Water Temperature Gradient Research Articles

A neutral‐metabolic theory of latitudinal biodiversity

AbstractAimLatitudinal gradients of species richness represent Earth's first‐order biodiversity pattern. Most species groups display a near‐monotonic decline in richness from the equator to the poles, yet there exists little mechanistic theory to derive such patterns from first principles. Here we integrate two key advances – neutral theory and the metabolic theory of ecology – to reconstruct global species richness gradients and test underlying causes.LocationSimulated global meta‐community.MethodsWe constructed a spatially explicit global meta‐community with constant per capita rates of disturbance, speciation and dispersal. No gradient emerged in this neutral base model. Focusing on the oceans as a model system, we added a water temperature gradient of 0–30°C that independently affected rates of community turnover and speciation based on established metabolic scaling laws. We also added a gradient in habitat area that roughly parallels the observed decrease in ocean area from tropical to polar waters.ResultsThermal effects on the community turnover rate caused a transient latitudinal gradient that ultimately disappeared. Thermal effects on speciation produced a dynamically stable but relatively weak gradient. Increasing habitat area towards the equator in combination with thermal effects on speciation rate produced a more realistic gradient that emerged from the combined effects of species–area and species–energy theory.Main conclusionsThis reasonably simple model provides a platform to explore support for processes underpinning large‐scale biodiversity gradients, and the ability of prominent ecological theories, independently or in combination, to capture them.

Movements of the thermocline lead to high variability in benthic mixing in the nearshore of a large lake

AbstractThe thermocline of Lake Ontario is in constant motion, and as it washes back and forth along the sloping lakebed there is a striking asymmetry in near‐bed stratification and benthic turbulence between its rise and fall. Detailed field observations of the stratification and water currents from the summers of 2012 and 2013 showed that the thermocline motions had large amplitudes (as high as 15 m) and a dominant period between 16 and 17.5 h, corresponding to a near‐inertial internal Poincaré wave. During the falling phase, the warmer down‐slope flow was strongly stratified with near‐bed water temperature gradients of 1°C m−1. In contrast during the rising phase of colder up‐slope flow, there was an unstable stratification in near‐bed water and large temperature overturns due to the differential advection of stratified waters, i.e., the shear‐driven convective mechanism. Using a Thorpe‐scale analysis of overturns, the inferred turbulent diffusivity during the up‐slope flow was Kz =5 × 10−4 m2 s−1. In striking contrast during the down‐slope flow, the strong stratification had lower turbulent diffusivities of Kz =10−6 m2 s−1. The near bottom region of Lake Ontario within the thermocline swash‐zone has intense biological activity and the highest concentrations of invasive dreissenid mussels. We discuss the potential biological implications of the striking variability in benthic mixing and near‐bed stratification for nutrient cycling in the Lake Ontario nearshore.

Environmental optimality, not heterogeneity, drives regional and local species richness in lichen epiphytes

AbstractAimWe evaluate the scale dependence of species richness–environment relationships with a continent‐wide analysis of lichen epiphyte communities. Specifically, our goals are to assess: (1) the dependence of local richness on regional processes, (2) whether species richness is primarily influenced by heterogeneity in environmental conditions or the central tendency of those conditions, and (3) whether the relative influence of these different aspects of the environment differs between local communities and regional species pools.LocationForests of the contiguous United States.MethodsWe used variation partitioning and model averaging of linear models to relate macrolichen richness at 1923 forest inventory plots (c. 4000 m2) to measures of environmental heterogeneity and mean conditions at local and regional scales. Data included 17 local environmental variables and 11 regional‐scale variables which were obtained from a national forest inventory, herbarium records and several climate data sources.ResultsRegional‐scale variables explained more unique variation in local species richness and generally had stronger effects than variables measured locally. However, most variation in local richness was explained jointly by local and regional variables. At both local and regional scales, variables measuring environmental heterogeneity explained little variation in species richness and had weaker effects than variables characterizing mean environmental conditions.Main conclusionsSpecies richness of epiphytic macrolichens is not regulated by environmental heterogeneity locally or regionally and instead tracks large‐scale climate gradients of water availability and temperature. Richness in local communities is influenced by processes operating at both regional and local scales, highlighting the importance of determining large‐scale drivers of lichen richness across the North American continent. This research demonstrates a general method for comparing the influence of different aspects of the environment on species richness across scales and should be applicable to many different taxonomic groups.

