Recent promotion in European environmental statute law ( Groundwater directive 2000/60/EC ) requires a more incorporate direction attack for Groundwater Dependent Ecosystems ( GDEs ) which are located on interfaces between surface and groundwater. GDEs provide a figure of environmental services among which are barrier map between tellurian and aquatic ecosystems, flux control, moderateness of surface H2O temperature, fading of certain pollutants by blending or biodegradation, environment for alimentary cycling etc. ( see Danielopol et al. , 2004 ; Boulton et al. , 2008 ; Tomlinson and Boulton, 2008 ) . Procedures such as ( bio ) geochemical transmutation, precipitation, sorption, debasement and simple conveyance differ between aquifers and surface Waterss, therefore the function of GDEs ‘ interfaces demands to be considered. Interface ‘s procedures are hard to measure because they depend on both micro big graduated tables groundwater forms ( e.g. Ward et al. , 1998 ) . In this context, the usage of natural tracers on assorted spatio-temporal graduated tables should allow to measure surface H2O ( SW ) groundwater ( GW ) biocenoses ‘ interactions and to suggest strategies of working in relation to hydrological conditions and interface constructions.
Interactions between SW and GW are governed by hydrological and geometrical drivers at assorted graduated tables. At the range graduated tables ( i.e. from 10s of metres up to kilometres ) , surface systems tend to lose or derive H2O to/from the land as a map of the difference between channel and next H2O table phase ( e.g. USGS, 1999 ) . Flow-through channels receive groundwater through the upgradient bank and a part of the channel underside, and lose H2O through the downgradient bank ( Figure 1 ) .
Figure 1. Conventional representation of H2O exchanges between river and groundwater on the range graduated table.
On a more local graduated table, upwelling and downwelling may be governed by discontinuities such as obstructions which protrude from the river bed ( e.g. log jam ) , alterations in the way of flow, or pool-and-riffle sequences ( Brunke and Gonser, 1997 ) ( Figure 2 ) .
SW-GW exchange occurs in the hyporheic or hypolentic ( Winter, 2001 ) zones ( HZ ) . HZ corresponds to the infinite below the stream/lake bed and next Bankss where some proportion of SW and GW meet ( Boulton et al. , 2010 ) . This consequences in a geochemically, physically and biologically assorted environment.
Figure 2. Conceptual strategy of hyporheic zone ( HZ ) operation at the streambed surface ( adapted from Environment Agency, 2009 and Boulton et al. , 2010 ) . Flows are controlled by creek bed topography, distribution and size of deposits which influence hydraulic conduction and extent of perpendicular hydraulic gradients. These forms impact H2O fluxes and mass conveyance from and to the HZ.
Methodological attacks for HZ monitoring
Assuming geochemical and hydrological difference between SW and GW monitoring techniques for HZ probes can be divided into hydrological, physical, chemical and physico-chemical ( Table 1 ) .
Hydrological methods such as H2O degree measurings into aquifer and river ( USGS, 1999 ; Kalbus et al. , 2006 ) , or differential flow estimating between upstream and downstream of a river subdivision ( Harvey and Wagner, 2000 ) give an thought about instant flow waies. By flow gauging and through a simple mass balance, the three type of SW-GW interactions ( Figure 1 ) can be determined.. In add-on, watercourse hydrographs ( Smakhtin, 2001 ) can be processed and analyzed to qualify the magnitude and timing of groundwater discharge to streams. Baseflow separation techniques use the time-series record of watercourse flow to deduce a baseflow hydrograph.
Physical methods such asdirect measuring of H2O flux across the SW-GW interface has been proposed and tested by Lee ( 1977 ) by utilizing bag-typed ooze metres. Subsequently this method was significantly developed by series of surveies ( Rosenberry and LaBaugh, 1998 ) . Seepage technique is instead precise for both intents but is limited by its spacial declaration which is some cm2. In combination with hydrograph separation and discharge estimating these methods permit to place discriminatory downwelling of upwelling zones in SW. hydraulic conduction ratings through grain size analysis, permeameter trials, or pumping trials ) ( Fetter, 2001 ; Rosenberry and Pitlick, 2009 and measurings of hydraulic gradient may besides allow to measure fluxes in HZ ( Kalbus et al. , 2006 ) . Scale for this group of methods screens cm2 ( riverbed texture analysis ) to km2 ( pumping trials ) country ( Hatch et al. , 2006 ) . Thermal and electromagnetic air picture taking covers big countries but is expensive and less detailed on a range graduated table.
