Stream Order Research Articles

Supporting proactive planning for climate change adaptation and conservation using an attributed road-river structure dataset

Freshwater species and their habitats, and transportation networks are at heightened risk from changing climate and are priorities for adaptation, with the sheer abundance and individuality of road-river structures complicating mitigation efforts. We present a new spatial dataset of road-river structures attributed as culverts, bridges, or fords, and use this along with data on gradient and stream order to estimate structure sensitivity and exposure in and out of special areas of conservation (SAC) and built-up areas to determine vulnerability to damage across river catchments in Wales, UK. We then assess hazard of flooding likelihood at the most vulnerable structures to determine those posing high risk of impact on roads and river-obligate species (fishes and mussels) whose persistence depends on aquatic habitat connectivity. Over 5% (624/11,680) of structures are high vulnerability and located where flooding hazard is highest, posing high risk of impact to roads and river-obligate species. We assess reliability of our approach through an on-ground survey in a river catchment supporting an SAC and more than 40% (n = 255) of high-risk structures, and show that of the subset surveyed >50% had obvious physical degradation, streambank erosion, and scouring. Our findings help us to better understand which structures pose high-risk of impact to river-obligate species and humans with increased flooding likelihood.

Evaluation of pesticide pollution in the Gualeguay Basin: An extensive agriculture area in Argentina

The current agricultural production model was established in the 1990s based on the use of genetically modified organisms and agrochemicals, mainly pesticides. Despite pesticide spread and prevalence, data on the associated concentrations in surface watercourses are comparatively scarce. The aim of this work was to evaluate to what extent the >20 years of agricultural activity with the use of pesticides has impacted on the Gualeguay-River basin, with respect to the different stream orders: the tributary streams and main channel. Thirteen sites within the lower Gualeguay basin were sampled once every season (autumn, winter, spring, and summer) in 2017–2018. The samples were analyzed by gas chromatography time-of-flight mass-spectrometry (GC-TOF-MS) and ultraperformance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS). The most frequently detected pesticide was glyphosate along with its metabolite (aminomethyl)phosphonic acid (AMPA), at 82 % and 71 % of surface water samples and 97 % and 92 % of bottom sediments, respectively; followed by atrazine in 73 % of the water samples. The concentrations of these compounds, each in their respective matrices, did not present sufficient statistically significant differences for differentiating a tributary stream from the main channel. Regardless of glyphosate's affinity for the suspended particulate and bottom sediments, over the entire basin the soluble fraction contributed on average to >80 % of the total concentration in surface water. Despite not being so frequently detected, certain insecticides, mostly deltamethrin, were likewise detected at concentrations above their water-quality guidelines for the protection of aquatic life, even in samples from the main channel. Upon comparison of the pesticide profiles of extensive- and horticultural-production systems in the country, atrazine emerged as a prime candidate to be used as a tracer of extensive agriculture contamination in the environment. Further research is required to establish to what degree pesticides used in agriculture and mobilized by watercourses have an impact on their associated wetland ecosystems.

Effects of forest management on mercury bioaccumulation and biomagnification along the river continuum

Forest management can alter the mobilization of mercury (Hg) into headwater streams and its conversion to methylmercury (MeHg), the form that bioaccumulates in aquatic biota and biomagnifies through food webs. As headwater streams are important sources of organic materials and nutrients to larger systems, this connectivity may also increase MeHg in downstream biota through direct or indirect effects of forestry on water quality or food web structure. In this study, we collected water, seston, food sources (biofilm, leaves, organic matter), five macroinvertebrate taxa and fish (slimy sculpin; Cottus cognata) at 6 sites representing different stream orders (1–5) within three river basins with different total disturbances from forestry (both harvesting and silviculture). Methylmercury levels were highest in water and some food sources from the basin with moderate disturbance (greater clearcutting but less silviculture). Water, leaves, stoneflies and fish increased in MeHg or total Hg along the river continuum in the least disturbed basin, and there were some dissipative effects of forest management on these spatial patterns. Trophic level (δ15N) was a significant predictor of MeHg (and total Hg in fish) within food webs across all 18 sites, and biomagnification slopes were significantly lower in the basin with moderate total disturbance but not different in the other two basins. The elevated MeHg in lower trophic levels but its reduced trophic transfer in the basin with moderate disturbance was likely due to greater inputs of sediments and of dissolved organic carbon that is more humic, as these factors are known to both increase transport of Hg to streams and its uptake in primary producers but to also decrease MeHg bioaccumulation in consumers. Overall, these results suggest that the type of disturbance from forestry affects MeHg bioaccumulation and trophic transfer in stream food webs and some longitudinal patterns along a river continuum.

