The study period was anything but ordinary. Portugal endured an unusually dry stretch in which every month except March recorded below-average precipitation, and the Portuguese Institute for the Ocean and Atmosphere logged six distinct heat waves between September 2021 and September 2022. Following World Meteorological Organisation guidelines, the researchers classified heat waves as periods lasting at least two consecutive days with maximum temperatures five degrees Celsius above the mean. The events they documented ranged from six to sixteen days in duration, and remarkably, one occurred in December 2021, demonstrating that extreme heat no longer respects seasonal boundaries. This relentless sequence of thermal shocks, layered on top of chronic drought, created a natural experiment that the team could exploit by sampling monthly across a full year.

The Minho River estuary, which forms roughly forty kilometres of the border between Portugal and Spain, is a mesotidal, partially mixed system that tends toward a salt wedge during high flows. The researchers selected two dominant submerged plants anchored at opposite ends of the salinity gradient. Fucus ceranoides, a brown alga typical of sheltered rocky estuaries from northern Portugal to Norway, grows on rocks near the river mouth in the polyhaline zone. Egeria densa, a submerged macrophyte native to subtropical South America that first appeared in the international section of the Minho in the early 1990s, forms dense monospecific mats along the upper estuary’s tidal freshwater zone. Because Egeria densa’s downstream distribution stops at the oligohaline-limnetic boundary, roughly sixteen kilometres from the mouth, saline intrusion during dry months poses a constant threat to its foothold.

Monthly sampling from September 2021 to September 2022 was conducted at low tide, with five replicate quadrats of 0.1 square metres collected by hand for each plant. In the laboratory, the team removed, sorted and counted every associated invertebrate to the lowest taxonomic level possible, then dried plant and animal material at sixty degrees Celsius for forty-eight hours to determine dry weight. Ash-free dry mass was obtained by burning samples in a muffle furnace at 550 degrees Celsius. In parallel, a multi-parameter probe recorded water temperature, salinity, dissolved oxygen, pH, conductivity and oxidation-reduction potential at each site, while suspended organic matter was quantified by filtering one-litre water samples through pre-weighed glass fibre filters. Statistical treatment included UPGMA clustering with Bray-Curtis similarity to group months by environmental and faunal composition, Kendall’s rank correlations for non-normal data, and Kruskal-Wallis tests with Dunn post hoc comparisons for biomass differences.

The environmental data told a clear story of stress. In the lower estuary, water temperature ranged from 10.9 degrees Celsius in January to 20.6 degrees in June, and salinity swung dramatically from 13.55 in March to 37.18 in September 2021. Upstream, conditions were harsher still: temperatures spanned 7.7 degrees in November to 25.3 degrees in August, and an August salinity peak of 0.16, modest by marine standards but anomalous for a freshwater zone, contrasted with values of 0.04 to 0.08 in other months. Oxidation-reduction potential, a proxy for the chemical redox state of the water, dipped in every heat wave month in the lower estuary and collapsed to 87.1 millivolts in July upstream, far below the 228 to 348 millivolts seen otherwise. Cluster analysis confirmed that July and August stood apart environmentally from all other months.

Against this backdrop, the two plants responded in opposite ways. Fucus ceranoides biomass varied little, averaging 589.77 grams of dry weight per square metre, with a November maximum of 770.71 and a July minimum of 429.4. The only significant differences separated April and July from most other months, and no correlations emerged between algal biomass and any measured environmental variable. The authors attribute this resilience to the euryhaline tolerance of a species adapted to daily tidal salinity fluctuations, noting that similar biomasses were recorded in a survey of the same site a decade earlier. Egeria densa, by contrast, declined relentlessly, falling from 289.9 grams of dry weight per square metre in October 2021 to just 84.8 by September 2022, with significant decreases from March onward. Its biomass correlated positively with pH and suspended organic matter but negatively with water temperature, suggesting that despite the species’ reputation for tolerating warm water, abrupt heat waves push it beyond its limits in estuarine conditions.

