Influence of number of visitors and weather conditions on airborne particulate matter mass concentrations at the Plitvice Lakes National Park, Croatia during summer and autumn.

We investigated the influence of local meteorological conditions and number of visitors on ambient particulate matter (PM) mass concentrations and particle fraction ratios at the Plitvice Lakes National Park between July and October 2018. Outdoor mass concentrations of particles with aerodynamic diameters of less than 1, 2.5, and 10 µm (PM1, PM2.5, and PM10, respectively) and indoor PM1 were measured with two light-scattering laser photometers set up near the largest and most visited Kozjak Lake. Our findings suggest that the particles mainly originated from background sources, although some came from local anthropogenic activities. More specifically, increases in both indoor and outdoor mass concentrations coincided with the increase in the number of visitors. Indoor PM1 concentrations also increased with increase in outdoor air temperature, while outdoor PMs exhibited U-shaped dependence (i.e., concentrations increased only at higher outdoor air temperatures). This behaviour and the decrease in the PM1/PM2.5 ratio with higher temperatures suggests that the production and growth of particles is influenced by photochemical reactions. The obtained spectra also pointed to a daily but not to weekly periodicity of PM levels.

Carbon isotope fractionation in karst aquatic mosses.

Radiocarbon activity (a14C) and 13C composition (δ13C) 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 δ13C 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 a14Cmoss and δ13Cmoss 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 (ωatm.C) and carbon fractionation factor from aquatic CO2 (DIC) to moss tissue (εmoss/g-aq) were calculated for each individual moss. Three species of mosses had ωatm.C ∼ 0 % implying that they turn to anabiosis during dry periods. The relation εmoss/g-aqvs.ωatm.C differentiates true aquatic and amphiphyte mosses. The first had a statistically significant negative correlation between εmoss/g-aq and ωatm.C. The amphiphyte mosses had lower εmoss/g-aq with higher water flow rates.

Heavy metal contents in water, sediment and fish in a karst aquatic ecosystem of the Plitvice Lakes National Park (Croatia).

An evaluation of the quality status of the pristine karst, tufa depositing aquatic environment of the Plitvice Lakes National Park based on the analysis of heavy (ecotoxic) metals was examined for the first time. Analyses of trace metals in water, sediment and fish (Salmo trutta, Oncorhynchus mykiss, Squalius cephalus) samples were conducted either by stripping voltammetry (Zn, Cd, Pb and Cu) or cold vapour atomic absorption spectrometry (Hg). The concentration of dissolved trace metals in water was very low revealing a pristine aquatic environment (averages were, in ng/L: 258 (Zn), 10.9 (Cd), 11.7 (Pb), 115 (Cu) and 1.22 (Hg)). Slightly enhanced concentrations of Cd (up to 50 ng/L) and Zn (up to 900 ng/L) were found in two main water springs and are considered as of natural origin. Observed downstream decrease in concentration of Cd, Zn and Cu in both water and sediments is a consequence of the self-purification process governed by the formation and settling of authigenic calcite. Anthropogenic pressure was spotted only in the Kozjak Lake: Hg concentrations in sediments were found to be up to four times higher than the baseline value, while at two locations, Pb concentrations exceeded even a probable effect concentration. The increase of Hg and Pb was not reflected on their levels in the fish tissues; however, significant correlations were found between Cd level in fish tissues (liver and muscle) and in the water/sediment compartments, while only partial correlations were estimated for Zn and Cu. A high discrepancy between values of potentially bioavailable metal fraction estimated by different modelling programs/models raised the question about the usefulness of these data as a parameter in understanding/relating the metal uptake and their levels in aquatic organism. The aquatic environment of the Plitvice Lakes National Park is characterized, in general, as a clean ecosystem.