Monitoring the impact of urbanisation on the Glinscica stream

Stream flow regimes are determined by watershed characteristics: climate, geology, topography, soil, vegetation and human activities. In the process of urbanisation, natural land surfaces are replaced by man made artificial coverage, such as paved roads, parking lots and roofs, which usually also implies vegetation clearing and soil compaction. Gutters, drains and storm sewers are built to accelerate the conveyance of runoff to stream channels, thus affecting the drainage system. The impact of urbanisation is complex and affects different elements of the hydrological cycle. The commonly observed hydrological responses of the watershed to urbanization are increased volume and peak of floodwaters. Concerning the ecological status of stream water, the intensified rainfall runoff induces increased pollution risks and diminishes the value of the stream water body as a habitat, especially during dry periods. In order to improve the flood safety, the regulations of the stream channel have further devaluated the ecological role of the urban streams. The magnitude of the impact is usually enlarged with the decrease in the stream size. The present paper aims at presenting the results of a two-year study monitoring the impacts of the urban environment on the watershed of the Glinscica stream situated in the central part of Slovenia. The study area of 19.3 km² represents a great complexity in terms of the land use pattern. The watershed was equipped with three rainfall stations, a Doppler velocity meter and a water quality multiprobe. In a short period of time more than 10 thunderstorm events were recorded and analyzed. The hydrological response of the watershed was analyzed and, interestingly, it did not show the “typical” urban impact on the runoff processes. The main water quality parameters such as temperature, pH, TDS, ORP, conductivity, dissolved oxygen and especially the concentrations of nitrate and ammonium, were measured to obtain an insight into seasonal and short time dynamics of the water quality. The results show substantial seasonal and along-the-channel variations of concentration of dissolved oxygen, nitrate and ammonium content due to biochemical processes in the channeled stream. The continuous tracing of nitrate and ammonium showed significant influence of stream regulation works on short time variations of the measured water quality parameters.     

Flood dynamics of a concrete-lined,urban stream in Kansas City,Missouri

Brush Creek drains a 76·1 km² watershed within urban Kansas City, Missouri and eastern Kansas. A concrete-lined reach trending 6·1 km through the Plaza District of Kansas City, Missouri has been the focus for several major floods over the past ten years. Channel geometry, slope, and floodwater elevations were determined in the field for segments of the concrete-lined section of Brush Creek for a flood event that occurred on September 18, 1986. Discharge was computed by indirect methods and compared to a value determined from a rating curve established by the Water Resources Division of the U.S.G.S. Boundary shear stress, unit stream power, and average velocity were also computed in order to establish a quantitative relationship between sediment distribution, volume, and size fractions; and flow dynamics operating throughout the channel during this event. Boundary shear stress ranged from 91-96 Nm^?2, stream power was 528-557 Wm^?2, while average velocity was 5-8 ms^?1. These values were sufficient to displace concrete slabs as large as 5 m long by 4·6 m wide by 0·23 m thick weighing an estimated 12 245 kg. As the channel was sediment free and unsecured prior to the flood, the distribution of deposits and subsequent channel scour provide valuable evidence for potentially hazardous sections of this urban stream.     

An index to assess hydromorphological quality of Estonian surface waters based on macroinvertebrate taxonomic composition

We developed an index (MESH – Macroinvertebrates in Estonia: Score of Hydromorphology) to assess hydromorphological quality of Estonian surface waters based on macroinvertebrate taxonomic composition. The MESH is an average score based on the affinities of selected indicator taxa to flow velocity and bottom type. As both parameters were highly correlated (r = 0.65) indicator response to both parameters were combined. The list of MESH indicators includes 394 freshwater macroinvertebrate taxa derived from 3282 samples collected from rivers and lakes during 1985–2009. The indicators were selected out of 690 taxa, by applying the information-theoretical Kullback–Leibler divergence. The individual scores of macroinvertebrates range from 0 to 3, the higher scores indicating faster flow and/or solid bottom substrate. For standing waters, flow velocity was always considered zero. Among the reference waterbodies, mean MESH was the highest for small streams followed by middle streams, large streams, and lakes. In lakes with medium water hardness (the prevailing type in Estonia), the MESH decreased gradually from stony to muddy bottom. The highest MESH values for standing waters were observed in the stony surf zone of very large lakes (area > 100 km²). The lowest values occurred for small lakes with exceptional hydrochemical characteristics (soft- and darkwater, and calcareous types). Similarly, MESH indicated stream degradation by damming. Mean MESH in reservoirs with a muddy bottom was significantly lower than in reservoirs with a hard bottom, or in unregulated stream sections.     

