The Balkan Macrophyte Index (BMI) for Assessment of Eutrophication in Lakes

Aquatic plants have long been used as indicators for nutrient enrichment in lakes. In the Mediterranean, however, the process of developing and intercalibrating macrophyte assessment methods for lakes has lagged behind Northern and Central Europe, likely due to the relatively small number and high variability of natural lakes in the Mediterranean but also because of the different monitoring traditions in different parts of Europe. We here present a macrophyte index for assessment of lake eutrophication, tailored to Balkan lakes (Balkan Macrophyte Index, BMI). We analysed submerged aquatic vegetation, water chemistry and sediment total phosphorus content at several sites in lakes Prespa, Ohrid, Lura, Biogradsko, Crno and Sava, located in Albania, North Macedonia, Montenegro and Serbia. Despite the restricted number of lakes in our dataset, the BMI was loosely related to water phosphorus, rather than nitrogen, concentrations. Our results show that macrophyte indices may not be applicable in lakes experiencing annual water level fluctuations of several meters, because the macrophyte vegetation in such lakes may be absent, or alternatively dominated by “oligotrophic” or “eutrophic” species. Once a larger number of lakes has been analysed using the same methods, reference conditions and status class boundaries may be derived from the phosphorus – BMI regression

Relating environmental pressures to littoral biological water quality indicators in Western Balkan lakes: Can we fill the largest gaps?

Along six transects in each of six lakes across the Western Balkans, we collected data for three groups of littoral biological water quality indicators: epilithic diatoms, macrophytes, and benthic invertebrates. We assessed the relationships between them and three environmental pressures: nutrient load (eutrophication), hydro-morphological alteration of the shoreline, and water level variation, separating the effect of individual lakes and continuous explanatory variables. Lake water total phosphorus concentration (TP) showed substantial variation but was not related to any of the tested biological indicators, nor to any of the tested pressures. We suggest that this may be due to feedback processes such as P removal in the lake littoral zone. Instead, we found that a gradient in surrounding land-use towards increasing urbanization, and a land-use-based estimate of P run-off, served as a better descriptor of eutrophication. Overall, eutrophication and water level fluctuation were most important for explaining variation in the assessed indicators, whereas shoreline hydro-morphological alteration was less important. Diatom indicators were most responsive to all three pressures, whereas macrophyte biomass and species number responded only to water level fluctuation. The Trophic Diatom Index for Lakes (TDIL) was negatively related to urbanization and wave exposure. This indicates that it is a suitable indicator for pressures related to urbanization, although a confounding effect of wave exposure is possible. Invertebrate abundance responded strongly to eutrophication, but the indicator based on taxonomic composition (Average Score Per Taxon) did not. Our results suggest that our metrics can be applied in Western Balkan lakes, despite the high number of endemic species present in some of these lakes. We argue that local water management should focus on abating the causes of eutrophication and water level fluctuation, whilst preserving sufficient lengths of undeveloped shoreline to ensure good water quality in the long run

Nutrient retention by the littoral vegetation of a large lake: Can Lake Ohrid cope with current and future loading?

Nitrogen and phosphorus budgets were compiled for the littoral (29 km2) and pelagic (329 km2) of ancient, deep, clear, and hard water Lake Ohrid (Albania and North Macedonia), to assess the importance of the littoral in nutrient retention. P originates mainly from domestic point sources (73%), for N this is karst seepage (50%). Total littoral loads are estimated at 1700 kg P and 23,200 kg N km−2 (area of littoral) yr−1; net littoral retention is 31% ± 13% for P and 40% ± 16% for N, largely in the dense charophyte belt. P retention is mainly due to detritus burial, but also due to coprecipitation; N retention is due to both detritus burial and denitrification. A Monte‐Carlo plausibility analysis balanced the budget by increasing nonconnected domestic household inputs (from 20% to 27% of external load), and decreasing pelagic sediment P burial by 27% and littoral denitrification by 25%. Scenario projections for 2100 corresponding to SRES A2 and B1 were linked to an AQUASIM lake ecosystem model. Under B1, the changes were small compared to the present. A2, however, led to a major reduction in precipitation, an increase in evapotranspiration, a reduction in river outflow (to ∼ 20%), a doubling in P‐loading, a drop in lake level of ∼ 1.5 m, and a decline in the extent of the charophyte belt. Areal loading of the littoral would increase accordingly, but water transparency would not decline much. Also, the littoral vegetation will witness a shift in species composition, and an increase in filamentous Cladophora cover

Nutrient retention by the littoral vegetation of a large lake: Can Lake Ohrid cope with current and future loading?

