Plant-based bioindicator development for monitoring urban air quality using epiphytic lichens and mosses

Project Abstract

Urban air pollution poses significant risks to human health and ecosystem integrity, yet routine monitoring often fails to capture spatial and temporal variability at the micro-environmental scale in dense urban landscapes. This study develops a plant-based bioindicator framework leveraging epiphytic lichens and mosses to monitor and map airborne contaminants, focusing on particulate matter (PM2.5 and PM10), heavy metals (e.g., lead, mercury, cadmium), nitrogen deposition, sulfur dioxide, and ozone exposure. The research integrates field-based biomonitoring with laboratory analyses to establish robust, site-specific relationships between pollutant loads and physiological and biochemical responses in selected bioindicator species. A systematic sampling design was implemented across multiple urban gradients, including residential, industrial, traffic-dominated, and green-space corridors, to capture variation in pollutant deposition and meteorological drivers. Lichen thalli and moss cushions were collected seasonally to account for temporal dynamics in uptake and detoxification processes. Morphological indicators (thallus color, tissue integrity) were recorded alongside physiological metrics such as chlorophyll fluorescence (Fv/Fm), primary photosynthetic efficiency, and photochemical quenching. Biochemical assays quantified oxidative stress markers (malondialdehyde, superoxide dismutase, catalase activities), secondary metabolite profiles, and antioxidant capacity. Accurate pollutant quantification was attained through inductively coupled plasma mass spectrometry (ICP-MS) for trace metals and high-resolution mass spectrometry for organic and inorganic species, complemented by X-ray diffraction and elemental mapping to discern localization within tissues. Statistical and geospatial analyses were employed to link biomonitoring responses with measured pollutant concentrations and meteorological parameters. Multivariate techniques, including principal component analysis and redundancy analysis, identified key biomarkers and composite indices that robustly discriminate pollution levels across sites. develop a standardized index, the Urban Lichen-Moss Bioindicator Index (ULMBI), integrating structural, physiological, and biochemical responses to produce high-resolution pollution maps. Temporal trend analyses examined seasonal responsiveness and potential lag effects between exposure and biological responses, while cross-validation with conventional air quality data from fixed monitoring stations assessed accuracy, sensitivity, and feasibility for supplementary monitoring networks. The study also evaluates the practicality of deploying lichens and mosses as citizen-science tools, including specimen preservation, field sampling protocols, and data quality assurance. Potential confounders such as microhabitat variation, host tree species, humidity, and light availability were controlled through stratified design and covariate adjustment. Findings demonstrate consistent, site-responsive biomarker patterns that correlate with PM, heavy metal, and gaseous pollutant regimes, with certain species exhibiting higher sensitivity and resilience, informing species selection for long-term monitoring. The research advances the applicability of plant-based bioindicators as cost-effective, scalable proxies for urban air quality, enabling spatially explicit exposure assessments, rapid screening of pollution hotspots, and integration with urban planning and public health initiatives to mitigate exposure risks and improve urban environmental quality.

Project Overview

What This Project Is About

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A simple, science-friendly look at using lichens and mosses to tell how clean or polluted city air is. The project tests whether these plants react in measurable ways to air pollutants and whether they can serve as cheap indicators of air quality over time.

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The Problem It Addresses

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Cities face varying pollution levels, and monitoring every street with expensive equipment isn’t practical. Lichens and mosses respond visibly to air quality, but it isn’t clear how best to use them as reliable, easy-to-interpret indicators for the public and policymakers.

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Objectives of the Project

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1. Identify which lichens and mosses are common enough in urban areas to study.
2. Determine which air pollutants influence their growth and appearance.
3. Develop simple scoring methods to describe air quality from plant observations.
4. Test measurements across different city sites to check consistency.
5. Propose practical guidelines for using these bioindicators in routine monitoring.

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What You Will Do Step by Step

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1. Review basic plant biology and what lichens and mosses are (definitions).
2. Collect plant samples from several urban sites with varied traffic and industrial activity.
3. Record visible changes and collect basic air data (e.g., dust, rain, humidity).
4. Analyze samples for specific pollutants if tools are available, or rely on visual scoring as a proxy.
5. Create simple scoring sheets and test them for reliability between observers.
6. Compare plant-based scores with available air-quality records to assess correlations.
7. Draft user-friendly guidelines for applying the method in other cities.

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Expected Outcome

Clear, repeatable indicators using lichens and mosses that reflect urban air quality, plus a practical protocol that teachers, students, or city planners can use to screen air pollution trends affordably.