Fortnightly Variation in the Bottom Thermal Front and Associated Circulation in a Semienclosed Sea

AbstractSummer hydrographic data from 1971 to 2000 demonstrate the presence of bottom cold water (BCW) and a bottom thermal front around the BCW in a semienclosed sea in the Seto Inland Sea of Japan. The horizontal gradient of water temperature across the bottom front was larger in neap tide than in spring tide, which is the opposite the pattern observed in the fortnightly variations in other areas (e.g., the Irish Sea). A numerical model for the Inland Sea reproduced the presence of BCW and a bottom front as well as the same fortnightly variation in the horizontal gradient of water temperature across the bottom front as in observational data. Being the same BCW as those in other areas, the presence of BCW in the Inland Sea is also caused by spatial variation in tidal mixing. The intensification of the bottom front in neap tide in the Inland Sea results from a combination of tidal mixing and horizontal advection of warm water to the BCW. The presence of a bottom residual current in the direction across the bottom front results in the horizontal advection of warm water to the BCW, and its fortnightly variation is responsible for the fortnightly variation of the bottom front in the Inland Sea. The presence of the BCW induces a surface cyclonic circulation in the direction approximately along the bottom front; the intensification and weakening of the bottom front with the spring–neap tidal cycle, combined with the fortnightly variation in the bottom boundary layer thickness, produce a slightly stronger surface cyclonic circulation in neap tide than in spring tide.

Windstorm disturbance effects on mountain stream ecosystems and the Plecoptera assemblages

Abstract Within the investigated river basins the deforestation ranged from 0-45.5%, dependent on the amount of windstorm damage. Our water temperature readings revealed that the canopy elimination above the streams in the areas damaged by the windstorm caused increase in daily and annual water temperature and also wider daily water temperature range, than those in the undisturbed reference stream, which caused the decline of cold stenotherm species abundance. The stream basins deforestation was collinear with FPOM and UFPOM concentrations, water temperature gradient and nitrate concentrations. Statistical analysis showed that size of stream, conductivity, catchment area and discharge were negatively correlated with the stonefly mesotherm ratio and nitrate contents. Higher average concentrations of nutrients (like NO−3) in samples from some streams are a consequence of their mobilization from disturbed forest soils due to the windstorm. Most streams located in the deforested area were found by us in a higher trophic status, especially due the particulate organic matter (POM) content and biofilms amount, what caused increase in some functional feeding groups occurrence (collectorgatherers, scrapers and mainly predators). Stream degradation positively correlated with the percentage of deforested area, ratio of eurytherm taxa, transported organic matter, dissolved organic matter, and biofilms occurrence. The conductivity values measured in water samples were collinear with alkalinity and pH values and increased with watersheds areal extent. We established environmental variables influenced by the windstorm event along the catchment degradation gradient using measurable characteristics of stonefly assemblages and metrics. The proportion of the Leuctridae family and the Nemoura genus expressed as the LN index (1) shows a negative correlation with part undisturbed forested areas and channel stability, and positive correlation with stream erosion (expressed as the TAM quantity) in river basins. Proportion of shredders among the investigated streams was significantly higher in deforested streams, and shows lower stability of stonefly community in these habitats, where significantly fluctuate channel stability, water temperature and discharge of these streams.

The influence of environmental variables on the functional structure of headwater stream fish assemblages: a study of two tropical basins in Central Brazil

We investigated functional patterns of fish assemblages of two adjacent basins (Araguaia and Tocantins) to test whether their headwater stream fish assemblages are more functionally (dis)similar than expected by chance and whether these (dis)similarities are related to differences of environmental conditions between basins. We used an analysis of similarities (ANOSIM) on a functional dissimilarity matrix to test for (dis)similarities between fish assemblages of both basins. We performed RLQ and fourth-corner analyses to determine fish species trait-environment relationship. Our results revealed functional dissimilarities between fish assemblages of both basins and significant species trait-environment relationships, suggesting that environmental conditions are driving such dissimilarities. Inter-basin dissimilarities are mainly driven by altitudinal and water temperature gradients, whereas dissimilarities among streams within the basins are influenced by channel depth, turbidity and conductivity. These five environmental variables mostly affected six fish species traits (body mass, water column position, substrate preference, parental care, foraging locality and migration) in different manners. This study is an attempt to understand functional trends of fish assemblages in a tropical region that remains poorly known but severely threatened.

