Water Chemistry Variables Research Articles

Co-occurrence, ecological profiles and geographical distribution based on unique molecular identifiers of the common freshwater diatoms Fragilaria and Ulnaria

Diatom taxonomy has evolved in recent years, with many new species described and new approaches such as molecular genetics showing the existence of cryptic diversity within currently accepted species. This cryptic diversity is not well understood even for common freshwater genera such as Fragilaria and Ulnaria. The purpose of our study was to define taxon-specific ecological profiles and geographical distributions for unique molecular identifiers (amplicon sequence variants, ASVs) linked to curated taxonomy for these genera. Our goal is to contribute to the development of ecological assessment methods, and to the understanding why we often observe so many diatom species co-occurring in a single sample. We filtered a large (770 samples) metabarcoding dataset with linked environmental data covering several countries in Europe for genetic variants (ASVs) assigned to currently accepted species of our target genera. We studied the geographical distribution of the ASVs, and tested for ASV-pair co-occurrence. We modelled ASV-specific preferences for pH, alkalinity, total nitrogen, total phosphorus and conductivity, and analysed their preference for lakes or streams as habitat. Our study confirmed that there seems to be no general geographical barrier for the distribution of freshwater benthic diatom ASVs in Europe, but that dispersal is not rapid enough to hide historical events. The Fragilaria and Ulnaria ASVs in our study showed considerable overlap in geographical distribution, habitat and ecological preferences. We found evidence that only large differences in preferences for the analysed water chemistry variables prevented the co-occurrence of ASVs at the same sites. Instead, Fragilaria and Ulnaria ASVs co-occurred frequently in samples. We found subtle differences in ecological preferences for some ASV pairs, which might in part explain the co-occurrence by the avoidance of direct competition. However, the great overlap in distribution and ecological preferences suggests that other factors not studied here were also responsible for the observed co-occurrences and high richness of ASVs found at many sites. To our knowledge, we are the first to use ASVs in combination with a curated taxonomy to understand co-occurrence, specific ecological profiles and large-scale geographical distribution for unique identifiers not biased by the quality of reference databases, clustering methods, or non-harmonized morphological identification. Thus, our results can now be used in subsequent projects to interpret ASV occurrences, e.g. for development of ecological assessment methods.

Abiotic and biotic correlates of the occurrence, extent and cover of invasive aquatic Elodea nuttallii.

Biological invasions, especially invasive alien aquatic plants, are a major and growing ecological and socioeconomic problem worldwide. Freshwater systems are particularly vulnerable to invasion, where impacts of invasive alien species can damage ecological structure and function. Identifying abiotic and biotic factors that mediate successful invasions is a management priority. Our aim was to determine the environmental correlates of Elodea nuttallii; a globally significant invasive aquatic species. Elodea nuttallii presence/absence (occurrence), extent (patch area) and percentage cover (density) was visually assessed from a boat throughout Lough Erne (approximately 144 km2), County Fermanagh, Northern Ireland during the active summer growth season (July–September). In addition, substrate type and zebra mussel Dreissena polymorpha occurrence was recorded. Fourteen water chemistry variables were collected monthly from 12 recording stations throughout the lake during the 9 years before the survey to spatially interpolate values and establish temporal trajectories in their change. Shoreline land use was derived from CORINE land cover maps. Environmental associations between E. nuttallii, substrate, D. polymorpha, water chemistry and land use were assessed. Elodea nuttallii occurrence was positively associated with water conductivity, alkalinity, suspended solids, phosphorus (both total and soluble) and chlorophyll‐a concentrations, but negatively associated with pH and total oxidised nitrogen. E. nuttallii patch extent and proportional cover were positively associated, to varying degrees, with the presence of D. polymorpha, biological oxygen demand, water clarity and soft substrate, but negatively associated with urban development and ammonium. Elodea nuttallii displayed high levels of phenotypic plasticity in response to environmental variation, allowing it to adapt to a wide range of conditions and potentially gain competitive advantage over native or other invasive macrophytes.It is evident that multiple abiotic and biotic factors, including facilitation by co‐occurring invasive dreissenid mussels, interact to influence the distribution and abundance of E. nuttallii. Thus, it is necessary to consider a more comprehensive environmental context when planning Elodea management strategies.

