River Drainage Research Articles

Terrestrial paleoclimate changes recorded by Pleistocene red earth deposits at the Gaolingpo Paleolithic site, Bose Basin, South China

The Quaternary river sediments at Gaolingpo, Bose Basin, Guangxi Province contain stone hand adzes and microliths of Paleolithic and Neolithic ages, providing information about the effect of climatic and environmental changes on hominin and early modern human activities. Gaolingpo is a representative Paleolithic site in the Bose Basin, containing numerous stone artifacts of different ages in the red earth sediments. We examined the clay mineralogy and geochemistry of the Gaolingpo profile using X-ray diffractometry (XRD), diffuse reflectance spectroscopy (DRS), and X-ray fluorescence (XRF) spectroscopy with the goal of reconstructing paleoclimatic and environmental changes in the study area since the late Early Pleistocene. Within this soil profile, kaolinite and vermiculite increase and illite decreases gradually up section. The red earth sediments exhibit uniform chondrite-normalized rare earth element (REE) distribution patterns, which are similar to those of upper continental crust (UCC), post-Archean Australian shale (PAAS), loess and paleosol of the Chinese Loess Plateau (CLP), and Yangtze River deposits. These confirm that the Gaolingpo red earth sediments originated from fine materials of well-mixed weathered continental crust within the upper Pearl River drainage basin. The chemical index of alteration (CIA) of the Gaolingpo sediments is 86.4–92.1, indicating that the sediments have undergone intense chemical weathering. Based on changes in clay mineral contents and geochemical compositions through the profile, the paleoclimatic evolution of the Gaolingpo area since the late Early Pleistocene can be divided into two stages with four sub-stages: (1) a generally humid climate prevailed during stage I can be further divided in two sub-stages. Sub-stage Ia was temperate with an alternating dry and wet climate, while sub-stage Ib was a transition to a warmer temperate climate. (2) A subtropical humid climate prevailed during stage II and transitioned to a cooler climate in the later stage. In this episode, sub-stage IIa was the warmest and the most humid period since the late Early Pleistocene in Bose Basin, and Stage IIb was a transition to a relatively cooler subtropical climate. This climate pattern is compatible with the regional palynological record at Chongzuo, south Guangxi and is in general agreement with the δ18O records from cave stalagmites in southern China, but is inconsistent with the δ18O record at ODP Site 1148 in the northern part of the South China Sea, though the age constraints limit a precise correlation. This reflects the predominant influence of Qinghai-Tibetan Plateau uplift on East Asian climate since the late Early Pleistocene. The development of warm, humid, and only weakly fluctuating climate conditions in the Bose Basin was favorable for early hominin settlement.

Non-native freshwater fish from drainages of Rio Grande do Sul State, Brazil

The present study catalogues exotic and allochthonous fish species found in the three main freshwater river drainages of Rio Grande do Sul State using records of scientific collections and literature, and discusses the main impacts caused by their introduction in natural environments. Ten exotic species are found in the area, i.e., Clarias gariepinus, Coptodon rendalli, Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Ictalurus punctatus, Micropterus salmoides, Oncorhynchus mykiss and Oreochromis niloticus, belonging to five orders, nine genera and seven families. These fishes are native from African, Asian, European and North American countries. The eight allochthonous species, i.e., Acestrorhynchus pantaneiro, Hoplerythrinus unitaeniatus, Hoplias lacerdae, Megaleporinus macrocephalus, Piaractus mesopotamicus, Pachyurus bonariensis, Serrasalmus maculatus, and Trachelyopterus lucenai, belong to three orders, eight genera, and six families, are native from the Río La Plata basin, that includes the Río Uruguay, and have been all registered in the Laguna dos Patos. Two of these species are further recorded in the Rio Tramandaí system (A. pantaneiro and T. lucenai). The study also presentes a brief history of the first records of exotic species in the state and in the country, and their main vectors of introduction. According to the records of exotic species in scientific collections, the two exotic species with the highest number of records in the country are tilapias Coptodon rendalii (508 records) and Oreochromis niloticus (376 records), and most records occurred in the last two decades. The two carps Cyprinus carpio and Ctenopharyngodon idella are the only exotic species recorded in the three main drainage basins of the state. In addition, we warn about the importance of studies about the biology and negative impacts of exotic species over native species on the understanding of management in wild environments.

