Current distribution, trends, abiotic and biotic preferences of two Elodea species in Bulgaria

Two invasive aquatic macrophyte species from the genus Elodea and their distribution in Bulgaria were studied. The research was based on 653 field surveys from the period 2009-2022. Elodea records constitute to only 6% of the database. Between the two species studied, E. nuttallii exhibited a wider distribution both in rivers and lakes (natural and artificial). Several instances of invaders’ dominance were observed, with E. nuttallii showing dominance patterns mainly in lakes, and E. canadensis in rivers. Both species were distributed in aquatic habitats with a wide variation in abiotic characteristics, except for the dominant substrate. E. nuttallii showed a more significant altitudinal range reaching above 1500 m. Such altitudinal variations resulted in diverse ecological habitats in terms of abiotic factors such as temperature and light intensity. The studied aquatic macrophyte communities demonstrated average species richness. Ceratophyllum demersum and Myriophyllum spicatum were the most commonly recorded representatives of the native aquatic flora. Canadian waterweed demonstrated the ability to form dense communities in rivers, while Nuttall’s waterweed retained average values of abundance. A case of natural disappearance within the Elodea species has been documented. The systematised information covering a 13-year period could serve to identify strategic areas for monitoring aquatic IAS and their management

Intercalibration of the national classifications of ecological status for Eastern Continental lakes: Biological quality Element: Macrophytes

Abstract The European Water Framework Directive (WFD) requires the national classifications of good ecological status to be harmonised through an intercalibration exercise. In this exercise, significant differences in status classification among Member States are harmonized by comparing and, if necessary, adjusting the good status boundaries of the national assessment methods. Intercalibration is performed for rivers, lakes, coastal and transitional waters, focusing on selected types of water bodies (intercalibration types), anthropogenic pressures and Biological Quality Elements. Intercalibration exercises were carried out in Geographical Intercalibration Groups - larger geographical units including Member States with similar water body types - and followed the procedure described in the WFD Common Implementation Strategy Guidance document on the intercalibration process (European Commission, 2011). The Technical reports are organized in volumes according to the water category (rivers, lakes, coastal and transitional waters), Biological Quality Element and Geographical Intercalibration group. This volume addresses the intercalibration of the Eastern Continental Lake GIG macrophyte ecological assessment methods. Three countries (Bulgaria, Hungary, Romania) participated in the intercalibration exercise and harmonised their lake macrophyte systems. The results were approved by the WG ECOSTAT and included in the EC Decision on intercalibration (European Commission, 2018).JRC.D.2-Water and Marine Resource

Can Biomarkers Respond Upon Freshwater Pollution?—A Moss-Bag Approach

Moss-bags were applied to study the effect of contamination in three standing water bodies in Bulgaria (Kardzhali, Studen Kladenets and Zhrebchevo Reservoirs), the first two with old industrial contamination and the last polluted with short-chain chlorinated paraffins (SCCPs). Fontinalis antipyretica Hedw. collected from background (unpolluted) site was placed in cages for a period of 30 days. The present study examined whether inorganic and organic pollution detected with moss-bags resulted in corresponding differences in molecular, chemical and micromorphological markers. Suppressed large subunit of ribulose-1,5-bisphosphate carboxylase (rbcL) expression was assessed in moss-bags from two of the reservoirs, contaminated with heavy metals. There was a decrease of the total phenolic content (TPC) in the moss-bags, which provides a basis for further studies of the chemical content of aquatic mosses. Fontinalis antipyretica also showed a response through leaf micromorphological characteristics. In the all three reservoirs, an increase of the twig leaf cell number was recorded (p ≤ 0.01 for Kardzhali and p ≤ 0.001 for Studen Kladenets and Zhrebchevo reservoirs), as well as of the stem leaf cell number in Zhrebchevo Reservoir (p ≤ 0.001). On the contrary, the width of the cells decreased in the studied anthropogenically impacted reservoirs. All three studied groups of biomarkers (molecular, chemical and micromorphological) appeared to be sensitive to freshwater pollution. The results achieved indicated that rbcL gene expression, TPC, cell number and size are promising biomonitoring tools

