Appendix 8 – Methods for measuring water quality

This Appendix details the methods for all water quality measurements and calculations as required in Criterion 2.6. Some calculations are only required for certain waterbody types as classified in Indicator 2.6.4, while others are applicable across all waterbodies.

8.1 Introduction

The water quality monitoring methods are based on the type of waterbody in which a site is situated and the type of effluent discharge from the culture system.

The first sections of the Appendix, sections 8.2 to 8.4, apply to all waterbody types and culture systems. They include methods to calculate nutrient releases, fines in feed and how to classify the type of receiving waterbody.

The methods in sections 8.5 to 8.7 outline the steps to determine the Waterbody Unit of Management, form a collaborative network with other aquaculture sites, how to conduct a 24-month water quality monitoring survey and characterise the baseline of the waterbody. These sections apply to sites located in waterbodies that are the most sensitive to nutrient loading, based on the classification outlined in section 8.4.

Calculations can be made using the ASC Water Quality Calculator provided by ASC.

For culture systems with point source discharges, methods outlined in sections 8.8 to 8.10 determine the steps to measure nutrients in effluent waters, calculate the effluent flow contribution to the receiving waterbody and monitor dissolved oxygen.

ASC has benchmarked the ASC Farm Standard methods for water quality against applicable regulatory requirements. Outcomes of the benchmark are available via the ASC Programme Centre.

8.2 Total Nitrogen and Total Phosphorous load (Indicators 2.6.1 and 2.6.2)

To calculate Total Nitrogen (TN) and Total Phosphorous (TP) load per tonne of production, one of the four following formulas shall be used per site:

Unless otherwise stated, all values shall apply over the previous 12-month period. Net production volume shall be calculated using the following formula:

$\text{Net production volume}\left(\mathrm{tonnes}\right)=\left(\text{harvested volume}\right(\mathrm{tonnes})+\text{other removed volume}(\mathrm{tonnes}\left)\right)-\text{stocked volume}\left(\mathrm{tonnes}\right))$

Formula 1:

TN load shall be calculated using the following formula:

$\text{TN load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{\text{TN release}\left(\mathrm{kg}\right)}{\text{net production volume}\left(\mathrm{tonnes}\right)}$

$\text{TN release}\left(\mathrm{kg}\right)=\text{TN in feed}\left(\mathrm{kg}\right)-\text{TN in animals}\left(\mathrm{kg}\right)$

$\text{TN in feed}\left(\mathrm{kg}\right)=\text{Feed use}(\mathrm{tonnes}/\mathrm{year})\times \text{TN content feed}(\%)\times 10$

$\mathrm{TN}\text{in animals}\left(\mathrm{kg}\right)=\text{net production volume}(\mathrm{tonnes}/\mathrm{year})\times \text{TN in animals}(\%)\times 10$

$\text{TP load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{\text{TP release}\left(\mathrm{kg}\right)}{\text{net production volume}\left(\mathrm{tonnes}\right)}$

$\text{TP release}\left(\mathrm{kg}\right)=\text{TP in feed}\left(\mathrm{kg}\right)-\text{TP in animals}\left(\mathrm{kg}\right)$

TP in feed shall be equal to the mass of feed used (tonnes, dry weight) multiplied by the feed TP content:

$\text{TP in feed}\left(\mathrm{kg}\right)=\text{Feed use}(\mathrm{tonnes}/\mathrm{year})\times \text{TP content feed}(\%)\times 10$

$\text{TP in animals}\left(\mathrm{kg}\right)=\text{net production volume}(\mathrm{tonnes}/\mathrm{year})\times \text{TP in animals}(\%)\times 10$

Formula 2:

TN load shall be calculated using the following formula:

$\text{TN load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{{\mathrm{TN}}_{\mathrm{out}}\left(\mathrm{kg}\right)-{\mathrm{TN}}_{\mathrm{in}}\left(\mathrm{kg}\right)}{\text{net production volume}\left(\mathrm{tonnes}\right)}$

