Coastal River Basins Research Articles

A typical coastal plain taxon in central Brazil: Relationships and description of a new species of non-annual killifish (Cyprinodontiformes; Rivulidae) from the Paraná River basin

We describe a new species of the genus Atlantirivulus from a small first-order stream on the right margin of the Paraná River basin in the Mato Grosso do Sul, Brazil. The region of occurrence of the new species is known to be a hotspot for Melanorivulus species. This area, however, is approximately 700 km away from the record of occurrence of its closest congeners, which are distributed along the Brazilian coast in different hydrographic basins. Atlantirivulus enigmaticus, new species, is distinguished from all congeners by it s unique coloration, which consists of the flank being purplish grey with light green iridescence with brownish red dots scattered along of the body, by the neuromasts of the infraorbital series being aligned around eye, and by the presence of the short ventral process of the posttemporal. The phylogenetic position of the new species within the Atlantirivulus genus was based on molecular phylogenetic analysis using sequences of the mitochondrial gene cytochrome oxidase subunit 1. The results show that the new species is closely related to Atlantirivulus luelingi from the coastal drainages of the Brazilian state Santa Catarina. The phylogenetic position of the new species among congeners endemic to coastal river basins may be related to ancestral connections between coastal drainages and the Paraná River basin. The new species constitutes the westernmost record for the genus, and the first record of Atlantirivulus in the Paraná River basin. Insufficient collection efforts in areas of potential occurrence for the group and extinction processes in the broad region between the locality of the new species and the distribution areas of the remaining species may be a possible explanation for this disjunct distribution.

Spatial variability in water strontium isotopes and trace metals from the Clarence River Basin, New South Wales, Australia

Understanding fish movement in river systems is essential in identifying habitats which are important for species to perpetuate. Water chemistry, paired with fish otoliths, can be used to trace movements among different habitats, although a detailed understanding of spatial variation in water chemistry is first required. To obtain this knowledge, we analysed surface water collected from 59 sites throughout the Clarence River Basin, a coastal river basin in northern New South Wales, Australia. The primary objective was to quantify the spatial variation of trace metals and strontium isotope ratios (87Sr:86Sr) for future and paired use with otolith microchemistry to track fish movement. Using ICP-OES, we identified that some trace metals, particularly strontium and barium as well as 87Sr:86Sr ratios, varied spatially when analysing all water samples and revealed three distinct regions centring around the estuary, interior and outer regions. These differences were driven by variation in the underlying surface geology between the Clarence–Moreton Basin and the New England Block. Tidal influence also affected trace metals and 87Sr:86Sr ratios throughout the estuarine area. We suggest that the level of differentiation identified in the current study has the potential to discriminate broad-scale fish movements among regions/habitats using otolith analysis, with fine scale movements best elucidated using complementary techniques.

Land-Use/Cover Change and Driving Forces in the Pan-Pearl River Basin during the Period 1985–2020

Land use/cover change (LUCC) is a vital aspect representing global change and humans’ impact on Earth’s surface. This study utilized the ESRI Land Cover 2020 and China Land Cover Dataset (CLCD), along with historical imagery from Google Earth, to develop a method for the assessment of land use data quality. Based on the assessment, the CLCD was updated to generate an improved Re-CLCD for the Pan-Pearl River Basin (PPRB) from 1985 to 2020, and to analyze LUCC in the PPRB over the past 35 years. The results indicate the following: (1) Among the seven land uses, built-up land experienced the most dramatic change, followed by cropland, forestland, grassland, shrubland, waterbody, and bare land, with notable increases in built-up land and forestland, and rapid decreases in cropland, grassland, and shrubland. (2) The magnitude of land use changed very widely, with the highest change in the Pearl River Delta, followed by small coastal river basins in southern Guangdong and western Guangxi, the Dongjiang River Basin, the Hanjiang River Basin, the Xijiang River Basin, the Beijiang River Basin, and lastly, Hainan Island. (3) The largest increase happened in built-up land, with a total increase of 12,184 km2, mainly due to the occupation of cropland and forestland, corresponding to the highest decrease in cropland, with a net loss of 10,435 km2, which was primarily converted to forestland and built-up land. The study results are valuable in providing a scientific basis for policy overhaul regarding land resources and management to safeguard ecological balance and promote sustainable development in the Pan-Pearl River Basin.

