Irradiance is regarded as a key factor determining the maximum colonization depth (Z 0) of submerged macrophytes. However, the relevance of acclimation capabilities to spectral composition under such low-light conditions remains poorly understood. To address this gap, the present study tested whether spectral composition, in addition to light intensity, affects physiological performance in Chara globularis Thuill. and Chara hispida L., two charophyte species differing in depth distribution. Individuals were cultivated for 5 weeks under three low irradiances below the photosynthesis light saturation level (6, 12, and 24 & micro;mol photons m-2s-1); each irradiance given at four different spectral compositions (full spectrum and blue-, green-, or yellow-wavelength dominated). Daily growth rate, biomass-related parameters, pigment composition (chlorophylls and carotenoids), and photosynthetic light-response parameters were quantified. Across treatments, growth declined with decreasing irradiance in both species, confirming light quantity as the primary constraint, whereas spectral composition had no significant effect on growth or biomass-related parameters. Pigment composition differed consistently between species, with C. globularis exhibiting higher chlorophyll a and carotenoid concentrations across all treatments. Spectral effects on pigment composition were weak, restricted to the highest irradiance, and observed exclusively in C. globularis. Despite these differences, photosynthetic parameters remained largely stable across treatments. The initial slope of the photosynthesis-irradiance curve (alpha) showed no interspecific differences, while the light saturation point (Ik) was consistently higher in C. globularis than in C. hispida. Overall, physiological responses were dominated by light intensity and species identity, while spectral effects were minor and conditional. These findings indicate that charophytes, owing to their comparatively low organizational complexity and maintenance demands, do not appear to gain a functional advantage from strong spectral acclimation under low irradiance. Instead, physiological stability emerges as the prevailing strategy, with the greater plasticity of C. globularis potentially facilitating persistence near the lower macrophyte limit.
ABSTRACT Hydrilla ( Hydrilla verticillata ) is an invasive submerged macrophyte that can dominate freshwater plant communities and complicate restoration efforts. Management options may be limited in systems containing sensitive native species, making competitive suppression by native macrophytes a potentially useful complementary strategy. We evaluated interactions between H. verticillata and two widespread native species, Heteranthera dubia and Potamogeton illinoensis , in greenhouse mesocosms using additive‐density and equal‐ratio experiments. Apical tips of the three species were planted into sediment‐filled 19 L mesocosms and grown under winter, summer, or spring greenhouse conditions. In additive‐density experiments, hydrilla root and shoot biomass and relative growth rate generally declined as the initial density of hydrilla decreased relative to the native species. Suppression of hydrilla growth was more evident in the winter experiment, although hydrilla tuber production was also greater during winter. In equal‐ratio experiments, H . dubia showed growth rates comparable to hydrilla, whereas P . illinoensis allocated proportionally more biomass to roots and had lower relative growth rates. Overall, the results suggest that dense plantings of native submerged macrophytes may reduce hydrilla growth under controlled conditions, particularly when combined with prior hydrilla removal. Field studies are needed to determine whether winter restoration plantings can suppress hydrilla regrowth from established tuber banks.
Tropical lotic ecosystems are important sources of greenhouse gas emissions, yet the magnitude and variability of such emissions remain poorly constrained. Here, we quantified spatial and short-term temporal variability of carbon dioxide (CO2) and methane (CH4) fluxes across tropical riverine systems spanning a gradient of human impact, while identifying potential biogeochemical and physical drivers of these fluxes. All systems acted as net sources of both gases. Fluxes varied widely among sites [49-1,701 (CO2) and 0.6-85.9 mmol m-2 d-1 (CH4)], while short-term temporal variability was limited, likely due to relatively uniform climatic conditions during the study period. In particular, treated wastewater inputs, not properly captured by conventional land use metrics, contributed to elevated emissions. CO2 emissions were driven by ecosystem respiration, highlighting the role of net heterotrophy, with additional contributions from sediment inorganic carbon and methane fluxes. By contrast, CH4 emissions were more closely linked to pH and gas exchange velocity, reflecting the combined influence of sediment production and physical transport processes. These findings advance understanding of the controls on carbon emissions in tropical riverine systems, emphasizing the role of wastewater inputs and metabolic processes in shaping and scaling emissions. They also provide a framework for improving the representation of tropical river networks in regional and global budgets and for guiding strategies to mitigate emissions in impacted freshwater systems.