Development of a benthic macroinvertebrate predictive model based on the physical and chemical variables of rivers in the Republic of Korea

Predictive models for the benthic macroinvertebrate community based on environmental variables facilitate the identification of the organisms expected to inhabit an area according to the target environmental conditions when restoring rivers. In this investigation, a biotic community predictive model was developed using benthic macroinvertebrate and environmental variable data collected from 1,210 sites in the Republic of Korea from 2010 to 2020. The sites were classified into six groups according to Two Way Indicator Species Analysis (TWINSPAN) and based on their individual abundance/m2 of benthic macroinvertebrates. The TWINSPAN groups were related to 14 variables by stepwise multi-discriminant analysis. The relative importance of the environmental variables that classified each TWINSPAN group was in the order of mean diameter of particle size, catchment area, altitude, velocity, total phosphorus, latitude, pH, longitude, conductivity, water depth, suspended solids, biochemical oxygen demand, stream order, and total nitrogen. Discriminant functions 1–4 showed statistically significant and a predictive model was developed using functions 1 and 2 based on Wilks’ lambda values. The fit of the derived model was confirmed using Sørensen similarity (number of taxa) and Bray–Curtis dissimilarity (individual abundance/m2) analyses between the predicted organisms and those observed at the sites. The distributions of similarity and dissimilarity that were confirmed by stream type ranged from 0.60 to 0.72 and 0.46–0.56, respectively, based on the mean. Based on the predicted and observed values, the ratio of shredders and scrapers to collectors showed similar results overall for each stream type. The predictive model derived using nationally managed available data is expected to be applicable to stream and river restorations in the future, as it provides a statistical assessment of the biotic communities that are expected to inhabit a given environment.

Biogeochemical functional responses to flow rate in a low order stream: implications for water quality monitoring.

In running waters, the concentration of components that define water quality can be subjected to ample fluctuations quantitatively linked to flow rate. If not properly considered, such variability may hinder assessment of the evolution of water quality, ofthe effects of management actions, and ultimately the understanding of processes driving water quality. The functional response to flow rate was characterized for multiple biogeochemical variables in a pristine, low order stream. Variability of responses spanned between a factor of 2 and > 34, and in all cases were associated to flow rate according to one of three patterns: positive asymptotic (for variables: seston, suspended particles, total nutrients, dissolved and particulated organic matter, dissolved inorganic nitrogen), negative asymptotic (conductivity and dissolved reactive silicon), and humped (dissolved inorganic phosphorous). Building on those results, a rationale is presented for an unambiguous, cost-effective approach to water quality evaluation in running systems with predominantly diffuse sources.

Assessment of the geomorphic indices in relation to tectonics along selected sectors of Borpani River Basin, Assam using Cartosat DEM data

• A total of eleven geomorphic indices were studied in detail for the assessment of tectonic activity along Borpani River. • Results indicates satellite imageries based Geomorphic indices can witnesses tectonic influences. • Overall tectonic activity indicates classes - active, moderately active and less active zones in the study region. • On average, 23.86%, 29.54%, and 46.58% of the geomorphic indices falls in active, moderately active and low active classes. We studied geomorphic indices related to tectonics along the Borpani River using Cartosat 10 m spatial resolution Digital Elevation Model (DEM) data. A total of 11 geomorphic indices such as transverse topographic symmetry factor (Tt), drainage basin asymmetry (AF), valley floor width to valley height ratio (Vf), bifurcation ratio (Rb), hypsometric integral (HI), basin elongation ratio (Re), basin shape index (Bs), circularity ratio (Rc), drainage density (Dd), relief ratio (Rh), hypsometric curves (HC) were studied to access the tectonics along the river in selected locations. Five locations along the river were selected for detailed analysis (sub-basin I, II a, II b, III, and IV). Horton's (1945) scheme was adopted for watershed delineation, while stream ordering was performed using Strahler's (1964) method. The results infer that the sub-basins along the Borpani River are tectonically active. In the case of sub-basin I, 3 geomorphic indices out of 11 falls in the category of highly active, and 2, 1, 2, and 4 indices out of 11 falls in the category of highly active in the case of sub-basins II a, II b, III, and IV. Similarly, 4, 1, 3, 6, 1 and 4, 8, 7, 3, 6 indices fall under moderately active and low active classes in sub-basins I, II a, II b, III, and IV. On average, 23.86 %, 29.54%, and 46.58% of the geomorphic indices fall in the active, moderately active, and low active classes.