Distribution of surface imperviousness in small urban catchments predicts runoff peak flows and stream flashiness

Urban growth is a global phenomenon, and the associated impacts on hydrology from land development are expected to increase, especially in peri‐urban catchments. It is well understood that greater peak flows and higher stream flashiness are associated with increased surface imperviousness and storm location. However, the effect of the distribution of impervious areas on runoff peak flow response and stream flashiness of peri‐urban catchments has not been well studied. In this study, a new geometric index, Relative Nearness of Imperviousness to the Catchment Outlet (RNICO), is defined to correlate imperviousness distribution of peri‐urban catchments with runoff peak flows and stream flashiness. Study sites include 21 suburban catchments in New York representing a range of drainage area from 5 to 189 km² and average imperviousness from 10% to 48%. On the basis of RNICO, all development patterns are divided into 3 classes: upstream, centralized, and downstream. Results showed an obvious increase in runoff peak flows and decrease in time to peak when moving from upstream to centralized and downstream urbanization classes. This indicates that RNICO is an effective tool for classifying urban development patterns and for macroscale understanding of the hydrologic behavior of small peri‐urban catchments, despite the complexity of urban drainage systems. We also found that the impact of impervious distribution on runoff peak flows and stream flashiness decreases with catchment scale. For small catchments (A < 40 km²), RNICO was strongly correlated with the average (R² = .95) and maximum (R² = .91) gaged peak flows due to the relatively efficient subsurface routing through stormwater and sewer networks. Furthermore, the Richards–Baker stream flashiness index in small catchments was positively correlated with fractional impervious area (R² = .84) and RNICO (R² = .87). For large catchments (A > 40 km²), the impact of impervious surface distribution on peak flows and stream flashiness was negligible due to the complex drainage network and great variability in travel times. This study emphasizes the need for greater monitoring of discharge in small peri‐urban catchments to support flood prediction at the local scale.     

Influence of bed heterogeneity and habitat type on macroinvertebrate uptake in peri-urban streams

The role of geomorphic structure, referred to as physical heterogeneity, and its influence upon the colonization of habitat by macroinvertebrates was analysed in the peri-urban, Twin Streams Catchment, in West Auckland, New Zealand. Using a cross-scalar approach, 4 riffle-run assemblages were analysed in each of 2 River Styles (a confined, low sinuosity, gravel bed river and a partly confined, low sinuosity, bedrock, cobble, and gravel bed river). Each of these 8 locations comprised 2 distinct sampling areas; the upstream zone had a more heterogeneous river bed with a high diversity of physical features and flow, whilst the downstream area had a more homogeneous structure. Microhabitat features sampled at each site included streambed material, bank margins, fine grained organic debris, wood, and boulders. Habitat mosaics and their associated macroinvertebrate relationships followed a semi-predictable but interrupted pattern, supporting the view that river systems are a patchy discontinuum. Homogeneous zones were more frequently characterised by higher proportions of Trichoptera than heterogeneous zones, whilst heterogeneous zones were frequently characterised by Plecoptera and Ephemeroptera. Diversity was maximised when the species pools from heterogeneous and homogeneous sites were combined for any given site. Functional habitats influenced macroinvertebrate assemblages in non-linear and complex ways. Wood and organic debris habitats were associated with high diversity, abundance, and sensitive species whereas streambed habitat was usually associated with low diversity. A diverse range of physical zones that approximates the 'natural range of behaviour' for the given type of stream was considered to provide a more effective platform for rehabilitation planning than emphasising heterogeneity of physical structure in its own right.     

