Primary Tributary Research Articles

Spatial and temporal assessment of environmental contaminants in water, sediments and fish of the Salton Sea and its two primary tributaries, California, USA, from 2002 to 2012

The Salton Sea, the largest inland surface water body in California, has been designated as a sensitive ecological area by federal and state governments. Its two main tributaries, the New River and Alamo River are impacted by urban and agriculture land use wastes. The purpose of this study was to temporally and spatially evaluate the ecological risks of contaminants of concern in water, sediments and fish tissues. A total of 229 semivolatile organic compounds and 12 trace metals were examined. Among them Selenium, DDTs, PAHs, PCBs, chlorpyrifos and some current-use pesticides such as pyrethroids exceeded risk thresholds. From 2002 to 2012, measurements of chlorpyrifos in sediments generally declined and were not observed after 2009 at the river outlets. In contrast, pyrethroid concentrations in sediments rose consistently after 2009. In water samples, the outlets of the two rivers showed relatively higher levels of contamination than the main water body of the Salton Sea. However, sediments of the main water body of the Salton Sea showed relatively higher sediment concentrations of contaminants than the two rivers. This was particularly true for selenium which showed reductions in concentrations from 2002 to 2007, but then gradual increases to 2012. Consistent with water evaluations, contaminant concentrations in fish tissues tended to be higher at the New River boundary and at the drainage sites for the Alamo River compared to sites along each river. The persistent contaminants DDTs, PAHs, chlorpyrifos and several pyrethroid insecticides were associated with the toxicity of sediments and water collected from the rivers. Overall, assessment results suggested potential ecological risk in sediments of the Salton Sea as well as in water and fish from the two rivers.

Apportionment of bioavailable phosphorus loads entering Cayuga Lake, New York

AbstractThe integration of the phosphorus (P) bioavailability concept into a P loading analysis for Cayuga Lake, New York, is documented. Components of the analyses included the: (1) monitoring of particulate P (PP), soluble unreactive P (SUP), and soluble reactive P (SRP), supported by biweekly and runoff event‐based sampling of the lake's four largest tributaries; (2) development of relationships between tributary P concentrations and flow; (3) algal bioavailability assays of PP, SUP, and SRP from primary tributaries and the three largest point sources; and (4) development of P loading estimates to apportion contributions according to individual nonpoint and point sources, and to represent the effects of interannual variations in tributary flows on P loads. Tributary SRP, SUP, and PP are demonstrated to be completely, mostly, and less bioavailable, respectively. The highest mean bioavailability for PP was observed for the stream with the highest agriculture land use. Point source contributions to the total bioavailable P load (BAPL) are minor (5%), reflecting the benefit of reductions from recent treatment upgrades. The BAPL represented only about 26% of the total P load, because of the large contribution of the low bioavailable PP component. Most of BAPL (>70%) is received during high flow intervals. Large interannual variations in tributary flow and coupled BAPL will tend to mask future responses to changes in individual inputs.

Velocities of the Amery Ice Shelf's primary tributary glaciers, 2004–12

AbstractMonitoring the rate of ice flow into ice shelves is vital to understanding how, where and when mass changes occur in Antarctica. Previous observations of ice surface velocity indicate that the Amery Ice Shelf and tributary glaciers have been relatively stable over the period 1968 to 1999. This study measured the displacement of features on the ice surface over a sequence of Landsat 7 images separated by approximately one year and spanning 2004 to 2012 using the surface feature tracking software IMCORR. The focus is on the region surrounding the southern grounding zone of the Amery Ice Shelf and its primary tributary glaciers: the Fisher, Lambert and Mellor glaciers. No significant changes in surface velocity were observed over this period. Accordingly, the velocity fields from each image pair between 2004 and 2012 were used to synthesize an average velocity dataset of the Amery Ice Shelf region and to compare it to previously published velocity datasets and in situ global positioning system velocity observations. No significant change in ice surface velocities was found between 2004 and 2012 in the Amery Ice Shelf region, which suggests that it continues to remain stable.

