Water Purification Plugin for QGIS

Overview

This QGIS plugin quantifies the water‑purification ecosystem service provided by natural landscapes and river channels. It estimates the capacity of soils, vegetation and channel processes to remove nitrogen (N) and phosphorus (P), delivering spatially‑explicit indicators of purification value in both monetary and biophysical terms.

Key Features

• Two complementary models

  • Landscape model (Water Purification (landscape)): evaluates load reduction across Landscape Spatial Units (LSUs).
  • Channel model (Water Purification (channel)): evaluates in‑stream load reduction along river reaches.

• Top‑N ranking approach – you define how many of the highest‑performing pixels/reaches (parameter ntop) are used to calculate mean purification increments.

• Economic valuation – converts kg of purified N/P to Euros using life‑cycle cost formulas (CAPEX & OPEX) with user‑supplied discount rate and life expectancy.

• Accepts SWAT+ spatial outputs (*.sqlite) for baseline and restoration scenarios.

• Produces ready‑to‑map layers (NitroPurVal_*, PhoshPurVal_*) plus an optional intermediate statistics layer.

Installation

From the official QGIS Plugin Repository (recommended)

1. In QGIS, open Plugins ▸ Manage and Install Plugins….
2. Search for “Water Purification”.
3. Click Install Plugin.

Manual installation (development copies)

Clone or download this repository into your local QGIS profile’s python/plugins directory and restart QGIS.

Usage

1. Prepare the required input layers/files:

   • lsus2.shp – Landscape units (polygons).
   • rivs1.shp – Channel network (lines).
   • Baseline SWAT+ nut*.sqlite.
   • Restoration SWAT+ nut*.sqlite.

2. Launch the model from Processing ▶ Toolbox ▶ MERLIN.

3. Fill in parameters:

   Parameter	Description	Default
   actualisationrate	Discount rate (decimal)	0.03
   lifeexpectancyyears / life_expectancy_years	Asset life (years)	50 (LSU) / 20 (channel)
   ntop	How many top‑performing cells/reaches to average	3
   yearlyoperationmaintenancecosteurosha	O&M cost (€/ha yr)	3 850

4. Run the model; the plugin writes the outputs to the Processing context and adds them to the map.

License

This plugin is released under the MIT License – see LICENSE for details.