Variation in benthic invertebrate abundance along thermal gradients within headwater streams of a temperate basin in Japan

To better understand the impacts of water temperature variation on stream invertebrates, we sampled benthic assemblages and measured water temperature monthly in headwater streams located in northeast Japan during 2011 and 2012. The sites in headwater streams had similar hydraulic and topographical settings, were free of man-made structures, and ranged in elevation from 100 to 850 m above sea level. The results of month-by-month analysis on the relationship between temperature and Plecoptera density revealed that the abundance declined with highly elevated temperatures in mid-summer (July, August). The strongest relationship between variation in Plecoptera abundance (June to October in 2012), however, and water temperature occurred during early summer (June). Thus, early summer temperatures contribute to greater seasonal increase in abundance, suggesting that snapshot data may be unreliable for detecting consistent relationships between the abundance and temperature. The degree of similarity in benthic fauna between sites was significantly negatively correlated with differences in water temperature but not correlated with geographical distance. These results suggest that faunal composition varies along the water temperature gradient rather than habitat connectivity in temperate headwater streams.

Thermal displacements of concrete dams: Accounting for water temperature in statistical models

Measurements of concrete dam displacements are influenced by various factors such as hydrostatic load, thermal effect and irreversible phenomena (creep, swelling, etc.). To interpret measurements and improve the assessment of irreversible effects, splitting the different influences is necessary. For this purpose, models based on statistics and physics are commonly employed in engineering studies. Although they are efficient in most cases to analyse the displacement of concrete dams, these models are built on a certain number of hypotheses, necessary to write “simple” mathematical relationships, but leading to uncertainties. To evaluate the suitability of these physico-statistical models (importance of the hypotheses) and to improve it, a 2D finite element (FE) model has been developed as a heuristic case. This study shows the importance of water temperature and temperature gradient in the assessment of the thermal displacements. So, a new physico-statistical model is proposed to account for these phenomena. The evaluation of its performance on both the FE heuristic case and real cases shows that the improved assessment of thermal effects on reversible phenomena leads to a reduced uncertainty on residuals. Thus, the proposed approach yields to a better assessment of irreversible trends.

Controls for multi-scale temporal variation in ecosystem methane exchange during the growing season of a permanently inundated fen

Wetlands are the largest natural sources for atmospheric methane (CH4). In wetlands with permanent shallow inundation, the seasonal variation of CH4 exchange is mainly controlled by temperature and phenology. In addition, ecosystem CH4 exchange varies considerably on smaller temporal scales such as days or weeks. Several single processes that control CH4 emissions on the local soil–plant–atmosphere continuum are well investigated, but their interaction on ecosystem level is not well understood yet. We applied wavelet analysis to a quasi-continuous eddy covariance CH4 flux time series to describe the temporal variation of ecosystem CH4 exchange within the growing season of a permanently inundated temperate fen. Moreover, we addressed time scale-specific controls and investigated whether their impact changes during the course of the growing season.On large time scales of two weeks to three months, temperature explained most of the variation in ecosystem CH4 exchange. In general, the temperature in the shallow water column had the largest impact as explanatory variable, however, air temperature and soil temperature became increasingly important as explanatory variables when water level dropped slightly up to June. The diurnal variation of ecosystem CH4 exchange shifted during the course of the growing season: During a short time period at the end of April, plant activity (expressed by canopy photosynthesis) caused a diurnal variation of ecosystem CH4 exchange with peak time around noon. In the following weeks, the daily cycle of convective mixing within the water column (expressed by the water temperature gradient) gradually gained importance and caused high night-time CH4 emissions, thereby levelling off the diurnal CH4 emission pattern. Moreover, shear-induced turbulence caused short-term fluctuations of ecosystem CH4 exchange on time scales up to two hours.Our study highlights the need for multi-scale approaches that consider the non-stationarity of the underlying processes to adequately describe the complexity of ecosystem CH4 exchange. Moreover, we show that CH4 release processes such as convective mixing of the water column which have been mainly considered for aquatic ecosystems (see recent exceptions in Godwin et al., 2013; Poindexter and Variano, 2013) might also be of importance in shallowly flooded terrestrial ecosystems.

