Stream Water Sources Research Articles

Mean transit times in headwater catchments: insights from the Otway Ranges, Australia

Abstract. Understanding the timescales of water flow through catchments and the sources of stream water at different flow conditions is critical for understanding catchment behaviour and managing water resources. Here, tritium (3H) activities, major ion geochemistry and streamflow data were used in conjunction with lumped parameter models (LPMs) to investigate mean transit times (MTTs) and the stores of water in six headwater catchments in the Otway Ranges of southeastern Australia. 3H activities of stream water ranged from 0.20 to 2.14 TU, which are significantly lower than the annual average 3H activity of modern local rainfall, which is between 2.4 and 3.2 TU. The 3H activities of the stream water are lowest during low summer flows and increase with increasing streamflow. The concentrations of most major ions vary little with streamflow, which together with the low 3H activities imply that there is no significant direct input of recent rainfall at the streamflows sampled in this study. Instead, shallow younger water stores in the soils and regolith are most likely mobilised during the wetter months. MTTs vary from approximately 7 to 230 years. Despite uncertainties of several years in the MTTs that arise from having to assume an appropriate LPM, macroscopic mixing, and uncertainties in the 3H activities of rainfall, the conclusion that they range from years to decades is robust. Additionally, the relative differences in MTTs at different streamflows in the same catchment are estimated with more certainty. The MTTs in these and similar headwater catchments in southeastern Australia are longer than in many catchments globally. These differences may reflect the relatively low rainfall and high evapotranspiration rates in southeastern Australia compared with headwater catchments elsewhere. The long MTTs imply that there is a long-lived store of water in these catchments that can sustain the streams over drought periods lasting several years. However, the catchments are likely to be vulnerable to decadal changes in land use or climate. Additionally, there may be considerable delay in contaminants reaching the stream. An increase in nitrate and sulfate concentrations in several catchments at high streamflows may represent the input of contaminants through the shallow groundwater that contributes to streamflow during the wetter months. Poor correlations between 3H activities and catchment area, drainage density, land use, and average slope imply that the MTTs are not controlled by a single parameter but a variety of factors, including catchment geomorphology and the hydraulic properties of the soils and aquifers.

Stream Nitrogen Inputs Reflect Groundwater Across a Snowmelt-Dominated Montane to Urban Watershed.

Snowmelt dominates the hydrograph of many temperate montane streams, yet little work has characterized how streamwater sources and nitrogen (N) dynamics vary across wildland to urban land use gradients in these watersheds. Across a third-order catchment in Salt Lake City, Utah, we asked where and when groundwater vs shallow surface water inputs controlled stream discharge and N dynamics. Stream water isotopes (δ(2)H and δ(18)O) reflected a consistent snowmelt water source during baseflow. Near-chemostatic relationships between conservative ions and discharge implied that groundwater dominated discharge year-round across the montane and urban sites, challenging the conceptual emphasis on direct stormwater inputs to urban streams. Stream and groundwater NO3(-) concentrations remained consistently low during snowmelt and baseflow in most montane and urban stream reaches, indicating effective subsurface N retention or denitrification and minimal impact of fertilizer or deposition N sources. Rather, NO3(-) concentrations increased 50-fold following urban groundwater inputs, showing that subsurface flow paths potentially impact nutrient loading more than surficial land use. Isotopic composition of H2O and NO3(-) suggested that snowmelt-derived urban groundwater intercepted NO3(-) from leaking sewers. Sewer maintenance could potentially mitigate hotspots of stream N inputs at mountain/valley transitions, which have been largely overlooked in semiarid urban ecosystems.

Investigation of iron-containing products from natural and laboratory cultivated Sphaerotilus-Leptothrix bacteria.

Bacterial biomass collected from sheath-forming bacteria of the genera Sphaerotilus and Leptothrix was collected from a high-mountain natural stream water source. The elemental constitution and oxide phases of the products after selective cultivation of the bacteria on two different elective media using neutron activation analysis (NAA), electron microscopy (SEM, TEM), and X-ray diffraction (XRD) were studied. A high enrichment level of iron was revealed by the NAA technique in cultivated isolates as compared to the reference sample from nature. Three types of iron oxide compounds were established after cultivation in Adler's medium: lepidocrocite (γ-FeOOH), magnetite (Fe3O4), and goethite (α-FeOOH). The cultivation in the Isolation medium yielded a single phase, that of goethite, excluding one sample with a distinguishable amount of lepidocrocite. XRD and EM investigations show that the biogenic oxides are nanosized. Our study exemplifies the possibilities of the biotechnology approach for obtaining, under artificial conditions, large quantities of iron-containing by-products that could be of further used in appropriate nano- and biotechnologies.