Quantifications and water quality implications of minerogenic particles in Cayuga Lake, New York, and its tributaries

An individual particle analysis technique, scanning electron microscopy interfaced with automated image and X-ray analyses (SAX), was applied to characterize the minerogenic particle populations of Cayuga Lake (New York) and its primary tributaries and quantify their effects on common water quality metrics. The primary summary metric of SAX results is demonstrated to be the total projected area of minerogenic particles per unit volume of water (PAVm). PAVm is documented to be linearly related to the minerogenic components of particulate phosphorus (PPm), turbidity (Tn/m), and the light scattering coefficient, and inversely related to Secchi depth (SD). SAX is demonstrated to support partitioning of PAVm into contributions of multiple size and geochemical classes. Clay mineral particles dominated in the tributaries and the lake, although they shifted somewhat to smaller sizes (1–15 μm) in the lake. Levels of PAVm were higher in a lake area that adjoins the tributary inputs than in pelagic waters, particularly after runoff events. This increased PAVm degraded water quality, including higher PPm and Tn/m and lower SD relative to the pelagic waters, although diminished (still recognizable) signatures are documented lake-wide. Advantages of SAX over gravimetric analyses for the minerogenic particle populations of lakes include (1) improved analytical performance, (2) insights from the more robust size and composition information, (3) theoretical advantages for optical impacts, and (4) stronger relationships with water quality metrics.

High frequency measurement of nitrate concentration in the Lower Mississippi River, USA

Nutrient concentrations in the Mississippi River have increased dramatically since the 1950s, and high frequency measurements on nitrate concentration are required for accurate load estimations and examinations on nitrate transport and transformation processes. This three year record of high temporal resolution (every 2–3 h) data clearly illustrates the importance of high frequency sampling in improving load estimates and resolving variations in nitrate concentration with river flow and tributary inputs. Our results showed large short-term (days to weeks) variations in nitrate concentration but with no diurnal patterns. A repeatable and pronounced seasonal pattern of nitrate concentration was observed, and showed gradual increases from the lowest values in September (during base-flow), to the highest in June – which was followed by a rapid decrease. This seasonal pattern was only moderately linked with water discharge, and more controlled by nitrogen transformation/export from watershed as well as mixing patterns of the two primary tributaries (the upper Mississippi and the Ohio Rivers), which have distinctly different nitrate concentrations and flow patterns. Based on continuous in situ flow measurements, we estimated 554–886 × 106 kg of nitrate-N was exported from the Mississippi River system during years 2004–2006, which was <9% and <16% lower than U.S. Geological Survey’s (USGS) estimates using their LOADEST or composite methods, respectively. USGS methods generally overestimated nitrate loads during rising stages and underestimated the loads during falling stages. While changes in nitrate concentrations in large rivers are generally not as responsive to alterations in diurnal inputs and/or watershed hydrology as small rivers, high-frequency water quality sampling would help in monitoring short-term (days to weeks) variations in nutrient concentration patterns and thus improve the accuracy of nutrient flux estimates.

Editor’s Perspective: The Isthmus of Uncertainty

Whether in the atrium or the ventricle, macro–reentrant tachyarrhythmias are among the most challenging arrhythmias to eliminate with ablation. Namdar et al,1 in this installment of Teaching Rounds in Cardiac Electrophysiology, present and explain insightful findings from a patient with a complex macro–reentrant circuit encountered after prior cardiac surgery. They take us through a step-by-step approach and their thought process in identifying the eventual curative ablation target. Article see p 171 In addition to the outstanding educational points specific to this case, several important principles for mapping and ablating macro–reentrant arrhythmia when multiple boundaries and isthmuses are possible can be gleaned from their report. Does identifying a site of early activation from an activation map of the arrhythmia facilitate ablation? Unlike focal tachycardias, reentrant arrhythmias have no true early or late sites of activation. Timing is based completely on the empirical choice of a reference electrogram and the setting of the mapping window.2 Although this principle is apparent and most experienced electrophysiologists will either map and define the entire circuit of tachycardia or use entrainment mapping to identify appropriate sites for ablation, several corollaries to this principle are equally important but not as readily recognized.3,4 ### P-Wave Morphology P-wave vector and morphology (or QRS morphology in the case of ventricular tachycardia) can be invaluable in estimating location of origin for a focal arrhythmia. With macro–reentry however, there is not necessarily a true onset for the P wave (or QRS). Thus, although patterns that have been identified as characteristic for cavotricuspid isthmus–dependent flutter are suggestive of the arrhythmia mechanism, general analysis of the flutter-wave morphology for other macro–reentrant arrhythmias and even common cavotricuspid isthmus–dependent arrhythmias in the presence of extensive atrial disease or prior surgery or ablation is often of little value. When an isoelectric segment is noted in …