Closer to the rear edge: ecology and genetic diversity down the core‐edge gradient of a marine macroalga

A fundamental goal in ecology is to understand distribution and abundance of species. Peripheral populations inhabiting the trailing‐edge of a species' distribution may carry considerable ecological and evolutionary value yet being most threatened under predicted climate change scenarios. However, the nature of species distributional limits and the ecological and genetic implications of living at low latitude rear edges remain unclear. The assumption that population abundance declines towards range edges, where environmental selective pressure increases, is the basis of a wide range of ecological and evolutionary predictions. Empirical data have provided contrasting evidence about the consequences of living at low latitude distributional limits, raising concerns regarding their generality and highlighting the need for combined multidisciplinary tests. Here, we provide a long‐term, comprehensive evaluation of latitudinal patterns in genetic diversity, demographic, morphological and life history traits in the marine macroalga Fucus guiryi.The center to edge transition was mirrored by increasing water and air temperature gradients, with sea surface temperature of coldest months being the most relevant influence on F. guiryi traits. Overall, we identified a strong correlation between ecological data, collected over one year at bimonthly intervals, and distance to the range center. We found decreasing population and individual size towards distributional margins. Similarly, reproductive capacity, threshold size for reproduction, density of reproductive population and recruitment rates showed a core to edge reduction. Temporal variability of individual reproductive effort and recruitment rates did not conform to the general pattern. In contrast, population genetic data did not show a core‐edge gradient, as gene diversity and allelic richness were not significantly lower at edge populations, contradicting predictions of higher drift and bottlenecks for smaller edge populations.The contrasting support provided by genetic and ecological data highlights the need to combine multiple and cross‐disciplinary evidence for a comprehensive understanding of ecological and evolutionary mechanisms linked to species ranges.

What causes cooling water temperature gradients in a forested stream reach?

Abstract. Previous studies have suggested that shading by riparian vegetation may reduce maximum water temperatures and provide refugia for temperature-sensitive aquatic organisms. Longitudinal cooling gradients have been observed during the daytime for stream reaches shaded by coniferous trees downstream of clear cuts or deciduous woodland downstream of open moorland. However, little is known about the energy exchange processes that drive such gradients, especially in semi-natural woodland contexts without confounding cool groundwater inflows. To address this gap, this study quantified and modelled variability in stream temperature and heat fluxes along an upland reach of the Girnock Burn (a tributary of the Aberdeenshire Dee, Scotland) where riparian land use transitions from open moorland to semi-natural, predominantly deciduous woodland. Observations were made along a 1050 m reach using a spatially distributed network of 10 water temperature data loggers, 3 automatic weather stations and 211 hemispherical photographs that were used to estimate incoming solar radiation. These data parameterised a high-resolution energy flux model incorporating flow routing, which predicted spatio-temporal variability in stream temperature. Variability in stream temperature was controlled largely by energy fluxes at the water-column–atmosphere interface. Net energy gains occurred along the reach, predominantly during daylight hours, and heat exchange across the bed–water-column interface accounted for <1% of the net energy budget. For periods when daytime net radiation gains were high (under clear skies), differences between water temperature observations increased in the streamwise direction; a maximum instantaneous difference of 2.5 °C was observed between the upstream reach boundary and 1050 m downstream. Furthermore, daily maximum water temperature at 1050 m downstream was ≤1 °C cooler than at the upstream reach boundary and lagged by >1 h. Temperature gradients were not generated by cooling of stream water but rather by a combination of reduced rates of heating in the woodland reach and advection of cooler (overnight and early morning) water from the upstream moorland catchment. Longitudinal thermal gradients were indistinct at night and on days when net radiation gains were low (under overcast skies), thus when changes in net energy gains or losses did not vary significantly in space and time, and heat advected into the reach was reasonably consistent. The findings of the study and the modelling approach employed are useful tools for assessing optimal planting strategies for mitigating against ecologically damaging stream temperature maxima.

