THE IMPACT OF PM2.5 FROM FOREST FIRES ON AIR POLLUTION DYNAMICS AND THE ECOSYSTEM OF LAKE OHRID

THE IMPACT OF PM2.5 FROM FOREST FIRES ON AIR POLLUTION DYNAMICS AND THE ECOSYSTEM OF LAKE OHRID Dhurata Premti University of Tirana, Faculty of Natural Sciences Department of Industrial Chemistry, Tirana, Albania ORCID ID: https://orcid.org/0000-0002-8018-2937 [email protected] Abstract This study focuses on emissions from forest fires in North Macedonia during the months of July and August 2024 and their role in air pollution dynamics in the protected area of Lake Ohrid, using a kinetic model based on differential equations. The aim is to assess the impact of PM2.5 concentrations (16.7 µg/m³ without fires and 40 µg/m³ during fires) on endemic biodiversity. The results show that without fires, biodiversity decreases by 24.7% in 60 days because of pollution, while during fires, biodiversity is reduced by 70.5% We modeled values of dissolved oxygen (DO) decreasing from 8.5 to 7.24 mg/L, increasing the risk of hypoxia and species extinction by 2-3 times. We emphasize the high sensitivity of Ohrid to particulate matter, providing a simple tool for ecological predictions and environmental management. Keywords: forest fires, air pollution, ecosystem Introduction Air pollution, especially from fine particles, constitutes a major and increasing threat to the ecological and functional integrity of protected ecosystems, including designated Heritage areas. These particles with an aerodynamic diameter of less than 2.5 μm, contain a complex matrix of toxic compounds, such as polycyclic aromatic hydrocarbons (PAHs), heavy metals, and secondary organic matter, which are transported over long distances and deposited in environments of sensitive aquatic and terrestrial, causing harmful cytotoxic, mutagenic, and ecotoxic effects (Vicente et al., 2018). Forest fires increase in number and intensity due to climate change and unsustainable land management, and become the main natural source of fine particles in the air. Recent studies, including those in regions affected by large wildfires such as California (USA) in 2008 and 2009, have shown that particulates emitted from biomass burning cause antioxidant and cytokine responses in the lung and increased pulmonary toxicity. (Wegesser et al., 2010; Wegesser et al., 2009). Southeastern Europe is characterized by a high frequency and intensity of fires, and this situation is particularly alarming. As pointed out in the analysis of Vicente et al. (2018), in southern Europe, where fires are becoming more frequent and severe, they pose serious health and ecological risks. Furthermore, the IUCN (2018) assessment of the state of nature protection systems in the South East European (SEE) region, which includes Albania and North Macedonia, suggests that fires represent one of the most widespread threats to the integrity of protected areas. European Forest Fire Information System (EFFIS), a component of the Copernicus Emergency Management Service, has reported that more than 85,000 hectares have burned during the 2024 summer (Figures 1 and 2.a) 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 48 of 199 Figure 1. Monthly fire frequency in the area influencing ecosystems around Ohrid Lake in 2024 a) b) Figure 2.a) Fires located in North Macedonia during summer 2024, source Copernicus, Sentinel 2, b) Environmental monitoring points according to the National Geospatial Data Infrastructure (NSDI) portal. Lake Ohrid is one of the most precious treasures of the Balkans, which lies on the border between Albania and North Macedonia. It is known as a transboundary lake and as a unique ecosystem among the oldest in Europe. Its early formation makes it a living testimony of Earth's history, 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 49 of 199 preserving a remarkable geological and biological heritage (Matzinger et al., 2007). With an area of 358 km² and a maximum depth of 289 meters, Lake Ohrid is one of the deepest and largest lakes in the region. Its volume of 55 km³ makes it a significant water reservoir, supporting not only biodiversity but also the local communities that depend on its resources. The average depth of 155 meters indicates a deep and complex structure, which has created conditions for the development of a rich and diverse ecosystem (Matzinger et al., 2006). Lake Ohrid enjoys a high protection status, being part of the UNESCO World Heritage and a candidate for the Natura 2000 network. In Albania, it has been declared a National Park, while at the international level, efforts to preserve it are based on the EU Water Directive (2000/60/EC) and the Habitats Directive (92/43/EEC). These measures, along with six environmental monitoring points (NSDI), aim to ensure a good ecological status (IUCN, 2016; IUCN, 2018). Materials