${\mathrm{TN}}_{\mathrm{out}}\left(\mathrm{kg}\right)=[\mathrm{TN}{]}_{\mathrm{effluent}}\left(\frac{\mathrm{mg}}{L}\right)\times 0.001\times {\mathrm{volume}}_{\mathrm{effluent}}(m^3)$

${\mathrm{TN}}_{\mathrm{in}}\left(\mathrm{kg}\right)=[\mathrm{TN}{]}_{\mathrm{influent}}\left(\frac{\mathrm{mg}}{L}\right)\times 0.001\times {\mathrm{volume}}_{\mathrm{influent}}(m^3)$

$\text{TP load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{{\mathrm{TP}}_{\mathrm{out}}\left(\mathrm{kg}\right)-{\mathrm{TP}}_{\mathrm{in}}\left(\mathrm{kg}\right)}{\text{net production volume}\left(\mathrm{tonnes}\right)}$

${\mathrm{TP}}_{\mathrm{out}}\left(\mathrm{kg}\right)=[\mathrm{TP}{]}_{\mathrm{effluent}}\left(\frac{\mathrm{\mu g}}{L}\right)\times 0.000001\times {\mathrm{volume}}_{\mathrm{effluent}}(m^3)$

${\mathrm{TP}}_{\mathrm{in}}\left(\mathrm{kg}\right)=[\mathrm{TP}{]}_{\mathrm{influent}}\left(\frac{\mathrm{\mu g}}{L}\right)\times 0.000001\times {\mathrm{volume}}_{\mathrm{influent}}(m^3)$

Formula 3:

The average daily water exchange rate (%/day x 0.01), multiplied by the total pond volume, multiplied by the numbers of days in a year shall give a proxy for the daily effluent volume and influent volume respectively. This formula assumes the influent volume equals the effluent volume.

Annual TN load shall be calculated using the following formula:

$\text{TN load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{{\left(\right[\mathrm{TN}]}_{\mathrm{effluent}}(\mathrm{mg}/L)-\left[\mathrm{TN}{]}_{\mathrm{influent}}\left(\frac{\mathrm{mg}}{L}\right)\right)\times {\mathrm{volume}}_{\mathrm{pond}}\left(m^3\right))\times \text{daily water exchange}(\%/\mathrm{day}\times 0.01)\times \mathrm{days}(n)}{\text{net production volume}\left(\mathrm{tonnes}\right)}\times 0.001$

Daily Total P load shall be calculated using the following formula:

$\text{TP load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{{\left(\right[\mathrm{TP}]}_{\mathrm{effluent}}(\mathrm{\mu g}/L)-\left[\mathrm{TP}{]}_{\mathrm{influent}}\left(\mu \frac{g}{L}\right)\right)\times {\mathrm{volume}}_{\mathrm{pond}}\left(m^3\right))\times \text{daily water exchange}(\%/\mathrm{day}\times 0.01)\times \mathrm{days}(n)}{\text{net production volume}\left(\mathrm{tonnes}\right)}\times 0.000001$

Formula 4:

Nutrient loads shall be calculated using the following formula:

$\text{TN load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{\text{TN input}\left(\mathrm{kg}\right)\times 0.3}{\text{net production volume}\left(\mathrm{tonnes}\right)}$

$\text{TP load}\left(\mathrm{kg}{\mathrm{tonne}}^{-1}\right)=\frac{\text{TP input}\left(\mathrm{kg}\right)\times 0.2}{\text{net production volume}\left(\mathrm{tonnes}\right)}$

8.3 Percentage of fines in feed (Indicator 2.6.3)

The site shall determine the percentage of fines in feed using one of the two methods outlined below. Testing shall take place either on-site (Appendix 8 (8.3.1)) after feed has been delivered to the site, or by the feed manufacturer prior to the feed arriving on-site (Appendix 8 (8.3.2)).

8.3.1 On-site testing

This method shall be used when the percentage of fines is determined on-site. The method encompasses the sampling and testing of feed and the calculation of fines. The determination of fines shall be conducted when the feed is delivered to site.