Urbanization modifies stream ecosystems through changes in land use and water quality, with particularly understudied effects in tropical regions. This study evaluates how the conservation status (reference, restored, and impacted) influences nutrient enrichment and organic matter decomposition-key indicators of ecosystem function-across five Neotropical streams in southeastern Brazil. We found large differences in nutrient availability, with impacted streams exhibiting 22.7-fold higher ammonium (1259.5 vs. 43.4 mu g L-1) and 7.3-fold higher total dissolved phosphorus (425.9 vs. 55.7 mu g L-1) concentrations than the reference stream. Functional assessments using cotton strip assays showed average decomposition coefficients in impacted streams (0.158 day(-1)) exceeded reference conditions (0.034 day(-1)) by 4.6-fold, with restored streams displaying intermediate values (0.093 day(-1)). Despite the limited number of streams, those with > 50% urban cover showed markedly higher decomposition rates and nutrient concentrations compared to less urbanized sites. Restored streams achieved near-reference habitat quality (Rapid Habitat Diversity Assessment RHDA scores: 63-64 vs. 65) but maintained intermediate nutrient levels and decomposition rates, indicating persistent watershed-scale influences. The studied Neotropical streams respond nonlinearly to land use intensity, with watershed management being equally critical as reach-scale restoration for maintaining ecosystem processes. These findings provide empirical support for implementing integrated urban planning approaches that address both local habitat quality and landscape-scale connectivity in Neotropical regions undergoing rapid development.
The European perch Perca fluviatilis and pikeperch Sander lucioperca can co-occur, potentially competing for food resources. However, few studies have addressed the potential feeding competition between these species. We used carbon and nitrogen stable isotope analysis to assess the potential trophic competition between these species in two Turkish ecosystems, a natural lake where both species are native (Lake Gala), and a reservoir where both have been introduced (S & imath;& gbreve;& imath;rc & imath;). We found a significant positive relationship for S. lucioperca between delta 13C and size in Lake Gala, suggesting higher consumption of benthic/littoral prey in bigger individuals, but not in the S & imath;& gbreve;& imath;rc & imath; reservoir nor for P. fluviatilis. A positive relationship between delta 15N and size was also found in the S & imath;& gbreve;& imath;rc & imath; reservoir for both species, indicating that trophic position increased with age, while in Lake Gala P. fluviatilis showed a negative relationship, possibly due to consumption of abundant prey from lower trophic levels. In Lake Gala, the isotopic niches overlapped and were larger in S. lucioperca, while in the S & imath;& gbreve;& imath;rc & imath; reservoir they were segregated and larger in P. fluviatilis. Our results show that the trophic niches of P. fluvatilis and S. lucioperca can overlap, leading to potential interspecific competition.
Antibiotic pollution and rising water temperature collectively pose serious challenges to wetlands. However, how invasive plants respond to such combined stressors remains poorly understood. This study examined the growth and physiological responses of Alternanthera philoxeroides, a widespread invasive plant in China, to tetracycline hydrochloride (TC) at four concentrations (0, 2, 20, and 200 mg L-1) under two water temperature conditions (20 degrees C and 35 degrees C). The results indicated that high TC concentrations (20 and 200 mg L-1) significantly inhibited plant growth and reduced chlorophyll content, while increasing oxidative stress as reflected by increased malondialdehyde (MDA) levels. In contrast, elevated temperature (35 degrees C) enhanced growth performance and reduced oxidative damage. Notably, elevated water temperature reduced the inhibitory effects of TC on A. philoxeroides. These findings suggest that warming may facilitate the invasion of A. philoxeroides in antibiotic-polluted wetlands. This study provides a critical perspective for predicting and managing plant invasions under global change and emphasizes the importance of considering interactive stressors in ecological risk assessment.
