Redundancy in the ecological assessment of lakes: Are phytoplankton, macrophytes and phytobenthos all necessary?

A new diatom-based multimetric index to assess lake ecological status

Eutrophication impairs lake ecosystems at a global scale. In this context, as benthic microalgae are well-established warnings for a large range of stressors, particularly nutrient enrichment, the Water Framework Directive required the development of diatom-based methods to monitor lake eutrophication. Here, we present the diatom-based index we developed for French lakes, named IBDL (Indice Biologique Diatomées en Lacs). Data were collected in 93 lakes from 2015 to 2020. A challenge arose from the discontinuous pressure gradient of our dataset, especially the low number of nutrient-impacted lakes. To analyze the data we opted for the so-called "Threshold Indicator Taxa ANalysis" method, which makes it possible to determine a list of "alert taxa." We obtained a multimetric index based on specific pressure gradients (Kjeldahl nitrogen, suspended matter, biological oxygen demand, and total phosphorous). Considering the European intercalibration process, the very good correlation between IBDL and the common metric (R2 from 0.52 to 0.87 according to the lake alkalinity type) makes us very confident in our ability to match future IBDL quality thresholds with European standards. The IBDL proved at last to be particularly relevant as it has a twofold interest: an excellent relationship with total phosphorus (R2 from 0.63 to 0.83 according to the lake alkalinity type) and a possible application to any lake metatype. Its complementarity with macrophyte-based indices moreover justifies the use of at least two primary producer components for lake ecological status classification.

Response of Macrophyte Diversity in Coastal Lakes to Watershed Land Use and Salinity Gradient

Coastal lakes are subject to multiple stressors, among which land use, hydrological connectivity, and salinity have the greatest effect on their biodiversity. We studied the effects that various land cover types (CORINE) of coastal lake watersheds had on macrophyte diversity in ten coastal lakes along the southern Baltic coast as characterised by twelve phytocenotic indices: these being a number of communities, Shannon-Wiener diversity, evenness, and indices of taxonomic distinctiveness of plant communities: vegetation coverage; colonisation index; share of the phytolittoral area in the total lake area, as well as shares of nympheides, pondweeds, charophytes, marine, emerged and submerged communities in the total lake area. The effects were checked for three groups of lakes distinguished by differences in salinity-freshwater (F, 5), transitional (T, 4), and brackish (B, 1)-in which a total of 48 macrophyte communities were identified. The most abundant in aquatic phytocoenoses were lakes of T type. A partial least squares regression model (PLS-R) showed a stronger impact of land-use types in immediate vicinities and entire watersheds than the impact of physico-chemical properties of water on phytocenotic indices in the lakes. Macrophyte diversity was relatively low in urban and agricultural catchments and relatively high in forest and wetland areas. Agriculture had a negative impact on the number of macrophyte communities in F lakes and, in T lakes, on the number of macrophyte communities, biodiversity, evenness, and proportion of emerged, submerged, and marine communities. Urban areas contributed to lower values of evenness, vegetation coverage, and share of marine communities in F, but, in T, to lower the number of macrophyte communities, evenness, and proportion of submerged and marine communities. Our results confirm the significant impact of land use on macrophyte diversity in coastal aquatic ecosystems. Combined analysis of anthropogenic and natural descriptors is a prerequisite for analysing human threats to biodiversity in coastal lakes. Macrophyte community-based measures of biodiversity are sensitive indicators of anthropogenic impact on the ecological condition of coastal ecosystems.

“One Out–All Out” Principle in the Water Framework Directive 2000—A New Approach with Fuzzy Method on an Example of Greek Lakes

The “One Out–All Out” (OOAO) principle imposed by the WFD selects the worst ecological status assessed by different biological quality elements (BQEs). Since it is a precautionary rule that can lead to problems of underestimation of the overall status, its amendment has been a matter of debate for WFD 20+. The use of fuzzy methods that express the functional relationships between variables in ecology and management has been gaining more ground recently. Here is attempted the inclusion of a fuzzy regression among the frequently monitored BQE (phytoplankton) and the outcome of OOAO application in six Greek lakes. The latter was determined by the comparison of four BQE indices in order to assess the extent to which BQEs might underpin the optimal/actual qualitative classification of a waterbody. This approach encompasses the uncertainty and the possibility to broaden the acceptable final EQR based on the character and status of each lake. We concluded that the fuzzy OOAO is an approach that seems to allow a better understanding of the WFD implementation and case-specific evaluation, including the uncertainty in classification as an asset. Moreover, it offers a deeper understanding through self-learning processes based on the existing datasets.

