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1.
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 Fmed200), 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.  相似文献   

2.
Surface water–groundwater interaction in the hyporheic zone may enhance biogeochemical cycling in streams, and it has been hypothesized that streams exchanging more water with the hyporheic zone should have more rapid nitrate utilization. We used simultaneous conservative solute and nitrate addition tracer tests to measure transient storage (which includes hyporheic exchange and in‐stream storage) and the rate of nitrate uptake along three reaches within the Red Canyon Creek watershed, Wyoming. We calibrated a one‐dimensional transport model, incorporating transient storage (OTIS‐P), to the conservative solute breakthrough curves and used the results to determine the degree of transient storage in each reach. The nitrate uptake length was quantified from the exponential decrease in nitrate concentration with distance during the tracer tests. Nitrate uptake along the most downstream reach of Red Canyon Creek was rapid (turnover time K?1c = 32 min), compared with nitrate uptake reported in other studies (K?1c = 12 to 551 min), but other sites within the watershed showed little nitrate retention or loss. The uptake length Sw‐NO?3 for the most downstream reach was 500 m and the mass transfer coefficient Vf‐NO?3 was 6·3 m min?1. Results from 15 other nitrate‐addition tracer tests were used to create a regression model relating transient storage and measures of stream flow to nitrate uptake length. The model, which includes specific discharge and transient storage area, explains almost half the variability in nitrate uptake length (adjusted R2 = 0·44) and is most effective for comparing sites with very different stream characteristics. Although large differences in specific discharge and storage zone area explain inter‐site differences in nitrate uptake, other unmeasured variables, such as available organic carbon and microbial community composition, are likely important for predicting differences in nitrate uptake between sites with similar specific discharge rates and storage zone areas, such as when making intra‐site comparisons. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
Streams can be classified as stable or unstable, depending on the stage of channel evolution. Many streams of the southern Piedmont in United States have high sediment loads and are listed as impaired under the total maximum daily load (TMDL) program and may be unstable. It is not clear as to what the target (reference) load or remediation measures should be for unstable streams. The objective of this study was to determine the relative channel stability for a typical southern Piedmont stream using rapid geomorphic assessments (RGAs) and sediment yield analysis. The results were supported through a sediment fingerprinting analysis. RGAs were performed along 52 reaches on the North Fork Broad River (NFBR) main stem and two tributaries. Annual sediment yields were calculated and compared with yields in the southern Piedmont for stable streams that are resilient to degradation or aggradation and unstable streams that are susceptible to such disturbances. Majority of the NFBR main stem was found to be unstable with signs of geomorphic instability in the form of degradation and aggradation. The estimated average annual sediment yield was 0·78 T ha?1 year?1. By comparison, the median annual yield is 0·20 T ha?1 year?1 for stable streams and 0·48 T ha?1 year?1 for unstable streams in the Piedmont ecoregion with comparable drainage basin size. We conclude that the NFBR is in an unstable stage of channel evolution. Sediment fingerprinting proved that majority of the stream‐suspended sediment emanated from eroding stream channels. The methods outlined in this study have implications for the reference condition and remediation efforts related to stream turbidity and stream channel restoration. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was low in the restored streams during summer baseflow conditions. Uptake length of NO3 −–N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3 −–N m−2 day−1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary, however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in response to the “flashy” hydrologic flow conditions during storms common in urban streams.  相似文献   

