Sources, transformations and sinks of nitrogen in watersheds with multiple anthropogenic pressures

Transcription

1 Sources, transformations and sinks of nitrogen in watersheds with multiple anthropogenic pressures Bartoli, M. Department of Life Sciences, University of Parma, Italy Roma, 2324/01/2014 Gli impatti dell inquinamento atmosferico sugli ecosistemi naturali e antropici

2 NNO 3 (µm) km Summer 2009 The NO 3 anomaly : Nitrate concentrations in the Oglio River increase by up to 500 µm but such increase is not explained by point souces nor N input by the main tributaries (green arrows)

3 1) Evidences of diffuse NO 3 contamination suggested to perform detailed N mass balance, according to the method proposed by Oenema et al. (2003) Soana E., E. Racchetti, A. Laini, M. Bartoli, and P. Viaroli, Soil Budget, Net Export, and Potential Sinks of Nitrogen in the Lower Oglio River Watershed (Northern Italy). Clean Soil, Air, Water 39(11): M. Bartoli, E. Racchetti, C.A. Delconte, E. Sacchi, E. Soana, A. Laini, D. Longhi, P. Viaroli, Nitrogen balance and fate in a heavily impacted watershed (Oglio River, Northern Italy): in quest of the missing sources and sinks. Biogeosciences 8(5): Link to the Italian Nitrogen Network initiative!

4 NH 3 volatilization Atmospheric deposition Fertilizers Redeposition Biological fixation ATMOSPHERE LAND SURFACE Denitrification Redeposition Manure NH 3 volatilization Wastewater sludges Runoff Leaching INPUT SURFACE WATER Crop uptake GROUND WATER OUTPUT

5 N balance terms tons N yr 1 INPUT Livestock manure 51,512 Synthetic fertilizers 33,564 Biological fixation 12,182 Atmospheric deposition 1,800 Wastewater sludge 1,057 input 100,115 OUTPUT Crop uptake 38,915 NH 3 volatilization 12,704 Denitrification in soils 8,440 output 60,060 Balance 40,056 N mass balance in the lower Oglio River basin (year 2008)

6 Ninput Noutput Nsurplus (kg N ha AL 1 yr 1 ) < >550 a) b) c) The amount of livestock N manure applicable to vulnerable and non vulnerable zones according to the EU Nitrates Directive are 170 and 340 kg N ha 1 yr 1, respectively, and are comparable to N surplus in most municipalites. The load of farmed animals is elevated (>1.5 tons ww ha 1 ) in ~64% of municipalities. The basin hosts some 650,000 cows and over 2,100,000 pigs

7 N loads from urban areas t N yr 1 Wastewater treatment plants (AE) The number of inhabitants is 1,280,000, corresponding to 5,834 t N y 1 potentially generated; 85% are connected to sewage treatment plants

8 4,5 4,0 Mella export (kg N km 2 yr 1 ) 3,5 3,0 2,5 Po Chiese lower Oglio Cherio NNO 3 2,0 1,5 1,0 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0 Population density (inhabitants km 2 ) Figure 5. Loglog plot reporting the relationship between NO 3 export at the closing section and the population density in a number of watersheds including those of the present study. Redrawn from Caraco & Cole, 1999.

9 INPUT Tons N yr1 Agricolture and farming 100,000 Sewage plants 6,000 OUTPUT From cultivated soils 60,000 SURPLUS Agricolture 40,000 EXPORT Oglio closing section 13,000 UNACCOUNTED 26,000

10 1) Evidences of diffuse NO 3 contamination suggested to perform a detailed N mass balance, according to the method proposed by Oenema et al. (2003) 2) The N mass balance suggests the presence of unaccounted for N sinks within the lower Oglio River Basin. We thus performed a comprehensive analysis of denitrification in perifluvial wetlands, in order to evaluate the fraction of the surplus permanently removed via this process. Racchetti E., Bartoli M., Soana E., Longhi D., R.R. Christian, Pinardi M., Viaroli P., Influence of hydrological connectivity of riverine wetlands on nitrogen removal via denitrification. Biogeochemistry 103:

11 Winter and summer samplings performed over 20 perifluvial wetlands, some isolated and some hydraulically connected with the Oglio River. Intact sediments collected via plexiglass liners and incubated in the dark for fux (DIN) and denitrification (IPT) measurements.

12 Rates of Denitrification Data are grouped in winter (W) and summer (S) values of connnected (C) and isolated (I) wetland types and show total denitrification rates (Dtot), denitrification of nitrate diffusing to anoxic sediments from the water column (D W ) and denitrification of nitrate produced within sediments by nitrification (D N )

13 INPUT Tons N yr1 Agricolture and farming 100,000 Sewage plants 6,000 OUTPUT From cultivated soils 60,000 SURPLUS Agricolture 40,000 EXPORT Oglio closing section 13,000 UNACCOUNTED 26,000 NSINK DENITRIFIED IN WETLANDS 250 (1% of unaccounted!)