and methods The biodiversity of Lake Ohrid is one of its most prominent features. It has over 200 endemic species, such as fish, Salmo letnica, and algae such as Cyclotella ohridana. These species are evidence of the unique evolution that has occurred in this ancient ecosystem. Conservation efforts for these species are in line with Natura 2000 objectives to ensure a favorable status for them (Matzinger et al., 2007; IUCN, 2018). According to the EU Water Directive (2000/60/EC), the concentration of total phosphorus (TP) for a good ecological status in lakes ranges from 10 to 60 µg/L, and increasing pollution is threatening this balance. In addition, global warming and forest fires that release PM2.5 particles are further endangering the health of this delicate ecosystem. The formation and impact of particles from forest fires contribute to the deposition of toxic particles, worsening anoxia and eutrophication, as observed in the sensitivity of Lake Ohrid to local anthropogenic impacts and global warming, as presented in the diagram below. 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 50 of 199 Figure 3. Chemical transformations of particulate matter and its influence on Ohrid Lake. For sensitive aquatic ecosystems, such as Lake Ohrid, a biodiversity hotspot with over 200 endemic species, deposition with its chemical toxicity is a key mechanism of degradation (Figure 3). This surface deposit causes: 1. Decrease of Dissolved Oxygen (DO): Toxic substances consume oxygen during oxidation in the water column, leading to hypoxia (DO), which is critical for sensitive species such as the fish Salmo letnica. 2. Increased Turbidity and Eutrophication: Inorganic and organic secondary materials from fires increase turbidity, inhibiting light penetration and promoting eutrophication, a process that adversely affects endemic algae such as Cyclotella ohridana. To carry out the assessment of the impact of fire-related concentrations (such as during fires, compared to baseline conditions) on the dynamics of and endemic biodiversity provides an essential tool for ecological management and risk prediction in transboundary protected areas such as Ohrid. The exponential kinetic model used to study the impact of particles on Lake Ohrid focuses on simulating the decline of DO as a consequence of the deposition of toxic particles from forest fires. This model is based on a simple exponential equation that relates the concentration of PM2.5 to the decrease in DO that reflects the sensitivity of the lake ecosystem to pollution. The model is designed to predict changes in water quality and help manage protected areas such as Lake Ohrid, a biodiversity hotspot. Base equation used to model dissolved oxygen: 𝐷𝑂𝑡= 𝐷𝑂0⋅ exp⁡(−𝑘 ⋅ 𝑃𝑀2.5) Where: 𝐷𝑂𝑡: dissolved oxygen at a fixed time 𝑡(mg/L). 𝐷𝑂0: Initial oxygen level, set as 8.5 mg/L (based on ideal lake conditions). k: Decomposition constant (0.05 1/(µg/m³)), which shows the sensitivity of DO to PM2.5. PM2.5: Concentration of PM2.5 particles (µg/m³), which varies based on conditions (without fires: 16.7 µg/m³; during fires: 40 µg/m³). The model takes into account the effects of PM2.5, such as polycyclic aromatic hydrocarbons (PAH) and heavy metals, which consume oxygen during oxidation and inhibit the photosynthesis of endemic algae such as Cyclotella ohridana. This leads to hypoxia and eutrophication, endangering species such as Salmo letnica. Input data for the model are taken from measurements during the period 1 July to 31 August 2024 and are supported by sources such as Copernicus (Sentinel 2, EFFIS) and NASA (FIRMS), which include: Daily average value 5.91 µg/m³ of PM2.5 concentrations with peaks up to 13.71 µg/m³ during fire peaks between July and August 2024. Extreme values include the baseline scenario (16.7 µg/m³ without fires) and the fire scenario (40 µg/m³). Initial DO (DO0): 8.5 mg/L, as a typical value for an oligotrophic lake like Ohrid. 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 51 of 199 Kinetic constant k: 0.05, based on the studies of Matzinger et al. (2006) on the sensitivity of the lake to pollutants. Simulation duration: 60 days (July to August 2024) to capture the impact of the North Macedonian fires. Data are supported by sources such as Copernicus (Sentinel-2, EFFIS) and NASA (FIRMS). Results and Discussions The PM2.5 concentration given in Figure 4 illustrates daily fluctuations in fine particulate matter levels around Lake Ohrid from July 1 to August 31, 2024, with values ranging from approximately 0.72 µg/m³ to 13.71 µg/m³, showing distinct peaks in mid-July and mid-August likely attributable to forest fire events in North Macedonia. The average daily PM2.5 was 5.91 µg/m³, frequently exceeding the baseline of 16.7 µg/m³ during non-fire periods but remaining below the fire scenario