Hydrogen storage in Majiagou carbonate reservoir in China: Geochemical modelling on carbonate dissolution and hydrogen loss

Underground hydrogen storage (UHS) appears to be promising means for large-scale hydrogen storage. Carbonate reservoirs can play an important role in hydrogen storage in particular in Western China and Middle East region. However, little work has been done to address the potential risks and uncertainties associated with carbonate dissolution and hydrogen loss as a result of hydrogen-brine-carbonate geochemical reactions. We thus performed geochemical modelling to assess the potential of UHS in Majiagou carbonate formation, China. Kinetic models of the dissolution/precipitation of calcite, dolomite and quartz were developed to characterize hydrogen loss, mineral dissolution and water chemistry variations up to 500 years.The results show that the percentage of hydrogen loss due to fluid-rock interactions is only 6.6% for the first year, but could increase to 81.1% at the end of 500 years during UHS in Majiagou formation, indicating that carbonate reservoirs is suitable for hydrogen seasonal storage but may not be a good candidate for long-term storage. Meanwhile, totally 0.0646% of calcite would dissolve into formation brine over 500 years, bringing potential risks on caprock and wellbore stability and formation integrity. Besides, we observed a considerable amount of methane generated along with H2-brine-carbonate interactions. Our works provide a framework to assess the hydrogen storage capacity of carbonate reservoirs using geochemical modelling, and can be also applied to other types of storage deposits.

Water chemistry variation in tropical high‐mountain lakes on old volcanic bedrocks

AbstractWater chemistry and its ecological implications have been extensively investigated in temperate high‐mountain lakes because of their role as sentinels of global change. However, few studies have considered the drivers of water chemistry in tropical mountain lakes underlain by volcanic bedrock. A survey of 165 páramo lakes in the Cajas Massif of the Southern Ecuador Andes identified 4 independent chemical variation gradients, primarily characterized by divalent cations (hardness), organic carbon, silica, and iron levels. Hardness and silica factors showed contrasting relationships with parent rock type and age, vegetation, aquatic ecosystems in the watershed, and lake and watershed size. Geochemical considerations suggest that divalent cations (and related alkalinity, conductivity, and pH) mainly respond to the cumulative partial dissolution of primary aluminosilicates distributed throughout the subsurface of watersheds, and silica and monovalent cations are associated with the congruent dissolution of large amounts of secondary aluminosilicates localized in former hydrothermal or tectonic spots. Dissolved organic carbon was much higher than in temperate high‐mountain lakes, causing extra acidity in water. The smaller the lakes and their watersheds, the higher the likelihood of elevated organic carbon and metals and low hardness. The watershed wetland cover favored metal levels in the lakes but not organic carbon. Phosphorus, positively, and nitrate, negatively, weakly correlated with the metal gradient, indicating common influence by in‐lake processes. Overall, the study revealed that relatively small tropical lake districts on volcanic basins can show chemical variation equivalent to that in large mountain ranges with a combination of plutonic, metamorphic, and carbonate rock areas.

Diatom evidence for a groundwater divide that limited the extent of Lake Estancia, New Mexico, USA, highstands during the Last Glacial Maximum