A spatially distributed model for the assessment of land use impacts on stream temperature in small urban watersheds

Stream temperatures in urban watersheds are influenced to a high degree by changes in landscape and climate, which can occur at small temporal and spatial scales. Here, we describe a modelling system that integrates the distributed hydrologic soil vegetation model with the semi‐Lagrangian stream temperature model RBM. It has the capability to simulate spatially distributed hydrology and water temperature over the entire network at high time and space resolutions, as well as to represent riparian shading effects on stream temperatures. We demonstrate the modelling system through application to the Mercer Creek watershed, a small urban catchment near Bellevue, Washington. The results suggest that the model was able to produce realistic streamflow and water temperature predictions that are consistent with observations. We use the modelling construct to characterize impacts of land use change and near‐stream vegetation change on stream temperatures and explore the sensitivity of stream temperature to changes in land use and riparian vegetation. The results suggest that, notwithstanding general warming as a result of climate change over the last century, there have been concurrent increases in low flows as a result of urbanization and deforestation, which more or less offset the effects of a warmer climate on stream temperatures. On the other hand, loss of riparian vegetation plays a more important role in modulating water temperatures, in particular, on annual maximum temperature (around 4 °C), which could be mostly reversed by restoring riparian vegetation in a fairly narrow corridor – a finding that has important implications for management of the riparian corridor. Copyright © 2014 John Wiley & Sons, Ltd.     

A spatially distributed model for assessment of the effects of changing land use and climate on urban stream quality

While the effects of land use change in urban areas have been widely examined, the combined effects of climate and land use change on the quality of urban and urbanizing streams have received much less attention. We describe a modelling framework that is applicable to the evaluation of potential changes in urban water quality and associated hydrologic changes in response to ongoing climate and landscape alteration. The grid‐based spatially distributed model, Distributed Hydrology Soil Vegetation Model‐Water Quality (DHSVM‐WQ), is an outgrowth of DHSVM that incorporates modules for assessing hydrology and water quality in urbanized watersheds at a high‐spatial and high‐temporal resolution. DHSVM‐WQ simulates surface run‐off quality and in‐stream processes that control the transport of non‐point source pollutants into urban streams. We configure DHSVM‐WQ for three partially urbanized catchments in the Puget Sound region to evaluate the water quality responses to current conditions and projected changes in climate and/or land use over the next century. Here, we focus on total suspended solids (TSS) and total phosphorus (TP) from non‐point sources (run‐off), as well as stream temperature. The projection of future land use is characterized by a combination of densification in existing urban or partially urban areas and expansion of the urban footprint. The climate change scenarios consist of individual and concurrent changes in temperature and precipitation. Future precipitation is projected to increase in winter and decrease in summer, while future temperature is projected to increase throughout the year. Our results show that urbanization has a much greater effect than climate change on both the magnitude and seasonal variability of streamflow, TSS and TP loads largely because of substantially increased streamflow and particularly winter flow peaks. Water temperature is more sensitive to climate warming scenarios than to urbanization and precipitation changes. Future urbanization and climate change together are predicted to significantly increase annual mean streamflow (up to 55%), water temperature (up to 1.9 °C), TSS load (up to 182%) and TP load (up to 74%). Copyright © 2016 John Wiley & Sons, Ltd.     

Quantifying and modelling urban stream temperature: a central US watershed study

Hydrologic models that rely on site specific linear and non‐linear regression water temperature (T_w) subroutines forced solely with observed air temperature (T_a) may not accurately estimate T_w in mixed‐use urbanizing watersheds where hydrogeological and land use complexity may confound common T_w regime assumptions. A nested‐scale experimental watershed study design was used to test T_w model predictions in a representative mixed‐use urbanizing watershed of the central USA. The linear regression T_w model used in the Soil and Water Assessment Tool (SWAT), a non‐linear regression T_w model, and a process‐based T_w model that accounts for watershed hydrology were evaluated. The non‐linear regression T_w model tested at a daily time step performed significantly (P < 0.01) better than the linear T_w model currently used in SWAT. Both regression T_w models overestimated T_w in lower temperature ranges (T_w < 10.0 °C) with percent bias (PBIAS) values ranging from ?28.2% (non‐linear T_w model) to ?66.1% (linear regression T_w model) and underestimated T_w in the higher temperature range (T_w > 25.0 °C) by 3.2%, and 7.2%, respectively. Conversely, the process‐based T_w model closely estimated T_w in lower temperature ranges (PBIAS = 4.5%) and only slightly underestimated T_w in the higher temperature range (PBIAS = 1.7%). Findings illustrate the benefit of integrating process‐based T_w models with hydrologic models to improve model transferability and T_w predictive confidence in urban mixed‐land use watersheds. The findings in this work are distinct geographically and in terms of mixed‐land use complexity and are therefore of immediate value to land‐use managers in similarly urbanizing watersheds globally. Copyright © 2015 John Wiley & Sons, Ltd.     

