Base Flow Values Research Articles

Analysis of the Performance of Base Flow Separation Methods Using Chemistry and Statistics in Sudano-Sahelian Watershed, Burkina Faso

This research aims to determine appropriate methods for base flow separation under Sudano-Sahelian climate in West Africa. Four Recursive Digital Filtering (RDF) methods and the Conductivity Mass Balance (CMB) method were used. Daily streamflow of the Mouhoun River (formerly Black Volta River) at Samendeni gauge station has been separated into base flow and runoff. The RDF methods are easy to use but cannot take into account the actual hydrological processes within the watershed, while CMB method does it well. But, given that regular discharge measurement is rarely coupled with Electrical Conductivity measurements, it is therefore not possible to apply CMB method over time at each outlet. The CMB method is frequently used on a short time as a reference to assess the performance or to calibrate RDF methods. In the present study, CMB method was used for the year 2017, especially during the rainy season (from July to October) to produce more realistic base flow values. Statistical analysis was used to compare RDF and CMB methods. It was found that all the four RDF methods used are significantly different from the CMB method in the study area. Among the RDF methods, the Eckhardt method which is two parameters filtering method was successfully calibrated using CMB method Base Flow Index (BFI) as constraint. With the calibration process, the parameter BFImax of the Eckhardt method was adjusted to 0.32 in the study area context. The achievements of this study can have several implications such as adequate base flow estimation over time at Samendeni gauge station and at other similar gauges of the Mouhoun watershed which will be particularly beneficial to the critical issue of assessment of climate change impact on base flow in the study area.

Benefits and limitations of using isotope-derived groundwater travel times and major ion chemistry to validate a regional groundwater flow model: example from the Centre-du-Québec region, Canada

Understanding groundwater dynamics at the regional scale (> 100 km) is essential to the development of sustainable water management regulations. Groundwater flow models are increasingly used to support these strategies. However, in order to be reliable, these models need to be calibrated and validated. The objective of this work is to evaluate the benefits and the limitations of using isotope-derived groundwater travel times and major ion chemistry to validate a regional-scale groundwater flow model in the humid continental climate of southern Québec (Canada). A three-dimensional regional-scale steady-state groundwater model was created using MODFLOW for the fractured bedrock aquifer of the Centre-du-Québec region (Québec, Canada), using data acquired during recent aquifer characterization projects. The model covers an area of 7452 km2, from the unconfined Appalachian Mountains to the confined St. Lawrence Platform. Groundwater travel times were simulated for 211 wells using particle tracking. The groundwater flow model was calibrated using 11,775 regionally distributed heads and 15 baseflow values. The model was validated using 23 3H/3He residence time (3 to 60 years), 17 14C residence time (226 to 22,600 years), and the major ion compositions from 211 wells. Results indicate that the model is able to satisfactorily simulate ³H/³He isotopic residence time, while 14C isotopic residence times are generally underestimated. These results suggest substantial mixing between groundwater recharged during the last deglaciation and recently recharged water. Regional groundwater flow is limited or absent, and most of the recharge discharges to the river network as baseflow. The analysis of travel times indicates a statistically distinct mean travel time for the different groundwater types. Median travel time is 68 years for recently recharged groundwater (Ca-HCO3), 274 years for semi-confined groundwater (Na-HCO3), and 738 years for confined groundwater (Na-Cl). This confirms that groundwater chemistry is a broad indicator of groundwater travel time.