threshold of 40 µg/m³, indicating moderate but episodic elevation due to transboundary smoke dispersion. These results align with the IUCN METT assessment (2016), which identified fire and fire suppression as the most significant threat to Albanian protected areas, affecting 85% of sites with high-level impacts on natural system modifications. It is very important to focus on the vulnerability of Ohrid's ecosystem to such pollution dynamics, exacerbating eutrophication and biodiversity loss in this UNESCO-protected hotspot. Future strategies should implement crossborder fire management to mitigate air quality degradation in Natura 2000 candidate sites. Figure 4. Daily fluctuations in fine particulate matter levels around Lake Ohrid from July 1 to August 31, 2024 Figure 5 shows the daily changes of the oxygen levels modeled in the waters of Lake Ohrid. With an initial oxygen level of 8.5 mg/L and a decay constant of 0.05, DO values range from 4.28 mg/L (maximum fall on August 20) to near 8.2 mg/L during periods of low PM2.5. A smoothed 5-day 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 52 of 199 trend reveals two major declines in DO, which coincide with the peak of wildfire pollution. In basic conditions with 16.7 µg/m³ PM2.5, DO stabilizes around 6.5 mg/L, while during fires, with 40 µg/m³ PM2.5, DO drops to 4.5 mg/L, approaching the hypoxia threshold (<5 mg/L), which threatens endemic species such as Salmo letnica. Prediction of a biodiversity decrease of up to 70.5% over 60 days under wildfire conditions shows the high sensitivity of Ohrid compared to similar ancient lakes. This underlines the need for integrated monitoring to prevent irreversible eutrophication and the risk of species extinction amplified by fires. Figure 5. Daily fluctuations of Dissolved oxygen levels around Lake Ohrid from July 1 to August 31, 2024 The air pollution assessment described in Figure 6 evaluates daily PM2.5 against EPA (9.0 µg/m³) and WHO (5.0 µg/m³) standards. It shows exceedances on 45% of days for EPA and 68% for WHO, with peak concentrations reaching 13.71 µg/m³ and exceedance percentages up to 152% (EPA) and 274% (WHO) during August fire episodes. The dual-axis plot reveals correlated spikes in exceedance rates, averaging 35% over EPA and 78% over WHO thresholds, underscoring chronic air quality violations in the Ohrid region. Integrating METT insights (IUCN, 2016). 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 53 of 199 Figure 6. Daily fluctuations in fine particulate matter levels and exceedances around Lake Ohrid from July 1 to August 31, 2024 This aligns with identified pollution threats from human intrusions and biological resource use in protected areas, where 79% of Albanian sites face high pollution risks and ecosystem degradation. Several studies have identified that these transboundary PM2.5 elevations are linked to forest fires, and they intensify deposition into Ohrid's waters. This way increases turbidity and hypoxia, as different mathematical models have predicted. Stricter emission controls are required and Natura 2000 compliance to safeguard biodiversity hotspots against escalating climate and anthropogenic pressures. Conclusions Air pollution from fine particles emitted from anthropogenic and natural sources, such as forest fires, is a significant threat to sensitive ecosystems, especially to ancient lakes such as Ohrid. PM2.5, with its toxicity (eg, from polycyclic aromatic hydrocarbons and heavy metals), is deposited in water and leads to reduced dissolved oxygen (DO) and increased turbidity, causing loss of biodiversity and eutrophication. This study focuses on emissions from forest fires in North Macedonia during the summer months of July and August 2024 and their role in air pollution dynamics in the protected area of Lake Ohrid. Using a kinetic model based on Lotka-Volterra-type differential equations. We adapted the model for PM2.5 and DO. We focused on the impact of PM2.5 concentrations on endemic biodiversity (eg, Salmo letnica, Cyclotella ohridana). The results show that without fires, biodiversity decreases by 24.7% in 60 days. During fires, biodiversity is reduced by 70.5%, with DO decreasing from 8.5 to 7.24 mg/L. The risk of hypoxia and species extinction is increased by 1st SMPA-EU — Tetor 2025 Libri i Artikujve/Book of Proceedings 54 of 199 2 to 3 times. We see a high sensitivity of Ohrid to particulate matter, providing a simple tool for ecological predictions and environmental management. References IUCN. (2016). Initial assessment of protected areas in Albania. International Union for Conservation of Nature. https://www.iucn.org/content/initial-assessment-protected-areas-albania IUCN. (2018). State of nature conservation systems in South-Eastern Europe. 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