A Small Warm Tributary Provides Prespawning Resources for Colorado Pikeminnow in a Cold Dam-Regulated River

Abstract Riverine habitat mosaics, including tributaries, are an important reason the Green River subbasin supports the largest remaining population of federally endangered Colorado Pikeminnow Ptychocheilus lucius in the Colorado River Basin. Upstream Colorado Pikeminnow distribution is limited by Flaming Gorge Dam and few typically occurred in the reach immediately downstream of the dam, which is the reach most affected by thermal and hydrologic alterations. However, fish captures and passive integrated transponder (PIT) antenna sampling of previously tagged individuals from 2011 to 2021 revealed seasonal congregations of up to 75 Colorado Pikeminnow annually in the mouth of Vermillion Creek, a small tributary in the regulated reach. Approximately 11% (N = 93 individuals) of the entire 2017–2018 Green River basin population were encountered in Vermillion Creek over the 11-y study, an underestimate of use considering that untagged fish were not detected by antennas. Colorado Pikeminnow used Vermillion Creek primarily when Green River spring flows from Flaming Gorge Dam were high and cold in May through mid-June when the confluence was a large, deep backwater warmer than the main channel and supported forage fishes. Intra-annual encounters revealed seasonal residence times for individual Colorado Pikeminnow up to 91 d, and multiple inter-annual encounters indicated site fidelity. Frequent detections of individual Colorado Pikeminnow in a Yampa River spawning area soon after their detections in Vermillion Creek indicate this tributary may be an important resource for reproductive adults. The intensive and basin-wide PIT tagging and detection program for Colorado Pikeminnow enhanced our understanding of the importance of small habitat nodes such as Vermillion Creek in the Green River drainage network. Understanding and protecting these seasonally available riverine habitat mosaics used for prespawning conditioning may assist with recovery of Colorado Pikeminnow.

Chemical Weathering and CO2 Consumption Inferred from Riverine Water Chemistry in the Xi River Drainage, South China.

Hydrochemistry and strontium isotope data were analysed in water samples from the Xi River Drainage system to reveal the spatial and seasonal variations in chemical weathering, associated CO2 consumption fluxes, and their control factors. The main ions were Ca2+, Mg2+, and HCO3-, which are characteristic of a drainage system on carbonate-dominated bedrock. The dissolved loads were derived from four major end-member reservoirs: silicate, limestone, dolomite, and atmosphere. The silicate weathering rates (SWRs) increased downstream from 0.03 t/km2/year to 2.37 t/km2/year. The carbonate weathering rates (CWRs) increased from 2.14 t/km2/year in the upper reaches, to 32.65 t/km2/year in the middle reaches, and then decreased to 23.20 t/km2/year in the lower reaches. The SWR values were 281.38 and 113.65 kg/km2/month during the high- and low-water periods, respectively. The CWR values were 2456.72 and 1409.32 kg/km2/month, respectively. The limestone weathering rates were 2042.74 and 1222.38 kg/km2/month, respectively. The dolomite weathering rates were 413.98 and 186.94 kg/km2/month, respectively. Spatial and seasonal variations in chemical weathering were controlled mainly by lithology, vegetation, and climate (temperature, water discharge, and precipitation). The CO2 consumption flux by chemical weathering was estimated at 189.79 × 109 mol/year, with 156.37 × 109 and 33.42 × 109 mol/year for carbonate and silicate weathering, respectively. The CO2 fluxes by chemical weathering are substantially influenced by sulfuric acid in the system. The CO2 flux produced by sulfuric acid weathering was estimated at 30.00 × 109 mol/year in the basin. Therefore, the Xi River Basin is a CO2 sink with a net consumption of CO2 flux of 3.42 × 109 mol/year.

Complete mitochondrial genome of Rectorisluxiensis (Teleostei, Cyprinidae): characterisation and phylogenetic implications.

Mitochondrial genomes (mitogenomes) are widely used in scientific studies on phylogenetic relationships, molecular evolution and population genetics. Here, we sequenced and analysed the mitogenome of Rectorisluxiensis, a Yangtze River drainage endemic, but threatened cyprinid fish of Labeoninae. The complete mitogenome of R.luxiensis was 16,592 bp in length, encoding 13 protein coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs) and a control region. The mitogenome showed a high A+T content (58.2%) and a positive AT-skew (0.10) and negative GC-skew (-0.25) base composition pattern. All the 13 PCGs were found to start with ATG codons, except for the COXI, in which GTG was the start codon. The ratio of non-synonymous and synonymous substitutions (Ka/Ks) of all the 13 PCGs were less than 1, indicating negative or purifying selection evolved in these genes. Comparatively speaking, the evolutionary rate of ATP8 was the fastest and ND4L was the slowest. All tRNAs could fold into a typical cloverleaf secondary structure, except tRNASer1 that lacked a dihydrouridine arm. Phylogenetic relationships, based on the PCGs dataset of 91 mitogenomes of Labeoninae, showed that R.luxiensis grouped with Rectorisposehensis and they formed a monophyletic Rectoris. However, many non-monophyletic genera were revealed in labeoninae fishes, such as Cirrhinus, Decorus, Garra, Labeo and Pseudocrossocheilus, which indicated that the validities of some traditional genera required a further check. This study reported the complete mitogenome of R.luxiensis for the first time, which provided valuable data for future molecular evolution and conservation related studies of Rectoris and other species in Labeoninae.