Hydro-geo-chemical streamflow analysis as a support for digital hydrograph filtering in a small, rainfall dominated, sandstone watershed

Summary The aim of the present study is an analysis of the ability of digital hydrograph filtering tools for the characterization of the baseflow source contributing to total streamflow for a typical, small, sandstone, rainfall dominated catchment. Daily streamflow and electrical conductivity data for an experimental catchment, the Ciciriello catchment, a 3km2 watershed located in Southern Italy, have been collected to the purpose since 2012. The application of a mass balance filter (MBF), using electrical conductivity as tracer data, has pointed out a seasonal characterization of the baseflow pattern, contributing to total streamflow by 90% during the low flow period and up to 40% during the high flow period. The Lyne and Hollick one parameter and the two parameters Eckhardt digital filters have been furthermore processed, both in an uncalibrated and calibrated application. Providing a preliminary total streamflow and baseflow recession analysis, the one parameter filter appears particularly suited for ungauged cases, as the uncalibrated and calibrated applications are almost identical, with relative prediction errors, compared to MBF, smaller than 5%. The uncalibrated two parameters filter generates instead large relative error of about 35%. To improve the baseflow description, in particular during the low flow period, and to correct large (28%) underestimation of the minimum baseflow value, a seasonal calibration for the BFImax parameter (the maximum BaseFlow Index that can be modeled by the filter algorithm) is in fact needed.

Extension to nonlinear stability theory of the circular Couette flow

A nonlinear stability analysis of the viscous circular Couette flow to axisymmetric finite-amplitude perturbations under axial periodic boundary conditions is developed. The analysis is based on investigating the properties of a reduced Arnol’d energy-Casimir function $\mathscr{A}_{rd}$ of Wang (Phys. Fluids, vol. 2, 2009, 084104). A weighted kinetic energy of the perturbation, which has a form of ${\rm\Delta}\mathscr{A}_{rd}$, the difference between the reduced Arnol’d function and its base flow value, is used as a Lyapunov function. We show that all the inviscid flow effects as well as all the viscous-dependent terms that are related to the flow boundaries vanish. The evolution of ${\rm\Delta}\mathscr{A}_{rd}$ depends only on the viscous effects of the perturbation’s dynamics inside the flow domain. The requirement for the temporal decay of ${\rm\Delta}\mathscr{A}_{rd}$ leads to two novel sufficient conditions for the nonlinear stability of the circular Couette flow in response to axisymmetric perturbations. The linearized version of these conditions for infinitesimally small perturbations recovers the recent linear stability results by Kloosterziel (J. Fluid Mech., vol. 652, 2010, pp. 171–193). By examining the nonlinear stability conditions, we establish a definite operational region of the viscous circular Couette flow that is independent of the fluid viscosity. In this region of operation, the flow is nonlinearly stable in response to perturbations of any size, provided that the initial total circulation function is above a minimum level determined by the operational conditions of the base flow. Comparisons with historical studies show that our results shed light on the experimental measurements of Wendt (Ing.-Arch., vol. 4, 1933, pp. 577–595) and extend the classical nonlinear stability results of Serrin (Arch. Rat. Mech. Anal., vol. 3, 1959, pp. 1–13) and Joseph & Hung (Arch. Rat. Mech. Anal., vol. 44, 1971, pp. 1–22). When the flow is nonlinearly stable and evolves axisymmetrically for all time, then it always decays asymptotically in time to the circular Couette flow determined uniquely by the set-up of the rotating cylinders. Finally, we derive upper-bound estimates on the decay rate of finite-amplitude perturbations for the solid-body rotation flow between two coaxial rotating cylinders and for the circular Couette flow. We demonstrate via numerical simulations that the theoretical upper bound is relevant to the dynamics of various axisymmetric perturbations tested, where it is strictly obeyed. This present study provides new physical insights into a classical flow problem that was studied for many decades.

