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

Zooplankton in Ancient and Oligotrophic Lake Ohrid (Europe) in Association with Environmental Variables

Zooplankton is studied in the ancient, tectonic, oligomictic and oligotrophic Lake Ohrid (Macedonia, South Eastern Europe). The main aim of this study was to assess the seasonal and spatial patterns of the zooplankton functional feeding guilds in relation to the environmental conditions. Metalimnion of the lake was detected as the most productive environment, where biomass of the phytoplankton and abundance of the zooplankton reached their maxima. Pelagial zooplankton of low abundance (25 ± 22 ind. L−1) consisted of 16 species including two endemic copepods, Arctodiaptomus steindachneri (Richard, 1897) and Cyclops ochridanus (Kiefer, 1932). Copepods obtained remarkable share (60%) in the zooplankton assemblage. Microphagous zooplankton was mainly comprised of the most abundant rotifer Kellicottia longispina (Kellicott, 1879) in summer, and copepod nauplii during the spring Eudiaptomus gracilis (Sars, 1862) and C.ochridanus, and autumn C.ochridanus. Due to their requirements for the bacterio-detritus suspension, this microphagous zooplankton occupied aphotic hypolimnion during the entire study period. Raptorials were typically represented by copepodites and adult copepods in the metalimnion, and were significantly and positively affected by temperature (r = 0.417, p = 0.001), dissolved oxygen (r = 0.463, p = 0.0001) and, particularly, phytoplankton biomass (r = 0.708, p < 0.00001). This is the first study in which the link between the lower and higher trophic levels is investigated in Lake Ohrid

Eutrophication of ancient Lake Ohrid: Global warming amplifies detrimental effects of increased nutrient inputs

Lake Ohrid in southeastern Europe is one of the few ancient, long-lived lakes of the world, and contains more than 200 endemic species. On the basis of integrated monitoring of internal and external nutrient fluxes, a progressing eutrophication was detected (similar to 3.5-fold increase in phosphorus (P) concentration in the lake over the past century). The lake is fortunately still oligotrophic, with high concentrations of dissolved oxygen (DO) in the deep water that are requisite for the unique endemic bottom fauna. Hypolimnetic DO is not only very sensitive to changes in anthropogenic P load-via mineralization of organic material-but also to global warming via decrease of vertical mixing and less frequent complete deep convection. Moreover, these two human effects amplify each other. To keep DO from falling below currently observed minimal levels-given the predicted atmospheric warming of 0.04 degrees C yr(-1)-the P load must be decreased by 50% in coming decades. However, even with such a reduction in P load, anoxia is still expected toward the end of the century if the rate of warming follows predictions

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

Testing the applicability of diatom indices for ecological assessment of Balkan lakes

During 2016-2017 six Balkan lakes were investigated: Sava Lake in Serbia, Ohrid Lake and Prespa Lake in North Macedonia and Albania, Great Lake in Albania, Biogradsko Lake and Crno Lake in Montenegro. Epilithic diatom samples were collected from 6 localities around each lake with the aim to test the applicability of diatom indices for ecological assessment of Balkan lakes. Also, water samples for chemical analysis were taken. Based on the concentrations of total phosphorus and BOD (biochemical oxygen demand) two lakes (Ohrid and Crno) were oligotrophic and oligosaprobic, while the other four lakes were mesotrophic and β-mesosaprobic, respectively. The highest diversity of dominant taxa was recorded in Ohrid and Prespa, and one of the dominant taxa was the endemic species Gomphonema paratergestinum. Diatom communities in lakes Sava and Crno were dominated by Achnanthidim minutissimum and Encyonopsis microcephala. According to Serbian legislation, the IPS index is used for the assessment of the ecological status of lakes, while in North Macedonia, Albania and Montenegro National Monitoring Systems do not yet include officially accepted diatom indices. In our results, the diatom indices IPS and IBD had the highest inclusion of diatom taxa, in some lakes almost 100%. The lowest inclusion of diatom taxa had the TDIL index. Values of IPS and IBD indices indicated very good water quality for Great Lake, Crno and Biogradsko, and good for Prespa. The water quality of Ohrid and Sava was between very good and good. Values of trophic indices (Rott TI and TDIL) indicated a very low concentration of nutrients in the Sava, Great Lake and Biogradsko, low in Ohrid and Prespa and low to the very low concentration of nutrients in Crno. The development and establishment of monitoring systems in lakes according to the requirements of the Water Framework Directive (WFD) is essential for all European countries and more comprehensive ecological investigations of Balkan lakes are necessary to be able to fulfill these demands.7th European Phycological Congress, Zagreb, Croatia, 25-30.08.201

Littoral eutrophication indicators are more closely related to nearshore land use than to water nutrient concentrations: A critical evaluation of stressor-response relationships