Abstract A high-resolution time series of diatoms from the Estancia Basin of central New Mexico, USA, reveals decadal to millennial changes in water chemistry during the Last Glacial Maximum (LGM) and suggests that groundwater leakage limited the size of Lake Estancia highstands. Previous work showed that the lake expanded at least five times during the LGM, with each highstand reaching the same elevation; numerical modeling experiments showed that highstands required increases in precipitation of 1.5–2 times that of modern times but also demonstrated that these conditions could have lasted for only a few decades or the lake would have overflowed the basin’s sill. The fact that the lake returned to the same elevation suggests that highstands were climatologically similar. Here we present an alternative scenario, that once the lake reached a particular threshold volume, groundwater leakage prevented further expansion, which means that precipitation increases may have been larger than previously thought. The LGM diatom sequence is dominated by freshwater planktonic species in the Lindavia ocellata complex, the freshwater to brackish littoral species Pseudostaurosira brevistriata, and the brackish to saline benthic species Diploneis cf. smithii, all of which show decadal to centennial oscillations that were likely driven by solar cycles. Canonical correspondence analyses using mineralogical time series as proxies for wetter and drier conditions reveal that diatom assemblages varied with salinity and pH/alkalinity and suggest that groundwater outflow led to variable water chemistry for different highstands of the same magnitude. Nonmetric multidimensional scaling confirms the uniqueness of each highstand in terms of the diatom assemblages. The diatom data presented here are among only a handful of such records for Pleistocene pluvial lakes in the American West and reveal that saline alkaline lakes can yield important information despite valve preservation issues.

Using large, open datasets to understand spatial and temporal patterns in lotic ecosystems: NEON case studies

AbstractLeveraging big, open data is the next frontier in ecology. The National Ecological Observatory Network (NEON) is a network of monitoring sites collecting ecological data from across the United States. Using a case study approach, we provide examples of how NEON data can be applied to address a few big questions in aquatic ecology. First, we examined spatial patterns in stream water chemistry, to determine whether sites tend to cluster into regions based on geographic proximity. We found that this was not the case, likely because the hydrologic, geologic, and anthropogenic factors that drive heterogeneity in stream water chemistry vary across smaller spatial scales. Second, we examined temporal variability in stream water chemistry. We determined that the majority of catchments are relatively chemostatic (i.e., discharge varies by orders of magnitude more than concentrations) and that differences between catchments are likely to shift across decades due to changes in network conductivity. Third, we tested predictions of the River Continuum Concept (RCC) along a gradient from a second‐order stream to a seventh‐order river. We found that longitudinal patterns in metabolism, carbon chemistry, and macroinvertebrate community composition generally follow the patterns predicted by the RCC. NEON is only in its third year of full operations, with a planned 30‐year life. The studies presented here show the utility of NEON data, while only using a subset of the many data products that NEON produces. The massive amounts and types of data NEON generates, in conjunction with other national‐scale datasets, will allow the research community to better understand how aquatic ecosystems function and respond to drivers of long‐term change.

Seasonal River Chemistry and Lithium Isotopes in the Min Jiang at Eastern Tibetan Plateau: Roles of Silicate Weathering and Hydrology

Riverine lithium (Li) isotopes have been considered as a robust tracer for silicate weathering, but processes controlling riverine δ7Li ratios remain controversial. To address the impacts of weathering and hydrology on riverine δ7Li, the seasonal variation of water chemistry in the Min Jiang at the eastern Tibetan Plateau was investigated over December of 2009 to the end of 2010. The results showed distinct seasonal variations in ionic chemistry and δ7Li. Increased river discharge in the monsoon season diluted dissolved ions, and monsoonal hydrological changes caused frequent δ7Li fluctuations. High discharge caused by monsoonal rainfall reduced Li isotope fractionation by shortened rock–fluid interaction time, resulting in lower δ7Li, whereas the input of high δ7Li groundwater and landslide seepage elevated riverine δ7Li, together with lengthened rock–fluid interaction time in less rain intervals. Based on the high-resolution sampling strategy and dataset over one hydrological year, this study highlights that changes of hydrological conditions can have a significant impact on weathering processes and water sources, and therefore on riverine δ7Li variation.

A data-driven method for estimating the composition of end-members from stream water chemistry time series

