Bryophytes play important role in forest ecosystem functioning and their distribution and diversity are driven by numerous environmental factors. The aim of the present study was to bring new ...insights in deeper understanding of terrestrial bryophytes diversity in temperate forests, as well as to determine the environmental factors which have predominant influence on ground-floor bryophytes. The survey was conducted in Fruška Gora Mountain (Serbia) across seven forest sites where ground-bryophytes were sampled. Soil moisture, temperature, and pH were measured as soil characteristics, while herbaceous cover, litter cover, stream distance, number of trees and shrubs were used as characteristics of stand structure. Species richness, Shannon diversity index, and evenness index were used as diversity measures. Generalised linear model and canonical correspondence analysis (CCA) were used to test the influence of environmental variables on bryophyte diversity. Litter cover was the most important explanatory variable, followed by soil moisture, stream distance and tree number, respectively. Overall, the stand structure was found to have a greater impact on ground-floor bryophyte diversity compared to soil characteristics. Identification of the most significant ecological factors affecting the diversity and distribution of bryophytes in forest ecosystems is of great importance in forest ecology with the aim of defining adequate management methods to preserve the biodiversity of forests, with particular emphasis on endangered and rare bryophyte species.
•The Danube water quality was predicted using macrophyte binary data.•The developed model showed good predictive performances in the main river channel.•The sensitive analysis selected 28 macrophytes ...as significant water quality indicators.
Ecological assessment of large rivers such as the Danube is a challenging task. Eutrophication was reported as one of the main drivers that structure aquatic communities in the Danube basin. Due to their sedentary nature, relatively slow growth/ long life spans, and engineering role in aquatic ecosystems, macrophytes are widely used in the detection of nutrient enrichment. In this study, macrophyte presence-absence data within the 3 km long reaches obtained from the Joint Danube Survey (JDS3) were used to predict the water quality of the Danube river and its main tributaries. For each water quality variable (dissolved oxygen, nitrate-nitrogen, and orthophosphates), a multi-layer feed-forward artificial neural network model (ANN) was constructed using the macrophytes as explanatory variables. Despite the limited number of samples (123) along the wide trophic gradient of the Danube, the model showed good predictive performances for the main river channel. The highest discrepancy between observed and predicted water quality was obtained for the samples collected in the tributaries or downstream from the tributaries' mouth, where the model predicted better trophic conditions compared to measured ones. From 64 analysed macrophyte species, 28 were selected by sensitivity analysis as key water quality indicators (KIS) for at least one environmental variable. KIS mainly belonged to the eutrophic tolerant submerged or emerged species with broad ecological amplitude, which reflects the significance of the developed model for use on rivers subjected to nutrient pollution. However, the use of the developed predictive model is restricted to the river sections having a water velocity suitable for macrophytes growth. The developed ANN architecture represents the modelling approach which could be applied to other lotic systems and biological quality elements.
The ecological state of the Danube River, as the world’s most international river basin, will always be the focus of scientists in the field of ecology and environmental engineering. The ...concentration of orthophosphate anions in the river is one of the main indicators of the ecological state, i.e., water quality and level of eutrophication. The sedentary nature and ability to survive in river sections, combined with the presence of high levels of orthophosphate anions, make macrophytes an appropriate biological parameter for in situ prediction of in-river monitoring processes. However, a preliminary literature review identified a lack of comprehensive analysis that can enable the prediction of the ecological state of rivers using biological parameters as the input to machine learning (ML) techniques. This work focuses on comparing eight state-of-the-art ML classification models developed for this task. The data were collected at 68 sampling sites on both river sides. The predictive models use macrophyte presence scores as input variables, and classes of the ecological state of the Danube River based on orthophosphate anions, converted into a binary scale, as outputs. The results of the predictive model comparisons show that support vector machines and tree-based models provided the best prediction capabilities. They are also a low-cost and sustainable solution to assess the ecological state of the rivers.
