High River Flow Research Articles

Karakteristik Hidrologi dan Pengelolaannya dengan Model Hidrologi Soil and Water Assessment Tool Sub DAS Cisadane Hulu

One of the priority watersheds to be managed in Indonesia is the Cisadane watershed due to the high degradation problems. The Cisadene watershed degradation could be indicated by a high river flow during rainy season, low baseflow in dry season, and high erosion and sedimentation. One of the main problems in the Cisadane watershed is a huge landcover changes in the Cisadane Hulu watershed that causes a decrease in water absorption region and a surface runoff. The study aimed to analyze landcover changes in the Cisadane Hulu Watershed during 2013-2018 and analyze the watershed conditions based on their hydrological characteristics. Analysis of landcover changes patterns was carried out by processing spatial data using GIS software. Analysis for hydrological characteristics was conducted by using SWAT modelling (Soil and Water Assessment Tool). The results showed that there were land cover changes during 2013-2018. The most significant landcover changes in the Cisadane Hulu watershed was residential area (455.95 ha). The result simulation scenario of the model SWAT showed scenario 2 was the best scenario for the management of the Cisadane Hulu watershed. The application of Soil and Water Conservation can decrease surface runoff by 32.1% and increase lateral flow by 8.89%. Therefore, it is expected that the results of this SWAT model simulation will be taken into consideration by the local government for the optimal management of the Cisadane Hulu watershed.
 
 Keywords: Cisadane watershed, land cover change, SWAT modelling

Responses of grasses to experimental submergence in summer: implications for the management of unseasonal flows in regulated rivers

River regulation has altered the seasonal timing of flows in many rivers worldwide, impacting the survival and growth of riparian plants. In south-eastern Australia, demand for irrigation water in summer often results in high river flows during a season that would naturally experience low flows. Although unseasonal high summer flows are thought to significantly impact waterways, their effects on vegetation are poorly quantified. We investigated the responses of five grass species commonly occurring in riparian zones to different durations of submergence in summer. We experimentally tested the response of three exotic and two native grasses to four submergence treatments (4 weeks, 8 weeks, 2-week pulses and no submergence), and two levels of shading (no shading and 80% light reduction), over 8 weeks in summer and early autumn. All submergence treatments, including the 2-week pulse, resulted in the death of all plants of three species (Bromus catharticus, Dactylis glomerata and Rytidosperma caespitosum). Lolium perenne exhibited moderate survival rates in the shorter-duration unshaded submergence treatments, while Poa labillardierei largely survived all treatments. Similar responses across species were observed for plant height and biomass, although height generally increased while biomass growth was reduced by shading. These results show that even 2-week periods of summer submergence can reduce growth and cause the death of some riparian grasses. Although some species may survive longer submergence durations, impacts on other aspects of fitness, and ongoing effects of repeated unseasonal submergence, remain uncertain. Our study highlights that the impacts of unseasonal flows require further investigation and careful management.

Dynamics of the Estuarine Turbidity Maximum Zone from Landsat-8 Data: The Case of the Maroni River Estuary, French Guiana

The estuarine turbidity maximum (ETM) zone occurs in river estuaries due to the effects of tidal dynamics, density-driven residual circulation and deposition/erosion of fine sediments. Even though tropical river estuaries contribute proportionally more to the sediment supply of coastal areas, the ETM in them has been hardly studied. In this study, surface suspended particulate matter (SPM) determined from OLI (Operational Land Imager)-Landsat 8images was used to gain a better understanding of the spatio-temporal dynamics of the ETM of the tropical Maroni estuary (located on the Guianas coast, South America). A method to estimate the remotely-sensed ETM location and its spatiotemporal evolution between 2013 and 2019 was developed. Each ETM was defined from an envelope of normalized SPM values > 0.6 calculated from images of the estuary. The results show the influence of the well-marked seasonal river discharge and of tides, especially during the dry season. The ETM is located in the middle estuary during low river-flow conditions, whereas it shifts towards the mouth during high river flow. Neap–spring tidal cycles result in a push of the ETM closer to the mouth under spring-tide conditions or even outside the mouth during the rainy season. An increase in SPM, especially since 2017, coincident with an extension of the ETM, is shown to reflect the periodic influence of mud banks originating from the mouth of the Amazon and migrating along the coast towards the Orinoco (Venezuela). These results demonstrate the advantages of ocean color data in an exploratory study of the spatio-temporal dynamics of the ETM of a tropical estuary, such as that of the Maroni.

