We compared stableisotopesofwater in plant stem (xylem) water and soil collected over a complete growing season from five well-known long-term study sites in north- ern/cold regions. These spanned a decreasing temperature gradient from Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf Creek (northern Canada). Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. The degree to which potential soil water sources could explain the isotopic composition of xylem water was assessed quanti- tatively using overlapping polygons to enclose respective data sets when plotted in dual isotope space. At most sites isotopes in xylem water from angiosperms showed a strong overlap with soil water; this was not the case for gymnosperms. In most cases, xylem water composition on a given sampling day could be better explained if soil water composition was considered over longer antecedent periods spanning many months. Xylem water at most sites was usually most dissimilar to soil water in drier summer months, although sites differed in the sequence of change. Open ques- tions remain on why a significant proportion of isotopically depleted water in plant xylem cannot be explained by soil water sources, particularly for gymnosperms. It is recommended that future research focuses on the potential for fractionation to affect water uptake at the soil-root interface, both through effects of exchange between the vapour and liquid phases of soil water and the effects of mycorrhizal interactions. Additionally, in cold regions, evaporation and diffusion of xylem water in winter may be an important process.
Stableisotopesofwater - particularly 1 H and 2 H as well as 16 O and 18 O - can assist in the so- lution of hydrogeochemical and biological problems due to their natural and overall existence in water cycles (Clark and Fritz, .1997). They improve the understanding of the origin, forma- tion, and flow path ofwater and, therefore, provide insights across a range of spatial scales from the cell to the plant community, ecosystem, region or global and over temporal scales (Dawson et al., 2002). Thereby, physicochemical differences, determined by the dissimilar numbers of neutrons and, therefore, by different masses of the stablewaterisotopes, lead to different chemical behaviours ofisotopes in the environment. This phenomenon is called iso- tope fractionation (Unkovich et al., 2001). This different behaviour in physical and chemical reactions is the major reason that in nature stablewaterisotopes exist in different ratios and can consequently be used as natural tracers. The differences in isotope ratios are expressed relatively to an international standard in per mil [‰] (Aggarwal et al., 2007).
As a last possible environmental influence we need to consider the living depth of T. heimii. We observed that the correlation between temperature and the 18 O composition of T. heimii shells from surface sediment samples in the Atlantic Ocean slightly increases when we consider temperatures at mixed layer depth (MLD) instead of sea surface temperatures or temperatures averaged over 200m water depth. The lower limit of the surface mixed layer is characterized by an abrupt density change (pycnocline) or temperature change (thermocline). And these gradients are often co-located with a maximum in chlorophyll-a concentration. The upper part of the photic zone and the area immediately above the deep chlorophyll maximum (DCM) is supposedly the living depth of T. heimii (Kohn & Zonneveld, 2010). Therefore we used the MLD from the Monterey & Levitus (1997) database as a measure for the depth of the DCM. It should be noted however, that the MLD is not a constant or permanent phenomenon. Temporal variabilities of the MLD can range from diurnally to interannually, including seasonally and interseasonally. Also the spatial variability of the MLD is very large. The MLD can be less than 20 m in the summer hemisphere, while reaching more than 500 m in the winter hemisphere (de Boyer Montégut et al., 2004 with all references therein). Unfortunately, so far no information is available on how these seasonal variabilities of the MLD or DCM effect the isotopic composition of T. heimii. But since we assume a year-round production of T. heimii shells (see discussion above), the use of annually averaged MLDs can be justified.
with sampling problems, as sampling off the central axis of the thecal walls in P. strigosa should also result in more positive δ 18 O and δ 13 C values, and larger Sr/Ca ratios (see Giry et al. 18 , their Fig. 5).
