Robinia pseudoacacia is one of the most widely introduced—but also controversial—tree species in Europe. On the one hand, it is valued for its productivity, timber quality, and melliferous blossom. On the other hand, it is highly invasive and causes habitat change and homogenization. The aim of the study reported on here was to assess the genetic diversity of selected R. pseudoacacia stands in Lithuania in districts with the highest black locust stands frequency and to evaluate its spatial distribution in self-establishing stands. To achieve this aim, we employed four nuclear SSR loci (Rops 02, Rops 05, Rops 06, and Rops 08) and investigated the genetic diversity of five R. pseudoacacia plots. The study results reveal that R. pseudoacacia in Lithuania is genetically diverse (the average allele number per plot was 3.66, and the average Ho was 0.83). R. pseudoacacia in the plots forms tight clonal groups that hardly intermix with each other; it also spreads by seeds (66 single-copy genotypes were found in total in all 5 investigated plots). R. pseudoacacia stands in Lithuania originate from different seed sources and from different introduction events, as revealed by the allelic pattern, genetic diversity, and genetic differentiation among the research plots.

The improvement of urban wastewater treatment systems remains a key priority across Europe in order to achieve the long-term objectives of the EU Urban Waste Water Treatment Directive 91/271/EEC and reduce nutrient loading to the Baltic Sea basin. This study evaluates the temporal development of wastewater treatment performance in Kaunas City (Lithuania) over a 25-year period (2000–2025), based on continuous laboratory monitoring and technological modernization of the treatment system. Five core parameters were analysed—biochemical oxygen demand (BOD ₇ ), chemical oxygen demand (COD), suspended solids, total nitrogen and total phosphorus—to quantify removal efficiencies and identify long-term performance trends. The results demonstrate substantial improvement in treatment effectiveness, with BOD ₇ removal reaching up to 98%, nitrogen up to 90%, and phosphorus 90–95%, while COD and suspended solids removal consistently exceeded 85%. Performance in most years met or exceeded EU regulatory thresholds. Since treated effluents are discharged into the Nemunas River—one of the largest contributors to the Baltic Sea catchment—enhanced nutrient removal contributes to broader international efforts aimed at reducing eutrophication pressure in this ecologically sensitive marine basin. This study highlights Kaunas as a relevant example of long-term transition toward advanced biological nutrient removal in Central and Eastern Europe. The findings provide evidence-based guidance for wastewater utilities and policymakers aiming to strengthen nitrogen removal stability and address future challenges such as emerging pollutants, pharmaceuticals and microplastics.