Using a New Cenozoic Glacial History Paradigm to Explain Saline-Smoky Hill River Drainage Divide Area Topographic Map Evidence: Kansas, USA

A recently proposed glacial history paradigm (new paradigm) explains previously ignored Saline-Smoky Hill River drainage divide area topographic map drainage system and erosional landform evidence by headward erosion of the east-oriented Saline River valley across large and prolonged south-oriented meltwater floods which flowed in complexes of closely-spaced anastomosing channels. The eastward sloping drainage divide extends from the Saline River’s western Kansas headwaters between the Saline River (north) and the Smoky Hill River (south) until in central Kansas the Smoky Hill River turns in a southeast and then north direction to join the Saline River with their combined flow continuing as the Smoky Hill River in an east direction to join the Republican River with the combined flow then becoming the Kansas River. Evidence for closely-spaced south-oriented anastomosing channels consists of previously undescribed low points (divide crossings) which are found along the drainage divide and which link north-oriented Saline River tributaries with south-oriented Smoky Hill River tributaries. Evidence that Saline River valley headward erosion beheaded and reversed south-oriented anastomosing channels also consists of the numerous low points along the drainage divide and of barbed tributaries to the now north-oriented Saline River tributaries which suggest large south-oriented meltwater floods extended much further west than commonly accepted glacial history interpretations permit. The topographic map evidence is consistent with the new paradigm interpretation that a thick continental icesheet by its weight and by deep erosion created and occupied a deep “hole” as massive south-oriented meltwater floods flowed across the rising deep “hole” rim until the deep “hole” rim uplift diverted the floodwaters toward what became the deep “hole’s” only remaining southern outlet (the Mississippi River valley).

Assessment of Microbial Contamination in the Infulene River Basin, Mozambique

Water microbial contamination is one of the major threats to human health. The study focus is on Infulene River Basin, a urban catchment with mainly informal settlements, with limited water supply and sanitation. In the catchment there are two wastewater treatment plants, one hospital and beer factory located on the banks of the main stream; water from this stream is used for urban agriculture and domestic uses by some dwellers. These factors present a significant health risk from water-borne diseases. At the moment there is limited knowledge about the level of microbial contamination of the different sources of water at the disposal of the communities. Thus, a preliminary study on fecal microbial contamination was conducted targeting the Infulene River and the drainage system from the nearby Maputo city draining into the system, with additional investigation on the drinking water provided by the city water supply company. The quantification of Total Coliforms (TC) and Escherichia coli (EC) was conducted at several sampling locations. Results were compared with official drinking water standards. Eighty two percent (82%) and 61% of Infulene river water and drainage water samples were positive for TC (105 to 109 NPN/100 mL) and EC (105 to 107 NPN/100 mL), respectively. For drinking water samples, 63% and 23% were positive for TC (up to 6000 NPN/100 mL) and EC (up to 1000 NPN/100 mL), respectively. Higher microbial contamination was found in neighborhoods with the poorest sanitation and shallow groundwater, i.e., Chamanculo, Xipamanine, Mafalala, Aeroporto and Maxaquene, a situation that was more expressive during the rainy season. Overall, the study confirmed the high vulnerability to microbial contamination of all sources investigated due to poor sanitation and lack of drainage infrastructure. The risks to human health might be even higher considering that contaminated water is used for gardening of vegetable watering and domestic use.

Revisiting Kelly Forks (10CW34): Current and Future Research at a Western Stemmed Tradition Occupation in the Nez Perce-Clearwater National Forest, Idaho, USA

ABSTRACT The Kelly Forks Work Center Site (10CW34) is a deeply buried and stratified late Pleistocene to late Holocene aged archaeological site located on the North Fork Clearwater River in the Nez Perce-Clearwater National Forest, Idaho. Previous research suggested the site contained buried archaeological components associated with the Western Stemmed Tradition. Here, we report preliminary results of ongoing reinvestigation of the site to assess the stratigraphy, geochronology, archaeology, and traditional Nez Perce use of the Clearwater River drainage.

