Phytoplankton functional traits and seston stable isotopes signature: a functional-based approach in a deep, subalpine lake, Lake Maggiore (N. Italy)

The seasonal variation of seston stable isotopes signature of carbon (13C) in Lake Maggiore during 2008 was related to seasonal variation of the lake phytoplankton community, investigated in terms of phytoplankton taxonomic groups, morpho-functional groups (MBFG), cell size classes and cell shape classes. Three open water stations were selected to reflect truly pelagic, influenced by littoral and riverine carbon sources; phytoplankton samples were collected from two water depths, 0-20 m and 25-50 m. Among stations differences in 13C signatures of seston were statistically non significant, confirming that allochthonous input may become important only after exceptional rainfall events. Nonparametric multiplicative regression (NPMR) was utilized to identify among the phytoplankton parameters (taxonomic groups, MBFG, cell shapes, cell sizes) which were the best predictors of the 13C variation. Bacillariophyceae and two morpho-functional groups, Group 6 (non-flagellated organisms with siliceous exoskeletons) and Group 3 (large filamentous algae with aerotopes) were statistically significant. Non-metric multidimensional scaling (NMS) ordination was used to investigate differences in phytoplankton samples and their relationship with 13C variation. When morphological and functional phytoplankton traits were superimposed, the NMS ordination showed that cylinder cells (for cell shape classes), class 500-2000 m3 (for cell size classes) and Group 6 (for MBFG) were the most related to 13C variation. Our study confirms that the variation in the pelagic 13C seston most probably reflects changes in phytoplankton carbon isotopic signature, consequent to changes in availability of carbon sources depending on the season and due to different isotopic fractionation of phytoplankton taxonomic groups. Statistical investigations have allowed us to investigate the potential role of phytoplankton morphological and functional traits in the seasonal variation of 13C and to suggest their importance in the interpretation of natural stable isotopes studies in lake ecosystems

Deriving nutrient criteria to support 'good' ecological status in European lakes: An empirically based approach to linking ecology and management

European water policy has identified eutrophication as a priority issue for water management. Substantial progress has been made in combating eutrophication but open issues remain, including setting reliable and meaningful nutrient criteria supporting ʽgoodʼ ecological status of the Water Framework Directive. The paper introduces a novel methodological approach - a set of four different methods - that can be applied to different ecosystems and stressors to derive empirically-based management targets. The methods include Ranged Major Axis (RMA) regression, multivariate Ordinary Least Squares (OLS) regression, logistic regression, and minimising the mismatch of classifications. We apply these approaches to establish nutrient (nitrogen and phosphorus) criteria for the major productive shallow lake types of Europe: high alkalinity shallow (LCB1; mean depth 3–15 m) and very shallow (LCB2; mean depth

Inhibition by steroids of the uptake of potassium by capillaries isolated from rat brain

The effect of steroids on the uptake and release of K+ by capillaries isolated from rat brain was investigated. 86Rb+ uptake was used as a transport analog of K+. The uptake of 86Rb+ by the capillaries was markedly inhibited by ouabain. The ouabain sensitive fraction of 86Rb+ uptake was inhibited by corticosterone with an I50 of 8 x 10-4 M. Inhibition was immediate in onset and rapidly reversible after removal of the steroid. Corticosterone did not alter the affinity of the transport carrier for K+ or the passive efflux of 86Rb+ from the capillaries. Other steroids inhibited ouabain sensitive 86Rb+ uptake in relation to their lipid solubility. These features suggest a direct membrane action for high dose steroid therapy, possibly on Na+,K+ATPase, rather than a nuclear mediated change in cell function.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24467/1/0000742.pd

Comparison and harmonization of eutrophication assessment criteria under the WFD and the Nitrate Directives

