Phosphorus from Agriculture: Riverine Impacts Study PARIS

1
Phosphorus from Agriculture Riverine Impacts
Study(PARIS)
Start date September 2003 End date August 2008
2
Diffuse Phosphorus Impacts in Rivers

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

• Questions
• Is riverine ecology sensitive to diffuse P
  inputs?
• What level of P input is a problem?
• How important is the timing of diffuse P inputs
  ?
• How significant are P-supplies from bed
  sediments and porewaters?
• How does P fractionation (e.g. DPPP ratio)
  affect impacts?

3
PARIS
Hypothesis Land management directly influences
river ecology by altering the concentration of P
in the water column bed sediments
Aim To better understand the impact of high-risk
farming practices on river nutrient chemistry and
ecology

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

4
PARIS Experimental Approach

• Paired study headwater streams (agriculturally
  impacted v. unimpacted) sites, with variable P
  loss risk
• Response to implementation of management change
• Apply manures to control area (Loddington)
• Adopt BMPs in high-risk area (Sem)

Loddington Arable farming on drained clay soils
Coughton Brook Intensive row crops on dispersive
silty soils.
Sem Intensive dairy farming on drained clay
soils.
Colebrook Mixed beef/dairy on drained clay
soils.
5
PARIS Work Programme

• Monitor flux and temporal pattern of PP and DP
  inputs from agriculture
• Examine chemical impacts P concentrations in
  water column and bed sediments/porewaters
• Examine in-stream fate of P inputs in relation
  to sediment dynamics and P uptake release by
  sediments and biota
• Monitor ecological structure (biodiversity) and
  function (processes)

Focus on headwater stream sites Single
agricultural practices are only detectable at
headwater stream level Eliminate effects
of point-source discharges
6
Importance of eliminating influence of point
sources PSYCHIC agricultural high risk/rural
sub-catchments (lt c. 100km2) appear strongly
influenced by small point-source inputs
Sewage SRPB 9.5
Importance of in-stream uptake of SRP by
sediments/biota
7
Role of river bed sediments

• 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 (i.e. spring summer low flows)
• Storage of diffuse sediment-associated P on
  river bed
• SRP exchange between bed-sediment and river
  water
• Dissolved P in porewaters sediment-associated
  P available to rooted plants and benthic
  algae

8
PARIS Bed sediment sampling

• River bed - highly heterogeneous environment
• Nature of substrate
• Water and sediment residence time
• Light exposure

• Reach-scale mapping of river-bed environment
• Sampling based on bio-geomorphologically defined
  Representative Functional Habitats allow
  comparison between impacted unimpacted streams
• Measurements
• Total sediment nutrient concentrations,
• Bioavailable P concentrations
• Equilibrium P concentrations,
• Porewater SRP concentrations

9

• PARIS - sediments and chemistry
• How does nutrient availability in different
  functional habitats vary with respect to
  unimpacted and impacted streams and for different
  high-risk agricultural practices?
• How do bed sediment nutrient availability and
  river water nutrient concentrations relate to
  ecological indicators?
• How does bed sediment nutrient availability
  change following the introduction of P-control
  measures?
• Can we quantify changes in river-water P-fluxes
  along the stream during the growing season and
  how might these be attributed to biotic (plant
  uptake) and abiotic (sediment exchange)
  processes?

10
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
• Targeted sampling of field surface/subsurface
  runoff to define potential P bioavailability of
  PP/DP forms

11

• PARIS - Ecology studies
• Functional habitat-based sampling of macrophyte
  biomass and macroinvertebrate density biomass
• Microbial biomass (bacteria fungi), respiration
  decomposition rates on standard leaf packs
• In-stream algal biomass primary production on
  standard experimental tiles

• Potential Ecological Impacts
• 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

12
PARIS assessment of diffuse source P impacts on
river ecology

• Agricultural P contributions to rivers often
  intermittent predominantly under winter high
  flows
• How significant are these diffuse inputs for
  ecological impacts in relation to background
  inputs?
• Issues of memory and lag effects linked to
  storage of diffuse sediment-associated P
  delivered during (winter) storm events
• New contributions to process understanding of
  thresholds, lag effects and ecological
  sensitivity to P in lowland agricultural streams