Plitvice Lakes National Park is the oldest protected area in the Republic of Croatia and the biggest by its surface. The park is designated as the UNESCO World Heritage Site. Outstanding universal value is recognized within significant natural and geological processes, habitats and biodiversity. Only 1% of the park’s large surface is the main focal point for visitors and active tourism. We evaluated management of the park through Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis interpreting internal and external factors. High conservation of biodiversity, investments in different projects and high number of employees are considered as strengths. High number of visitors in small area and lack of visitor management plan, educational programs and marketing strategy are weaknesses. Threats are present through the inadequate management of drinking water supplies, lack of wastewater treatment plant and excessive construction in villages. Our opportunity definitely lies in protected nature and biodiversity. Considering very good status of the park’s finances, there aren’t any significant barriers for sustainable tourism approach, development of educational programs, various investments and adoption of new management plans. However, these activities must be beyond any potential political influence and they should have continuity in order for the park to be an example of quality management in the years to come.

Carbon isotope composition of dissolved inorganic carbon (DIC) was studied at springs, lakes and tributaries of the Plitvice Lakes. The Plitvice Lakes are a unique and complex karst lakes system consisting of 16 flow-through lakes connected by waterfalls and streams and characterized by intense calcium carbonate precipitation in the form of tufa and lake sediments. Two main springs have different ¹⁴ C concentrations due to different geology and their variations were controlled by flow rates. Further downstream, at lakes to the Korana River that outflows from the lakes, the ¹⁴ C activity and δ ¹³ C consistently increased down the flow. Carbon isotope composition from 2010 to 2015 was compared with the values measured 30 years earlier. The variation in δ ¹³ C _DIC was accounted for seasonal change, while ¹⁴ C activity of surface water DIC decreased 7–12% during the 30 years. Using a semi-empiric model, it is calculated that the downstream increase is controlled by the exchange of DIC and atmospheric CO ₂ carbon and by introduction of decomposed biogenic carbon from the top soil organic matter of the lakes surrounding area in almost equal proportions.

Radiocarbon activity (a¹⁴C) and ¹³C composition (δ ¹³C) were measured in hygrophyte and mesophyte (land) mosses collected in the natural habitat of the Plitvice Lakes and along the Zrmanja and Krupa Rivers (typical continental and Mediterranean climates, respectively), Croatia. a¹⁴C and δ ¹³C values of mosses, of atmospheric CO₂ and dissolved inorganic carbon (DIC) were compared with contemporary data and with data from 30 years ago at the Plitvice Lakes when ¹⁴C activity of atmospheric CO₂ was ∼30% higher. A positive correlation between a¹⁴C_moss and δ ¹³C_moss was observed for all data reflecting the change of carbon isotopic composition in DIC along the water flows and in atmospheric CO₂ regardless of the climatic regions and historic period. Fraction of the atmospheric carbon in moss $({\omega }_{\mathrm{atm}.\mathrm{C}})$ and carbon fractionation factor from aquatic CO₂ (DIC) to moss tissue $({\epsilon }_{\mathrm{moss}/\mathrm{g}-\mathrm{aq}})$ were calculated for each individual moss. Three species of mosses had ω _atm.C ∼ 0 % implying that they turn to anabiosis during dry periods. The relation ${\epsilon }_{\mathrm{moss}/\mathrm{g}-\mathrm{aq}}\text{vs}.{\omega }_{\mathrm{atm}.\mathrm{C}}$ differentiates true aquatic and amphiphyte mosses. The first had a statistically significant negative correlation between ${\epsilon }_{\mathrm{moss}/\mathrm{g}-\mathrm{aq}}$ and ${\omega }_{\mathrm{atm}.\mathrm{C}}$. The amphiphyte mosses had lower ${\epsilon }_{\mathrm{moss}/\mathrm{g}-\mathrm{aq}}$ with higher water flow rates.

Plitvice Lakes National Park (PLNP) is the oldest protected area in Croatia (since 1949) and was placed on the UNESCO World Heritage List in1979. It is an area of outstanding universal value consisting of a freshwater ecosystem of 16 lakes divided by tufa barriers. Recently, this area has experienced pressure from visitors and significant infrastructural development. When the previous Management Plan expired in 2017, the PLNP initiated and adopted a new Management Plan. This involved the zonation of management in order to better conserve and use this protected area. Management zonation was based on spatial and other data on the distributions of the species and habitats (Natura 2000 and others); cultural values and geo-localities; visitor experiences; existing and planned infrastructure and settlements. Visitor classes and zones were determined using the Recreation Opportunity Spectrum (ROS) methodology. The new management zonation resulted in an increase of 13.9% in the area of the Park included in the Strict Conservation Zone, while succession and habitat degradation resulted in a decrease in the area of the Park in the Active Management Zone, especially in terms of grassland. Six ROS classes were defined. The established ROS classes and the new management zonation were interconnected, each reflecting the need to manage the protected area in terms of conserving its specific biodiversity and geodiversity, while offering visitors various experience opportunities and meeting the needs of the local community.

The process of tufa deposition created the Plitvice Lakes, a unique freshwater cascade system of 16 lakes separated by tufa barriers. This complex karst hydrosystem reacts very sensitively to even small changes, and eutrophication can directly and indirectly affect tufa formation. With the purpose of determining the influence of nitrogen (N) and phosphorus (P) on periphyton’s chlorophyll a concentration, tufa deposition, and macrozoobenthos, we used nutrient-diffusing substrates. The in situ experiment combined the effects of seasons, stronger/weaker tufa deposition, and the presence/absence of macrophytes. The season was the dominant factor influencing hydrology, physicochemical factors, tufa deposition, and the effects of eutrophication. Phosphorus was the limiting factor for periphyton developing on artificial substrates, as evidenced by the highest chlorophyll a level on P and N+P substrates. Lower tufa deposition supported a higher chlorophyll a level, while macrophytes reduced the chlorophyll a concentration and tufa deposition, possibly through effects on the flow and via root respiration. The effects of nutrients on tufa deposition were not recorded. P and N+P treatment increased macrozoobenthos abundance only in some seasons. Trophic groups of macrozoobenthos responded to the addition of P and N+P in the form of higher proportions of gazers and detritivores; however, the response of macrozoobenthos was generally weaker than that of autotrophs.

Amphibians are a significantly and globally threatened group of vertebrates. In the European context, this particularly refers to the fire salamander (Salamandra salamandra Linnaeus, 1758), assessed as a vulnerable species due to a decreasing population trend. Threats affecting the population include climate change, habitat fragmentation due to road and infrastructure construction, and the fungal disease Bsal. Roadkill of amphibians during migration cycles also affects their abundance. In Plitvice Lakes National Park we monitored the number of fire salamander individuals on the road during spring and autumn migrations in 2023, including animals captured in passive traps along eight sections, and those found road-killed. Seven amphibian and one reptile species were recorded during this research. Selected mitigation measures to prevent fire salamander roadkill with the installation of temporary fences with pitfalls and funnel traps, singled out certain sections as more active, providing insight into the sex ratio of individuals and recording the number of casualties. The fire salamander was the most represented amphibian with 170 individuals captured in passive traps, 36 counted alive on the road, and 50 road-killed. Using individual recognition software Amphibian and Reptile Wildbook, 93.81% of individuals were confirmed to be captured only once during the study period. Through ongoing activity, additional data will be gathered on the number of migration routes, including road-killed individuals opposite the temporary fences, identifying new critical points, and documenting roadkills.