1 / 29

Reducing phosphorus concentration in rivers: wetlands not always to the rescue

Reducing phosphorus concentration in rivers: wetlands not always to the rescue. Ben Surridge, Catchment Science Centre Louise Heathwaite, Lancaster Environment Centre Andrew Baird, Queen Mary, University of London.

travis
Download Presentation

Reducing phosphorus concentration in rivers: wetlands not always to the rescue

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Reducing phosphorus concentration in rivers: wetlands not always to the rescue Ben Surridge, Catchment Science Centre Louise Heathwaite, Lancaster Environment Centre Andrew Baird, Queen Mary, University of London

  2. Macro-nutrient, 2-4% dry weight of most cells, mostly PO4 Constituent of DNA and RNA Cell structure – phospholipids Cell energy – ATP and ADP Phosphorus: a life-support element

  3. Limiting primary productivity • Phosphorus limitation or co-limitation of many freshwater environments • Phosphorus limitation of oceanic primary productivity?

  4. Limiting primary productivity • At what concentration does P become limiting? • Autotrophic activity: • Individual algal species – 0.001 to >0.30 mg l-1 P • Confounding issues e.g. luxury uptake • Heterotrophic activity • Habitats Directive guideline – 0.20 mg l-1 P • UK TAG EQS under the WFD – 0.12 mg l-1 P

  5. Hampshire Avon Non-limited UK rivers • Phosphorus enrichment Environment Agency (2005)

  6. Enrichment costs you more • Increased autotrophic growth rate and biomass • Shifts in community structure: macrophyte → epiphytic algae → benthic and filamentous algae • Damage costs ~£100 million yr-1 in England and Wales (Pretty et al. 2003)

  7. Contributors to phosphorus loads Morse et al (2003) Defra (2004) Defra (2006)

  8. Reducing phosphorus in rivers • Range of statutory and non-statutory instruments • 90% of costs of these instruments borne by water industry (Pretty et al. 2003) • UWWTD most significant – discharge limits to sensitive areas of 1-2 mg l-1 P as total phosphorus • Capital expenditure: £50 million yr-1 between 2000-2005 on improved phosphorus removal

  9. River Kennet Jarvie et al. (2004) Justified water industry investment?

  10. …….but • Macrophyte growth still affected by epiphytic and benthic algae • Because of compounding factors – phosphorus is not the only factor affecting productivity • Because targeting WWTPs is not sufficient – baseline and spikes in river phosphorus concentration

  11. The diffuse problem • Engagement – changing nutrient management at source – Defra’s CSF • Inducement – nutrient management and targeted mitigation – Environmental Stewardship • Entry level – 3.5 million hectares • Higher level – 65,000 hectares

  12. Kronvang et al (2005) Wetlands at our service? • Nutrient attenuation function • Riparian zone an effective sediment and P trap

  13. Wetlands at our service? • Drive to re-establish and create wetlands: • UK BAP ~18,000 ha wetland • 50-year wetland vision – 12% of Yorkshire and Humber study area has potential for restoring wetland habitat

  14. A second nutrient time bomb? • Riparian zones are productive agricultural land ~30% of applied phosphorus removed in produce ~70% remains in soil or is exported • UK floodplain sediments ~500 - >2500 mg kg-1 total phosphorus (Walling et al. 2000) • How stable is this phosphorus? • Could chemical, and potentially ecological, status be affected?

  15. Riparian wetlands in the Norfolk Broads

  16. External nutrient loads River Yare Lackford Run Environment Agency (2005)

  17. Phosphorus retained in sediment

  18. Chemical extraction of phosphorus • Majority of TP present as organic P • Up to 30% of TP as inorganic P: • Ca/Mg-P pH sensitive • Fe-P sensitive to redox conditions • During seasonal water table fluctuation both pH and redox change significantly

  19. Simulate P release following reflooding Surface water and pore water sampling Analysis of sediment-P pools Laboratory mesocosm incubations

  20. MRP release to surface and subsurface

  21. -1 MRP (mg l P) Subsurface MRP and Fe2+ release -1 2+ Fe (mg l ) 1.0 1.5 0.0 0.5 2.0 2.5 3.0 3.5 30.0 20.0 0.0 10.0 0.0 0.0 2.5 2.5 10.0 10.0 Depth (cm) Depth (cm) 17.5 17.5 32.5 32.5 47.5 47.5

  22. Stoichiometry of MRP and Fe2+ release

  23. Comparing field and lab P concentration Laboratory Field

  24. P delivery to receiving waters Ditch 4.08 0.50 5 m MRP 0.40 4.04 P) 0.30 -1 Water level (mAAD) 4.00 MRP (mg l 0.20 3.96 0.10 3.92 0.00 1200 0000 1200 0000 1200 0000 0000 Time (hours)

  25. P delivery to receiving waters 0.60 4.15 1050.0 Ditch 5 m 25 m 4.10 MRP 950.0 0.45 4.05 P) 4.00 -1 850.0 Water level (m AAD) 0.30 MRP (mg l 3.95 3.90 750.0 0.15 3.85 0.00 3.80 650.0 323 325 327 329 319 321 331 Julian Day

  26. Concluding comments • Wetlands may effectively remove and store phosphorus • Store is potentially soluble and therefore bioavailable • Soluble phosphorus may be delivered to adjacent aquatic ecosystems – a second nutrient time bomb? • Not all wetland functions can be restored, and restoration may have negative consequences

More Related