Filling in a biogeographic gap: the first Trichomycteridae from the Parnaíba River basin (Siluriformes: Trichomycteridae)

Abstract Trichomycterid catfishes have long been considered as absent in the Parnaíba River basin, Northeastern Brazil, in what constitutes their most conspicuous gap in geographic distribution. Herein we report on the first occurrence of the family in that basin. The new species is described from the riacho da Volta, right tributary to the upper rio Parnaíba, Piauí State. It is distinguished from its congeners by the combination of two or three pairs of ribs; 36–38 post Weberian vertebrae; a color pattern composed of round, similar-sized, non-coalescent spots; I,5 pectoral-fin rays; the first haemal arch on the 5th or 6th vertebrae; and the first completely fused (to the tip) haemal spine on the 15th vertebra. A putative autapomorphy is the partial (minimally 50% of their length) or total fusion between the anterior arms of the basipterygium. Preliminary evidence suggests that the new species can be related to northern South American forms, a pattern that fits the general Amazonian relationships of the fishes in the Parnaíba River drainage. Although the new species fills in an important qualitative gap in trichomycterid continental distribution, the taxon is apparently rare and extremely restricted in distribution, with the type series being its only record so far. The paucity of trichomycterids in the Parnaíba remains a puzzling biogeographical phenomenon.

Description of two new species of Bujurquina (Teleostei: Cichlidae) from the Bolivian Amazon

Abstract Two new species of Bujurquina are described from the Bolivian Amazon basin. The first new species inhabits the Beni River drainage and is distinguished from its congeners in the combination of the following characters: longer snout, deeper head, body and caudal peduncle, shorter pectoral fin, more scales in the E1 series, discontinuous longitudinal band, bars 5 and 6 not fused, preopercular spot and coloration pattern on flank scales absent. The second new species inhabits the Mamoré and Iténez river drainages, and differs from its congeners in the combination of the following characteristics: longer and deeper head, longer snout and pectoral fin, deeper caudal peduncle, fewer scales in the E1 series and lower lateral line, preopercular spot absent, bars 6 and 7 separated from longitudinal band and discontinuous longitudinal band. An identification key for species reported from Bolivia and complementary morphological data for B. oenolaemus and B. vittata are presented.

Length-weight relationship, sex ratio, and diet of three fish species (Actinopterygii: Teleostei) in streams of the Pomba River basin, Paraíba do Sul river drainage, Southeastern Brazil

This study aimed to estimate the parameters of length-weight relationship, sex ratio, and diet of three freshwater fish species that inhabit streams in the Pomba River basin (Rio de Janeiro, Brazil). Fishes were sampled with seine nets (2.0 × 1.20 m, 2 mm mesh size) and dip nets (0.46 × 0.33 m, 2 mm mesh size) from October to December 2018. Measurements were taken for total length (TL - 0.1 cm precision) and total weight (TW - 0.01 g precision). Growth model parameters were estimated. This study provides new length-weight relationship data for Deuterodon intermedius (Eigenmann, 1908), Australoheros paraibae Ottoni & Costa, 2008, and Hypostomus punctatus Valenciennes, 1840. All of them ingested a wide variety of food items, including plant material like algae, animal material such as terrestrial and aquatic insects, and undefined matter such as detritus or mud. The three species showed a higher number of females. Our study provides basic information for functional diversity studies, as well as for future investigations associated with the evaluation of anthropic impacts, either occasional or chronic, on the fish assemblage structure of the Pomba River basin.

Redescription of Astyanax brevoortii (Gill, 1858) (Characiformes, Characidae) and description of three new species of Astyanax subgenus Poecilurichthys, from Caribbean Sea basins, Venezuela