Seasonal changes in runoff generation in a small forested mountain catchment

AbstractThis study aimed to investigate the seasonal variability of runoff generation processes, the sources of stream water, and the controls on the contribution of event water to streamflow for a small forested catchment in the Italian pre‐Alps. Hydrometric, isotopic, and electrical conductivity data collected between August 2012 and August 2013 revealed a marked seasonal variability in runoff responses. Noticeable differences in runoff coefficients and hydrological dynamics between summer and fall/spring rainfall events were related to antecedent moisture conditions and event size. Two‐component and three‐component hydrograph separation and end‐member mixing analysis showed an increase in event water contributions to streamflow with event size and average rainfall intensity. Event water fractions were larger during dry conditions in the summer, suggesting that stormflow generation in the summer consisted predominantly of direct channel precipitation and some saturated overland flow from the riparian zone. On the contrary, groundwater and hillslope soil water contributions dominated the streamflow response during wet conditions in fall. Seasonal differences were also noted between event water fractions computed based on isotopic and electrical conductivity data, likely because of the dilution effect during the wetter months. Copyright © 2014 John Wiley & Sons, Ltd.

Contributions of bedrock groundwater to the upscaling of storm‐runoff generation processes in weathered granitic headwater catchments

AbstractWe examined the contributions of bedrock groundwater to the upscaling of storm‐runoff generation processes in weathered granitic headwater catchments by conducting detailed hydrochemical observations in five catchments that ranged from zero to second order. End‐member mixing analysis (EMMA) was performed to identify the geographical sources of stream water. Throughfall, hillslope groundwater, shallow bedrock groundwater, and deep bedrock groundwater were identified as end members. The contribution of each end member to storm runoff differed among the catchments because of the differing quantities of riparian groundwater, which was recharged by the bedrock groundwater prior to rainfall events. Among the five catchments, the contribution of throughfall was highest during both baseflow and storm flow in a zero‐order catchment with little contribution from the bedrock groundwater to the riparian reservoir. In zero‐order catchments with some contribution from bedrock groundwater, stream water was dominated by shallow bedrock groundwater during baseflow, but it was significantly influenced by hillslope groundwater during storms. In the first‐order catchment, stream water was dominated by shallow bedrock groundwater during storms as well as baseflow periods. In the second‐order catchment, deeper bedrock groundwater than that found in the zero‐order and first‐order catchments contributed to stream water in all periods, except during large storm events. These results suggest that bedrock groundwater influences the upscaling of storm‐runoff generation processes by affecting the linkages of geomorphic units such as hillslopes, riparian zones, and stream channels. Our results highlight the need for a three‐dimensional approach that considers bedrock groundwater flow when studying the upscaling of storm‐runoff generation processes. Copyright © 2014 John Wiley & Sons, Ltd.

Lateral inflows, stream‐groundwater exchange, and network geometry influence stream water composition

AbstractThe role of stream networks and their hydrologic interaction with hillslopes and shallow groundwater in modifying and transporting watershed signals is an area of active research. One of the primary ways that stream networks can modify watershed signals is through spatially variable stream gains and losses, described herein as hydrologic turnover. We measured hydrologic gain and loss at the reach scale using tracer experiments throughout the Bull Trout watershed in the Sawtooth Mountains of Idaho. We extended the results of reach scale experiments to the stream network using empirical relationships between (1) watershed area and stream discharge and (2) stream discharge and percent stream water loss to the groundwater system. We thus incorporate linkages between (1) hillslopes and stream networks via lateral inflows and (2) stream networks and shallow groundwater via hydrologic exchange. We implemented these relationships within a concise analytical framework to simulate hydrologic turnover across stream networks and estimate the variable influence exerted by upstream reaches and streamflow source locations on stream water composition across stream networks. Application to six natural Sawtooth watersheds and seven synthetic watersheds with varying topographic structure and stream network geometry indicated that contributions to discharge from any upstream source depend on the magnitude of the initial input, but also on the distribution of hydrologic turnover occurring along the stream network. The evolution of stream water source compositions along stream networks was unique in each watershed due to the combination of watershed structure and stream network geometry. Our results suggest that a distributed representation of hydrologic turnover at the stream network scale can improve understanding of how the stream network can modify source water compositions along the stream.