Eutrophication of surface water bodies is the most significant water quality problem worldwide. The EU has developed an extensive regulatory and policy framework to protect the environment from nutrient pollution. Although efforts have been made to integrate and create connections between directives, the various requirements and implementation regarding monitoring, assessment and reporting may be different thus hindering the efficient implementation of water policy. The Nitrates Directive (ND) aims at the protection of European surface and ground waters from agricultural pollution due to nitrates, and to promote good agricultural practices. All surface waters should be classified regarding their eutrophication status thus contributing to designation of Nitrate Vulnerable Zones where nutrient management measures are implemented. Since the ND does not stipulate the methodology to assess eutrophication, a plethora of eutrophication assessment criteria have been used by countries which have not been compiled and analysed so far. On the other hand, the Water Framework Directive (WFD) is a comprehensive legislation that mandates the assessment of ecological status of all surface waters based on a variety of elements. It is important that both directives use similar eutrophication assessment criteria achieving consistent implementation of management measures. In this study, for the first time, the criteria used to assess eutrophication under the WFD and the ND are compared and analysed. Furthermore, two case studies are used in order to evaluate the differences. The results show that eutrophication criteria used under different legislations are often incompatible and lead to dissimilar designation of the status of water bodies.JRC.D.2 - Ocean and Wate

Investigating the Impact of Wildfires on Lake Water Quality Using Earth Observation Satellites

A study was carried out to investigate the effects of wildfires on lake water quality using a source dataset of 2024 lakes worldwide, covering different lake types and ecological settings. Satellite-derived datasets (Lakes_cci and Fire_cci) were used and a Source Pathway Receptor approach applied which was conceptually represented by fires (burned area) as a source, precipitation/drought representing transport dynamics, and lakes as the ultimate receptor. This identified 106 lakes worldwide that are likely prone to be impacted by wildfires via a terrestrial pathway. Satellite-derived chlorophyll-a (Chl-a) and turbidity variables were used as indicators to detect changes in lake water quality potentially induced by wildfires over a four-year period. The lakes with the largest catchment areas burned and characterized by regular annual fires were located in Africa. Evidence for a strong influence of wildfires was not found across the dataset examined, although clearer responses were seen for some individual lakes. However, among the hydro-morphological characteristics examined, lake depth was found to be significant in determining Chl-a concentration peaks which were higher in shallow and lower in deep lakes. Lake turbidity responses indicated a dependence on lake catchment and weather conditions. While wildfires are likely to contribute to the nutrient load of lakes as found in previous studies, it is possible that in many cases it is not a dominant pressure and that its manifestation as a signal in lake Chl-a or turbidity values depends to a large part on lake typology and catchment characteristics. Assessment of lake water quality changes six months after a fire showed that Chl-a concentrations either increased, decreased, or showed no changes in a similar number of lakes, indicating that a lake specific ecological and hydro-morphological context is important for understanding lake responses to wildfires

Assessing the impact of wildfires on water quality using satellite remote sensing: the Lake Baikal case study

Lakes have been observed as sentinels of climate change. In the last decades, global warming and increasing aridity has led to an increase in both the number and severity of wildfires. This has a negative impact on lake catchments by reducing forest cover and triggering cascading effects in freshwater ecosystems. In this work we used satellite remote sensing to analyse potential fire effects on lake water quality of Lake Baikal (Russia), considering the role of runoff and sediment transport, a less studied pathway compared to fire emissions transport. The main objectives of this study were to analyse time series and investigate relationships among fires (i.e., burned area), meteo-climatic parameters and water quality variables (chlorophyll-a, turbidity) for the period 2003-2020. Because Lake Baikal is oligotrophic, we expected detectable changes in water quality variables at selected areas near the three mains tributaries (Upper Angara, Barguzin, Selenga) due to river transport of fire-derived burned material and nutrients. Time series analysis showed seasonal (from April to June) and inter-annual fire occurrence, precipitation patterns (high intensity in summer) and no significant temporal changes for water quality variables during the studied periods. The most severe wildfires occurred in 2003 with the highest burned area detected (36,767 km2). The three lake sub-basins investigated have shown to respond differently according to their morphology, land cover types and meteo-climatic conditions, indicating their importance in determining the response of water variables to the impact of fires. Overall, our finding suggests that Lake Baikal shows resilience in the medium-long term to potential effects of fires and climate change in the region

Establishing supporting element standards. A revised approach and applications.