Integrating spatial stream network models and environmentalDNAto estimate current and future distributions of nonnative Smallmouth Bass

AbstractObjectiveClimate change is fueling the rapid range expansion of invasive species in freshwater ecosystems. This has led to mounting calls from natural resource managers for more robust predictions of invasive species distributions to anticipate threats to species of concern and implement proactive conservation and restoration actions. Here, we applied recent advances in fish sampling and statistical modeling in river networks to estimate the current and future watershed‐scale spatial distribution of nonnative Smallmouth BassMicropterus dolomieu.MethodsWe integrated a spatial stream network (SSN) model of stream temperature, landscape environmental covariates, and Smallmouth Bass occurrence data based on environmental DNA (eDNA) detections to develop an SSN species distribution model (SDM) representing current Smallmouth Bass distributions in the Chehalis River, Washington State, a large coastal river basin of ongoing watershed‐scale restoration. The SDM was informed by spatially intensive eDNA sampling from 135 locations in the main stem and major tributaries. We then applied downscaled climate change projections to the SSN SDM to predict Smallmouth Bass range expansion in the basin by late century.ResultWe identified high levels of spatial autocorrelation at hydrological distances of ≤10 km in our eDNA data set, underscoring the importance of applying an SSN modeling framework. Stream temperature was identified as the most important environmental covariate explaining variability in Smallmouth Bass occurrence. Model predictions estimated that current suitable summer habitat for Smallmouth Bass habitat spans 681 km and is projected to nearly double by late century (1333 km) under a moderate climate change scenario. Current and future suitable habitat for Smallmouth Bass is prevalent in important tributaries for spring Chinook SalmonOncorhynchus tshawytscha, a species of major conservation concern in the Chehalis River and more broadly along the Pacific coast. In both the main stem and tributaries, the SSN SDM predictions of the upstream leading edges of Smallmouth Bass closely align with (within 4.8 km) edges identified by spatially intensive eDNA sampling.ConclusionOur study highlights the value of integrating SSN models with rapidly growing eDNA data sets for accurate and precise riverine fish distribution estimation. Our application provides crucial insights for anticipating the impacts of shifting invasive species on Pacific salmon Oncorhynchusspp. in a warming world.

Thirty-Year Prediction of 137Cs Supply from Rivers to Coastal Waters off Fukushima Considering Human Activities

The Fukushima Daiichi Nuclear Power Plant accident caused an accumulation of 137Cs in coastal sediment. The 137Cs supply from rivers to the ocean can affect the long-term fate of 137Cs in coastal sediment. Since the Fukushima coastal river basins include large decontaminated and evacuation order areas, considering the decontamination work and resumption of agriculture is important for predicting the 137Cs supply. We conducted a 30-year prediction of the 137Cs supply from the Fukushima coastal rivers to the ocean using a distributed radiocesium prediction model, considering the effects of human activities. In river basins with decontaminated and evacuation order areas, human activities reduced the total 137Cs outflow from agricultural lands, urban lands, and forest areas to the rivers and the 137Cs supply to the ocean by 5.0% and 6.0%, respectively. These results indicated that human activities slightly impacted the 137Cs outflow and supply. The 137Cs supply from rivers impacted by the accident to the coastal sediment was estimated to correspond to 11–36% of the total 137Cs in the coastal sediment in the early phase of the accident. Therefore, the 137Cs supply from rivers to the ocean is important for the long-term behavior of 137Cs in coastal sediment.

Anatomy, ecology, and behavior of a new species of Scleronema Eigenmann, 1917 (Siluriformes: Trichomycteridae) from coastal drainages in the southern Brazilian Atlantic Rainforest, with comments on the monophyly and phylogeny of the genus.

