Freshwater Aquatic Ecosystems Research Articles

Simultaneous methane mitigation and nitrogen removal by denitrifying anaerobic methane oxidation in lake sediments

Methane (CH4) is a potent greenhouse gas, with lake ecosystems significantly contributing to its global emissions. Denitrifying anaerobic methane oxidation (DAMO) process, mediated by NC10 bacteria and ANME-2d archaea, links global carbon and nitrogen cycles. However, their potential roles in mitigating methane emissions and removing nitrogen from lake ecosystems remain unclear. This study explored the spatial variations in activities of nitrite- and nitrate-DAMO and their functional microbes in Changdanghu Lake sediments (Jiangsu Province, China). The results showed that although the average abundance of ANME-2d archaea (5.0 × 106 copies g−1) was significantly higher than that of NC10 bacteria (2.1 × 106 copies g−1), the average potential rates of nitrite-DAMO (4.59 nmol 13CO2 g−1 d−1) and nitrate-DAMO (5.01 nmol 13CO2 g−1 d−1) showed no significant difference across all sampling sites. It is estimated that nitrite- and nitrate-DAMO consumed approximately 6.46 and 7.05 mg CH4 m−2 d−1, respectively, which accordingly achieved 15.07–24.95 mg m−2 d−1 nitrogen removal from the studied lake sediments. Statistical analyses found that nitrite- and nitrate-DAMO activities were both significantly related to sediment nitrate contents and ANME-2d archaeal abundance. In addition, NC10 bacterial and ANME-2d archaeal community compositions showed significant correlations with sediment organic carbon content and water depth. Overall, this study underscores the dual roles of nitrite- and nitrate-DAMO processes in CH4 mitigation and nitrogen elimination and their key environmental impact factors (sediment organic carbon and inorganic nitrogen contents, and water depth) in shallow lake, enhancing the understanding of carbon and nitrogen cycles in freshwater aquatic ecosystems.

Exploring the relationship between land-use and pesticides in freshwater ecosystem: A case study of the Araguaia River Basin, Brazil

Freshwater aquatic ecosystems are vulnerable to human activities within their surroundings, presenting a concerning scenario for aquatic organisms and human subsistence. Therefore, understanding the occurrence of pesticide contamination is a necessary condition to safeguard aquatic biodiversity and human health. We analysed the pesticide residues in water samples, using the solid-phase extraction (SPE) technique and determination by ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC‒MS/MS). We also we investigated whether land use influences water contamination by pesticides in the middle and upper Araguaia River basin, situated in the central region of Brazil in the Cerrado biome. We evaluated the effect of land use and land cover type on pesticide occurrence in nine subbasins using mixed linear models. We registered the occurrence of pesticides in all subbasins. After water analysis a total of eight pesticides were found: atrazine, carbendazim, cyanazine, imidacloprid, 2,4-D, clomazone, chlorpyrifos-ethyl, and imazalil. Atrazine and carbendazim were detected during both sampling years. The active ingredient atrazine and clomazone were registered in all studied subbasins, with concentrations ranged from 0.006–0.207 µg L−1 and 0.183–0.373 µg L−1, respectively. There were no significant relationships observed between the number of pesticides and the type of land use and land cover, a result possibly related to the short sampling period, as these pesticides are largely used for fungi and insect control in agricultural areas. The presence of pesticides in the water may have potentially detrimental effects on aquatic biodiversity because sampled pesticides have been associated with anomalies in ontogenetic development, diseases, and mortality in organisms. Based on European legislation, it was evident that most of the subbasins had pesticide concentrations in the water exceeding the safety levels for human consumption. Thus, it is crucial for Brazilian legislation to establish maximum limits for pesticide concentrations in water to ensure safe drinking water for the Brazilian population. Additionally, a permanent monitoring system should be established to understand contamination trends in this basin and to take appropriate actions to mitigate adverse impacts.