Anthropogenic Stressors in Upland Rivers: Aquatic Macrophyte Responses. A Case Study from Bulgaria

Upland rivers across Europe still exhibit undisturbed conditions and represent a treasure that we cannot afford to lose. We hypothesize that the combination of pristine and modified conditions could demonstrate biological responses along the stressor gradients. Thus, the response of aquatic macrophyte communities to anthropogenic stressors along upland rivers in Bulgaria was studied. Six stressors were selected out of 36 parameters grouped into hydromorphological, chemical variables and combined drivers (catchment land use). The stressors strongly affected species richness on the basis of biological type (bryophytes vs. vascular plants) and ecomorphological type (hydrophytes vs. helophytes). Hydrological alteration expressed by the change of the river’s base flow and altered riparian habitats has led to a suppression of bryophytes and a dominance of riverbank plant communities. Seventy-five percent of mountain sites were lacking bryophytes, and the vegetation at semi-mountainous sites was dominated by vascular plants. It can be concluded that hydropeaking, organic and inorganic pollution, and discontinuous urban structures caused important modifications in the aquatic macrophyte assemblages. Macrophyte abundance and the biological and ecomorphological type of aquatic macrophytes reflect multi-stressor effects in upland rivers

Integrated Monitoring with Moss-Bag and Mussel Transplants in Reservoirs

For the first time, transplants with moss-bags and mussels together were applied to study the water quality in standing water bodies. The tested species: Fontinalis antipyretica Hedw. and Sinanodonta woodiana (Lea, 1834) were collected from unpolluted sites and analyzed to obtain background levels. Then, the moss and mussels were left in cages for a period of 30 days in three reservoirs where both are not present naturally. Two of the reservoirs suffer from old industrial contamination and one is affected by untreated wastes. Twenty-four compounds were studied, among them trace elements Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn and organic priority substances: six polybrominated diphenyl ethers (PBDEs) congeners and short-chain chlorinated paraffins (SCCPs). The trace element accumulation was significant after the exposition period in all studied stations. PBDEs and SCCPs were also accumulated up to two times more in the moss tissues. PBDEs in the mussels exceeded the environmental quality standard (EQS). The applied combined transplants, and especially the moss-bags, revealed severe contamination with heavy metals not detected by the water samples. The moss and the mussel followed a different model of trace element and PBDEs accumulation. The SCCPs levels were alarmingly high in all plant samples. The study confirmed PBDEs and SCCPs as bioaccumulative compounds and suggested that an EQS for SCCPs in biota needs to be established

Macrophyte- and Macrozoobenthic-Based Assessment in Rivers: Specificity of the Response to Combined Physico-Chemical Stressors

The importance of adequate biological assessments of rivers based on aquatic assemblages is essential to establish recovery measures. Macrophyte and macroinvertebrate communities react differently in time and in response strength to diverse stressors. Our hypothesis was that each group response is a result of specific and combined abiotic factors and each stressor’s impact. To address the above, both biological quality elements (BQEs) and values of the ecological quality ratio (EQR) were studied in relation to four abiotic parameters and five physico-chemical stressors. Discrepancies of more than one degree between the ecological status assessments of Bulgarian river sites determined using macrophytes and macrozoobenthos were discussed. The RDA analysis showed that altitude had a determining role in shaping the abundance of macrophyte and macrozoobenthos communities. Aquatic flora richness positively correlated with nitrogen enrichment and macroinvertebrate fauna—with altitude and biochemical oxygen demand (BOD). Nutrients and shading were most significant for the ecological status evaluation defined with both macrophytes and macrozoobenthos. Macrophyte-based EQR was related to oxygen concentration and shading, while macroinvertebrate-based EQR was better at sites with coarser substrates. Among tested stressors, mainly total nitrogen and BOD explained the lower macrophyte-based assessment at half of the studied sites. In conditions of increased nitrogen and BOD, but remaining in the range of good status, macrophytes as primary producers gave a faster and stronger response. Despite the differences in the assessment, both BQEs have higher values in conditions of lower BOD and total phosphorus