Changes in the landscape surrounding aquatic systems can alter the physical and chemical properties of water, leading to shifts in species composition and ecosystem services. Aquatic macrophytes are among the biological groups affected by local and landscape changes. In this study, we investigate the species richness and beta diversity of macrophytes in streams and ponds under different land uses in Maraj & oacute; Island, Par & aacute;, Brazil. Sampling was conducted in 36 ponds and 26 streams in October 2022 and June 2023. Limnological variables were measured at each sampling site using a multiparameter probe, and land use was determined using satellite images. We recorded 120 species belonging to 38 families. In streams, 89 species were recorded (74% of the total species sampled), and in the lakes, 85 species were recorded (71%). There was no significant difference in macrophyte species richness between ponds and streams; however, macrophyte species composition differed between these systems, with exclusive species in each system. Dissolved oxygen, pH, and conductivity showed substantial variation among sites but were not associated with macrophyte composition or richness; only temperature was associated with species composition. Our findings highlight the great diversity of macrophyte species and the importance of conserving different water bodies to maintain biodiversity. Future studies should incorporate flood pulse dynamics and connectivity to enhance understanding of the factors shaping macrophyte species and to inform the development of effective conservation strategies.
Lentic ecosystems are vulnerable to contamination by trace elements, which can accumulate and pose risks to aquatic life and human health. In a large, developing country such as Brazil, marked by vast geographic, environmental, and socioeconomic diversity, it is crucial to understand how these factors shape research on this group of contaminants. Here, we conducted a systematic review of 65 studies published between 1980 and 2023 on Brazilian urban lentic systems, retrieved from Web of Science and Scopus databases. Research output increased sharply after 2011, with 73% of studies published in the last decade. Geographically, half of the studies were conducted in the Southeast region, especially in large urban areas within the Atlantic Forest biome, while the North and Central-West regions together accounted for less than 15%. Industrial zones were the most frequently studied land use, and sediment was the most common matrix. Copper, lead, chromium, zinc, and nickel were the most frequently reported trace elements, whereas toxic elements such as arsenic and mercury were infrequently studied. This review provides a quantitative synthesis of research on trace element contamination in Brazilian urban lentic ecosystems. The findings highlight critical gaps, including the underrepresentation of North and Central-West regions, the limited use of biological matrices, and the neglect of mercury and arsenic, despite their ecological and toxicological relevance. Addressing these gaps is essential to improve ecotoxicological risk assessments, strengthen the integration between environmental monitoring and public health, and guide evidence-based policies for pollution control in vulnerable aquatic systems.
Barrier removal is a common stream restoration practice aimed at restoring longitudinal connectivity, yet its effects on biofilm structure and function, through alteration of near-bed hydrodynamics, remain unclear. Using a space-for-time substitution approach, we assessed how the presence and removal of a low-head dam affect biofilm structure and function. We quantified near-bed hydrodynamics and biofilm structure and function across three reaches in a temperate stream: one impacted by a low-head dam, one in reference condition, and one restored where a low-head dam was removed over a decade ago. In each reach, we quantified near-bed hydrodynamics, and biofilm structural (microbial alpha-diversity, biomass, Chlorophyll a, bacterial abundance) and functional parameters (nitrate (N-NO3 -) and dissolved organic carbon (DOC) uptake), along with microbial community composition. We found that the low-head dam altered near-bed hydrodynamics, as well as biofilm structure and function. Restoration successfully reestablished near-bed hydrodynamics similar to those observed at the reference site, which coincided with the recovery of impaired biofilm structural parameters. However, biofilm DOC uptake remained significantly lower in the restored reach compared to the control, indicating a persistent impairment despite restoration. Presence-absence patterns of specific taxa explained a small (15%), but consistent, fraction of the variance in DOC uptake, suggesting that the occurrence of particular microbial groups may be linked to the incomplete DOC uptake recovery. Our results suggest that dam-induced alterations in near-bed hydrodynamics largely explain the structural changes observed in biofilms. Restoring near-bed hydrodynamics supports the recovery of biofilm structure, but functional recovery remains incomplete. Therefore, hydromorphological restoration alone, while necessary, is unlikely to fully restore ecosystem functioning. Our study highlights the need to integrate biological and biogeochemical targets when assessing restoration success.
