Water Temperature Time Series Research Articles

Environmental factors controlling stream water temperature in a forest catchment

Heat budget of a stream, the Putoisaroma Stream, Hokkaido, Japan, in a forest catchment was estimated in order to investigate environmental factors controlling stream water temperature. In August 2008–October 2009, water temperature was measured at six sites along the stream channels, and the streambed temperature was measured at depths of 5 cm and 30 cm at one of the sites. In order to quantify incoming and outgoing radiations at the stream surface, hemispherical photographs were taken and the shading factors (ratio of the shade to the whole sky) were calculated at the observation sites over the summer. The shading factors, exhibiting seasonal and spatial variations, produced seasonal and spatial changes of shortwave and longwave radiations. The wind speed above stream surface was much smaller than in an open field, which produced turbulent heat fluxes one third as large as that in the open field. The shortwave and longwave radiations and the advective heat flux from upstream showed the major contribution to the stream heat budget, while the streambed heat conduction was secondary. The time series of stream water temperature were simulated well (RMSE = 0.771 ℃, NASH = 0.888) by applying the estimated heat budget. This evidences that the quantification of the shade above stream surface and the calculation of the heat budget are both reasonable. The sensitivity analysis for the simulation indicates that the shading factors along the stream channels control the stream water temperature.

Estimating trends in atmospheric water vapor and temperature time series over Germany

Abstract. Ground-based GNSS (Global Navigation Satellite System) has efficiently been used since the 1990s as a meteorological observing system. Recently scientists have used GNSS time series of precipitable water vapor (PWV) for climate research. In this work, we compare the temporal trends estimated from GNSS time series with those estimated from European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-Interim) data and meteorological measurements. We aim to evaluate climate evolution in Germany by monitoring different atmospheric variables such as temperature and PWV. PWV time series were obtained by three methods: (1) estimated from ground-based GNSS observations using the method of precise point positioning, (2) inferred from ERA-Interim reanalysis data, and (3) determined based on daily in situ measurements of temperature and relative humidity. The other relevant atmospheric parameters are available from surface measurements of meteorological stations or derived from ERA-Interim. The trends are estimated using two methods: the first applies least squares to deseasonalized time series and the second uses the Theil–Sen estimator. The trends estimated at 113 GNSS sites, with 10 to 19 years temporal coverage, vary between −1.5 and 2.3 mm decade−1 with standard deviations below 0.25 mm decade−1. These results were validated by estimating the trends from ERA-Interim data over the same time windows, which show similar values. These values of the trend depend on the length and the variations of the time series. Therefore, to give a mean value of the PWV trend over Germany, we estimated the trends using ERA-Interim spanning from 1991 to 2016 (26 years) at 227 synoptic stations over Germany. The ERA-Interim data show positive PWV trends of 0.33 ± 0.06 mm decade−1 with standard errors below 0.03 mm decade−1. The increment in PWV varies between 4.5 and 6.5 % per degree Celsius rise in temperature, which is comparable to the theoretical rate of the Clausius–Clapeyron equation.

Within-lake habitat heterogeneity mediates community response to warming trends.

Climate change is rapidly altering many aquatic systems, and life history traits and physiological diversity create differences in organism responses. In addition, habitat diversity may be expressed on small spatial scales, and it is therefore necessary to account for variation among both species and locations when evaluating climate impacts on biological communities. Here, we investigated the effects of temperature and spatial heterogeneity on long-term community composition in a large boreal lake. We used a five-decade time series of water temperature and relative abundance of fish species captured in the littoral zone throughout the summer at 10 discrete locations around the lake. We applied a spatial dynamic factor analysis (SDFA) model to this time series, which estimates the sensitivity of each species to changing water temperature while accounting for spatiotemporal variation. This analysis described the trend in community composition at each sampling location in the lake, given their different trends in temperature over time. The SDFA indicated different magnitude and direction of species responses to temperature; some species increased while others decreased in abundance. The model also identified five unique trends in species abundance across sites and time, indicating residual dynamics in abundance after accounting for temperature effects. Thus, different regions in the lake have experienced different trajectories in community change associated with different rates of temperature change. These results highlight the importance of considering habitat heterogeneity in explaining and predicting future species abundances, and our model provides a means of visualizing spatially-explicit temporal variation in species' dynamics.