We hypothesize that the physical features of river habitats and anthropogenic hydromorphological alterations influence macrophyte communities and lead to habitat fragmentation. Sampling included 1081 ...contiguous survey units positioned in the main channel and side arms along 588km of the Danube River, along its middle course. To identify habitat fragments, Multivariate Regression Tree analysis (MRT) was applied on macrophyte and environmental data. Indicator species analyses were combined with MRT. To identify habitat fragments on a scale larger than final MRT groups, we set thresholds for an MRT complexity parameter. We identified 20 fine, 7 medium, and 3 large scale habitat fragments. Damming was the main fragmentation agent. Macrophyte communities show continuous variation at all scales of habitat fragmentation. High species diversity indicates major anthropogenic alteration of the river's hydrology and decline of the natural riparian zone. Future studies of the macrophyte communities, and their habitat fragmentation must include more factors (e.g. nutrient status, physicochemical quality of the water, etc.), as well as assessment of the importance of tributaries.
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•River habitat fragmentation occurs on fine, medium and large scale.•Dams are the main fragmentation agent.•High species diversity indicates major hydro-morphological pressure.•Edge habitat has high conservation value.
UAV technologies provide a time- and cost-efficient framework for a variety of environmental monitoring domains. It also increases data resolution and provides new insights into observed objects and ...phenomena, especially within the difficult-to-access and complex for monitoring aquatic habitats. The objective of this study was to develop UAV-based acquisition and GIS-based image processing guidelines for aquatic macrophyte detection and monitoring in large temperate rivers. According to the European standard CEN EN -14184:2014, the assessment of aquatic macrophytes should be performed using the transect approach. Large rivers, such as the Danube, represent an exception and should be evaluated using 1km transects. Therefore, seven transects of the Middle Danube in Serbia were simultaneously surveyed using traditional field methods and novel UAV technology. UAV images were acquired using RGB and multispectral cameras carried by a fixed-wing drone. The images were processed and orthomosaics were classified using Object Based Image Analysis (OBIA), to create digital GIS maps of the river transects. During the traditional monitoring approach, the relative abundance of 22 macrophyte species was recorded along the transects. Using the UAV technology and OBIA approach eight macrophyte classes were distinguished based on dominant macrophyte taxa or plant life form traits. Aquatic macrophytes were 'almost perfectly' distinguished from the orthomosaics, achieving a high classification accuracy of 96 % / 88 % / 0.84 for RGB and 94 % / 97 % / 0.95 Producers /Users accuracy/Kappa index for the multispectral approach. Individual macrophyte classes accuracy varied between 0.5 and 1 Kappa and were generally higher for the multispectral imagery approach. Although the resolution of the taxonomic data is lower, UAV monitoring provided the necessary spatial context of macrophytes distribution and absolute area occupied by macrophytes. It also provided information on the diversity and distribution of habitats along the river. Therefore, the UAV-assisted monitoring approach described in this study can be effectively integrated into macrophyte monitoring during large river expeditions such as the JDS.
Riparian areas experience strong invasion pressures worldwide and represent important points of spread for invasive alien plants (IAPs) in the European mainland. The Danube Basin is a well-known ...point of high plant invasion levels. Given that the middle part of the Danube Basin is critically understudied and the general lack of data for Serbia, the study aimed to provide an insight into the spatial patterns of plant invasions in the riparian areas of Serbia (Middle Danube Basin area). A total of 250 field sites, distributed along 39 rivers (nine catchment areas) and six canal sections, were studied during a four-year period (2013–2016) for the presence and abundance of IAPs. At the landscape scale, we studied distribution patterns of IAPs, differences in invasion levels in different catchment areas and between rivers and canals. At the local scale, we investigated how the proximity to roads/railway lines, housing areas, different land-use types (primarily agriculture), and dominant vegetation on site related to invasion patterns. Of the 26 studied IAPs, those with a well-known weedy behavior, long history of cultivation and strong affinity for riparian areas prevailed in the study area. Riparian zones of the Danube catchment exhibited the highest invasion levels in terms of IAPs richness and abundance, followed by the catchment areas of the Timok, Sava and Zapadna Morava rivers. Surprisingly, the Danube-Tisa-Danube canal network had the lowest invasion level. At the local scale, agriculture in proximity of the field site and dominant vegetation on site were observed as significant predictors of the invasion level. On the other hand, proximity to roads/railway lines and housing areas was not related to the invasion level. Finally, our study provides the first systematic overview of IAPs’ distribution data for riparian areas of the Middle Danube Basin in Serbia, which could provide a basis for long-term monitoring of IAPs and development of future management plans.
