Catchment science and the Wensum Demonstration Test Catchment Project

Transcription

1 Catchment science and the Wensum Demonstration Test Catchment Project UK-China Sustainable Agriculture Innovation Network Workshop 18 March 2011 Kevin Hiscock

2 What's the problem? Water nitrate concentrations continue to rise unabated in many areas of Europe Diffuse pollution from NO 3 is a significant water quality problem (and maybe for water resource management) in UK In UK c. 10% of public supply boreholes affected So far mostly dealt with by blending and treatment but future opportunities reducing fast and treatment for pollution is not an option under the Water Framework Directive (WFD)

3 Nitrate leaching losses: cereals 30kg/ha sugar beet 30 kg/ha beans 60 kg/ha oilseed rape 75 kg/ha potatoes 100 kg/ha 200 mm/a effective rainfall (East Anglia/Midlands) 1 ha of oilseed rape 75 kg N/ha leached average 0.2 m x 10,000 m 2 = 2,000 m 3 = 2 million litres recharge/ha 75,000g/N /2 million L = g/L = 37.5mg/L as N = 165 mg/l as NO 3

4 100 Duckaller Typical nitrate concentration trend for groundwater in Eastern England 50 0 Nitrate mg/l as NO

5 Tracing the sources and fate of diffuse nitrate contamination in a lowland agricultural catchment using a dual isotope method Sarah Wexler, Kevin Hiscock, Paul Dennis School of Environmental Sciences, University of East Anglia, Norwich, UK Contact: s.wexler1@uea.ac.uk

6 Food security Intensive agriculture Fertiliser use Nitrate contamination Environmental impacts Water quality impacts Do small lowlands rivers provide natural attenuation of nitrate contamination? Google Earth Field sampling Analysis of dual isotopes of nitrate Modelling of results

7 Wensum Catchment (647 km 2 ) Norfolk, East Anglia, UK Land use 80% agricultural Site of Special Scientific Interest (chalk stream ecosystem) Geology: The Chalk, glacial sands and gravels, clay rich deposits River Wensum: High nitrate concentration:[no 3 ] 480 μm, 30 mg/ L High Baseflow Index: 0.78 River length 75 km Mean river flow at catchment outlet 4 m 3 s 1 River Wensum source

8 Nitrate δ 15 Nvs. δ 18 Osource plot: coloured areas represent samples from this study. Samples analysed using Denitrifier Method 1. Adapted from Kendall (1998) Precipitation Dry deposition Precipitation Fertiliser Manure and sewage Soil Boreholes Tributaries Tributaries River Boreholes Below low permeability clay rich deposits Below high permeability sands and gravels 1 Sigman et al., Anal. Chem. 2001, Casciotti et al., Anal. Chem. 2002

9 Concentration Decrease Denitrification Microbial nitrate reduction Anaerobic conditions Organic carbon Isotopic Enrichment 2NO 3 2NO 2 2NO N 2 O N 2 δ = δ 0 + ε ln (C/C 0 ) (Mariotti et al. 1988) ε: Isotope enrichment factor (negative; with respect to product: N 2 O, N 2 ) ε = δ δ 0 ln (C/C 0 )

10 Wensum River survey, seasonal data sets, various flow conditions Nitrate Concentration δ 15 N NO 3 δ 18 O NO 3

11 flow gauging stations δ 15 N NO 3 Mid river section: length ~ 25 km Flow increased 500 L/s to 2000 L/s flow gauging stations δ 18 O NO 3 Nitrate concentration decreased 550 μm to 340 μm

12 Freshwater denitrification dual isotope diagnostics δ 15 N NO 3 vs. ln [NO 3 ] plots a straight line 1 Fourfold increase in flow = mixing δ 18 O NO 3 vs. δ 15 N NO 3 plots a straight line, slope ε (N) = 5 to 10 (groundwater studies, rapid denitrification) 3 ε = Mariotti et al., 1988 Geochim. Cosmochim. Acta (1988) 2 Cey et al., J. Cont. Hydrol. (1999) 3 Clement et al., J. Appl. Ecol. (2003)

13 Coupled mixing and denitrification model: Constraints: field measurements (flow, NO 3 concentration, isotopes, start & end) ε = 7.00 ε = (i). δ a+b = (mass a x δ a )+ (mass b x δ b ) mass (millimoles) = [NO 3 ] (μm) x volume (L) (mass a + mass b ) 1 (ii). [NO 3 ] a+b = (mass a + mass b ) then δ a+b = δ 0 and [NO 3 ] a+b = C 0 (volume a + volume b ) 2. δ= δ 0 + ε ln (C/C 0 )

14 Coupled mixing and denitrification model: Constraints: field measurements (flow, NO 3 concentration, isotopes, start & end) ε = 7.00 ε = 5.75 ε 7.00 ε (i). δ a+b = (mass a x δ a )+ (mass b x δ b ) mass (millimoles) = [NO 3 ] (μm) x volume (L) (mass a + mass b ) 1 (ii). [NO 3 ] a+b = (mass a + mass b ) then δ a+b = δ 0 and [NO 3 ] a+b = C 0 (volume a + volume b ) 2. δ= δ 0 + ε ln (C/C 0 )

15 Streambed Denitrification Optimised by channel dimensions 1 : Shallow and wide High ratio of streambed area to water volume Low gradient Low velocity Low energy Stable riverbed Sediment accumulation Denitrification matrix: Gravel + fine sediment +organic matter The difference between the modelled nitrate concentration at the catchment outlet and the observed concentration at the catchment outlet for mean flow conditions, gives an estimated removal of 931 kg nitrate-nitrogen per day, representing 31% of the predicted load. The solute flux model is controlled by the baseflow index which provides a general estimation of baseflow and surface accretion apportionment for the River Wensum. 1 Mulholland et al., Nature (2008), Alexander et al., Nature (2000)