Characterisation of boundary layer turbulent processes by the Raman lidar BASIL in the frame of HD(CP)<sup>2</sup> Observational Prototype Experiment

Abstract. Measurements carried out by the University of Basilicata Raman lidar system (BASIL) are reported to demonstrate the capability of this instrument to characterise turbulent processes within the convective boundary layer (CBL). In order to resolve the vertical profiles of turbulent variables, high-resolution water vapour and temperature measurements, with a temporal resolution of 10 s and vertical resolutions of 90 and 30 m, respectively, are considered. Measurements of higher-order moments of the turbulent fluctuations of water vapour mixing ratio and temperature are obtained based on the application of autocovariance analyses to the water vapour mixing ratio and temperature time series. The algorithms are applied to a case study (11:30–13:30 UTC, 20 April 2013) from the High Definition Clouds and Precipitation for Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE), held in western Germany in the spring 2013. A new correction scheme for the removal of the elastic signal crosstalk into the low quantum number rotational Raman signal is applied. The noise errors are small enough to derive up to fourth-order moments for both water vapour mixing ratio and temperature fluctuations.To the best of our knowledge, BASIL is the first Raman lidar with a demonstrated capability to simultaneously retrieve daytime profiles of water vapour turbulent fluctuations up to the fourth order throughout the atmospheric CBL. This is combined with the capability of measuring daytime profiles of temperature fluctuations up to the fourth order. These measurements, in combination with measurements from other lidar and in situ systems, are important for verifying and possibly improving turbulence and convection parameterisation in weather and climate models at different scales down to the grey zone (grid increment ∼ 1 km; Wulfmeyer et al., 2016).For the considered case study, which represents a well-mixed and quasi-stationary CBL, the mean boundary layer height is found to be 1290 ± 75 m above ground level (a.g.l.). Values of the integral scale for water vapour and temperature fluctuations at the top of the CBL are in the range of 70–125 and 75–225 s, respectively; these values are much larger than the temporal resolution of the measurements (10 s), which testifies that the temporal resolution considered for the measurements is sufficiently high to resolve turbulent processes down to the inertial subrange and, consequently, to resolve the major part of the turbulent fluctuations. Peak values of all moments are found in the interfacial layer in the proximity of the top of the CBL. Specifically, water vapour and temperature second-order moments (variance) have maximum values of 0.29 g2 kg−2 and 0.26 K2; water vapour and temperature third-order moments have peak values of 0.156 g3 kg−3 and −0.067 K3, while water vapour and temperature fourth-order moments have maximum values of 0.28 g4 kg−4 and 0.24 K4. Water vapour and temperature kurtosis have values of ∼ 3 in the upper portion of the CBL, which indicate normally distributed humidity and temperature fluctuations. Reported values of the higher-order moments are in good agreement with previous measurements at different locations, thus providing confidence in the possibility of using these measurements for turbulence parameterisation in weather and climate models.In the determination of the temperature profiles, particular care was dedicated to minimise potential effects associated with elastic signal crosstalk on the rotational Raman signals. For this purpose, a specific algorithm was defined and tested to identify and remove the elastic signal crosstalk and to assess the residual systematic uncertainty affecting temperature measurements after correction. The application of this approach confirms that, for the present Raman lidar system, the crosstalk factor remains constant with time; consequently an appropriate assessment of its constant value allows for a complete removal of the leaking elastic signal from the rotational Raman lidar signals at any time (with a residual error on temperature measurements after correction not exceeding 0.18 K).

Warming trends of perialpine lakes from homogenised time series of historical satellite and in-situ data

The availability of more than thirty years of historical satellite data is a valuable source which could be used as an alternative to the sparse in-situ data. We developed a new homogenised time series of daily day time Lake Surface Water Temperature (LSWT) over the last thirty years (1986–2015) at a spatial resolution of 1km from thirteen polar orbiting satellites. The new homogenisation procedure implemented in this study corrects for the different acquisition times of the satellites standardizing the derived LSWT to 12:00 UTC. In this study, we developed new time series of LSWT for five large lakes in Italy and evaluated the product with in-situ data from the respective lakes. Furthermore, we estimated the long-term annual and summer trends, the temporal coherence of mean LSWT between the lakes, and studied the intra-annual variations and long-term trends from the newly developed LSWT time series. We found a regional warming trend at a rate of 0.017°Cyr−1 annually and 0.032°Cyr−1 during summer. Mean annual and summer LSWT temporal patterns in these lakes were found to be highly coherent. Amidst the reported rapid warming of lakes globally, it is important to understand the long-term variations of surface temperature at a regional scale. This study contributes a new method to derive long-term accurate LSWT for lakes with sparse in-situ data thereby facilitating understanding of regional level changes in lake's surface temperature.

