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IBZ — Intelligent Buffer Zone (Intelligente BufferZoner)

Summary

IBZ = Intelligent Buffer Zones (Danish: Intelligente BufferZoner). A precision drainage interception structure installed in the riparian zone along ditches, streams, and lakes to intercept N- and P-loaded drain water from sloping fields. Unlike BZ10/BZ20 (which are dry buffer strips along the full watercourse), an IBZ is a constructed drainage interception system with two components: (1) an open water section where drain water is held for denitrification, and (2) an infiltration zone where water percolates through the riparian soil before reaching the watercourse. IBZ must be sited ≥10 m from the watercourse edge; a minimum 1 m head difference between the IBZ water level and the watercourse is required to maintain flow.

Eligibility

PotV(i,"IBZ") = IBZ_pot(i) × Countcy(i) × IniPotV(i) / 5
IBZ_pot(i) from IBZ_pot.inc — identifies fields with potential for in-stream buffer implementation.

P Effect

IBZ_P_eff(up_lakecatch) = Sum(i$(up_lake_i AND PotV(i,"IBZ")>0), IBZ_eff(i) × x(i,"IBZ"))
IBZ_eff(i) is field-specific, from IBZ_eff.inc. Note: IBZ enters the P reduction equation directly (not via P_Effects_Total), and is aggregated at up_lakecatch level.

N Effect

In the model: None — IBZ is classified as a P-only measure.

In the catalog (N catalog, DCA 174, p. 394–402): IBZ removes 20–40% of the nitrogen entering the installation with drain water (confidence: **). Effect cannot be expressed in kg N/ha — it depends on the drain catchment area and inlet N concentration. Two full-scale Danish IBZ installations have been measured for one year each (very limited data). The percentage removal is achieved through denitrification in the water-saturated zone and plant/tree uptake in the IBZ structure.

Reason for zero in model: The N removal depends on the drainage network configuration (not the field area or leaching rate), making it impossible to express as kg N/ha without additional spatial data. The model therefore conservatively assigns no N effect.

Note: There is overlap with catch crops — if catch crops are grown on the drained field above an IBZ, the IBZ will remove less N (because less N reaches the drain).

Cost

CostM(i,"IBZ") = 7,938 DKK/ha/yr — one of the most expensive field measures per ha.

Mutual exclusions

IBZ has the most restrictions in the model — it cannot co-exist with: - BZ10 (mutexc11) - BZ20 (mutexc10) - LRh (mutexc12) - LRl (mutexc13) - WL (mutexc16) - FO (mutexc17) - VP2 WL (mutexc14) - VP2 FO (mutexc15) - VP2 LRl (mutexc7)

This extensive list reflects IBZ's specific hydrological positioning — it is incompatible with any other measure that significantly alters the field–stream interface.

IBZ is in the onlyIBZ(j) set — defined as its own separate subset, reflecting its unique characteristics.

Data sources

  • Eligibility potential (IBZ_pot(i)): IBZ_pot.inc
  • Field-specific P effect (IBZ_eff(i)): IBZ_eff.inc
  • Cost structure: hard-coded in TargetEcon 2026.gms

Catalog source

N catalog: DCA Rapport nr. 174 (Eriksen et al., 2020), Chapter "Intelligente BufferZoner" (p. 394–402). Authors: Brian Kronvang, Sofie G.M. van't Veen, Dominik Zak et al. (Bioscience, Aarhus University).

P catalog: SR379 (Andersen et al., 2020), Chapter "Intelligente BufferZoner" (p. 120–133). Same author team.

Key findings from catalogs: - IBZ is a drain interception system — not a simple buffer strip. It physically intercepts drain pipes from sloping fields and forces the drain water to pass through a constructed wetland before reaching the watercourse. - Typical installation serves up to 25 ha of drained catchment. - N removal: 20–40% of drain inflow (confidence: ). Only two full-scale Danish sites measured (one year each) → very limited evidence base. - P removal: Positive, primarily via sedimentation of particle-bound P. At one measured site (Spjald), P loss from adjacent field was 1.39 kg P/ha — most expected to be retained. - Cost: "Not assessed" in both catalogs. The model's 7,938 DKK/ha is therefore a model-internal parameter, not derived from the catalogs. - Confidence (N):** ** (somewhat uncertain; limited data)

Open questions

  1. IBZ_eff is field-specific — what is the range of values and how was it computed? (Likely derived from GIS analysis of drainage patterns and field slope)
  2. The 7,938 DKK/ha model cost is not from the catalog — what is its source? (Possibly from a separate IBZ cost study or SEGES estimate)
  3. ⚠️ IBZ is a relatively new measure; only two full-scale Danish sites were measured as of 2020. Are there newer monitoring results?
  • BZ10, BZ20 — dry buffer strips (different concept; mutually exclusive with IBZ)
  • PWET — P wetland (different construction; no mutual exclusion with IBZ)
  • P loss pathways — IBZ intercepts drain-transported P at the watercourse
  • P Reduction — IBZ enters P equation directly at up_lakecatch level
  • Constraints — IBZ has the most mutual exclusion rules in the model
  • Cost concepts — fixed cost (7,938 DKK/ha/yr); most expensive field measure