Watershed Glacier Coverage Influences Dissolved Organic Matter Biogeochemistry in Coastal Watersheds of Southeast Alaska

The Coast Mountains of southeast Alaska are currently experiencing some of the highest rates of glacier volume loss on Earth, with unknown implications for proglacial stream biogeochemistry. We analyzed streamwater for δ18O and dissolved organic matter (DOM) biogeochemistry (concentration, δ13C-dissolved organic carbon (DOC), and fluorescence characterization) during the 2012 glacial runoff season from three coastal watersheds in southeast Alaska that ranged in glacier coverage from 0 to 49% and a glacier outflow stream. Our goal was to assess how DOM biogeochemistry may change as receding glaciers are replaced by forests and glaciers contribute less meltwater to streamflow. Discharge and streamwater δ18O varied seasonally reflecting varying contributions of rainfall and snow/icemelt to streamflow over the runoff season. Mean DOC concentrations were lowest in the glacial outflow and highest in the non-glacial stream reflecting an increasing contribution of vascular plant-derived carbon with decreasing watershed glaciation. Fluorescence and δ13C-DOC signatures indicated that DOM shifted from vascular plant-derived, humic-like material in the non-glacial stream toward more δ13C-DOC enriched, glacier-derived DOM in the glacial outflow. Streamwater δ18O was significantly correlated to DOC concentration, δ13C-DOC, and protein-like fluorescence of streamwater DOM (all P < 0.05), demonstrating that changes in the source of streamwater across the glacial watershed continuum have important implications for the amount and quality of stream DOM export. Overall, our findings show that continued glacial recession and subsequent changes in glacial runoff could substantially influence the biogeochemistry of coastal temperature watersheds by altering the timing, magnitude, and chemical signature of DOM delivered to streams.

Nitrogen production from geochemical weathering of rocks in southwest Montana, USA

AbstractA 30 day time course laboratory weathering experiment was conducted using rock samples collected from the West Fork of the Gallatin River watershed (WFW) in southwestern Montana, USA. The goal of these experiments was to quantify the amount of labile nitrogen in rock samples collected from the watershed and determine if chemical weathering is a source of dissolved nitrogen in stream water. Several rock samples investigated produced nitrate in significantly higher concentrations than the silica bead control (p &lt; 0.05), and the data were consistent with elevated NO3− concentrations measured in associated WFW streams. Isotopic analyses of 15N‐NO3 in 22 stream water samples from the WFW and four rock:water extracts from the laboratory experiments indicated that the isotopic composition of NO3 was comparable with rocks and stream water samples in the same watershed and differed strongly from waters downstream of development. We suggest that the NO3− measured in WFW streams includes nitrogen derived from mineral dissolution products from soils and rock. The results presented herein further indicate that rock weathering is a source of stream water N in the West Fork watershed and inform water quality assessment, total maximum daily load development, and the relative influences of natural and anthropocentrically derived N sources across this developing mountain watershed.

English

An investigation on the incidence of Staphylococcus aureus, coliforms and antibiotic resistant Escherichia coli strains in both treated and untreated rural water supplies was carried out in Calabar South Local Government Area of Cross River State, Nigeria. Analysis revealed significant differences between the different water sources, locations and the months of sampling, with the stream and well water showing higher bacterial contamination compared to the tap water source (P<0.05). The isolation of S. aureus, Bacillus species,Pseudomonas aeruginosa and other bacterial pathogens present enough evidence that water from these sources are unfit for human consumption and constitute significant public health implications except subjected to further treatment. High percentages of the E. colistrains isolated from the water sources showed multiple resistances to most of the antibiotics commonly used by humans. Strains recovered from the stream and well water sources were most resistant and showed significantly higher minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) (P < 0.05) than those from the tap water source. The results of this investigation therefore revealed that the bacteriological quality of both the treated tap and untreated well and stream water sources failed to meet the standards for drinking water. Key words: Incidence, Staphylococcus aureus, coliforms, Escherichia coli, antibiotic resistance, water supplies.

