1. Deriving river TP standards from lake standards
Contribution to sub-chapter of guidance
Anne Lyche Solheim and Geoff Phillips
Berlin meeting 9th November 2016
Anne Lyche Solheim
9. november 2016

2. Rationale and Objective
Current river TP standards (GM boundary) are often quite high compared to lake standards
Very high river standards may not allow downstream lakes to achieve good status, as the TP load may exceed the critical TP-load compatible with good status
Difficult to derive valid river standards from dose-response relationships with nutrient sensitive river biota (phytobenthos) due to noisy relationships with biology (caused by multiple pressures and hydrological variation)
Aim is to find an alternative approach to set river standards, in cases where the dose-response relationships of river nutrients versus river biology are weak.
The river standards derived from lake standards can also be used to validate and adjust river standards that are based on other methods
Anne Lyche Solheim
9. november 2016

3. Methodology
Lake stds are often derived from good dose-response relationships with intercalibrated biological metrics, mainly phytoplankton, for different lake types.
River stds can be derived from lake stds using TP retention estimates for different lake types:
TP GM river = TP GM lake/(1-TP retention)
Requires
matching broad lake types with broad river types
acceptable estimates of TP retention for broad lake types
Proposed standards is compared to current river stds and also to river stds derived from good dose-response relationships with river biota
Anne Lyche Solheim
9. november 2016

4. Methodology: Matching broad types of lakes and rivers
Using ETC-ICM broad types report 2015:
Broad lake type (BTx)
Corresponding Broad river type (BTx)
lowland, calcareous, very shallow BT4
lowland, calcareous or mixed geology, BT4/5
lowland, calcareous, shallow (stratified) BT3
lowland, siliceous, shallow (stratified) BT2
lowland, siliceous, BT2/3
lowland, humic, shallow (stratified) BT5/6
lowland, organic, BT6/7
mid-altitude, calcareous, shallow (stratified) BT8/12
mid-altitude, calcareous or mixed geology, BT10/11
mid-altitude, siliceous, shallow (stratified) BT7
mid-altitude, siliceous, BT8/9
highland, calcareous, shallow (stratified), BT12
highland, calcareous, BT15
highland, siliceous, shallow (stratified), BT11
highland, siliceous, BT14
Anne Lyche Solheim
9. november 2016

5. Methodology: TP retention
Limnological knowledge:
Natural TP retention in lakes is lake specific depending on water retention time and mean depth and varies from negative (if internal loading) to close to 100% of external TP load
Internal loading in stratified lakes mainly occurs in strongly eutrophic lakes,
Therefore, we may assume that negative retention does not occur in lakes in high, good or moderate status
Mean retention in >300 American lakes including some very shallow and some very eutrophic lakes with internal loading was found to be 40% (Brett & Benjamin 2008)
We may therefore assume that mean TP retention in stratified oligotrophic and mesotrophic /slightly eutrophic lakes is higher than 40%, e.g. 50%?
Very shallow lakes are likely to have lower TP retention than stratified lakes due to shorter retention time and more resuspension of sediments: 20%?
Humic lakes are also likely to have lower TP retention than clear lakes, due to adsorption of P to humic substances, 30%?
Very large and very deep lakes will have higher TP retention due to long water retention time and very little resuspension of sediments, e.g. 70%?
Anne Lyche Solheim
9. november 2016

6. Methodology: TP retention
Broad lake type (BTx)
Lake mean depth
P-retention (mean) m
% of inflow TP
lowland, calcareous, very shallow BT4
<3
20 %
lowland, calcareous, shallow (stratified) BT3
3-15
50 %
lowland, siliceous, shallow (stratified) BT2
lowland, humic, shallow (stratified) BT5/6
30 %
mid-altitude, calcareous, shallow (stratified) BT8/12
mid-altitude, siliceous, shallow (stratified) BT7
highland, calcareous, shallow (stratified), BT12
highland, siliceous, shallow (stratified), BT11
very large and very deep lakes, BT1
>15
70%
Anne Lyche Solheim
9. november 2016

7. TP Standard for lake type (µg/l)* TP Standard for river type (µg/l)
Results
Broad river type (BTx) corresponding to the broad lake type
TP Standard for lake type (µg/l)*
TP Standard for river type (µg/l)
25th%ile
75th%ile
lowland, calcareous or mixed geology, BT4/5 33 62 41 78 26 55 52
110
lowland, siliceous, BT2/3 11 23 22 46
lowland, organic, BT6/7 21 28 30 40
mid-altitude, calcareous or mixed geology, BT10/11 18 34 36 68
mid-altitude, siliceous, BT8/9 13
highland, calcareous, BT15 12 24
highland, siliceous, BT14 9 56
rivers of any type flowing into large, deep lakes ?  ?
n.a.
n.a. 
*from table 4.2 in draft guidance, p.27
Anne Lyche Solheim
9. november 2016

8. Results interpretation
lowland rivers with calcareous or mixed geology can have total phosphorus standards ranging from ca µg/l (merging river types BT4&5), this can potentially include very large rivers
lowland siliceous, humic, as well as mid-altitude calcareous rivers can have standards ranging from µg/l (merging river types BT2,3,6,7,8,9,10,11)
in highland rivers (BT14,15) the standards are lower, e.g µg/l
Within each altitude category, the 25th percentile of the standards are lower in siliceous rivers than in calcareous rivers
For the 75th percentile this pattern is also seen for lowland rivers, but not for mid-altitude and highland rivers.
Anne Lyche Solheim
9. november 2016

9. How do the results compare to currently used river TP standards?
Broad river type (BTx)
TP Standard for broad river types derived from lake stds in equivalent broad types (µg/l)
TP Standards reported by countries aggregated to broad river types , µg/l
25th%ile
75th%ile
median*
lowland, calcareous or mixed geology, BT4/5 41
110
100
lowland, siliceous, BT2/3 22 46 50
lowland, organic, BT6/7 30 40 35
mid-altitude, calcareous or mixed geology, BT10/11 36 68
mid-altitude, siliceous, BT8/9 26
highland, calcareous, BT15 24
highland, siliceous, BT14 18 56 20
*tbc
Green: current std in line with lake derived std
Red: current std higher than lake derived std
Anne Lyche Solheim
9. november 2016

10. Validation using river dose-response relationships
Work to be done selecting the best GIG relationships.
Adding national examples?, e.g. Norway:
Phytobenthos Benthic fauna:
These boundaries (TP=17 µg/l) are in line with lake derived river stds for siliceous clear rivers
Anne Lyche Solheim
9. november 2016