Fatty acids (FAs) are biochemical molecules with vital structural and metabolic functions in all living organisms. Over the last decades, FA analysis in ecological studies has garnered significant attention due to its diverse applicability, such as taxonomic support for species identification, investigations on trophic interactions, and environmental monitoring of aquatic ecosystems. Here, we reviewed the usage of FAs in ecological studies analyzing environmental changes in freshwater systems by applying a Topic Modelling Analysis to a total of 119 papers previously extracted by a systematic search in Web of Science, followed by ordination analyses. The analysis revealed topic similarities among publications and assessed topic popularity—hot, neutral, and cold topics—based on their prevalence over the years. Topics such as “Seasonality and land-use effects”, “Environmental/temperature stress in biofilms”, “Highly Unsaturated Fatty Acids (HUFAs) in plankton”, and “FAs in fish tissues” were classified as hot topics, with the first two experiencing an increasing trend since 2015. Topics classified as neutral included “Total lipids in invertebrates” and “FAs in river organic matter”. Cold topics included “Food quality for Daphnia”, “FA markers in sediments”, and “Trophic transfer in reservoirs/fish farms”. Topic modeling revealed 12 distinct research topics, indicating that the use of FAs as markers for environmental changes in freshwater ecosystems is a diverse and multifaceted field. This research spans various communities, ecosystem compartments, and types of environmental change, with most topics showing a stable publication trend over time. To enhance future research in this area, it is recommended that FA fingerprinting be further developed to target specific impacts and communities, particularly in the context of multiple stressors on freshwater ecosystems.
About 50 years after the first publications on the existence of alternative stable states (ASS) in ecosystems, the concept has become widely accepted. However, there is still a diverse terminology and no consensus about which criteria must be fulfilled, and what kind of investigations or data are suitable for proving the existence of ASS. Most empirical observations report sudden shifts between stable states or equilibria. However, they usually fail to demonstrate that forward and backward shifts occur at different threshold levels of a gradually changing external driver. This is a key requirement for hysteresis and ecosystem states to be considered “alternative.” We suggest that evidence for ASS should be based on field observations or experimental field investigations, ideally combined with modeling and laboratory experiments on specific stabilizing mechanisms, and fulfill all four of the criteria: (1) sudden shifts between states, (2) the occurrence of a hysteresis, (3) sufficient spatial and temporal scales, and (4) the presence of efficient feedback mechanisms stabilizing each state. In marine and brackish ecosystems, a number of investigations, especially from shallow environments, seem to fulfill these criteria, but few come from large and deep bodies of water. Several studies have assumed the presence of ASS in shallow brackish lagoons along the Baltic Sea. Strong feedback is exhibited in the turbid state when it is dominated by cyanobacteria, while feedback mechanisms in the macrophyte-dominated state require further investigation. For successful management, understanding ASS and, especially, the most efficient stabilizing feedback mechanisms is essential to reach and maintain a good ecosystem status.
Large bloom-forming dinoflagellates can alter aquatic biodiversity and impact human use, posing conservation challenges. We used the maximum entropy (MaxEnt) model to predict the potential distribution of two Ceratium congeners, C. hirundinella and C. furcoides and reviewed known temperature tolerances across their introduced ranges in the American continent. MaxEnt models performed well, predicting 59% global environmental suitability for C. furcoides and 19% for C. hirundinella, with a 22% overlap in suitable areas. Reported co-occurrences in the literature occurred within these predicted overlap areas. Model response curves reflected patterns consistent with the observed water temperature distributions, with C. furcoides associated with higher mean temperatures than C. hirundinella. Future research should integrate bloom event records with quantitative measures of cell density and biomass, as the correspondence between high-suitability areas and reported impacts indicates that such data could enhance risk assessments and support more effective mitigation of the ecological impacts caused by the continuing spread of Ceratium.