Medium to long term
Differential flow gauging
Ten of m
Harvey and Wagner, 2000
Channel/aquifer H2O degree measurings
m to km
Variable ( depends on length of monitoring record )
Kalbus et al. , 2006
K probes ( grain size analysis, permeameter trials, or pumping trials ) ( used in combination with the old techniques )
centimeter to km
Fetter, 2001 ;
Thermal IR, electro-magnetic remote detection
m to km
Brodie et Al, 2007
Bag-type ooze metres
centimeter to m
Lee ( 1977 )
Artificial tracer trial ( in combination with numerical modeling )
m to km
Triska et al. , 1993
?18O ; ?D monitoring
Depends on figure of trying points ; 1 point: cm-m
Aseltyne et al. , 2006
Radon 222 monitoring ( in combination with temperature )
Depend on figure of trying points ; 1 point: cm-m
Hohen and Cirkpa, 2006
Dissolved Oxygen monitoring
Soulsby et al. , 2009
Major ions supervising
Kalbus et al. , 2006
Metallic elements monitoring ( e.g. Fe )
Gandy et al. , 2007
Soulsby et al. , 2009 ; Vogt et al. , 2010
Hatch et al. , 2006
Table 1. Summary of methods leting appraisal of SW-GW interactions. Long term means decades-centuries ; Medium-term means season-years graduated table ; short-run corresponds to daily or monthly clip graduated tables.
Chemical methods are preferred when environment demonstrates sufficient difference between GW and SW. Groundwater flowpaths can be assessed by utilizing an unreal tracer. Groundwater kineticss ( speed, scattering ) and aquifer belongingss ( e.g. matrix and crevices porousnesss ) may be estimated cognizing distance between injection and discharge zones and supervising damages curves. ( e.g. Malozweski and Zuber, 1985 ) . The defect is the anterior cognition of groundwater flow way, besides those instance surveies where it is a research inquiry. The above-named method is punctual and may be completed by natural tracer trials ( Kalbus et al. , 2006 ) by supervising major elements ( e.g. Na+ , K+ , NO3- etc. ) ( Cook and Herczeg, 2000 ; Ladouche et al. , 2001 ; Carey and Quinton, 2005 ) , trace elements ( Fe2+ , Cd2+ , Mn2+ … etc ) ( Morrice et al. , 1997 ; Hart et al. , 1999 ) , isotopic composing of H2O ( ?18O ; ?D ) ( Coplen et al. , 2000 ; Hinkle et Al, 2001 ) . The methods differ in their declaration, sampled volume, and clip graduated table and normally the pick between them is a kind of tradeoff with impact on the consequences ( Vogt et al. , 2010 ; Cox et al. , 2007 ; Dahm et al. , 2003 ; Cook and Herczeg, 2000 ; Kendall and McDonnel, 1998 and mentions in this ) .
Finally, Physico-chemical methods provide alternatoive picks for HZ probes and are progressively used. Indeed, they belong to easy and comparatively cheap techniques that allow aggregation of uninterrupted informations series with the aid of simple and dependable measuring instruments.. Sing the GDE ‘s subjects, these environmental tracers may supply information on hydrological exchanges but may besides be considered as indexs of environmental ( abiotic ) conditions for the life parts of ecosystems ( e.g. Van der Kamp, 1995 ; Malcolm et al. , 2009 ) . In the followers, a reappraisal of these tools and illustrations of their applications will be synthetized.
Temperature as index
Mistake: Reference beginning non foundGroundwater temperatures are comparatively stable throughout the twelvemonth ( Younger, 2007 ) . In contrast, river, watercourse or lake heat pattern to a great extent depends on day-to-day and seasonal air temperature fluctuations. Consequently the monitoring of temperature spatio-temporal forms into HZ can be used to apportion zones of groundwater recharge or discharge ( Mistake: Reference beginning non found ) . Schematically, Deriving river ranges or lake shores are characterized by comparatively stable temperatures ( Figure 4 ) , whereas losing ranges demonstrate immensely variable heat balance behaviour ( Shimada et al. , 1993 ) .
Figure 3. Conceptual strategy of the usage of Temperature to measure SW-GW H2O exchanges ( from USGS, 1999 ) .
Figure 4: A ) Fring range where heater H2O from the river enter the GW and becomes attenuated ; B ) Deriving range with colder GW streaming into the river keeping colder SW conditions.
The thermic method is based on the rule that heat ( energy ) in the subsurface is transported by fluxing H2O ( advection ) , every bit good as by heat conductivity via the fluid and solid parts of the dirt matrix. The advective flow strongly influences the temperature distribution in the blending zone between groundwater and surface H2O. Hence H2O fluxes between groundwater and surface H2O can be traced by mensurating temperature distributions between the two systems ( Stonestrom and Constantz, 2003 ; Anderson, 2005 ) . Flux estimations are obtained by suiting solutions of the heat flow equation to ascertained temperature distributions in the dirt.
Suzuki ( 1960 ) ; Stallman ( 1965 ) and Lapham ( 1989 ) describe the 1D, perpendicular, anisothermal flow of heat through an incompressible fluid through a homogenous, porous media as:
( eq.1 )
where K is the thermic conduction of the soil-water matrix in J.s-1.m-1.K-1, T the temperature at depth omega in m and clip T in the dirt in K ( C ) , cw the particular heat capacity of the fluid in J.kg-1K-1, _w the denseness of the fluid in kg.m-3, vz the perpendicular constituent of the darcian fluid speed in the dirt in m.s-1, c the specific heat capacity of the rock-fluid matrix in J.kg-1.K-1, and _the wet-bulk denseness ( denseness of the rock-fluid matrix ) in kg.m-3. The footings cw_w and c_ represent severally the volumetric heat capacity of the fluid and the rock-fluid matrix in J m-3.K-1. The first term of the left manus side of equation 1 represents the conductive and the 2nd term the advective portion of heat conveyance. Valuess for cw and _w can easy be obtained from the literature. In contrast to hydraulic conduction, the thermic conduction K has a little scope across different deposit textures ( Stonestrom and Constantz, 2003 ) .
Figure 5 presents the construct of typical fluid and heat conveyance between groundwater and surface H2O. The upper thermic boundary is normally given by the surface H2O temperature clip series ( e.g. the temperature at the interface surface water-river/lakebed ) , while for the lower boundary a quasi-constant groundwater temperature is assumed at a sufficient deepness. Under a hydraulic steady-state ( changeless exchange flux between groundwater and surface H2O ) , Equation 1 can be used to imitate the form of the perpendicular temperature profile at any given clip ( denoted by the dotted line in Figure 5 ) . Upward flow of H2O ( i.e. deriving conditions, negative mark of vz ) is referred to as groundwater discharge, whereas groundwater recharge is defined as downward motion of surface H2O ( i.e. a losing status, positive mark of vz ) .
Figure 5: Concept of transeunt simulation of perpendicular 1D-fluid-heat conveyance in a river or lake bed ; portion a indicates the continuously measured surface H2O temperature used as upper boundary status ; portion B indicates the dirt column and its changing temperature distribution represented in the numerical theoretical accounts ( in Anibas et al. , 2009 )
Constantz and Stonestrom, 2003 ; Silliman and Booth, 1993 ) . Conant ( 2004 ) every bit good as Schmidt et Al. ( 2007 ) obtained spacial forms of groundwater exfiltration utilizing temperature and piezometer informations from a dense monitoring web. They analyzed snapshots of perpendicular temperature profiles with a theoretical account presuming steady-state heat transportation. Anibas et Al. ( 2009 ) , in a river located in Belgium, by comparing the obtained fluxes between groundwater and surface H2O with fluxes inverted from suiting ascertained perpendicular temperature profiles to an analytical solution for 1D steady-state heat flow, showed good understanding of fluxes during and towards the terminal of the summer and winter. Underestimate and overestimate of transient fluxes by the steady-state solution occurs in autumn and spring severally. It is concluded that for a temperate clime like in Western and Central Europe during certain periods of the twelvemonth, viz. from mid-July, August up to mid-September in the summer season and January, February up to mid- March in the winter season, exchange fluxes between groundwater and surface H2O can be inverted from a steady-state heat flow theoretical account. In other words, during those times the premise that perpendicular temperature distributions at the interface between groundwater and surface H2O are at a quasi-steady-state, is acceptable. Under certain meteoric conditions it might be possible to besides acquire accurate flux estimations outside of those periods. The advantage of this attack is that if the temperature distribution is at a steady-state, merely the temperatures at the upper and lower boundaries, every bit good as the thermic conduction of the porous medium demand to be known to find the exchange flux or speed ( vz in equation 1 ) , cut downing the necessary input informations significantly. As this solution assumes that the temperature distribution in the subsurface is non altering over clip, no uninterrupted input informations is necessary to depict the boundary conditions. A temperature profile dwelling of a few measuring points with deepness and the temperatures at the upper and lower boundaries are sufficient to verify the tantrum between steady-state premise with existent procedures.
