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

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

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

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

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

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

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

Results interpretation lowland rivers with calcareous or mixed geology can have total phosphorus standards ranging from ca. 40-110 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 20-70 µg/l (merging river types BT2,3,6,7,8,9,10,11) in highland rivers (BT14,15) the standards are lower, e.g. 20-50 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

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

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