Improving biological condition assessment accuracy by multimetric index approach with microalgae in streams and lakes

Multimetric index (MMI) approach is a broadly used in ecological assessment because it can integrate information of various kinds of ecologically related metrics of freshwater ecosystems and provide an easily understandable score for purpose of further evaluation and managements. Accounting for natural variation and disentangling covariation between natural environmental factors and human disturbance factors are imperative for an accurate assessment. Lots of progress has been made recently on the aforementioned two aspects. Three approaches, a priori classification of sites by regions or typologies, site-specific modeling of expected reference condition and varying metrics in site groups, have been tested in lakes and streams to improve assessment accuracy. All existed studies support that site-specific modeling can efficiently account for natural variation and generate a MMI with good performance. However, until now, no strong evidence has shown that diatom/blue-algae typologies are better than regionalization frameworks on accounting for natural variation either in lakes or in streams. To separate the natural variation explained by site specific modeling from that of varying metrics is necessary for a thorough and accurate evaluation on the valuableness of site-grouping by typologies. Different performance of varying metrics among site groups of streams and lakes was most probably caused by the lack of representativeness of diatom metrics on biological condition rather than the complex multi-stressor gradients in streams and rivers. A recent study showed that blue-green algae enhanced performance of diatom-based MMI on defining lake condition under high level of human disturbance. On the other hand, with more and more extensive and intensive use of statistics techniques in developing MMI, we also discussed some statistical challenges faced by scientists in field of ecological assessment, especially on setting significance level of a statistical test and multiple comparison issue in MMI performance comparison.

How diatom-, invertebrate- and fish-based diagnostic tools can support the ecological assessment of rivers in a multi-pressure context: Temporal trends over the past two decades in France

The degradation of aquatic ecosystems, induced by worldwide intensification in the use of both land and aquatic resources, has highlighted the critical need for innovative methods allowing an objective quantification and ranking of anthropogenic pressure effects on aquatic organisms. Such diagnostic tools have a great potential for defining robust management responses to anthropogenic pressures. Our objective was to explore how the outputs of three diagnostic tools (based on benthic diatoms, macroinvertebrates and fishes) could be combined to (i) disentangle the temporal effects of multiple pressures over two decades and (ii) provide policy-relevant information for stream managers and decision makers. The diagnostic tools estimated, using taxonomy- and trait-based metrics, the impairment probabilities of biotic assemblages over time by different pressure categories, describing the alteration of water quality, hydromorphology and land use related to anthropogenic activities, in French streams (number of sites = 312). The main result shows that a large proportion of the time series exhibited no significant temporal patterns over the two decades (61.5% to 87.8%, depending on the used tests). Among time series exhibiting significant change, positive trends in impairment probabilities (i.e., degradation) were less frequent than negative ones, indicating a modest improvement in water quality at national scale over the study period. However, trends can be substantially different according to hydroecoregion and pressure category. The three biological compartments displayed convergent temporal responses according to the pressure category and regional context (e.g., lowland plains vs. mountains, pristine vs. agricultural regions). Altogether, this study proposes a unifying approach to integrate a vast amount of information in a single ecological diagnosis using an unparalleled database on natural and anthropized environments. Strengthening the synthesis of biological information provided by various biological compartments should be a priority before implementing evidence-based sustainable conservation and restoration actions.