Abstract. End-member mixing analysis (EMMA) is a method of interpreting stream water chemistry variations and is widely used for chemical hydrograph separation. It is based on the assumption that stream water is a conservative mixture of varying contributions from well-characterized source solutions (end-members). These end-members are typically identified by collecting samples of potential end-member source waters from within the watershed and comparing these to the observations. Here we introduce a complementary data-driven method (convex hull end-member mixing analysis – CHEMMA) to infer the end-member compositions and their associated uncertainties from the stream water observations alone. The method involves two steps. The first uses convex hull nonnegative matrix factorization (CH-NMF) to infer possible end-member compositions by searching for a simplex that optimally encloses the stream water observations. The second step uses constrained K-means clustering (COP-KMEANS) to classify the results from repeated applications of CH-NMF and analyzes the uncertainty associated with the algorithm. In an example application utilizing the 1986 to 1988 Panola Mountain Research Watershed dataset, CHEMMA is able to robustly reproduce the three field-measured end-members found in previous research using only the stream water chemical observations. CHEMMA also suggests that a fourth and a fifth end-member can be (less robustly) identified. We examine uncertainties in end-member identification arising from non-uniqueness, which is related to the data structure, of the CH-NMF solutions, and from the number of samples using both real and synthetic data. The results suggest that the mixing space can be identified robustly when the dataset includes samples that contain extremely small contributions of one end-member, i.e., samples containing extremely large contributions from one end-member are not necessary but do reduce uncertainty about the end-member composition.

Chemistry conditions and corrosion behaviour in simulated crevices of alloy steel

ABSTRACT Control and mitigating crevice corrosion demand a thorough understanding of the prevailing chemistry conditions inside the crevice. To match and predict the dynamics in chemistry conditions occurring inside a crevice appropriately, good crevice models necessitate extensive experimental data. This paper presents the accurate determination of the ionic species in the minute volume of crevice solution and redox potential measurements in fabricated simulated crevices of different dimensions/geometry in different stainless steel alloys. Crevice geometries fabricated from carbon steel (CS) 106 B and stainless steel (SS) 316 materials were exposed to varying water chemistry conditions in a static autoclave at high temperatures. The change in pH, conductivity, ionic concentrations, electrochemical potential and effectof corrosion inhibitors inside the crevice were monitored after exposure in an alkaline medium with and without chloride. Bulk solution pH showed a reduction in alkalinity, conductivity and enhancement in anion concentrations. About 58 times increase in Cl− was measured.

Differential selenium uptake by periphyton in boreal lake ecosystems

The largest and most variable step of selenium (Se) assimilation into aquatic ecosystems is the rapid uptake of aqueous Se by primary producers. These organisms can transfer more harmful forms of Se to higher trophic levels via dietary pathways, although much uncertainty remains around this step of Se assimilation due to site-specific differences in water chemistry, hydrological and biogeochemical characteristics, and community composition. Thus, predictions of Se accumulation are difficult, and boreal lake systems are relatively understudied. To address these knowledge gaps, five static-renewal field experiments were performed to examine the bioaccumulation of low, environmentally relevant concentrations of Se, as selenite, by naturally grown periphyton from multiple boreal lakes. Periphyton rapidly accumulated Se at low aqueous Se concentrations, with tissue Se concentrations ranging from 8.0 to 24.9 μg/g dry mass (dm) in the 1–2 μg Se/L treatments. Enrichment functions ranged from 2870 to 12 536 L/kg dm in the 4 μg Se/L treatment, to 11 867–22 653 L/kg dm in the 0.5 μg Se/L treatment among lakes. Periphyton Se uptake differed among the five study lakes, with periphyton from mesotrophic lakes generally accumulating more Se than periphyton from oligotrophic lakes. Higher proportions of charophytes and greater dissolved inorganic carbon in more oligotrophic lakes corresponded to less periphyton Se uptake. Conversely, increased proportions of bacillariophytes and total dissolved phosphorus in more mesotrophic lakes corresponded to greater periphyton Se uptake. Periphyton community composition and water chemistry variables were correlated, limiting interpretation of differences in periphyton Se accumulation among lakes. The results of this research provide insight on the biodynamics of Se assimilation at the base of boreal lake food webs at environmentally relevant concentrations, which can potentially inform ecological risk assessments in boreal lake ecosystems in North America.