Feed sampling

The steps to conduct the sampling of feed lots per site are as follows:

Feed testing

Feed testing can be conducted by either a manual test or by using a sifting machine. The sample of fines shall be sieved with a sieve of a maximum sieve opening of:

Manual feed testing

The steps to conduct the testing are as follows:

Sifting machine feed testing

The steps to conduct testing with a sifting machine are as follows:

Calculations – both methods:

The following equation shall be used to calculate the percentage of fines in the feed sampled: fines percentage (%) = (md/m0) x 100.

8.3.2 Feed manufacturer testing

If fines testing is conducted by the feed manufacturer, results shall demonstrate a <0.25% difference between manufacturer-tested fines content and on-site tested fines content. Either the manual feed testing or sifting machine feed testing method shall be used to determine on-site fines content.

The requirements for feed manufacturer testing are as follows:

8.4 Receiving Waterbody classification (Indicator 2.6.4)

The site shall classify the Receiving Waterbody (RW) according to Table 1 based on:

Table 1. Overview of the Receiving Waterbody types and thresholds for the classification parameters.

8.4.1 Hydraulic Retention Time (HRT)

HRT shall be calculated using the following formula, where HRT is used to classify the RW (according to Table 1):

$\text{Mean Hydraulic Retention Time}\left(\mathrm{days}\right)=\left(\frac{1,000,000*A*z}{(86,400*Q)}\right)$

8.4.1.1 Flow rate calculation

Flow rate data is required to calculate the HRT of the RW. The method to calculate flow rate is based on the characteristics of the waterbody:

Marine waterbodies:

Freshwater and brackish waterbodies:

8.4.1.2 Determination of total suspended solids (TSS) at low flow

Flow rate and TSS calculations are used to distinguish between Type B and C freshwater and brackish waterbodies only (TSS is >20mg/L at low flow, according to Table 1). The following method shall be used to determine TSS:

8.5 Waterbody Unit of Management (WUM) (Indicator 2.6.5)

A Waterbody Unit of Management (WUM) is the geographic or spatial scope of the waterbody. The WUM shall be defined per site and include information on aquaculture sites discharging effluents in the waterbody.

Using one of the following methods, the site shall demonstrate that a WUM has been created per site:

A map shall be created or presented for the WUM which indicates the following characteristics:

8.6 Components of a Water Quality Monitoring Network (Indicator 2.6.7)

The intent of the Water Quality Monitoring Network (WQMN) is to establish a mechanism for collaboration and the sharing of information between aquaculture sites in Type A waterbodies. This will provide the foundation for an Area Management Agreement (AMA) in a future version of the ASC Farm Standard.

Based on the WUM characterised according to the method outlined in Appendix 8 (8.5), the site shall establish, join a WQMN or present evidence of an area-based approach to manage water quality at a national level.

The steps to establish a WQMN per site are as follows:

If water quality is managed using an area-based approach by the national or regional regulatory body in which a site is located, the site shall present evidence demonstrating that the area-based approach meets the requirements of the WQMN, as outlined in Appendix 8 (8.6.1).

8.6.1 WQMN Requirements

The requirements of the WQMN are as follows:

8.7 Site level monitoring survey and baseline characterisation(Indicators 2.6.8 to 2.6.12)

The site level monitoring survey outlines a method to collect data to establish the trophic status and baseline characterisation of Type A waterbodies.

8.7.1 Site level monitoring survey

The steps to conduct the monitoring survey per site are as follows:

8.7.2 Trophic status

The steps to determine trophic status are as follows:

Table 2. The Trophic Status Index (TSI) for four classification parameters: Secchi depth (SD), total phosphorous (TP) concentration, total nitrogen (TN) concentration and Chlorophyll-a (Chl-a).