5.
In the McMurdo Dry Valleys of Antarctica, glaciers are the source of meltwater during the austral summer, and the streams and adjacent hyporheic zones constitute the entire physical watershed; there are no hillslope processes in these systems. Hyporheic zones can extend several metres from each side of the stream, and are up to 70 cm deep, corresponding to a lateral cross‐section as large as 12 m2, and water resides in the subsurface year around. In this study, we differentiate between the near‐stream hyporheic zone, which can be characterized with stream tracer experiments, and the extended hyporheic zone, which has a longer time‐scale of exchange. We sampled stream water from Green Creek and from the adjacent saturated alluvium for stable isotopes of D and 18O to assess the significance and extent of stream‐water exchange between the streams and extended hyporheic zones over long time‐scales (days to weeks). Our results show that water residing in the extended hyporheic zone is much more isotopically enriched (up to 11‰ D and 2·2‰ 18O) than stream water. This result suggests a long residence time within the extended hyporheic zone, during which fractionation has occurred owing to summer evaporation and winter sublimation of hyporheic water. We found less enriched water in the extended hyporheic zone later in the flow season, suggesting that stream water may be exchanged into and out of this zone, on the time‐scale of weeks to months. The transient storage model OTIS was used to characterize the exchange of stream water with the extended hyporheic zone. Model results yield exchange rates (α) generally an order magnitude lower (10?5 s?1) than those determined using stream‐tracer techniques on the same stream. In light of previous studies in these streams, these results suggest that the hyporheic zones in Antarctic streams have near‐stream zones of rapid stream‐water exchange, where ‘fast’ biogeochemical reactions may influence water chemistry, and extended hyporheic zones, in which slower biogeochemical reaction rates may affect stream‐water chemistry at longer time‐scales. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

6.
Trevor Klein  Laura Toran 《水文研究》2016,30(17):2948-2957
The hydrologic and biogeochemical processes that control nutrient export in urban streams are not well understood. Attenuation can occur by tributary dilution, groundwater discharge, and biological processing both in the water column and the hyporheic zone. A wastewater treatment plant on Pennypack Creek, an urban stream near Philadelphia, PA, provided high nitrate concentrations for analysis of downstream attenuation processes. Longitudinal sampling for an 8‐km reach revealed decreases in nitrate concentration of 2 mg l?1 at high flow and 4.5 mg l?1 during low flow. During high flow, δ15N‐NO3 increased from 9.5 to 10.5‰ and during low flow increased from 10.1 to 11.1‰. Two reaches were sampled at fine spatial intervals (approximately 200 m) to better identify attenuation processes. Mixing analysis indicated that groundwater discharge and biological processing both control nitrate concentration and isotope signatures. However, fine‐scaled sampling did not reveal spatially discrete zones; instead, these processes were occurring simultaneously. While both processes attenuate nitrate, they have opposite isotope signatures, which may have muted changes in δ15N‐NO3. At high flow, a decrease in Cl/NO3 ratios helped distinguish groundwater discharge occurring along both finely sampled reaches. At low flow, biological processing seemed to be occurring more extensively, but the δ15N‐NO3 signature was not consistent with either a single process or a sequential combination of groundwater dilution and biological nitrate attenuation. The collocation of processes makes it more difficult to assess biological processing hot spots and predict how urbanization and subsequent stream restoration influence nitrate attenuation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

7.
Background aqueous chemistry and 15Nnitrate tracer injection methods were used to calculate in‐stream nitrate uptake metrics at Red Canyon Creek, a third‐order stream in the Rocky Mountains in the state of Wyoming, United States. ‘Net’ nitrate uptake lengths, which reflect both nitrate uptake and regeneration, and ‘gross’ nitrate uptake lengths, which exclude re‐mineralization, were quantified separately from background nitrate chemistry and 15N labelling tracer data, respectively. Gross nitrate uptake lengths, from tracer injections of 15N labelled nitrate, ranged from 502 to 3140 m. Net nitrate uptake lengths, from background nitrate chemistry downstream of a point source, ranged from 1170 to 4330 m. Diurnal changes in uptake lengths suggest the importance of nitrate utilization by autotrophs in the stream and benthic zone. The differences between net and gross nitrate uptake lengths along lower reaches of Red Canyon Creek allowed us to estimate the nitrate regeneration rate, which was 0·056–0·080 µmol m?2 s?1 during the day and 0·0062–0·0083 µmol m?2 s?1 at night. Spatial patterns of streambed pore water chemistry indicate those areas of the hyporheic zone where denitrification was likely occurring. Permanent log dams generated stronger redox gradients in the hyporheic zone than areas with transient beaver dams. By combining isotopically labelled nitrate additions, estimates of uptake from background aqueous nitrate chemistry and characterization of redox conditions in the hyporheic zone, we were able to determine the nitrate regeneration rate and the redox processes responsible for nitrogen cycling in the hyporheic zone. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Investigations of phosphorus cycling and transport in streams lend insight into potential mechanisms of nutrient sequestration and can help mitigate human impacts. In this study, we examined the relationship between transient storage and phosphorus uptake in a cold‐water stream in western Wisconsin. Hydrological characteristics, nutrient spiralling metrics, macrophyte biomass, and geomorphological properties were quantified in 7 reaches of Spring Coulee Creek using injections of a conservative tracer alone or with added PO43?. Fraction of median travel time due to transient storage (Fmed200) was correlated with macrophyte biomass (r = .794, p = .033), and PO43? uptake velocity was correlated with Fmed200 (r = .756, p = .049). Stepwise linear regression was used to build models for transient storage and uptake velocity. Macrophyte biomass, stream bed slope, and riffle to pool ratio accounted for 99.6% of the variation in transient storage (p < .001). Transient storage, canopy cover, and slope accounted for 98.0% of the variation in uptake velocity (p = .002). This study shows that transient storage, primarily resulting from macrophyte beds, can be a significant factor regulating phosphorus uptake in stream ecosystems.  相似文献   