Changes to Subaqueous Delta Bathymetry Following a High River Flow Event, Wax Lake Delta, USA

The construction of the subaqueous delta front is foundational to deltaic land building and field data is needed to validate conceptual models of delta front evolution. The bathymetric change that occurred across the entire delta front (~ 75.9 km2) of the Wax Lake Delta (WLD) in coastal Louisiana was measured between February 2015 and July 2016. Sediment removal (− 9.85 × 106 m3) exceeded sediment accumulation (7.64 × 106 m3), making the delta front net-erosional (− 2.21 × 106 m3) despite the occurrence of a flood. These results factor in an estimated 4.28 cm of subsidence during the survey period. Deposition on the delta front was localized around channels and the northern and eastern flanks of the delta whereas erosion was more spatially uniform. This erosion coincides with an anomalously strong winter storm season that may have exported this sediment offshore and is consistent with a growing body of research that identifies winter storms as a significant mechanism for sediment removal from Atchafalaya Bay. Winter storm erosion is crucial to understanding and predicting volumetric growth of the WLD and has important implications to land building from sediment diversions. Future models of deltaic growth need to account for significant volume export and erosive episodes on the delta front.

Speciation and bioavailability of particulate phosphorus in forested karst watersheds of southern Ontario during rain events

Understanding riverine phosphorus (P) dynamics, its transport, and transformation mechanisms from sources in the watersheds to receiving water bodies are essential for the development of effective strategies to decrease excess P loading and reduce eutrophication. Karst watersheds are thought to be especially vulnerable to P pollution due to their geomorphological features. In this study, we investigated the dynamics of particulate P (PP) chemical phases in two karst watersheds from a Great Lakes Area of Concern in southern Ontario (Bay of Quinte, Canada). Suspended solids were collected during different hydrological regimes representing storm events with low and high discharge, and particulate P binding forms were measured using extraction techniques. Our results show that in these karst watersheds, particulate P is dominated by chemical species that are likely to be highly bioavailable and contribute 62–75% to total PP. Concentrations of these bioavailable P binding forms in suspended solids increase two- to three-fold on dry mass basis during periods of high river flow. Electron microprobe and energy dispersive X-ray spectroscopy suggest that the primary carriers of particulate P are aggregates of Fe oxyhydroxides and Al-silicates. Our results underscore the influence of particulate P sources on the ongoing eutrophication in the Bay of Quinte Area of Concern.

Heavy Metals and Related Human Health Risk Assessment for River Waters in the Issyk-Kul Basin, Kyrgyzstan, Central Asia.

The water resources of Central Asia play an important role in maintaining the fragile balance of ecosystems and the sustainable development of human society. However, the lack of research on the heavy metals in river waters has a far−reaching influence on public health and the sustainable development in Central Asia. In order to reveal the possible sources of the heavy metals and to assess the associated human health risks, thirty−eight water samples were collected from the rivers of the Issyk−Kul Basin during the period with low river flow (May) and the period with high river flow (July and August), and the hydrochemical compositions and major ions of heavy metals were analyzed. No changes in hydrochemical facies were observed between the two periods and the river water type was calcium bicarbonate. Carbonate dissolution and silicate weathering controlled the variation of cations and anions in river waters from the Issyk−Kul Basin. There were some differences in the sources of heavy metals in water bodies between the two periods. During the period with low river flow, heavy metals (Cr) were closely clustered with major ions, indicating that they were mainly affected by water–rock interactions. During the period with high river flow, all heavy metals studied in this paper had different sources of major ions, and the heavy metals maybe influenced by human activities. From the human health risk assessment, the hazard quotients for all samples were less than 1, reflecting that there was no noncarcinogenic risk in the river waters of the Issyk−Kul Basin during the two sampling periods. However, the water samples with carcinogenic risk of arsenic exceeding the threshold (10−4) accounted for 21.1% of the total, indicating that there were some certain carcinogenic hazards for human health via water drinking with direct oral ingestion. The results are of certain significance for the utilization and protection of water resources in the basin as well as the protection of public health.