8.7.3 Biological oxygen demand (BOD) calculation

BOD shall be calculated per site per closed calendar year, based on:

BOD shall be calculated according to the following formula:

$\mathrm{BOD}\left(\text{kg O}2\right)=\left(\right(\left(\text{TN in feed}\right(\mathrm{kg})+\text{TN in fertiliser}(\mathrm{kg}\left)\right)-\text{TN in animals}\left(\mathrm{kg}\right))\times 4.57)+\left(\right(\left(\text{TC in feed}\right(\mathrm{kg})+\text{TC in fertiliser}(\mathrm{kg}\left)\right)-\text{TC in animals}\left(\mathrm{kg}\right))\times 2.67)$

8.7.4 Baseline characterisation

The results of the site level monitoring survey shall be used to characterise the baseline of the RW per site. The steps to characterise the baseline are as follows:

8.8 Point source effluent measurement (Indicators 2.6.15 to 2.6.17)

The steps to conduct sampling of point source effluents are as follows:

8.9 Effluent flow contribution (Indicator 2.6.16)

The steps to determine the effluent flow contribution to the RW for sites discharging point-source effluents are as follows:

Alternative methods to determine flow rate shall be permitted if data is available from the point-source discharge or culture treatment system.

8.10 Dissolved oxygen measurement (Indicators 2.6.18 to 2.6.21)

Measurements of DO are used to determine whether limits on DO concentration (mg/L) and percent saturation (%) are met.

8.10.1 Diffuse-source effluent release measurements

One of the following methods shall be used to conduct sampling of DO at 5m depth per site:

Method 1

Method 2

DO shall be measured by conducting continuous monitoring using an electronic probe and recorder, with a 15-minute sampling frequency for at least one week.

Method 3

DO shall be measured at a ‘downstream, near-field’ impacted location immediately downstream of the site, and at an ‘upstream, far-field’ non-impacted reference location at a minimum 500m upstream from the site.

8.10.2 Point-source effluent release DO measurements

One of the following methods shall be used to conduct sampling of DO at 0.5m depth per site:

Method 1

DO concentration (mg/L) shall be recorded at sampling locations immediately downstream from the outflow point where mixing is complete. The steps to conduct sampling of DO per site are as follows:

Method 2

DO shall be measured by conducting continuous monitoring using an electronic probe and recorder, with a 15-minute sampling frequency for at least one week.

Method 3

DO shall be measured at a ‘downstream, near-field’ impacted location: immediately downstream of the site, and at an ‘upstream, far-field’ non-impacted reference location at a minimum 500m upstream from the site.

8.10.3 Daily diurnal dissolved oxygen fluctuation

Daily diurnal dissolved oxygen (DDDO) fluctuation shall be calculated according to the following formula:

$\mathrm{DDDO}=[\frac{\text{maximum dissolved oxygen}(\mathrm{mg}/L)}{{\text{tabulated dissolved oxygen at saturation}}_{\max }(\mathrm{mg}/L)}\times 100]-[\frac{\text{minimum dissolved oxygen}(\mathrm{mg}/L)}{{\text{tabulated dissolved oxygen at saturation}}_{\min }(\mathrm{mg}/L)}\times 100]$

8.11 Water quality analytical methods (Indicators 2.6.8 to 2.6.11, 2.6.16 and 2.6.18)

Total Phosphorus (TP):

TP shall be measured in unfiltered 500ml samples collected in clear plastic bottles. These shall be placed on ice in a cooler and analysed within 48 hours.

A VanDorn, Kemmerer or Ruttner type sampler shall be used to collect water for field or laboratory analysis. Samples of TP shall be collected using one of the following methods:

Total Nitrogen (TN):

TN shall be measured in unfiltered 500ml samples collected in clear plastic bottles. These shall be placed on ice in a cooler and analysed within 48 hours.

A VanDorn, Kemmerer or Ruttner type sampler shall be used to collect water for field or laboratory analysis. Samples of TN shall be collected using one of the following methods:

Total Suspended Solids (TSS):

TSS shall be measured in unfiltered 500ml samples collected in clear plastic bottles. These shall be placed on ice in a cooler and analysed within 48 hours.

A VanDorn, Kemmerer or Ruttner type sampler shall be used to collect water for field or laboratory analysis. Samples of TSS shall be analysed using one of the following methods:

Chlorophyll-a (chl-a) sensor:

Chl-a shall be measured in-situ using an electronic sensor and calibrated to manufacturer’s instructions according to the following method:

Dissolved Oxygen (DO) sensor:

DO shall be measured in-situ using an electronic sensor and calibrated to manufacturer’s instructions. The sensor shall record both percentage saturation and temperature corrected/compensated concentrations. The sensor shall be calibrated according to the following method: