistent approach to the assessment of estuary eutrophication, including nutrient load thresholds. The purpose of this project, called the NZ Estuary Trophic Index (ETI), is to assist regional councils in determining the susceptibility of an estuary to eutrophication, assess its current trophic state, and assess how changes to nutrient load limits may alter its current state. The project does this by providing tools for determining estuary eco-morphological type, where an estuary sits along the ecological gradient from minimal to high eutrophication, and providing stressor-response tools (e.g., empirical relationships, nutrient models) that link the ecological expressions of eutrophication (measured using appropriate trophic state indicators) with nutrient loads (e.g., macroalgal biomass/nutrient load relationships).

In terms of the regional council planning framework, the ETI provides vital supporting guidance for underpinning the ecological health component of regional plans by identifying relevant estuary attributes and outcomes for inclusion in plans, defining methods and indicators to measure ecosystem health attributes, and providing guidelines to assess whether or not the outcomes are being met.

The ETI provides three tools:

Details of when to use each tool and the knowledge underpinning the tools can be found on the Welcome and Background Information tabs, respectively, for each tool.


Concept diagram of the ETI

Concept diagram of the ETI, showing relationships between ETI Tools 1, 2 and 3. Tool 1 provides information on estuary susceptibility to eutrophication based on estuary type, its physical attributes and nutrient loading. Tool 2 provides scores for estuary trophic health based on measured trophic indicator values. Tool 3 provides trophic scores under under scenarios of changed land use or load limits, and/or when values of trophic state indicators are lacking.

Disclaimer

Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this website is accurate, NIWA does not give any express or implied warranty as to the accuracy of the information contained herein. This website has been reviewed internally by NIWA and meets NIWA standards for website delivery.

Links to the ETI Tools


Please email us at eti-tools@niwa.co.nz for more information about the ETI Tools or to provide feedback. We welcome comments about how to make this webtool more useful.

Suggested Citation

Zeldis, J., Plew, D., Whitehead, A., Madarasz-Smith, A., Oliver, M., Stevens, L., Robertson, B., Burge, O., Dudley, B. (2017). The New Zealand Estuary Trophic Index (ETI) Tools: Web Tool 1 - Determining Eutrophication Susceptibility using Physical and Nutrient Load Data. Ministry of Business, Innovation and Employment Envirolink Tools: C01X1420. https://shiny.niwa.co.nz/Estuaries-Screening-Tool-1/

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Glossary


CLUES: The Catchment Land Use for Environmental Sustainability (CLUES) model is a GIS-based modelling system which assesses the effects of landuse change on water quality and socio-economic indicators. More information about CLUES is available on the CLUES – Catchment Land Use for Environmental Sustainability model website.

Estuary type: the ETI toolset has adopted a simple four-category typology specifically suited to the assessment of estuarine eutrophication susceptibility in New Zealand:

  1. Shallow intertidal dominated estuaries (SIDEs)
  2. Shallow, short residence time tidal river and tidal river with adjoining lagoon estuaries (SSRTREs)
  3. Deeper subtidal dominated, longer residence time estuaries (DSDEs)
  4. Coastal lakes

Intermittently closed/open estuary states (ICOEs) are subtypes of SIDEs and SSRTREs that describe estuary closure state.

Potential nutrient concentrations: nutrient concentrations in the absence of nutrient uptake or losses through biogeochemical processes, representing the trophic pressure on an estuary due to nutrient loading.


Welcome to ETI Tool 1

Two approaches are combined to enable the user to assess estuary susceptibility to eutrophication (i.e., the risk that an estuary will be eutrophic based on its physical characteristics), along with advice about when each approach is applicable. For more detailed information about each approach, please refer to the Background information and References tabs.

Nutrient loads and flows are needed and are supplied for most NZ estuaries in the provided .csv file. For other estuaries, these values need to be provided by the user, either from their own data or outputs from the Catchment Land Use for Environmental Sustainability model (CLUES, Elliott et al. 2016).

CLUES Estuary approach

The CLUES Estuary approach predicts potential nutrient concentrations in New Zealand coastal waters by combining predictions of nutrient loads from catchments with simple dilution models to determine the mixing between ocean- and river- water in estuaries (see Glossary for definitions of words in bold). The tool chooses the appropriate dilution model to use based on estuary volume, tidal prism and freshwater inflow (Elliott et al. 2016, Plew et al. 2018). The CLUES Estuary approach calculates an ETI susceptibility band that combines macroalgae and phytoplankton banding, while considering the proportion of the estuary that is intertidal. If the user identifies an estuary as an ICOE, susceptibility bands are provided for both its open and closed state.

When to use the CLUES Estuary approach results

The CLUES Estuary approach toward assessing susceptibility can be used on any estuary for which the appropriate input data are available. Banding is provided for susceptibility to both macroalgal and phytoplankton blooms. However, the main effects of phytoplankton eutrophication are oxygen depletion and high light attenuation in deeper and often stratified estuarine systems, which typically do not occur in New Zealand SIDEs when they are permanently open. Phytoplankton effects are more likely in SSRTREs, particularly those with longer flushing times. Using the Tool 1 database, we have found that the great majority of estuaries with intertidal areas less than 20% are SSRTREs, while the great majority of SIDEs have intertidal areas greater than 40%. Therefore, we also provide an overall ETI susceptibility band that takes into the proportion of intertidal area into consideration. For estuaries with intertidal areas greater than 40% (e.g., SIDEs), ETI susceptibility is banded using the macroalgae band. For estuaries with intertidal areas less than 5%, ETI susceptibility is banded using the phytoplankton band. If the intertidal area is between 5% and 40% or the estuary is an ICOE, ETI susceptibility is banded using the worst of the macroalgae and phytoplankton bands.

ASSETS approach

The ASSETS approach to gauging estuary susceptibility to eutrophication is adapted from the Assessment of Estuarine Trophic Status (ASSETS) protocol developed in the United States (Bricker et al. 2003). This approach is based on physical characteristics of estuaries and nutrient input load-estuary response relationships for key New Zealand estuary types. The tool produces a single physical susceptibility score that can be used to classify either physical susceptibility (e.g., very high, high, moderate, low susceptibility) or be combined with nutrient load data to produce a combined physical and nutrient load susceptibility score.

When to use the ASSETS approach results

The estuaries used in the USA ASSETS application were large and relatively deep, and consequently had high dilution of nutrient loads from land. The ASSETS banding system was developed for such estuaries. This presents a problem for ASSETS application in New Zealand where over half of estuaries are too small and shallow to be assigned rating categories in ASSETS. Consequently, its use is only appropriate for New Zealand’s larger volume estuaries (i.e., fiords, embayments, some larger tidal lagoons and larger tidal rivers; see Page 30, Robertson et al. 2016a). We do not recommend using ASSETS for NZ estuaries with an estuary volume of less than 2.8 million m3.

Links to the ETI Tools


Please email us at eti-tools@niwa.co.nz for more information about the ETI Tools or to provide feedback. We welcome comments about how to make this webtool more useful.

Suggested Citation

Zeldis, J., Plew, D., Whitehead, A., Madarasz-Smith, A., Oliver, M., Stevens, L., Robertson, B., Burge, O., Dudley, B. (2017). The New Zealand Estuary Trophic Index (ETI) Tools: Web Tool 1 - Determining Eutrophication Susceptibility using Physical and Nutrient Load Data. Ministry of Business, Innovation and Employment Envirolink Tools: C01X1420. https://shiny.niwa.co.nz/Estuaries-Screening-Tool-1/

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Glossary


CLUES: The Catchment Land Use for Environmental Sustainability (CLUES) model is a GIS-based modelling system which assesses the effects of landuse change on water quality and socio-economic indicators. More information about CLUES is available on the CLUES – Catchment Land Use for Environmental Sustainability model website.

Estuary type: the ETI toolset has adopted a simple four-category typology specifically suited to the assessment of estuarine eutrophication susceptibility in New Zealand:

  1. Shallow intertidal dominated estuaries (SIDEs)
  2. Shallow, short residence time tidal river and tidal river with adjoining lagoon estuaries (SSRTREs)
  3. Deeper subtidal dominated, longer residence time estuaries (DSDEs)
  4. Coastal lakes

Intermittently closed/open estuary states (ICOEs) are subtypes of SIDEs and SSRTREs that describe estuary closure state.

Potential nutrient concentrations: nutrient concentrations in the absence of nutrient uptake or losses through biogeochemical processes, representing the trophic pressure on an estuary due to nutrient loading.


Data download for ETI Tool1

To use ETI Tool 1, you need to download the provided default data. This dataset contains data for 443 estuaries in New Zealand. Once downloaded, you may wish to replace the default data for estuaries where you have more recent or precise data, or remove estuaries that you are not interested in. For information about each of the variables in the data template, including the correct units, please download the metadata file.

Once you have downloaded, amended, and saved the data template, you need to upload it on the 2. Upload data tab under the Run Tool 1 menu.

The default data were sourced from Coastal Explorer, a database compiled using expert panels, including regional council staff, knowledgeable locals, university staff, and consultants. Information was mined from various sources including 1:50,000 topographic maps, aerial photographs, New Zealand Land Resources Inventory, the National Land Cover Data Base, the NZ Estuarine Environment Classification database, the New Zealand tidal model, wave hindcast models, RNZN Hydrographic charts, and numerous publications and reports.