Ecological River Health Assessment Using Multi-Metric Models in an Asian Temperate Region with Land Use/Land Cover as the Primary Factor Regulating Nutrients, Organic Matter, and Fish Composition.

This study was performed to determine the ecological health of a temperate river over nine years (2011–2019); it also analyzed the trophic structure and linkage of nutrients (nitrogen [N] and phosphorus [P]), sestonic chlorophyll-a (CHL-a), and the top trophic fish in the Asian monsoon region. Water chemistry, trophic indicators, and tolerance guilds were primarily influenced by land use and land cover (LULC); the magnitude of variation was also related to geographic elevation, artificial physical barriers (weirs), and point sources. Levels of nutrients, organic matter, and CHL-a largely influenced by the intensity of the monsoon seasonality for a particular LULC and stream order. Mann–Kendall tests based on a long-term annual dataset showed that annual organic matter and CHL-a increased over time because of longer hydraulic residence time after weir construction. The results of empirical nutrient models suggested that P was the key determinant for algal growth (CHL-a); the strong P-limitation was supported by N:P ratios > 17 in ambient waters. Linear regression models and canonical correspondence analysis (CCA) were used to determine the influences of LULC and water quality on the trophic/tolerance linkages, fish community compositions and structures, and river health. Tolerant species had a positive functional relationship with nutrient enrichment through total phosphorus (TP) (R2 = 0.55, p < 0.05) and total nitrogen (TN) (R2 = 0.57, p < 0.05), organic pollution in terms of biological oxygen demand (BOD) (R2 = 0.41, p < 0.05) and chemical oxygen demand (COD) (R2 = 0.49, p < 0.05), and algal growth (R2 = 0.47, p < 0.05); sensitive species exhibited the opposite pattern. The degradation of river health, based on the multi-metric index of biotic integrity (IBI) model, was evident in the downriver region (“fair–poor” condition) and was supported by the quantitative fish community index (QFCI) model. The outcomes suggested that the degradation and variation of ecological river health, trophic linkages of water chemistry (N, P)-algal biomass-fish, were largely controlled by the land use pattern and construction of physical barriers in relation to the Asian monsoon.

Morphometric evaluation of Ranikhola watershed in Sikkim, India using geospatial technique

Morphological parameters are linked with the hydrological behaviour of the watershed. It helps to understand different basin characteristics. Characterization of quantitative morphology and river basin analysis is the way to implement proper river basin planning and management of soil and water conservation measures. In the present study, Cartosat-1 Digital Elevation Model (DEM) was used in Geographic Information System (GIS) environment to determine the morphometric parameters (stream length, stream order, stream frequency, bifurcation ratio, form factor, drainage density, circulatory ratio, etc.) of the Ranikhola watershed of Sikkim state, India. The slope of a major portion of the watershed area was found to be less than 30% (42 km2) and has a drainage density of 0.585 km-1. The lower value of drainage density in the watershed indicates a relatively lower streams frequency over the watershed. The elongation ratio, form factor, and circulatory ratio were estimated as 0.665, 0.347, and 0.510, respectively, which indicate that the watershed is elongated in shape, having gentle slopes and long flow paths. The relief ratio for the watershed was estimated to be 0.187, which indicates the watershed has a low elevation difference, low runoff, and high groundwater potential. This kind of morphometric analysis is required for the watershed characterization and helps to understand the hydrogeological behavior of the watershed.