Embracing Uncertainty: Using Probabilistic Weather Forecasts to Make Ensemble Hydraulic Predictions at Remote Low-Water Crossings

AbstractLow-water crossings are structures designed to be overtopped during high river flows. These structures are usually constructed in remote locations, making timely emergency response difficult in case of flooding. In this work, five historical flooding events were hindcasted at a remote low-water crossing in central Texas. An ensemble of model-simulated precipitation forcing cascades uncertainty through hydrologic and hydraulic models. Each precipitation ensemble member corresponds to an independent model run, resulting in an ensemble 24-h streamflow forecast initialized at 0000 UTC. In addition to the hydrologic conditions, the forecast is expanded to predict river hydraulics, through flow velocity and depth. Analysis of the five hindcast events indicates that cascading probabilistic precipitation through hydrologic and hydraulic models adds robustness to river forecasts compared to deterministic methods. The approach provides a means to communicate the uncertainty of predictions through the ensemble spread. Analysis of deterministic hazard thresholds suggest that a hydraulic stability threshold, calculated as the multiplication of flow velocity and depth, is a useful alternative approach to NWS high-water categories for communicating hydrologic/hydraulic risk, as well as associated model uncertainty in the simplest manner possible.

Modeling Mud and Sand Transfers Between a Macrotidal Estuary and the Continental Shelf: Influence of the Sediment Transport Parameterization

AbstractCoastal environments are directly influenced by terrigenous inputs coming from rivers through estuaries. Quantifying the amount of nutrients and contaminants transported by sediments from continental areas to the sea is crucial for marine resources protection. However, the complexity of estuarine dynamics makes it difficult to quantify sediment fluxes from field measurements alone and requires numerical modeling. Thus, using a realistic 3‐D hydrodynamic and sediment transport model, this study aims at evaluating the influence of model empirical parameters on sediment fluxes and estimating uncertainties on mud and sand transfers at a macrotidal estuary mouth. A sensitivity analysis, considering changes in sediment transport parameters, revealed that the system is sensitive not only to settling and erosion parameterizations but also to the spin‐up period and the sediment sliding process. Both estuarine circulation and tidal pumping induce a residual up‐estuary transport, which is balanced by seaward export during spring tides. Although more fine sediments are exported within the surface turbid plume during high river discharge, the net mud transport is directed up‐estuary due to increased baroclinic circulation. Besides, model results highlighted a strong seasonal variability in sediment fluxes with a short and high import during high river flow and a long and weak export during low river flow. Uncertainties associated with the simulated fluxes were about 93% for mud and 51% for noncohesive classes, based on the best performing parameter sets for surface suspended sediment concentrations. These results can be reliably extrapolated to similar macrotidal estuarine systems.

Trace metals in the water and margin sediments of the Rio Doce Basin in Linhares municipality, ES, Brazil

The Rio Doce Basin (DRB) is the largest freshwater source in Espírito Santo (ES) state, Brazil. In November 2015, the disruption of the iron tailings dam in the Mariana municipality, Minas Gerais state, Brazil, severely affected this river. In this study, we showed the trace metals concentrations in the water and margin sediments of the DRB during the dry and wet seasons. This new data was obtained in 2011, prior to the environmental disaster caused by disruption of the dams. We observed Cr, Ni and Pb contaminations in the sediments. The concentrations of these elements in the high river flow (wet season) were higher than the guideline values (GV) of level II and geoacumulation Index (Igeo). However, Fe and Mn concentrations were well above the GV in the wet season. The levels of these two elements were lower than the values found in the region's Haplic Cambisol. Furthermore, the comparison between our data and those of the technical reports released after the dams rupture shows that iron ore mine tailings greatly alter the trace metals concentration in water and sediments. However, we have observed a trend of resilience that requires more systematic and careful studies in DRB.