Comparison of water-lifting aerator type for algae inhibition in stratified source water reservoirs

Abstract Non-submerged and submerged water-lifting aerators have been recently developed to improve the water quality of source water reservoirs, but the non-submerged aerator has the drawbacks of higher initial investment and being more difficult to operate and maintain compared with the submerged aerator. To explore whether the submerged water-lifting aerator also has better performance on in-situ algae inhibition in source water reservoirs, the effects of submerged and non-submerged water-lifting aerators on algae inhibition were numerically investigated under different hydrological and operational conditions. Taking Jinpen Reservoir as a study case, under different conditions of water depth, temperature gradient and inlet velocity period, the flow outside the aerators, core algae inhibition zones and mixing of algae were numerically analyzed, and the simulated results were validated against the measured data. Simulated results showed that the flow outside any water-lifting aerator was characterized as one large clockwise circulation under a stable state, but the circulated flow was developed further for the submerged case. When the water depths were 77.25 m, 87.25 m and 97.25 m, the percentages of the core algae inhibition zone to the whole flow domain were 39.71%, 41.14% and 42.73% respectively, which were 5.88%, 3.68% and 1.15% larger than those for the non-submerged case; the periods required for complete mixing of algae were 10 days, 12 days and 14 days respectively for the submerged case, which were 8 days, 7 days and 6 days shorter than those for the respective non-submerged cases. Algae were transported from the surface layer to the bottom layer mainly by advection generated from the circulated flow arising from water-lifting aeration. Under similar hydrological and operational conditions, the core algae inhibition zones were larger and the mixing of algae was quicker for the submerged case. Submerged water-lifting aerators have advantages over the non-submerged aerators in the investment required and the operation and performance of algae inhibition and are recommended for in-situ algae inhibition in stratified source water reservoirs.

The relationship between water and air temperature in chironomid-based paleoclimate reconstructions: Records from boreal and subarctic Finland

Fossil remains of larval chironomids are one of the most useful paleolimnological proxies to reconstruct Holocene paleoclimate. We investigate the within-lake distribution of chironomids in relation to water temperature and test the usability of intralake calibration in chironomid-based temperature reconstructions. We compare our findings against the traditional multilake calibration technique in Holocene sediment cores from Finland. The results show that intralake water temperature optima of common taxa correspond closely with mean July air temperature optima in a regional multilake dataset, with exception of a few vegetation-associated taxa. A calibration model based on intralake water temperatures shows performance statistics that correspond to the general performance statistics level of multilake calibration models. However, the intralake model has somewhat increased prediction error. Despite the fact that the intralake model is sensitive to poor modern analogues, it shows correlation with the results using the multilake calibration approach in the Holocene reconstructions. Our results confirm that the within-lake distribution of chironomids along a water depth gradient is closely linked with water temperature gradient. This provides evidence for the close relationship between chironomids and temperature in general and suggests that, in addition to the regional scale, water temperature is a key variable in determining chironomid distribution at the site-specific scale. However, long-term changes in intralake gradients in other depth-related factors, such as hypolimnetic oxygen conditions, extent of photic zone and habitat distribution, may hamper the quantitative accuracy of chironomid-based temperature reconstructions, though the results also suggest that these changes are likely to have little general impact on the trends of chironomid-based air temperature reconstructions.

Photosynthetic Performance of Marestail (<i>Hippuris vulgaris</i> Linn.) across a Water Temperature Gradient

we examined the photosynthetic responses of submerged marestail in three lakes using pulse amplitude modulated (PAM) fluorometry. Three lakes were studied across a gradient of water temperature, with low water temperature conditions in Grass Lake and Arrow Bamboo Lake, and higher water temperature in Five Colored Lake. In the field, electron transport rates (ETRmax) were measured as rapid light curves (RLCs) by in situ yield measurements. Submerged marestail showed higher photosynthetic activity in Five Colored Lake compared to the other lakes, a response consistent with the adaptation of marestail in Five Colored Lake to high water temperature. The optimal temperature for photosynthesis of submerged marestail in Jiuzhaigou is about 12 °C. These results indicate that in different lakes the function of these aquatic plants is associated with a diversity of place-dependent environmental conditions, especially water temperature that leads to pronounced differences in the plant’s ecophysiological reactions.

Temperature dependence of an estuarine harmful algal bloom: Resolving interannual variability in bloom dynamics using a degree day approach.

Observations of harmful algal blooms (HABs) of the dinoflagellate Alexandrium fundyense in an estuary over multiple years were used to assess drivers of their spatial and temporal variability. Nauset Estuary on Cape Cod, Massachusetts has a recurrent, self-seeding A. fundyense population that produces paralytic shellfish poisoning toxins and leads to nearly annual closure to shellfishing. Weekly surveys of the entire estuary were made in 3 of 4 consecutive years, with surveys of a subembayment during the intervening year. Major A. fundyense blooms were observed all 4 years, with maximum concentrations >106 cells L-1. Concentrations were greatest in three salt ponds at the distal edges of the estuary. The bloom timing varied among the salt ponds and among years, although the blooms had similar durations and maximum cell concentrations. Nutrient concentrations did not correlate with the growth of the bloom, but differences in water temperature among years and ponds were significant. Net growth rates inferred from the surveys were similar to those from laboratory experiments, and increased linearly with temperature. A growing degree day calculation was used to account for effects of interannual variability and spatial gradients in water temperature on population development. The approach collapsed variability in the timing of bloom onset, development, and termination across years and among ponds, suggesting that this relatively simple metric could be used as an early-warning indicator for HABs in Nauset and similar areas with localized, self-seeding blooms.

Global warming effects on benthic macroinvertebrates: a model case study from a small geothermal stream

The aim of this study was to predict global warming effects on benthic macroinvertebrate community structure by using a small temperate geothermal stream as a model system. We collected benthic macroinvertebrates, measured physical and chemical water properties at eight localities up the Kudoski stream steep water temperature gradient, and used 11 metrics and indexes to characterize community structure. Species richness and evenness decreased, but total abundance increased with the increase of average annual water temperature (t av), with species richness being most and total abundance least sensitive to this parameter. The increase of Gastropoda relative abundance and the decrease of Ephemeroptera, Plecoptera and Trichoptera richness, respectively, were the earliest responses of taxonomic groups to t av increase. Relative abundance of Orthocladiinae decreased and that of Chironomini increased with the increase of t av. This indicates that Chironomidae are not reliable predictors of global warming effects in running waters, and that lower taxonomic levels, subfamily or tribe, are more suitable for that purpose. Changes in community structure did not linearly follow t av increase, since a great community shift was observed at t av ≈ 20°C indicating that present trends of community responses to changes in climatic conditions should not be linearly extrapolated to future warming.

무각 와편모조류 Akashiwo sanguinea의 수온, 염분 그리고 광 조건에 따른 생장반응과 그에 따른 종 천이의 이점

-2 s -1 으로 나타났다. 결론적으로 A. sanguinea는 하계에 충분한 광, 높은 수온, 염분의 변동 폭이 큰 연안해역에서 종 천이를 위한 유리한 생리학적 특성을 보이는 것으로 판단된다. 핵심용어 : 와편모조류, Akashiwo sanguinea, 수온, 염분, 광 Abstract : The effects of temperature, salinity and irradiance on the growth of the dinoflagellate Akashiwo sanguinea isolated from Jaran Bay were examined in the laboratory. Maximum specific growth rate(0.28 day -1 ) was observed with combination of 25 and 30 psu. Optimal growth ( 80 % of maximum specific growth rate) was obtained at 25 with salinities of 15 35 psu. This results indicated that A. sanguinea is a stenothermal of the high water temperature and euryhaline species. The irradiance-growth curve was described as μ=0.31(I-16.87)/(I+51.19). The compensation photon flux density (I0) and half-saturation photon flux density (KI) were 16.87 μmol m -2 s -1 and 84.93 μmol m -2 s -1 , respectively. In conclustion, A. sanguinea has advantage physiological characteristics for the species succession at the coastal areas in summer with sufficient irradiance, high water temperature and large salinity gradient.

