New Dune Value Index Grades Bulgaria’s Black Sea Dunes From Near-Pristine to Degraded

Coastal dunes are among the most dynamic and most threatened landforms on Earth, continuously reshaped by waves, wind and storms while squeezed by tourism, infrastructure and mechanical beach grooming. Along the southern Bulgarian Black Sea coast, a new study has now introduced a standardised way to measure just how valuable — and how vulnerable — each dune system really is. The Eco-Geomorphological Dune Value Index, or EGDVI, integrates 31 indicators spanning geomorphology, ecology, human pressure, legal protection and scientific value into a single weighted score, and its pilot application to 16 dune systems along the Strandzha coast reveals a coastline split between near-pristine strongholds and advanced degradation hotspots.

The index was developed specifically for the Black Sea’s unusual coastal regime. Unlike the macro- and mesotidal environments where most existing dune assessment frameworks were conceived, the Black Sea is a microtidal, fetch-limited basin in which wind-generated waves, episodic storm surges and aeolian transport dominate, while tidal forcing is negligible. Under these conditions dune systems persist over longer timescales, sediment–vegetation feedbacks are more stable and successional stages reach greater maturity than on high-energy tidal coasts. Directly transferring indices built for tidal environments is therefore problematic, a limitation the study’s authors set out to address.

Technically, the EGDVI groups its 31 indicators into eight thematic categories: Geomorphology (five indicators, weighted 30%), Aeolian Dynamics (four indicators, 6%), Ecology (five indicators, 26%), Pressure/Risk/Stress (four indicators, 7.5%), Human Footprint (four indicators, 9.5%), Legal Protection and Management (five indicators, 10%), Scientific Importance (two indicators, 4%) and Nature Conservation (two indicators, 7%). Every indicator is scored on a standardised 0–4 scale, where higher values indicate greater natural value or better condition; for pressure-type indicators the logic is inverted so that higher scores always mean lower risk. Weighted scores are calculated as the product of each indicator score and its percentage weight, and the total EGDVI score is the sum of all 31 weighted scores, with a theoretical maximum of 400 corresponding to an ideal state in which every indicator reaches its highest value.

Indicator weights were not chosen arbitrarily. An interdisciplinary panel of coastal geomorphologists, dune ecologists and conservation practitioners first submitted independent weight proposals with justifications for each indicator and category; a second consensus round then reconciled differences and normalised the final weights to sum to 100%. Indicator scores themselves were derived from field surveys conducted between May and September 2025, high-resolution UAV photogrammetry and LiDAR transects, GIS analysis of shoreline position, dune width and infrastructure footprints, legislative and cadastral databases, and scientific literature and habitat inventories. Where data for a given indicator were unavailable, its weight was redistributed proportionally within the same category to preserve the overall balance.

Classification followed a hybrid two-step strategy. Jenks Natural Breaks optimisation was first applied to the pilot dataset to identify natural groupings and knife-edge cases, after which fixed reference thresholds were defined as percentages of the maximum score: Class A (Very High) at 320 or above, Class B (High) at 280–319, Class C (Moderate) at 220–279, Class D (Low) at 160–219 and Class E (Degraded) at 159 or below. This preserves Jenks’s statistical robustness for initial diagnostics while providing stable, transferable benchmarks for national monitoring frameworks. Sensitivity analyses confirmed the framework’s reliability: across one-at-a-time weight perturbations of ±10–20% and category-level scenarios shifting weight shares by up to ±15% between paired thematic categories, the rank order of dune systems remained highly stable, with changes limited to at most one class step and Spearman’s rank correlation between baseline and perturbed ranks exceeding 0.90.

Applied to the 16 Strandzha dune systems — which together cover 101.89 hectares, roughly 10.3% of Bulgaria’s total dune area — the index produced total scores ranging from 154.0 to 364.5 out of 400, a striking spread for a relatively compact coastal sector. Four systems (25.0%) achieved Class A Very High Value: Primorsko (Stomopolu–Perla), Primorsko (International Youth Centre), Koral, and Camping Yug and Lipite, with a class mean of 347.4 and a narrow interquartile range indicating that all four approach near-reference conditions. These sites combine wide, continuous dune belts often exceeding 100–150 metres, well-developed morphological sequences from embryonic dunes to foredunes and secondary ridges, high vegetation integrity with clear zonation, comparatively low anthropogenic pressure and favourable legal protection. Atliman stood alone in Class B with a score of 283.5, occupying a knife-edge transitional position where relatively minor shifts in management effectiveness could trigger upward or downward reclassification.