Impacts of climate variability and human activity on streamflow decrease in a sediment concentrated region in the Middle Yellow River

The Kuye River is the primary tributary located in the sediment concentrated regions in the Middle Yellow River in China. Significant decrease in streamflow has been observed in the Kuye River. The non-parametric Mann-Kendall test was applied to detect the change in annual streamflow for the period of 1960 to 2006. Mean annual streamflow in the Kuye River was 84.9 mm from 1960 to 1979 (period I), while it decreased to 58.2 mm from 1980 to 1998 (period II) and 20.5 mm from 1999 to 2006 (period III), respectively. The climate elasticity method and the hydrological modeling method were individually employed to assess the impact of climate variability and human activities on the decrease in streamflow . The results showed that climate variability was responsible for 29.6 and 27.1 % of the streamflow decrease from the climate elasticity method and the hydrological modeling method, respectively; while human activities accounted for 70.4 and 72.9 % of the streamflow decrease in period II. In period III, climate variability contributed 40.9 and 39.3 % of the streamflow decrease from the climate elasticity method and the hydrological modeling method, respectively; while human activities accounted for 59.1 and 60.7 % of the streamflow decrease. Therefore, human activities were the main reason of the streamflow decrease. Soil conservation measures (planting trees, improving pastures, building terraces and sediment-trapping dams) and coal mining led to the streamflow reduction in the Kuye River.

Polyhalogenated aromatic hydrocarbons in surface sediments from Three Gorges Reservoir

This study was conducted to investigate the current contamination status of polyhalogenated aromatic hydrocarbons (PHAHs) in sediments from the mainstream and 22 primary tributaries of the Yangtze River in the Three Gorges Reservoir region. To accomplish this, the concentrations of 22 polybrominated biphenyl (PBB) congeners, 27 polybrominated diphenyl ether (PBDE) congeners, and 27 polychlorinated biphenyl (PCB) congeners in sediment samples were measured by GC-MS/MS. The result showed that the observed values of PBBs and PBDEs were 22.41 and 35.24 pg g−1 dw, respectively. PBB1, 31 and 103 were the predominant PBB congeners, while PBDE28, 47, 77 and 99 were the predominant PBDE congeners. PBB209 and BDE209 were detected in >39% of the samples, with geometric means 2.43 and 11.92 pg g−1 dw, respectively. PCBs were found to be the predominant compounds in sediment samples among the three PHAH subfamilies, with a geometric mean of 1,231.11 pg g−1 dw, and PCB8, 18, 28, 52 and 66 were the primary PCB congeners. The measured levels of PHAHs were compared with results recently reported in the literature and their respective sediment quality guidelines recommended by the USEPA. The levels of PHAHs in the present study were generally lower than their respective threshold-effect levels, or were comparable to those reported in relatively uncontaminated freshwater samples from other regions. Taken together, these results suggest that, in the reservoir, toxic biological effects on aquatic biota in response to PHAHs contamination of sediments can be expected to be negligible.

Seasonal stream habitat of adult Sakhalin taimen, Parahucho perryi, in the Bekanbeushi River system, eastern Hokkaido, Japan

AbstractBehavioural tracking of endangered adult Sakhalin taimen (Parahucho perryi) by acoustic telemetry was conducted in the Bekanbeushi River system that flows through eastern Hokkaido in 2008–2010. A total of 39 tracked P. perryi showed extensive use of the river system, both upstream and downstream, regardless of the month or year. No tracked adult P. perryi stayed in the ocean for more than 1 day. Some of the fish (20%) dwelled in upstream habitat consistently from spring to autumn, while 40% of individuals showed wide utilisation of the entire upstream and downstream systems. Although 39.4% of tracked fish utilised two or more primary tributaries to the main river, 6.1% used only the main river system. Distinct variability was observed between individuals based on the proportion of time spent in each stream reach (up‐, mid‐, and downstream). A trend was observed in 2008 and 2010 showing that tracked fish moved to the upper stream reaches when water temperatures downstream increased. This trend was not observed in 2009 when the summer water temperature downstream was more than 2 °C below average when compared to 2008 and 2010. Our results suggest that adult P. perryi in the Bekanbeushi River system exhibit high behavioural plasticity, that is, the fish can select habitats based on their own individual requirements. Our results also demonstrate the importance of physical continuity among river reaches both upstream and downstream such that P. perryi does not experience barriers in moving to optimal habitats.