Comparison of Three Small-Scale Devices for the Investigation of the Electrical Conductivity/Resistivity of Swelling and Other Clays

AbstractElectrical measurements are used in various fields of geoscience and technology, e.g. gas/oil exploration or landslide-barrier monitoring. Although clays are amongst the most conducting geomaterials their electrical properties are not yet fully understood. For example, in a recent high-level-radioactive-waste repository large-scale test, a bentonite barrier was monitored geoelectrically. To facilitate interpretation of the results, the reasons for the observed differences in the electrical conductivity must be understood (e.g. changes in water content, temperature, salinity of pore water, etc.). To improve understanding of the electrical properties of clay minerals, in situ measurements must be combined with laboratory measurements. In situ measurements allow the characterization of the material in its natural state and laboratory measurements, for small sample amounts, allow the user to vary relevant parameters systematically such as water content, temperature, the salinity of the pore water, or even the cation population if swelling clay minerals are present. In situ measurements using different electrode distances, from m to cm range, proved that small-scale investigations are essential because of small-scale material heterogeneities. In the laboratory, all the relevant parameters mentioned above can be controlled more easily for small sample amounts. In the present study three different small-scale devices (SSM1–SSM3) were compared. The geometry factor, K, was determined both by calculation and by a calibration against solutions of different conductivity. Calculated and measured geometry factors were in good agreement. SSM1 and SSM2 — both with four pin-shaped electrodes — were found to be particularly applicable for in situ measurements. SSM2, with point contacts at the tips of the pins, was considered to be an improvement over SSM1 because the effects of both water content and temperature gradients (which are particularly relevant near the surface) were less pronounced using SSM2. SSM3, in which the contacts are placed at the bottom of a 4.5 mL trough, proved to be useful when systematically varying all of the parameters influencing the electrical properties in the laboratory.

Effect of flow rate of side-type orifice intake on withdrawn water temperature.

Side-type orifice intake is a type of selective withdrawal facility used in managing reservoirs to mitigate the negative effects of low-temperature water. Based on the temperature data of a thermal stratified reservoir in China, an experiment was conducted in flume to study the influence of intake flow rate on withdrawn water temperature with different temperature distributions. Results indicated that withdrawn water temperature changed with different flow rates. The temperature change was determined by the water temperature gradients above and below the intake, whereas the change trend of temperature depended on the difference between the water temperature gradient above and below the intake. We likewise proposed a new equation with which the withdrawn water temperature of a thermal stratified reservoir using a side-type orifice could be calculated. These findings could be directly applied to the design and operation of side-type orifice intake in thermal stratified reservoirs.

Seasonal changes in the vertical distribution and community structure of Antarctic macrozooplankton and micronekton

The macrozooplankton and micronekton community of the Lazarev Sea (Southern Ocean) was investigated at 3 depth layers during austral summer, autumn and winter: (1) the surface layer (0–2m); (2) the epipelagic layer (0–200m); and (3) the deep layer (0–3000m). Altogether, 132 species were identified. Species composition changed with depth from a euphausiid-dominated community in the surface layer, via a siphonophore-dominated community in the epipelagic layer, to a chaetognath-dominated community in the deep layer. The surface layer community predominantly changed along gradients of surface water temperature and sea ice parameters, whereas the epipelagic community mainly changed along hydrographical gradients. Although representing only 1% of the depth range of the epipelagic layer, mean per-area macrofauna densities in the surface layer ranged at 8% of corresponding epipelagic densities in summer, 6% in autumn, and 24% in winter. Seasonal shifts of these proportional densities in abundant species indicated different strategies in the use of the surface layer, including both hibernal downward and hibernal upward shift in the vertical distribution, as well as year-round surface layer use by Antarctic krill. These findings imply that the surface layer, especially when it is ice-covered, is an important functional node of the pelagic ecosystem that has been underestimated by conventional depth-integrated sampling in the past. The exposure of this key habitat to climate-driven forces most likely adds to the known susceptibility of Antarctic pelagic ecosystems to temperature rise and changing sea ice conditions.