Evaluation of Central Valley Spring-Run Chinook Salmon Passage Through Lower Butte Creek Using Hydraulic Modelling Techniques

River2D was used to develop a hydraulic model of an upstream passage impediment for adult spring-run Chinook salmon (Oncorhynchus tshawytscha) on Butte Creek, Tehama County, California. Topographic data were collected by using a total station, survey-grade real-time kinematic global positioning system, and terrestrial light detection and ranging. Stage-discharge relationships were developed at the upstream and downstream ends of the site to use as boundary conditions and to calibrate the 2D model. A pressure transducer was installed at the downstream boundary of the site to provide a time series of flow and water temperatures. Parameters of the hydraulic model were examined to assess upstream passage including minimum thalweg depth along the least width-limiting pathway, velocity, and water surface elevation above and below a jump, and flow partitioning between a split in the main flow paths through the site. The results of the River2D model were used to identify flow levels that met the minimum depth and width thresholds needed for adult spring-run Chinook salmon (SRCS) to migrate upstream through the study reach. A minimum passage depth criterion of 0.27 m was used for adult SRCS. Site-specific passage width criteria were derived from the literature for the study site and ranged from 0.3 to 0.9 m. Model results indicated that a flow of 3.40 cms met the depth criterion and the lower bound of the width criterion. A flow level of 6.8 cms met the depth criterion and the upper bound of the width criterion. Data from the VAKI Riverwatcher fish passage counting device installed just upstream of the study site were related to the stage/passage limiting width and water temperature monitoring data. The monitoring data and results of the predictive modelling will be used by the California Department of Fish and Wildlife to recommend flow criteria that protect migrating adult SRCS. Copyright © 2016 John Wiley & Sons, Ltd.

A disconnectivity index for improving choices in managing protected areas for rivers

Abstract Ecological processes in freshwater lotic systems are disrupted when upstream–downstream connectivity is broken. Changes in catchment land use, catchment density of small dams, and instream impoundments result in changes to thermal and flow regimes, which in turn affect natural biological turnover patterns and rates, as well as organism exchange and dispersal. This study describes the development of a comprehensive connectivity index for rivers, and how this can be used as a spatial product to prioritize areas of freshwater importance within the province of KwaZulu‐Natal, South Africa. A longitudinal connectivity index (i.e. in‐channel barriers) reflected as a cumulative downstream score, as well as the characterization of these barriers as a spectrum from absolute to partial, was developed for the main rivers in the province of KwaZulu‐Natal, South Africa. This was combined with a lateral connectivity index based on the effects of catchment fragmentation and a density index for small dams. The impacts of instream barriers on flow and water temperature time series were assessed using metrics describing magnitude, frequency, duration and timing of thermal and flow events for time series before and after impoundment. These impacts were spatially mapped using a surrogate function that related reset distance to average discharge, and the assumption that should the unimpounded downstream river length exceed the reset distance, the river species patterns would revert to natural conditions. It is concluded that a multi‐metric connectivity surface should be used as a cost layer for freshwater conservation plans for the province. Assessed in tandem with protected areas, it provides a tool for setting priorities for whole river systems suitable for immediate conservation versus systems that may require rehabilitation. Copyright © 2016 John Wiley & Sons, Ltd.

Characterization of Turbulent Processes by the Raman Lidar System Basil in the Frame of the HD(CP)2Observational Prototype Experiment – Hope

Measurements carried out by the Raman lidar system BASIL are reported to demonstrate the capability of this instrument to characterize turbulent processes within the Convective Boundary Layer (CBL). In order to resolve the vertical profiles of turbulent variables, high resolution water vapour and temperature measurements, with a temporal resolution of 10 sec and a vertical resolution of 90 and 210 m, respectively, are considered. Measurements of higher-order moments of the turbulent fluctuations of water vapour mixing ratio and temperature are obtained based on the application of spectral and auto-covariance analyses to the water vapour mixing ratio and temperature time series. The algorithms are applied to a case study (IOP 5, 20 April 2013) from the HD(CP)2 Observational Prototype Experiment (HOPE), held in Central Germany in the spring 2013. The noise errors are demonstrated to be small enough to allow the derivation of up to fourth-order moments for both water vapour mixing ratio and temperature fluctuations with sufficient accuracy.