It is likely that councils will hold more accurate and recent information than that available from the Coastal Explorer database. This database should be relied on only for coarse scale surveys of vulnerability to eutrophication.







Data upload


Use the Browse button to upload your datafile. If loaded correctly, the sites you have uploaded should show on the map below. After you have uploaded your data and are satisfied with it, select the 3. Calculate susceptibility tab under the Run Tool 1 menu to calculate estuarine susceptibility. If you wish to upload a second file, you will either need to change the file name or refresh the app (F5 on most browsers) for the upload to be successful.







Download Results

Calculate susceptibility

Click the Calculate susceptibility button to run the ETI Tool 1 Calculator. Susceptibility results can be downloaded using the Download Results button. Definitions and units for the results are described in the metadata, available for download from the 1. Download data tab under the Run Tool 1 menu. Downloadable plots of the results can be generated using the 4. Plot results tab under the Run Tool 1 menu.


Note that sites with missing data will have NA returned for their CLUES Estuaries bands or ASSETS scores, with the reasons calculations were unsuccessful provided in the CLUES Estuary comments or ASSETS comments columns, respectively. ICOE results for the CLUES Estaury approach are only calculated for estuaries where values for Typical Closure Length have been provided. ASSETS calculations for ICOEs use the preferred method outlined on Page 19 of Robertson et al. 2016 and do not generate values for flushing or dilution potential.






Select which plot type you would like
If you would like to export (save) your plot, you can choose the type using the options below.
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(pdf is recommended)
Download Plot
Background to ETI Tool 1

Estuary Typologies

The morphological types are based on the original estuary classification of Hume et al. (2007) and its more recent revision (Hume et al. 2016). The ETI uses a simplification of the Hume typology into four ETI classes (Hume 2018): Shallow Intertidally Dominated Estuary (SIDE), Shallow Short Residence Time Tidal River Estuary (SSRTRE), Deeper Subtidal Dominated Estuary (DSDE) and Coastal Lakes. Intermittently closed/open lakes and lagoons estuaries (ICOEs) are classified as sub-types of SIDEs and SSRTREs. Robertson et al (2016a, 2016b) refers to ICOLLs - this terminology is no longer used and has been replaced by sub-types of SIDEs and SSRTREs called ICOEs.

CLUES Estuary approach

The CLUES Estuary approach is derived from the GIS-based CLUES Estuary component of CLUES and uses the same model formulations (see Glossary for definitions of words in bold). This tool allows the user to run the CLUES Estuary approach without requiring access to CLUES. The tool currently gives a single time- and space-averaged concentration as a function of mean flow and nutrient input, with the capability to include seasonal nutrient and flow differences. It provides susceptibility bandings for macroalgal and phytoplankton eutrophication potentials, as well as an overall ETI susceptibility band that considers the intertidal area of the estuary. The tool has the potential to offer a relative comparison between different land-use scenarios (by virtue of CLUES), and to identify estuaries likely to be highly sensitive to current nutrient loads based on their physical attributes. See Elliott et al. (2016) and Plew et al. (2018) for a detailed description of CLUES Estuary.

By default, the CLUES Estuary approach assumes that all estuaries are open to the sea (other than coastal lakes, which are considered permanently closed). For systems that intermittently close, (i.e., intermittently closed/open estuary states - ICOEs), predictions for the potential nutrient concentrations and bandings for macro-algae and phytoplankton susceptibilities are made for the closed state if the user provides an estimate of typical closure duration in days (Tl in the input file).

ASSETS approach

The ASSETS approach is a quick screening method for assessing estuary susceptibility that takes into account estuary morphology when producing its ratings. The ASSETS approach takes into account stratification, estuary volume, freshwater inflow, and tidal range, in two physical susceptibility indicators dilution potential and flushing potential. Daily nitrogen load per square metres is used for a third susceptibility indicator N load susceptibility. The dataset used to derive the susceptibility response relationships for ASSETS in the USA used large estuaries, which were primarily subtidal, open, 7.5m mean depth, long residence time embayments with moderate to high eutrophic symptoms. The most commonly occurring eutrophic symptom was high, widespread concentrations of elevated chlorophyll-a levels (i.e., phytoplankton), although most estuaries also exhibited at least one other moderate to high symptom (e.g., dissolved oxygen).

Links to the ETI Tools


Please email us at eti-tools@niwa.co.nz for more information about the ETI Tools or to provide feedback. We welcome comments about how to make this webtool more useful.