Sex difference in polybrominated diphenyl ether concentrations of walleyes

Polybrominated diphenyl ether (PBDE) concentrations were determined for mature male and mature female walleyes (Sander vitreus) sampled from the Saginaw Bay population during 2007. PBDE concentrations in prey fish caught in the Saginaw River, the primary tributary to Saginaw Bay, and in Saginaw Bay during 2005 and 2007 also were determined. Mature male and mature female walleyes averaged 70.3ng/g and 24.8ng/g, respectively, in ΣPBDE, which was equal to the sum of concentrations of six PBDE congeners (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, and BDE-154). This sex difference was likely due to males spending more time in the Saginaw River system than females. Prey fish captured in the Saginaw River were roughly ten times higher in ΣPBDE than those caught in Saginaw Bay. BDE-47 was the predominant congener in both walleyes and prey fish, and this congener contributed about 50%, on average, to ΣPBDE. Congener profiles differed significantly between the two sexes of walleyes. In contrast, congener profiles of the prey fish did not differ significantly between the river-caught fish and the bay-caught fish. One plausible explanation for these congener profile results was that net trophic transfer efficiencies of PBDEs to walleyes from their prey were similar for all congeners except BDE-28, and that diet composition differed between the two sexes of walleyes.

Temporal inequality in catchment discharge and solute export

A framework is developed for characterizing the temporal inequality of stream discharge and solute loads to receiving waters using Lorenz diagrams and the associated Gini coefficient, G. These descriptors are used to illustrate a broad range of observed flow variability with a synthesis of multidecadal flow data from 22 rivers in Florida. Multidecadal phosphorus load data from four of the primary tributaries to Lake Okeechobee, Florida, and sodium and nitrate load data from nine of the Hubbard Brook, New Hampshire, long‐term study site catchments are used to examine the relation between the inequality of flow and load. The intra‐annual loads to Lake Okeechobee are shown to be highly unequal, such that 90% of the annual load is delivered in as little as 15% of the time. Analytic expressions are developed for measures of inequality in terms of parameters of the lognormal distribution under general conditions that include periods of zero flow. In cases where variability of concentrations is low compared to that of flows (chemostatic conditions), such as for phosphorus in the Lake Okeechobee basin and sodium in Hubbard Brook, the temporal inequality of flow is a strong surrogate for load inequality. However, in cases where variability of concentrations is high compared to that of flows (chemodynamic conditions), such as for nitrate in the Hubbard Brook catchments, load inequality is greater than flow inequality. The measured degree of correspondence between flow and load inequality for these data sets is shown to be well described using the general inequality framework introduced here.

Mining acid rock passive treatment for closure of a lignite mine in Spain: Achieving necessary water quality for discharge into lakes and drinking water reservoirs

AbstractThis study discusses the theory behind the passive treatment systems for controlling the acid drainage of the Meirama mine and illustrates how this approach can be applied to obtain the necessary water quality to allow the discharge of the drainage into the Barcés River, which is the primary tributary to the drinking water supply Cercebre Reservoir (Spain). Characterization analysis was carried out for 13 sampling sites, with a total of 52 tests and 780 determinations and analyses. Passive systems have been monitored over 27 sampling days, with a total of 186 samples taken, plus 1914 determinations and analyses. The passive tests treated a total of 415 000 m3 of water. The tests were designed based on several factors relevant to the sites, including hydrological characteristics, drainage composition, flow rate, climatic conditions and previous company technology experience. Different weather conditions were considered, including drought, flood and normal conditions. The horizontal system (Line A) produced a 55 mg L−1 increase in alkalinity, and iron, aluminium and manganese reductions of 90%, 91% and 30%, respectively. The eliminations for the vertical system (line B) were 40 g/m2 × day acidity, and iron, aluminium and manganese reductions of 71%, 80%, and 60%, respectively. The annual average precipitation was 150 mm, and annual average temperature, 12.4°C. It was found during the course of this study that the development and application of passive treatment systems have the following advantages: (i) they can substantially reduce costs during the active mining phase, being a pre‐treatment of the wastewater treatment plant, raising the pH and reducing the metal cation content and (ii) It is not feasible to actively operate wastewater treatment plants because, after mine closure, the land must be rehabilitated with the property then being used for other purposes. The acid rock drainage, which is a major concern, will continue to be generated for many years, requiring aftercare monitoring of these waters. Based on the results of this study, it was concluded that passive systems can achieve the necessary water quality to allow the drainage to be discharged into the Barcés River, and subsequently into the drinking water supply Cercebre Reservoir.