Studies on diversity of aquatic insects in Tamasi lake, Tahsil- Bhadravati, Dist- Chandrapur (M.S) India

Aquatic insects are found abundantly and exhibits high diversity in fresh water aquatic ecosystems. They serve as food item for the vertebrate and invertebrate predators and thus play a significant role in aquatic ecosystem. Insects responded well to a wide range of environmental disturbances and thus often are employed as proxies for water quality. The present study was carried out at Tamasi Lake, situated in Bhadravati Taluka of Chandrapur district, Maharashtra which comes under Tribal area. The year round investigation was carried out to evaluate the diversity of aquatic insects for a period of one year from June 2022 to May 2023. The present investigation shows the presence of total 28 species of aquatic insects from 5 orders and 18 families. The rich and varied diversity of aquatic insects indicate the moderate environmental condition of freshwater ecosystem under study and functioning properly.

Giant DNA Viruses Infecting Unicellular Protists

Giant DNA Viruses Infecting Unicellular Protists

Microcosm experiment combined with process-based modeling reveals differential response and adaptation of aquatic primary producers to warming and agricultural run-off.

Fertilizers, pesticides and global warming are threatening freshwater aquatic ecosystems. Most of these are shallow ponds or slow-flowing streams or ditches dominated by submerged macrophytes, periphyton or phytoplankton. Regime shifts between the dominance of these primary producers can occur along a gradient of nutrient loading, possibly triggered by specific disturbances influencing their competitive interactions. However, phytoplankton dominance is less desirable due to lower biodiversity and poorer ecosystem function and services. In this study, we combined a microcosm experiment with a process-based model to test three hypotheses: 1) agricultural run-off (ARO), consisting of nitrate and a mixture of organic pesticides and copper, differentially affects primary producers and enhances the risk of regime shifts, 2) warming increases the risk of an ARO-induced regime shift to phytoplankton dominance and 3) custom-tailored process-based models support mechanistic understanding of experimental results through scenario comparison. Experimentally exposing primary producers to a gradient of nitrate and pesticides at 22°C and 26°C supported the first two hypotheses. ARO had direct negative effects on macrophytes, while phytoplankton gained from warming and indirect effects of ARO like a reduction in the competitive pressure exerted by other groups. We used the process-based model to test eight different scenarios. The best qualitative fit between modeled and observed responses was reached only when taking community adaptation and organism acclimation into account. Our results highlight the importance of considering such processes when attempting to predict the effects of multiple stressors on natural ecosystems.

Impacts of divalent cations (Mg2+ and Ca2+) on PFAS bioaccumulation in freshwater macroinvertebrates representing different foraging modes

Per- and polyfluoroalkyl substances (PFAS) have extensively contaminated freshwater aquatic ecosystems where they can be transported in water and partition to sediment and biota. In this paper, three freshwater benthic macroinvertebrates with different foraging modes were exposed to environmentally relevant concentrations of eight perfluoroalkyl carboxylates (PFCA), three perfluoroalkyl sulfonates (PFSA), and three fluorotelomer sulfonates (FTS) at varying divalent cation concentrations of magnesium (Mg2+) and calcium (Ca2+). Divalent cations can impact PFAS partitioning to solids, especially to sediments, at higher concentrations. Sediment dwelling worms (Lumbriculus variegatus), epibenthic grazing snails (Physella acuta), and sediment-dwelling filter-feeding bivalves (Elliptio complanata) were selected due to their unique foraging modes. Microcosms were composed of synthetic sediment, culture water, macroinvertebrates, and PFAS and consisted of a 28-day exposure period. L. variegatus had significantly higher PFAS bioaccumulation than P. acuta and E. complanata, likely due to higher levels of interactions with and ingestion of the contaminated sediment. “High Mg2+” (7.5 mM Mg2+) and “High Ca2+” (7.5 mM Ca2+) conditions generally had statistically higher bioaccumulation factors (BAF) than the “Reference Condition” (0.2 mM Ca2+ and 0.2 mM Mg2+) for PFAS with perfluorinated chain lengths greater than eight carbons. Long-chain PFAS dominated the PFAS profiles of the macroinvertebrates for all groups of compounds studied (PFCA, PFSA, and FTS). These results indicate that the study organism has the greatest impact on bioaccumulation, although divalent cation concentration had observable impacts between organisms depending on the environmental conditions. Elevated cation concentrations in the microcosms led to significantly greater bioaccumulation in the test organisms compared to the experimental reference conditions for long-chain PFAS.