Fine scale variations of surface water chemistry in an ephemeral to perennial drainage network

AbstractAlthough temporal variation in headwater stream chemistry has long been used to document baseline conditions and response to environmental drivers, less attention is paid to fine scale spatial variations that could yield clues to processes controlling stream water sources. We documented spatial and temporal variation in water composition in a headwater catchment (41 ha) at the Hubbard Brook Experimental Forest, NH, USA. We sampled every 50 m along an ephemeral to perennial stream network as well as groundwater from seeps and 35 shallow wells across varying flow conditions. Groundwater influences on surface water in this region have not been considered to be important in past studies as relatively coarse soils were assumed to be well drained in steep catchments with flashy runoff response. However, seeps displayed perennial discharge, upslope accumulated areas (UAA) smaller than those for channel initiation sites and higher pH, Ca and Si concentrations than streams, suggesting relatively long groundwater residence time or long subsurface flow paths not bound by topographic divides. Coupled with a large range in groundwater chemistry seen in wells, these results suggest stream chemistry variation reflects the range of connectivity with, and quality of, groundwater controlled by hillslope hydropedological processes. The magnitude of variations of solute concentrations seen in the first order catchment was as broad as that seen at the fifth order Hubbard Brook Valley (3519 ha). Reduction in variation in solute concentrations with increasing UAA suggested a representative elementary area (REA) value of less than 3 ha in the first order catchment, compared with 100 ha for the fifth order basin. Thus, the REA is not necessarily an elementary catchment property. Rather, the partitioning of variation between highly variable upstream sources and relatively homogenous downstream characteristics may have different physical significance depending on the scale and complexity of the catchment under examination. Copyright © 2012 John Wiley &amp; Sons, Ltd.

MICROBIOLOGICAL EVALUATION OF STREAM WATER FOR DOMESTIC USE IN RURAL AREAS: A CASE STUDY OF IJEBU NORTH LOCAL GOVERNMENT, OGUN STATE. NIGERIA

This study aimed at evaluating the microbial quality of stream water sources for domestic purposes by rural communities in Ijebu North Local Government to determine their fitness for human consumption. The evaluated streams include Erilobinla, Imosun, Okenugbo, Odoralamo, Odoye, loji, Mamu and Tekunle oga. Physicochemical parameters were determined; pour plate method using selective media were employed to determine the enteric bacteria present in water samples. Bacterial isolates were characterized adopting the standard methods, and isolates were further subjected to antimicrobial sensitivity testing using the disc diffusion technique. The result of physicochemical parameters showed that temperature value varied from 25 - 290C, pH varied from 7.30 - 8.50, and total dissolved solid (TDS) of samples were not in agreement with WHO standards. Two of the eight streams analysed had odour, three had taste and two had colour . The total bacteria count revealed that Erilobinla stream water had the highest total bacteria count of 9.0 x 104 cfu/ml while Okenugbo and Odoye had the lowest total bacteria count of 1.0 x 101 cfu/ml. The microorganisms isolated were Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Campylobacter species, Salmonella species, Klebsiella species, Proteus species and Pseudomonas aeruginosa. The antimicrobial sensitivity testing showed that these organisms were resistant to some antimicrobials. In conclusion, most of the stream waters are unsafe for drinking as they are of low quality thresholds. Thus, the stream waters require further purification to ensure suitability for human consumption and there is urgent need for provision of potable water to prevent outbreak of waterborne diseases.Â

Hillslope hydrologic connectivity controls riparian groundwater turnover: Implications of catchment structure for riparian buffering and stream water sources

Hydrologic connectivity between catchment upland and near stream areas is essential for the transmission of water, solutes, and nutrients to streams. However, our current understanding of the role of riparian zones in mediating landscape hydrologic connectivity and the catchment scale export of water and solutes is limited. We tested the relationship between the duration of hillslope‐riparian‐stream (HRS) hydrologic connectivity and the rate and degree of riparian shallow groundwater turnover along four HRS well transects within a set of nested mountain catchments (Tenderfoot Creek Experimental Forest, MT). Transect HRS water table connectivity ranged from 9 to 123 days during the annual snowmelt hydrograph. Hillslope water was always characterized by low specific conductance (∼27 μS cm−1). In transects with transient hillslope water tables, riparian groundwater specific conductance was elevated during base flow conditions (∼127 μS cm−1) but shifted toward hillslope signatures once a HRS groundwater connection was established. The degree of riparian groundwater turnover was proportional to the duration of HRS connectivity and inversely related to the riparian: hillslope area ratios (buffer ratio; r2 = 0.95). We applied this relationship to the stream network in seven subcatchments within the Tenderfoot Creek Experimental Forest and compared their turnover distributions to source water contributions measured at each catchment outlet. The amount of riparian groundwater exiting each of the seven catchments was linearly related (r2 = 0.92) to their median riparian turnover time. Our observations suggest that the size and spatial arrangement of hillslope and riparian zones along a stream network and the timing and duration of groundwater connectivity between them is a first‐order control on the magnitude and timing of water and solutes observed at the catchment outlet.