Modelling of ecological status of Polish lakes using deep learning techniques

Since 2000, after the Water Framework Directive came into force, aquatic ecosystems' bioassessment has acquired immense practical importance for water management. Currently, due to extensive scientific research and monitoring, we have gathered comprehensive hydrobiological databases. The amount of available data increases with each subsequent year of monitoring, and the efficient analysis of these data requires the use of proper mathematical tools. Our study challenges the comparison of the modelling potential between four indices for the ecological status assessment of lakes based on three groups of aquatic organisms, i.e. phytoplankton, phytobenthos and macrophytes. One of the deep learning techniques, artificial neural networks, has been used to predict values of four biological indices based on the limited set of the physicochemical parameters of water. All analyses were conducted separately for lakes with various stratification regimes as they function differently. The best modelling quality in terms of high values of coefficients of determination and low values of the normalised root mean square error was obtained for chlorophyll a followed by phytoplankton multimetric. A lower degree of fit was obtained in the networks for macrophyte index, and the poorest model quality was obtained for phytobenthos index. For all indices, modelling quality for non-stratified lakes was higher than this for stratified lakes, giving a higher percentage of variance explained by the networks and lower values of errors. Sensitivity analysis showed that among physicochemical parameters, water transparency (Secchi disk reading) exhibits the strongest relationship with the ecological status of lakes derived by phytoplankton and macrophytes. At the same time, all input variables indicated a negligible impact on phytobenthos index. In this way, different explanations of the relationship between biological and trophic variables were revealed.

How to Assess the Ecological Status of Highly Humic Lakes? Development of a New Method Based on Benthic Invertebrates

Highly humic lakes are typical for the boreal zone. These unique ecosystems are characterised as relatively undisturbed habitats with brown water, high acidity, low nutrient content and lack of macrophytes. Current lake assessment methods are not appropriate for ecological assessment of highly humic lakes because of their unique properties and differing human pressures acting on these ecosystems. This study proposes a new approach suitable for the ecological status assessment of highly humic lakes impacted by hydrological modifications. Altogether, 52 macroinvertebrate samples from 15 raised bog lakes were used to develop the method. The studied lakes are located in the raised bogs at the central and eastern parts of Latvia. Altered water level was found as the main threat to the humic lake habitats since no other pressures were established. A multimetric index based on macroinvertebrate abundance, littoral and profundal preferences, Coleoptera taxa richness and the Biological Monitoring Working Party (BMWP) Score is suggested as the most suitable tool to assess the ecological quality of the highly humic lakes.

Phytoplankton distribution characteristics and its relationship with bacterioplankton in Dianchi Lake

Phytoplankton and bacterioplankton perform important ecological functions in lake ecosystem. In this paper, the abundance and composition of phytoplankton and bacterioplankton at 13 sites of Dianchi lake during the wet and dry seasons were monitored, and the relationship between phytoplankton and bacterioplankton in this plateau lake was studied. Phytoplankton community structure analysis was carried out by ocular method, and bacterioplankton was investigated by high-throughput 16S rRNA gene Illumina sequencing. The relationship between phytoplankton and bacterioplankton was observed using redundancy analysis. The results showed that 87 species of phytoplankton belonging to 5 phyla and 29 genera were identified in Dianchi lake. Phytoplankton diversity and richness were higher in the wet season than those in the dry season. In the wet season, Cyanophyta was the dominant phylum whose density was 2.01 × 10⁸ cells/L, accounting for more than 90% of the total algae, then followed by Chlorophyta, Bacillariophyta, Chrysophyta, and Cryptophyta. The spatial distribution of phytoplankton in the wet season and dry seasons showed significant differences. In the dry season, the north-central part of Dianchi lake was dominated by Limnothrix redekei and Microcystis minutissima of Cyanophyta, while Pseudanabaena moniliformis and Coelosphaerium nagelianum of Cyanophyta mainly was dominated in the south of Dianchi lake. In the wet season, Microcystis minutissima of Cyanophyta was the dominant species all the area, while Limnothrix redekei of Cyanophyta was second dominant. Proteobacteria and Bacteroidetes were the dominant phyla among bacterioplankton. The community structure of bacterioplankton was influenced by Cyanophyta and Bacillariophyta. Cyanophyta had a major influence on Pseudomonas, Acinetobacter of Proteobacteria, and Flavobacterium of Bacteroidetes. Bacillariophyta showed a strong correlation with Gemmobacter, Stenotrophomonas, and Aeromonas of Proteobacteria. Cyanophyta and Bacillariophyta produced the most significant impact on predicted functional genes of bacterioplankton, and the predicted functional genes of the samples were different in different seasons. Cell densities of Cyanophyta were positively related to metabolism-predicted functional genes of bacterioplankton. Bacillariophyta and Cryptophyta had an impact on most of the cellular processes and signaling predicted functional genes. Bacterioplankton-predicted functional gene information storage and processing were significantly affected by cell densities of Chlorophyta. Therefore, the analysis of the phytoplankton community and the bacterioplankton-predicted functional gene in Dianchi lake exerts a great significance in revealing the ecosystem function of plateau lakes and harmful algal bloom control.

