Thresholds of terrestrial nutrient loading for the development of eutrophication episodes in a coastal embayment in the Aegean Sea

Thresholds of terrestrial nutrient loading (inorganic N and P) for the development of eutrophication episodes were estimated in an enclosed embayment, the gulf of Kalloni, in the Aegean, Eastern Mediterranean. Terrestrial loading was quantified by a watershed runoff model taking into account land use, geomorphology, sewerage, industrial and animal farming by-products. The eutrophication episodes were assessed by an existing scale for the Aegean coastal waters based on chl a, whereas the necessary nutrient concentrations (N and P) for the development of such episodes were defined using a probabilistic procedure. Finally, for the linking between nutrient loading arriving at the gulf and the resulting nutrient enrichment of the marine ecosystem, three loading factors were applied, developed by Vollenweider for lake and marine ecosystems. The first assumes no exchange between the embayment and the open sea, whereas the two others take into account water renewal time. Only the threshold for inorganic nitrogen estimated by the first factor was exceeded in the study area during February after a strong rainfall event coinciding with a eutrophication episode observed in the interior of the gulf, implying that the waters of the gulf are rather confined and the receiving body operates as a lake. The degree of confinement was further examined by studying the temperature, salinity, and density distributions inside the gulf and across the channel connecting the gulf to the open sea. It was found that the incoming freshwater from the watershed during winter results to the formation of a dilute surface layer of low salinity and density, clearly isolated from the open sea. The nutrients from the river inputs are diluted into this isolated water mass and the eutrophication threshold for nitrogen is exceeded. Although phosphorus loading was also high during winter, the corresponding limits were never exceeded. The proposed methodology sets a quantitative relationship between terrestrial nutrient loading and the development of eutrophication episodes in coastal embayments, assuming that information on the physical setting of the system is available. These cause-and-effect relationships can be invaluable tools for managers and decision makers in the framework of Integrated Coastal Zone Management

New tools and recommendations for a better management of harmful algal blooms under the European Marine Strategy Framework Directive

Marine harmful algal blooms (HABs), caused by various aquatic microalgae, pose significant risks to ecosystems, some socio-economic activities and human health. Traditionally managed as a public health issue through reactive control measures such as beach closures, seafood trade bans or closure of mollusc production areas, the multifaceted linkages of HABs with environmental and socio-economic factors require more comprehensive ecosystem-based management approach tools to support policies. This study promotes a coordinated understanding and implementation of HAB assessment and management under the Marine Strategy Framework Directive (MSFD), targeting the achievement of Good Environmental Status (GES) in European marine waters. We introduce two novel tools: GES4HABs (GES for HABs) decision tree, and MAMBO (environMental mAtrix for the Management of BlOoms), a decision support matrix. These tools aim to streamline HABs reporting and prioritize resource allocation and management interventions. The GES4HABs decision tree defines a sequence of decision steps to identify HAB management strategies according to their state (evaluated against predefined baselines) and causes (anthropic or natural). MAMBO is proposed to address different HABs and their interaction with human and environmental pressures. The matrix utilizes two axes: natural trophic status and level of human influence, capturing major aspects such as nutrient supply. While acknowledging the limitations of this simplified framework, MAMBO categorizes marine regions into quadrants of varying management viability. Regions with high human influence and eutrophic conditions are identified as most suitable for effective management intervention, whereas regions with minimal or mixed human influence are deemed less amenable to active management. In addition, we explore and describe various indicators, monitoring methods and initiatives that may be relevant to support assessments of HAB status and associated pressures and impacts in the MSFD reporting. Finally, we provide some recommendations to promote the consideration of HABs in ecosystem-based management strategies, intensify efforts for harmonizing and defining best practices of analysis, monitoring and assessment methodologies, and foster international and cross-sectoral coordination to optimize resources, efforts and roles

Changes of photosynthesis and carbon metabolism in Typha angustifolia L grown in conditions of nitrate nitrogen overload

Nitrates may induce alterations in NO-signaling system and change photosynthesisin plants. Significant reduction of 14CO2 fixation was noted at concentration of 3.96mM NaNO3 in an aquatic macrophyte (Typha angustifolia L.). Assimilation of 14CO2 seven days after the introduction of nitrates did not differ between control and experimental samples. There were changes in distribution of 14C among products of 4CO2 fixation 4 h after NaNO3 addition, resulting in increased sugar radioactivity in experimental plants. It was suggested that the observed changes may have regulatory importance

Ecological quality scales based on phytoplankton for the implementation of Water Framework Directive in the Eastern Mediterranean

Structural changes of phytoplankton communities, often expressed through ecological indices, constitute one of the metrics for the implementation of the European Water Framework Directive (WFD). In the current study a thorough analysis of the efficiency of 22 ecological indices was performed and a small number was selected for the development of five-level water quality scales (High, Good, Moderate, Poor, and Bad). The analysis was performed on simulated communities free of the noise of field communities due to uncontrolled factors or stochastic processes. Two criteria were set for the sensitivity of indices, namely their monotonicity and linearity across the studied eutrophication spectrum. The whole procedure was based on the development of a five-level quality assessment scheme based on phytoplankton abundance. Among the indices tested, the Menhinick diversity index and three indices of evenness were the most efficient, showing consistency (monotonic behavior) and linearity and were therefore used for the development of quality scales for the WFD. An Integrated Phytoplankton Index (IPI) based on three phytoplankton metrics, chlorophyll a, abundance, and diversity is also proposed. The efficiency of these indices was evaluated for a number of sites in the Aegean, already classified in the past by various methods based on nutrient concentrations or phytoplankton data. The results indicate that the various phytoplankton metrics (chlorophyll a, abundance, and diversity) assessed or proposed in the current study, carry their own information showing differences in the final classification of areas. Therefore the establishment of synthetic indices as the IPI seems to be advantageous for the integrated assessment of coastal water quality in the framework of European policies as the WFD