The invertebrate communities living within these plants proved even more sensitive than the plants themselves. In the Fucus zone, thirteen species were recorded, including the exotic barnacle Austrominius modestus, and diversity dipped during the December, July and August heat waves. Yet one species bucked the trend spectacularly: the amphipod Echinogammarus marinus, whose abundance and biomass peaked during the hottest months, driving annual abundance to 461.68 individuals per square metre, nearly double the figure from the 2011-2012 survey. This adaptable euryhaline crustacean appears poised to thrive under climate change, potentially released from predation as the shore crab Carcinus maenas declined. Upstream, the Egeria beds hosted twenty-three species, nine of them exotic, including two, the snail Ferrissia californica and the leech Barbronia weberi, recorded in the estuary for the first time. Total invertebrate counts upstream plummeted from 2,490 individuals in June to just 106 in September, and the number of taxa collapsed in the final month.

Perhaps the most provocative finding concerns which animals flourished amid the chaos. The exotic gastropods Physella acuta and Menetus dilatatus surged in abundance during the December and May heat waves, confirming earlier evidence that non-native freshwater snails tolerate elevated temperatures better than European natives. However, both species crashed when salinity rose in the upper estuary during summer, with Menetus dilatatus abundance negatively correlated with salinity and Physella acuta biomass negatively correlated with temperature. Other freshwater residents fared worse: the bryozoan Paludicella articulata and the mite Lebertia insignis were both strongly and negatively correlated with rising temperatures, while several species, including the planarian Girardia sinensis and the damselfly Ischnura elegans, depended directly on Egeria densa biomass for their persistence. As the macrophyte withered, so did the animals that rely on it as habitat.

The broader implications reach beyond a single river. Salt intrusion in estuaries is projected to increase worldwide, and prolonged heat waves reduce river flow, amplifying saline penetration into upstream habitats. The study suggests that while compensatory mechanisms such as functional redundancy and species replacement can buffer communities against moderate disturbances, increasingly severe heat waves disrupt these safety nets, leaving freshwater assemblages vulnerable to lasting structural change. In the Minho, the synergy of heat and salinity appears to favour a small cast of hardy generalists, including invasive snails and one opportunistic amphipod, at the expense of the diverse communities that healthy submerged vegetation supports. The authors caution that because sampling covered only one exceptional year, continuous monitoring is needed to establish baseline biomass levels for Egeria densa and to separate seasonal abundance cycles from genuine extreme-event impacts. Controlled experiments on Fucus ceranoides temperature tolerance would further sharpen predictions. For estuary managers across the Iberian Peninsula and beyond, the message is stark: the plants that anchor these ecosystems are not equally equipped for a hotter world, and the animals that depend on them will inherit whatever the heat leaves behind.

Subject of Research: Effects of marine and freshwater heat waves on estuarine macrophytes and their associated invertebrate fauna in the Minho River estuary

Article Title: Effects of heat wave events on the brown alga Fucus ceranoides and on the established exotic species Egeria densa and associated fauna in the Minho river estuary (NW Iberian Peninsula)

Article References: Gomes, N., Sousa-Pinto, I., & Antunes, C. (2025). Effects of heat wave events on the brown alga Fucus ceranoides and on the established exotic species Egeria densa and associated fauna in the Minho river estuary (NW Iberian Peninsula). Discover Ecology, 1(1), Article 4. https://doi.org/10.1007/s44396-025-00004-x

Image Credits: AI Generated

DOI: 10.1007/s44396-025-00004-x

Keywords: heat waves, estuarine ecology, Fucus ceranoides, Egeria densa, invasive species, invertebrates, salinity intrusion, climate change, Minho River, macrophytes, biodiversity, NW Iberian Peninsula

Macrophytes encompass a diverse array of submerged, emergent, and floating primary producers visible to the naked eye, including vascular plants, macroalgae, and bryophytes. Long regarded as ecological pillars of aquatic ecosystems, these plants perform an extraordinary range of functions: they stabilize sediments, oxygenate the water column, provide habitat and foraging grounds for fish, invertebrates, and amphibians, and drive nutrient cycling. Their ecophysiological adaptations—such as aerenchyma formation and radial oxygen loss that allow them to survive in waterlogged conditions—translate into ecosystem-level consequences that ripple through entire food webs, making them uniquely suited to serve as the biological foundation of nature-based restoration strategies.