In Astyanax (Poecilurichthys), we recognize six species-groups defined by the distribution of melanophores on the body: 1. bimaculatus; 2. rupununi; 3. abramis: 4. orthodus; 5. asuncionensis; and 6. anterior, which are named for a representative species. Astyanax brevoortii1 is redescribed using specimens from Trinidad (including types). This species, as a member of the bimaculatus species-group, is distinguished by lacking a concentration of melanophores outlining the scale margins on the sides of body. Three new species of the bimaculatus species-group are described: A. caroni n. sp. from the Caroni River drainage, which differs in having all of the teeth of the internal premaxillary series pentacuspid (vs. heptacuspid), and the length of the caudal-peduncle spot which is less than two times the eye diameter (vs. at least twice eye diameter). A. garuttii n. sp. from the San Juan River and Gulf of Cariaco drainages is distinguished by osteological characters and by morphological characters identified by principal component analysis. A. cuyuni n. sp. from the Cuyuni River (Essequibo River Basin), is distinguished by having a foramen in the pterotic and sphenotic bones (vs. absent), and the shape of the last two neural spines that form a posteriorly directed arc, that covers the epineurals.

Analysis of a new species of the Astyanax orthodus group (Characiformes: Characidae) from the upper Madre de Dios River, Amazon River Basin, Peru

Based on ten specimens, using morphometric, meristic and osteological characters, Astyanax leoni n. sp. is described from the upper Madre de Dios River drainage, Amazon River Basin of Peru. A. leoni n. sp. is a member of the Astyanax orthodus species group and is distinguished (except from A. multidens, A. villwocki, and A. gandhiae) in having an inconspicuous rod-shaped stripe on the caudal peduncle that extends anteriorly on top of a silver lateral stripe. It differs from the species mentioned above as follows: from A. multidens by having shorter chevron marks that cover up to only two series of scales above and below the apex of the chevron (vs. chevrons taller, with extensions that cover three series of scales); from A. villwocki by having chevron markings along the entire body (vs. no chevrons on the caudal peduncle); It differs from Astyanax gandhiae in having the caudal peduncle spot extending anteriorly to beyond the tip of the dorsal fin (vs. caudal peduncle spot not reaching anteriorly to tip of dorsal fin), and not of a uniform width as in A. villwocki. A dichotomous key to the species of Astyanax orthodus group is included.

Late Quaternary fluvial terrace formation in the Luan River drainage basin, north China and its possible linkages with climate change and tectonic activation

Late Quaternary fluvial terrace formation in the Luan River drainage basin, north China and its possible linkages with climate change and tectonic activation

Redescription of Hemibrycon jelskii, with comments on H. huambonicus, and description of five new species from the Amazon River basin (Characiformes: Characidae: Stevardiinae)

We examined 407 specimens and images of Hemibrycon jelskii1 and H. huambonicus2 (31 types and 376 non-types) and analyzed them using four analytical approaches: (i) traditional morphometry, (ii) morpho-geometric analysis, (iii) comparison of meristics (scales and fin rays), and (iv) comparison of color and pigment patterns. Our study determined that only 18 individuals from the 28 type specimens have characters that correspond with the description of H. jelskii. Hemibrycon jelskii was described from specimens of unknown, possibly multiple origins, raised in aquaria by Konstanty Jelski. A high morphological disparity exists among the individuals that make up the type series, so it is assumed that they are different forms, probably from different locations in the Huambo River drainage, in the Peruvian Andes. The reported variation in morphological and pigmentation characters observed in the type specimens is due to two main facts: 1) the incorrect taxonomic identification of one lot, which is a curimatid, Cyphocharax sp., and 2) the probability that specimens of the type series were collected from different localities. In addition, morphological differences were observed in the type series of H. huambonicus, consisting of three specimens in two lots. Our study also revealed five new species of Hemibrycon described herein.

Simulating Dynamic of Suspended Sediment Flow Based on Data of Primorskaya Water Balance Station

Soil loss rate, suspended load, and suspended sediment discharge were simulated for the drainage basin of the Komarovka R., located at the territory of the former Primorskaya Water Balance, Russian Far East. The study was based on an open-code SWAT model. The model was calibrated and verified using archive measurement data on sediment load and suspended sediment discharge at PWBS by data of Tsentral’nyi hydrological gage (157 km2). The simulation efficiency of the suspended load and suspended sediment discharge corresponds to categories satisfactory and higher. On the average for the drainage basin, the rate of soil washout is 11–12 t/ha per year. The washout rate is maximal in the period of active snow melting. The mean monthly value for April–May is 75 thous. t. The mean annual washout is 171 thous. t, and the maximal is 800 thous. t/year. The mean annual runoff of suspended sediments in the outlet section of the drainage basin is 2.6 thous. t. The highest monthly values of sediment runoff correspond to the period of summer floods in August, when with average of 1 thous. and maximum of 7.7 thous. t. The obtained data on the heterogeneity of the spatial distribution of the simulated values of washout rate are in good agreement with the landscape and climatic features of runoff formation in the drainage river basin. The major errors in the estimation of sediment load are due to the simulation quality of the hydrological regime and dynamics of runoff components that form flood hydrographs.