However, the pertinence of the steady-state theoretical account is questionable because river temperatures typically exhibit a diurnal rhythm so that the streambed temperature is transeunt. Under infiltrating conditions, the steady-state part to temperature profiles is theorically non appliable for the quantification of ooze rates. The amplitude of diurnal temperature fluctuations must be significantly higher than the truth of the temperature detector. If the ooze flux is changeless, retrieval of the diurnal signal is simple. In extremely dynamic instances, dividing the diurnal part topic to time-varying auto-correlated parametric quantities from the tendency part, which is besides assumed to be auto-correlated, may go delicate.
Because diurnal temperature fluctuations are periodic and more or less sinusoidal, Stallman ‘s ( 1965 ) analytical look of the convection-conduction equation for sinusoidal boundary conditions is a good starting point for the analysis of temperature informations. Hatch et Al. ( 2006 ) applied a band-pass filter to braces of temperature clip series obtained at different deepnesss within the deposit. Mean flow rates were estimated from the amplitude and stage angle determined for each twenty-four hours utilizing a semi-automated computing machine plan. Kerry et Al. ( 2007 ) extracted sinusoidal constituents with periods of one twenty-four hours from temperature clip series at assorted deepnesss utilizing Dynamic Harmonic Regression ( Young et al. , 1999 ) . In this attack, the amplitude and stage angle were estimated as uninterrupted, auto-correlated clip variables. Following the analysis of amplitude and phase-angle information of Stallman ( 1965 ) , Kerry et Al. ( 2007 ) obtained the ooze rate as a uninterrupted clip variable instead than as a set of day-to-day values. Detailss for the application of this methods can be found in Young et Al. ( 1999 ) ; Kerry et Al. ( 2007 ) , and Vogt et Al. ( 2010 ) .
As this attack requires clip series of temperature development at assorted deepness in the bed, the recent technological inventions such as uninterrupted logging detectors ( Hoehn and Cirpka, 2006 ; Vogt et al. , 2010 ) for in situ monitoring over drawn-out periods and let to obtain a elaborate position of the fluctuation of river bed temperature over deepness and clip. Their incorporation into 3D numerical theoretical accounts ( Poole, 2010 ) will likely allow a better apprehension of groundwater-surface H2O interactions in a close hereafter.
Electrical conduction as index
Electrical conduction ( EC ) is another option of environmental following techniques in the field of SW-GW interplay and fundamentally can be used in the same manner as temperature. Fluctuations of EC consequences from fluctuation of entire dissolved solids ( Appelo and Postma, 2007 ) . In aquatic ecosystems EC variableness may be caused by C turnover by aquatic biology on seasonal graduated table, and such factors as photosynthesis and respiration on diurnal footing ( Odum, 1956 ) . Rainfall events and snowmelt introduce a dilution. These alterations besides affect inorganic C rhythm equilibrium, arousing stage alterations ( either precipitation or disintegration ) of Ca and Mg carbonates. Assuming a changeless EC in the subsurface waters SW-GW interactions may be evaluated through deconvolutions of the chemical variableness at the GDE ‘s interface. As it has been observed by Hatch et Al. ( 2006 ) daily EC fluctuations are preponderantly distinguishable at low river H2O degree and high temperatures. Diurnal phosyntetical procedures responsible for CO2 fluctuations, maintain EC highest in the early forenoon, and lowest in the afternoon. Seasonal fluctuations normally introduce disagreements between the river and groundwater informations sets and can be mathematically removed. Electrical conduction has the advantage and propagates quicker through the media than temperature at the same time demoing less smooth tendency ( Cirpka et al. , 2007 ) .
Combined attack and description of the trial site
Coincident application of EC and temperature. improves appraisal of SW-GW interaction ( Cox et al. , 2006 ) . Thermal forms of the HZ can be used to deduce hydraulic conductions. Vogt et Al. ( 2010 ) have every bit good noticed that combined information is normally more characteristic since EC does n’t undergo deceleration while propagating through the HZ. More stable signal from EC varies on a diurnal footing due to fluctuations in hydrogen carbonate and hardness, on several yearss footing as a consequence of drawn-out precipitation, and on seasonal footing reflecting winter base flow conditions dominated by the groundwater flow ( in bulk of the instances ) . Different infiltration governments can be registered by analysing diurnal and seasonal EC forms.