The concept of nature-based solutions, formally introduced by the International Union for Conservation of Nature in the late 2000s and consolidated at the 2016 World Conservation Congress, defines actions to protect, sustainably manage, and restore natural or modified ecosystems that address societal challenges while simultaneously delivering human well-being and biodiversity benefits. Macrophytes have been quietly working within this framework for decades. Species such as the common reed Phragmites australis, cattails of the genus Typha, and water hyacinth Eichhornia crassipes have long been deployed in constructed and floating treatment wetlands to strip nutrients, metals, and organic pollutants from water. Recent research shows that the performance of these systems hinges on hydraulic retention time and plant functional traits: submerged species like Vallisneria spiralis and Ceratophyllum demersum enhance nitrification and phosphorus immobilization under moderate flows, while emergent species tolerate heavy metal loads and support microbial degradation of contaminants.

To assess the current state of knowledge, Bolpagni conducted a systematic search of literature published from 2020 onward across Scopus, Web of Science, and Google Scholar, screening more than 2,100 records and ultimately identifying 16 exemplary case studies in which macrophytes act as genuine restoration players rather than passive indicators of ecosystem condition. The studies spanned themes from nutrient legacy mitigation and biotic interactions to climate impacts and practical planting techniques. Across all cases, macrophyte-based interventions produced measurable improvements in habitat restoration, water quality, and biodiversity, with outcomes shaped primarily by light availability, nutrient loading, hydrology, and the remediation capacity of the plants themselves.

The mechanisms behind these successes are becoming increasingly well understood. By anchoring sediments, macrophytes reduce resuspension and turbidity, allowing more light to penetrate the water column and creating conditions favorable to further plant growth—a classic positive feedback loop. In shallow lakes studied in New Zealand, researchers emphasized that understanding macrophyte light and depth tolerances is essential for predicting restoration success. Danish lake studies have identified trophic thresholds beyond which macrophytes decline, with total phosphorus concentrations above roughly 0.13 to 0.20 milligrams per liter or total nitrogen above 1.2 to 2.0 milligrams per liter marking danger zones. Beyond light, macrophyte restoration increases dissolved oxygen, shifts microbial community composition, and enhances the microbial carbon pump, which can bolster aquatic carbon sequestration—a finding with profound implications for climate change adaptation.

The evidence for water quality gains is striking. One study of an urban shallow lake reported reductions exceeding 50 percent in nitrogen, phosphorus, and chlorophyll a following macrophyte restoration, alongside increases in recalcitrant dissolved organic matter. In a three-year study of a subtropical lake in China, submerged macrophyte restoration led to marked decreases in cyanobacteria and other algal taxa, with these changes negatively correlated with nutrient concentrations. Rooted plants also improve sediment chemistry: research on Vallisneria spiralis demonstrated that the species improves pore water conditions and increases potential nitrification in organically polluted sediments, effectively transforming contaminated substrates into more functional biological layers.

Success, however, is far from guaranteed, and the article is candid about the conditions that lead to failure. Restoration efforts falter when depth, turbidity, or shading limit light; when storms, waves, or dredging repeatedly disturb plantings; when invasive species or high grazing pressure suppress regrowth; or when propagule banks and genetic diversity are depleted. Perhaps most insidiously, short-term interventions without maintenance can backfire—when accumulated plant biomass is never harvested, nutrients released during decomposition can re-fertilize the very system the restoration was meant to save, triggering self-fertilization processes that undermine the entire effort. Modeling work based on the PCLake framework suggests that maintaining an optimal biomass window of roughly 5.5 kilograms of fresh weight per square meter, with substantial harvesting of about 80 percent during the decline period, can prevent this nutrient leakage.

Trade-offs are equally real. Biomass harvesting removes nutrients but demands significant labor and investment; floating and constructed wetlands must occupy considerable areas to be effective; and in some contexts, evapotranspiration from dense plant stands can reduce water volumes and accelerate the drying of colonized water bodies. Climatic extremes such as droughts and floods can disrupt restored systems in unpredictable ways. Quantitative operational thresholds are emerging to guide practitioners: in Chesapeake Bay, total suspended solids above 15 milligrams per liters signaled unfavorable conditions for submerged vegetation, while sediment organic matter contents above roughly 20 percent caused drastic growth reductions in even highly reactive species like Hydrilla verticillata and Myriophyllum spicatum.

