Comparing Agricultural and Urban Nutrient Loads to Coastal Systems João Pedro NUNES, João Gomes FERREIRA University of Aveiro, Portugal NOVA University of Lisbon, Portugal Longline Environment, UK
Nutrient loads and aquaculture Aquaculture and nutrients: an ambivalent relation Nutrients support primary production and food, but Excessive loads can cause eutrophication Nutrient management has focused on wastewater Point sources: easy to locate, measure and control Agricultural sources are more difficult to manage Variable in space, depend on weather Difficult to measure and to identify sources Difficult to design control measures
Objectives of this work Compare nutrient loads to coastal systems from wastewater and agriculture Recent evolution Spatio temporal patterns Sources and potential impacts Lough Foyle Lough Foyle for two coastal systems with important aquaculture sites Lough Foyle, UK, Portugal
Study systems Lough Foyle Rainfall (mm) Lough Foyle Oceanic climate Aquaculture: mussels and native oysters (bottom culture) Trophic status: High nutrient loads, mostly N Few eutrophication symptoms: shellfish filtration (?) and P limitation (?) Lough Foyle (Malin Head) 15 1 5 1 2 3 4 5 6 7 8 9 11112 Month 3 25 2 15 1 5 Temperature (ºC) Rainfall (mm) 15 1 5 (Faro) 1 2 3 4 5 6 7 8 9 11112 Month 3 25 2 15 1 5 Temperature (ºC) Rainfall Temperature Mediterranean climate Aquaculture: clams (traditional) and mussels (offshore, developing) Trophic status: High nutrient loads Few eutrophication symptoms due to strong water exchange but occasional water quality issues and macroalgae blooms Lough Foyle: Loughs Agency 212: Lough Foyle Status Report : Ferreira et al. 213: FORWARD project report
Lough Foyle watershed Lough Foyle Area: 379 Km 2 Wastewater discharge: 21, inhabitants Landuse: Pasture: 54% Rangelands: 43% Croplands, urban: 3%
Watershed Area: 745 Km 2 Wastewater discharge: 3, inhabitants Tavira Landuse: Croplands intensive orchards: 18% Croplands rainfed orchards: 29% Rangelands: 48% Other crops, urban, pasture: 5% Faro Olhão Contaminated coastal aquifer
Research framework Large scale aquaculture assessment projects in both systems Linking catchments to coasts Linking management agencies and research institutes Tool: complex modelling framework Lough Foyle Nutrients Wastewater, agriculture and stream network Water Coastal water circulation EASE: Enhanced SMILE for Lough Foyle Framework for Ria Formosa water quality, aquaculture & resource development Coastal ecosystems and aquaculture
Wastewater nutrient loads Point sources: Measured, easy to quantify Relatively constant along the year Recent trends: Improved wastewater treatment by adding nutrient removal : increase in population served by treatment plants Wastewater treatment close to maximum Nitrogen (ton/yr) N loads (g/person.dy) 7 6 5 4 3 2 1 14 12 1 8 6 4 2 Untreated Nitrogen load (per inhabitant) Before 2 After 21 Before 2 After 21 Lough Foyle Total N loads Lough Foyle Before 2 After 21 Population served Phosphorus (ton/yr) 35, 3, 25, 2, 15, 1, 5, Lough Foyle Before 2 After 21 14 12 1 8 6 4 2 Population served Total P loads Lough Foyle Before 2 After 21
Agriculture nutrient loads 7 6 5 4 3 2 1 y = 3E 5x + 2.28 R² =.154 3.5 3 2.5 2 1.5 1.5 1/1994 1/1995 1/1996 1/1997 1/1998 1/1999 1/2 1/21 1/22 1/23 1/24 1/25 1/26 1/27 1/28 1/29 1/21 1/211 1/212 1/213 1/214 Streamflow (m 3 /s) Nitrates (mg N/L) Diffuse sources: Difficult to measure, quantify and assign to sources 16 14 12 1 8 6 4 2 Streamflow Nitrate concentration Linear (Nitrate concentration) y = 8E 6x +.4324 R² =.38 1 1.8 1.6 1.4 1.2.8.6.4.2 1/199 1/1991 1/1992 1/1993 1/1994 1/1995 1/1996 1/1997 1/1998 1/1999 1/2 1/21 1/22 1/23 1/24 1/25 1/26 1/27 1/28 Streamflow (m 3 /s) Nitrates (mg N/L) Trends difficult to assess: Monthly measurements do not capture peak flows High temporal variability What was the impact of fertilizer control measures? Lough Foyle (Mourne) (Alportel) Nitrate Action Plan 1994 214 No streamflow data 199 28 Streamflow Nitrate concentration Linear (Nitrate concentration)