Non-contrast magnetic resonance imaging for guiding left ventricular lead position in cardiac resynchronization therapy

A left ventricular lead position concordant to viable myocardium at the site of latest mechanical activation is associated with a better response to cardiac resynchronization therapy (CRT). The present study aimed to guide left ventricular (LV) lead implantation into a vein over the area of latest mechanical activation with no transmural scar as determined by radial strain measured by non-contrast magnetic resonance imaging (MRI). Patients admitted for CRT implantation underwent MRI on the day before pacemaker implantation. Time to peak radial strain in ventricular segments was measured to define the site of latest mechanical activation. Areas with peak radial strain less than 16.5% were defined as transmural scar. Venograms were visualized to define the optimal vein for LV lead positioning. Echocardiograms, 6-min hall walk test, and NYHA class were obtained at baseline and after 6 months of follow-up. Sixteen patients were included. In nine patients the lead was positioned at the primary target site, and in six patients a secondary was used owing to phrenic nerve stimulation (one patient), unstable lead position (two patients) and lack of suitable vein (three patients) at the primary target site. In three patients pre-implant MRI changed the implanters primary target vein. Non-contrast MRI can be used to detect the site of latest mechanical activation by radial strain to guide LV lead positioning in candidates for CRT. Image guided LV lead implantation in CRT patients may in some patients change the primary target tributary of the coronary sinus.

English

Although recent construction of tailings dams has dramatically decreased solids discharge rates, pyrite-dominated polymetallic sulfide mine tailings persist as the primary in-stream substrate of the upper Rio Pilcomayo, a crucial water resource in the arid Southeastern Bolivian highlands. Rio Tarapaya is a primary tributary of the upper Rio Pilcomayo that drains Potosi, Bolivia, where intensive hard rock mining and ore processing has occurred for five centuries. In conjunction with standard water quality testing, field leach tests were performed on saturated sediment within the active channel as well as unsaturated sediment deposited on the banks of the Rio Tarapaya during high- flow events. Results indicate that weathering of in-stream tailings is contributing to deleterious concentrations of various ecotoxic metals. Of special concern is the mobilization of metals and acidity with increases in water level, such as occurs at the onset of the rainy season. The highly seasonal, arid climate provides for long periods of mineral oxidation followed by large precipitation events which mobilize weathered oxidation products. The reactivity of the millions of tonnes of in-stream tailings in Rio Tarapaya suggests that the upper Rio Pilcomayo will remain severely degraded for the foreseeable future and remediation will continue to be a daunting task.

Surficial Geologic Map of the Upper Conejos River Drainage, Southeastern San Juan Mountains, Southern Colorado, USA

Please click here to download the map associated with this article. During the Last Glacial Maximum (LGM), the San Juan Mountains of southern Colorado, USA were covered by one of the largest ice caps in North America. The deposits formed subsequent to LGM retreat provide a record of the interaction between post-LGM climate change and late Quaternary landscape evolution. In order to determine the role of post-LGM climate change in alpine landscape modification, a high resolution surficial geologic map was produced for the four primary tributaries and the main stem of the upper Conejos River watershed in the southeastern San Juan Mountains. Soil development, 14C ages, and stratigraphic relationships provide evidence for three distinct periods of hillslope, alluvial fan and/or stream terrace deposition (∼9.5–13 k.y.a., ∼1.2–2.1 ybp, and modern) in the upper Conejos River watershed. We interpret the first of these periods to be the result of paraglacial hillslope adjustment. The lack of subsequent early to mid-Holocene deposits suggests that an interval of relatively warm climate coincided with landscape stability. We attribute late-Holocene deposition to an interval of cooling that has been documented in nearby proxy records. Modern deposits in the field are limited both in extent and occurrence, and are interpreted to be the result of erosion localized outcrops of soft, volcaniclastic bedrock. In addition to post-LGM depositional units, relatively flat erosional bedrock surfaces that sit 1–100 m above the modern stream, and that are capped with glacial till, are present in all four tributaries of the field area. These are interpreted as former glacial valley bottoms. The modern streams are incised into the floors of these hanging valleys. Headward erosion presumably initiated following deglaciation and is still active today. Modern channel long profiles differ between the four tributaries. We attribute the variability of incision into these hanging valleys to differences in basin size and bedrock erodibility, with more extensive incision occurring in basins characterized by more erodible rocks (poorly welded volcaniclastics) and larger basin size. Overall we see that the post-LGM landscape evolution in this alpine environment is the result of the complex interaction of Holocene climate change acting on basins of varying size and bedrock type.

