How to Implement User-Friendly BLMs in the Absence of DOC Monitoring Data: A Case Study on Bulgarian Surface Waters

The metal bioavailability concept is implemented in the Water Framework Directive (WFD) compliance assessment. The bioavailability assessment is usually performed by the application of user-friendly Biotic Ligand Models (BLMs), which require dissolved metal concentrations to be used with the “matching” data of the supporting physicochemical parameters of dissolved organic carbon (DOC), pH and Cadissolved. Many national surface water monitoring networks do not have sufficient matching data records, especially for DOC. In this study, different approaches for dealing with the missing DOC data are presented: substitution using historical data; the appropriate percentile of DOC concentrations; and combinations of the two. The applicability of the three following proposed substitution approaches is verified by comparison with the available matching data: (i) calculations from available TOC data; (ii) the 25th percentile of the joint Bulgarian monitoring network DOC data (measured and calculated by TOC); and (iii) the 25th percentile of the calculated DOC from the matching TOC data for the investigated surface water body (SWB). The application of user-friendly BLMs (BIO-MET, M-BAT and PNEC Pro) to 13 surface water bodies (3 reservoirs and 10 rivers) in the Bulgarian surface waters monitoring network outlines that the suitability of the substitution approaches decreases in order: DOC calculated by TOC > the use of the 25th percentile of the data for respective SWB > the use of the 25th percentile of the Bulgarian monitoring network data. Additionally, BIO-MET is the most appropriate tool for the bioavailability assessment of Cu, Zn and Pb in Bulgarian surface water bodies.

Impact of Irrigation Erosion on the Agrochemical Properties of Mountain-brown Soils and the Productivity of Cereals and Legumes

The cultivation of perennial grasses in mountainous areas protects the slopes from erosion and provides animals with good food. According to the results of the studies, it was determined that the restoration of fertility and the ecological balance of erosional lands and the implementation of soil and agrotechnical measures is of great importance for increasing yields. Thanks to the application of these measures, as a result of the improvement of the water-physical properties of the affected lands, runoff of surface waters is prevented. Perennial grasses accumulate the nitrogen atmosphere of legumes, enrich the soil with organic substances, accelerate the formation of a water-resistant granular-fuel structure and improve its water-physical properties, which in turn contributes to the rapid assimilation of minerals.