Agriculture nutrient loads 7 6 5 4 3 2 1 y = 3E 5x + 2.28 R² =.154 3.5 3 2.5 2 1.5 1.5 1/1994 1/1995 1/1996 1/1997 1/1998 1/1999 1/2 1/21 1/22 1/23 1/24 1/25 1/26 1/27 1/28 1/29 1/21 1/211 1/212 1/213 1/214 Streamflow (m 3 /s) Nitrates (mg N/L) 16 14 12 1 8 6 4 2 Streamflow Nitrate concentration Linear (Nitrate concentration) y = 8E 6x +.4324 R² =.38 1 1.8 1.6 1.4 1.2.8.6.4.2 1/199 1/1991 1/1992 1/1993 1/1994 1/1995 1/1996 1/1997 1/1998 1/1999 1/2 1/21 1/22 1/23 1/24 1/25 1/26 1/27 1/28 Streamflow (m 3 /s) Nitrates (mg N/L) Streamflow Nitrate concentration Linear (Nitrate concentration) 4 35 3 25 2 15 1 5 3.5 3 2.5 2 1.5 1.5 1/213 2/213 3/213 4/213 5/213 6/213 7/213 8/213 9/213 1/213 11/213 12/213 Streamflow (m 3 /s) Nitrates (mg N/L) Diffuse sources: Difficult to measure, quantify and assign to sources 8 7 6 5 4 3 2 1 Streamflow Nitrate concentration 6 5 4 3 2 1 1/25 11/25 12/25 1/26 2/26 3/26 4/26 5/26 6/26 7/26 8/26 9/26 Streamflow (m 3 /s) Nitrates (mg N/L) Trends difficult to assess: Monthly measurements do not capture peak flows High temporal variability What was the impact of fertilizer control measures? Lough Foyle (Mourne) (Alportel) Nitrate Action Plan 1994 214 No streamflow data 199 28 213 25/6 Streamflow Nitrate official Nitrate storm Storm measurements : Stigter et al., 26
Nutrients and aquifers Lough Foyle: impermeable geology Delays part of nutrient loads: spread during several months Fertilization WWtW: WasteWater treatment Works WWtW WWtW : coastal aquifer Permeable and already contaminated Flows under the coastal system: only part resurfaces Delays part of nutrient loads: spread during years/decades LANDSCAPE Percolation Especially N AQUIFER Stream network COASTAL SYSTEM
Nutrients and aquifers Lough Foyle: impermeable geology Delays part of nutrient loads: spread during several months Fertilization LANDSCAPE WWtW: WasteWater treatment Works WWtW WWtW Stream network : coastal aquifer Permeable and already contaminated Flows under the coastal system: only part resurfaces Delays part of nutrient loads: spread during years/decades Percolation Especially N AQUIFER? Sediments COASTAL SYSTEM OCEAN
Nutrient load assessment strategy Sediment measurements: Leote et al., 28 Calculate daily loads and assess sources: Wastewater: direct measurements Agricultural loads: hydrological model SWAT Aquifer loads (): measurements on the sediment bed 7 WWtW SWAT: 331 landscape units in 5 streams Representative year: 1.27 to 9.28 WWtW: WasteWater treatment Works Lough Foyle 11 WWtW SWAT: 33 landscape units in 29 streams Representative year: 214
SWAT: Soil and Water Assessment Tool ROUTING PHASE HUMAN MANAGEMENT CLIMATE daily Δt LAND PHASE (for each landscape unit) Lake and reservoir processes Plant growth Nutrient cycling Hydrology Water and nutrient export Stream Water and nutrient in stream processes Wastewater discharges Landscape unit: unique combination of stream location, land cover, soil type and slope WATERSHED OUTPUT