European aquatic ecological assessment methods: A critical review of their sensitivity to key pressures

The European Union has embarked on a policy which aims to achieve good ecological status in all surface waters (i.e. rivers, lakes, transitional and coastal waters). In theory, ecological status assessment methods should address the effects of all relevant human pressures. In this study, we analyze the degree to which methods European countries use to assess ecological status tackle various pressures affecting European waters. Nutrient pollution is by far the best-covered pressure for all four water categories. Out of total of 423 assessment methods, 370 assess eutrophication and pressure-specific relationships have been demonstrated for 212 of these. "General degradation" is addressed by 238 methods, mostly validated by relationships to combined pressure indices. Other major pressures have received significantly less effort: hydromorphological degradation is assessed by 160 methods and pressure-specific relationships have been demonstrated for just 40 of these. Hydromorphological pressures are addressed (at least by one BQE) only by 25% countries for coastal waters and 70-80% for lakes and transitional waters. Specific diagnostic tools (i.e. single-pressure relationships) for hydromorphology have only been developed by a few countries: only 20% countries have such methods for lakes, coastal and transitional waters and less than half for rivers. Toxic contamination is addressed by 90 methods; however, pressure-specific relationships have been demonstrated for just eight of these. Only two countries have demonstrated pressure-specific acidification methods for rivers, and three for lakes. In summary, methods currently in use mostly address eutrophication and/or general degradation, but there is not much evidence that they reliably pick up the effects of other significant pressures such as hydromorphology or toxic contamination. Therefore, we recommend that countries re-examine: (1) those pressures which affect different water categories in the country; (2) relevant assessment methods to tackle those pressures; (3) whether pressure-response relationships have been developed for each of these.

Mazor R, Theroux S, J. Gillett D, Lane B, Gearheart G. The importance of open science for biological assessment of aquatic environments

Open science principles that seek to improve science can effectively bridge the gap between researchers and environmental managers. However, widespread adoption has yet to gain traction for the development and application of bioassessment products. At the core of this philosophy is the concept that research should be reproducible and transparent, in addition to having long-term value through effective data preservation and sharing. In this article, we review core open science concepts that have recently been adopted in the ecological sciences and emphasize how adoption can benefit the field of bioassessment for both prescriptive condition assessments and proactive applications that inform environmental management. An example from the state of California demonstrates effective adoption of open science principles through data stewardship, reproducible research, and engagement of stakeholders with multimedia applications. We also discuss technical, sociocultural, and institutional challenges for adopting open science, including practical approaches for overcoming these hurdles in bioassessment applications.

Assessing lake ecological status across a trophic gradient through environmental and biological variables

The Water Framework Directive was widely welcomed because it sought to integrate chemical and biological elements of aquatic ecosystems to achieve 'good ecological status', reflecting at most slight anthropogenic impact. However, implementation has been criticised because of the failure to adequately integrate these elements and assess status of the whole ecosystem. In this study, a suite of environmental and biotic variables was measured to assess their relative importance as predictors of lake status for 50 lakes in the north of the island of Ireland. Total Phosphorus (TP) had a strong effect on taxon biomasses and ecological quality ratios (EQR) for most taxa, as expected, but other environmental variables, such as pH, water colour and spatial location, were also important. Most variance in mean EQR, the average of the taxon values, was predicted by five environmental variables (chlorophyll a, TP, population density, water colour and elevation) and whether (alien) cyprinid fish were present. Oligotrophic lakes with cyprinid fish had lower mean EQRs than cyprinid-free lakes, indicating the importance of recording species introductions when assessing lake status. Strong evidence for bottom-up effects was also detected, and cyprinids probably influenced trophic structure by increasing nutrient release from the sediment rather than by top-down effects. Phytoplankton biomass, fish biomasses, and the percentage of predatory fish, increased with TP. Our results further emphasize the need to adopt a more integrated approach when assessing lake status.