Zipf–Mandelbrot model behavior in marine eutrophication: two way fitting on field and simulated phytoplankton assemblages

Zipf–Mandelbrot (ZM) model, linking the evenness and predictability of communities (parameter gamma) to environmental diversification (parameter beta), was fitted on a phytoplankton dataset, representing a wide productivity spectrum characteristic of Eastern Mediterranean. To reveal community characteristics explaining observed patterns in gamma and beta, ZM model was also fitted on simulated assemblages generated by three niche-based models. Parameter gamma showed a decreasing trend with evenness in agreement with theory and related field studies. High gamma values corresponded to phytoplankton assemblages characterized by the presence of a dominant species, the rest being evenly distributed, whereas low gamma was observed for even assemblages. For ZM beta with evenness, a characteristic U-shaped relationship was observed in field and simulated assemblages, implying that high environmental diversification may lead to either high or low evenness. These assemblages are described by MacArthur fraction and dominance decay niche-based models and their only difference is the dominance of a single species, the rest being evenly distributed. At intermediate environmental diversification, more often encountered in the field, phytoplankton assemblages are described by random fraction model resulting to slightly steeper RADs. Two-way fitting approach on field and simulated assemblages provided useful insights on both ZM model behavior and its underlying hypotheses

Simulating the structure of natural phytoplankton assemblages: descriptive vs. mechanistic models

Simulated phytoplankton assemblages (species richness and allocation of cells to species) retaining the diversity, evenness, and redundancy of natural assemblages were generated in the present paper. The methodology was validated against phytoplankton data from coastal Mediterranean waters, characteristic of oligotrophy to eutrophication. Two modelling approaches were used: a descriptive based on the log series statistical distribution, and a mechanistic based on the random fraction niche-apportionment model. Two characteristic relationships extracted from field data (888 samples), relating species richness and the abundance of the most dominant species with cell density, formed the basis of the modelling procedure. Simulated assemblages generated by both log series and random fraction models closely matched the structure of natural phytoplankton assemblages, showing however differences in their behaviour and easiness of application. Simulation by the log series model resulted in a wider range of assemblage diversity, closer to reality compared to random fraction model. Nevertheless, the latter includes a stochastic element always present in field assemblages, it is mathematically simpler to be applied, and it is based on a sound theoretical basis linking assemblage structure and resource availability. The proposed simulated assemblages can be used in a variety of applications ranging from the development of systematic methodologies for water quality assessment to the incorporation of a multispecies phytoplankton component in biogeochemical dynamic models

Recurrent Pseudo-nitzschia calliantha (Bacillariophyceae) and Alexandrium insuetum (Dinophyceae) winter blooms induced by agricultural runoff

A winter bloom dominated by Pseudo-nitzschia calliantha Lundholm, Moestrup et Hasle (Bacillariophyceae), a potential domoic acid producer, is reported for the first time in the Aegean Sea, Greece, in a semi-enclosed embayment (Kalloni Gulf) surrounded by agricultural land and drained by intermittent rivers. Abundances of this species in the inner part of the Gulf during February were extremely high (max 1.1 × 107 cells l−1). The species Alexandrium insuetum Balech (Dinophyceae) was also found in considerable cell numbers (max 1.4 × 105 cells l−1) during the bloom and reached up to 40% of the total biovolume. This study demonstrates an evident cause and effect relationship between nutrient inflows originating from agricultural activities in the watershed and the development of a potential HAB. The massive bloom formation was observed soon after an episodic rainfall event during the fertilizer application period (December to February). A bloom was also observed the following year, but it was less pronounced due to the fact that rainfalls were more evenly spaced in time and were of moderate intensity

Recurrent Pseudo-nitzschia calliantha (Bacillariophyceae) and Alexandrium insuetum (Dinophyceae) winter blooms induced by agricultural runoff

A winter bloom dominated by Pseudo-nitzschia calliantha Lundholm, Moestrup et Hasle (Bacillariophyceae), a potential domoic acid producer, is reported for the first time in the Aegean Sea, Greece, in a semi-enclosed embayment (Kalloni Gulf) surrounded by agricultural land and drained by intermittent rivers. Abundances of this species in the inner part of the Gulf during February were extremely high (max 1.1 × 107 cells l-1). The species Alexandrium insuetum Balech (Dinophyceae) was also found in considerable cell numbers (max 1.4 × 105 cells l-1) during the bloom and reached up to 40% of the total biovolume. This study demonstrates an evident cause and effect relationship between nutrient inflows originating from agricultural activities in the watershed and the development of a potential HAB. The massive bloom formation was observed soon after an episodic rainfall event during the fertilizer application period (December to February). A bloom was also observed the following year, but it was less pronounced due to the fact that rainfalls were more evenly spaced in time and were of moderate intensity. © 2007 Elsevier B.V. All rights reserved