9.
Fluvial seed dispersal considers both the transport and deposition of seeds where channel geomorphic structures, hydrology and seed dispersal traits contribute to transport times and depositional locations. This study examines the influence of stream flow patterns on fluvial seed dispersal of buoyant white alder (Alnus rhombifolia) seeds by applying a one‐dimensional transport model. Conceptually, the model separates the stream into two components: (i) the main channel where the seeds are transported downstream; and (ii) the transient storage zone where seeds are temporarily detained or deposited on the river bank. Transport processes are characterized by an advection–dispersion equation which is coupled to a transient storage model using an exponential decay term. The model parameters: longitudinal dispersion (DL), exchange coefficient (α), main channel area (A) and storage zone (As) are estimated based on field experiments conducted in a confined, bedrock‐gravel bed river with pool‐riffle morphology located in coastal northern California. The riparian zone is inhabited by Alnus rhombifolia that disperse buoyant seeds in mid‐spring coinciding with the end of the wet, Mediterranean season. Artificial seeds, with similar traits of buoyancy and density to alder seeds, were used to quantify transport times and depositional locations. Preferential deposition resulted in stream reaches with larger As, high As/A ratios, and faster exchange coefficients corresponding to divergent stream flow (back‐eddies, re‐circulating flow, flow expansions) caused by geomorphic structures such as the ends of bar/riffle features and bends in the stream. The results demonstrate the importance of transient storage for seed transport and depositional processes. Morphological features that increase a channel's complexity create complex flow structures that detain seeds and provide a greater opportunity for deposition to occur. The model provides a simplification of river hydraulics to represent dispersal dynamics and lends itself to further understanding of hydrochory processes and associated population structure. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

10.
Little research has examined whether forests reduce stream water eutrophication in agricultural areas during spring snowmelt periods. This study evaluated the role of forests in ameliorating deteriorated stream water quality in agricultural areas, including pasture, during snowmelt periods. Temporal variation in stream water quality at a mixed land‐use basin (565 ha: pasture 13%, forestry 87%), northern Japan, was monitored for 7 years. Synoptic stream water sampling was also conducted at 16 sites across a wide range of forest and agricultural areas in a basin (18.3 km2) in spring, summer and fall. Atmospheric nitrogen (N) and phosphorus (P) deposition were measured for 4 years. The results showed that concentration pulses of nitrate, organic N and total P in stream water were observed when discharge increased during spring snowmelt. Their concentrations were high when silicate concentrations were low, suggesting surface water exported from pasture largely contributed to stream water pollution during snowmelt. Atmospheric N and P deposition (4.1 kg N ha?1 y?1; 0.09 kg P ha?1 y?1, respectively) was too low to affect the background concentrations of N and P in streams from forested areas. Reduction of eutrophication caused by nutrients from pasture was mainly due to dilution by water containing low concentrations of N and P exported from forested areas, whereas in‐stream reduction was not a dominant process. Results indicate that forests have a limited capacity to reduce the concentration pulses of N and P in stream water during snowmelt in this study basin. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