Base flow separation: A comparison of analytical and mass balance methods

Summary Base flow is the ground water contribution to stream flow. Many activities, such as water resource management, calibrating hydrological and climate models, and studies of basin hydrology, require good estimates of base flow. The base flow component of stream flow is usually determined by separating a stream hydrograph into two components, base flow and runoff. Analytical methods, mathematical functions or algorithms used to calculate base flow directly from discharge, are the most widely used base flow separation methods and are often used without calibration to basin or gage-specific parameters other than basin area. In this study, six analytical methods are compared to a mass balance method, the conductivity mass-balance (CMB) method. The base flow index (BFI) values for 35 stream gages are obtained from each of the seven methods with each gage having at least two consecutive years of specific conductance data and 30 years of continuous discharge data. BFI is cumulative base flow divided by cumulative total discharge over the period of record of analysis. The BFI value is dimensionless, and always varies from 0 to 1. Areas of basins used in this study range from 27 km 2 to 68,117 km 2 . BFI was first determined for the uncalibrated analytical methods. The parameters of each analytical method were then calibrated to produce BFI values as close to the CMB derived BFI values as possible. One of the methods, the power function ( aQ b + cQ ) method, is inherently calibrated and was not recalibrated. The uncalibrated analytical methods have an average correlation coefficient of 0.43 when compared to CMB-derived values, and an average correlation coefficient of 0.93 when calibrated with the CMB method. Once calibrated, the analytical methods can closely reproduce the base flow values of a mass balance method. Therefore, it is recommended that analytical methods be calibrated against tracer or mass balance methods.

Diffuse flow characteristics and their relation to hydrochemistry conditions in the Petoyan Spring, Gunungsewu Karst, Java, Indonesia

This study was conducted on the Petoyan Spring, one of the most important springs in the western part of Gunung Sewu Karst, Java, Indonesia. The main purpose of the study is to define the diffuse flow characteristics of the spring. It also focuses on identifying the relationship between the diffuse flow proportion and several hydrochemical parameters to provide a better aquifer characterization. Water-level monitoring and discharge measurements were conducted over an eight months period in order to define the discharge hydrograph. The calculation of recession constants, including the diffuse flow (Kb), fissure flow (Ki), and conduit flow (Kc), was done by selecting several flood hydrograph events. Furthermore, the base flow-separation analysis was conducted to determine the diffuse flow proportion throughout the research period. Water sampling for hydrogeochemical analysis was taken every week and every hour for two selected flood events. A bivariate plot analysis between the diffuse flow proportion and certain hydrochemical parameters was made in order to describe the hydrogeochemical processes. The results showed that the diffuse- flow significantly dominates the spring discharge during non-flooding and flooding recession periods. Conversely, during the rising limb period, the diffuse proportion decreased drastically due to the conduit flow supply. This fact was also supported by the high Kb and short Tp (time to peak) and Tb (time to base flow) values. Hydrogeochemically the correlation between the diffuse flow proportion and major dissolved elements during the flood recession periods was strong because the conduit flow domination was replaced by the diffuse flow, causing the domination of water-rock interaction. According to the diffuse flow and its relation to its hydrochemistry, it is apparent that small fractures in the Petoyan Spring aquifer still provide good storage for the diffuse flow, even though the conduit fracture has already been developed.

Global drivers effect in multi-annual variability of runoff

Abstract Changes in runoff parameters are very important for Slovakia, where stream-flow discharges, being supplied by precipitation and groundwater runoff, are preferentially influenced by climatic conditions. Therefore, teleconnections between runoff parameters, climate parameters and global atmospheric drivers such as North Atlantic Oscillation, Southern Pacific Oscillation, Quasi-biennial oscillation and solar activity were studied in the Nitra River Basin, Slovakia. Research was mostly based on records of 80 years (1931-2010) for discharges and baseflow, and 34 years for groundwater heads. Methods of autocorrelation, spectral analysis, cross-correlation and coherence function were used. Results of auto- correllograms for discharges, groundwater heads and base flow values showed a very distinct 11-year and 21-year periodicity. Spectrogram analysis documented the 11-year, 7.8-year, 3.6-year and 2.4-year periods in the discharge, precipitation and air temperature time series. The same cycles except of 11-years were also identified in the long-term series of the North Atlantic Oscillation and Southern Pacific Oscillation indices. The cycle from approximately 2.3 to 2.4-years is most likely connected with Quasi-biennial oscillation. The close negative correlation between the North Atlantic Oscillation winter index and the hydrological surface and groundwater parameters can be used for their prediction within the same year and also for one year in advance.