A new species of Scleronema (Trichomycteridae) is described from the lowlands of three coastal river basins in the Atlantic Forest of the Santa Catarina state, Southern Brazil. Aspects of the anatomy, reproduction, diet, feeding behavior and habitat of the new species are described and discussed in comparison with related taxa. The conservation status of the new species, which currently faces several threats due to environmental impacts on its region of occurrence, is established. Based on characteristics observed in the new species, as well as in most of its congeners, the phylogenetic position and monophyly of Scleronema are discussed and traits considered synapomorphic for the subgenera Plesioscleronema and Scleronema are reviewed. The monophyly of the genus Scleronema is supported by a new synapomorphy. In addition, two new synapomorphies, one of which based on behavior, are suggested for the subgenus Scleronema, justifying the inclusion of the new species. Within the subgenus Scleronema, the new species is assigned to the S. minutum group, which currently includes the majority of species of the genus, due to the presence of synapomorphic traits related to the body shape, maxillary barbel, skin flap of the opercle, caudal and pectoral fins, as well as osteological features of the lower jaw, hyoid arch, and postcranial axial skeleton. The species herein described differs from all its congeners by a combination of characters from various morphological complexes, which are described in detail using different methodologies, including radiography, whole-specimen clearing and double-staining procedures, and tridimensional computer nanotomography (3D nano-CT).

Evaluating the Efficacy of Different DEMs for Application in Flood Frequency and Risk Mapping of the Indian Coastal River Basin

Floods are among the most occurring natural hazards that cause severe damage to infrastructure and loss of life. In India, southern Gujarat is affected during the monsoon season, facing multiple flood events in the Damanganga basin. As the basin is one of the data-scarce regions, evaluating the globally available dataset for flood risk mitigation studies in the Damanganga basin is crucial. In the present study, we compared four open-source digital elevation models (DEMs) (SRTM, Cartosat-1, ALOS-PALSAR, and TanDEMX) for hydrodynamic (HD) modeling and flood risk mapping. The simulated HD models for multiple flood events using HEC-RAS v6.3 were calibrated by adopting different roughness coefficients based on land-use land cover, observed water levels at gauge sites, and peak flood depths in the flood plain. In contrast to the previous studies on the Purna river basin (the neighboring basin of Damanganga), the present study shows that Cartosat-1 DEM provides reliable results with the observed flood depth. Furthermore, the calibrated HD model was used to determine the flood risk corresponding to 10, 25, 50, and 100-year return period floods calculated using Gumbel’s extreme value (GEV) and log-Pearson type III (LP-III) distribution techniques. Comparing the obtained peak floods corresponding to different return periods with the observed peak floods revealed that the LP-III method gives more reliable estimates of flood peaks for lower return periods, while the GEV method gives comparatively more reliable estimates for higher return period floods. The study shows that evaluating different open-source data and techniques is crucial for developing reliable flood mitigation plans with practical implications.

A new species of Rineloricaria (Siluriformes: Loricariidae) from coastal drainages of Rio de Janeiro, southeastern Brazil

Abstract A new species of Rineloricaria is described from the Iguaçu, Magé, Saracuruna, Guapiaçu, Macacu, Macaé, and Paraíba do Sul River basins in southeastern Brazil based on morphological and molecular data. The new species is diagnosed among congeners by the combination of the following characters: absence of plates in most of the ventral surface of pectoral girdle; snout tip with elliptical naked area reaching posteriorly the anteriormost pore of the infraorbital ramus of sensory canal; dorsal-fin spinelet present; supraoccipital and predorsal plates with smooth keels; five series of lateral plates below the dorsal fin; median and mid-ventral series of plates with well-developed keels. The new species is distinguished from congeners that inhabit the rivers draining the Serra do Mar in Rio de Janeiro state by the partial plate coverage of the ventral surface of the pectoral girdle and the abdomen (vs. pectoral girdle and abdomen completely covered by plates in Rineloricaria nigricauda, R. steindachneri, and R. zawadzkii). The new species shares the absence of plates on the abdominal surface with other species from the Paraná, Uruguay, and other Brazilian coastal river basins.