Critical Control Points in the Processing of Cassava Tuber for Ighu Production

Determination of the critical control points in the processing of cassava tuber into Ighu was carried out. The critical control points were determined according to the Codex guidelines for the application of the HACCP system by conducting hazard analysis. Hazard analysis involved proper examination of each processing step in order to know the possible source(s) of hazard, which could be biological, chemical or physical. Results showed that the critical control points in the processing of Ighu include washing (CCP2), drying (CCPI) and storage (CCPI). Use of water of high microbial quality such as rainwater resulted to a product of lesser microbial content and most of the unit operations such as washing and pre drying led to reduction in cyanide content of the product. There was no significant difference (P>0.05) in the total solids content of samples washed in rain and stream waters but there was significant difference (P<0.05) in total solid content of the pre dried and un-pre-dried samples when washed in both the rain and stream water sources.

Trace metal Contamination in Water from abandoned mining and non-mining areas in the Northern Parts of the Ashanti Gold Belt, Ghana

A survey was conducted on the levels of trace metals (Ni, Cu, Hg, Pb, Mn, Fe, Zn, Cr, Cd, Mg and Ca) in ground and surface water sources from the northern parts of the Ashanti gold belt. Water samples were collected from 67 boreholes, 24 wells, and 10 streams during dry and wet seasons for trace metal analyses using Philips PU 9200 atomic absorption spectrophotometer. The main objective was to determine whether trace metal contamination in the study area was as a result of mining or geochemical and biochemical processes within the aquifer. The results showed that ground water (pH range 4.09–7.29 and mean 5.87 pH units) was slightly acidic (low pH) than surface water (pH range 5.81–7.74 and mean 7.12 pH units). The ground waters (with conductivity range 96–1553 mS/cm and mean 407.7 mS/cm) in the study area were also more mineralized than surface waters (with conductivity range 113–540 mS/cm and mean 323.30 mS/cm). Correlations between the trace metals revealed expected process-based relationship between Mg2+ and Ca2+ (r = 0.76), derived mainly from the geochemical and biochemical processes within the aquifer. However, there were also other strong linear relationships between trace metals, such as Fe2+ and Ca2+ (r = 0.61); Mg2+ and Mn2+(r = 0.72), Hg2+ and Mn2+ (r = 0.61), that are not normally expected to be linked in terms of processes. All the well and stream water sources had one or more trace metal level outside acceptable limits set by the World Health Organization for drinking water, and only three borehole water samples at Konongo (Abronikrom), Ntronang (Ahenbronoso) andBomfa (Nkubem) were safe for human consumption

Elucidation of the relationship between geographic and time sources of stream water using a tracer approach in a headwater catchment

Tracer approaches have been used worldwide to clarify time and geographic sources of stream water in catchments, although the relationship between these two sources is poorly discussed. We considered the mean residence time (MRT) and its spatial distribution to determine the relationship between geographic source components and time source components. There were clear differences in solute concentrations and MRT among shallow, middle, and bottom layers along the vertical profile of the riparian groundwater body. Those in the stream water were intermediate compared to those in the shallow and middle layers; thus, the consistent geographic sources were groundwater in these layers. In the context of end‐members mixing analysis (EMMA), however, the end‐members were rainfall, hillslope groundwater, and riparian groundwater in the bottom layer. The other riparian groundwaters were a mixture of end‐members. The discrepancy between the geographic sources and the end‐members was resolved by considering the MRT, the time required to move the end‐member or geographic source within the catchment. Our approach clarified the relationships among the geographic sources, time sources, and hydrological pathways, which are the essential factors of runoff generation processes and hydrochemical processes. Therefore, to go beyond previous applications of EMMA on the basis of systematic learning from observed data, it is insightful to combine the common approaches to analyze landscape heterogeneity and process complexity and to reconsider the framework of the hydrobiogeochemical models in various regions and at multiple spatial scales.