We also researched other possible explanations for this baseline shift. For example, cloud cover data do not show significant changes after 1998 (Fig. 3). Thus, a change in light levels/solar irradiance, that could potentially influence photosynthesis, is ruled out. Observations from the MNP, west of the study site, suggest additional influence from other stressors on coastal Venezuelan reefs starting in the mid-1990s: A mortality event in early 1996 in the MNP was described as one of the greatest massive die-offs reported in Venezuela. It has been attrib- uted to an abnormal upwelling and expansion of cold (< 20 °C) and nutrient-rich water along the central-west coast, combined with a lack of winds that produced a plankton bloom leading to anoxic conditions on the sea- floor 14 . Detailed surveys in the MNP revealed that corals suffered mortalities from 60 to 98%, depending on the
Coastal zones are reported being vital source regions of halocarbons. In these salt water affected systems halocarbon producers comprise phytoplankton (Scarratt and Moore, 1996, 1998), macroalgae (Gschwend et al., 1985), salt marshes (Rhew et al., 2000), and mangroves (Manley et al., 2007). Seagrass meadows are one of the most productive ecosystems with a similar global abundance as mangroves and salt marshes (Duarte et al., 2005). They cover huge areas of the intertidal and subtidal as well in temperate as in subtropical/tropical regions. Thus, they may represent an additional source for halocarbons to the atmosphere which is not sufficiently studied, yet. Seagrass meadows are highly diverse ecosystems with respect to potential halocarbon producers. Along with the seagrass itself, they comprise epiphytes such as microalgae and diatoms, and sediment reassembling microphytobenthos and bacteria communities. All these constituents of the benthic community have been generally reported to produce halocarbons (Tokarczyk and Moore, 1994; Moore et al., 1996; Amachi et al., 2001; Rhew et al., 2002; Urhahn, 2003; Manley et al., 2006; Blei et al., 2010a). While first evidence for the release of halocarbons from seagrass was obtained by incubation experiments (Urhahn, 2003), we could recently confirm this production potential in a field study of a temperate seagrass meadow in Northern Germany (Weinberg et al., 2013).
N and C/N ratio) for each lithological unit (Table S2), namely F-tests (Tables S3–S5) and Student’s t-tests (Tables S6– S8) conducted on both sites show that there are significant differences between the two sites. A com- parison of the recent climatic settings of both sections reveals that the section of Irig is nowadays in a more humid environment than Semlac, with a mean annual precipitation of around 690 mm compared to 590 mm in Semlac. Projecting the recent precipitation patterns to the carbon isotope ratios, the d 13 C org ratio should be depleted in Irig compared to Semlac, since the enhanced moisture decreases the water stress. The stomata of the plants can be opened wider, and therefore a stronger fractionation against 13 C is possible, which leads to lower d 13 C org values (O ’Leary 1981; Farquhar et al. 1989). The results, however, reveal that the mean values for all layers in Irig are higher compared to Semlac, indicating drier conditions (Fig. 8). This is supported by d 13 C values from Crvenka (Zech et al. 2013) and Surduk sections (Hatte et al. 2013), which show similar values to the Irig section and suggest that the southern part of the Carpathian Basin was dryer than the rest of the basin. C 3 grasses, which are the most probable dust trap in the Carpathian Basin (Zech et al. 2013), tend to have higher d 13 C org values under drier conditions (Wooller et al. 2007). The local palaeoclimate south of the Fruska Gora was drier compared to other parts of the Carpathian Basin (Markovic et al. 2006, 2007, 2008; Vandenberghe et al. 2014), whereas the Petrovaradin LPS north of the mountain range shows evidence for more humid conditions during the last glacial cycle (Markovic et al. 2005). Increasing wind exposure may be a crucial factor as well, since it has a negative correlation with the water availability (Zech et al. 2007),
Elbe estuary were too low to account for an input of this magnitude, our observation was in accord with nitrification of ammonia derived from the degradation of organic matter and its subsequent rapid oxidation by particle-associated nitrifying bacteria within the turbidity maximum. A comparably intense nitrification has been observed in the Scheldt estuary (De Wilde and De Bie 2000) and, via complete conversion of organic matter-derived ammonia, in the upper Seine estuary (Sebilo et al. 2006). In our case, however, the internal nitrate input must have been even higher than the net addition: Nitrate from nitrification had an oxygen value deriving partly from dissolved oxygen and partly from oxygen atoms from water. We note that there are some arguments about the ratio of oxygen atoms deriving from these different sources. While incubation experiments indicated that no more than two out of three oxygen atoms derive from ambient water, other studies suggest that the δ 18 O-NO 3 - signature of nitrate
In the depressed polygon centers drainage was impeded by the underlying permafrost. Thus, the soils of the polygon centers were mostly water-saturated with a varying water level close to the surface. During soil sampling on 18 July 2009, the unsaturated polygon center had a water level of 25 cm below the soil surface while the saturated polygon centers A (18 July 2009) and B (27 July 2010) featured 7 cm and 5 cm above soil surface (Table 4, Table 5 and Table 6). All polygon centers were characterized by reducing conditions facilitating anaerobic microbial degradation of organic matter. The two saturated polygon centers and the unsaturat- ed polygon center showed a very high gravimetric organic carbon content in the upper hori- zons (> 12 % OC, designated as Oi according to US Soil Taxonomy (2010)). Subjacent hori- zons (A, Oi) showed an accumulation of humified organic matter mixed with fine sand bands and hydromorphic features (Bg). According to the US Soil Taxonomy the soils of these three polygon centers were classified as Typic Aquorthels (USDA 2010), as Histic Cryosols accord- ing to the WRB (WRB 2006) and as Permafrost tundra humic-peatish (saturated polygon center A), Permafrost tundra peat (saturated polygon center B) and Permafrost tundra silty- peatish (unsaturated polygon center) according to the Russian Classification (Elovskaya 1987).