The examination of the performances of methods used in separating the total stream flow in different rivers

In this study, the performances of methods of flow separation into the surface flow and base flow of the total stream flow in rivers with different hydraulic features have been examined. For this purpose, daily mean stream flow data of Büyük Melen and Aksu Rivers which are in the same watershed but with different features (average flow value, catchment area, mean elevation) have been separated as surface flow and base flow with the use of Digital Filtering Method (DFM) and United Kingdom Institute of Hydrology Method (UKIH). The recession coefficient in DFM has been used as α = 0.830; and the number of elements for the groups formed to determine the turning points of flow data in UKIH has been used as N = 5. The study has revealed that the results of surface and base flows obtained by both flow separation methods show similarity in all rivers in an acceptable level; and the surface flow values agree better (R2 > 0,76) compared to base flow values (R2 > 0.63). However, it has been seen that as long as the total flow values decrease, the surface flow results for both methods come closer to each other; but the results of base flow get differentiated. This situation has been clearly seen in the results of surface (R2 > 0.89) and base (R2 > 0.63) flows belonging to Aksu River which has lower values of flow when compared to the ones of Büyük Melen River.

The importance of roads, nutrients, and climate for invasive plant establishment in riparian areas in the northwestern United States

Natural and anthropogenic site characteristics play a role in determining the current distribution of invasive plant species. An understanding of these characteristics can be used to prioritize areas for monitoring and control efforts and to determine appropriate management actions to lower site invasion risk. We used species distribution models to look for attributes associated with invasion and to determine the extent to which these attributes varied across a suite of species. We modeled the presence-absence of 11 invasive plant species along riparian areas in the northwestern United States using the model Random Forests. We found that climate variables were most important for predicting species distributions across the large study area and factors related to nutrients, land cover, and disturbance had moderate importance. We also found that there was a general pattern related to invasion for almost all species. Invasion was more likely to occur at hotter, drier sites near roads in unforested areas. In addition, high nutrient levels and proximity to streams with lower baseflow values also generally increased the likelihood that at least one invasive species would be present. Examining patterns across a broad range of regions can help suggest general mechanisms of invasion as well as provide region-specific management recommendations.

Influence of model structure on base flow estimation using Bilan, frier and HBV-light models / Vplyv štruktúry modelu na stanovenie veľkosti podzemného odtoku využitím modelov bilan, frier a hbv-light. j. hydrol. hydromech., 60, 2012, 4; 29 lit., 7 obr., 1 tab.

Hydrological models are widely used tools to solve a broad range of hydrological issues. Each model has its own structure defining inter-relationships of hydrological balance components, and comparative differences in the models’ inner structure must be taken into account when discrepancies result from the same data. Results of base flow simulation by three different models BILAN, FRIER and HBV-light were compared based on knowledge of the models’ internal structure. It was proven that the courses of modelled parameters are quite similar, but that the respective values differ. The highest base flow values were simulated by the BILAN model, due to the threshold value of the soil moisture storage incorporated within this model’s structure. The lowest values were obtained by HBV-light model. Simulated base flow values were compared with groundwater heads and minimum monthly discharges. This comparison showed that the base flow values in the Nitra catchment at Nedožery profile simulated by BILAN and FRIER models are closer to the reality than those, simulated by HBV-light model.

Groundwater Drought in the Nitra River Basin - Identification and Classification

Groundwater Drought in the Nitra River Basin - Identification and Classification Drought as a natural phenomenon becomes more often the subject of the research. It is because of the increasing frequency of extreme climatic events also in mild climate conditions. Groundwater drought indices could be derived for different groundwater parameters, among them for base flow, groundwater head stage, spring yield, or groundwater recharge. Base flow drought assessment methods were proposed in the paper. Base flow values were separated from the discharge hydrograms using the new HydroOffice 2010 program package, lately developed by Gregor. The base flow drought severity index was applied, calculated as the value of the base flow drought deficit volume divided by the drought duration. After that, the standardized base flow drought severity index was proposed as the ratio of the base flow drought index and the average long-term annual base flow. Proposed methods were applied in the Nitra River basin. Base flow drought occurrence was characterized also from the seasonality point of view.