The regional picture is dominated by the middle of the scale. Eight systems (50.0%) — including the Veleka River Mouth, Kiten, Butamyata, Ahtopol, Listi, Silistar, Nestinarka and Oazis — fall within Class C Moderate Value, with a class mean of 258.9 and limited internal dispersion. Most retain functional dune units and key geomorphological elements yet show varying degrees of fragmentation, reduced sediment connectivity and visible anthropogenic influence in the foredune zone. Lozenets scored as Class D Low Value, marked by a narrow, discontinuous dune belt, disrupted vegetation cover and diminished morphodynamic function, while Tsarevo (Popski plazh) and Arapya landed in Class E Degraded, exhibiting extensive loss of frontal dune ridges, sparse psammophytic vegetation and a near absence of coastal-protection function. The regional mean score of 266.1 and median of 261.2 both fall within the moderate-value class, confirming that transitional dune systems dominate the Strandzha coast rather than a landscape uniformly pristine or uniformly ruined.

A detailed case study of the top-scoring site, Primorsko (Stomopolu–Perla), with its total of 364.5, illustrates how the index dissects a dune system dimension by dimension. All five geomorphological indicators received the maximum score of 4, reflecting dunes both higher than 5 metres and wider than 100 metres with fully functional hydrogeomorphic connectivity and no fragmentation. Aeolian dynamics indicators scored 3, indicating a system that is active but stable, with blowouts limited to under 10% of extent and sand supply sufficient to sustain development. Ecological indicators also reached 4, confirming vegetation cover above 60% with strong representation of pioneer species such as Ammophila and Elytrigia alongside typical psammophytes and several conservation-priority habitat types. Pressure indicators told a more nuanced story: marine exposure scored just 1, reflecting strong wave energy and frequent storm overwash at the dune front, while degradation risk scored 3, macro-litter pollution 3 and invasive alien species 2, signalling limited but detectable ecological disturbance.

The governance dimension of the case study proved equally revealing. Land ownership and access regulation, cadastral recognition and scenic value all scored 4, and protected area status scored 3, yet the absence of designation under EU or national restoration frameworks scored 0 — a clear policy gap showing that even Bulgaria’s most valuable dune system is not yet integrated into strategic restoration planning. Recreational use intensity scored 2, indicating moderate visitor pressure with localised trampling during peak seasons, and periodic mechanical beach cleaning scored 3. This capacity to capture both outstanding conservation value and subtle institutional shortcomings is precisely what distinguishes the EGDVI from simple ranking approaches, the authors argue, and what strengthens the science–policy interface by ensuring that legal recognition and research relevance are explicitly quantified rather than treated qualitatively.

The study’s authors position the EGDVI as complementary to, rather than a replacement for, the conservation status assessments Bulgaria reports under Article 17 of the EU Habitats Directive, which suffer from considerable uncertainty due to limited standardised field-based monitoring and methodological inconsistencies in Natura 2000 implementation. By combining fixed classification thresholds with sensitivity analysis and explicitly linking classes to management pathways — strict protection and monitoring for Class A, preventative measures such as boardwalks and fencing for Class B, targeted restoration for the numerically dominant Class C, and progressively more demanding rehabilitation for Classes D and E — the index moves beyond descriptive assessment towards actionable conservation planning. Its conceptual structure is considered transferable to other microtidal and enclosed-sea coastal environments, from the Baltic to parts of the Mediterranean, provided that indicators are locally calibrated, and future refinements incorporating time-series observations, UAS- and LiDAR-based mapping and machine-learning approaches are expected to further enhance its analytical resolution.

Subject of Research: Development and pilot application of a multi-criteria dune conservation assessment index on the Bulgarian Black Sea coast

Article Title: Development and application of the Eco-Geomorphological Dune Value Index (EGDVI) for assessment of conservation status: a pilot case at the Strandzha Black Sea Coast, Bulgaria

Article References: Prodanov, B., Bekova, R., Valcheva, M., Tzonev, R., & Baltakova, A. (2026). Development and application of the Eco-Geomorphological Dune Value Index (EGDVI) for assessment of conservation status: a pilot case at the Strandzha Black Sea Coast, Bulgaria. One Ecosystem, 11, Article e189660. https://doi.org/10.3897/oneeco.11.e189660

Image Credits: AI Generated

DOI: 10.3897/oneeco.11.e189660

Keywords: coastal dunes, EGDVI, conservation index, Black Sea, Bulgaria, Strandzha, coastal geomorphology, dune ecology, microtidal coast, science-policy interface, Development, application