Nitrogen and phosphorus budgets were compiled for the littoral (29 km2) and pelagic (329 km2) of ancient, deep, clear, and hard water Lake Ohrid (Albania and North Macedonia), to assess the importance of the littoral in nutrient retention. P originates mainly from domestic point sources (73%), for N this is karst seepage (50%). Total littoral loads are estimated at 1700 kg P and 23,200 kg N km−2 (area of littoral) yr−1; net littoral retention is 31% ± 13% for P and 40% ± 16% for N, largely in the dense charophyte belt. P retention is mainly due to detritus burial, but also due to coprecipitation; N retention is due to both detritus burial and denitrification. A Monte‐Carlo plausibility analysis balanced the budget by increasing nonconnected domestic household inputs (from 20% to 27% of external load), and decreasing pelagic sediment P burial by 27% and littoral denitrification by 25%. Scenario projections for 2100 corresponding to SRES A2 and B1 were linked to an AQUASIM lake ecosystem model. Under B1, the changes were small compared to the present. A2, however, led to a major reduction in precipitation, an increase in evapotranspiration, a reduction in river outflow (to ∼ 20%), a doubling in P‐loading, a drop in lake level of ∼ 1.5 m, and a decline in the extent of the charophyte belt. Areal loading of the littoral would increase accordingly, but water transparency would not decline much. Also, the littoral vegetation will witness a shift in species composition, and an increase in filamentous Cladophora cover

Macrophyte vegetation as a structuring factor of the macrozoobenthic communities in Lake Ohrid

The macrophyte communities in Lake Ohrid have a key role in general maintaining of the lake’s metabolism. They are particularly important for the distribution and structuring of rich benthic macroinvertebrate assemblages, in as much as they provide a constant stream of oxygen, are an important source of food and serve as shelter from predators. A survey at six sites along the coastal zone of Lake Ohrid was conducted in order to determine the role of macrophyte communities in structuring of the macrozoobenthos inhabiting the littoral zone of the lake. With respect to species composition, the results point to the Gastropoda, with 23 registered taxa, as the most diverse among the seven groups of benthic fauna. The second most diverse was the group of Insecta with 11 species, followed by Hirudinea and Oligochaeta with seven species, while six species from Crustacea were registered. The lowest biodiversity was registered for Bivalvia and Turbellaria – three species from each group. It was also found that mixed stands of Charophyta with other macrophytes where Charophyta species predominate represent the most attractive habitats, being inhabited by 54 species, versus homogenous stands of Chara tomentosa, where 36 species were registered. The most abundant species were Dreissena presbensis and Radix relicta, which reached their maximum densities on homogenous stands of Chara tomentos

The Balkan macrophyte index (BMI): a new tool for assessing the ecological status of lakes

In Europe, macrophytes have for a long time been used as indicators of eutrophication and for the assessment of ecological status of lakes. Almost twenty assessment systems were developed in the last years, but most of them focused on lakes in Northern and Central Europe. The Mediterranean region, and especially the Balkan, lag behind, probably because of the relatively small number and high variability of natural lakes and the lack of collaboration among Balkan countries. The Balkan macrophyte index (BMI) we developed is designed to assess eutrophication in lakes in the Balkan region. The data we used were gathered in six Balkan lakes: Ohrid, Prespa, Lura, Biogradsko, Crno and Sava, located in Macedonia, Albania, Montenegro and Serbia. Submerged aquatic vegetation, water chemistry and sediment total phosphorus were analysed. Our results show that calculating a macrophyte index can be a problem in lakes with water level fluctuations of several meters, because the macrophyte vegetation may be absent or these lakes are dominated by “oligotrophic” or “eutrophic” species. Even though the number of lakes was small in our study, the BMI was loosely related to water phosphorus concentrations. If we analyse a larger number of lakes using the same methods, reference conditions and status class boundaries may be derived from the phosphorus BMI regression

Nutrient retention by the littoral vegetation of a large lake: Can Lake Ohrid cope with current and future loading?

Nitrogen and phosphorus budgets were compiled for the littoral (29 km2) and pelagic (329 km2) of ancient, deep, clear, and hard water Lake Ohrid (Albania and North Macedonia), to assess the importance of the littoral in nutrient retention. P originates mainly from domestic point sources (73%), for N this is karst seepage (50%). Total littoral loads are estimated at 1700 kg P and 23,200 kg N km−2 (area of littoral) yr−1; net littoral retention is 31% ± 13% for P and 40% ± 16% for N, largely in the dense charophyte belt. P retention is mainly due to detritus burial, but also due to coprecipitation; N retention is due to both detritus burial and denitrification. A Monte‐Carlo plausibility analysis balanced the budget by increasing nonconnected domestic household inputs (from 20% to 27% of external load), and decreasing pelagic sediment P burial by 27% and littoral denitrification by 25%. Scenario projections for 2100 corresponding to SRES A2 and B1 were linked to an AQUASIM lake ecosystem model. Under B1, the changes were small compared to the present. A2, however, led to a major reduction in precipitation, an increase in evapotranspiration, a reduction in river outflow (to ∼ 20%), a doubling in P‐loading, a drop in lake level of ∼ 1.5 m, and a decline in the extent of the charophyte belt. Areal loading of the littoral would increase accordingly, but water transparency would not decline much. Also, the littoral vegetation will witness a shift in species composition, and an increase in filamentous Cladophora cover