The Water Framework Directive requires member states to determine thresholds for a range of supporting chemical quality elements that will support good ecological status. This is a fundamental step in maintaining natural biodiversity as well as ensuring ecosystem service provision. All countries have defined thresholds, which have been used to report status in river basin planning cycles. The original intention of the work was to determine from empirical analysis a likely range of boundary values using pan-European data, which could be used to help inform any revision of current national boundary values. However, the analysis revealed relatively high levels of uncertainty, emphasising the challenge in establishing these boundary values. This highlighted the need for a more robust method. Binary logistic regression presented advantages over other methods, especially for complex data. However, a probability value must be selected objectively to derive the nutrient threshold. This can be achieved by comparing the proportions of matching and mismatching status classifications of nutrients and a BQE using a confusion matrix. The method is applied to selected supporting elements for rivers and lakes.JRC.D.2 - Ocean and Wate

Physico-chemical criteria to support Good Ecological Status in Europe

This report summarises approaches to setting robust criteria to achieve Water Framework Directive (WFD) objectives for the Annex V physico-chemical supporting elements: transparency, oxygenation, temperature, salinity and acidification. Nutrients have been considered in previous reports. This work is intended to complement existing guidance on statistical approaches to setting thresholds. A general conclusion is that thresholds that were set for older directives (e.g. Freshwater Fish Directive) may not be sufficiently stringent to protect Good Ecological Status and that Member States should check the validity of these. The current approach to data collection and aggregation may also need to be revisited. For example for oxygen or salinity, concern is warrented for both persistent chronic impacts and episodic acute incidents which are becoming more frequent with climate change events such as heatwaves. We tested the latest version (2023) of the toolkit for setting thresholds on transparency and oxygenation conditions using EU-wide data demonistrating its potential. We identify situations where it may be possible to use historical time series, ecotoxicological data and peer-reviewed literature to set thresholds. However, thresholds are highly context specific, so it is rarely possible to give specific guidelines that apply across the EU. Each chapter ends with a summary table to help guide on the appropriatness of the different approaches to set thresholds.JRC.D.2 - Ocean and Wate

Setting nutrient boundaries to protect aquatic communities: The importance of comparing observed and predicted classifications using measures derived from a confusion matrix

Defining nutrient thresholds that protect and support the ecological integrity of aquatic ecosystems is a fundamental step in maintaining their natural biodiversity and preserving their resilience. With increasing catchment pressures and climate change, it is more important than ever to develop clear methods to establish thresholds for status classification and management of waters. This must often be achieved using complex data and should be robust to interference from additional pressures as well as ameliorating or confounding conditions. We use both artificial and real data to examine challenges in setting nutrient thresholds in unbalanced and skewed data. We found significant advantages to using binary logistic regression over other techniques. However, one of the key challenges is objectively selecting a probability from which to derive the nutrient threshold. For this purpose, the examination of the proportions of matching and mismatching status classifications of nutrients and a biological quality element using a confusion matrix is a key step that should be more widely adopted in threshold selection. We examined a large array of statistical measures of classification accuracy and their performance over combinations of skewness and imbalance in the data. The most appropriate threshold probability is a compromise between maximising overall classification accuracy and reducing mismatches expressed as commission (false positives) without excessive omission (false negatives). An application to a lake type indicated total phosphorus thresholds that would be around 50 μg l−1 lower than the threshold achieved by an ‘unguided’ approach, indicating that this approach is a very significant development meriting attention from national authorities responsible for water management.publishedVersio