Comparative biogeography of North American turtle faunas: Neogene regionalization

North America harbors substantial species diversity in nonmarineturtles (includes tortoises and terrapins), much of which arose in the Neogene Period (Miocene and Pliocene epochs) within Kinosternon, Emydinae, Trachemys, Pseudemys, Graptemys, and Gopherus. This diversity is distributed among 16 biogeographical provinces, but natural, hierarchical relations among provinces are unresolved. We used three-item analysis to identify such relations among provinces for these clades, following a recent, relatively complete phylogenetic reconstruction. The final three-item analysis identified 53,353 taxon‐area cladograms — free of paralogy and multiple areas on a single branch. The final intersection tree has a retention index of 73.6% and a completeness index of 75.4%, both indicating moderately strong congruence in patterns among turtle clades. All six turtle clades support some nodes on the intersection tree, which is divided into eastern and western forks. The crown group on the eastern fork includes four provinces almost entirely east of the Mississippi River drainage, whereas the western fork is split into wet tropics and aridlands sub-forks. The east-west transition zone spans the Mississippi River drainage and Great Plains. Our summary of divergence estimates and geological history suggests that although phylogenetic synchrony existed between select taxa, there was general asynchrony because provincial turtle faunas developed over an extended period (Neogene). Temperature-sensitive distributions of various taxa responded to climatic cycles by expanding during periods of warming, but contracting during periods of cooling. Grassland expansion and geomorphic change in the Neogene created provincial boundaries that, although sometimes crossed under favorable climates, more commonly acted as dispersal barriers. Despite asynchrony in faunal assembly, existence of shared patterns reveals natural relations among provinces, producing a regionalization for North American turtles, useful for understanding their evolution as well as the biogeography of North America.

Comparison of SMOS, SMAP and In Situ Sea Surface Salinity in the Gulf of St. Lawrence

ABSTRACT The Gulf of St. Lawrence (GSL) is an Eastern Canada semi-enclosed sea under the influence of the freshwater discharge from the Great Lakes – St. Lawrence River drainage basin. Studying the variability of oceanographic conditions in the GSL under a changing climate is important for ecosystem and fisheries management. To supplement the available in situ sea surface salinity (SSS) measurements with satellite SSS data, this study compares all available years of Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active and Passive (SMAP) satellite SSS to in situ SSS observations. Despite the relatively cold water and proximity to land and sea ice, the satellite SSS is able to capture the interannual variability and annual cycle of SSS in the GSL, with correlations ranging from 0.80 to 0.85 in the Southern GSL, and 0.22 to 0.77 in the Northern GSL. All satellite SSS data products were able to detect the very low salinity year of 2017 in the Southern GSL.

A greater source of methane from drainage rivers than from rice paddies with drainage practices in southeast China

Rice paddies and rivers draining agricultural watersheds have been documented as two major sources of atmospheric methane (CH4), while parallel flux measurements have been rarely taken on CH4 from rice paddies against the drainage rivers in agricultural watersheds. Moreover, the drainage events during the rice growing season deliver sufficient organic and inorganic nutrients to rivers, which makes there an increasing concerned source of atmospheric CH4. Here, we compared CH4 emissions from rice paddies and the associated rivers draining agricultural watersheds by a parallel field experiment in southeast China. Over the whole rice–growing season (June–November), CH4 fluxes from drainage rivers averaged 25 mg m–2 h–1, which were 82 % higher than those from rice paddies (13.7 mg m–2 h–1). Besides the dependence of riverine CH4 fluxes on water dissolved oxygen (DO), both ecosystem CH4 fluxes were significantly correlated with water/soil dissolved organic carbon (DOC), oxidation-reduction potential (Eh) and the microbial functional genes that drive CH4 production or uptake [methanogens (mcrA and methanogenic archaeal 16S rRNA) and methanotrophs (pmoA)]. Our results highlighted that the CH4 mitigation potential benefited from the drainage practice in rice paddies might have been totally offset by its induced increases in CH4 emissions from rivers draining agricultural watersheds at the regional scale.

Clarifying water clarity: A call to use metrics best suited to corresponding research and management goals in aquatic ecosystems

Clarifying water clarity: A call to use metrics best suited to corresponding research and management goals in aquatic ecosystems