Anomalies and trends of high river flow under temperate climatic conditions in north-eastern Romania

Abstract Regional water resource management plans include various scenarios related to the anomalies and trends of hydro-climatic parameters. Two methods are used for the identification of the anomalies and trends associated with high flow (annual and seasonal) of the rivers in Eastern Romania, namely the quantile perturbation method (QPM) and the partial trend method (PMT). These methods were selected due to the fact that they are suitable for data sets which do not rely on restrictive statistical assumption as common parametric and nonparametric trend tests do. For six of the nine stations analyzed, the decreasing trend in high extremes for annual high flow based on the PTM is the same as the annual trend obtained with the QPM. Using the PI index (associated with PTM) for the estimation of trend intensity, values between −2.280 and −9.015 m3/s were calculated for the decreasing trend of the annual high flow and between +1,633 m3/s (in autumn) and −9.940 m3/s (in summer) for the seasonal high flow. The results obtained on the anomalies and trends of high river flow may represent a starting point in the analysis of the evolution of water resources and their effective management.

Numerical modelling of suspended-sediment transport in a geographically complex microtidal estuary: Sydney Harbour Estuary, NSW

A numerical study was conducted to investigate the sediment dynamics in a geographically complex estuary, the Sydney Harbour Estuary (SHE). The SHE is a good example of a microtidal estuary, with irregular shorelines and a complex bathymetry, characterized by many headlands and islands forming a meandering main channel. Horizontal sediment transport showed a local estuarine turbidity maximum (ETM) as a result of complex topography, independent of salinity fields and river flows during dry weather. The along-estuary advection of sediment was mainly driven by the mean advection, with a minor contribution by tidal pumping. Mean advection associated with barotropic forcing drives sediment flux seaward in the upper estuary and landward in the middle estuary, leading to a longitudinal convergence of sediment transport, without upstream or downstream migration of ETM during high river flows. The interactions between tidal currents, complex topography and asymmetric vertical mixing led to spring-neap and flood-ebb variations in sediment distribution. The Singular Spectrum Analysis (SSA) method was used to calculate the relative contributions of the identified environmental forcing frequencies (tidal range, tidal frequency, river discharges, wind stress) to the variability in suspended-sediment concentration. Tidal frequency and river discharges were the major contributors to this variability. Tidal range made the highest contribution in the middle estuary, where the ETM was located, driving the spring-neap cycle of the ETM.

Water transfer imposes hydrochemical impacts on groundwater by altering the interaction of groundwater and surface water

How the water transfer imposes impacts on the groundwater in the water-receiving area is still unknown. Here, we employed hydrometric observations, hydrogeochemical analyses and data analysis methods to address this issue, taking one of the Yellow River water transfer project of China for example. We found that the interaction between river and groundwater is totally changed by the water transfer and the impact of the water transfer on groundwater is confined by the high stream gradient. With the water transfer, the natural annual pattern of rainy-season high river flow is inversed with low flow in rainy seasons and high flow during the water transfer. Moreover, the river stage is always higher than the groundwater level throughout the year. The usual bidirectional river–groundwater hydraulic gradient is altered to be a gradient always away from the river. The groundwater directly connects with the river water. The regime of groundwater level follows the change of the river stage, even in the valley side. A long-term standing groundwater mound is formed within the riparian zone due to the continuous recharge from the water-receiving river. The transferred Yellow River water is hydrochemically featured by high EC value and concentrations of Na+ and Cl−. The hydrochemical features of the water-receiving river are obviously changed by the transferred Yellow River water. The hydrochemical impact of the river on the groundwater is mainly confined to the riparian zone and some low-reach transections, despite of the dominated control of the river on the valley groundwater table. The high stream gradient trends to produce the downstream groundwater flow and hinder the lateral groundwater flow from river to valley sides in the upper reaches, responsible for the confined impact on groundwater. Our study highlights that the stream gradient could obviously influence the river water and groundwater interaction promoting or confining the impact of river water on groundwater.