Significance of processes in the near‐stream zone on stream water acidity in a small acidified forested catchment

The near‐stream zone has received increasing attention owing to its influence on stream water chemistry in general and acidity in particular. Possible processes in this zone include cation exchange, leaching of organic matter and redox reactions of sulphur compounds. In this study the influences of processes in the near‐stream zone on the acidity in runoff from a small, acidified catchment in central southern Sweden were investigated. The study included sampling of groundwater, soil water and stream water along with hydrological measurements. An input–output budget for the catchment was established based on data from the International Co‐operative Programme on Integrated Monitoring at this site. The catchment was heavily acidified by deposition of anthropogenic sulphur, with pH in stream water between 4·4 and 4·6. There was also no relationship between stream flow and pH, which is indicative of chronic acidification. Indications of microbial reduction of sulphate were found in some places near the stream, but the near‐stream zone did not have a general impact on the sulphate concentration in discharging groundwater. The near‐stream zone was a source of dissolved organic carbon (DOC) in the stream, which had a median DOC of 6·8 mg L¹. The influence on stream acidity from organic anions was overshadowed by the effect of sulphate, however, except during a spring flow episode, when additional organic matter was flushed out and the sulphate‐rich ground water was mixed with more diluted event water. Ion exchange was not an important process in the near‐stream zone of the Kindla catchment. Different functions of the near‐stream zone relating to discharge acidity are reported in the literature. In this study there was even a variation within the site. There is therefore a need for more case studies to provide a more detailed understanding of the net effects that the near‐stream zone can have on stream chemistry under different circumstances. Copyright © 2001 John Wiley & Sons, Ltd.     

Influences of sudden changes in discharge and physical stream characteristics on transient storage and nitrate uptake in an urban stream

Changes in the physical structure of urban streams can occur abruptly due to flashy high‐flow events and subsequently alter stream processes, including transient storage and nitrate uptake. We examined temporal variability in transient storage and nitrate uptake by exploring the effects of altered physical characteristics resulting from a single high‐flow event in three reaches of Spring Creek, an urban stream in Fort Collins, Colorado, USA. Study reaches of varying geomorphic and hydraulic characteristics were chosen to represent distinct geomorphic settings in terms of substrate size, sinuosity, bed slope, and degree of rehabilitation and structural controls. We performed detailed physical characterizations and multiple nutrient injections of Br^? and NO₃^? to estimate transient storage and nitrate uptake in each reach. A comparison of pre‐flood and post‐flood data indicates that transient storage and nitrate uptake are highly context specific and mediated by interactions between geomorphic setting and flood discharge. In the two reaches that showed significant post‐flood increases in transient storage (250% to 350% increases in F_med²⁰⁰), the pool‐riffle reach exhibited a significant increase in uptake velocity, while the channelized reach did not. In contrast, transient storage decreased post‐flood in the third reach containing hydraulic structures. These complex responses likely reflect reach‐specific differences in hyporheic versus in‐channel storage. This study shows that repeat injections are necessary to describe nutrient dynamics because transient storage and nitrate uptake can be highly variable over time (showing changes on the order of 100%) due to variation in discharge and geomorphically influential flow events. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterisation of natural streams using community indices and basal resources of macroinvertebrates in the upper Euphrates Basin

The characterisation of natural stream conditions is the first important step to analyse ecological quality of streams in the Euphrates basin. We found that the community indices correspond to very good ecological conditions in five natural streams of that region. The macroinvertebrates composition differed significantly between September and May. Number of taxa and Shannon index were significantly higher in autumn than in spring. FPOM and biofilm were the most relevant basal resources of benthic invertebrates.     

A model to predict stream water temperature across the conterminous USA

Stream water temperature (t_s) is a critical water quality parameter for aquatic ecosystems. However, t_s records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict t_s at the site scale across the USA. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow database, describes the linear relationship between monthly mean air temperature (t_a) and t_s. Multiple linear regression models are used to predict the slope (m) and intercept (b) of the t_a–t_s linear relation as a function of climatic, hydrologic and land cover characteristics. Model performance to predict t_s resulted in a mean Nash–Sutcliffe efficiency coefficient of 0.78 across all sites. Application of the model to predict t_s at additional 89 nonreference sites with a higher human alteration yielded a mean Nash–Sutcliffe value of 0.45. We also analysed seasonal thermal sensitivity (m) and found strong hysteresis in the t_a–t_s relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However, groundwater contributions are negatively related to mean t_s in all seasons. Finally, we found that elevation and mean basin slope are negatively related to mean t_s in all seasons, indicating that steep basins tend to stay cooler because of shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on t_s across the USA. Copyright © 2014 John Wiley & Sons, Ltd.     