Declining water resources in response to global warming and changes in atmospheric circulation patterns over southern Mediterranean France

Abstract. Warming trends are responsible for an observed decrease of water discharge in southern France (northwestern Mediterranean). Ongoing climate change and the likely increase of water demand threaten the availability of water resources over the coming decades. Drought indices like the Reconnaissance Drought Index (RDI) are increasingly used in climate characterization studies, but little is known about the relationships between these indices, water resources, and the overall atmospheric circulation patterns. In this study, we investigate the relationships between the RDI, water discharge, and four atmospheric teleconnection patterns (TPs) for six coastal river basins in southern France, both for the historical period of the last 60 years and for a worst-case climatic scenario (RCP8.5) reaching the year 2100. We combine global and regional climate model (CGM and RCM, respectively) outputs with a set of observed climatic and hydrological data in order to investigate the past relationships between the RDI, water discharge, and TPs and to project their potential evolution in space and time. Results indicate that annual water discharge can be reduced by −49 % to −88 % by the end of the century under the extreme climate scenario conditions. Due to unequal links with TPs, the hydroclimatic evolution is unevenly distributed within the study area. Indeed a clustering analysis performed with the RDI time series detects two major climate clusters, separating the eastern and western part of the study region. The former indicates stronger relationships with the Atlantic TPs (e.g. the North Atlantic Oscillation (NAO) and the Scandinavian Oscillation (Scand) patterns), whereas the latter is more closely related to the Mediterranean TPs (Mediterranean Oscillation (MO) and Western Mediterranean Oscillation (WeMO)). The future climate simulations predict an antagonistic evolution in both clusters which are likely driven by decreasing trends of Scand and WeMO. The former provokes a general tendency of lower P in both clusters during spring, summer, and autumn, whereas the latter might partly compensate for this evolution by enhanced precipitation in the eastern cluster during autumn and winter. However, compared to observations, representation of the Mediterranean TPs WeMO and MO in the considered climate models is less satisfactory compared to the Atlantic TPs NAO and Scand, and further improvement of the model simulations therefore requires better representations of the Mediterranean TPs.

Assessment of satellite precipitation products at different time scales over a cyclone prone coastal river basin in India

Abstract Precipitation is a fundamental input for many hydrological and water management studies. With the advancement in science, a variety of satellite precipitation products are available. In this study, the ability of three satellite precipitation products (TRMM-3B42v7, PERSIANN-CDR and GPM-IMERGv6) to capture rainfall were evaluated with ground-based Indian Meteorological Department (IMD) gridded data and also by driving the Soil Water Assessment Tool (SWAT) hydrological model for a cyclone prone coastal river basin in the southeast of India. Results indicate that among the three, GPM-IMERG v6 outperformed in all the statistical metrics, followed by TRMM-3B42 v7 at different temporal scales. GPM-IMERG v6 exhibited the highest correlation coefficient (0.48) and lowest root mean square error (9.52 mm/day), followed by TRMM-3B42 v7 (CC = 0.44, RMSE = 9.58 mm/day) at daily scale. In contrast to other studies in similar regions, IMERGV6 showed better performance than the PERSIANN CDR in detection skills of low, medium and high intensity rainfall events as well as False Alarm Ratio. Hydrological evaluation of the three products using the SWAT model over the study area showed satisfactory results at daily and monthly scale during the calibration and validation period. IMERGV6 is found to have better performance in hydrological evaluation as well.