Modelling the effects of climate change on urban coastal-fluvial flooding

AbstractIn coastal floodplains, high river flows and high coastal water levels can result in extensive flooding. Twenty-first century climate change is expected to alter these flood mechanisms. In this study, a coastal city of Cork, Ireland is used as a case study to investigate changes in flood mechanisms, dynamics and extents due to climate change. A hydrodynamic flood model MSN_Flood was used to compute potential future inundation patterns for a range of climate scenarios based on estimates of current, medium-range and high-end projections of extreme river flows and sea levels. Results illustrate that the flood mechanism is critical in controlling patterns and extent of inundation. Peak river discharges are the primary contributor to extreme flood events under the current climate scenario, however, high-end climate change could result in coastal inundation of comparable magnitude. The most extreme flood events affect the entire city centre – occurring as a result of a combination of fluvial and coastal drivers. The interaction of extreme fluvial discharges and coastal water levels is complex and characterised through comparison of multiple scenarios. This research establishes a best practice methodology for assessment of urban coastal-fluvial flood risk under a changing climate and can be used to determine climate-resilient flood management measures.

On a razor's edge: Status and prospects of the critically endangered Bellinger River snapping turtle, Myuchelys georgesi

Abstract In the summer and autumn of 2015, the Bellinger River snapping turtle (Myuchelys georgesi), a narrow‐range endemic of eastern New South Wales, Australia, suffered mass mortality from epidemic disease, apparently caused by a previously unknown virus. Information on the current population size and structure of M. georgesi, and the body condition and growth of the surviving individuals, is needed to support planning of conservation actions. Population estimates are also needed for a sympatric population of the widely distributed Macquarie turtle (Emydura macquarii), which has probably been introduced to the Bellinger River and may threaten the persistence of M. georgesi through hybridization, competition, and disease transmission. Data from five turtle surveys between November 2015 and November 2018 were used to estimate populations of the two species in the Bellinger River by an analysis based on habitat extent and turtle detectability. Changes in the body condition of M. georgesi and the body growth of both species were also assessed. Current populations of ~150 M. georgesi and ~500 E. macquarii are indicated, although the uncertainty of these estimates is high. The estimate for M. georgesi represents a decline of >90% from the historical population. Moreover, about 88% of the surviving M. georgesi are immature, and only about 5% are mature females. However, the body condition of the survivors has improved recently. Growth models suggest that M. georgesi matures later than E. macquarii, which may provide the latter with a competitive advantage. Evidence presented here does not support a previous hypothesis that M. georgesi were predisposed to disease through malnutrition and consequently reduced immune competence caused by high water temperatures and low river flows. Continuing disease, hybridization, and interspecific competition are probably the greatest threats to the persistence of the species.

The Study of the Hurricane-Induced Storm Surge and Bay-Ocean Exchange Using a Nesting Model

Lagoon systems are more heavily impacted by hurricanes, whereas the relevant storm surge modeling studies have been paid little attention to lagoon systems and the storm-induced exchange in lagoon systems is even less understood. To address this gap, a three-dimensional unstructured grid-based model was configured for the Maryland Coastal Bays, a typical lagoon system with two unique inlets (Ocean City Inlet (OCI) and Chincoteague Inlet (CI)), to investigate how Hurricane Sandy impacted inlet dynamics. A nesting model framework was applied to provide the necessary remote forcing from a large model domain and maintain the intricate shoreline and bathymetry of an inner model domain. Results indicated that the flux patterns varied in response to the change in wind direction and rising/falling high water levels from the coastal ocean, rather than a single flow pattern during the passage of Sandy. From October 29 05:00 to 17:00 UTC, mild (> 10 m/s) and strong (> 15 m/s) northerly winds accompanied by the rising high water level from the coastal ocean promoted a mean inflow pattern at the OCI and a mean outflow pattern at the CI. Strong southwesterly winds (> 15 m/s) dominated in the bays from October 30 03:00 to 15:00 UTC. Under strong southwesterly winds and falling high water levels from the coastal ocean, flux was transported landward at the CI and seaward at the OCI. Sensitivity experiments on various storm temporal scales showed that a net inflow pattern occurred in the bays, and the net exchange amounts became smaller in response to longer storm durations. Residual effect of relatively high river flow from Sandy could still influence the salinity at the OCI, whereas the CI salinity was not affected by river flow owing to a long distance between the CI and river locations.