The Pantanal, one of the largest wetlands on Earth, stores substantial carbon in its diverse ecosystems but faces increasing threats, such as fires, poor soil management, deforestation, and climate change impacts that may elevate CH4 emissions. Given the importance of this ecosystem, we investigated methane (CH4) emissions from the limnetic zone and marginal soils in a drying lagoon in the Pantanal during a drought period unprecedented in over 75 years. To this end, CH4 flux measurements were conducted along a transect with three replicates in each of the evaluated compartments, with four samples collected per day during both a dry-season and a wet-season campaign (2019-2020). The highest emissions occurred during the drying event, primarily in the aquatic compartment (7.43 mg +/- 5.51 CH4 m(-)(2) day(-)(1), mean +/- SD, n = 20), representing a 56-fold increase in CH4 emissions compared to the wet season, and along the margins (3.43 +/- 3.55 mg CH4 m(-)(2) day(-)(1), n = 12). This indicates that the lowering of the water column and exposed sediments became a significant source of CH4 emissions. Our results suggest that these environments can become large CH4 emitters during drying events. Accordingly, current CH4 emission models underestimate their contribution due to neglecting sediment exposure effects. With the expected increase in drying events in the Pantanal, CH4 emissions will likely rise in the coming years, exacerbating global warming and intensifying climate change.
Freshwater ecosystems are highly susceptible to degradation, underscoring the importance of assessing their health using ecological indicators. In this study, we developed an Ecopath mass-balance model for Lake Tinshu Abaya, Ethiopia, and analyzed its trophic structure and energy flows. The model integrated seven functional groups using data on fish catch, diet composition, and plankton biomass collected from March to August 2022. The seven functional groups were detritus, phytoplankton, herbivorous zooplankton, carnivorous zooplankton, zoobenthos, Nile Tilapia (Oreochromis niloticus), and birds. Four trophic levels were determined, ranging from 1.00 for primary producers and detritus to 3.56 for birds of prey. The calculated values for the EE of the primary producers (phytoplankton: 0.87; detritus: 0.75) indicated that they were highly exploited compared to the secondary producers, the herbivorous zooplankton (0.40), the carnivorous zooplankton (0.065), and the zoobenthos (0.60). The computed primary production to total respiration (P/R) ratio of 1.19 suggested that the ecosystem is in a developing, net autotrophic state. The ecosystem exhibited a high degree of internal recycling (Finn's Cycling Index = 15.2%), reflecting efficient energy and nutrient utilization. The trophic connectivity index of 0.56 suggested a moderately interconnected food web. Collectively, these metrics indicate that Lake Tinshu Abaya is a developing ecosystem in a transitional stage, not yet having reached full ecological maturity.
The abundance and vertical distribution of Dreissena polymorpha (zebra mussel), Dreissena rostriformis bugensis (quagga mussel), and Corbicula fluminea (Asian clam) at two sites characterized by different dominant sediment types, and the fouling rate of Corbicula by dreissenids were studied. Sediment samples were taken, using a sediment grab (base area 22 x 25 cm = 550 cm2), at depths of 3, 6, 10, 15, 20, 50, and 100 m. The abundance of Corbicula was significantly higher at the sandy substrate site (Schussen Estuary) than at the site where coarse, gravelly substrate predominated (Nonnenhorn), whereas no difference in the abundance of quagga mussels was observed between the two sites. No living zebra mussels were found at either station. However, the quantification of dead zebra mussel, that is, their shells, revealed a much higher former abundance at Nonnenhorn than at the Schussen Estuary. Depth distribution revealed that Corbicula and quagga vertical distributions overlapped at the Schussen Estuary. Fouling rates on Corbicula were low when all individuals were considered: only 44 (5%) of the overall 871 living Corbicula individuals examined were fouled by quagga mussels. However, Corbicula larger than 1 cm showed a considerably higher fouling rate of 31%. Comparison of Corbicula abundances in the years 2016, 2021, and 2023 indicated that no overall decrease in abundance had occurred but a decrease of the proportion of large individuals relative to small ones had. Consequently, we recommend further investigations on the topic of Corbicula fouling by quagga mussels.