Overview of integrative tools and methods in assessing ecological integrity in estuarine and coastal systems worldwide

In recent years, several sets of legislation worldwide (Oceans Act in USA, Australia or Canada; Water Framework Directive or Marine Strategy in Europe, National Water Act in South Africa, etc.) have been developed in order to address ecological quality or integrity, within estuarine and coastal systems. Most such legislation seeks to define quality in an integrative way, by using several biological elements, together with physico-chemical and pollution elements. Such an approach allows assessment of ecological status at the ecosystem level ('ecosystem approach' or 'holistic approach' methodologies), rather than at species level (e.g. mussel biomonitoring or Mussel Watch) or just at chemical level (i.e. quality objectives) alone. Increasing attention has been paid to the development of tools for different physico-chemical or biological (phytoplankton, zooplankton, benthos, algae, phanerogams, fishes) elements of the ecosystems. However, few methodologies integrate all the elements into a single evaluation of a water body. The need for such integrative tools to assess ecosystem quality is very important, both from a scientific and stakeholder point of view. Politicians and managers need information from simple and pragmatic, but scientifically sound methodologies, in order to show to society the evolution of a zone (estuary, coastal area, etc.), taking into account human pressures or recovery processes. These approaches include: (i) multidisciplinarity, inherent in the teams involved in their implementation; (ii) integration of biotic and abiotic factors; (iii) accurate and validated methods in determining ecological integrity; and (iv) adequate indicators to follow the evolution of the monitored ecosystems. While some countries increasingly use the establishment of marine parks to conserve marine biodiversity and ecological integrity, there is awareness (e.g. in Australia) that conservation and management of marine ecosystems cannot be restricted to Marine Protected Areas but must include areas outside such reserves. This contribution reviews the current situation of integrative ecological assessment worldwide, by presenting several examples from each of the continents: Africa, Asia, Australia, Europe and North America.     

Air‐stream temperature correlation in forested and urban headwater streams in the Southern Appalachians

Air temperature can be an effective predictor of stream temperature. However, little work has been done in studying urban impacts on air‐stream relationships in groundwater‐fed headwater streams in mountainous watersheds. We applied wavelet coherence analysis to two 13‐month continuous (1 hr interval) stream and air temperature datasets collected at Boone Creek, an urban stream, and Winkler Creek, a forest stream, in northwestern North Carolina. The main advantage of a wavelet coherence analysis approach is the ability to analyse non‐stationary dynamics for the temporal covariance between air and stream temperature over time and at multiple temporal scales (e.g. hours, days, weeks and months). The coherence is both time and scale‐dependent. Our research indicated that air temperature generally co‐varied with stream temperature at time scales greater than 0.5 day. The correlation was poor during the winter at the scales of 1 to 64 days and summer at the scales of 1.5 to 4 days, respectively. The empirical models that relate air temperature to stream temperature failed at these scales and during these periods. Finally, urbanization altered the air‐stream temperature correlation at intermediate time scales ranging from 2 to 12 days. The correlation at the urban creek increased at the 12‐day scale, whereas it decreased at scales of 2 to 7 days as compared with the forested stream, which is probably due to heated surface runoff during summer thunderstorms or leaking stormwater or wastewater collection systems. Our results provide insights into air‐stream temperature relationships over both time and scale domains. Identifying controls over time and scales are needed to predict water temperature to understand the future impacts that interacting climate and land use changes will have on aquatic ecosystem in river networks. Copyright © 2014 John Wiley & Sons, Ltd.     