In future research, two main issues will have to be addressed in order to establish an appropriate description of the dependence of the non-equilibrium fractionation factor k on wind velocity (or, alternatively, to show in a more definite way that this dependence is negligible). First, more measurements of isotope ratios in atmospheric water vapor should be made available that al- low to test newly developed parameterizations of k. As isotope ratios in the evaporation flux cannot be measured directly, complex models, which include processes like the advection ofwater vapor (e.g. GCMs or the Lagrangian approach used here) have to be applied to compare theoretical predictions from a Craig-Gordon model with measurements. Second, more recent parameterizations ofwater evaporation from the ocean (see e.g. Fairall et al., 2003) might pro- vide the theoretical basis for the description of k. These parameterizations have the advantage that they are grounded on measurement data in a much stronger way than the mostly theoretical Brutsaert model applied by MJ79. However, they usually do not contain an explicit formulation of molecular diffusion, but subsume the properties of the diffusive surface layer in a parameter called moisture roughness length, which is then parameterized with an empirical equation. Ba- sically, the moisture roughness length can also be expressed in terms of a diffusion coefficient or Schmidt number (and thus calculated for the different waterisotopes) (cf. Liu et al., 1979; Brutsaert, 1982). But, owing to its empirical formulation, it is not straightforward to employ these more recent parameterizations of evaporation for the deduction of the isotope fractionation factor. In our opinion, this issue will have to be addressed with the help of a comprehensive ex- perimental (e.g. wind tunnel) study analyzing the dependence of the moisture roughness length on the Schmidt number, extending the work of Merlivat (1978a).
To assess past variations in continental rainfall, we additionally use Ti/Ca ratios in GeoB 17419-1 as well as Nd/Ca ratios that were measured along with Mg/Ca on P. obliquiloculata samples of GeoB 17419-1 (Figure 5.6). As discussed in detail in Tachikawa et al. , element ratios such as Ti/K or Ti/Ca in core MD05-2920 reflect past rainfall variations over PNG and continental runoff, and indicate that rainfall above PNG predominantly varies in response to precession. The Ti/Ca record of GeoB 17419-1 is in close correlation to the Ti/Ca record of MD05-2920 and thus shows comparable variations (Figures 5.6 and A2.1). High (low) Ti/Ca ratios indicate an increased (decreased) terrigenous input and reflect enhanced (decreased) precipitation over PNG when precession is high (low). A spectral analysis confirms that the Ti/Ca varies on the precession band (Figure 5.5c). A similar pattern is also observed in Nd/Ca (Figures 5.5d and 5.6). Most likely, Nd is delivered by fine particles originating from PNG. Elevated Nd concentrations are reported within the Bismarck Sea downstream the Sepik River [Grenier et al., 2013]. Provenance studies consistently indicate that increased particulate concentrations of REEs in the western equatorial Pacific are river-derived [Sholkovitz et al., 1999; Tachikawa et al., 2011]. We therefore assume enhanced Nd concentrations to be associated with increased precipitation and Sepik River discharge from PNG. However, an additional dust input of Nd from volcanic sources is possible [Grenier et al., 2013]. Nd particles could either be incorporated into the foraminifera tests within the water column [Liu et al., 2015;
Another prominent oceanographic feature around the Falkland Islands is the Falkland Cur- rent. The Falkland Current originates from the Antarctic Circumpolar Current and branches into two main northward flowing currents when it reaches the continental shelf to the south of the Falkland Islands [ 29 ]. The eastern branch of the Falkland Current runs along the Patago- nian Shelf slope and is associated with meso-scale fronts, quasi-stationary eddies and regions of upwelling [ 31 , 32 ]. The weaker western branch is also associated with quasi-stationary eddies and regions of upwelling, but bottom topography, water structure and the seasonal abundance of fish and squid varies around the Falkland Islands [ 31 – 33 ]. It is possible that colony-level dif- ferences in adult female SSL habitat use (and differences between West and East Falkland) reflect differences in the proximity of colonies to predictable oceanographic features, which may in turn influence the abundance, distribution and availability of preferred prey. Given that Big Shag Island has a pup production over five times that of Turn Island, an alternative expla- nation is that population size could have contributed towards differences in the prevalence of inshore and offshore habitat use if there was density dependant depletion of resources around breeding colonies (e.g., [ 34 ]). To distinguish between these possibilities it would be necessary to gather detailed data on local oceanography, SSL diet and patterns of prey availability, which are currently lacking.