Causes and Impact of Industrial Effluents on Receiving Water Bodies: A Review

Industrial development has begun to have a negative impact on the entire environment. The constant need and agreed of humans has resulted in the formation of massive polluting industries. Manufacturing, chemical and fertilizer industries are among those that are depleting the earth’s resources while also putting enormous strain on the environment and ecological system. Water pollution is well-known to be a growing problem of 21st century all over the earth. The planet’s natural diversity is affect seriously by any human activity. Rapid industrialization is an index of development of a nation, however; a rising in population growth alters it unfavorably. India, a developing nation has a challenge of maintaining a balance between these and the environment. In India, there has been a rapid growth in industrialization after freedom. The aims of this review paper represent the link between industrial effluents and define sources of water pollution present development in the research on the fresh water aquatic ecosystems.

Coarse woody habitat use by local fish species and structural integrity of enhancements over time in a shallow northern boreal lake assessed in a Bayesian modelling approach

Abstract The introduction of coarse woody habitat has been a widely adopted management practice for restoring and enhancing freshwater aquatic ecosystems. Although responses of aquatic fish and invertebrate communities have largely been documented for lotic systems, benefits for lentic ecosystems have been mostly unevaluated. We tested the responses of fish populations to coarse woody habitat structures through a Bayesian modelling approach in a northern boreal lake in Alberta, Canada by enhancing a stretch of littoral zone with low structural complexity through introduction of coarse wood bundles and whole tree structures. The study site was split into three treatments, a Spaced treatment (structures 30 m apart), a Clustered treatment (structures 15 m apart) and an unaltered area (Control). Catch per unit effort and catch per unit area data were collected over 2 years and posterior model predictions showed an increase in habitat use of the enhanced areas by spottail shiner—Notropis hudsonius; northern pike—Esox lucius; white sucker—Catostomus commersonii; brook stickleback—Culaea inconstans. No probable effect on overall fish condition, measured in Relative Weight, was linked to the enhancements. Across the 2‐year study, wood bundles degraded faster compared to the whole tree drops, coinciding with levelling off catch per unit effort and catch per unit area predictions near wood bundles, although catch predictions increased near the whole tree structures. Structural degradation set in as early as 1 week post‐construction for wood bundles and was mostly related to anchoring aspects. Results from our study provide evidence for the benefits provided by coarse woody habitat within northern boreal lake systems. They furthermore highlight the short‐lived nature of wood bundles built with biodegradable substances. Methodologically our results offer evidence on the feasibility and utility of predictive modelling frameworks in addressing pseudoreplication and providing informative value for ecological studies.

Multiple Introduction and High Genetic Diversity: Drivers for Successful Establishment of Invasive Peacock Bass (Cichla spp.) in Peninsular Malaysia

The introduction of invasive Cichla spp. was followed by the several reports regarding the decline of local freshwater native species in Malaysia. The purpose of this research was to generate information concerning the introduction history of Cichla spp. in Malaysia. Studies on genetic diversity and structure provides the essential baseline data for monitoring and conservation of invasive species. This will help to clearly understand the propagule pressure and genetic distribution of Cichla spp. in the invaded freshwaters of Malaysia. A total of 61 samples of Cichla spp. were collected from 9 sampling location in Malaysia for mitochondrial DNA (control region) analysis. Overall samples showed high genetic diversity (Hd, 0.6700; π, 0.0254) and yielded 9 haplotypes resulted from different Cichla spp. present. The maximum likelihood tree with strong bootstrap support revealed that Cichla spp. forms 3 clusters, and confirmed to be C. monocoulus, C. occelaris and C. temensis. Except for Malacca populations, other populations were largely dominated by either C. monocoulus or C. occelaris. The current study suggesting that more than one introduction event of invasive Cichla spp. occurred in Malaysia. HIGHLIGHTS One of the common problem in the conservation effort for Malaysia’s freshwater aquatic ecosystem is failure to understand the introduction events of invasive species (Cichla) Mitochondrial DNA analysis (control region) conducted in order to find the genetic diversity and genetic structure of invasive Cichla across freshwater habitats in Malaysia High genetic diversity was observed, suggesting multiple introduction occurance of invasive Cichla in the country GRAPHICAL ABSTRACT