Influence of permafrost and hydrogeology on seasonal and spatial variations in water chemistry of an alpine river in the northeastern Qinghai-Tibet Plateau, China

Known as the third pole of the world, the Qinghai-Tibet Plateau has been experiencing rapid permafrost warming and thawing over the last few decades. However, the impact of permafrost distribution and hydrogeology on river hydrochemistry in alpine areas remains unclear. This study conducted four sampling campaigns to reveal the temporal and spatial variations in and factors driving river hydrochemistry in the upper reaches of the Heihe River, the northeastern Qinghai-Tibet Plateau. We found that the concentrations of major ions and total dissolved solids (TDS) in river water showed substantial seasonal variations; the concentrations were generally lower during the initial thawing and thawed periods than during the initial freezing period. However, solute fluxes during the thawed period were much higher than those during the frozen period. The concentrations of major ions and TDS gradually decreased to a minimum from the permafrost meander (PM) section to the seasonal frost meander (SFM) section and then increased the seasonal frost canyon section. Using the revised forward model, we found that river solutes were contributed by carbonate weathering (mean 38.9%) > sulfide oxidation (22.9%) > evaporite dissolution (20.2%) > atmospheric precipitation (8.7%) > silicate weathering (5.0%) > glacial meltwater (4.3%). The higher TDS, Na+, Cl−, Ca2+, Mg2+, and SO42− concentrations in the PM section reflected the influence of freeze-out fractionation. The concentrations of major ions and TDS were lowest in the SFM section, indicating that the riparian porous aquifer was essential in regulating river hydrochemistry, thus reducing its spatiotemporal variations in the alpine area. In the mountain glacier–hillslope–riparian porous aquifer–river system, the river was mainly recharged by groundwater with insufficient water–rock interactions due to the rapid flow owing to the high elevation difference and high permeability of the riparian quaternary porous aquifers. Our findings provide insights into the construction of hydrogeochemical models in alpine areas and are practically important for the scientific management of water resources in the Qinghai-Tibet Plateau.

Land-cover, climate and fjord morphology drive differences in organic matter and nutrient dynamics in two contrasting northern river-fjord systems

Climate and land-use changes are leading to impacts on individual ecosystems as well as shifts in transfer dynamics between interconnected systems. At the land-ocean interface, changes in riverine inputs of organic matter (OM) and nutrients have the potential to lead to shifts in coastal carbon and nutrient cycling with consequences for ecosystem structure and function. In this study, we assess OM and nutrient dynamics for two contrasting Norwegian river-to-fjord systems: a boreal system with a forested catchment draining into a narrow fjord (‘narrow boreal system’), and a subarctic system where lowland forests and mountainous regions drain into a broad fjord (‘broad subarctic system’). We characterized seasonal organic carbon and nutrient concentrations and DOM absorption properties for samples collected along transects from river to outer fjord during 2015/2016. While differences in catchment properties drove contrasts in river chemistry between the two study rivers, fjord morphology and hydrodynamics as well as dissolved organic carbon (DOC) and nutrient concentrations in marine receiving waters predicted water-chemistry patterns along the transect. The narrow boreal system, with high riverine DOC and nutrient concentrations, was structured mainly by a horizontal salinity gradient from river to outer fjord, with limited impact of seasonality. In contrast, the broad subarctic system tended to be dominated by vertical salinity stratification, with strong between-date differences in surface water salinity linked to seasonality in river discharge. These dynamics were also reflected in the strong horizontal gradients in DOC, nutrients and DOM properties in the narrow boreal system, in contrast to the broad subarctic system, where strong seasonality paired with a lack of strong contrast between riverine and marine concentrations of DOC and most nutrients led to an uncoupling between salinity and other water chemistry variables. In the narrow boreal system, terrestrial OM dominated both the particulate and dissolved OM pools, while OM in the broad subarctic system was derived primarily from marine phytoplankton. Non-linear declines in NO3 + NO2 were observed consistently in the boreal system and during the productive spring season in the subarctic system, suggesting biological uptake and a potentially important role of these rivers as sources of bioavailable N to coastal ecosystems. The results from these two case studies highlight the complex and interacting effects of catchment land-cover, river water chemistry and discharge, fjord morphometry and hydrodynamics in structuring the transport, fate and potential impacts of terrestrially-derived nutrients and organic matter in northern coastal environments.