14 1) Evidences of diffuse NO 3 contamination suggested to perform a detailed N mass balance, according to the method proposed by Oenema et al. (2003) 2) The N mass balance suggests the presence of unaccounted for N sinks within the lower Oglio River Basin. We thus performed a comprehensive analysis of denitrification in perifluvial wetlands, In order to evaluate the fraction of the surplus permanently removed via this process. 3) As denitrification in wetlands removes only a minor fraction of excess N we analyzed the potential N removal in other aquatic compartments: the Oglio River and the secondary drainage system. Delconte, C.A., Sacchi, E., Racchetti, E., Bartoli, M., MasPla, J., Re, V. Nitrogen inputs to a river course in a heavily impacted watershed: A combined hydrochemical and isotopic evaluation (Oglio River Basin, N Italy) (2014) Science of the Total Environment, , pp Sacchi, E., Acutis, M., Bartoli, M., Brenna, S., Delconte, C.A., Laini, A., Pennisi, M. Origin and fate of nitrates in groundwater from the central Po plain: Insights from isotopic investigations (2013) Applied Geochemistry, 34, pp

15 δ 18 O vs SMOV A Middle part of Oglio Oglio downstream 4 5 Legend: = Oglio River = Natural tributaries = Wastewater ffftreatment plants δ 15 N vs AIR Isotopic composition of dissolved nitrates. 1 = synthetic fertilizers; 2 = nitrification processes on mineralized synthetic fertilizers; 3 = mineralized synthetic fertilizers; 4 = soil organic matter; 5 = manure and septic tank effluents; 6 = evolution during denitrification. A = August Isotopic data suggest weak denitrificazion in the oglio River.

16 Secondary drainage channels (SDC) Very great potential for Nremoval as their network sums 12,500 km, with a density of 5.5 km km 2 AL. Theoretical denitrification and N retention in SDC was calculated according to the model proposed by Christensen (1990) and according to the literature dealing with nitrogen removal in vegetated buffer strips. More recently we started experimental activities in small canals aiming at detailed N budgets in open systems.

17 2) Whole reach denitrification (N 2 /Ar) (Laursen and Seitzinger, 2002) NH 4 + NO 2 NO 3 TN Nprocesses In small channels 2) 4) 1) Mass balance (Δ=outin) a) at the basin level (Kronvang and Bruhn, 1996; Letcher et al., 2002) b) at the canal level (Burns, 1998) N 2 1) 4) N 2 3) N 2 NH 4 + NO 2 NO 3 TN 4) Vegetation N uptake : random sampling for plant density, biomass and N content of the species found 3) Intact core incubation: DIN & N 2 net flux (Dalsgaard et al. 2000)

18 Nitrificationcoupled denitrification in submerged macrophytes growing in SDC

19 Nitrification coupled denitrification in vegetated Nitrification (V) and coupled unvegetated denitrification (S) sediments 120 µmol N 2 m 2 h /04/08 21/07/08 21/10/08 D14 D VL VD SL SD Evidences of oxygen transport during the light and dark phase

20 INPUT Tons N yr1 Agricolture and farming 100,000 Sewage plants 6,000 OUTPUT From cultivated soils 60,000 SURPLUS Agricolture 40,000 EXPORT Oglio closing section 13,000 NSINKS UNACCOUNTED DENITRIFIED IN WETLANDS DENITRIFICATION IN SDC 26, (1% of unaccounted!) 5,500 (~25% of unaccounted)

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22 1) Evidences of diffuse NO 3 contamination suggested to perform a detailed N mass balance, according to the method proposed by Oenema et al. (2003) 2) The N mass balance suggests the presence of unaccounted for N sinks within the lower Oglio River Basin. We thus performed a comprehensive analysis of denitrification in perifluvial wetlands, In order to evaluate the fraction of the surplus permanently removed via this process. 3) As denitrification in wetlands removes only a minor fraction of excess N we analyzed the potential N removal in other aquatic compartments: the Oglio River and the secondary drainage system. 4) We end up > 60% of the N surplus following unknown pathways. Can the groundwater represent another potentially important permanent or temporary N sink?

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24 NNO 3 concentration (µm) in groundwater

25 On the short time scale groudwater can represent a N sink but on a larger time scale springs can recycle substantial amounts of nitrogen (NO 3 but also N 2 O) to the surface network of canals. Springs To our opinion this is an extremely important point, also due to expected recover of impacted sites (>20 years). Investments won t bring to substantial changes in 23 years

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27 µm NO 3 N km The NO 3 anomaly : The increase of nitrate concentration in the Oglio River is due to rivergroundwater interactions. Estimated N load from below : kg N day 1

28 Conclusions/Perspectives/Future Research in this watershed In the Oglio River basin a large Nsurplus is coupled to: permeable soils limited extension and limited connection of wetlands with main water bodies simplified lanscape As a result, the NO 3 pool in ground water is increasing, meaning that recover is far. Isotopic analyses and hydrogeological models can help in dating the age and the pathways of the nitrate recycled by springs; this would give realistic perspectives on expected recover. Taken actions were demonstrative and not necesserily realized in the right places.

29 New mass balances in subbasins of the Po river are available! F. Oglio F. Mincio Po di Volano T. Agogna Superficie (km 2 ) Terreno agricolo (%) Abitanti (km 2 ) N bestiame (bovini e suini) km 2 N zootecnia/ N input (%) N fertilizzanti/ N input (%) N uptake/ N input (%) Media N input (kg N ha1 year1) Media surplus (kg N ha1 year1)

30 Many thanks for your attention!