A study on hydogeomorphological status of kadalundi river basin in kerala using geospatial technology

Detailed hydro geomorphologic study has been carried out for Kadalundi River Basin in Kerala to understand the drainage pattern, spatial and temporal water availability using secondary data collected from different Departments. Geomorphological parameters have been estimated as a part of this study and it is found that Kadalundi river basin is a sixth order stream. The drainage pattern is complex with considerable variation in spatial arrangements, which are controlled by topography, slope, rock type and structural deformations. The basin is characterized by dendritic type of drainage pattern with variable density. The densest dendritic pattern is developed on the hard Charnockite and Gneissic rocks. In some areas, the drainage pattern is sub dendritic reflecting structural control. The existing land use pattern is derived from Indian Remote Sensing Satellite (IRS – LISS II1, P6) using ERDAS software. Using hydrological toolset of Spatial Analyst, an extension of ArcGIS software, slope map, aspect map and Digital Elevation Model (DEM) have been derived. In addition, the basic thematic map on geology and soil also been derived.. For annual period, the rainfall varies from 1800- 4100 mm, 1400- 2600 mm for South –West monsoon period and 600-1100 mm for the North-East monsoon period.

Analysis of geo-morphometric and topo-hydrological indices using COP-DEM: a case study of Betwa River Basin, Central India

ABSTRACT The open source 30 m Copernicus DEM (COP-DEM) has been used to derive the geo-morphometric and topo-hydrological characteristics of Betwa River Basin. Drainage network with 7th order stream and mostly dendritic pattern has been delineated using the Strahler’s method. The drainage density, stream frequency, form factor, length of overland flow and circulatory ratio of the basin were computed as 0.38 Km/Km2, 0.08 Km−2, 0.23, 1.31, and 0.20, respectively. These outcomes suggest less available surface flow, lesser relative relief, poor drainage network, and nearly elongated shape of the basin. The mean bifurcation ratio for entire basin was calculated as 4.0 that signifies gradient dependent drainage network of the basin. The ruggedness number was computed as 0.24, which reflects the geology dominated (granite–gneiss) rocky and undulated topography of the basin. The dissection index ranges from 0.06 to 0.3, which implies less degree of dissection and mature stage of the basin. The topographic wetness index (TWI), stream power index (SPI), terrain ruggedness index (TRI), and sediment transport index (STI) ranges from 3.13 to 26.35; 0 to 6; 0 to 30; and 0 to 121.4, respectively. It implies that the lower basin is less susceptible towards erosion as compared to upper basin.

Comparison of caddisfly (Insecta, Trichoptera) assemblages from lake and river habitats of the Huron Mountains of Michigan (USA).

The caddisfly assemblages of six lakes and 12 1st-4th order streams of the Huron Mountains of northern Upper Michigan (USA) were sampled monthly with ultraviolet lights during June-September 2019. A total of 169 species representing 63 genera and 19 families was collected, including five species not found elsewhere in Michigan and two species endemic to the state. Species assemblages between lotic and lentic habitats were distinct from each other, with 11 species indicating lakes and 23 indicating rivers. Despite the taxonomic differences, biomass of functional feeding groups (FFGs) was similar between lakes and rivers, except for higher biomass of predators in the former and higher biomass of filtering collectors in the latter. The FFG biomass of both habitat types was dominated (50-70%) by shredders. Considering the undisturbed condition of the habitats, the caddisfly assemblages and FFG biomass of the Huron Mountains can serve as regional biological monitoring reference conditions.