11.
We examined the relevance of dissolved inorganic nitrogen (DIN) forms (nitrate and ammonium) in stream water as N sources for different macrophyte species. To do this, we investigated the variability and relationships between 15N natural abundance of DIN forms and of four different macrophyte species in five different streams influenced by inputs from wastewater treatment plants and over time within one of these streams. Results showed that 15N signatures were similar in species of submersed and amphibious macrophytes and in stream water DIN, whereas 15N signatures of the riparian species were not. 15N signatures of macrophytes were generally closer to 15N signatures of nitrate, regardless of the species considered. Our results showed significant relationships between 15N signatures of DIN and those of submersed Callitriche stagnalis and amphibious Veronica beccabunga and Apium nodiflorum, suggesting stream water DIN as a relevant N source for these two functional groups. Moreover, results from a mixing model suggested that stream water DIN taken up by the submersed and amphibious species was mostly in the form of nitrate. Together, these results suggest different contribution to in-stream N uptake among the spatially-segregated species of macrophytes. While submersed and amphibious species can contribute to in-stream N uptake by assimilation of DIN, macrophyte species located at stream channel edges do not seem to rely on stream water DIN as an N source. Ultimately, these results add a functional dimension to the current use of macrophytes for the restoration of stream channel morphology, indicating that they can also contribute to reduce excess DIN in streams.  相似文献   

12.
Urbanization negatively impacts water quality in streams by reducing stream-groundwater interactions, which can reduce a stream's capacity to naturally attenuate nitrate. Meadowbrook Creek, a first order urban stream in Syracuse, New York, has an inverse urbanization gradient, with heavily urbanized headwaters that are disconnected from the floodplain and downstream reaches that have intact riparian floodplains and connection to riparian aquifers. This system allows assessment of how stream-groundwater interactions in urban streams impact the net sources and sinks of nitrate at the reach scale. We used continuous (15-min) streamflow measurements and weekly grab samples at three gauging stations positioned longitudinally along the creek to develop continuous nitrate load estimates at the inlet and outlet of two contrasting reaches. Nitrate load estimates were determined using a USGS linear regression model, RLOADEST, and differences between loads at the inlet and outlet of contrasting reaches were used to quantify nitrate sink and source behaviour year-round. We observed a nitrate load of 1.4 × 104 kg NO3− per water year, on average, at the outlet of the urbanized reach while the nitrate load at the outlet of the downstream, connected reach was 1.0 × 104 kg NO3− per water year, on average. We found the more heavily urbanized, hydrologically-disconnected reach was a net source of nitrate regardless of season. In contrast, stream-groundwater exchange caused the hydrologically connected reach to be both a source and sink for nitrate, depending on time of year. Both reaches alter nitrate source and sink behaviour at various spatiotemporal scales. Groundwater connection in the downstream, connected reach reduces annual nitrate loads and provides more opportunities for sources and sinks of nitrate year-round than the hydrologically disconnected stream reach. Mechanisms include groundwater discharge into the stream with variable nitrate concentrations, surface-water groundwater interactions that foster denitrification, and stream load loss to surrounding near-stream aquifers. This study emphasizes how loads are important in understanding how stream-groundwater interactions impact reach scale nitrate export in urban streams.  相似文献   