Evaluation on sabo dam construction planning Matakabo River at East Seram island

The Matakabo River is one of the major rivers in Maluku Province that crosses the Eastern Seram Regency. The Matakabo River is currently used for the Matakabo Irrigation Area through Matakabo Weir, with an area of + 3,050 Ha. Considering the number of tributaries entering the Matakabo River system and the risk of changes in land conversion in upstream, the development of Sabo Dam is seen as crucial for securing the water supply to irrigation as well as functioning as flood control. The location of 6 Sabo Dam is in Wai Sop, Wai Mol, Wai Sol, Wai Bemis, Wai Jana, and Wai Ines areas were based on visuals in the field where these areas are vulnerable to erosion and sedimentation. The calculation of flood discharge uses two methods, namely Nakayasu and ITB. Based on the highest river flow and flood capacity in the Q2: 401.68 m3 / second field which is close to the results of the synthetic discharge calculation from the ITB Method. Evaluation of 6 Sabo Dam with 1 Groundsill in Matakabo based on the calculation of the Van Rijn and Meyer Peter Muller (MPM) method will be able to accommodate sediment beds and suspended load around 1,275,958.63 m3 / year or around 0.581 mm / year. With 6 unit additional Sabo Dam locations (vol: 9,563,750 m3) equipped with groundsill, the estimated useful life of the river will not be disturbed by the sediment for about 7.5 years.

Campylobacter jejuni Strains Associated with Wild Birds and Those Causing Human Disease in Six High-Use Recreational Waterways in New Zealand.

Campylobacter jejuni, a leading cause of gastroenteritis worldwide, has been frequently isolated from recreational rivers and streams in New Zealand, yet the public health significance of this is unknown. This study uses molecular tools to improve our understanding of the epidemiology and sources of Campylobacter in recreational waterways, with a view to preventing human infection. Epidemiological and microbiological data were collected between 2005 and 2009 from six high-use recreational waterways in the Manawatu-Wanganui region of the North Island. Campylobacter spp. and C. jejuni were isolated from 33.2% and 20.4% of 509 samples, respectively. Isolation of Campylobacter was observed in both low and high river flows. After adjusting for the confounding effects of river flow, there was a significantly higher likelihood of isolating Campylobacter in the winter month of June compared to January. A high diversity of C. jejuni multilocus sequence types was seen, with the most commonly isolated being the water rail-associated ST-2381 (19/91 isolates [20.9%]), ST-1225 (8/91 isolates [8.8%]), and ST-45 (6/91 isolates [6.6%]). The ST-2381 was found in all rivers, while the most commonly isolated ST from human cases in New Zealand, the poultry-associated strain ST-474, was isolated only in one river. Although the majority of Campylobacter sequence types identified in river water were strains associated with wild birds that are rarely associated with human disease, poultry and ruminant-associated Campylobacter strains that are found in human infection were also identified and could present a public health risk.IMPORTANCE In 2016, there was a large-scale waterborne outbreak of campylobacteriosis in New Zealand, which was estimated to have affected over 5,000 people. This highlighted the need for a greater understanding of the sources of contamination of both surface and groundwater and risks associated with exposure to both drinking and recreational water. This study reports the prevalence and population structure of Campylobacter jejuni in six recreational waters of the Manawatu-Wanganui region of New Zealand and models the relationship between Campylobacter spp. and ruminant-associated Campylobacter and the parameters "sites," "months," and "river flow." Here, we demonstrate that both low and high river flows, month of the year, and recreational sites could influence the Campylobacter isolation from recreational waters. The presence of genotypes associated with human infection allowed us to describe potential risks associated with recreational waters.