Calibration & validation Measurements do not capture the major peaks, especially in Streamflow: good model performance Nutrients: model not easy to evaluate; best available estimate 6 5 4 3 2 1 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 1/28 1/29 4/29 7/29 1/29 1/21 4/21 7/21 1/21 1/211 4/211 7/211 1/211 1/212 4/212 7/212 1/212 1/213 4/213 7/213 1/213 1/214 4/214 7/214 1/214 Streamflow (m 3 /s) 6 5 4 3 2 1 5 Measured Simulated 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 1/28 1/29 4/29 7/29 1/29 1/21 4/21 7/21 1/21 1/211 4/211 7/211 1/211 1/212 4/212 7/212 1/212 1/213 4/213 7/213 1/213 1/214 4/214 7/214 1/214 Nitrate (ton N) 4.5 4 3.5 3 2.5 2 1.5 1.5 16 Lough Foyle (Mourne) 14 (Alportel) Measured Simulated 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 1/28 1/29 4/29 7/29 1/29 1/21 4/21 7/21 1/21 1/211 4/211 7/211 1/211 1/212 4/212 7/212 1/212 1/213 4/213 7/213 1/213 1/214 4/214 7/214 1/214 Phosphate (ton P) Measured Simulated Measured Simulated 24 214 21 28 12 1 8 6 4 2 1/21 12/21 4/22 7/22 1/22 1/23 4/23 7/23 1/23 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 Streamflow (m 3 /s) 4.5 4 3.5 3 2.5 2 1.5 1.5 5 Measured Simulated 1/21 12/21 4/22 7/22 1/22 1/23 4/23 7/23 1/23 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 Nitrate (ton N) 2 1.8 1.6 1.4 1.2 1.8.6.4.2 Measured Simulated 1/21 12/21 4/22 7/22 1/22 1/23 4/23 7/23 1/23 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 Phosphate (ton P) Phosphate Nitrate Streamflow Phosphate Nitrate Streamflow
Calibration & validation Measurements do not capture the major peaks, especially in Streamflow: good model performance Nutrients: model not easy to evaluate; best available estimate 6 5 4 3 2 1 Lough Foyle (Mourne) 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 1/28 1/29 4/29 7/29 1/29 1/21 4/21 7/21 1/21 1/211 4/211 7/211 1/211 1/212 4/212 7/212 1/212 1/213 4/213 7/213 1/213 1/214 4/214 7/214 1/214 Streamflow (m 3 /s) Measured Simulated 16 14 12 1 8 6 4 2 1/21 12/21 4/22 7/22 1/22 1/23 4/23 7/23 1/23 1/24 4/24 7/24 1/24 1/25 4/25 7/25 1/25 1/26 4/26 7/26 1/26 1/27 4/27 7/27 1/27 1/28 4/28 7/28 Streamflow (m 3 /s) 5 4.5 4 3.5 3 2.5 2 1.5 1.5 Measured Simulated 1/25 11/25 12/25 1/26 2/26 3/26 4/26 5/26 6/26 7/26 8/26 9/26 Nitrate (ton N) Measured Simulated Streamflow Streamflow 6 5 2 (Alportel).6 Nitrate Phosphate.5.4.3.2.1 1/25 11/25 12/25 1/26 2/26 3/26 4/26 5/26 6/26 7/26 8/26 9/26 Phosphate (ton P) 1.8 1.6 1.4 1.2 1.8.6.4.2 1/213 2/213 3/213 4/213 5/213 6/213 7/213 8/213 9/213 1/213 11/213 12/213 Phosphate (ton P) 4 3 2 1 Nitrate Phosphate 1/213 2/213 3/213 4/213 5/213 6/213 7/213 8/213 9/213 1/213 11/213 12/213 Nitrate (ton N) Measured Simulated Measured Simulated Measured Simulated
Nutrient budgets & sources Agriculture loads dominate in Lough Foyle: large watershed, no aquifer losses high N mobilization N/P ratio: Redfield Ratio (mass): N/P = 7.2 Lough Foyle: N/P = 19.8 : N/P = 5.6 Agriculture per area (kg/ha.yr) System Nitrogen Phosphorus Lough Foyle 21.9.9 2.8.7 Lough Foyle N = 8 332 ton/yr 25% Total Nitrogen 2% 71% Total Nitrogen 3% % 7% N = 642 ton/yr Aquifer: 7% Stream: 21% 72% 2% Total Phosphorus WWtW 17% Cropland 37% 7% Rangeland Pasture 39% Aquifer: 3% WWtW Stream: 36% P = 421 ton/yr P = 115 ton/yr Total Phosphorus % 6% Cropland 33% Rangeland 61% Pasture WWtW Cropland Rangeland Pasture WWtW Cropland Rangeland Pasture 54% 48% Area Area 379 Km 2 3% 43% 745 Km 2 1% 51%
Lough Foyle: time patterns Loads concentrated in Autumn and Winter: N:regular baseflow (groundwater) + stormflow peaks P:stormflow peaks Seasonality: Autumn/Winter: dominated by watershed and N Summer: dominated by wastewater, N&P equilibrium 2 15 1 5 2 4 6 8 1 1/214 2/214 3/214 4/214 5/214 6/214 7/214 8/214 9/214 1/214 11/214 12/214 Total N (ton N/dy) Rainfall (mm) 2 15 1 5 WWtW Watershed Rainfall 2 4 6 8 1 1/214 2/214 3/214 4/214 5/214 6/214 7/214 8/214 9/214 1/214 11/214 12/214 Total P (ton P/dy) Rainfall (mm) WWtW Watershed Rainfall 1% 8% 6% 4% 2% % 2 4 6 8 1 1/214 2/214 3/214 4/214 5/214 6/214 7/214 8/214 9/214 1/214 11/214 12/214 WWtW fraction Rainfall (mm) 18 16 14 12 1 8 6 4 2 Rainfall Total N Total P 2 4 6 8 1 1/214 2/214 3/214 4/214 5/214 6/214 7/214 8/214 9/214 1/214 11/214 12/214 N/P ratio Rainfall (mm) Lough Foyle Rainfall Total N Total P Rainfall N/P Foyle Redfield ratio Agricultural loads cause: seasonality, irregularity and N dominance