Lake Nakuru, historically a hypersaline lake in Kenya's Rift Valley, has undergone a significant ecological transformation due to a sustained saline-freshwater inversion driven by increased rainfall, catchment degradation, and anthropogenic inputs. This study provides a spatially resolved assessment of the lake's current physico-chemical status, biological structure, and socioeconomic dynamics. Results show a dramatic decline in salinity from historical levels of 20-40 to 2.58-2.6 g/kg, weakening the lake's buffering capacity and altering nutrient stoichiometry. Molar TN/TP ratios across all sites were exceptionally low (0.09-0.19), indicating persistent nitrogen limitation and conditions conducive to cyanobacterial dominance. Microcystis comprised 27.58% +/- 3.78% of the mean dietary contribution of Oreochromis niloticus, whose proliferation reflects a major shift in the lake's food web. Flamingo populations have declined, likely due to the collapse of their specialized food base. Microbial contamination was highest at river inflow sites. Further, we found elevated concentrations of arsenic and lead in fish tissue, raising critical public health concerns. The emergence of an informal tilapia fishery, driven by ecological changes and declining tourism, has introduced new economic opportunities but also sparked conflict due to its illegality within the protected national park. Vulnerable groups, particularly women, face heightened exposure to both economic instability and health risks. The findings indicate that Lake Nakuru has moved beyond early pollution symptoms into a phase of advanced ecological disruption, underscoring the need for urgent, multisectoral interventions.
Forestry plantations occur across the globe, and they are important in many tropical countries for timber supply. Plantations of non-native species, such as those of Eucalyptus species, may greatly affect the functioning of detritus-based ecosystems. However, despite eucalyptus plantations covering about 20 million hectares in tropical and subtropical regions (from a total of about 25 million hectares globally), there is scarce information about their effects on forest stream functioning. Our aim was to assess the effects of catchment-scale eucalyptus plantations (with native riparian buffers) on the functioning of tropical streams in the Cerrado biome. For that, three streams in catchments with eucalyptus plantations (eucalyptus streams) and three streams in catchments with native vegetation (native streams) were compared regarding water characteristics, litter inputs (vertical and lateral), decomposition of leaf litter (from a common native species, an eucalyptus species used in plantations, and a palatable exotic species) and litter-associated aquatic communities. We hypothesized that catchment-scale Eucalyptus plantations negatively affect stream characteristics (reduced water flow, heightened water acidity), litter inputs, aquatic communities, and litter decomposition in streams because dense, even-aged monocultures of eucalyptus trees have higher water consumption rates and produce recalcitrant litter. We also hypothesized that the effects of plantations would be stronger on shredders, as they are directly influenced by changes in litter input compared to other functional feeding groups. Finally, we hypothesized that plantation impacts on leaf litter decomposition would be stronger for palatable leaf litter, where invertebrate shredders play a major role, than for more recalcitrant and less palatable leaf litter. We found lower dissolved oxygen concentrations, lateral litter inputs, and litter decomposition in eucalyptus streams than in native streams. Conversely, fungal biomass on decomposing litter did not differ between eucalyptus streams and native streams. Eucalyptus plantations reduced overall invertebrate densities but did not affect shredder densities. Our study shows that catchment-scale eucalyptus plantations can change water characteristics and litter inputs to streams, thus slowing down litter decomposition in tropical streams, even when a native buffer is present. Increasing the width of the native buffer vegetation may contribute to increasing its protective role.