16 Study outcomes: Spatial and temporal data show gradual decrease in nitrate downstream The dual isotope approach is useful for diagnosing nitrate sources and fate Data explained by a model including both DN and mixing Denitrification is responsible for major removal of river nitrate Therefore: DN can be an important natural attenuation mechanism in lowland rivers DN possibly occurring in the riverbed sediment

17 Introducing the Kevin Hiscock

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21 The Wensum Demonstration Test Catchment Project Aims to evaluate the extent to which on-farm land management measures can cost-effectively reduce the impacts of water pollution on river ecology while maintaining food production capacity Objectives: Develop a conceptual model of the Wensum catchment. Plan an experimental monitoring approach for selected subcatchment areas. Arrange access, instrument and manage flow-proportional and storm event sampling and analysis of a range of diffuse pollutants. Plan packages of on-farm measures for diffuse pollution mitigation through farmer liaison. Establish methods of knowledge exchange for wider dissemination of results and guidance.

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24 Catchment characteristics land use

25 Catchment characteristics cropping

26 Catchment characteristics field drains and ditches

27 Areas for testing enhanced individual and sets of onfarm measures & precision farming / minimum tillage methods Areas for monitoring sets of measures under current agrienvironmental stewardship Locations for testing sustainable drainage / wetland creation schemes Plan of field installations

28 Hydro-meteorology weather station & rain gauge

29 Rain gauge data Logger tag: WENSUM 1 Logger description: EAST ANGLIA UNI Channel tag: RAINFALL Channel no: 1 From: :00:00 To: :00:00 Number of records: 1892 Isodaq Data File: Sensor units: mm Latitude: 52.3 Longitude: /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : /02/ : Isodaq Timeview Telemetery

30 Hydrological data stream gauging Stream gauging with the acoustic doppler continuous profiler (ADCP) on the Blackwater Drain (09/11/10)

31 Hydrological data groundwater monitoring Completed borehole installation at Merrison s Lane, Salle

32 Water quality data Equipment Hach Lange nutrient analyser YSI Argonaut Measurement/purpose TP and orthophosphate (autoanalyser), Ammonium (probe or autoanalyser), nitrate (probe) Flow Analite Turbidity YSI multi parameter sonde DO, ph, temperature, conductivity, blue green algae, chlorophyll a ISCO sampler Automatic water sampler Meteor GSM box Telemetery and data visualisation Measures Control

33 High spec monitoring station at Stinton Hall Farm, Salle

34 High spec monitoring station at Park Farm, Salle

35 Water sampling intake point at Park Farm, Salle

36 Mains power in LHS view RHS view Ammonium analyser Pump Meteor telemetry unit Flow cell Multi-parameter sonde Nutrient analyser

37 Low-spec monitoring station in the Eden

38 Water quality data analytical determinands Flow proportional sampling Laboratory analysis for: Nitrate, nitrite, ammonium, TN, TDN Total P, ortho-p, MRP Suspended solids Dissolved organic carbon (DOC) Chloride, sulphate, alkalinity, electrical conductivity, ph Silica Calcium, magnesium, sodium, potassium Boron Faecal indicator organism (FIO) sampling: High and low flow events Summer and winter Aseptic hand-sampling

39 Stinton Hall Farm (09 10 March 2011) Park Farm (09 10 March 2011) Meteor Data Centre Stinton Hall Farm DATE TIME TEMP COND DO PCENT DO MGL PH AMMONIUM TURBIDITY CHLOROPHYLL 10/03/ : /03/ : /03/ : /03/ : /03/ : /03/ : /03/ : /03/ : /03/ :

40 Biological monitoring data Aim to expand current CSF monitoring Invertebrates x 3 p.a. Fish x 1 p.a. at one site Diatoms x 2 p.a. Macrophytes x 1 p.a. 1 River Habitat Survey during DTC Project Ecological status expressed using Biological Monitoring Working Party (BMWP) biotic scoring method for bottom dwelling (benthic) invertebrates and abundance of aquatic insects

41 Farm business data DTC Farm Baseline Survey Farm business details Key farm attributes Farmer interview Land areas Livestock Livestock feed Livestock housing Organic manures & slurries Cropping Pesticide use Irrigation Acceptability of diffuse pollution mitigation measures to the farm business Land use change options Soil management options Crop & livestock breeding options Fertiliser management options Livestock management options Manure management options Farm infrastructure options Checklists of key attributes to be recorded and marked on a farm map Fields, watercourse margins, habitats, links between fields & watercourses, farm steading survey

42 Looking forward to testing on-farm measures from autumn 2011 Possible new ELS management options: 6 m buffer strips for all water courses on cultivated land Natural regeneration of field corners Winter cover crops Permanent grassland areas with low/very low inputs We are particularly interested in evaluating the effects of: Increased use of minimum tillage and/or precision agriculture techniques on arable land Provision of sustainable drainage systems (SuDS) e.g. scrapes, in-ditch wetlands and wet woodland at key points in the stream network Possible new HLS management options: Creation of wood pasture or reed beds. The ECSFDI Capital Grants Scheme has an option to support the construction of sediment ponds or traps, mentioned as a priority for the Wensum catchment

43 Further Information? Website at: