Ecological Monitoring and Assessment of Freshwater Ecosystems: New Trends and Future Challenges

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Biodiversity and Functionality of Aquatic Ecosystems".

Deadline for manuscript submissions: closed (10 April 2024) | Viewed by 27557

Special Issue Editors


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Guest Editor
Department of Biology, School of Natural Sciences, University of Patras, University Campus Rio, GR 26500 Patras, Greece
Interests: freshwater ecology and management; biodiversity; aquatic and riparian vegetation; plant communities
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Guest Editor
Hellenic Centre for Marine Research, Institute of Marine Biological Resources and Inland Waters, 46.7 km of Athens-Sounio Ave., Anavyssos, 19013 Attiki, Greece
Interests: ecology; ecohydrology; hydromorphology; aquatic plants; ecological assessment
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Regional/local (e.g., land cover transformation, pollution, hydromorphological alterations and invasive species) and global (e.g., climate change) environmental changes are responsible for the loss of many aquatic biota and ecosystem functions. In addition, freshwater resources, especially rivers and lakes, are under severe pressure due to increasing anthropogenic activities, such as water extraction, flow regulation, pollution, and habitat fragmentation. As a result, these changes greatly alter the delivery ecosystem services, affecting human well-being. Due to the multifunctionality of freshwater ecosystems, conservation management and restoration measures could lead to an improvement in biodiversity, ecological quality, and supply of clean water and other ecosystem services or benefits to humans. Over recent decades, extensive national and international regulations have been adopted to protect water resources. Biological monitoring/assessment methods and classification systems were greatly improved by the EU Water Framework Directive (WFD 2000/60) through monitoring programs based on species composition and abundance. Recently, the functional assessments (species traits) and molecular data (eDNA-based bioassessment) have been proposed to assess ecological status and biomonitoring.

We welcome innovative submissions to this Special Issue, which provides a platform to highlight new research findings and significant advances concerning all aspects of bio-assessment and aquatic ecosystems processes. This Special Issue will gather selected papers on the dynamics and functioning of freshwater ecosystems, as well as contributions on monitoring and assessment of ecological quality, biotic metrics/indices, environmental DNA, diversity and functional trait patterns, taxonomic composition, species declines and invasions.

Prof. Dr. Eva Papastergiadou
Dr. Konstantinos Stefanidis
Guest Editors

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Keywords

  • aquatic habitats, flora, and fauna species
  • biological monitoring and assessment
  • climate change
  • ecological quality
  • indicator species
  • freshwaters (streams, ponds, lakes)
  • transitional waters
  • functional diversity
  • functional assessment tools
  • eDNA bioassessment
  • conservation management
  • ecosystem services

Published Papers (12 papers)

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Research

13 pages, 9942 KiB  
Article
Anomalies of Sponge Spicules: Exploring Links to Environmental Pollution
by Stefan Andjus, Bojana Tubić, Božica Vasiljević, Vera Nikolić and Momir Paunović
Water 2024, 16(2), 332; https://doi.org/10.3390/w16020332 - 19 Jan 2024
Viewed by 945
Abstract
The aim of this study was to assess the frequency of spicule malformations in freshwater sponges in relation to selected environmental parameters of the streams and the presence of river pollutants. A total of 50 sponge samples were collected from ten rivers in [...] Read more.
The aim of this study was to assess the frequency of spicule malformations in freshwater sponges in relation to selected environmental parameters of the streams and the presence of river pollutants. A total of 50 sponge samples were collected from ten rivers in Serbia. Selected parameters of the water varied considerably at every site where sponges were found. After spicule preparation, the samples were subjected to morphological analysis by light and scanning electron microscopy, and the number of anomalies were recorded (spicules with bulbous enlargements, sharply bent, bifurcated, scissor- and cross-like, and t-shaped). The frequencies and types of malformations within the analyzed specimens varied from 1 to 100 per 1000 spicules, with an average number of 12 per 1000. The main types of anomalies were single- and double-bent spicules. The highest number of anomalies was found in a specimen of Eunapius fragilis collected at Markovac (Velika Morava River), and the lowest number was found in a specimen of Ephydatia fluviatilis from Kanjiža (Tisa River). The sites with the lowest and the highest numbers of anomalies showed statistically significant differences in concentrations of ammonia, orthophosphates, sodium, chloride, manganese, and lead. This study indicates that several pollutants potentially affect the occurrence of spicule anomalies. Full article
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15 pages, 2844 KiB  
Article
Water and Sediment Chemistry as Drivers of Macroinvertebrates and Fish Assemblages in Littoral Zones of Subtropical Reservoirs
by Linton F. Munyai, Thendo Liphadzi, Thendo Mutshekwa, Mulalo I. Mutoti, Lubabalo Mofu and Florence M. Murungweni
Water 2024, 16(1), 42; https://doi.org/10.3390/w16010042 - 21 Dec 2023
Viewed by 984
Abstract
Reservoirs are human-made ecosystems with diverse purposes that benefit humans both directly and indirectly. They however cause changes in geomorphological processes such as sediment cycling and influence the composition and structure of aquatic biota. This study aimed to identify water and sediment quality [...] Read more.
Reservoirs are human-made ecosystems with diverse purposes that benefit humans both directly and indirectly. They however cause changes in geomorphological processes such as sediment cycling and influence the composition and structure of aquatic biota. This study aimed to identify water and sediment quality parameters as drivers of macroinvertebrates and fish communities during the cool-dry and hot-wet seasons in the littoral zones of three subtropical reservoirs (Albasini, Thathe and Nandoni). Macroinvertebrates and fish were collected from three sites (n = 3 from each site) in each reservoir. A total of 501 and 359 macroinvertebrates and fish individuals were collected throughout the sampling period, respectively. The present study employed a two-way ANOVA in conjunction with redundancy analysis (RDA) to assess the relationships that exist between water and sediment variables, macroinvertebrates diversity and species abundances across seasons. Based on the two-way ANOVA model, significant differences were observed across reservoirs for evenness, Simpson’s diversity, and total abundance, while seasonal differences were observed for most metrics, with exception for evenness. The RDA results identified four water variables (i.e., water temperature, oxidation–reduction potential, pH and conductivity) and one sediment metal (Mg) as the most important parameters in driving the fish community structure. Field observations and metal results attest that the Nandoni reservoir shows high concentrations of metals in sediments as compared to other reservoirs, suggesting that anthropogenic activities such as car washing, brick making, recreation, fishing, wastewater treatment work and landfill site may be the major contributor of metals to the Nandoni reservoir, which accumulate in the littoral zones. Findings of this study highlight the need to analyze reservoir ecological conditions at several scales. The study of macroinvertebrates and fish, water, and sediment chemistry in the littoral zone laid the groundwork for proposing measures for conserving aquatic ecosystems. Full article
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17 pages, 14768 KiB  
Article
Effect of Land Use on Stream Water Quality and Biological Conditions in Multi-Scale Watersheds
by Jong-Won Lee, Se-Rin Park and Sang-Woo Lee
Water 2023, 15(24), 4210; https://doi.org/10.3390/w15244210 - 6 Dec 2023
Viewed by 1122
Abstract
Understanding the relation between watershed land use and stream conditions is critical for watershed planning and management. This study investigated the effects of land use on stream water quality and biological conditions in sub-watersheds and micro-watersheds across the Han River watershed in South [...] Read more.
Understanding the relation between watershed land use and stream conditions is critical for watershed planning and management. This study investigated the effects of land use on stream water quality and biological conditions in sub-watersheds and micro-watersheds across the Han River watershed in South Korea. We developed random forest models for each water quality and biological indicator using the proportions of urban, agricultural, and forested areas. Our results indicate that water quality and biological indicators were significantly affected by forest area at both scales, and the sub-watershed models performed better than the micro-watershed models. Accumulated local effects were used to interpret the effect of each explanatory variable on the response variable. The plots for water quality and biological indicators with proportions of watershed land use demonstrated similar patterns at both scales, although the relation between land use and stream conditions was slightly more sensitive in micro-watersheds than in sub-watersheds. Urban and agricultural areas showed a lower proportion of water quality and biological condition variability in the micro-watersheds than in the sub-watersheds, while forests showed the opposite results. The findings of this study suggest that different spatial scales should be considered when developing effective watershed management strategies to maintain stream ecosystems. Full article
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11 pages, 1754 KiB  
Article
Analyzing the Akinete Protein of the Harmful Freshwater Cyanobacterium, Dolichospermum circinale
by Keonhee Kim, Chae-Hong Park and Soon-Jin Hwang
Water 2023, 15(15), 2746; https://doi.org/10.3390/w15152746 - 29 Jul 2023
Viewed by 785
Abstract
Akinete is a survival structure in cyanobacteria that has overcome unfavorable environmental conditions and influences their perennial blooms in the freshwater system. However, the akinete cellular and biochemical properties are insufficiently explored. We analyzed the akinete structure, as well as akinete-specific proteins and [...] Read more.
Akinete is a survival structure in cyanobacteria that has overcome unfavorable environmental conditions and influences their perennial blooms in the freshwater system. However, the akinete cellular and biochemical properties are insufficiently explored. We analyzed the akinete structure, as well as akinete-specific proteins and their amino acid sequence. Akinetes of Dolichospermum circinale were produced from their vegetative cells isolated from the North Han River, Korea. The akinete protein was obtained using electrophoresis, and utilizing its amino acid sequences, its antibody-binding reaction potential (ig-score) was quantified. Akinete protein masses were 17 kDa–180 kDa, and the akinete protein mass was 110 kDa. The ig score was high (average 5.0121 points) in the first half of the amino acid sequence, indicating a β-turn form. The amino acid sequence, having over 50% homology with the D. circinale akinete protein, was not present in GenBank. The homology of the D. circinale akinete-specific protein was very low (9.8%) compared to that of Anabaena variabilis, indicating that its composition was substantially different, even among phylogenetically close taxa. To the best of our knowledge, this is the first report on the D. circinale akinete protein and its amino acid sequence, with preliminary information for their practical application for detecting akinetes in freshwater systems. Full article
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17 pages, 2876 KiB  
Article
Ecological Responses of Meiofauna to a Saltier World—A Case Study in the Van Uc River Continuum (Vietnam) in the Dry Season
by Hien Thanh Nguyen, Lucie Gourdon, Hoi Van Bui, Duong Thanh Dao, Huong Mai, Hao Manh Do, Thanh Vu Nguyen and Sylvain Ouillon
Water 2023, 15(7), 1278; https://doi.org/10.3390/w15071278 - 24 Mar 2023
Viewed by 1309
Abstract
Increasing intensity of storms, typhoons, and sea level rise in conjunction with high water demand, especially for agriculture, in dry seasons in the Red River Delta may have led to seawater intruding deeper into the rivers’ estuaries. Given that losses of agricultural productivity [...] Read more.
Increasing intensity of storms, typhoons, and sea level rise in conjunction with high water demand, especially for agriculture, in dry seasons in the Red River Delta may have led to seawater intruding deeper into the rivers’ estuaries. Given that losses of agricultural productivity and shortages of freshwater resources are projected, a reliable early warning of salinity invasion is, therefore, crucially needed. To evaluate the impact of salinity variations on riverine ecosystems, distribution patterns of meiofauna were examined at 20 stations along the Van Uc River continuum in the dry season. Meiofaunal richness indices were higher in the estuary and slightly decreased upriver. Nematoda was the most dominant taxon in salty stations, while Rotifera was more abundant in the less salty ones. A multiple variate analysis showed a strong interplay among salinity, nutrients, and pore water conductivity, which shaped the meiofaunal distribution. The inclusion of pore water salinity, nutrients, and meiofaunal community structure indicated a greater extent of the saline ecosystem in the estuary, posing a greater risk of freshwater salinization. Our results highlight the potential role of meiofauna as bioindicators but also call for a reformation of salinity assessment for better freshwater conservation and management. Full article
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15 pages, 3208 KiB  
Article
Ecological Quality Assessment of Greek Lowland Rivers with Aquatic Macrophytes in Compliance with the EU Water Framework Directive
by Konstantinos Stefanidis, Georgios Dimitrellos, Maria Sarika, Dionysios Tsoukalas and Eva Papastergiadou
Water 2022, 14(18), 2771; https://doi.org/10.3390/w14182771 - 6 Sep 2022
Cited by 5 | Viewed by 1762
Abstract
Aquatic macrophytes are one of the four biological quality elements (BQE) used for assessing the ecological status of inland waters according to the EU Water Framework Directive (WFD 2000/60). With this article, we present the methodological approach for the implementation of a WFD [...] Read more.
Aquatic macrophytes are one of the four biological quality elements (BQE) used for assessing the ecological status of inland waters according to the EU Water Framework Directive (WFD 2000/60). With this article, we present the methodological approach for the implementation of a WFD compliant macrophyte index to the riverine systems of Greece. In addition to the definition and harmonization of the ecological quality class boundaries, the results from the pilot application of the index and the ecological classification of the monitored river reaches are also presented. Aquatic plants and environmental parameters were sampled from 93 river reaches between 2012 and 2015. A multivariate analysis with optimal scaling (MVAOS) was conducted to define the main stressor gradient and to identify the least disturbed sites and the reference conditions that are required for the derivation of the ecological quality classes. The Macrophyte Biological Index IBMR for Greek rivers (IBMRGR) was calculated for all the sites and the boundaries for the five quality classes were derived according to the methodology proposed by the Mediterranean Geographic Intercalibration Group (MedGIG). The main findings showed that the hydromorphological modifications were the main environmental stressors that correlated strongly with the IBMRGR, whereas physicochemical stressors were of lesser importance. More specifically, the first principal component explained 51% of the total variance of the data, representing a moderately strong gradient of hydromorphological stress, whereas the second component explained 22.5%, representing a weaker gradient of physicochemical stress. In addition, the ecological assessment showed that almost 60% of the sites failed the WFD target of the “Good” ecological quality class, which agrees with classification assessments based on other BQEs for Greece and many Mediterranean countries. Overall, this work provides a first assessment of the ecological classification of Greek rivers with the BQE of aquatic macrophytes with significant implications for ecological monitoring and decision making within the frame of the WFD implementation. Full article
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13 pages, 1404 KiB  
Article
Improving Environmental DNA Sensitivity for Dreissenid Mussels by Targeting Tandem Repeat Regions of the Mitochondrial Genome
by Nathaniel T. Marshall, Henry A. Vanderploeg and Subba Rao Chaganti
Water 2022, 14(13), 2069; https://doi.org/10.3390/w14132069 - 28 Jun 2022
Viewed by 2234
Abstract
The recent genetic revolution through the analysis of aquatic environmental DNA (eDNA) has become a powerful tool for improving the detection of rare and/or invasive species. For the majority of eDNA studies, genetic assays are designed to target mitochondrial genes commonly referred to [...] Read more.
The recent genetic revolution through the analysis of aquatic environmental DNA (eDNA) has become a powerful tool for improving the detection of rare and/or invasive species. For the majority of eDNA studies, genetic assays are designed to target mitochondrial genes commonly referred to as “barcode” regions. However, unlike the typical structure of an animal mitochondrial genome, those for the invasive zebra and quagga mussels are greatly expanded with large extended tandem repeat regions. These sections of repeated DNA can appear hundreds of times within the genome compared to a single copy for the mitochondrial barcode genes. This higher number of target copies per mitochondrial genome presents an opportunity to increase eDNA assay sensitivity for these species. Therefore, we designed and evaluated new eDNA assays to target the extended repeat sections for both zebra and quagga mussels. These assays lower the limit of detection of genomic DNA by 100-fold for zebra mussels and 10-fold for quagga mussels. Additionally, these newly developed assays provided longer durations of detection during degradation mesocosm experiments and greater sensitivity for eDNA detection from water samples collected across western Lake Erie compared to standard assays targeting mitochondrial genes. This work illustrates how understanding the complete genomic structure of an organism can improve eDNA analysis. Full article
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30 pages, 3636 KiB  
Article
Land Use Change to Reduce Freshwater Nitrogen and Phosphorus will Be Effective Even with Projected Climate Change
by Andrew J. Wade, Richard A. Skeffington, Raoul-Marie Couture, Martin Erlandsson Lampa, Simon Groot, Sarah J. Halliday, Valesca Harezlak, Josef Hejzlar, Leah A. Jackson-Blake, Ahti Lepistö, Eva Papastergiadou, Joan Lluís Riera, Katri Rankinen, Maria Shahgedanova, Dennis Trolle, Paul G. Whitehead, Demetris Psaltopoulos and Dimitris Skuras
Water 2022, 14(5), 829; https://doi.org/10.3390/w14050829 - 6 Mar 2022
Cited by 6 | Viewed by 4008
Abstract
Recent studies have demonstrated that projected climate change will likely enhance nitrogen (N) and phosphorus (P) loss from farms and farmland, with the potential to worsen freshwater eutrophication. Here, we investigate the relative importance of the climate and land use drivers of nutrient [...] Read more.
Recent studies have demonstrated that projected climate change will likely enhance nitrogen (N) and phosphorus (P) loss from farms and farmland, with the potential to worsen freshwater eutrophication. Here, we investigate the relative importance of the climate and land use drivers of nutrient loss in nine study catchments in Europe and a neighboring country (Turkey), ranging in area from 50 to 12,000 km2. The aim was to quantify whether planned large-scale, land use change aimed at N and P loss reduction would be effective given projected climate change. To this end, catchment-scale biophysical models were applied within a common framework to quantify the integrated effects of projected changes in climate, land use (including wastewater inputs), N deposition, and water use on river and lake water quantity and quality for the mid-21st century. The proposed land use changes were derived from catchment stakeholder workshops, and the assessment quantified changes in mean annual N and P concentrations and loads. At most of the sites, the projected effects of climate change alone on nutrient concentrations and loads were small, whilst land use changes had a larger effect and were of sufficient magnitude that, overall, a move to more environmentally focused farming achieved a reduction in N and P concentrations and loads despite projected climate change. However, at Beyşehir lake in Turkey, increased temperatures and lower precipitation reduced water flows considerably, making climate change, rather than more intensive nutrient usage, the greatest threat to the freshwater ecosystem. Individual site responses did however vary and were dependent on the balance of diffuse and point source inputs. Simulated lake chlorophyll-a changes were not generally proportional to changes in nutrient loading. Further work is required to accurately simulate the flow and water quality extremes and determine how reductions in freshwater N and P translate into an aquatic ecosystem response. Full article
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12 pages, 1602 KiB  
Article
Functional Responses and Additive Multiple Predator Effects of Two Common Wetland Fish
by Linton F. Munyai, Tatenda Dalu, Ryan J. Wasserman, Lutendo Mugwedi, Farai Dondofema, Gordon O’Brien and Ross N. Cuthbert
Water 2022, 14(5), 699; https://doi.org/10.3390/w14050699 - 23 Feb 2022
Viewed by 2307
Abstract
Understanding trophic interactions is essential for the prediction and measurement of structure and function in aquatic environments. Communities in these ecosystems may be shaped by variables such as predator diversity, prey density and emergent multiple predator effects (MPEs), which are likely to influence [...] Read more.