Suggested Citation

Zeldis, J., Plew, D., Whitehead, A., Madarasz-Smith, A., Oliver, M., Stevens, L., Robertson, B., Burge, O., Dudley, B. (2017). The New Zealand Estuary Trophic Index (ETI) Tools: Web Tool 1 - Determining Eutrophication Susceptibility using Physical and Nutrient Load Data. Ministry of Business, Innovation and Employment Envirolink Tools: C01X1420. https://shiny.niwa.co.nz/Estuaries-Screening-Tool-1/

Download citation

Glossary


CLUES: The Catchment Land Use for Environmental Sustainability (CLUES) model is a GIS-based modelling system which assesses the effects of landuse change on water quality and socio-economic indicators. More information about CLUES is available on the CLUES – Catchment Land Use for Environmental Sustainability model website.

Estuary type: the ETI toolset has adopted a simple four-category typology specifically suited to the assessment of estuarine eutrophication susceptibility in New Zealand:

  1. Shallow intertidal dominated estuaries (SIDEs)
  2. Shallow, short residence time tidal river and tidal river with adjoining lagoon estuaries (SSRTREs)
  3. Deeper subtidal dominated, longer residence time estuaries (DSDEs)
  4. Coastal lakes

Intermittently closed/open estuary states (ICOEs) are subtypes of SIDEs and SSRTREs that describe estuary closure state.

Potential nutrient concentrations: nutrient concentrations in the absence of nutrient uptake or losses through biogeochemical processes, representing the trophic pressure on an estuary due to nutrient loading.


References


  • Bricker, S., Ferreira, J., Simas, T. (2003) An integrated methodology for assessment of estuarine trophic status. Ecological Modelling 169: 39-60. [view online]

  • Elliott, A.H., Semadeni-Davies, A.F., Shankar, U., Zeldis, J.R., Wheeler, D.M., Plew, D.R., Rys, G.J., Harris, S.R. (2016) A national-scale GIS-based system for modelling impacts of land use on water quality. Environmental Modelling & Software 86: 131-144. [view online]

  • Hume, T. (2018) The fit of the ETI trophic state susceptibility typology to the NZ coastal hydrosystems typology. NIWA Client Report 2017007CH: 34. [view online]

  • Hume, T., Gerbeaux,P., Hart, D., Kettles, H., Neale, D. (2016) A classification of New Zealand's coastal hydrosystems. NIWA Client Report HAM2016-062: 112.

  • Hume, T., Snelder, T., Weatherhead, M., Liefting, R. (2007) A controlling factor approach to estuary classification. Journal of Ocean and Coastal Management 50: 905-929. [view online]

  • Plew, D.R., Zeldis, J.R., Shankar, U., Elliott, A.H. (2018). Using simple dilution models to predict New Zealand estuarine water quality. Estuaries and Coasts 41: 1643-1659. [view online]

  • Robertson, B., Stevens, L., Robertson, B., Zeldis, J., Green, M., Madarasz-Smith, A., Plew, D., Storey, R., Hume, T., Oliver, M. (2016) NZ Estuary Trophic Index Screening Tool 1. Determining eutrophication susceptibility using physical and nutrient load data. Prepared for Envirolink Tools Project: Estuarine Trophic Index, MBIE/NIWA Contract No: C01X1420: 47. [view online]

Links to the ETI Tools


Please email us at eti-tools@niwa.co.nz for more information about the ETI Tools or to provide feedback. We welcome comments about how to make this webtool more useful.

Suggested Citation

Zeldis, J., Plew, D., Whitehead, A., Madarasz-Smith, A., Oliver, M., Stevens, L., Robertson, B., Burge, O., Dudley, B. (2017). The New Zealand Estuary Trophic Index (ETI) Tools: Web Tool 1 - Determining Eutrophication Susceptibility using Physical and Nutrient Load Data. Ministry of Business, Innovation and Employment Envirolink Tools: C01X1420. https://shiny.niwa.co.nz/Estuaries-Screening-Tool-1/

Download citation

Glossary


CLUES: The Catchment Land Use for Environmental Sustainability (CLUES) model is a GIS-based modelling system which assesses the effects of landuse change on water quality and socio-economic indicators. More information about CLUES is available on the CLUES – Catchment Land Use for Environmental Sustainability model website.

Estuary type: the ETI toolset has adopted a simple four-category typology specifically suited to the assessment of estuarine eutrophication susceptibility in New Zealand:

  1. Shallow intertidal dominated estuaries (SIDEs)
  2. Shallow, short residence time tidal river and tidal river with adjoining lagoon estuaries (SSRTREs)
  3. Deeper subtidal dominated, longer residence time estuaries (DSDEs)
  4. Coastal lakes

Intermittently closed/open estuary states (ICOEs) are subtypes of SIDEs and SSRTREs that describe estuary closure state.

Potential nutrient concentrations: nutrient concentrations in the absence of nutrient uptake or losses through biogeochemical processes, representing the trophic pressure on an estuary due to nutrient loading.