Oxygen dynamics in a boreal lake responds to long‐term changes in climate, ice phenology, and DOC inputs

AbstractBoreal lakes are impacted by climate change, reduced acid deposition, and changing loads of dissolved organic carbon (DOC) from catchments. We explored, using the process‐based lake model MyLake, how changes in these pressures modulate ice phenology and the dissolved oxygen concentrations (DO) of a small boreal humic lake. The model was parametrized against year‐round time series of water temperature and DO from a lake buoy. Observed trends in air temperature (+0.045°C yr−1) and DOC concentration (0.11 mg C L−1 yr−1, +1% annually) over the past 40 years were used as model forcings. A backcast of ice freezing and breakup dates revealed that ice breakup occurred on average 8 days earlier in 2014 than in 1974. The earlier ice breakup enhanced water column ventilation resulting in higher DO in the spring. Warmer water in late summer led to longer anoxic periods, as microbial DOC turnover increased. A long‐term increase in DOC concentrations caused a decline in lake DO, leading to 15% more hypoxic days (<3 mg L−1) and 10% more anoxic days (<15 µg L−1) in 2014 than in 1974. We conclude that climate warming and increasing DOC loads are antagonistic with respect to their effect on DO availability. The model suggests that DOC is a stronger driver of DO consumption than temperature. The browning of lakes may thus cause reductions in the oxythermal habitat of fish and aquatic biota in boreal lakes.

Observation of Flood-driven Sediment Transport and Deposition Off a River Mouth

A series of field observation of turbidity and current velocity etc. were carried out at the sea bottom off a river mouth during flood periods. The measurement location was 1.2km off the mouth of Tenryu River, Japan, where water depth was about 18m. Four flood events of which the maximum mean hourly discharge ranged from 1,570m3/s to 4,620 m3/s were selected and the time series of river discharge, turbidity, water temperature, salinity and current velocity were compared with each other and the relationships between them were discussed. Furthermore, vertical profiles of turbidity and salinity observed after a flood were used in the discussion. Bathymetric changes surveyed off the river mouth were also taken into account.

Mean diel variability of surface energy fluxes over Manso Reservoir

Mean diel cycle of latent (E), sensible (H), net longwave (Lwnet), net shortwave (Sw), and net surface heat flux balance (S) were estimated from hourly meteorological and subsurface water temperature time series acquired for ~1 month during mid-austral autumn by a buoy system in a large tropical reservoir in Brazil. E and H were in phase and had their maximum (E = 163 Wm−2; H = 39 Wm−2) at early morning and minimum (E = 112 Wm−2; H = 6 Wm−2) midafter-noon, resulting in Bowen ratios of 0.24 and 0.06, respectively. Heat loss by evaporation therefore dominates over sensible heat used to warm surface atmosphere. Atmospheric instability was present almost all the time, increasing latent and sensible heat flux exchange coefficients by ~50% over their neutral values (from 1.4 × 10−3 to 2.2 × 10−3). Mean Lwnet varied from 76 at late afternoon to 89 Wm−2 at early morning, indicating its importance in the overall surface heat flux balance. All 3 fluxes (E, H, and Lwnet) were positive (reservoir losing energy) throughout the day. The integrated daily average net energy budget S (net short wave radiation minus E + H + Lwnet) was ~ −60 Wm−2; nighttime energy loss exceeded daytime gain, with consequent cooling of the reservoir. A mean temperature drop of about −0.1 °C d−1 was obtained by fitting a linear trend line to observed daily mean surface temperatures. In a qualitative way, diel time variations of surface water temperature were consistent to the time variability of S, indicating the dominant role of the surface heat budget in modulating surface layer temperatures of the reservoir.