Technical Note: Analytical sensitivity analysis of a two parameter recursive digital baseflow separation filter

Abstract. A sensitivity analysis for a well-established baseflow separation technique, a two parameter recursive digital filter, is presented. The sensitivity of the calculated baseflow index to errors or uncertainties of the two filter parameters and of the initial baseflow value is analytically ascertained. It is found that the influence of the initial baseflow value is negligible for long time series. The propagation of errors or uncertainties of the two filter parameters into the baseflow index is expressed by a dimensionless sensitivity index, the ratio between the relative error of the baseflow index and the relative error of the respective parameter. Representative index values are derived by application of the resulting equations to 65 North American catchments. In the mean the parameter a, the recession constant, has a stronger influence on the calculated baseflow index than the second filter parameter BFImax. This is favourable in that a can be determined by a recession analysis and therefore should be less uncertain. Whether this finding also applies for a specific catchment can easily be checked by means of the derived equations.

Analysis of groundwater regime on the basis of stream flow hydrograph

During the drought the flow in streams is reduced and is dominated by base flow. Baseflows are characteristic of low flow periods and provide information on available water resources in the basin during the drought, particularly on the aquifer and retention basin characteristics. This paper deals with the possibility of analysis and simulation of baseflow, and the determination of the pattern of its changes based on the total registered streamflow hydrograph at the catchment outlet. The basis for modeling the base flow changes in the time were base flow values obtained from the streamflow hydrograph by application of the graphical local minimum method. Applying the simulation model developed in this study, simulations of base flow hydrographs were performed for three characteristic years (1970, 1985, and 1990). It was shown that discrepancies between values of the base flows obtained through application of the local minimum method and the model are within the limits of tolerance.

Modelling of base flows by analysing the streamflow hydrograph

During dry periods, the flow of medium and small streams is significantly reduced and equal to groundwater flow. Since the base flows provide information about aquifer characteristics and retention characteristics of a basin, the possibilities of analysis and simulation of base flows gain importance under the conditions of intensive water use and the increasing demand for adequate water quality protection. In this paper, a model was established and used for the description of the principles governing the changes of base runoff on the basis of a streamflow hydrograph registered at the outlet of the basin on the example of the Kolubara basin up to the ?Valjevo? profile. Since the amount of base runoff from a basin cannot be measured, the results of base flows obtained using the local minimum method were adopted as the criterion for the comparison of the modelled values of base runoffs. The created model was applied for making simulations of the base runoff hydrograph during three characteristic years (rainy 1970, average 1985, and dry 1990). Deviations between the base flow values obtained using the established model and by applying the local minimum method are acceptable from the standpoint of general hydrological accuracy.

Baseflow control on sediment flux connectivity: Insights from a nested catchment study in Central Mexico

In order to assess the extent of sediment connectivity between uplands and lowlands and to quantify the processes of in-channel deposition and remobilization, measurements of suspended sediment fluxes were conducted in a nested rural catchment of the Mexican Volcanic Belt. Data were collected over one year at three upland sites (3 to 12 km2) and two downstream stations (390-630 km2). Our results show that a structural discontinuity in the catchment (i.e. abrupt slope decrease at the junction between piedmonts and the alluvial plain from 2 to 10% to < 0.1%) could be compensated by functional continuity during floods. Direct conveyance of fine sediment to the outlet occurred when a high stream transport capacity was reached. Erosion of the streambed was observed on various occasions and accounted for up to 50% of the flux leaving the catchment during one event. Conversely, temporary in-channel storage was apparent on other occasions, amounting to up to 52% of the flux recorded upstream during one storm. These two distinct behaviours were approximately equally distributed along the rainy season and strongly driven by the extent of coupling between surface and subsurface water. This work indeed highlights the role of baseflow spatial variations in determining the extent of lowland sediment conveyance. Riverbed erosional processes occurred when large differences in pre-event baseflow values (i.e. at least a twofold longitudinal increase) were observed between the 5-km distant lowland stations. Our findings outline the importance of systematically taking into consideration the baseflow parameter in research focusing on fine sediment transport across scales.