Spatial heterogeneity of water temperature across an alpine river basin

AbstractRiver temperature remains a subject of major worldwide research, yet understanding of multi‐scale thermal variability across river systems is limited. Such studies are necessary to elucidate the relative importance of site‐specific (reach‐scale) versus landscape controls. This article addresses this research need by identifying water temperature variability across an alpine river basin, using high‐resolution (15 min) water column temperature data at 29 sites in the Taillon–Gabiétous basin, French Pyrénées. Thermal patterns were examined in relation to a suite of meteorological (incoming shortwave radiation, air temperature, and precipitation) and basin characteristics (altitude, azimuth, stream length, and stream order). Mean water temperature for the monitoring period varied markedly across the river basin, ranging from 0·4 °C at the Taillon Glacier to 14·6 °C in a south‐facing hillslope groundwater stream. Basin‐scale water temperature patterns were strongly influenced by stream water source. Stream temperature was also significantly associated with basin characteristics, most notably altitude, azimuth, and stream length. Thermal heterogeneity across the basin was higher than that along the Taillon Glacier stream, despite rapid longitudinal warming rates with distance from the glacier snout. The timing of thermal extremes (maximum/minimum) during two contrasting hydrometeorological events (hot summer day vs intense hail/rain storm) revealed a clear synchronicity of thermal response among sites, although notable exceptions included karstic groundwater streams that were weakly influenced by concurrent meteorological conditions. Overall, the study demonstrates high thermal heterogeneity at the basin scale (being equal to, or greater than, that found in previous investigations), and the major effect of water source and landscape factors such as altitude, azimuth, and stream length on alpine stream temperature. Copyright © 2008 John Wiley &amp; Sons, Ltd.

An approach to understanding hydrologic connectivity on the hillslope and the implications for nutrient transport

Hydrologic processes control much of the export of organic matter and nutrients from the land surface. It is the variability of these hydrologic processes that produces variable patterns of nutrient transport in both space and time. In this paper, we explore how hydrologic “connectivity” potentially affects nutrient transport. Hydrologic connectivity is defined as the condition by which disparate regions on the hillslope are linked via subsurface water flow. We present simulations that suggest that for much of the year, water draining through a catchment is spatially isolated. Only rarely, during storm and snowmelt events when antecedent soil moisture is high, do our simulations suggest that mid‐slope saturation (or near saturation) occurs and that a catchment connects from ridge to valley. Observations during snowmelt at a small headwater catchment in Idaho are consistent with these model simulations. During early season discharge episodes, in which the mid‐slope soil column is not saturated, the electrical conductivity in the stream remains low, reflecting a restricted, local (lower slope) source of stream water and the continued isolation of upper and mid‐slope soil water and nutrients from the stream system. Increased streamflow and higher stream water electrical conductivity, presumably reflecting the release of water from the upper reaches of the catchment, are simultaneously observed when the mid‐slope becomes sufficiently wet. This study provides preliminary evidence that the seasonal timing of hydrologic connectivity may affect a range of ecological processes, including downslope nutrient transport, C/N cycling, and biological productivity along the toposequence. A better elucidation of hydrologic connectivity will be necessary for understanding local processes as well as material export from land to water at regional and global scales.

Macroinvertebrate stream communities along regional and physico‐chemical gradients in Western Greenland

1. Macroinvertebrates were collected and physico‐chemical variables measured at 16 stream sites in Western Greenland during July 1999. Eight sites were located on Disko Island in an arctic oceanic climate and eight sites in the Kangerlussuaq area close to the icecap where the climate is arctic continental. The streams had different water sources (glacial, groundwater, snowmelt and lake water).2. The streams showed pronounced differences in water temperature (2.2–17.3 °C), concentrations of suspended solids (0–2400 mg L−1), and conductivity (10–109 μS cm−1). Principal component analysis (PCA) analysis of the physico‐chemical variables separated the Disko Island sites into a distinct group, whereas the sites in the Kangerlussuaq area were more dispersed.3. A total of 56 macroinvertebrate species were found, including 31 species of Chironomidae, the most abundant of which was Orthocladius thienemanni. Diamesa sp. was only the sixth most abundant chironomid taxon. Species composition varied between sites, and abundance varied from about 20 individuals m−2 in a glacier fed stream to more than 16 000 m−2 in a lake outlet.4. The macroinvertebrate communities of the 16 streams were separated into five TWINSPAN groups reflecting water source, irrespective of region. Lake outlets and ground‐water‐fed streams had the highest species richness and abundance, temperature and bed stability, while glacier‐fed streams were characterized by low species richness, abundance, temperature, bed stability and high concentrations of suspended solids. Macroinvertebrate species richness was positively correlated with water temperature and negatively with bed stability. Conductivity was positively correlated with invertebrate abundance.5. The results of this study suggest that the source of stream water can be used to predict invertebrate community composition in Greenlandic streams and thus the effects of changes in water balance and flow regime, and to identify sites of special conservation interest.