The Sava Lake – charophyte gem in the heart of Belgrade

The Sava Lake, originating from a branch of the Sava river, is situated next to the island Ada Ciganlija on the right bank of the Sava river in Belgrade (Serbia). It is an urban recreational lake under strong anthropogenic influence, especially during the summer days. Investigations of aquatic vegetation were conducted several times during the last decades and the latest systematic survey was conducted in summer 2017 as a part of STARWALK project. Since then, sampling was continued sporadically, revealing a great diversity of charophyte algae. Overall,we discovered eight charophyte species in the lake, which is a remarkable number even for unimpacted natural lakes. The species found belong to four out of six genera of living charophytes. The genus Chara is represented with three species, C. globularis, C. contraria and C. virgata, the genus Nitella also with three, Nitella mucronata, N. gracilis, N. flexilis, and genera Tolypella and Nitellopsis with one species, respectively, T. intricata and N. obtusa. Moreover, almost all discovered species are red listed in Serbia and the Balkans, according to IUCN criteria. Six of them are strictly protected according to national legislation. The finding of Nitella flexilis was the first finding of this species for Serbia

Anti-quorum sensing activity of selected sponge extracts: a case study of Pseudomonas aeruginosa

The anti-quorum sensing activities towards the bacterium Pseudomonas aeruginosa PA01 (pyocyanin production, biofilm formation and twitching and flagella motility) of two crude extracts (methanol and acetone) of the freshwater sponge Ochridaspongia rotunda (Arndt, 1937) were evaluated in vitro for the first time. Both extracts demonstrated P. aeruginosa pyocyanin inhibitory activity, reducing its production for 49.90\% and 42.44\%, respectively. In addition, they both showed higher anti-biofilm activity (48.29\% and 53.99\%, respectively) than ampicillin (30.84\%). Finally, O. rotunda extracts effectively reduced twitching and flagella motility of P. aeruginosa. Taken all together, these results suggest that endemic sponge species from the oldest lake in Europe may offer novel bioactive natural products with promising medicinal potential towards P. aeruginosa infections.Ministry of Education, Science and Technological Development of the Republic of Serbia {[}172053, 173032

Eutrophication impacts littoral biota in Lake Ohrid while water phosphorus concentrations are low

Eutrophication has traditionally been measured as increased phosphorus concentrations. In some lakes, however, such as transboundary Lake Ohrid situated between Macedonia and Albania, pelagic phosphorus concentrations are low, in spite of known sources of nutrient input. We assumed that littoral biota may be more responsive to phosphorus load than water chemistry, and studied nearshore water chemistry, macrophytes, diatoms and macroinvertebrates at 30 sites around the lake, analyzing functional groups as well as standard eutrophication metrics. We hypothesized that the incorporation of nutrients into benthic biomass will conceal correlations between water phosphorus concentrations and biological eutrophication metrics, but that analysis of functional groups in addition to eutrophication metrics may help draw a plausible picture of how phosphorus is transferred through the food web. Water total phosphorus concentrations in the Lake Ohrid littoral were generally low, while all three analyzed organism groups indicated at least some degree of eutrophication. This shows that littoral biota are more sensitive indicators of nutrient input than hydrochemistry. The abundance of the benthic alga Cladophora sp. correlated positively with water total phosphorus concentrations, indicating that P-loading at local scales may be an important driver of Cladophora biomass. In contrast, none of the biotic metrics (macrophyte index, diatom index, and macroinvertebrate ICM) correlated with ambient water P-concentrations. We argue that this is not a sign of poorly working biological metrics, but a consequence of ecosystem processes in the lake littoral. Analysis of macrophyte and benthic algae abundance, and macroinvertebrate feeding types together with the biotic metrics suggests a meso- to slightly eutrophic littoral ecosystem where nutrient supply is incorporated into macrophyte and benthic algae biomass, and transferred through the food web from benthic algae to grazers, and from macrophytes to shredders and gatherers. Macroinvertebrate filter feeders correlate negatively with water total phosphorus concentrations, suggesting they remove phosphorus from the water. Our results indicate that the combined use of classical biological eutrophication metrics and functional groups may be a way to not only distinguish between oligotrophic and eutrophic ecosystems, but in addition give information as to whether or not nutrient input and nutrient removal in an ecosystem are balanced. This may eventually also give information about ecosystem functioning and ecosystem stability, and thus provide a basis for the development of “second generation” metrics for ecosystem assessment.acceptedVersio