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ANNEX 3: SURFACE WATER QUALITY - PROPOSED STANDARDS FOR NITROGEN IN TRANSITIONAL WATERS AND COASTAL WATERS

Dissolved inorganic nitrogen standards for coastal waters

1. For coastal waters, or parts thereof, with mean salinities for the period 1st November to 28th February of > 34.5, SEPA shall apply, as applicable, the 'high', 'good', 'moderate' or 'poor' dissolved inorganic nitrogen standards specified in Columns 2, 3, 4 and 5 of Table A, respectively, for coastal waters with mean salinities > 34.5.

2. For a coastal water, or part thereof, with a mean salinity for the period 1st November to 28th February in the range 30 - 34.5, SEPA shall calculate, as applicable in accordance with paragraph 3:

(i) the equation for the linear regression line, y = mx + c, describing the relationship between the variables dissolved inorganic nitrogen concentration and salinity for such periods; or

(ii) the series of equations for the linear regression lines, (y = mx + c) _n, describing the relationship between the variables dissolved inorganic nitrogen concentration and salinity for each set of relevant sampling data collected during such periods

where:

"y" is dissolved inorganic nitrogen concentration in micromoles per litre;

"x" is salinity;

"m" is the slope of the regression line;

"c" is the value of "y" when "x" = 0; and

" _n" is the number of sets of sampling data from which linear regression lines are calculated.

3. SEPA may use either of the methodologies specified in points (i) and (ii) of paragraph 2 provided that, given the available sampling data, the methodology used ensures that the estimate of the mean dissolved inorganic nitrogen concentration calculated in accordance with paragraph 4 is a reliable estimate.

4. SEPA shall use the equation or the series of equations calculated in accordance with paragraph 2 above to estimate the mean dissolved inorganic nitrogen concentration for the period 1st November to 28th February, as if the mean salinity in the coastal water, or part thereof, were 32.

5. SEPA shall compare the value for the mean dissolved inorganic nitrogen concentration estimated for a salinity of 32 in accordance with paragraph 4 with, as applicable, the 'high', 'good', 'moderate' or 'poor' dissolved inorganic nitrogen standard specified in Columns 2, 3, 4 and 5 of Table A, respectively, for coastal waters with mean salinities in the range of 30 - 34.5.

Table A: Dissolved inorganic nitrogen standards for coastal waters

Note to Table A:

⁽ⁱ⁾The standard refers to the concentration of dissolved inorganic nitrogen at a mean salinity for the period 1st November to 28th February of 32.

Dissolved inorganic nitrogen standards for transitional waters

6. To determine the dissolved inorganic nitrogen standards applicable to a transitional water, or part thereof, SEPA shall classify the transitional water or part as being of the Type specified in Column 1 of Table B which corresponds with the applicable description of the transitional water or part thereof in Column 2 of that Table.

Table B: Criteria for identifying types of transitional water to which the dissolved inorganic nitrogen standards for transitional waters apply

7. To apply, as applicable, the dissolved inorganic nitrogen standard for:

(i) 'high' specified in Column 2 of Table C for transitional waters of any type listed in Column 1 of that Table; or

(ii) 'good', 'moderate' or 'poor' specified in Columns 3, 4 and 5 of Table C, respectively, for transitional waters classified in accordance with paragraph 6 as being of the Type 'clear',

SEPA shall calculate, as applicable in accordance with paragraphs 8:

(iii) the equation for the linear regression line, y = mx + c, describing the relationship between the variables dissolved inorganic nitrogen concentration and salinity for the period 1st November to 28th February and resulting from the increasing dilution of dissolved inorganic nitrogen inputs in the transitional water; or

(iv) the series of equations for the linear regression lines, (y = mx + c) _n, describing the relationship between the variables dissolved inorganic nitrogen concentration and salinity for each set of relevant sampling data collected during such periods and resulting from the increasing dilution of dissolved inorganic nitrogen inputs in the transitional water

where:

"y" is dissolved inorganic nitrogen concentration in micromoles per litre;

"x" is salinity;

"m" is the slope of the regression line;

"c" is the value of "y" when "x" = 0;

" _n" is the number of sets of sampling data from which linear regression lines are calculated.

8. SEPA may use either of the methodologies specified in points (i) and (ii) of paragraph 7 provided that, given the available sampling data, the methodology used ensures that the estimate of the mean dissolved inorganic nitrogen concentration calculated in accordance with paragraph 9 is a reliable estimate.

9. SEPA shall use the equation or equations determined in accordance with paragraph 7 above to estimate the mean dissolved inorganic nitrogen concentration for the period 1st November to 28th February, as if the mean salinity in the transitional water, or part thereof, for that period, were 25.

10. SEPA shall then compare the value for the mean dissolved inorganic nitrogen concentration estimated for a salinity of 25 in accordance with paragraph 9 with, as applicable,

(i) the 'high' dissolved inorganic nitrogen standard specified in Column 2 of Table C; or

(ii) the 'good', 'moderate' or 'poor' dissolved inorganic nitrogen' standard specified in Columns 3, 4 and 5 of Table C, respectively, for transitional waters or parts thereof classified as being of the Type 'clear' in accordance with paragraph 6.

11. For transitional waters, or parts thereof, classified in accordance with paragraph 6 as being of one of the Types 'intermediate', 'turbid' or 'very turbid' specified in Column 1 of Table C, SEPA shall apply, as applicable, the corresponding 'good', 'moderate' or 'poor' dissolved inorganic nitrogen standard specified in Columns 3, 4 and 5, respectively, of that Table to the transitional water or part.

Table C: Dissolved inorganic nitrogen standards for transitional waters, or parts thereof

Note to Table C:

⁽ⁱ⁾The standard refers to the concentration of dissolved inorganic nitrogen at a mean salinity for the period 1st November to 28th February of 25.

New definitions

"99-percentile standard" means a standard that is failed if the concentration of the substance is greater than the standard for 1 % or more of the time.

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