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Table 4 Nutrients and oxygen values found in the literature for reference sites, covering a global geographical gradient with a focus on Europe and Mediterranean countries. Information is presented by continent/country

From: Italian reference rivers under the Water Framework Directive umbrella: do natural factors actually depict the observed nutrient conditions?

 

Geographical

TP

NO3-N

NH4-N

DO

 

Rationale

Area

(mg/l)

(mg/l)

(mg/l)

%

Reference

Median of reference data

USA (all states)

0.013–0.048

na

na

na

[76]

75th percentile of reference data

USA (Montana)

0.003–0.170

0.01–0.25

0.004–0.09

na

[78]

80th of least disturbed condition

Canada

0.011–0.062

na

na

na

[81]

75th percentile of reference data

Northeast China

0.046

na

na

na

[82]

Thresholds for environmental Class I quality standards for surface water

China

0.020

na

0.15

na

[83]

Rough values at 4 least disturbed sites

Australia (New South Wales)

0.033–0.077

na

na

94.5–97.8

[84]

Mean reference data

Europe (Central- Baltic)

0.020–0.040*

2–6

0.05–0.10

95–105

[20]

90th percentile of reference data

Europe (Mediterranean)

0.070

1.15

0.09

73.7–127.9

[19]

75th percentile of reference data

Europe (IT, UK, FR, CY)

0.050

2.82

0.04

100

[18]

90th percentile of reference data

Finland

0.015–0.020 (0.040**)

na

na

na

[47]

Reference thresholds based on predictive models

Sweden

0.025 (0.030**)

na

na

na

[47]

Natural and semi-pristine conditions derived from expected output rates from the catchment (mean values)

UK

0.006–0.493

na

na

na

[10]

High-quality thresholds (very low anthropogenic influence)

UK

0.020*

1.1

na

na

[85]

75th percentile of reference data

Cyprus

0.005

0.1

na

105

[86]

75th percentile of reference data

Greece

0.0865

0.18

0.016

na

[87]

75th percentile of reference data

Spain

0.082*

0.672

0.038

98.9–116.4

[88]

Reference thresholds values

Portugal (Mondego basin)

0.060

0.67

0.1

 

[89]

75th percentile of reference data (90th for TP)

Italy (state wide, all river types)

0.050

0.60

0.03

90

[27]

75th percentile of reference data

Italy (state wide)

0.049

0.88

0.03

100

This paper

90th percentile of reference data

Italy (state wide)

0.060

1.39

0.05

104

This paper

  1. With few exceptions explicitly described, values are based on statistical descriptors of reference site data distribution. In some cases, values are generically referred to high quality or undisturbed river sites, not precisely to reference sites. Ranges are reported when different values are considered in different river types or ecoregions.
  2. * P-PO4
  3. ** Lowland clay-rich rivers
  4. na: not available