CHANGES IN PHYSICAL ENVIRONMENT OF THE SOUTHWESTERN COASTAL BANGLADESH: A RIVER BASIN APPROACH

This study deals with the nature and state of geomorphic environmental changes of a coastal river basin at southwestern Bangladesh over a period of three decades (1973-2009). The study concentrates on the Kholpetua river basin, which receive fresh water flow from Betna in the upstream and tidal flow in the middle from Morichapa and finally drains to the Bay of Bengal through Kapotakshi River. The whole Kholpetua basin may be divided into three distinct parts: fresh water upstream, brackish water middle part and saline lower part.
 Large-scale population increase, both in the upper and middle basin; infrastructure development, in the form of road network and introduction of HYV rice in the floodplain of Betna and shrimp farming on the brackish water have lead to the loss of both quality and extent of wetland resources in the basin area, endangering the geomorphological balance in terms of input and output between upstream and downstream. A large section of Betna has dried-up, and most of the tributaries and distributaries of the Morichapa have been silted up, partly because of extensive polders of the sub-basin. As a result, energy exchange (through tide) between basin plains and channels ways has lost vitality.
 Multi-spectral remote sensing data, in conjunction with topographical maps and ancillary data analysis reveals that throughout the basin, a wide range of anthropogenic interference have physically altered the characteristic ecosystem of the basin. The agricultural land is about 79,395 ha. in 1973, which is reduced at about 53,328 ha in 2009. With 1779 to 2001, a strip of about 20 km wide mangrove forest has been disappeared. Such physical alteration has been initiated with the poldering of middle brackish water part of the basin and later with the introduction of extensive shrimp cultivation. Attempt has been made to explore the linkage of upstream landuse activities and drainage alteration to the hydrological and geomorphological behavior of the downstream basin areas, extrapolate ecological sensitivity of the basin.

River flooding on the French Mediterranean coast and its relation to climate and land use change over the past two millennia

River flooding triggered by extreme rainfall events is a major natural hazard that frequently causes fatalities and damages in southeastern France. A 2000-year record of flooding from the Hérault River basin was reconstructed using magnetic susceptibility data from lagoon deposits, supported by documentary databases of floods in coastal river basins from Languedoc over the last centuries. Flooding was particularly important between 800 and 1350 cal CE, i.e. during the warm climatic conditions of the Medieval Climate Anomaly. Moreover, several periods of increased flooding occurred in the 2nd, 6th-7th, 16th, 18th and 20th centuries. Increased flooding was significantly correlated with higher air temperature in the northwestern Mediterranean and with higher sea surface temperature in the Gulf of Lions. The analysis of relationships between river flooding and atmospheric conditions shows that autumn flood events in Languedoc were generally more frequent during the positive phase of the East Atlantic pattern, which is associated with southerly to southeasterly winds in the Gulf of Lions. Besides, increased flooding could also have been controlled by forest decline and human activities after 500 cal CE. Between 1400 and 1800 cal CE, palaeobotanical data show an intensification of land use characterized by an expansion of grasslands and cultivated areas in the coastal lowlands east of the Hérault River. Forest clearings and the development of agriculture seem to have led to a relative increase in river flooding, especially in the late Middle Ages and early modern period.

A century of anthropogenic river alterations in a highly diverse river coastal basin: Effects on fish assemblages

The global increase in human population is driving a continuous conversion of land to anthropogenic uses. This is a major threat to lotic ecosystems worldwide, as it compromises the biotic integrity and health of rivers and streams. Studies in the northern hemisphere have shown that the effects of urbanization on fish assemblages include decrease and/or loss of diversity and abundance of native species, and a proliferation of tolerant exotic species. Such effects have not been widely studied in developing countries like Chile, where urbanization has impacted several river ecosystems. Over decades, the lower zone of the Andalién River in Central Chile has gone over intense non-planned urbanization stemming from the city of Concepción, leading to several physical alterations. The native fish and lamprey fauna of this coastal river basin has been reported as very diverse, with a total of 16 native species. However, this fauna has been affected by multiple effects of different land uses and direct alterations in the riverbed. To study how these fish and lamprey assemblages have changed, this paper compiles records from 1919 to 2018 and analyzes them in relation to the direct and indirect anthropogenic alterations in the basin. The results show a significant reduction in richness and abundance of native species, with only nine species currently. The two migratory lampreys, one of them endemic (Mordacia lapicida), have been extirpated from the Andalién River basin. Conversely, the richness and distribution of introduced species has increased throughout the river basin. The invasive species Gambusia holbrooki, first registered in 1999, is currently the most abundant in the urban zone of the river. Although the more substantial direct alterations of the riverbed occurred in the lower areas, a steeper reduction in native species richness occurred in the middle areas subjected to a long history of agricultural and forestry land use. We suggest the loss of resilience of the river ecosystem, and that the collapse of biodiversity in this river system demonstrates the lack of urban planning and the inefficiency of environmental regulations in protecting native species and ecosystems with high conservation value in Chile.