Policy-driven monitoring and evaluation: Does it support adaptive management of socio-ecological systems?

Inadequate Monitoring and Evaluation (M&E) is often thought to hinder adaptive management of socio-ecological systems. A key influence on environmental management practices are environmental policies: however, their consequences for M&E practices have not been well-examined. We examine three policy areas - the Water Framework Directive, the Natura 2000 Directives, and the Agri-Environment Schemes of the Common Agricultural Policy - whose statutory requirements influence how the environment is managed and monitored across Europe. We use a comparative approach to examine what is monitored, how monitoring is carried out, and how results are used to update management, based on publicly available documentation across nine regional and national cases. The requirements and guidelines of these policies have provided significant impetus for monitoring: however, we find this policy-driven M&E usually does not match the ideals of what is needed to inform adaptive management. There is a tendency to focus on understanding state and trends rather than tracking the effect of interventions; a focus on specific biotic and abiotic indicators at the expense of understanding system functions and processes, especially social components; and limited attention to how context affects systems, though this is sometimes considered via secondary data. The resulting data are sometimes publicly-accessible, but it is rarely clear if and how these influence decisions at any level, whether this be in the original policy itself or at the level of measures such as site management plans. Adjustments to policy-driven M&E could better enable learning for adaptive management, by reconsidering what supports a balanced understanding of socio-ecological systems and decision-making. Useful strategies include making more use of secondary data, and more transparency in data-sharing and decision-making. Several countries and policy areas already offer useful examples. Such changes are essential given the influence of policy, and the urgency of enabling adaptive management to safeguard socio-ecological systems.

Protecting and restoring Europe's waters: An analysis of the future development needs of the Water Framework Directive

The Water Framework Directive (WFD) is a pioneering piece of legislation that aims to protect and enhance aquatic ecosystems and promote sustainable water use across Europe. There is growing concern that the objective of good status, or higher, in all EU waters by 2027 is a long way from being achieved in many countries. Through questionnaire analysis of almost 100 experts, we provide recommendations to enhance WFD monitoring and assessment systems, improve programmes of measures and further integrate with other sectoral policies. Our analysis highlights that there is great potential to enhance assessment schemes through strategic design of monitoring networks and innovation, such as earth observation. New diagnostic tools that use existing WFD monitoring data, but incorporate novel statistical and trait-based approaches could be used more widely to diagnose the cause of deterioration under conditions of multiple pressures and deliver a hierarchy of solutions for more evidence-driven decisions in river basin management. There is also a growing recognition that measures undertaken in river basin management should deliver multiple benefits across sectors, such as reduced flood risk, and there needs to be robust demonstration studies that evaluate these. Continued efforts in 'mainstreaming' water policy into other policy sectors is clearly needed to deliver wider success with WFD goals, particularly with agricultural policy. Other key policy areas where a need for stronger integration with water policy was recognised included urban planning (waste water treatment), flooding, climate and energy (hydropower). Having a deadline for attaining the policy objective of good status is important, but even more essential is to have a permanent framework for river basin management that addresses the delays in implementation of measures. This requires a long-term perspective, far beyond the current deadline of 2027.