Morphometric Analysis of Chilenahalli Micro-watershed in the North-eastern Dry Zone of Karnataka using GIS and Remote Sensing Techniques

The structure and landform of watershed and their associated stream networks are described mainly by their morphometric parameters and Watershed analysis based on morphometric parameters is very important for watershed planning, since it gives an idea about the basin characteristics regarding slope, topography, soil condition, runoff characteristics, surface water potential and quantify the linear, areal and relief aspects of watershed. Geographic information system and remote sensing techniques were employed for the identification of morphological features, drainage pattern and its planning in basin area. The Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) 30m resolution was used to digitize study watershed and generate drainage pattern and analysis done using GIS software and excel spreadsheet. The study reveals that Chilenahalli micro-watershed designated as 4thstream order and drainage indicate dendritic pattern with mature geomorphic stage and stream order verifies the Horton’s law of stream number. The Mean Bifurcation Ratio was found to be 4.46, which indicates low rainfall, shallow weathering and low dissection of the valley and it shows low to medium relief aspect during investigation of the basin. This can be visualised using DEM, relief ratio, ruggedness number, and slope maps of the study area. The drainage density was found to be 2.13 km/km2which indicate a low class Dd value, thereby indicating a poorly drained watershed with low response to hydrological parameters. The texture ratio of the micro-watershed is 3.52, which indicated coarse texture of drainage basin and the values of Form Factor, Circulatory ratio and Elongation ratio may imply an oval shape of the basin with a slightly elongated main stream and the length of overland flow values in this study is 0.23 km which shows moderate infiltration and percolation characteristics of soil. The study which also helps in planning erosion control strategy, prioritization of watershed and management practices for soil and rainwater conservation. The research study helps to formulate the selection and adoption of crop management practices by preparing soil map of the watershed in future.

Signals of Potential Species Associations Offer Clues about Community Organisation of Stream Fish across Seasons

Simple SummarySpecies interactions are one of the main factors affecting community assembly, yet the role of such interactions remains mostly unknown. Here, we investigated roles of potential species associations in fish community assembly in the Qiupu River, China. Our results suggested that potential species associations might have been underestimated in stream fish community assembly. The contribution of potential species associations to fish community assembly can be reflected by interaction network structures. Omnivorous species play an important role in maintaining network structure as they may have more associations with other species. This study highlights the importance of capturing species associations in river ecosystems across different geographical and environmental settings.Environmental filtering, spatial factors and species interactions are fundamental ecological mechanisms for community organisation, yet the role of such interactions across different environmental and spatial settings remains mostly unknown. In this study, we investigated fish community organisation scenarios and seasonal species-to-species associations potentially reflecting biotic associations along the Qiupu River (China). Based on a latent variable approach and a tree-based method, we compared the relative contribution of the abiotic environment, spatial covariates and potential species associations for variation in the community structure, and assessed whether different assembly scenarios were modulated by concomitant changes in the interaction network structure of fish communities across seasons. We found that potential species associations might have been underestimated in community-based assessments of stream fish. Omnivore species, since they have more associations with other species, were found to be key components sustaining fish interaction networks across different stream orders. Hence, we suggest that species interactions, such as predation and competition, likely played a key role in community structure. For instance, indices accounting for network structure, such as connectance and nestedness, were strongly correlated with the unexplained residuals from our latent variable approach, thereby re-emphasising that biotic signals, potentially reflecting species interactions, may be of primary importance in determining stream fish communities across seasons. Overall, our findings indicate that interaction network structures are a powerful tool to reflect the contribution of potential species associations to community assembly. From an applied perspective, this study should encourage freshwater ecologists to empirically capture and manage biotic constraints in stream ecosystems across different geographical and environmental settings, especially in the context of the ever-increasing impacts of human-induced local extinction debts and species invasions.

Hydro-morphological investigations of Neeru watershed using DEM and geospatial techniques

Morphometric analysis is very popular among the hydro-geomorphological investigation of the river basins that deals with the linear, areal, shape and landscape aspects of river catchment. Neeru watershed, a left-bank tributary of the Chenab River (Doda, Jammu and Kashmir, India). Carto-DEM, Sentinel-2B multispectral satellite image and Topographical maps taken into account for extracting and computing watershed’s various parameters adopting the geospatial techniques. This northern aligned watershed has a length, width, and perimeter of 65 km, 22.4 km, and 106.03 km, respectively, and covers 415.19 sq. km area. It is a 5th stream order watershed, with lower-order streams predominating. The drainage density of 0.81 km/km2 indicates that it is highly permeable and thus has increased subterranean water storage capacity. The bifurcation ratio varies from 2 to 4.74, with a mean of 3.67, demonstrating strong structural control over drainage development. The study area's elongation ratio (0.67) indicates that it has an elongated shape with high relief, steep slope, high sediment load discharge, and susceptible soil erosion. The assessment indicates the role of geospatial techniques in quick appraisal of ecological indicators they will be helpful for decision makers in managing natural resource, planning, and watershed management.

Experimental and Numerical Simulations of Sediment in Fusre River Basin, Nepal

This study presents about the analysis of sediment generation of the ungauged basin Fusre basin by modeling and also with the help of rainfall simulator. Many rivers in Nepal are either ungauged or poorly gauged due to extreme complex terrains, monsoon climate and lack of technical and financial supports. The Soil and Water Assessment Tool (SWAT) was applied for watershed delineation of the Fusre basin and the basin delineated into seven sub-basin that generate the river network, which also provides the information like stream link, stream order, stream length, slope etc. The calibration was performed using data from 2003 to 2010 and validation for the period from 2011 to 2015 at a daily time step. The model performance was evaluated based on computed statistical parameters. For the calibration period of the discharge and sediment flow, the performance of the model was very good, with a coefficient of determination R2= 0.9528, Nash-Sutcliffe Efficiency NSE = 0.942, RMSE = 0.24, and Percent Bias= 14.78, Similarly, the continuous model performance for the validation period was good, with R2 = 0.8655, NSE = 0.925, RMSE = 0.275 and Percent Bias = 18.03. Also a series of laboratory experiments was also carried out by changing the land use, soil parameter, and rainfall intensity by varying depth of soil sample and slope for comparative study with model but just for performance of apparatus. The performance of rainfall simulator was good. From the experimental method the calculation value of coefficient of determination R2 is equal to 0.67, NSE value is equal to 0.865 and PBIAS was equal to 30. The performance of both experimental and simulated data was satisfactory.

Hydromorphometric Analysis of Wadi Al-Batin Alluvial Fan Using Remote Sensing and GIS Techniques, Southwestern Iraq

Wadi Al-Batin alluvial fan starts from Wadi Al-Rummah in Saudi Arabia and passes through the Kuwait and Iraq borders. The fan represents the southern and northern limits of the Iraq and Kuwait national boundary, respectively, deposited by Wadi Al-Batin on the southern border of the main wide depression formed by the effectiveness of the Abu Jir-Euphrates Fault. The present study aims to evaluate the hydrological properties of the fan and perform a morphometric analysis to find the groundwater flow, structural, and drainage network of the study area based on fieldwork information and satellite images using remote sensing technique and GIS environment. The hydrological analysis shows that the drainage density pattern direction in Wadi Al-Batin alluvial fan is from the southwestern to the northeastern parts of the Wadi Al-Batin alluvial fan. The morphometric analysis results show that the Wadi Al-Batin fan is divided into five watersheds; each has seven stream orders, watershed 1 has the highest value of stream order, and watershed 2 has the lowest value of stream order. The drainage texture value range between fine, moderate, and very fine, which indicates the geological setting of the region consists of the Dibdibba Formation exposed in the study area. Watershed 3 has the highest value, and watershed 1 has the lowest value of stream frequency. The form factor value for all watersheds is less than 0.5 and has an elongated shape. The watershed 3 has the highest basin relief value, while the watershed 4 has the lowest value of basin relief.

Evaluation of Morphometric and Hypsometric Analysis of the Bagh River Basin using Remote Sensing and Geographic Information System Techniques

Water availability and scarcity are impacted by geomorphological changes that occur within a catchment. As a result, determining the influence of geomorphological processes on the catchment's hydrology requires a quantitative study of the catchment geometry. Approaches based on remote sensing (RS) and geographic information systems (GIS) have grown in popularity in recent years because they assist strategists and decision-makers in making accurate and effective choices and plans. For this research, the Bagh River basin was chosen. The study shows that GIS and RS data can be used to analyse and approximate the period and erosional operations' speed in a Bagh river basin for better design and maintenance. The method utilises a 30-metre shuttle radar topography mission digital elevation model (SRTM-DEM) for morphometric parameters and hypsometric analysis extraction that is both operative and time-saving. The thirteen morphometric parameters were applied to the Bagh catchment's linear, shape, and relief aspects. An elongated basin shape is suggested by the Re, Rc, and Ff. Statistical analysis shows that there is a good relationship between stream order and stream length, as well as stream order and stream number. The hypsometric curves' structure as well as estimated hypsometric integral results reflects the Bagh river basin's erosional stages. As a result, the study concludes that morphometric and hypsometric analysis findings may be useful to stakeholders participating in catchment development and management projects.

The Dominant Role of the Water Column in Nitrogen Removal and N2O Emissions in Large Rivers

AbstractRivers are important sites for nitrogen (N) cycling processes. N removal is thought to occur predominantly in the benthic zone and the role of the water column is frequently neglected. Here, we find that the water‐air and sediment‐water fluxes of N2 and N2O decreased, while the water column production increased with stream order through 4‐year observations across six river networks in China. The water column contribution increased with stream order and accounted for more than 50% in rivers above fifth order. The increase in the contact area of suspended sediment (SPS)‐water caused by higher SPS concentrations and river depths resulted in the shift as river size increased. N removal and N2O emissions would be underestimated approximately by 50% if neglecting water column processes for the six river networks. This study highlights the necessity and provides a pathway to incorporate water column processes into models to balance the global N budget.

Basin‐scale estimates of greenhouse gas emissions from the Mara River, Kenya: Importance of discharge, stream size, and land use/land cover

AbstractGreenhouse gas fluxes (CO2, CH4, and N2O) from African streams and rivers are under‐represented in global datasets, resulting in uncertainties in their contributions to regional and global budgets. We conducted year‐long sampling of 59 sites in a nested‐catchment design in the Mara River, Kenya in which fluxes were quantified and their underlying controls assessed. We estimated annual basin‐scale greenhouse gas emissions from measured in‐stream gas concentrations, modeled gas transfer velocities, and determined the sensitivity of up‐scaling to discharge. Based on the total annual CO2‐equivalent emissions calculated from global warming potentials (GWP), the Mara basin was a net greenhouse gas source (294 ± 35 Gg CO2 eq yr−1). Lower‐order streams (1–3) contributed 81% of the total fluxes, and higher stream orders (4–8) contributed 19%. Cropland‐draining streams also exhibited higher fluxes compared to forested streams. Seasonality in stream discharge affected stream widths (and stream area) and gas exchange rates, strongly influencing the basin‐wide annual flux, which was 10 times higher during the high and medium discharge periods than the low discharge period. The basin‐wide estimate was underestimated by up to 36% if discharge was ignored, and up to 37% for lower stream orders. Future research should therefore include seasonality in stream surface areas in upscaling procedures to better constrain basin‐wide fluxes. Given that agricultural activities are a major factor increasing riverine greenhouse gas fluxes in the study region, increased conversion of forests and agricultural intensification has the possibility of increasing the contribution of the African continent to global greenhouse gas sources.

A Large-Scale MaxEnt Model for the Distribution of the Endangered Pygmy Madtom

Abstract Aquatic resource managers often need detailed knowledge of the distributional patterns of imperiled species to facilitate conservation and recovery actions. The Pygmy Madtom Noturus stanauli is a rare catfish in family Ictaluridae that is federally listed as endangered under the U.S. Endangered Species Act. To better understand and forecast its distributional patterns, we assembled Pygmy Madtom occurrence records from past collections in the Clinch and Duck rivers in Tennessee, the only two waterways known to support populations of this species. We entered these presence-only coordinates into the maximum entropy species distribution model integrated with layers from geographic information systems. This approach produced suitability score maps and response curves for each environmental variable: flow rate, water velocity, stream order, gradient, air temperature, precipitation, canopy cover, and drainage area. The variables flow rate, drainage area, and canopy cover were important in predicting the distribution of the Pygmy Madtom throughout its range. The maximum entropy model predicted a high suitability score of Pygmy Madtom occurrence at new sites throughout the Upper Clinch River and the lower middle reaches of the Duck River. Our analytical approach gives managers a large-scale tool to better delineate the Pygmy Madtom's distributional range by identifying and prioritizing locations in the field for sampling at a later date to verify species presence and absence.