5 4 3 2 1 5 1 15 2 1/27 11/27 12/27 1/28 2/28 3/28 4/28 5/28 6/28 7/28 8/28 9/28 Total N (ton N/dy) Rainfall (mm) 2 15 1 5 WWtW Aquifer Watershed Rainfall 5 1 15 2 1/27 11/27 12/27 1/28 2/28 3/28 4/28 5/28 6/28 7/28 8/28 9/28 Total P (ton P/dy) Rainfall (mm) WWtW Aquifer Watershed Rainfall 1% 8% 6% 4% 2% % 5 1 15 2 1/27 11/27 12/27 1/28 2/28 3/28 4/28 5/28 6/28 7/28 8/28 9/28 WWtW fraction Rainfall (mm) 4 35 3 25 2 15 1 5 Rainfall Total N Total P 5 1 15 2 1/27 11/27 12/27 1/28 2/28 3/28 4/28 5/28 6/28 7/28 8/28 9/28 N/P ratio Rainfall (mm) : time patterns Relatively regular loads, with irregular stormflow peaks Small seasonality: Autumn to Spring: dominated by wastewater except for a few days dominated by watershed stormflow Summer: dominated by wastewater Rainfall Total N Total P 27 28 27 28 Rainfall N/P R Formosa Redfield ratio Agricultural loads cause: high irregularity (with small seasonality)
: spatial patterns Contrast between annual and stormflow loads annual: mostly western RF WWtW stormflow: mostly eastern RF rivers more sensitive coastal area due to restricted ocean exchange Agricultural loads may cause localized, short term problems Total N (ton N/dy) WWtW (ton N) Streams (ton N) 5 4 3 2 1 5 2 1/27 11/27 12/27 1/28 2/28 3/28 4/28 5/28 6/28 7/28 8/28 9/28 1 15 Rainfall (mm) Annual loads N: 72% P: 65% 8 to 12 Apr 28 N: 5% P: 9% N: 23% P: 26% Fraction of annual load in 8 to 12 Apr 28 Nutrient WWtW Watershed Total Nitrogen 1.6% 3% 8% Phosphorus 1.6% 44% 19% WWtW Aquifer Watershed Rainfall WWtW (ton N) Streams (ton N) N: 22% P: 2% N: 22% P: 3% N: 56% P: 5%
Agricultural impacts Lough Foyle Lough Foyle nutrient loads Wet climate: strong seasonality + peaks after rainfall Wet climate + Pasture: Abundant water mobilizes N Vegetation cover: low P exports Simple geography: most loads from the estuary of River Foyle Simple geology: strong N load seasonality via baseflow nutrient loads Dry climate: loads concentrated in peaks after rainfall Dry climate + Orchards: Less water available to mobilize N Lower vegetation cover: P exports Complex geography: load locations vary with weather Complex geology: not all N loads reach the coastal system
Nutrient loads and aquaculture Aquaculture and nutrients: an ambivalent relation Nutrients support primary production and hence food, but Excessive loads can limit aquaculture through eutrophication Lough Foyle: low impacts despite high N loads; P limitation? : occasional impacts due to agriculture High loads counteracted by strong exchange with ocean but occasional acute water quality issues: stormflow loads? Wastewater control should be supplemented with agricultural nutrient management
Agricultural nutrient management Water Framework Directive quality goals might require load reduction to streams and coastal systems Challenges for agricultural nutrient management: Monitoring: often too infrequent to understand issues Fertilization control: limited by plant requirements Agricultural abandonment: negative economic impacts Long term contamination: nutrient stocks remain in soils and groundwater decades after fertilization control Innovative solutions: limiting the connectivity between fields and streams through landscape management http://connecteur.info/
Conclusions Agricultural nutrient loads can impact coastal systems With wastewater treatment widespread, nutrient management should focus on agriculture Often as important as wastewater loads Irregular loads, complex impacts More challenging to monitor and control If farmers (land and sea) understand their watersheds, they can participate on nutrient management decisions