13.
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14.
Nutrient dynamics in karst agroecosystems remain poorly understood, in part due to limited long‐term nested datasets that can discriminate upland and in‐stream processes. We present a 10‐year dataset from a karst watershed in the Inner‐Bluegrass Region of central Kentucky, consisting of nitrate (nitrate‐N [NO3?]), dissolved reactive phosphorus (DRP), total organic carbon (TOC), and total ammoniacal‐N (TAN) measurements at nested spring and stream sites as well as flowrate at the watershed outlet. Hydrograph separation techniques were coupled with multiple linear regression and Empirical Mode Decomposition time‐series analysis to determine significance of seasonal processes and to generate continuous estimates of nutrient pathway loadings. Further, we used model results of benthic algae growth and decomposition dynamics from a nearby watershed to assess if transient storage in algal biomass could explain differences in spring and downstream watershed nutrient loading. Results highlight statistically significant seasonality for all nutrients at stream sites, but only for NO3? at springs with longitudinal variability showing significant decreases occurring from spring to stream sites for NO3? and DRP, and significant increases for TOC and TAN. Pathway loading analysis highlighted the importance of slow flow pathways to source approximately 70% of DRP and 80% of NO3?. Results for in‐stream dynamics suggest that benthic autotroph dynamics can explain summer deviations for TOC, TAN, and DRP but not NO3?. Regarding upland dynamics, our findings agree well with existing perceptions in karst for N pathways and upland source seasonality but deviate from perceptions that karst conduits are retentive of P, reflecting the limited buffering capacity of the soil profile and conduit sediments in the Inner‐Bluegrass. Regarding in‐stream fate, our findings highlighted the significance of seasonally driven nutrient processing in the bedrock‐controlled streambed to influence nutrient fluxes at the watershed outlet. Contrary to existing perceptions, we found high N attenuation and an unexplained NO3? sink in the bedrock stream, leading us to postulate that floating macrophytes facilitate high rates of denitrification.  相似文献   

15.
The relationship between solute concentrations and discharge can inform an integrated understanding of hydrological and biogeochemical processes at watershed scales. Recent work from multiple catchments has shown that there is typically little variation in concentration relative to large variations in discharge. This pattern has been described as chemostatic behavior. Pond Branch, a forested headwater catchment in Maryland, has been monitored for stream nitrate (NO3?) concentrations at weekly intervals for 14 years. In the growing season and autumn of 2011 a high‐frequency optical NO3? sensor was used to supplement the long‐term weekly data. In this watershed, long‐term weekly data show that NO3? concentrations decrease with increasing discharge whereas 6 months of 15‐minute sensor observed concentrations reveal a more chemostatic behavior. High‐frequency NO3? concentrations from the sensor collected during different storm events reveal variable concentration–discharge patterns highlighting the importance of high resolution data and ecohydrological drivers in controlling solute export for biologically reactive solutes such as NO3?.  相似文献   

16.
Glacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m?2 in wide, low‐gradient valley segments to as high as 51 700 W m?2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

17.
The hydrology and nitrogen biogeochemistry of a riparian zone were compared before and after the construction of beaver dams along an agricultural stream in southern Ontario, Canada. The beaver dams increased surface flooding and raised the riparian water table by up to 1·0 m. Increased hydraulic gradients inland from the stream limited the entry of oxic nitrate‐rich subsurface water from adjacent cropland. Permeable riparian sediments overlying dense till remained saturated during the summer and autumn months, whereas before dam construction a large area of the riparian zone was unsaturated in these seasons each year. Beaver dam construction produced significant changes in riparian groundwater chemistry. Median dissolved oxygen concentrations were lower in riparian groundwater after dam construction (0·9–2·1 mg L?1) than in the pre‐dam period (2·3–3·9 mg L?1). Median NO3‐N concentrations in autumn and spring were also lower in the post‐dam (0·03–0·07 mg L?1) versus the pre‐dam period (0·1–0·3 mg L?1). In contrast, median NH4‐N concentrations in autumn and spring months were higher after dam construction (0·3–0·4 mg L?1) than before construction (0·13–0·14 mg L?1). Results suggest that beaver dams can increase stream inflow to riparian areas that limit water table declines and increase depths of saturated riparian soils which become more anaerobic. These changes in subsurface hydrology and chemistry have the potential to affect the transport and transformation of nitrate fluxes from adjacent cropland in agricultural landscapes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.
This study was designed to improve our understanding of, and mechanistically simulate, nitrate (NO3) dynamics in a steep 9.8 ha rural headwater catchment, including its production in soil and delivery to a stream via surface and subsurface processes. A two‐dimensional modelling approach was evaluated for (1) integrating these processes at a hillslope scale annually and within storms, (2) estimating denitrification, and (3) running virtual experiments to generate insights and hypotheses about using trees in streamside management zones (SMZs) to mitigate NO3 delivery to streams. Total flow was mathematically separated into quick‐ and slow‐flow components; the latter was routed through the HYDRUS software with a nitrogen module designed for constructed wetlands. Flow was monitored for two years. High surface‐soil NO3 concentrations started to be delivered to the stream via preferential subsurface flow within two days of the storm commencing. Groundwater NO3‐N concentrations decreased from 1.0 to less than 0.1 mg l?1 from up‐slope to down‐slope water tables, respectively, which was attributed to denitrification. Measurements were consistent with the flushing of NO3 mainly laterally from surface soil during and following each storm. The model accurately accounted for NO3 turnover, leading to the hypotheses that denitrification was a minor flux (<3 kg N ha?1) compared to uptake (98?127 kg N ha?1), and that SMZ trees would reduce denitrification if they lowered the water table. This research provides an example of the measurement and modelling of NO3 dynamics at a small‐catchment scale with high spatial and temporal resolution. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