Identification of Bacterial Flora and Metabolic Function of Sediments in Different Channels of Duliujian River Basin, Tianjin

Bacterial communities are highly sensitive to environmental changes, but their metabolic functions may be convergent under similar ecological conditions. In order to test this environmental attribute of the bacterial community and verify the feasibility in using the bacterial metabolic data to divide functional units at the river basin scale, the surface sediments in three continuous spatial units of the main stream (MS), left tributary (LT), and right tributary (RT) of the Duliujian River basin were selected as the research objects. Therefore, 16S rDNA high-throughput sequencing and the PICRUSt platform were used to analyze the bacterial diversity and metabolic function of sediments in different units. The results showed that there were no significant differences for the Shannon and Simpson indices between the different river channels (P>0.05); however, the bacterial diversity indices of Chao1, ACE, Observed_species, and PD_whole_tree of LT and RT were significantly higher than those of the MS (P<0.05). Moreover, the dominant bacterial phyla were not significantly different among the different river channels. In the present study, a total of 41 metabolic pathways were predicted based on the KEGG database, among which 34 metabolic pathways such as membrane transport, amino acid metabolism, and carbohydrate metabolism were significantly different. The functional metabolic abundance was higher in MS than that in RT and LT (P<0.05); however, there was no significant difference between those of RT and LT (P>0.05). Except for exchangeable phosphorus and nitrate nitrogen, there were no significant differences in other physicochemical properties among the different river channels (P>0.05). Furthermore, pH and iron/aluminum-phosphorus were found to significantly affect the bacterial structure, and SOM and TN were found to significantly affect the bacterial metabolic function. Overall, the sediments of MS and tributaries (LT and RT) of the river were clearly divided into level-1 and level-2 groups, indicating that the metabolic abundance of the bacterial community can be used as the key indicator in the division of functional units at the river basin scale. This study provided a theoretical basis and technical support for ecological functional division and management in coastal river basins.

Allometric releases of nitrogen and phosphorus from sediments mediated by bacteria determines water eutrophication in coastal river basins of Bohai Bay

Although the Chinese government has conducted much work in recent years to reduce land-based pollutant discharge, eutrophication continues to occur frequently in many rivers, estuaries, and coastal waters. This may indicate that sediment is a major source rather than a sink for nitrogen (N) and phosphorus (P). To clarify the endogenous mechanisms of eutrophication in coastal river basins, the eutrophication status, physicochemical properties, and bacterial parameters of overlying waters and sediments in the catchment (CA), estuarine (EA), and offshore (OA) areas in the Duliujian River Basin of Bohai Bay were investigated. The results showed that the eutrophication index (EI) of CA, EA, and OA were 62.71, 57.86, and 36.51, respectively. The EI was more sensitive to increases in P (slope = 3.887) than to increases in N (slope = 0.734) of the overlying water, indicating that P is the main factor driving eutrophication in the coastal river basin. However, a nonlinear relationship was found between P in sediments and overlying waters, suggesting that bacterial mediation may occur during P release. As speculated in this study, P in the overlying water increased more quickly than N with increasing bacterial diversity and metabolic abundance, indicating that the allometric release of N and P mediated by bacteria increases the risk of eutrophication. Redundancy analysis showed that organic matter and total N in sediment have positive effects on bacterial communities, which explains 21.8% and 23.7% variation in bacterial diversity, and explains 31.3% and 7.1% variation in bacterial metabolism. This also suggests that the accumulation of N in the sediment promotes the release of P and further aggravates the eutrophication of water. Therefore, simultaneous control of N and P is necessary to control water eutrophication in coastal river basins.