Effects of tributary inputs on nutrient export from the Mississippi and Atchafalaya Rivers to the Gulf of Mexico

In order to better understand the seasonal patterns of nutrient loadings from the Mississippi River to the Gulf of Mexico, nutrient mass balance analyses were performed for the Mississippi River system to separate the effects of primary tributary inputs from in-channel processes. Our results showed that seasonal changes in dissolved inorganic nutrients resulted from conservative mixing of primary tributaries. Maximal values of nitrate plus nitrite (NO3+2) and soluble reactive phosphorus (SRP) fluxes during May through July were largely attributed to inputs from the upper Mississippi River (UMR), which was highest in NO3+2 and SRP levels and contributed more water during this period. Mass balances also showed net losses of particulate nitrogen and phosphorus (29% and 18%, respectively), with the highest values occurring during the falling stage. We speculate that one possible reason was retention of coarse suspended sediments that were mainly derived from the Missouri River. The loss of dissolved organic nitrogen and phosphorus was also apparent (∼12% and 20%, respectively), and the largest loss occurred during summer. This study highlights the importance of divergent processes in controlling different forms of nutrients in large rivers.

Century-long record of Mo isotopic composition in sediments of a seasonally anoxic estuary (Chesapeake Bay)

A double-spike method was used to obtain Mo isotope data for sediments and waters of the seasonally anoxic Chesapeake Bay, and its primary tributary, the Susquehanna River. The dissolved Mo distribution in the estuary is non-conservative, reflecting minor Mo loss to the sediments, although removal of Mo to the sediments does not have a large influence on the isotopic composition of the water column. The δ 98Mo of dissolved Mo in most of the estuary is dominated by seawater. Six samples with salinity > 15 have an average δ 98Mo = + 2.17‰ (± 0.12), which agrees well with a δ 98Mo value for the CASS-4 seawater standard of + 2.23‰. A single sample of Susquehanna River water has a δ 98Mo of + 1.02‰, consistent with recent findings of positive δ 98Mo in rivers worldwide. Susquehanna river sediments, in contrast, have δ 98Mo ∼ − 0.1‰. The difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin. The δ 98Mo values for estuarine sediments are offset from values in the overlying water. Most samples deposited before 1925 have δ 98Mo less than 0‰, similar to the Susquehanna sediments. Subsequently, there is an increase in the variability of δ 98Mo, with values ranging up to + 0.8‰. The transition to increased variability coincides with the onset of authigenic Mo deposition, which was previously attributed to escalating summertime anoxia. Authigenic Mo concentrations correlate poorly with δ 98Mo in core samples, suggesting that independent mechanisms influence the two parameters. Authigenic Mo concentrations may be controlled by shifting pore water H 2S levels, while δ 98Mo may be primarily affected by annual variations in Mn refluxing.

Turbidity and temperature patterns in a reservoir and its primary tributary from robotic monitoring: Implications for managing the quality of withdrawals

A robotic water quality monitoring network, consisting of 2 in-reservoir profiling platforms and a unit positioned in the primary tributary, was used to document patterns of temperature (T) and turbidity (Tn) and the impact of runoff events on Tn levels over the spring to fall interval of 3 years. The patterns were evaluated in the context of water quality goals for T and Tn for reservoir withdrawal and potential benefits of specified management alternatives. Exceedences of a proposed withdrawal T goal of 21.1 °C (70 °F) and a conservative representation of the Tn goal of 15 NTU were demonstrated. The exceedences occurred in late summer during intervals of extensive drawdown for T and irregularly following runoff events for Tn. Conspicuous increases in Tn in the tributary and lacustrine portions of the reservoir were demonstrated in response to all monitored runoff events (n = 34). Lacustrine levels exceeded 75 NTU following several major events. The turbidity load from the tributary usually enters the reservoir as a turbid density current during runoff events, at a depth predicted well by stream temperature. The high frequency and vertical resolution attributes of the robotic monitoring (2 profiles per day for reservoir deployments) were invaluable in resolving impacts because these were usually attenuated within a week following events. The diminishment of reservoir Tn levels following events was demonstrated to be well represented by a first-order loss rate. The loss rate for the largest runoff event of the study (return interval ~25 y) was more than an order of magnitude lower than any other, indicating a difference in settling attributes of turbidity-causing particles for this extreme case. Benefits from a shift to delayed withdrawals for the existing intake, or installation of a multi-level intake facility, for improving status with respect to the water quality goals are suggested from the monitoring data. However, continuously meeting the Tn goals for particularly severe events may not be feasible through these approaches.