Impact of Human Activities and Natural Processes on the Seasonal Variability of River Water Quality in Two Watersheds in Lampung, Indonesia

This study identified seasonal water quality characteristics in two adjacent mountainous rivers (Sangharus and Sekampung Hulu Rivers) in Lampung, Indonesia and determined the impacts of fertilizer application on river chemistry as a result of social forestry management. In 2016, we measured water chemistry and conducted a farmers’ questionnaire survey to obtain information on fertilizer application. The water quality results indicated that several parameters, including nitrate (NO3) and phosphate (PO4), were significantly higher in the Sangharus River than in the Sekampung Hulu River. In addition, several parameters were influenced by dilution from high river flow in the rainy season. Some parameters were likely influenced by the weathering of parent materials. By contrast, electrical conductivity (EC) and NO3 were higher in the rainy season, which was likely linked to the dominant timing of urea fertilizer application during this season. Despite the application of fertilizers in the watersheds, NO3 levels remained below the recommended standard. However, aluminum and iron concentrations were higher than the recommended level for drinking water, which was likely due to elevated soil erosion from improper land management. Therefore, we recommend that effective land management policies be implemented through the adoption of soil conservation practices for nutrient loss prevention.

Tidally resolved observations of organic carbon exchange through Eastern Long Island Sound

Long Island Sound (LIS), is an urban estuary on the US east coast that undergoes seasonal hypoxia in its western and central regions. Approximately 90% of the water exchange between LIS and the adjacent continental shelf, the Mid Atlantic Bight, occurs through its eastern boundary. Recent estimates of organic carbon (OC) export from LIS have shown that this value varies appreciably, both seasonally and inter-annually. In this study, the spatial, tidal, and seasonal variability were resolved by measuring dissolved and particulate organic carbon (DOC and POC) concentrations and currents at a cross-section in eastern LIS near the estuary mouth. Fluxes were extrapolated from these high-resolution observations collected in May, August, and November 2016, and August 2017. In August of 2016 (a low flow year), an OC flux of 41 × 106 kg C month−1 resulted from a net import of DOC and an export of POC. In August of 2017 (an average flow year), there was an OC flux of 30 × 106 kg C month −1 due to both DOC and POC export, indicating significant seasonal and inter-annual variability. The seasonally weighted-average total OC flux for 2016 was −41 × 106 ± 9 kg C yr−1 (net import). Results show that spot sampling in tidal estuaries can lead to spatial and tidal bias in concentrations of DOC (6–15%) and POC (31–18%) under high and low river flow conditions, respectively. This uncertainty is recommended for spot sampling in future OC studies and flux estimates in LIS.

Movement and Apparent Survival of Acoustically Tagged Juveline Late-Fall Run Chinook Salmon Released Upstream of Shasta Reservoir, California

Stakeholder interests have spurred the reintroduction of the critically endangered populations of Chinook Salmon to tributaries upstream of Shasta Dam, in northern California. We released two groups of acoustically tagged, juvenile hatchery, late-fall Chinook Salmon to determine how juvenile salmon would distribute and survive. We measured travel times to Shasta Dam, and the number of fish that moved between locations within Shasta Reservoir. We used mark-recapture methods to determine detection and apparent survival probabilities of the tagged fish as they traveled through five reaches of the Sacramento River from the McCloud River to San Francisco Bay (~590 km) over the two 3-month observation periods. After our first (February) release of 262 tagged fish, 182 fish (70%) were detected at least once at the dam, 41 (16%) were detected at least once downstream of Shasta Dam, and 3 (1%) traveled as far as San Francisco Bay. After the second (November) release of 355 tagged fish, only 4 (1%) were detected at Shasta Dam. No fish were detected below Shasta Dam, so we could not estimate survival for this second release group. The first release of fish was fortuitously exposed to exceptionally high river flows and dam discharges, which may have contributed to the more distant downstream migration and detection of these fish — though other factors such as season, diploid versus triploid, and fish maturation and size may have also contributed to release differences. The reported fish travel times as well as detection and survival rates are the first estimates of juvenile salmon emigration from locations above Shasta Dam in more than 70 years. This information should help inform resource managers about how best to assess juvenile winter-run Chinook Salmon and assist in their reintroduction to watersheds upstream of Shasta Dam.