Impacts of future climate on the hydrology of a transboundary river basin in northeastern North America

Climate change introduces substantial uncertainty in water resources planning and management. This is particularly the case for the river systems in the high latitudes of the Northern Hemisphere that are more vulnerable to global change. The situation becomes more challenging when there is a limited hydrological understanding of the basin. In this study, we assessed the impacts of future climate on the hydrology of the Saint John River Basin (SJRB), which is an important transboundary coastal river basin in northeastern North America. We also additionally performed model benchmarking for the SJRB using four different meteorological forcing datasets. Using the best performing forcing data and model parameters, we studied the water balance of the basin. Our results show that meteorological forcing data play a pivotal role in model performance and therefore can introduce a large degree of uncertainty in hydrological modelling. The analysis of the water balance highlights that runoff and evapotranspiration account for about 99% of the total basin precipitation, with each constituting approximately 50%. The simulation of future flows projects higher winter discharges, but summer flows are estimated to decrease in the 2041–2070 and 2071–2100 periods compared to the baseline period (1991–2020). However, the evaluation of model errors indicates higher confidence in the result that future winter flows will increase, but lower confidence in the results that future summer flows will decrease.

From local measures to regional impacts: Modelling changes in nutrient loads to the Baltic Sea

Study RegionOur study region is the Baltic Sea Drainage Basin (BSDB), which covers an area of 1.8 Mio km2 distributed over 14 countries in northern Europe. Study FocusWe use a large-scale hydrological and nutrient transport model (E-HYPE) to model basin-wide impacts of measure scenarios on the Baltic Sea, where eutrophication is a critical issue for the marine ecosystem. We constructed measure scenarios based on stakeholder acceptance, established in workshops in different regions around the Baltic. These measures include local stream reach to catchment scale measures aiming to reduce nutrient transport into the stream network (buffer strips, stormwater ponds) and measures aiming to reduce regional nutrient source releases (fertiliser leaching rates, rural household emissions). New Hydrological Insights for the RegionNutrient load reductions are often needed to reduce eutrophication and improve overall surface water quality in fresh-water and enclosed bays and seas, where dilution is limited and load emissions have long residence times. To reduce riverine nutrient loads, remediation measures are necessary, e.g. establishment of buffer strips or improved wastewater treatment. Such measures are, however, typically not designed to target nutrient load reductions at sea outlets, but rather focus on local improvements. Here, we show that measures, notwithstanding other meliorating ecosystem benefits, must include reductions in load emissions across large basin areas to impact integrated net loads into coastal sea basins, because reduction measures that only target nutrient delivery to the stream network typically cannot be implemented in a significant enough proportion of the total drainage area of large coastal river basins. Our impact scenarios show BSDB-wide nutrient reductions of up to 9 % for nitrogen and phosphorus compared to a reference scenario, if load emissions are reduced in the scenario assumptions.

Flood hazard mapping for data-scarce and ungauged coastal river basins using advanced hydrodynamic models, high temporal-spatial resolution remote sensing precipitation data, and satellite imageries

This paper presents an integrated approach to simulate flooding and inundation for small- and medium-sized coastal river basins where measured data are not available or scarce. By coupling the rainfall–runoff model, the one-dimensional and two-dimensional models, and the integration of these with global tide model, satellite precipitation products, and synthetic aperture radar imageries, a comprehensive flood modeling system for Tra Bong river basin selected as a case study was set up and operated. Particularly, in this study, the lumped conceptual model was transformed into the semi-distributed model to increase the parameter sets of donor basins for applying the physical similarity approach. The temporal downscaling technique was applied to disaggregate daily rainfall data using satellite-based precipitation products. To select an appropriate satellite-derived rainfall product, two high temporal-spatial resolution products (0.1 × 0.1 degrees and 1 h) including GSMaP_GNRT6 and CMORPH_CRT were examined at 1-day and 1-h resolutions by comparing with ground-measured rainfall. The CMORPH_CRT product showed better performance in terms of statistical errors such as Correlation Coefficient, Probability of Detection, False Alarm Ratio, and Critical Success Index. Land cover/land use, flood extent, and flood depths derived from Sentinel-1A imageries and a digital elevation model were employed to determine the surface roughness and validate the flood modeling. The results obtained from the modeling system were found to be in good agreement with collected data in terms of NSE (0.3–0.8), RMSE (0.19–0.94), RPE (− 213 to 0.7%), F1 (0.55), and F2 (0.37). Subsequently, various scenarios of flood frequency with 10-, 20-, 50-, and 100-year return periods under the probability analysis of extreme values were developed to create the flood hazard maps for the study area. The flood hazards were then investigated based on the flood intensity classification of depth, duration, and velocity. These hazard maps are significantly important for flood hazard assessments or flood risk assessments. This study demonstrated that applying advanced hydrodynamic models on computing flood inundation and flood hazard analysis in data-scarce and ungauged coastal river basins is completely feasible. This study provides an approach that can be used also for other ungauged river basins to better understand flooding and inundation through flood hazard mapping.