Macroinvertebrate communities along the main stem and tributaries of a pre-Alpine river: composition responds to altitude,richness does not

We collected quantitative macroinvertebrate samples and measured environmental and geographical parameters at 13 sites: six along the main stem and seven in tributaries close to the main channel over a 700 m gradient in altitude and 22 km longitudinal distance along the River Kokra in the Slovenian Alps. Our objectives were 1) to compare longitudinal patterns in richness and community composition between main stem and tributary sites, and 2) to determine the relative importance of the replacement and richness difference component for overall beta diversity and of environmental versus spatial distance on beta diversity among main stem and tributary sites.In total 138 taxa were identified. There were no differences between main stem and tributary sites in mean abundance or taxon richness (67 and 58, respectively). A nMDS and ANOSIM based on Bray-Curtis similarities found no separation of main stem and tributary sites, but that upper (≥880 m a.s.l) and lower sites (≤680 m a.s.l.) formed two different groups. In both main stem and tributaries taxon richness increased only slightly going downstream while the community composition (DCA1) was much better explained by altitude and distance from source.Overall, beta diversity (Sørensen and Bray-Curtis dissimilarity) was similar for the two groups, and total Sørensen dissimilarity was driven mainly by replacement in main stem (78 %) and tributary sites (77 %). Mantel tests showed that main stem dissimilarities were significantly correlated to environmental PCA distance, watercourse distance, overland distance and altitudinal differences. Tributary dissimilarities were not correlated to any of these four factors. GLMs showed that dissimilarity among main stem sites was explained only by altitude difference, while no factors were significant among tributary sites, even though nearly so for environmental PCA distance.The study illustrates the importance of measuring beta diversity along ecological gradients, such as river continua and/or altitudinal gradients, where alpha diversity may fail to detect relatively minor changes in assemblage composition. Such changes are likely to occur due to present and future climate warming.     

Local‐scale and watershed‐scale determinants of summertime urban stream temperatures

The influence of urbanization on the temperature of small streams is widely recognized, but these effects are confounded by the great natural variety of their contributing watersheds. To evaluate the relative importance of local‐scale and watershed‐scale factors on summer temperatures in urban streams, hundreds of near‐instantaneous temperature measurements throughout the central Puget Lowland, western Washington State, were collected during a single 2‐h period in August in each of the years 1998–2001. Stream temperatures ranged from 8.9 to 27.5 °C, averaging 15.4 °C. Pairwise correlation coefficients between stream temperature and four watershed variables (total watershed area and the watershed percentages of urban development, upstream lakes, and permeable glacial outwash soils as an indicator of groundwater exchange) were uniformly very low. Akaike's information criterion was applied to determine the best‐supported sets of watershed‐scale predictor variables for explaining the variability of stream temperatures. For the full four‐year dataset, the only well‐supported model was the global model (using all watershed variables); for the most voluminous single‐year (1999) data, Akaike's information criterion showed greatest support for per cent outwash (Akaike weight of 0.44), followed closely by per cent urban development + per cent outwash, per cent lake area only, and the global model. Upstream lakes resulted in downstream warming of up to 3 °C; variability in riparian shading imposed a similar temperature range. Watershed urbanization itself is not the most important determining factor for summer temperatures in this region; even the long‐recognized effects of riparian shading can be no more influential than those imposed by other local‐scale and watershed‐scale factors. Copyright © 2013 John Wiley & Sons, Ltd.     

Predicting high-frequency variation in stream solute concentrations with water quality sensors and machine learning

Stream solute monitoring has produced many insights into ecosystem and Earth system functions. Although new sensors have provided novel information about the fine-scale temporal variation of some stream water solutes, we lack adequate sensor technology to gain the same insights for many other solutes. We used two machine learning algorithms – Support Vector Machine and Random Forest – to predict concentrations at 15-min resolution for 10 solutes, of which eight lack specific sensors. The algorithms were trained with data from intensive stream sensing and manual stream sampling (weekly) for four full years in a hydrologic reference stream within the Hubbard Brook Experimental Forest in New Hampshire, USA. The Random Forest algorithm was slightly better at predicting solute concentrations than the Support Vector Machine algorithm (Nash-Sutcliffe efficiencies ranged from 0.35 to 0.78 for Random Forest compared to 0.29 to 0.79 for Support Vector Machine). Solute predictions were most sensitive to the removal of fluorescent dissolved organic matter, pH and specific conductance as independent variables for both algorithms, and least sensitive to dissolved oxygen and turbidity. The predicted concentrations of calcium and monomeric aluminium were used to estimate catchment solute yield, which changed most dramatically for aluminium because it concentrates with stream discharge. These results show great promise for using a combined approach of stream sensing and intensive stream discrete sampling to build information about the high-frequency variation of solutes for which an appropriate sensor or proxy is not available.     

