PE0116 Phosphorus from Agriculture: Riverine Impacts Study PARIS

1
PE0116Phosphorus from Agriculture Riverine
Impacts Study(PARIS)

• P J A Withers
• ADAS Catchment Management Group
• Start date September 2003
• End date August 2008
• Total cost 550K

2
Research Consortium
Paul Withers Catchment Management Group
David Harper, Dept. of Biology Mark Powell, Dept.
of Geography Katarzyna Kwiatkowska, PhD
Helen Jarvie Water Quality Group
Bob Foy DARD
3
Diffuse Phosphorus Impacts in Rivers

• Current knowledge
• Eutrophication impacts based on lakes
• Diffuse P inputs in PP and DP (0.45 um) forms
• Variable, episodic and arrive in winter

• Questions
• Is riverine ecology sensitive to diffuse P
  inputs?
• What level of P loss is a problem?
• How does DPPP ratio affect impacts?

4
PARIS
Hypothesis Land management directly influences
river ecology by altering the concentration of P
in the water column
Aim To better understand the impact of high-risk
farming practices on river chemistry and ecology

• Benefits
• Quantify the extent of P load reduction required
• Target key practices for control
• Justify catchment management planning

5
High-risk practices
Over-fertilisation with P
Increase DPPP ratio
Repeated application of manures
Increase DP and PP
Increased vulnerability to erosion
Increase PPDP ratio
6
PARIS Objectives

• To compare the chemical and ecological status of
  agriculturally unimpacted v impacted streams
• To assess the chemical and biological response
• to a management change
• To distinguish the relative contribution of P
  sources within the stream channel
• To link P inputs to stream chemistry/ecology
• To develop an index of impact potential

7
PARIS Work Programme

• Select paired study sites with variable P loss
  risk (impacted v control)
• Monitor flux and temporal pattern of PP and DP
  inputs from agriculture
• Select a range of habitats/reaches at each site
• Determine in-stream fate of P inputs in relation
  to sediment dynamics and P release
• Monitor ecological structure (biodiversity) and
  function (processes)

8
Selection of Study Sites
Colebrook (N. Ireland)
Sem (Avon)
Loddington (Leicestershire)
Coughton Brook (Wye)
Intensive dairy farming on drained clay soils.
Average soil P fertility
Intensive row crops on dispersive silty
soils. High soil P fertility
Mixed beef/dairy on drained clay soils. Average
soil fertility
Arable farming on drained clay soils. Average
soil P fertility
Outdoor pigs on light-textured soils?
9
Agricultural P inputs

• Diffuse P signal
• Characterise land use, P inputs and land
  management in each headwater catchment
• Routine and storm-event based monitoring of PP
  and DP forms over 2 years
• Targeted sampling of field surface/subsurface
  runoff to define potential P bioavailability of
  PP/DP forms

• Effect a management change
• Apply manures to control area at Loddington
• Adopt BMPs in high-risk area in Sem catchment

10

• PARIS Sediments and chemistry
• (1) River water chemistry - characterise nutrient
  concentrations on a weekly basis throughout the
  annual cycle
• SRP, TDP, TP
• NO3, NO2, NH4, TDN, TN
• Si
• DOC
• pH, Gran Alkalinity, temperature - inorganic C
  speciation
• major ions

(2) Bed sediment nutrient chemistry (details to
follow..) Sampling during the growing season -
summer low flows (3) Reach-based river water P
flux surveys Synchronized with bed-sediment
surveys Flow gauging and river-water P sampling
to detect changes in P-fluxes linked to
in-stream P-processing
11

• Bed sediments provide a key link between
• Agricultural inputs of sediment-associated P,
  delivered under winter high flows
• and
• P-availability at times of ecological
  sensitivity (spring/summer low flows)
• - exchange of SRP between sediment and river
  water
• - dissolved P in porewaters sediment
  associated P available to rooted plants and
  benthic algae

12

• PARIS River Bed Sediments
• River bed - highly heterogeneous environment
• Nature of substrate (zones of sediment erosion
  and deposition, organic matter accumulation etc.)
• Water and sediment residence times
• Light exposure
• Classification of river bed according to
  bio-geomorphologically defined Functional
  Habitats
• Comparison between nutrient chemistry of bed
  sediments and ecology for impacted and unimpacted
  streams (and for different land use practices),
  will be based on sampling representative
  Functional Habitats

13

• Bed sediment sampling in Representative
  Functional Habitats
• Sediment cores/bulk sediment samples
• Porewater chemistry
• Trapping of particulates deposited during summer
  low-flow period

14
Bed sediment SRP measurements (1) Bulk nutrient
status of sediments TP, bioavailable P, TC,
TN, organic content (2) In-situ measurement of
SRP in porewaters, using DGT probes. (possibly
also TDN, Fe, Ca using DET probes) (3) In-situ
measurement of porewater redox potential, pH (4)
Measurement of Equilibrium P Concentration of
bulk bed sediment samples to assess whether
sediments act as net sources or sinks for river
water SRP
15
Sediments and chemistry - key questions (1)
What is the P/nutrient status of the bed
sediments and porewaters in different functional
habitats? Can we identify hotspots of nutrient
availability within the bed sediments? (2) How
does nutrient availability in different
functional habitats vary with respect to
unimpacted and impacted streams and for different
high-risk agricultural practices? (3) How do bed
sediment nutrient availability and river water
nutrient concentrations relate to ecological
indicators? (4) How does bed sediment nutrient
availability change with time through the
growing season? following the introduction of
P-mitigation measures? (5) Are bed sediments
acting as sources/sinks of river water SRP? (6)
Can we detect changes in river-water P fluxes
along the stream during the growing season and
how might these flux changes be attributed to
biotic (plant uptake) and abiotic (sediment
exchange) processes?
16
Ecological aspects of loss of phosphorus and
sediment into streams
17

• Concepts
• Single agricultural practices are only detectable
  at headwater stream level
• Natural headwater streams are dominated by
  allochthonous inputs
• Control sites as near to natural as possible
• Agricultural controls low-intensity pasture
• Ideal experimental design a Y of pasture and
  practice, with downstream confluence

18

• Research design
• Woodland, pasture, agri-practice, confluence.
• Reach-scale mapping of sediment and mesohabitats,
  quarterly at each site.
• Habitat-based sampling of macrophyte biomass and
  macroinvertebrate density biomass, quarterly at
  each site.
• Microbial biomass (bacteria fungi), respiration
  decomposition rate on standard leaf packs 1
  month exposure, quarterly each site.
• Instream algal biomass primary production on
  standard experimental tiles, quarterly each site.

19

• Interpretation of results?
• Change in processes from P-limited heterotrophy
  increased decomposition rates
• Increase in proportion of autotrophy
• Decrease in phosphatase activity.
• Shift in primary production towards macrophytes
• Increased shredder activity, lower diversity