Bioavailability of phosphorus emissions and loadings in surface waters of Germany Markus Venohr, Peter Fischer, Judith Mahnkopf Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Department Ecohydrology 20.11.2017 5th Biennial Symposium of the International Society for River Science, Hamilton, New Zealand
Bioavailability of Phosphorus SRP or PO4 represent the major part of Directly Bioavailable Phosphorus (BAP) BAP in emissions represent the share of directly bioavailable phosphorus. The rest has to differentiated as potentially or not bioavailable (nonbap). For potentially BAP different time delays to become BAP have to be considered. The effective share of bioavailable Phosphorus from potentially BAP can only be determined via uptake experiments. 2
Key questions Would it make difference to focus on %BAP in emissions for management measures to reduce eutrophication? What is the share of BAP in emissions (%BAP)? How do spatial pattern of BAP in emissions correlate with the share of PO4-P on TP (%PO4) observed in surface waters? 3
Model short introduction Semi-empirical/conceptual model for basin-wide analysis: Regionalized pathway, landuse and source specific emissions In-stream retention and resulting loads Scenarios on effect of climate change and management options External framework Phytoplankton growth Catchment characteristics Pathways Surface waters Venohr et al., 2011 DOI: 10.1002/iroh.201111331 4
Monitored P concentrations All data derived from regular monitoring programs Period: 2000-2010 Frequency: fortnightly - monthly No. of stations 3823 No. monitoring month 224318 5
Monitored P concentrations All data derived from regular monitoring programs Period: 2000-2010 Frequency: fortnightly - monthly TP in mg/l No. of stations 3823 No. monitoring month 224318 excluded PO 4 and TP values 16 % PO 4 > TP 7 % share of PO 4 is integer 13 % < 24 values per station 3 % Total removed 39 % used stations 1550 monitoring month 137319 6
Monitored P concentrations PO 4 in mg/l %-share of PO 4 on TP Can this pattern be explained by the %BAP in emissions? 7
Breaking down TP to BAP emissions Pathway short name % share BAP Source Atmospheric deposition on surface waters AD 100 % Bruhm (1985) surface run-off SR Sharpley (1992), Fischer erosion ER 80 % (2017), Ruf and Henning (2008) tile drainages TD 20% - 80 % f(org. fertilizer) Schelde et al. (2006) groundwater GW 100% Ruf and Henning (2008) urban sources US 60 % Ruf and Henning (2008), LFU (2000) WWTP PS f(effluent concentration) Li & Brett (2012) 8
Erosion and surface run-off Traditional definition: erosion 5 % BAP surface run-off: 100 % BAP Here: erosion & surface run-off: 80 % BAP Fischer, Pöthig & Venohr (2017) DOI: 10.1016/j.scitotenv.2017.03.143 But During transport sorption and desorption processes take place and the share of BAP cannot easily be determined in surface runoff Once particulate associated P enter surface waters it can easily become dissolved P (BAP) 9
Waster water treatment plants Li and Brett found an increasing %BAP with increasing TP effluent concentrations for a scientific test WWTP. Re-calculated for 532 WWTP in Germany, same selection criteria applied as for monitoring stations 10
Spatial distribution of TP emissions and %BAP TP emissions in kg/km²/yr 11
Spatial distribution of %PO4 and %BAP %-PO4 %BAP 12
To be explained by %PO4? %PO 4 10 % 20 % 40 % 60 % 80 % Water temperature low high 13
Case study Weser %PO4 14
Weser along the main river Observed data 15
Weser along the main river modelled PO4 without riverine transformation and retention and represent mean concentrations of emissions nonbap --> BAP transformation? Difference: uptake by primary producers 16
Conclusions The mean %BAP in emissions amounts to 74 % with a large spatial variability %BAP does not show spatial agreement with %PO4 in surface waters Uptake in lowland streams must be extremely high to explain the decrease from %BAP to %PO4 modelled %BAP has to be re-evaluated but, if correct There must be an almost complete transformation from nonbap to BAP in hilly regions (and lowland rivers?) Abiotic and biotic/bio-chemical in-stream processes have to be considered in more detail Re-evaluation of the concept of BAP in management Re-evaluation of the effect of measures to control eutrophication 17
We will keep on searching for the missing parts in the puzzle. Thank you for your attention! We acknowledge funding from the European Commission 7th Framework Program through the project MARS project (www.mars-project.eu), the German Ministry of Education and Research through the projects RESI (http://www.igbberlin.de/projekt/resi) 18