Assessment of Physico-chemical Characteristics of Vairtarna Estuary of Palghar, (M.S.) India

The study of estuarine water quality plays an important role in evaluating and determining the pollution status and health of the water. Vaitarna River estuary is one of the important water bodies in the Palghar district. Entire stretch of the estuary was arbitrarily divided into three zones. Physical and chemical variables of water were monitored season-wise in the year 2016. In the present study, the entire stretch of estuary showed high values of Temperature, pH, BOD, C.O.D. Acidity, Salinity, Hardness and Sulphate different physicochemical parameters were studied in 3 stations of the estuary. There was no previous data from the Vaitarna estuary. The study revealed that one-year data (January 2016 to December 2016) shows good environmental conditions to differences in physicochemical characteristics within the permissible limit. It concluded that the water quality is good, and it is the responsibility of our society the importance of such water bodies to keep free from pollution. Because of the fishery point of view the local fishermen depend on this area of water resources.

Drones can reliably, accurately and with high levels of precision, collect large volume water samples and physio-chemical data from lakes

The rapid development and application of drone technology has included water sampling and collection of physiochemical data from lakes. Previous research has demonstrated the significant potential of drones to play a future pivotal role in the collection of such data from lakes that fulfil requirements of large-scale monitoring programmes. However, currently the utilisation of drone technology for water quality monitoring is hindered by a number of important limitations: i) the low rate of successful sample captured; ii) the relatively low volume of water sample retrieved for analyses of multiple water chemistry parameters; and critically iii) differences between water chemistry parameters when using a drone versus samples collected by boat.Here we present results comparing the water chemistry results of a large number of parameters (pH, dissolved oxygen concentration, temperature, conductivity, alkalinity, hardness, true colour, chloride, silica, ammonia, total oxidised nitrogen, nitrite, nitrate, ortho-phosphate, total phosphorous and chlorophyll) sampled via drone with samples collected by boat in a number of lakes. The drone water sampling method used here is the first to collect a sufficiently large volume of water to meet the monitoring requirements of large scale water monitoring programmes, 2 L, at a 100% success rate and most crucially, with water chemistry variables that are not significantly different to those taken using traditional boat water sampling. This study therefore shows that drone technology can be utilised to collect water chemistry data and samples from lakes in a reliable, more rapid and cost effective manner than traditional sampling using boats, that is safer for personnel and poses less of a biosecurity risk.

The Influence of Fertilizer Regimen on Water Chemistry and Filamentous Green Algae in Earthen-Substrate Ponds

Water chemistry patterns can be indicative of production potential during pond culture of walleye (Sander vitreus, ≈30 mm total length). However, achieving desired water chemistry patterns that reflect an increase in zooplankton, a reduction in phytoplankton, and a lack of nuisance filamentous green algae in large, earthen-substrate ponds can be challenging. During 2020, water chemistry variables and the occurrence of filamentous green algae were compared in fishless, earthen-substrate ponds (0.72 ha) that received either alfalfa meal (AFM, n=2) or alfalfa meal combined with inorganic nitrogen (AFM+28:0:0, n=2) over an approximate 30-day period. Alfalfa meal use was standard across all ponds (476 kg), while the concentration of inorganic nitrogen (ammonia-N + nitrate-N) was initially raised to 1.25 mg/L with subsequent applications, at three to five-day intervals, having a target concentration of 0.64 mg/L. Initial pH and dissolved oxygen were significantly higher, but pH became significantly lower over time in the AFM+28:0:0 treatment. Ammonia-nitrogen began similarly low (<0.1 mg/L) in both treatments but became and remained significantly higher (peaked 0.44 mg/L on June 9) with 28:0:0 supplementation. Nuisance, filamentous green algae were not observed with 28:0:0 supplementation but were present on the substrate of both ponds in the AFM treatment. Supplementing an alfalfa meal regimen with inorganic nitrogen every three to five days in earthen-substrate ponds deterred filamentous green algae and promoted water chemistry indicative of enhanced walleye fingerling production in previous trials.