Spatio-temporal variations of activity of nitrate-driven anaerobic oxidation of methane and community structure of Candidatus Methanoperedens-like archaea in sediment of Wuxijiang river

Nitrate-driven anaerobic oxidation of methane (AOM), catalyzing by Candidatus Methanoperedens-like archaea, is a new addition in the global CH4 cycle. This AOM process acts as a novel pathway for CH4 emission reduction in freshwater aquatic ecosystems; however, its quantitative importance and regulatory factors in riverine ecosystems are nearly unknown. Here, we examined the spatio-temporal changes of the communities of Methanoperedens-like archaea and nitrate-driven AOM activity in sediment of Wuxijiang River, a mountainous river in China. These archaeal community composition varied significantly among reaches (upper, middle, and lower reaches) and between seasons (winter and summer), but their mcrA gene diversity showed no significant spatial or temporal variations. The copy numbers of Methanoperedens-like archaeal mcrA genes were 1.32 × 105–2.47 × 107 copies g−1 (dry weight), and the activity of nitrate-driven AOM was 0.25–1.73 nmol CH4 g−1 (dry weight) d−1, which could potentially reduce 10.3% of CH4 emissions from rivers. Significant spatio-temporal variations of mcrA gene abundance and nitrate-driven AOM activity were found. Both the gene abundance and activity increased significantly from upper to lower reaches in both seasons, and were significantly higher in sediment collected in summer than in winter. In addition, the variations of Methanoperedens-like archaeal communities and nitrate-driven AOM activity were largely impacted by the sediment temperature, NH4+ and organic carbon contents. Taken together, both time and space scales need to be considered for better evaluating the quantitative importance of nitrate-driven AOM in reducing CH4 emissions from riverine ecosystems.

Fungi biodiversity in freshwater aquatic ecosystems of "La Izvor" park from Chisinau city

The fungal biodiversity of the La Izvor water basin was studied. The filamentous fungal strains were isolated from water, silt, and biofilm on specific agar media for fungal cultivation. As a result of research on cultural and morphological features, 18 genera of filamentous fungi Penicillium, Aspergillus, Trichoderma, Alternaria, Fusarium, Botrytis, Monilinia, Mucor, Rhizopus, Acremonium, Cladisporium, Trichocladium, Phoma, Chaetomium, Arthrinium, Ulocladium, Talaromyces, but also some strains that have not been identified, for which additional research is needed. The predominant genera found in the La Izvor water basin are Penicillium and Aspergillus, followed by Trichoderma and Alternata.

The effects of road salt (NaCl), predation, and competition on the growth and community interactions of spotted salamanders (Ambystoma maculatum) and wood frogs (Lithobates sylvaticus)

Road deicing salts are frequently used in northern regions of the world during the winter and early spring months. As a result, a significant portion of road runoff into surrounding aquatic habitats contains road deicing salts. Previous studies found road salt contaminations in vernal pools that pond-breeding amphibians commonly use, including spotted salamanders (Ambystoma maculatum) and wood frogs (Lithobates sylvaticus). Studies have examined the impact of road salt on both amphibian species, but to our knowledge no previous studies have examined how road salt impacts the interspecific competition between both amphibians. We hypothesized that road salt would negatively impact growth and survivorship of both amphibian species. During the spring and summer of 2017, we conducted an outdoor mesocosm experiment in which we created eight experimental conditions with three main factors: presence/absence of NaCl (1000 mg/L Cl−), presence/absence of interspecific competition between the two amphibian species (A. maculatum and L. sylvaticus), and presence/absence of predatory dragonfly larvae (Family Libellulidae). Our experiment revealed that salt delayed hatching and increased deformity in spotted salamander hatchlings. Additionally, salt reduced salamander survivorship by 62% and frog survivorship by 30%. Wood frog tadpoles and road salt interacted to diminish salamander survivorship a further 80% beyond salt alone, likely through an increase in interspecific competition. Road salt increased the larval period of salamanders and decreased the proportion metamorphosed by the end of the experiment. Dragonfly larvae reduced salamander survivorship by 35%, whereas they increased wood frog tadpole development rates. Dragonfly larvae and salt interacted to alter tadpole denticle size, with salt negating the impact of dragonfly larvae. Thus, we found that salt interfered with aquatic predatory chemical cues. Overall, the results of this study suggest that management strategies should be implemented in order to reduce the impact of road salts on freshwater aquatic ecosystems.