Ordered diatom species loss along a total phosphorus gradient in eutrophic lakes of the lower Yangtze River basin, China

As global changes begin to affect the biosphere profoundly, the impacts on ecosystem health will become more significant. Understanding the sequence of functional species loss along an environmental or ecological gradient remains a research priority for ecosystem conservation. In this paper, nestedness, β-diversity and its components in diatom communities are used as ecological indicators of the dynamic change in functional species along environment gradients in 76 lakes of the lower Yangtze River basin, China. The results indicate that species turnover is typically the dominant component of β-diversity and that the influence of nestedness is generally low. However, changes in nestedness denote a significant threshold of lake eutrophication at a total phosphorus (TP) level of 0.06 mg/l, which is lower than the threshold indicated by diatom diversity. This finding was coupled with theoretical predictions about the successive proportional loss of 'canary' and 'keystone' species, which are replaced by 'weedy' species. These results show that nestedness of diatom communities can provide an additional metric for evaluating lake ecosystem health in this region. As management targets for nutrient control have already been introduced in the region, a revision of the identified critical phosphorus level (i.e., TP = 0.087-0.1 mg/l) to TP = 0.06 mg/l is proposed to keep lakes under low risk.

Multi-sensor satellite and in situ monitoring of phytoplankton development in a eutrophic-mesotrophic lake

Phytoplankton indicated by its photosynthetic pigment chlorophyll-a is an important pointer on lake ecology and a regularly monitored parameter within the European Water Framework Directive. Along with eutrophication and global warming cyanobacteria gain increasing importance concerning human health aspects. Optical remote sensing may support both the monitoring of horizontal distribution of phytoplankton and cyanobacteria at the lake surface and the reduction of spatial uncertainties associated with limited water sample analyses. Temporal and spatial resolution of using only one satellite sensor, however, may constrain its information value. To discuss the advantages of a multi-sensor approach the sensor-independent, physically based model MIP (Modular Inversion and Processing System) was applied at Lake Kummerow, Germany, and lake surface chlorophyll-a was derived from 33 images of five different sensors (MODIS-Terra, MODIS-Aqua, Landsat 8, Landsat 7 and Sentinel-2A). Remotely sensed lake average chlorophyll-a concentration showed a reasonable development and varied between 2.3±0.4 and 35.8±2.0mg·m^-3 from July to October 2015. Match-ups between in situ and satellite chlorophyll-a revealed varying performances of Landsat 8 (RMSE: 3.6 and 19.7mg·m^-3), Landsat 7 (RMSE: 6.2mg·m^-3), Sentinel-2A (RMSE: 5.1mg·m^-3) and MODIS (RMSE: 12.8mg·m^-3), whereas an in situ data uncertainty of 48% needs to be respected. The temporal development of an index on harmful algal blooms corresponded well with the cyanobacteria biomass development during summer months. Satellite chlorophyll-a maps allowed to follow spatial patterns of chlorophyll-a distribution during a phytoplankton bloom event. Wind conditions mainly explained spatial patterns. Integrating satellite chlorophyll-a into trophic state assessment resulted in different trophic classes. Our study endorsed a combined use of satellite and in situ chlorophyll-a data to alleviate weaknesses of both approaches and to better characterise and understand phytoplankton development in lakes.

Water quality of a coastal lagoon (ES, Brazil): abiotic aspects, cytogenetic damage, and phytoplankton dynamics

Assessment of water resources requires interdisciplinary studies that include multiple ecosystem aspects. This study evaluated the water quality of Juara Lagoon (ES, Brazil) based on physical and chemical variables, cytogenetic responses in Allium cepa and phytoplankton dynamics. Three sampling sites were defined and water samples were collected during two sampling periods. Analyses such as determination of photic zone, conductivity, and concentrations of nutrients and metals were conducted as well as cytotoxic, mutagenic, and genotoxic potentials using A. cepa test. The main attributes of phytoplankton community, such as total richness, total density, density by class, dominance, and diversity, were also evaluated. Results have revealed that Juara Lagoon has signs of artificial eutrophication at two sampling sites due to high levels of total phosphorus and ammonia nitrogen. Cytotoxic, genotoxic, and mutagenic potentials were detected as well as high concentrations of Fe and Mn. Furthermore, 165 phytoplankton taxa were recorded, with highest richness in Chlorophyceae and Cyanophyceae classes. In addition, Cyanophyceae presented as the highest density class. A. cepa test and phytoplankton community evaluation indicated that the ecological quality of Juara Lagoon is compromised.