Unravelling the spatiotemporal variation of pCO2 in low order streams: Linkages to land use and stream order

Headwater streams make the majority of cumulative stream length in a river basin, carbon dioxide (CO2) emission from headwater (low order) streams is thus an essential component. Anthropogenic activities in headwater areas such as land use change and land use practices can strongly modify terrestrial carbon and nutrient input, which could affect the level of partial pressure of dissolved carbon dioxide (pCO2) and CO2 degassing from streams. However, there are large uncertainties in estimates due to the lack of data in subtropical rivers of rapidly developing rural regions. The spatiotemporal variation and driving factors of the pCO2 and CO2 degassing from low-order streams remain to be explored. In this study, we assess multi-spatial scale effects of land use on pCO2 dynamics in seven headwater tributary rivers in Central China during 2016, 2017 and 2018 in rainy and dry seasons. Our results reveal that the stream pCO2 level consistently increases as the stream order increases from 1 to 3 under apparent seasonal variations. Riverine pCO2 is positively related to the percentage of urban land and cropland surrounding the river segments, but is negatively related to the percentage of forest land. The stream pCO2 is more closely correlated with the 1000 and 2000 m diameters of circular buffers at upstream sampling sites than the circular buffers with 100 and 500 m diameters. There exist significant relationships of pCO2 with the concentrations of TN, TP, DO, and DOC in the low-order streams. The partial redundancy analysis quantifies the relative importance of anthropogenic land uses, natural factors and water chemical variables in mediating stream pCO2, showing that influences of anthropogenic land uses (urban and cropland) on pCO2 decrease, with a percentage role of 34%, 14%, and 4% in the 1st-, 2nd- and 3rd-order streams, respectively. The impact of nutrients on pCO2, however, increases as the stream order increases. Urban influence on stream pCO2 also decreases as stream order increases. Our study highlights the effect of land use/land cover types and stream order on riverine pCO2 and provides new insight into estimating CO2 emission in headwater streams. Future studies are needed on the linkage between riverine CO2 degassing and stream orders under changing land use conditions.

Environmental DNA‐based methods detect the invasion front of an advancing signal crayfish population

AbstractAquatic invasive species, such as the signal crayfish (Pacifastacus leniusculus), present a major threat to freshwater ecosystems. However, these species can be challenging to detect in recently invaded habitats. Environmental DNA (eDNA)–based methods are highly sensitive and capable of detecting just a few copies of target DNA from non‐invasively collected samples. Therefore, they have considerable potential for broad‐scale use in mapping and monitoring the spread of invasive species. In this study, we aimed to increase our understanding of the current distribution of signal crayfish in a headwater stream system in the United Kingdom (tributaries of the River Wharfe, Addingham, Yorkshire). Environmental DNA sampling, assessment of water chemistry variables, and conventional crayfish hand‐searching were conducted across 19 study sites in five tributary streams. Using hand‐searching, we detected signal crayfish at 26% of the sites (5/19 study sites). However, using eDNA‐based methods, occupancy increased to 47% of study sites (9/19). Our sampling revealed previously unknown sites of crayfish occupancy, and using eDNA‐based methods, we were able to define the geographical extent of the invasion front in each headwater stream sampled. This study highlights that eDNA‐based methods are well‐suited for detecting newly established signal crayfish populations in recently invaded habitats, even when the invasive species is at low abundance and, therefore, might otherwise be under‐represented or undetected using conventional survey methods. Our study provides further evidence that headwater stream ecosystems are particularly vulnerable to signal crayfish invasion. However, their geomorphological features may make methods used to reduce or prevent invasive crayfish dispersal more effective than in other freshwater ecosystems.

Temporal and vertical variation of phytoplankton and zooplankton in two tropical reservoirs with different trophic states.