Anomalous behaviour of specific electrical conductivity at a karst spring induced by variable catchment boundaries: the case of the Podstenjšek spring, Slovenia

AbstractAnomalous behaviour of specific electrical conductivity (SEC) was observed at a karst spring in Slovenia during 26 high‐flow events in an 18‐month monitoring period. A conceptual model explaining this anomalous SEC variability is presented and reproduced by numerical modelling, and the practical relevance for source protection zoning is discussed. After storm rainfall, discharge increases rapidly, which is typical for karst springs. SEC displays a first maximum during the rising limb of the spring hydrograph, followed by a minimum indicating the arrival of freshly infiltrated water, often confirmed by increased levels of total organic carbon (TOC). The anomalous behaviour starts after this SEC minimum, when SEC rises again and remains elevated during the entire high‐flow period, typically 20–40 µS/cm above the baseflow value. This is explained by variable catchment boundaries: When the water level in the aquifer rises, the catchment expands, incorporating zones of groundwater with higher SEC, caused by higher unsaturated zone thickness and subtle lithologic changes. This conceptual model has been checked by numerical investigations. A generalized finite‐difference model including high‐conductivity cells representing the conduit network (“discrete‐continuum approach”) was set up to simulate the observed behaviour of the karst system. The model reproduces the shifting groundwater divide and the nearly simultaneous increase of discharge and SEC during high‐flow periods. The observed behaviour is relevant for groundwater source protection zoning, which requires reliable delineation of catchment areas. Anomalous behaviour of SEC can point to variable catchment boundaries that can be checked by tracer tests during different hydrologic conditions. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Analysis of Hydrological Processes Applying the HSPF Model in Selected Watersheds in Alabama, Mississippi, and Puerto Rico

The goal of this study was to evaluate the Hydrological Simulation Program FORTRAN (HSPF) to gain more insight in the underlying causes and mechanisms of hydrological processes in an upland basin in Alabama and Mississippi (1,856-km2 Luxapallila Creek), a humid subtropical watershed in coastal Alabama (140-km2 Fish River), and a steep-slope tropical catchment in Puerto Rico (99-km2 Rio Caonillas). For each watershed model, rainfall, potential evapotranspiration, and streamflow time series from January 1999 to December 2000 were used to calibrate model parameters and 2001 time series were applied to verify model results. In each study area, actual evapotranspiration was the main mechanism of water loss followed by river discharge. Annual baseflow values ranged from 58% of total discharge in Luxapallila Creek basin to 84% of total discharge in Fish River watershed. In Luxapallila Creek and Fish River, interflow was the primary mechanism of direct runoff; however, surface runoff was the main process of direct runoff in Rio Caonillas. The HSPF model was successfully adapted to model daily streamflow processes in Luxapallila Creek basin and Rio Caonillas catchment with coefficient of determination and Nash and Sutcliffe coefficient values between 0.61 and 0.71 for the entire period; however, the Fish River watershed model performance was poor. The poor performance is likely due to the lack of rainfall time series available within the watershed boundaries. In general, this study showed the robustness of the HSPF model in extreme environments (small catchments vs. large basins, flat vs. hilly areas, low vs. moderate/high runoff potential, tropical marine vs. humid subtropical climates).