Understanding trophic interactions is essential for the prediction and measurement of structure and function in aquatic environments. Communities in these ecosystems may be shaped by variables such as predator diversity, prey density and emergent multiple predator effects (MPEs), which are likely to influence trophic dynamics. In this study, we examined the effect of key predatory fish in floodplain wetlands, namely Oreochromis mossambicus and Enteromius paludinosus, towards Chironomidae prey, using a comparative functional response (FR) approach. We used single predator species as well as intra- and interspecific paired species to contrast FRs under multiple predator scenarios. Attack rate and handling time estimates from single predator FRs were used to predict multiple predators’ feeding rates, which were compared to observe multiple predators’ feeding rates to quantify potential MPEs. From single fish trials, each species displayed a significant Type II FR, characterized by high feeding rates at low prey densities. Oreochromis mossambicus had a steeper (initial slope, i.e., higher attack rate) and higher (asymptote of curve, i.e., shorter handling time and higher maximum feeding rate) FR, whereas E. paludinosus exhibited lower-magnitude FRs (i.e., lower attack rate, longer handling time and lower feeding rate). In multiple predator scenarios, feeding rates were well-predicted by those of single predators, both in conspecific and interspecific pairs, and thus we did not find evidence for antagonistic or synergistic MPEs. Predator–prey interactions in wetland systems can have significant consequences on the structure and dynamics of ecological communities. In turn, this could have destabilizing effects on resources in tropical wetlands. These results, although experimental, help us understand how trophic interaction among conspecific or interspecific fish species in Austral tropical wetlands might influence their aquatic prey species. This will help us to understand food web dynamics better. Full article
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17 pages, 23367 KiB  
Article
Classification and Assessment Methods for Mountain Channel Habitats in the Chishui River Basin, China
by Fandong Yu, Fei Liu, Zhijun Xia, Pengcheng Lin, Chunsen Xu, Jianwei Wang, Miaomiao Hou and Xinhua Zou
Water 2022, 14(4), 515; https://doi.org/10.3390/w14040515 - 9 Feb 2022
Cited by 4 | Viewed by 2115
Abstract
Mountain channels have received relatively little study compared to lowland rivers due to their complicated fluvial geomorphology and inconvenient traffic. Classification schemes and habitat assessments in mountain channels should be strengthened to provide a scientific basis for river ecological restoration. Therefore, we tried [...] Read more.
Mountain channels have received relatively little study compared to lowland rivers due to their complicated fluvial geomorphology and inconvenient traffic. Classification schemes and habitat assessments in mountain channels should be strengthened to provide a scientific basis for river ecological restoration. Therefore, we tried to simplify the habitat assessment of mountain channels using a suitable habitat classification scheme based on high-resolution satellite imagery. We used China’s Chishui River basin because it is a typical mountain river system. Five parameters (stream order, elevation, slope, sinuosity and river network density) and 120 sites were used for habitat classification. In addition, we recorded 20 metrics in four categories (water environmental status, river morphology, riparian zone and human disturbance). Our results identified a total of 40 representative sampling sections belonging to six habitat types that were useful for habitat assessment across the Chishui River basin. The basin was given a mean comprehensive habitat quality index (CHQI) score of 130.66 ± 24.14 and classified under the status “good.” However, the headwaters, Tongmin River, Tongzi River and Xishui River were disturbed by various human activities. We conclude that the process of developing and simplifying our habitat assessment systems can be regarded as a reference for biomonitoring in other mountain river systems. Full article
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17 pages, 3429 KiB  
Article
Physiological Responses of the Submerged Macrophyte Stuckenia pectinata to High Salinity and Irradiance Stress to Assess Eutrophication Management and Climatic Effects: An Integrative Approach
by Lamprini Malea, Konstantinia Nakou, Apostolos Papadimitriou, Athanasios Exadactylos and Sotiris Orfanidis
Water 2021, 13(12), 1706; https://doi.org/10.3390/w13121706 - 20 Jun 2021
Cited by 3 | Viewed by 2730
Abstract
Stuckenia pectinata, a submerged macrophyte of eutrophic to hyper-eutrophic fresh to brackish waters, faces management and climatic-forced increment of salinity and irradiance in Vistonis Lake (Greece) that may endanger its existence and the ecosystem functioning. A pre-acclimated clone under low irradiance and [...] Read more.