Insights for the structure of a reservoir turbidity model from monitoring and process studies

An array of in situ and laboratory measurements were made and in situ settling velocity experiments were conducted to support identification of model structure features necessary to simulate transient turbidity impacts in Schoharie Reservoir, NY, from runoff events. The program included: (1) extended deployments of recording instruments measuring temperature (T) and specific conductivity (SC) in the primary tributary and the reservoir surface waters; (2) automatic sampling of the tributary during runoff events for laboratory turbidity (Tn) measurements; (3) collection of vertically detailed profiles of T, SC, and the beam attenuation coefficient at 660 nm (c660; a surrogate of Tn) at multiple sites along the longitudinal and lateral axes of the reservoir with rapid profiling instrumentation; (4) chemical and morphometric characterizations of individual particles from the tributary and reservoir during dry weather conditions and for a runoff event with scanning electron microscopy coupled with automated image analysis and X-ray microanalysis (SAX); and (5) in situ measurements of settling velocity (SV) as a function of particle size with a LISST-ST®. A strong positive relationship between Tn, associated primarily with clay minerals, and tributary flow (Q), and a negative relationship between SC and Q, were reported. The entry of the primary tributary as a plunging turbid density current because of its lower T, and associated spatial and temporal patterns in c660 and SC imparted in the reservoir, were documented for two runoff events. SC was identified as a viable tracer of the movement of density currents in the reservoir, and the internal contribution of resuspension to c660 levels was depicted. The results of SAX analyses demonstrated a substantial fraction (i.e., 30–40%) of the Tn that enters the reservoir from the primary tributary was associated with particles >9.1 μm in diameter that do not contribute to Tn levels in the lacustrine portions of the reservoir. Higher SV values were observed for larger particles, but were much lower than Stokes Law conditions, suggesting that they existed as aggregates. The monitoring and SV experiment results were considered within the context of the structural needs of turbidity models, for two levels of complexity, to simulate the transient impacts of runoff events on the reservoir. A two- or three-dimensional transport submodel will be necessary to represent spatial patterns, and a kinetics submodel will need to represent (either implicitly or explicitly) size dependent settling, particle coagulation, and sediment resus-pension.

Geomorphic Work during a “150-Year” Storm: Contrasting Behaviors of River Channels in a New Zealand Catchment

The geomorphic work accomplished during an extreme storm event by three primary tributaries in the western Manawatu river catchment (New Zealand) is assessed using sequential aerial photographs. Areas of floodplain and channel erosion were quantified as a measure of the work accomplished during floods triggered by a “150-year” storm in February 2004. Of the three rivers studied, the smallest (Kiwitea, 225 km2) accomplished the most geomorphic work, eroding 1.1 km2 of floodplain along a 30 km long reach. Here spatially discontinuous channel transformation was associated with large-scale bank erosion in response to a flood estimated to be more than five times bigger than the mean annual flood (annual recurrence interval [ARI] ∼100 years). Total energy expenditure in the Kiwitea flood was ∼14,900 × 103 joules. The larger Pohangina (547 km2) and Oroua (329 km2) rivers were less effective, expending ∼14,400 × 103 joules and ∼5,300 × 103 joules and eroding 0.36 and 0.6 km2 of floodplain, respectively. The contrasting amount of geomorphic work between these tributaries relates to valley floor and channel configurations, which prime discrete reaches for instability, sensitizing them to perturbation by this flood event. In the Kiwitea, greatest erosion occurred where floodwaters were confined by terrace bluffs at bends that locally enhance stream powers. The wider channels of the Pohangina and Oroua Rivers wander across broader gravelly floodplains, permitting widespread dissipation of flood flows across the wider active channel and valley floor. Hydrologic, hydraulic, and geomorphic variables thus explain the variability in geomorphic work accomplished during the event. Ultimately, diverse channel behaviors reflect varied catchment and reach sensitivity to the flood event.