Ba/Sr, Ca/Sr and 87Sr/ 86Sr ratios in soil water and groundwater: implications for relative contributions to stream water discharge

Barium/Sr and Ca/Sr ratios have been used to model the relative importance of different sources of stream water. Major and trace element concentrations together with 87Sr/ 86Sr ratios were measured in precipitation, soil water, groundwater and stream water in a small (9.4 km 2) catchment in northern Sweden. The study catchment is drained by a first order stream and mainly covered with podzolized Quaternary till of granitic composition. It is underlain by a 1.8 Ga granite. A model with mixing equations used in an iterative mode was developed in order to separate the stream water into 3 subsurface components: soil water, shallow groundwater, and deep groundwater. Contributions from precipitation are thus not included in the model. This source may be significant for the stream water generation, but it does not interfere with the calculations of the relative contributions from the subsurface components. The results show that the deep groundwater constitutes between 5 and 20% of the subsurface water discharge into the stream water. The highest values of the deep groundwater fraction occur during base flow. Soil water dominates during snowmelt seasons, whereas during base flow it is the least important fraction. Soil water accounts for 10–100% of the subsurface water discharge into the stream water. Shallow groundwater accounts for up to 80% of the subsurface water discharge with the lowest values at peak discharge during snowmelt seasons and the highest values during base flow. The validity of the model was tested by comparing the measured 87Sr/ 86Sr ratios in the stream water with the 87Sr/ 86Sr ratios predicted by the model. There was a systematic difference between the measured and modelled 87Sr/ 86Sr ratios which suggests that the fraction of soil water is overestimated by the model, especially during spring flood. As a consequence of this overestimation of soil water the amount of shallow groundwater is probably underestimated during this period. However, it is concluded that the differences between measured and predicted values are relatively small, and that element ratios are potentially effective tracers for different subsurface water flowpaths in catchments.

Impact of Nitrogen and Phosphorus on [ 14 C]Lignocellulose Decomposition by Stream Wood Microflora

Nutritional and physical factors affecting the decomposition of [C]lignocellulose prepared from Douglas fir (Pseudotsuga menziesii) were examined by incubating the labeled substrate with homogenized surface wood scrapings obtained from a Douglas fir log in a Pacific Northwest stream. Incubations were conducted in distilled water, in stream water collected from four different sources, or in a defined mineral salts solution with or without supplemental N (KNO(3)). Decomposition rates of [C]lignocellulose, as measured by CO(2) evolution, were greater in each of the four filter-sterilized sources of stream water than in distilled water alone. Decomposition experiments conducted in stream water media with the addition of defined mineral salts demonstrated that [C]cellulose decomposition was stimulated 50% by the addition of either KNO(3) or KH(2)PO(4)/K(2)HPO(4) and further enhanced (167%) by a combination of both. In contrast, [C]lignin decomposition was stimulated (65%) only by the addition of both N and P. Decomposition of [C]lignocellulose was greatest when supplemental KNO(3) was supplied in concentrations of at least 10.0 mg of N liter but not increased further by higher concentrations. The decomposition of [C]lignocellulose increased as the incubation temperature was raised and NO(3)-N supplementation further increased these rates between three-and sevenfold over the range of temperatures examined (5 to 22 degrees C). Accumulation of NH(4) (2 to 4 mg of N liter) was always observed in culture filtrates of incubations which had been supplemented with KNO(3), the quantity being independent of NO(3) concentrations >/= 10 mg of N liter. The role of supplemental NO(3) in the decomposition of [C]lignocellulose is discussed in relation to wood decomposition and the low concentrations of N found in stream ecosystems of the Pacific Northwest.