An intercalibration of classification metrics of benthic macroinvertebrates in coastal and transitional ecosystems of the Eastern Mediterranean ecoregion (Greece)

Three coastal and three lagoonal sites located in Greece (Eastern Mediterranean) were selected to test and intercalibrate classification methods developed for benthic invertebrates ecological quality assessments. These methods were developed for the purposes of the European Water Framework Directive which is a European legislation adopted for the protection and improvement of the coastal and transitional waters. However, through testing these methods, this work addresses in general the issue of determining and comparing the ecological status of the coastal and transitional macrobenthic communities in Eastern Mediterranean ecosystems. Among methods tested were the biotic indices AMBI and BENTIX, the multivariate method M-AMBI and the biomass size structure index ISD in lagoonal sites only. ISD index is a rather new method developed especially for transitional ecosystems and in this contribution its performance is intercalibrated with the other benthic classification metrics. Comparison and intercalibration of the indices results in assessing the ecological quality status (EQS) are presented graphically and statistically performing the Kappa analysis. Results of the comparison and the indices' performance are evaluated based on the knowledge of the sites' environmental condition and baseline studies. Based on an extended dataset of coastal and transitional ecosystems benthic invertebrates, an evaluation of each index performance and effectiveness is attempted through an insight and comparative analysis of each methods' structure and design. Results showed that in these Eastern Mediterranean coastal sites the BENTIX index seems to give a more biologically relevant classification and gives a higher confidence level regarding the classification compared to the other indices. In the coastal areas AMBI showed a tendency for the "good" class classification, while the factorial M-AMBI gave more consistent results with the BENTIX. In the lagoonal sites the biotic indices tested were not proved efficient enough and the biomass based ISD index proved more appropriate for these ecosystems. AMBI showed the highest agreement with the ISD which is due to the better performance of this index in the slightly and moderately polluted lagoons, compared to the other indices. However, AMBI failed to classify the polluted lagoon, in which case the BENTIX gave a more relevant classification.     

Relationships between hydraulic parameters in a small stream under varying flow and seasonal conditions

Twenty conservative tracer injections were carried out in the same reach of a small woodland stream in order to determine how variation in discharge and leaf accumulation affect stream hydraulic parameters. The injections were made at various discharge rates ranging from 2·6 to 40 l/s. Five of the injections were made during late autumn, when there were large accumulations of leaves in the stream. Estimates of hydraulic parameters were made by fitting a transient storage solute transport model to conservative tracer concentration profiles. Velocity increased almost linearly with increasing discharge, indicating a decline in the Darcy friction factor. Dispersion also increased with increasing discharge, especially for the lower flow injections. The relative size of the storage zone was small (∽0·1). There was no definable relationship between discharge and the relative storage zone size, but the rates of exchange between the storage zone and the main channel increased markedly with increasing discharge. The presence of large accumulations of leaves had a clear effect on the hydraulic characteristics of the stream, producing much higher friction factors, larger storage zone sizes and lower velocity than would have been predicted by discharge alone. Copyright © 1999 John Wiley & Sons, Ltd.     

Influence of a rock glacier spring on the stream energy budget and cold‐water refuge in an alpine stream

The thermal regimes of alpine streams remain understudied and have important implications for cold‐water fish habitat, which is expected to decline due to climatic warming. Previous research has focused on the effects of distributed energy fluxes and meltwater from snowpacks and glaciers on the temperature of mountain streams. This study presents the effects of the groundwater spring discharge from an inactive rock glacier containing little ground ice on the temperature of an alpine stream. Rock glaciers are coarse blocky landforms that are ubiquitous in alpine environments and typically exhibit low groundwater discharge temperatures and resilience to climatic warming. Water temperature data indicate that the rock glacier spring cools the stream by an average of 3 °C during July and August and reduces maximum daily temperatures by an average of 5 °C during the peak temperature period of the first two weeks in August, producing a cold‐water refuge downstream of the spring. The distributed stream surface and streambed energy fluxes are calculated for the reach along the toe of the rock glacier, and solar radiation dominates the distributed stream energy budget. The lateral advective heat flux generated by the rock glacier spring is compared to the distributed energy fluxes over the study reach, and the spring advective heat flux is the dominant control on stream temperature at the reach scale. This study highlights the potential for coarse blocky landforms to generate climatically resilient cold‐water refuges in alpine streams.