Temperature appears a really utile index in hyporheic exchange when high frequence constituents can be registered, e.g. diurnal temperature fluctuations of fring watercourse Waterss come ining the HZ ( Hoehn and Cirpka, 2006 ; Vogt et al. , 2010 ) . The low frequence signals, i.e. seasonal temperature fluctuations, are characterized by slower travelling clip and indicate commixture of groundwater constituents of different age. This type of signatures normally can non be employed in SW-GW exchange kineticss. On the other manus temperature fluctuations on a few yearss footing are really utile in gauging H2O abode clip and hyporheic exchange due to their singularity of frequence. These signals are hard to mismatch in their extremums ( Hoehn and Cirpka, 2006 ) .
Temperature tied with EC measurings is non the lone yoke attack, but can be applied with other tracer techniques like 222Rn or sulphate to follow beginning and age of the immature groundwater constituents.
It has been observed that in some site specific conditions seasonal and/or diurnal fluctuations of one of the parametric quantities can be negligible and hence will present no understanding on exchange between surface and groundwater. Laroque et Al. ( 1998 ) speculated that temperature entirely is non a conservative tracer and in such complex environment as karst aquifer is non advantageous as stand-alone technique. Thermal exchange of the groundwater with the environing bedrock is of a really high importance in the karstic environment. Therefore, combination of different techniques is advantageous. ( Laroque et al. , 1998 ; Hoehn and Cirpka, 2006 ; Cirpka et al. , 2007 ; Vogt et al. , 2010 ) .
Hyporheic exchange is besides studied within Genesis undertaking. The trial site is located in the locality of the regulated Lule & A ; aring ; River in northern Sweden. Hyporheos appear under menace and is capable to diurnal and seasonal river degree fluctuations. The trial site has been equipped with series of groundwater Wellss placed extraneous to the river on different distance. Continuous monitoring of temperature, H2O degrees and conduction was established. Measurements were settled in July 2010 and are still ongoing. Temperature and conduction were registered by combined four-electrode measurement cell. TetraCon 325 has a temperature response t99 & A ; lt ; 20s ( informations from the manufacturer ) , declaration and truth of the temperature detector ± 0.2 oC. Conductivity is measured with declaration of ±0.1 % , and truth of ±0.5 % in the scope 1µS/cm – 2S/cm. Collected clip series represent informations with 1 hr temporal declaration. Water exchange between the river and the HZ is complicated by instead clogged river bed which is the consequence of extended low flow conditions during the experimental period. We expect increased eroding to happen during the winter and the spring snowmelt when hydropower release is higher ( Hoehn and Cirpka, 2006 ) . However, there is a really tight connexion between the aquifer and the river. Hydraulic caputs deviate at the same time in the river and the nearest the shore good. A spot more complicated form occurs while look intoing EC and temperature clip series. Raw information does n’t present so much information and therefore clip series analysis is required. Data sets incorporate mistake measurings stand foring care periods, fouling of detectors, times when they are on occasion buried into the deposits, electrical failures, impetuss and minor divergences. All these events are non desirable in the clip series. Fiddling plotting, informations transmutation and general statistics have to be applied in order to have preprocessing informations. In extremely frequent H2O degree fluctuation conditions diurnal temperature and EC are of the highest importance. We would wish to except seasonal tendencies ensuing from the diverse part of upwind dependent factors. For this purpose least-square adjustment can be employed to assist to place the seasonal impetus and spectral filtering to divide it ( Jenkin and Watts, 1968 ; Hipel and McLeod, 1994 ; Laroque et al. , 1998 ) . Cross correlativity analysis of the clip series between the river signals of temperature and EC and those from the groundwater wells is supposed to reflect the strongest responses ( Hohen and Cirpka, 2006 ) . One of the effectual ways to observe smaller extremum of the same beginning both in the river and the HZ is to use non-parametric deconvolution. By taking day-to-day constituent utilizing every bit leaden traveling norm ( Laroque et al. , 1998 ) different infiltration governments can be identified ( Vogt et al. , 2010 ) ( Figure 6 ) .
Temperature and EC of the Lule & A ; aring ; River will be affected by the conditions related factors every bit good as H2O releases from hydropower operation. As the following measure it will be of import to divide these effects and pull out the signal caused by hydropower ordinance.
Figure 6: Scheme of the planned methodological attack for the survey of SW-GW exchanges in the Lule & A ; aring ; river.