To maximize effectiveness, the article proposes an operational framework for implementing macrophyte-based solutions, beginning with comprehensive pre-intervention assessments of nutrient loads, sediment phosphorus, light profiles, and hydrodynamics. It calls for climate-resilient design incorporating buffer zones and species redundancy, multifunctional approaches that combine submerged plantings with emergent buffers and floating wetlands, and careful attention to propagule banks and genetic diversity, prioritizing native species adapted to local stressors. Notably, mixing aquatic plant functional types appears to pay dividends: communities combining up to eight species across three functional groups form more stable stands, support clear-water states, reduce methane emissions through enhanced rhizosphere processes, and can outperform monocultures in nitrogen removal due to metabolic complementarity.

Ultimately, the synthesis signals a paradigm shift in freshwater restoration—away from short-term engineering fixes and toward system-level agendas grounded in adaptive management, stakeholder engagement, and long-term governance and financing. Success depends less on planting effort alone than on establishing the enabling conditions for recovery: reduced external nutrient loads, adequate light and hydrodynamic regimes, and sufficient propagule availability. As invasive taxa reshape freshwater communities in ways that may constitute nothing less than an ecological revolution, the stakes could hardly be higher. Macrophytes, the article concludes, should be recognized not only as vital targets of restoration but as essential tools for climate adaptation in the Anthropocene—living infrastructure already growing in the waters we are struggling to save.

Subject of Research: Macrophyte-based nature-based solutions for restoring freshwater ecosystems

Article Title: Macrophytes-based solutions as tools to halt the collapse of freshwater biodiversity, functions and benefits

Article References: Bolpagni, R. (2026). Macrophytes-based solutions as tools to halt the collapse of freshwater biodiversity, functions and benefits. Discover Ecology, 2(1), Article 8. https://doi.org/10.1007/s44396-026-00027-y

Image Credits: AI Generated

DOI: 10.1007/s44396-026-00027-y

Keywords: macrophytes, freshwater restoration, nature-based solutions, aquatic plants, eutrophication, water quality, biodiversity, shallow lakes, phytoremediation, ecosystem services, adaptive management, climate change

The research team, led by Dionissis Latinopoulos of Democritus University of Thrace together with colleagues from Aristotle University of Thessaloniki, ESAIP in France, and the Greek Biotope/Wetland Centre (EKBY), built their analysis on data collected between 2012 and 2021 under the Greek National Water Monitoring Network. For every lake-year, they compiled ecological quality ratios for phytoplankton, macrophytes and benthic macroinvertebrates, alongside physicochemical measurements including total phosphorus, chlorophyll-a, Secchi disk transparency, dissolved oxygen, pH and nitrates. These biological and physicochemical quality elements are the building blocks of ecological status assessment under the European Union’s Water Framework Directive (WFD), the legislation that obliges member states to restore surface waters to good condition.

The scale of the challenge is considerable. Across Europe, 54 percent of surface waters are subject to significant hydromorphological pressures, and in Greece 45 percent of all lakes—covering 47 percent of the total lake area—exhibit such alterations, making them the second-largest source of pressure after diffuse pollution. Meanwhile, 58 percent of Greek lake water bodies fail to achieve good ecological status. Yet until 2012, parameters such as water abstraction and flow regulation were not even classified as hydromorphological pressures in Greece, and the connection between physical alteration and biological response had never been systematically evaluated for Mediterranean lakes.

To close that gap, the researchers began with an ambitious pool of candidate metrics—115 for natural lakes and 46 for reservoirs—and subjected them to a rigorous screening process. Spearman rank correlations removed redundant variables, box plots eliminated metrics with narrow ranges or extreme outliers, and transformations tamed skewed distributions. What survived was a compact toolkit: seven hydromorphological metrics for natural lakes and eleven for reservoirs, spanning maximum macrophyte colonization depth, shoreline modification, arable and non-natural land cover within a 100-meter buffer zone, mean depth, and absolute water level. This disciplined reduction was essential to avoid the multicollinearity that plagues large environmental datasets.

Redundancy analysis then revealed striking patterns. In natural lakes, mean depth emerged as the most statistically significant hydromorphological predictor, positively associated with the ecological quality of both phytoplankton and macrophytes. The interpretation is rooted in limnological theory: deeper lakes possess greater dilution capacity and stronger self-purification, buffering them against eutrophication stressors. Deep, transparent systems such as Amvrakia, Kourna and Trichonida clustered at one end of the main environmental gradient, while shallow, eutrophication-impacted lakes like Voulkaria, Zazari and Ismarida—each ringed by more than 69 percent arable land—sat at the opposite pole, marked by elevated chlorophyll-a and total phosphorus.