Estimation of aquifer lower layer hydraulic conductivity values through base flow hydrograph rising limb analysis

The estimation of catchment‐averaged aquifer hydraulic conductivity values is usually performed through a base flow recession analysis. Relationships between the first time derivatives of the base flow and the base flow values themselves, derived for small and large values of time, are used for this purpose. However, in the derivation of the short‐time equations, an initially fully saturated aquifer without recharge with sudden drawdown is assumed, which occurs very rarely in reality. It is demonstrated that this approach leads to a nonnegligible error in the parameter estimates. A new relationship is derived, valid for the rising limb of a base flow hydrograph, succeeding a long rainless period. Application of this equation leads to accurate estimates of the aquifer lower layer saturated hydraulic conductivity. Further, it has been shown analytically that, if base flow is modeled using the linearized Boussinesq equation, the base flow depends on the effective aquifer depth and the ratio of the saturated hydraulic conductivity to the drainable porosity, not on these three parameters separately. The results of the new short‐time expression are consistent with this finding, as opposed to the use of a traditional base flow recession analysis. When base flow is modeled using the nonlinear Boussinesq equation, the new expression can be used, without a second equation for large values of time, to estimate the aquifer lower layer hydraulic conductivity. Overall, the results in this paper suggest that the new methodology outperforms a traditional recession analysis for the estimation of catchment‐averaged aquifer hydraulic conductivities.

Groundwater recharge trends in CanadaGeological Survey of Canada Contribution 20090009.

Groundwater plays a major role in social and economic development and in human and ecosystem health. However, little is known about the potential impacts of climate change on this resource in Canada, namely if groundwater recharge is increasing or decreasing over time. This paper focuses on trend statistical analysis of historical series of baseflow and groundwater levels and their field significance as indicators of recharge. Monitoring wells are mainly located in the southern half of western Canada, where few gauging stations either are available or provide significant trends. Both data sets are thus complementary. Results show that most available groundwater level series have significant trends (80%), whereas most available baseflow series have not (3%–33%). However, groundwater level series usually show smaller slope magnitudes than baseflow series. Mixed trends are often observed across Canada for a given variable, period, or series length, although some regions can have marked trends. For instance, values below the 55°N latitude, and especially values in Atlantic Canada, show mostly downward trends (decreasing recharge). Values north of the 55° parallel often show upward trends. All groundwater level results are field significant at the 10% level, versus only 35% for baseflow results, but they show mixed results. Baseflow values show a majority of downward trends for annual values and the summer period for 40- and 50-year series, thus showing field significance, whereas mixed results are observed for 30-year series and the spring, fall, and winter seasons.

Exports of dissolved ammonium (NH4 +) during storm events across multiple catchments in a glaciated forested watershed

Storm event exports of dissolved NH(4)(+) were explored for multiple events in the Point Peter Brook watershed (PPBW), a glaciated, forested watershed located in Western New York, USA. Investigations were performed across four catchments (1.6-696 ha) with varying topography and the extent of surface-saturated areas. While wetland and riparian waters were important sources of NH(4)(+) during non-storm periods, throughfall and litter leachate were the dominant contributors of NH(4)(+) during storm events. Ammonium concentrations in catchment discharge displayed a sinusoidal seasonal pattern with a maximum during early spring (March) and a minimum in late summer (August-September). Storm event concentrations of NH(4)(+) in streamflow were much greater than baseflow values and showed a consistent temporal pattern with an increase in concentrations on the hydrograph rising limb, a peak at or before the discharge peak, followed by a decline in concentrations. Storm event patterns of DON were similar to NH(4)(+) while the patterns of [Formula: see text]differed from NH(4)(+) for the summer and fall events. The storm event expression of NH(4)(+) was attributed to throughfall and throughfall-mediated leaching of the litter layer. The reactive behavior of NH(4)(+) precluded its use in an end member mixing model (EMMA) for predicting streamflow concentrations. While concentrations of NH(4)(+) in precipitation and streamflow were high for the spring events, exports of NH(4)(+) in streamflow were highest for the large and intense storm events. Baseflow NH(4)(+) concentrations increased with the percent wetland/saturated area in the catchment but the same trend did not hold for storm-event concentrations.