19.
Knowledge on groundwater–surface water interaction and especially on exchange fluxes between streams and aquifers is an important prerequisite for the study of transport and fate of contaminants and nutrients in the hyporheic zone. One possibility to quantify groundwater–surface water exchange fluxes is by using heat as an environmlental tracer. Modern field equipment including multilevel temperature sticks and the novel open‐source analysis tool LPML make this technique ever more attractive. The recently developed LPML method solves the one‐dimensional fluid flow and heat transport equation by combining a local polynomial method with a maximum likelihood estimator. In this study, we apply the LPML method on field data to quantify the spatial and temporal variability of vertical fluxes and their uncertainties from temperature–time series measured in a Belgian lowland stream. Over several months, temperature data were collected with multilevel temperature sticks at the streambed top and at six depths for a small stream section. Long‐term estimates show a range from gaining fluxes of ?291 mm day?1 to loosing fluxes of 12 mm day?1; average seasonal fluxes ranged from ?138 mm day?1 in winter to ?16 mm day?1 in summer. With our analyses, we could determine a high spatial and temporal variability of vertical exchange fluxes for the investigated stream section. Such spatial and temporal variability should be taken into account in biogeochemical cycling of carbon, nutrients and metals and in fate analysis of contaminant plumes. In general, the stream section was gaining during most of the observation period. Two short‐term high stream stage events, seemingly caused by blockage of the stream outlet, led to a change in flow direction from gaining to losing conditions. We also found more discharge occurring at the outer stream bank than at the inner one indicating a local flow‐through system. With the conducted analyses, we were able to advance our understanding of the regional groundwater flow system. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

20.
This study examined if riparian land use (forested vs agricultural) affects hydraulic transport in headwater streams located in an agriculturally fragmented watershed. We identified paired 50‐m reaches (one reach in agricultural land use and the other in forested land use) along three headwater streams in the Upper Sugar Creek Watershed in northeast Ohio, USA (40° 51′42″N, 81° 50′29″W). Using breakthrough curves obtained by Rhodamine WT slug injections and the one‐dimensional transport with inflow and storage model (OTIS), hydraulic transport parameters were obtained for each reach on six different occasions (n = 36). Relative transient storage (AS:A) was similar between both reach types (As: A = 0·3 ± 0·1 for both agricultural and forested reaches). Comparing values of Fmed200 to those in the literature indicates that the effect of transient storage was moderately high in the study streams in the Upper Sugar Creek Watershed. Examining travel times revealed that overall residence time (HRT) and residence time in transient storage (TSTO) were both longer in forested reaches (forested HRT = 19·1 ± 11·5 min and TSTO = 4·0 ± 3·8 min; agricultural HRT = 9·3 ± 5·3 min and TSTO = 1·7 ± 1·4 min). We concluded that the effect of transient storage on solute transport was similar between the forested and agricultural reaches but the forested reaches had a greater potential to retain solutes as a result of longer travel times. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

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