Land use told its own damning story. The percentage of non-natural land cover correlated negatively with benthic macroinvertebrate quality, and agricultural metrics tracked closely with nutrient concentrations and chlorophyll-a. The authors emphasize that agricultural land cover acts as a compound stressor: beyond the familiar route of fertilizer runoff, cultivated fields accelerate sediment delivery that smothers macrophyte beds and benthic habitats, while agricultural expansion typically strips away the riparian vegetation that stabilizes banks, filters diffuse pollutants and maintains the structural complexity of littoral zones. In other words, a plowed shoreline damages a lake through physics as much as through chemistry.

Reservoirs obeyed a different logic. Variation partitioning showed that land use variables within the 100-meter buffer zone dominated, explaining a unique fraction of 0.329 of the variance in quality elements—by far the strongest single signal. Intensive agriculture was the dominant gradient-structuring factor, fallow land cover the primary driver of the second axis, and water level a secondary but significant explanatory variable. Phytoplankton quality declined where intensive agriculture pressed against the water’s edge, while natural cover types such as shrubs, forest and low vegetation worked as counterweights. Unlike natural lakes, where water level and depth carried the greatest weight in individual regression models, reservoir quality emerged from a broader, more evenly distributed combination of landscape and hydrological factors, with no single variable exceeding roughly 38 percent relative contribution in any model.

Principal component analysis added a typological layer to the picture, sorting both natural lakes and reservoirs into four distinct groupings. For natural lakes, the clusters separated along gradients of water level elevation, mean depth and arable land share—one group united by more than 40 percent arable land in the buffer zone, another of low-elevation lakes, a third of shallow systems, and a fourth of high-elevation lakes defined jointly by depth and elevation. For reservoirs, the ratio of mean depth to lake area and the diversity of natural land cover types structured the ordination, distinguishing forested catchments from intensively farmed ones. These typological groupings matter because they hint that management prescriptions cannot be one-size-fits-all: a mountain reservoir surrounded by forest responds to different levers than a lowland lake hemmed in by wheat fields.

The study is candid about its limitations. The ratio of explanatory variables to water bodies fell below the conventional guideline of roughly ten observations per predictor, so the authors frame their identified gradients as exploratory rather than definitive. Corine Land Cover data at 25-hectare minimum mapping units may underrepresent fine-scale shoreline heterogeneity within 100-meter buffers, and ecological water level data exist for only five Greek natural lakes. Residual overlap between macrophyte-based metrics and the macrophyte quality index also cannot be fully eliminated. Still, the team argues that these constraints do not blunt the central message: hydromorphological functioning is a genuine mediator of ecological quality, not a background detail.

The policy implications are immediate. The authors propose that system-specific hydromorphological metrics—shoreline naturalness, mean depth, water level, and buffer-zone land use—should be woven into WFD assessment methods and ecohydrological management strategies, distinguishing natural lakes from reservoirs. They point to candidate metrics already used in Greek River Basin Management Plans, such as the proportion of perimeter under intensive land use, and suggest that remote sensing and higher-resolution land cover products such as the CLCplus Backbone could sharpen future monitoring. As climate change lengthens droughts and reshapes inflow patterns across the Mediterranean, the study’s core insight becomes more urgent: protecting a lake means protecting not only its water chemistry, but its very shape, shoreline and hydrological heartbeat.

Subject of Research: Quantifying how hydromorphological pressures and land use metrics influence the ecological quality of Mediterranean natural lakes and reservoirs in Greece.

Article Title: How Hydromorphological Pressures Co-govern Lake Water Quality in a Mediterranean Environment. A Study for Greek Natural Lakes and Reservoirs

Article References: How Hydromorphological Pressures Co-govern Lake Water Quality in a Mediterranean Environment. A Study for Greek Natural Lakes and Reservoirs. (n.d.). https://doi.org/10.1007/s00267-026-02627-6

Image Credits: AI Generated

DOI: 10.1007/s00267-026-02627-6

Keywords: hydromorphology, lake water quality, Mediterranean lakes, reservoirs, Water Framework Directive, eutrophication, land use, phytoplankton, macrophytes, ecological status, Greece, ecohydrological management