Externally driven changes in the abundance of summer and winter flounder

Abstract Marine organisms that utilize nearshore environments for major components of their life histories are subject to both local-scale forcing such as water quality and estuarine degradation as well as large-scale forcing such as fishing and decadal-scale climate variability. Large-scale forcing has the potential to synchronize the dynamics of subpopulations, while local-level forcing can produce asynchronous subpopulation trends. Summer flounder (Paralichthys dentatus) and winter flounder (Pseudopleuronectes americanus) are important commercial and recreational flatfish along the east coast of North America which spend their first year of life in coastal habitats. We found that the two exhibited significant within-species coherence in commercial landings and fisheries-independent surveys across the northeast shelf of the United States, suggesting large-scale external drivers. In laboratory studies, temperature has been found to be an important factor regulating survival during the egg, larva and settlement phases of both species. We reconstructed a 40-year time-series of coastal water temperature for the major spawning and nursery areas to examine changes in the thermally available habitat. Estimates of winter flounder abundance were negatively correlated with the winter water temperature, but not with fishing mortality. Summer flounder abundance, by contrast, was negatively correlated with fishing mortality, but exhibited no link with temperature. In addition, time-varying stock–recruitment relationships indicated that stock productivity declined for winter flounder over time, while summer flounder productivity has varied without a trend. While both species declined in the 1980s and early 1990s due to heavy fishing pressure, the reduction in fishing over the last two decades has led to rebuilding of the summer flounder stock and an expansion of its age structure. Declining productivity due to warming estuarine conditions has kept the winter flounder stock at low levels despite low fishing pressure. The two stocks illustrate the importance of controlling fishing mortality in the management of natural marine resources while also accounting for changes in productivity due to climate variability and change.

Long-term temperature evolution in a deep sub-alpine lake, Lake Bourget, France: how a one-dimensional model improves its trend assessment

Water temperature and the alternation of stratification and mixing count amongst key drivers of lake ecology. Reliable long time-series of water temperature are rare. Here, we investigated how a numerical model can fill the gaps in heterogeneous time-series and make it possible to identify a significant trend in the lake thermal regime. We computed the mean water temperature and the Schmidt stability, an indicator of the stratification strength, in a deep and well-stratified lake (Lake Bourget, France), between 1976 and 2008. We first used temperature measurements and then a one-dimensional vertical model, which we describe here. The model performs as well as the best existing models. During the 1976–2008 periods, whereas no statistically significant trend came out of the measurements, we found in the simulation results an increase of 0.12 °C per decade in the water temperature and of 5.9 days per decade in the stratification duration. This shows that the temperature history of a lake can be reconstructed and a reliable long-term trend computed when weather data and a calibrated temperature model are available. Our results also suggest that different local climatic influences cause a slower warming in this lake of the south-western Alps than in other sub-alpine lakes.

Impact of Climate Change on Estuarine Zooplankton: Surface Water Warming in Long Island Sound Is Associated with Changes in Copepod Size and Community Structure

In coastal ecosystems with decades of eutrophication and other anthropogenic stressors, the impact of climate change on planktonic communities can be difficult to detect. A time series of monthly water temperatures in the Central Basin of Long Island Sound (LIS) from the late 1940s until 2012 indicates a warming rate of 0.03 °C year−1. Relative to the early 1950s, there has been a concurrent decrease in the mean size of the dominant copepod species Acartia tonsa and Acartia hudsonica, an increase in the proportion of the small copepod Oithona sp., and the disappearance of the two largest-sized copepod genera from the 1950s. These changes are consistent with predictions of the impact of climate change on aquatic ectotherms. This suggests that even in eutrophic systems where food is not limiting, a continued increase in temperature could result in a smaller-sized copepod community. Since copepods dominate the zooplankton, which in turn link primary producers and upper trophic levels, a reduction in mean size could alter food web connectivity, decreasing the efficiency of trophic transfer between phytoplankton and endemic larval fish.

Quantifying streambed deposition and scour from stream and hyporheic water temperature time series

[1] We propose a new method based on temperature time series of surface and streambed pore waters to monitor local changes in streambed surface elevations at a nominally daily time scale. The proposed method uses the naturally occurring daily temperature signal changes in amplitude and phase between stream water and the water flowing within the streambed sediment. Application of the method in a fine-bedded stream predicts the timing and magnitude of a prescribed sequence of scour and deposition. This provides a new, effective, easy to use, and economic methodology to monitor the temporal evolution of erosion and depositional patterns in rivers.