Stuckenia pectinata, a submerged macrophyte of eutrophic to hyper-eutrophic fresh to brackish waters, faces management and climatic-forced increment of salinity and irradiance in Vistonis Lake (Greece) that may endanger its existence and the ecosystem functioning. A pre-acclimated clone under low irradiance and salinity conditions was treated to understand the effects of high salinity and irradiance on a suite of subcellular (chlorophyll a fluorescence kinetics and JIP-test, and chlorophyll content) to organismal (relative growth rate—RGR) physiological parameters. The responses to high irradiance indicated the plant’s great photo-acclimation potential to regulate the number and size of the reaction centers and the photosynthetic electron transport chain by dissipation of the excess energy to heat. A statistically significant interaction (p < 0.01) of salinity and irradiance on Chl a, b content indicated acclimation potential through adjusting the Chl a, b contents. However, no significant (p > 0.05) difference was observed on Chl a/b ratio and the RGR, indicating the species’ potential to become acclimatized by reallocating resources to compensate for growth. Thus, the regulation of photosynthetic pigment content and photosystem II performance consisted of the primary growth strategy to present and future high salinity and irradiance stressful conditions due to eutrophication management and the ongoing climatic changes. Full article
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15 pages, 14641 KiB  
Article
Modelling Freshwater Eutrophication with Limited Limnological Data Using Artificial Neural Networks
by Ekaterini Hadjisolomou, Konstantinos Stefanidis, Herodotos Herodotou, Michalis Michaelides, George Papatheodorou and Eva Papastergiadou
Water 2021, 13(11), 1590; https://doi.org/10.3390/w13111590 - 4 Jun 2021
Cited by 42 | Viewed by 5098
Abstract
Artificial Neural Networks (ANNs) have wide applications in aquatic ecology and specifically in modelling water quality and biotic responses to environmental predictors. However, data scarcity is a common problem that raises the need to optimize modelling approaches to overcome data limitations. With this [...] Read more.
Artificial Neural Networks (ANNs) have wide applications in aquatic ecology and specifically in modelling water quality and biotic responses to environmental predictors. However, data scarcity is a common problem that raises the need to optimize modelling approaches to overcome data limitations. With this paper, we investigate the optimal k-fold cross validation in building an ANN using a small water-quality data set. The ANN was created to model the chlorophyll-a levels of a shallow eutrophic lake (Mikri Prespa) located in N. Greece. The typical water quality parameters serving as the ANN’s inputs are pH, dissolved oxygen, water temperature, phosphorus, nitrogen, electric conductivity, and Secchi disk depth. The available data set was small, containing only 89 data samples. For that reason, k-fold cross validation was used for training the ANN. To find the optimal k value for the k-fold cross validation, several values of k were tested (ranging from 3 to 30). Additionally, the leave-one-out (LOO) cross validation, which is an extreme case of the k-fold cross validation, was also applied. The ANN’s performance indices showed a clear trend to be improved as the k number was increased, while the best results were calculated for the LOO cross validation as expected. The computational times were calculated for each k value, where it was found the computational time is relatively low when applying the more expensive LOO cross validation; therefore, the LOO is recommended. Finally, a sensitivity analysis was examined using the ANN to investigate the interactions of the input parameters with the Chlorophyll-a, and hence examining the potential use of the ANN as a water management tool for nutrient control. Full article
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