Biological assessment metrics and water chemistry measurements are used to quantify the link between stressors and their effects on lake ecosystems, for the Water Framework Directive. However, correlations between metrics and water chemistry are often poor. This is seen as major weaknesses of Water Framework Directive-related monitoring and assessment. We analyzed macrophytes, benthic algae, benthic macroinvertebrates, water chemistry and sediment total phosphorus content in the littoral of six lakes in the Western Balkans and used CORINE land use data to estimate nutrient enrichment via runoff from the adjacent land. Lakes with a higher estimated phosphorus runoff from the adjacent land did not have higher littoral water nutrient concentrations, but littoral diatom assemblages indicated more eutrophic conditions. These lakes also had higher abundances of littoral benthic primary producers, which in turn were associated with low concentrations of dissolved nutrients, but only in autumn, not in spring. This is consistent with primary producers taking up nutrients during the summer growth season. In lakes with high abundances of benthic primary producers, it is likely that the littoral vegetation plays a large role in the transfer of nutrients from the water to the benthos. This process impairs correlations between biological metrics and water nutrient concentrations. Our results suggest that CORINE land cover may be more useful to characterize littoral nutrient enrichment than lake water chemistry. Increased benthic primary producer biomasses and “eutrophic” diatom indices may indicate littoral nutrient enrichment even if water nutrient concentrations are low

Littoral eutrophication indicators are more closely related to nearshore land use than to water nutrient concentrations: A critical evaluation of stressor-response relationships

Biological assessment metrics and water chemistry measurements are used to quantify the link between stressors and their effects on lake ecosystems, for the Water Framework Directive. However, correlations between metrics and water chemistry are often poor. This is seen as major weaknesses of Water Framework Directive-related monitoring and assessment. We analyzed macrophytes, benthic algae, benthic macroinvertebrates, water chemistry and sediment total phosphorus content in the littoral of six lakes in the Western Balkans and used CORINE land use data to estimate nutrient enrichment via runoff from the adjacent land. Lakes with a higher estimated phosphorus runoff from the adjacent land did not have higher littoral water nutrient concentrations, but littoral diatom assemblages indicated more eutrophic conditions. These lakes also had higher abundances of littoral benthic primary producers, which in turn were associated with low concentrations of dissolved nutrients, but only in autumn, not in spring. This is consistent with primary producers taking up nutrients during the summer growth season. In lakes with high abundances of benthic primary producers, it is likely that the littoral vegetation plays a large role in the transfer of nutrients from the water to the benthos. This process impairs correlations between biological metrics and water nutrient concentrations. Our results suggest that CORINE land cover may be more useful to characterize littoral nutrient enrichment than lake water chemistry. Increased benthic primary producer biomasses and “eutrophic” diatom indices may indicate littoral nutrient enrichment even if water nutrient concentrations are low

Littoral eutrophication indicators are more closely related to nearshore land use than to water nutrient concentrations: A critical evaluation of stressor-response relationships

Biological assessmentmetrics and water chemistry measurements are used to quantify the link between stressors and their effects on lake ecosystems, for the Water Framework Directive. However, correlations between metrics andwater chemistry are often poor. This is seen as majorweaknesses ofWater Framework Directive-relatedmonitoring and assessment.We analyzed macrophytes, benthic algae, benthic macroinvertebrates, water chemistry and sediment total phosphorus content in the littoral of six lakes in the Western Balkans and used CORINE land use data to estimate nutrient enrichment via runoff from the adjacent land. Lakes with a higher estimated phosphorus runoff fromthe adjacent land did not have higher littoralwater nutrient concentrations, but littoral diatom assemblages indicated more eutrophic conditions. These lakes also had higher abundances of littoral benthic primaryproducers, which in turnwere associatedwithlowconcentrations of dissolved nutrients, but only in autumn, not in spring. This is consistent with primary producers taking up nutrients during the summer growth season. In lakeswith high abundances of benthic primary producers, it is likely that the littoral vegetation plays a large role in the transfer of nutrients from the water to the benthos. This process impairs correlations between biological metrics and water nutrient concentrations. Our results suggest that CORINE land cover may be more useful to characterize littoral nutrient enrichment than lake water chemistry. Increased benthic primary producer biomasses and “eutrophic” diatom indicesmay indicate littoral nutrient enrichment even ifwater nutrient concentrations are lo

Applications for zoosporic parasites in aquatic systems (ParAqua)

Zoosporic parasites (i.e. fungi and fungi-like aquatic microorganisms) constitute important drivers of natural populations, causing severe host mortality. Economic impacts of parasitic diseases are notable in the microalgae biotech industry, affecting production of food ingredients, biofuels, pharma- and nutraceuticals.While scientific research on this topic is gaining traction by increasing studies elucidating the functional role of zoosporic parasites in natural ecosystems, we are currently lacking integrated and interdisciplinary efforts for effectively detecting and controlling parasites in the microalgae industry. To fill this gap we propose to establish an innovative, dynamic European network connecting scientists, industries and stakeholders to optimize information exchange, equalize access to resources and to develop a joint research agenda. ParAqua aims at compiling and making available all information on the occurrence of zoosporic parasites and their relationship with hosts, elucidate drivers and evaluate impacts of parasitism in natural and man-made aquatic environments. We aim to implement new tools for monitoring and prevention of infections, and to create protocols and a Decision Support Tool for detecting and controlling parasites in the microalgae biotech production. Applied knowledge on zoosporic parasites can feed back from industry to ecology, and we therefore will explore whether the developed tools can be applied for monitoring lakes and reservoirs. Short-Term Scientific Missions and Training Schools will be organised specifically for early stage scientists and managers – with a specific focus on ITC – with the aim to share and integrate both scientific and applied expertise and increase exchange between basic and applied researchers and stakeholders