Enhancement of sustainable agricultural production system by integrated natural resources management framework under climatic and operational uncertainty

Constant decline of freshwater reserve poses a major challenge for coastal agricultural systems. The present study focuses on the integrated land and water resources management framework under operational and climatic uncertainties to achieve sustainable agricultural production in a tropical coastal river basin. To capture the operational and climatic uncertainties, Grey Linear Programming (GLP) and Acceptability Constrained Linear Programming (ACLP) optimization models were developed. GLP can consider both climatic and operational uncertainties. However, ACLP can accommodate operational uncertainty only. Groundwater model was coupled within the optimization models (GLP and ACLP) by a grey response matrix. The SWAT estimated recharge rates were utilized in the MODFLOW model as the groundwater flux. The calibrated (R2 = 0.80) and validated (R2 = 0.84) groundwater flow simulation model was utilized to generate the grey response matrix. The eight plausible scenarios were tested for GLP (Scenarios I, II, III, IV, V, VI, VII, VIII) and ACLP (Scenarios Ia, IIa, IIIa, Iva, Va, VIa, VIIa, VIIIa) with groundwater table fluctuation (GWTF) method and grey response matrix as drawdown constraint. A reduction in net annual return was observed in Scenarios III and IV (with grey response matrix) in comparison to Scenarios I and II (with groundwater table fluctuation) under any change in crop yield. Decrease was more prominent for Rabi (winter) season compared to Kharif (monsoon) season. Futuristic Scenarios (V, VI, VII, VIII) considering crop yield reduction showed a possible change required in cropping pattern (specifically rice area reduction in Kharif Season). ACLP model results showed similar trends. Results suggest that the GWTF method overestimates the groundwater availability compared to the physically based simulation model. Obtained land and water resources management plans were cross-validated for the safe yield limit using MODFLOW simulation model.

Filling distribution gaps: Two new species of the catfish genus Cambeva from southern Brazilian Atlantic Forest (Siluriformes, Trichomycteridae)

The fauna and flora of the Brazilian Atlantic Forest have been intensively inventoried since the 19thcentury, but some components of this rich biota are still poorly known, and some areas have been poorly sampled. Recent studies on a rich collection of mountain catfishes of the genusCambevahave revealed a high diversity of species still undescribed in the region. Here we provide formal descriptions for two of these species, found in areas inserted in a broad gap of the presently known genus distribution. The first one is endemic to small coastal river basins of Santa Catarina state, southern Brazil; it is tentatively placed in an intrageneric clade, also includingC. castroi,C. davisi,C. guareiensisandC. zonata, by all sharing the presence of a flat small process on the dorsal margin of the quadrate, laterally overlapping metapterygoid and situated just posterior to the syncondrial joint between the metapterygoid and the quadrate. Phylogenetic relationships of the second new species, endemic to the Rio Itajaí-Mirim basin, are still obscure, but it shares a derived morphology of the mesethmoid with some species of theC. baliosgroup. Although species ofCambevahave little external morphological variation when compared to other trichomycterine groups, the present study once more shows the importance of recording and using osteological characters to diagnose externally similar trichomycterine species.