Preservation of urban aquatic ecosystems is of primary importance for human well-being, biodiversity protection and the future of society. Lake-groundwater-river interactions within urban floodplains harbour intrinsic fragility, yet remain largely understudied. Appropriate environmental management can help assure the conservation of these sites through strategies that are based on physical, chemical and isotope constraints. Here we present the example of the Groundwater and Lakes Urban Observatory (GLUO) in Magdeburg, Germany, where monitoring has been carried out since 2022. Our database for the year 2023 includes data from the Elbe River, two lakes named Lake Salbker South and Lake Salbker North, and two groundwater wells. Major ion patterns point to the Elbe River and Lake Salbker South as the end-members for water compositions within the system, although contributions from the former appear less significant. Stiff plots suggest the existence of a more saline end-member that may receive inputs from the Zechstein Formation and drives the geochemistry of Lake Salbker South. Dissolved oxygen (DO) concentrations in Lake Salbker South during stratification show a marked depletion in the hypolimnion with values down to 1.8 mg L-1 that we attribute to mineralization of organic matter as well as oxidation of sulphur compounds. This feature acknowledges Lake Salbker South as a natural hydrogen sulphide (H2S) reactor. Water stable isotope compositions (delta 2HH2O and delta 18OH2O) of the water bodies within the GLUO outline a trend that is compatible with moderate evaporation. We discuss that dissolution of saline deposits may also play a role. These findings emphasize the need to implement the study of lake-groundwater-river interactions within floodplains, especially when hypertrophic or sulphur-rich water bodies are involved. Due to the inherent vulnerability and potential hazards associated to these environments, we stress the importance of establishing a multidisciplinary monitoring framework to evaluate their geochemical fluxes and ecological integrity.
Understanding the trophic ecology and nutrient dynamics of freshwater invertebrates is crucial for evaluating the function and resilience of ecosystems. Although bulk stable isotope analysis is widely used to investigate food web structures, it lacks the resolution required to differentiate between carbon and nitrogen sources at a molecular level. Compound-specific isotope analysis (CSIA) of amino acids (AAs) offers a more detailed approach; however, its application in freshwater ecosystems, particularly across spatial and temporal gradients, remains limited. This study addresses this issue by applying AA-specific delta 15N and delta 13C analysis to the key detritivore Gammarus spp. across the North Rhine-Westphalia catchment in Germany over 4 years (2016, 2018, 2020, and 2022). Significant spatial variation in delta 13C values was observed, while temporal trends were less pronounced. Nonessential AAs exhibited higher delta 13C values than essential AAs, with glycine being the most enriched in 13C and lysine and phenylalanine the most depleted. Principal component analysis (PCA) of delta 13C values revealed variability in carbon sourcing, reflecting shifts between primary producers, microbial inputs, and detrital material. Regarding delta 15N, trophic AAs such as leucine and glutamic acid were enriched, whereas source AAs such as phenylalanine were depleted, confirming their roles in nitrogen metabolism. PCA of delta 15N values revealed that some sites maintained stable nitrogen inputs from autotrophic sources, while others showed increasing contributions from microbial or detrital nitrogen over time. Trophic position (TP) estimates for Gammarus spp. were consistent across sites and years, ranging from 1.1 to 1.5 using the TPGlu-Phe method and from 1.4 to 1.8 using the TP5AA method. This confirms their role as primary consumers. These findings emphasize the ecological importance of Gammarus spp. in nutrient cycling and demonstrate the effectiveness of CSIA-AA in unraveling complex trophic interactions and food web dynamics.
This study analysed how macroinvertebrate communities in Lake Kivu responded to Nile tilapia cage farming. Macroinvertebrates were collected at two sampling stations impacted by fish farms and a control station without fish farming, and physicochemical variables were measured in situ. Water samples were analysed in the laboratory for nutrients and chlorophyll-a. Only turbidity, water transparency, dissolved oxygen, and phosphate significantly differed between the three stations. Three macroinvertebrate phyla (Arthropoda, Mollusca, and Annelida), nine orders (Gastropoda, Diptera, Decapoda, Annelida, Odonata, Ephemeroptera, Coleoptera, Heteroptera, and Hemiptera), and 37 families were identified. Three groups, Diptera, Gastropoda, and Odonata, were abundant and dominated both cage and control stations. Predators, collector-gatherers, and scavengers were more dominant than scrapers and shredders. The composition of macroinvertebrate communities significantly differed between the three stations, but not between the fish cage and control stations. Moreover, there were no significant seasonal differences in community composition. Accordingly, cage farming does not yet seem to pose a threat to Lake Kivu's ecological condition. Nonetheless, we recommend frequent monitoring of water and sediment quality to detect early signals and avoid fish farms impacting the ecosystem health of the lake.