Influence of the physical environment on polar phytoplankton blooms: A case study in the Fram Strait

The Fram Strait is the main gateway for water, heat and sea-ice exchanges between the Arctic Ocean and the North Atlantic. The complex physical environment results in a highly variable primary production in space and time. Previous regional studies have defined key bottom-up (ice cover and stratification from melt water controlling the light availability, and wind mixing and water transport affecting the supply of nutrients) and top-down processes (heterotrophic grazing). In this study, in situ field data, remote sensing and modeling techniques were combined to investigate in detail the influence of melting sea-ice and ocean properties on the development of phytoplankton blooms in the Fram Strait region for the years 1998–2009. Satellite-retrieved chlorophyll-a concentrations from temporarily ice-free zones were validated with contextual field data. These were then integrated per month on a grid size of 20×20km, resulting in 10 grids/fields. Factors tested for their influence on spatial and temporal variation of chlorophyll-a were: sea-ice concentration from satellite and sea-ice thickness, ocean stratification, water temperature and salinity time-series simulated by the ice-ocean model NAOSIM. The time series analysis for those ten ice-free fields showed a regional separation according to different physical processes affecting phytoplankton distribution. At the marginal ice zone the melting sea-ice was promoting phytoplankton growth by stratifying the water column and potentially seeding phytoplankton communities. In this zone, the highest mean chlorophyll concentration averaged for the productive season (April–August) of 0.8mgC/m3 was observed. In the open ocean the phytoplankton variability was correlated highest to stratification formed by solar heating of the upper ocean layers. Coastal zone around Svalbard showed processes associated with the presence of coastal ice were rather suppressing than promoting the phytoplankton growth. During the twelve years of observations, chlorophyll concentrations significantly increased in the southern part of the Fram Strait, associated with an increase in sea surface temperature and a decrease in Svalbard coastal ice.

Atmospheric forcing intensifies the effects of regional ocean warming on reef‐scale temperature anomalies during a coral bleaching event

We investigate how local atmospheric conditions and hydrodynamic forcing contributed to local variations in water temperature within a fringing coral reef‐lagoon system during the peak of a marine heat wave in 2010–2011 that caused mass coral bleaching across Western Australia. A three‐dimensional circulation model Regional Ocean Modeling System (ROMS) with a built‐in air‐sea heat flux exchange module Coupled Ocean Atmosphere Experiment (COARE) was coupled with a spectral wave model Simulating Waves Nearshore (SWAN) to resolve the surface heat exchange and wave‐driven reef circulation in Coral Bay, Ningaloo Reef. Using realistic oceanic and atmospheric forcing, the model predictions were in good agreement with measured time series of water temperature at various locations in the coral reef system during the bleaching event. Through a series of sensitivity analyses, we found that the difference in temperature between the reef and surrounding offshore waters (ΔT) was predominantly a function of both the daily mean net heat flux ( ) and residence time, whereas diurnal variations in reef water temperature were dependent on the diurnal fluctuation in the net heat flux. We found that reef temperatures were substantially higher than offshore in the inner lagoon under normal weather conditions and over the entire reef domain under more extreme weather conditions (0.7°C–1.5°C). Although these temperature elevations were still less than that caused by the regional ocean warming (2°C–3°C), the arrival of peak seasonal temperatures in the summer of 2010–2011 (when net atmospheric heat fluxes were positive and abnormally high) caused substantially higher thermal stresses than would have otherwise occurred if offshore temperatures had reached their normal seasonal maxima in autumn (when net atmospheric heat fluxes were negative or cooling). Therefore, the degree heating weeks calculated based on offshore temperature substantially underestimated the thermal stresses experienced by the reef in the period leading up to the observed bleaching event (3 versus 11°C‐weeks).

The annual particle cycle in Lake Van (Turkey)

The varved sediments of Lake Van provide a high-quality continental archive of seasonal to decadal-scale climate variability. In order to read the natural record, modern varve formation was studied on the basis of (1) remotely-sensed total suspended-matter (TSMrs) concentrations; (2) time-series of particle flux and water temperatures; and (3) turbidity, temperature, and oxygen profiles. TSMrs, validated by contemporaneous water-column sampling, shows great temporal and lateral variations (whitings and turbidity plumes). From 2006 to 2009, sequential sediment traps recorded high particle fluxes during spring and fall, medium fluxes during summer, and almost zero flux during winter. The mean total mass flux of 403mgm−2day−1 comprised 33% (seasonally up to 67%) calcium carbonate, 7% aquatic organic matter, 6% biogenic opal, and 54% detrital minerals. The CaCO3 fluxes are controlled by river discharge (precipitation and snowmelt) during spring, by high productivity during summer, and by river discharge (precipitation before snowfall starts) and mixing during fall. In November 2007, an anomalously high CaCO3 flux occurred as a result of a warm water surface supersaturated with calcite coinciding with an anomalous runoff event. The results demonstrate that the couplets of light and dark laminae in the short sediment cores are true varves representing spring–summer–fall and winter conditions, respectively. Consequently, varve formation can be linked to the seasonal climate pattern, providing a calibration that can be used to interpret the partially varved paleo-record of Lake Van and related environmental processes.