Portulaca oleracea L. is one of the most widely distributed plant species, invading a host of worldwide regions. Rivers and canals, as corridors connecting neighboring habitats, are known to exhibit ...high invasion levels. Consequently, the aim of this paper was to show which catchment areas, environmental factors and habitat types can be seen as predictors of the presence of this invasive species in the riparian areas of Serbia. Field research was carried out at 250 field sites, where the cover and abundance of P. oleracea, relevant environmental variables and habitat type were recorded. Redundancy analysis (RDA) and response curves fitted using a generalized linear model (GLM) were used to show the relation of the cover of P. oleracea and the following variables: catchment area, predominant bank material, elevation, and the total number of invasive species on site. A non-metric multidimensional scaling (NMDS) was used to group sites where P. oleracea was found, based on the values of its cover. In general, primarily the rivers in the northern, low-lying part of Serbia can be seen as important corridors of the spread of P. oleracea. Its dominance is especially associated with areas draining into the Danube and Sava rivers and field sites characterized by a high pressure of invasive plants. Of the total number of records, the highest number of invaded field sites was recorded along the Danube, Tisa and Zapadna Morava rivers. Regarding the environmental and habitat predictors, the results have shown that the abundance of P. oleracea is associated with gravelly and sandy banks and grassland habitat types, primarily anthropogenic herb stands.
Massive gravel excavation is one of the most destructive forces affecting riverine habitats in Europe. However, gravel pit lakes are also recognized as valuable wildlife refuge areas. Different ...hydromorphological characteristics of gravel pits may influence aquatic biota differently. Optimal selection of gravel excavation procedures may create favorable conditions for ecosystem diversity. The aim of this study was to correlate hydromorphological variables against macrophyte composition and metrics in gravel pit lakes along the lower course of the Drina River. Field research was carried out at 18 gravel pit lakes (60 survey sectors) and four fluvial lakes (13 survey sectors), during the summer months of 2015, 2016 and 2018. The role of hydromorphological variables in structuring macrophyte assemblages was tested using the partial Canonical Correspondence Analysis, while the Generalized Linear Model was performed to test the ability of selected hydromorphological attributes to predict macrophyte quantitative metrics. The results demonstrated high habitat quality and conservation value of the gravel pit lakes compared to natural sites. Hydromorphological predictors for different macrophyte assemblages were defined. General recommendation is that two pit types should be excavated within a single extraction field, with the minimal impact to the riparian and shore zones. The first type should be located up to 100 m from river main channel, having area < 1000 m
2
and a relative depth ratio > 5%. The second type should be optimally located 300 m form river main channel, with maximum depth of 3–4 m, surface area of 10,000–20,000 m
2
, and a relative depth ratio < 5%.
We explored the long-term influence of land use in the riparian zone on the water quality of the Tisza River, as a model of a non-wadeable lowland river located in a temperate, predominantly ...agricultural landscape. The analysis was based on a comparison of water quality variables between three river sites having contrasting, but constant land use patterns (in 500 m upstream radius) during the study period (2006-2019). While the first river site was characterized primarily by forests, the second and the third were dominated by urban and agricultural areas respectively. The variables which showed a significant difference between the pairs of sampling sites were oxygen saturation, nitrite nitrogen, total nitrogen, and orthophosphates. In contrast to urban and agricultural land, riparian forests showed a positive long-term influence on the river water quality. Natural and seminatural forests and shrubs had a favorable long-term influence on nutrient concentrations and oxygen regime of the Tisza River. However, the retention effects of orthophosphates and nitrite/nitrate content here were relatively low, demonstrating the limited performance of riparian buffers as a main or only management option in the Pannonian landscape, as the agricultural hotspot of Central and Eastern Europe. In conclusion, the riparian buffer assessment design applied in this study may be successfully used in pre-restoration monitoring, prior to the construction of buffer strips.
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