In tropical reservoirs, limnological factors are responsible for changes in plankton and vary at temporal and vertical scales. The aim of this study was to evaluate the effects of temporal and vertical variation of the water column on phytoplankton and zooplankton dynamics in two tropical reservoirs (mesotrophic and supereutrophic) in Northeastern Brazil. Monthly collections from three depths in the limnetic region of the reservoirs were performed to analyze the phytoplankton, zooplankton, and limnological variables. The temporal and vertical variation of the physical and chemical water variables, including their interactions, influenced the phytoplankton and zooplankton community. In the supereutrophic reservoir, decreased nitrogen and increased phosphorus and temperature contributed to the dominance of Microcystis panniformis Komárek, Komárková-Legnerová, Sant'Anna, M.T.P.Azevedo & P.A.C.Senna. Conversely, Planktothrix agardhii (Gomont) Anagnostidis & Komárek was dominant under high nitrogen concentrations and low temperatures. In the mesotrophic reservoir, the desmids were dominant and showed a positive relationship with nitrogen. Copepoda Calanoida was dominant and correlated to phytoplankton in both reservoirs. The results showed that nitrogen forms directly influenced phytoplankton, and the importance of nitrogen for management strategies of tropical reservoirs, as well as demonstrated the ability of Calanoida to adapt to different trophic conditions and phytoplankton compositions.

Key abiotic parameters for the management of the richness of bryolichenic communities in bogs of North Patagonia (Chile)

Peatlands are ecosystems that play a special role in conserving biodiversity because they are refugia for unusual wetland-dependent species. Nevertheless, these ecosystems are threatened in southern South America by the overharvesting of Sphagnum moss, used in horticulture as substrate. Moreover, the biodiversity measurement as species richness has not been considered in management practices. Thus, our purpose was to study the bryophyte and lichen diversity and abiotic factors of Chiloé peatlands to distinguish habitat preferences and key abiotic factors to improve peatland management. The study was conducted in eight peatlands of Chiloé Island in Chile (42-43° S and 75-73° W). We found good predictors to overall species richness and each organism group. The observed patterns of cryptogamic species richness are well explained by microtopographic variables and moisture, increasing in tree base, and decreasing in saturated substrate and carpet. We highly recommend conserving “tree base” microtopographic areas as reservoirs of species richness in intervened areas by harvesting. Furthermore, we also suggest monitoring water chemistry variables such as pH or ionic ratio (IR), to provide information to predict impacts on the biodiversity of peatlands under Sphagnum harvesting. These recommendations give rise to sustainable management and to transforming moss into a renewable resource for farmers.

Hydrochemistry of the Lhasa River, Tibetan Plateau: Spatiotemporal Variations of Major Ions Compositions and Controlling Factors Using Multivariate Statistical Approaches

Spatiotemporal variations of the hydrochemical major ions compositions and their controlling factors are essential features of a river basin. However, similar studies in the southern Tibetan Plateau are relatively limited. This study focuses on the chemical compositions of the dissolved loads in the Lhasa River (LR) in the southern Tibetan Plateau. Two sampling campaigns were conducted during the rainy and dry seasons across the LR basin to systematically investigate the spatiotemporal variations of water chemistry and sources of the dissolved loads. The results show that the river water possesses slight alkalinity with an average pH of 8.05 ± 0.04. Total dissolved solids (TDS) and oxidation-reduction potential (ORP) range widely from 39.8 mg/L to 582.6 mg/L with an average value of 165.6 ± 7.7 mg/L and from −9.4 mV to 295 mV with a mean value of 153.7 ± 6.9 mV, respectively. The major cations follow the decreasing order of Ca2+, Mg2+, Na+, and K+ while HCO3−, SO42−, Cl−, and NO3− for anions. Ca2+ and Mg2+ account for 87.8% of the total cations, while HCO3− and SO42− accounts for 93.9% of the total anions. All the major ions show higher concentrations in the dry season. NO3−, HCO3−, and Mg2+ show significant spatial variations due to the influence of basin lithology and anthropogenic activity. Multi-variables statistical analysis reveals that the mechanisms controlling the LR hydrochemistry are mainly carbonate weathering followed by silicate weathering. Geothermal springs and anthropogenic activities also play crucial roles in altering river water ions composition in the middle stream and downstream. The relatively high NO3− value (3 ± 0.2 mg/L) suggests water quality will be under the threat of pollution with the increase of anthropogenic activities.