Molecular phylogenetic investigation of toads based on sequencing of the mitochondrial 16S ribosomal RNA gene

Amphibians inhabit a wide variety of habitats and environments, such as arboreal, terrestrial and freshwater aquatic ecosystems, and are considered among the vertebrate classes to exhibit one of the most diverse distributions. Their life histories, behaviour and diversity play vital roles in assessing environmental and evolutionary theories. The mitochondrial 16S rRNA gene sequence analysis has been widely used in molecular taxonomy and is frequently used in systematic analyses of families and genera. This study examines taxonomic relationships among 18 specimens of the Arabian toad (Sclerophrys arabica) and the Dhofar toad (Bufo dhufarensis) from Al Madinah Province, Saudi Arabia by estimating phylogenetic relationships using the mitochondrial 16S ribosomal RNA gene (16S rRNA). Results indicate the presence of four new lineages of toads among the samples in this study. The generated phylogenetic tree grouped all samples of Arabian toad in one clade, while the Dhofar toad samples were divided into three subclades. This is the first study to be reported the genetic diversity of Al Madinah Province toads.

Valuation of Key Freshwater Ecosystem Services: A Case Study in Yagirala Rainforest

Tropical lowland rainforests in Sri Lanka are subjected to degradation due mainly to conversion to other uses and population pressure. Valuation of ecosystem services has become important in terms of conservation of such landscapes. This study intends to estimate economic value of key freshwater aquatic ecosystem services associated with tributary ecosystem in the Yagirala Forest Reserve, a fragmented tropical lowland rainforest in south-west Sri Lanka. Surface water discharged from the tributary and the ornamental fish were identified as main provisioning services and recreation and education were identified as cultural services of the tributary. Physical measurements on freshwater resource and fish fauna were carried out at eleven sampling points along the selected tributary during the rainy season. Water flow was measured at the end point of the tributary, which connects to the main stream using flow rate measuring method. Economic value of water used for agriculture/industrial and potable/domestic use were estimated based on the tariff rates available. Ornamental fish fauna was counted using transects and valued using market prices related to export trade. Cultural services were valued based on visitor data maintained at the Research Centre at Yagirala. Economic value of water available for agricultural activities and industrial purposes were estimated as LKR 39 million and 3 million respectively. Value of water used for domestic purposes was LKR 9 million. Economic value of potential ornamental fish of the tributary was estimated as LKR 41 thousand for three species and considering sustainable extraction. Cultural services were estimated as LKR 14 thousand. The total value of the selected ecosystem services of the tributary for 3 months was estimated as LKR 51 million. The study highlights the importance of combining physical data in the economic valuation. The estimated values could provide justification for the protection of these ecosystems and investments for further value additions.
 Keywords: Ecosystem services, Yagirala forest reserve, Economic value, Fresh water

Hardness-Dependent Water Quality Criteria for Protection of Freshwater Aquatic Organisms for Silver in China.