Time series analysis of water surface temperature and heat flux components in the Itumbiara Reservoir (GO), Brazil

AIM: Water temperature plays an important role in ecological functioning and in controlling the biogeochemical processes of the aquatic system. Conventional water quality monitoring is expensive and time consuming. It is particularly challenging for large water bodies. Conversely, remote sensing can be considered a powerful tool to assess important properties of aquatic systems because it provides synoptic and frequent data acquisition over large areas. The objective of this study was to analyze time series of surface water temperature and heat flux to advance the understanding of temporal variations in a hydroelectric reservoir. METHOD: MODIS water-surface temperature (WST) level 2, 1 km nominal resolution data (MOD11L2, version 5) were used. All available clear-sky MODIS/Terra images from 2003 to 2008 were used, resulting in a total of 786 daytime and 473 nighttime images. Time series of surface water temperature was obtained computing the monthly mean in a 3×3 window of three reservoir selected sites: 1) near the dam, 2) at the centre of the reservoir and 3) in the confluence of the rivers. In-situ meteorological data from 2003 to 2008 were used to calculate surface energy budget time series. Cross-wavelet, coherence and phase analysis were carried out to compute the correlation between daytime and nighttime surface water temperatures and the computed heat fluxes. RESULTS: The monthly mean of the day-time WST shows lager variability than the night-time WST. All time series (daytime and nighttime) have a cyclical pattern, passing for a minimum (June - July) and a maximum (December and January). Fourier and the Wavelet Analysis were applied to analyze this cyclical pattern. The daytime time series, presents peaks in 4.5, 6 12 and 36 months and the nighttime WST shows the highest spectral density at 12, 6, 3 and 2 months. The multiple regression analysis shows that for daytime WST, the heat flux terms explain 89% of the annual variation (RMS = 0.89 °C, p < 0.0013). For nighttime, the heat flux terms explain 94% (RMS = 0.53 °C, p < 0.0002). CONCLUSION: The daytime WST and shortwave radiation presents a good agreement for periods of 6 (with shortwave retarded) and 12 months (with shortwave advanced); For nighttime WST and longwave the good agreement is present for 1, 3, 6 and 12 months, all with longwave advanced in relation to WST.

Estimation of forest harvesting-induced stream temperature changes and bioenergetic consequences for cutthroat trout in a coastal stream in British Columbia, Canada

Data from a paired-catchment study in south coastal British Columbia, Canada, were analyzed to assess the thermal effects of clearcut harvesting with no riparian buffer on a fish-bearing headwater stream. The approach used time series of daily mean water temperatures for East Creek (control) and A Creek (treatment), both before and after harvest. Statistical models were developed to predict (a) what the temperatures would have been in the post-harvest period had harvesting not occurred, and (b) what temperatures would have been in the pre-harvest period had harvesting already occurred. The Wisconsin Bioenergetics Model was used to simulate growth of coastal cutthroat trout (Oncorhynchus clarki clarki) for the first year following fry emergence using the predicted and observed stream temperatures to generate scenarios representing with-harvest and no-harvest thermal regimes. A Monte Carlo approach was used to quantify the effects of uncertainty associated with the regression models on predicted stream temperature and trout growth. Summer daily mean temperatures in the with-harvest scenario were up to $$5^{\circ}\hbox{C}$$ higher than those for the no-harvest scenario. Harvesting-induced warming reduced growth rates during summer, but increased growth rates during autumn and spring. In the with-harvest scenario, trout were 0.2–2.0 g (absolute weight) smaller throughout the winter period than in the no-harvest scenario. However, the bioenergetic simulations suggest that trout growth may be more sensitive to potential changes in food supply following harvesting than to direct impacts of stream temperature changes.