Silver is toxic to freshwater aquatic organisms and aquatic ecosystems, and it is necessary to develop regional water quality criteria (WQC) for silver to protect the freshwater aquatic organisms in China. The toxicity database of silver for freshwater aquatic organisms involved 121 acute toxicity values for 35 species (6 phyla and 27 families) and 15 chronic toxicity values for 4 species (2 phyla and 4 families). Teleost fish showed the most sensitivity to silver after both short-term and long-term exposure. Significant correlations between the natural logarithms of hardness and the natural logarithms of acute silver toxicity were found for Daphnia magna, Oncorhynchus mykiss, and Pimephales promelas. The criterion maximum concentration (CMC) was calculated by the species sensitivity distribution method with sigmoid as the best fitting model (Adj R2 0.9797), and the criterion continuous concentration (CCC) was obtained by the acute-to-chronic ratio method. The CMC and CCC of silver were , and respectively, in China, with water hardness (, mg/L) as an independent variable. This research can provide a basis and reference for the management of silver to protect freshwater aquatic organisms in China.

Short-term seawater inundation induces metal mobilisation in freshwater and acid sulfate soil environments

Climate change is leading to global sea level rise. Storm surges and higher tides will generate short-term ‘pulses’ of seawater into freshwater systems, often for the first time in over 3000 years. The effect of increased seawater inundation upon soil geochemistry is poorly understood. We identified 12 sites in South Australia which are predicted to be inundated by seawater storm surges in the next 20 years. Within these 12 sites are three distinct environments; fresh water streams and lakes, hypersaline saltmarsh and mangroves, and acid sulfate soils. Soils were inundated with seawater under laboratory conditions to replicate a short-term (two weeks) inundation by a storm surge. Lowering of redox potential and dissolution of high concentrations of reactive Mn and Fe in freshwater environments lead to the release of dissolved Fe and Mn in the soils from freshwater environments. Soils also released As, Cu, Ni, Cd and Co, while Zn and Pb were less mobilised. Concentrations of metals released exceeded water quality guidelines to protect freshwater aquatic ecosystems in most cases. By comparison, hypersaline soils only released minor amounts of Mn, Fe, Cd and Ni, and only in some of the soils. The moderately acidic acid sulfate soil (pH 5.41) reductively dissolved Mn and Fe releasing significant amount of Fe and Mn as well as As, Cu, Ni, Cd and Co, whereas almost all metal species decreased in the porewaters of the strongly acidic acid sulfate soil (pH 2.77). The response to short-term seawater inundation in acid sulfate soils was dependent upon the baseline soil acidification status. This study highlights the need for further research on seawater inundation of coastal soils as sea levels rise and storm surges penetrate further inland.

Assessing Hydrological Alteration Caused by Climate Change and Reservoir Operations in the San Joaquin River Basin, California

Freshwater aquatic ecosystems are highly sensitive to flow regime alteration caused by anthropogenic activities, including river regulation and atmospheric warming-induced climate change. Either climate change or reservoir operations are among the main drivers of changes in the flow regime of rivers globally. Using modeled unregulated and simulated regulated streamflow under historical and future climate scenarios, this study evaluated potential changes to the flow regime due to climate change and reservoir operations for the major tributaries of the San Joaquin River Basin, California United States. We selected a set of Indicators of Hydrologic Alteration (IHA) to evaluate historical and projected future trends of streamflow dynamics: rise and fall rates, durations and counts of low and high pulses, and the magnitude of extremes. Results show that most indicators have pronounced departures from baseline conditions under anticipated future climate conditions given existing reservoir operations. For example, the high pulse count decreases during regulated flow conditions compared to increased frequency under unregulated flow conditions. Finally, we observed a higher degree of flow regime alteration due to reservoir operations than climate change. The degree of alteration ranges from 1.0 to 9.0% across the basin among all future climate scenarios, while reservoir operations alter the flow regime with a degree of alteration from 8.0 to 25%. This study extends multi-dimensional hydrologic alteration analysis to inform climate adaptation strategies in managed river systems.

Make visible the invisible: Optimized development of an environmental DNA metabarcoding tool for the characterization of trematode parasitic communities

AbstractThe world's parasitic and mutualistic biodiversity is undergoing major upheavals related to modifications in host community structures, changes in interactions between species, and through coextinction events. Trematodes are an important component of this invisible biodiversity, in terms of species richness, but also because of their role in ecosystems functioning and in the emergence of associated diseases. Taken together, these elements point to the need for a better assessment and understanding of the structure and dynamics of trematode diversity. In this context, our aim was to develop an optimized eDNA‐based metabarcoding approach to detect trematodes and characterize their communities, most of which associated with aquatic environments. The efficiency of this newly developed tool was first assessed by exhaustive in‐silico and in‐vitro validation steps. We next assessed the ability of our eDNA‐based approach to reconstruct trematode communities compared to a classical trematode monitoring method over four freshwater aquatic ecosystems. Our eDNA‐based monitoring tool displayed a high amplification enrichment of trematode DNA, a 100% detection score for tracking back an in‐vitro mock community composed of 28 trematode species, and high genetic resolution, which makes it relevant to discriminate between even phylogenetically close trematode species. Over the four natural ecosystems screened in natura, 33 OTUs were generated from the eDNA‐based approach, from which 11 trematode species were identified. In comparison, we identified five trematode species using the classical monitoring method, three of which were also detected by the eDNA‐based approach. We believe that this new eDNA‐based metabarcoding tool will open new perspectives for fundamental and applied research in community ecology, conservation, and health survey.

Detection of the maximum resistance to the herbicides diuron and glyphosate, and evaluation of its phenotypic cost, in freshwater phytoplankton.

One of the most important anthropogenic impacts on freshwater aquatic ecosystems close to intensive agriculture areas is the cumulative increase in herbicide concentrations. The threat is especially relevant for phytoplankton organisms because they have the same physiological targets as the plants for which herbicides have been designed. This led us to explore the evolutionary response of three phytoplanktonic species to increasing concentrations of two herbicides and its consequences in terms of growth and photosynthesis performance. Specifically, we used an experimental ratchet protocol to investigate the differential evolution and the limit of resistance of a cyanobacterium (Microcystis aeruginosa) and two chlorophyceans (Chlamydomonas reinhardtii and Dictyosphaerium chlorelloides) to two herbicides in worldwide use: glyphosate and diuron. Initially, the growth rate of M. aeruginosa and D. chlorelloides was completely inhibited when they were exposed to a dose of 0.23 ppm diuron or 40 ppm glyphosate, whereas a higher concentration of both herbicides (0.46 ppm diuron or 90 ppm glyphosate) was necessary to abolish C. reinhardtii growth. However, after running a ratchet protocol, the resistance of the three species to both herbicides increased by an adaptation process. M. aeruginosa and D. chlorelloides were able to grow at 1.84 ppm diuron and 80 ppm glyphosate and C. reinhardtii proliferated at twice these concentrations. Herbicide-resistant strains showed lower growth rates than their wild-type counterparts in the absence of herbicides, as well as changes on morphology and differences on photosynthetic pigment content. Besides, herbicide-resistant cells generally showed a lower photosynthetic performance than wild-type strains in the three species. These results indicate that the introduction of both herbicides in freshwater ecosystems could produce a diminution of primary production due to the selection of herbicide-resistant mutants, that would exhibit lower photosynthetic performance than wild-type populations.

Impact of Tourist Behavior on the Discharge of Sunscreen Contamination in Aquatic Parks, Sinkholes, and Beaches of the Mexican Caribbean

The Mexican Caribbean is part of the Mesoamerican Barrier Reef System, considered the second largest reef system globally. This system, as well as inland aquatic ecosystems, are at risk of contamination due to the intensive use of sunscreen by the tourists who visit the Riviera Maya each year. At present, the regulation and management of sunscreens are inconsistent, with most policies and legislation focused on the protected marine areas with little current focus on inland aquatic ecosystems. An estimated 229.76 tons of sunscreen are used annually, with residues putting the health of the marine and freshwater aquatic ecosystems and residents at risk. Groundwater is used recreationally (e.g., tourists swimming in sinkholes or cenotes) and as household drinking water. To understand the environmental impacts of sunscreen use and the management implications, a mixed-methods study was carried out, combining survey and interview data on how tourists use sunscreen and their perceptions of discharge of sunscreens into the water, with analysis of regional, national and international policies and legislation. Our findings of touristic behaviors, gaps in current legislation, and the pollution implications of different sunscreen types provide useful information for future decision-making and the creation of stronger environmental regulations.