In agriculture, mineral phosphate (P) fertilizer application leads to an unintended input of Cadmium (Cd) into agricultural systems. Cd is highly toxic and its incorporation into the food chain endangers human health. Copper (Cu) and zinc (Zn) are used as feed additives and pharmaceuticals and can accumulate with farmyard manure in agricultural soils. Although being micronutrients, high Cu and Zn concentrations are toxic. Former studies revealed Cd, Cu and Zn accumulations in Swiss agricultural soils in the past decades. However, these studies were not completely based on in-situ measured data. The aim of this study was to fill this gap and measure Cd, Cu and Zn fluxes at selected Swiss agricultural sites. Specifically, we aimed to trace the metals in the soil and to differentiate between anthropogenic and geogenic sources. Additionally, we further elucidated metal redistribution in Swiss agricultural systems, based on the measurements ofstable metal isotope ratios of different system pools. For that purpose, metal balances of three arable (Cd) and three grassland (Cu & Zn) sites were determined by measuring the soil metal concentrations and all inputs (bulk deposition, mineral P fertilizers, manure & parent material) and outputs (seepage water, crop & grass harvest) during one hydrological year (May 2014 – May 2015).
Ion exchange resins on plastic membranes have been used since the 1960s for sampling of dissolved analytes from soil . When combined with a semipermeable layer, the ion exchange membrane acts as a plant root simulator (PRS). PRS is a simple and cost-saving method and, therefore, it has found a wide range of applications in soil science [21, 22]. The easiness of application, quickness, and possibility to re-use the membrane several times make the anion exchange resin on a plastic membrane an ideal candidate for sulfate separation in a high number ofwater samples. Kwon et al. tested an anion exchange resin placed on a polystyrene matrix for isotopic analysis of oxygen and sulfur in sulfate by IRMS . They observed that the sampling method does not cause a significant isotopic fractionation of sulfur, even in the presence of other anions (competitive anion exchange). Although their method worked well, the sampled sulfate still had to be precipitated as BaSO 4
Our MTT calculations did not provide a good fit between the observed and calculated data. Just by comparing mean precipitation, stream, and groundwater isotopic signatures (Table 1), one could expect that simple mixing calculations would not work to derive MTTs, i.e. showing predominant groundwater contribution. The same observations were made by Jin et al. (2012), indicating good hydraulic connectiv- ity between surface water and shallow groundwater. Just as in the results presented here, Klaus et al. (2015) had dif- ficulties to apply traditional methods of isotope hydrology (MTT estimation, hydrograph separation) to their data set due to the lack of temporal isotopic variation in stream wa- ter of a forested low mountainous catchment in South Car- olina (USA). Furthermore, stablewaterisotopes can only be utilised for estimations of younger water (< 5 years) (Stewart et al., 2010) as they are blind to older contributions (Duvert et al., 2016). In our catchment, transit times are orders of magnitudes longer than the timescale of hydrologic response (prompt discharge of old water) (McDonnell et al., 2010) and the range used for stablewaterisotopes.
employed in our experiments corresponds to a spectral truncation of T31 and 26 hybrid levels in the vertical. The related Gaussian grid has a spatial resolution of approximately 3.75 ◦ (48 grid points in latitude and 96 grid points in longitude). The stable isotope ratios ofwater in the hydrological cycle of IsoCAM are transported through the atmosphere by the same processes (advection, moist convection, evapo- transpiration etc.) used to transport normal water ( Noone and Sturm , 2010 ) and undergo fractionation associated with the phase changes ofwater. The atmospheric model is coupled to a land model (Community Land Model - CLM, Bonan et al. , 2002 ) at the same resolution as the atmospheric model. The land surface isotope scheme in IsoCAM is limited to a simple bucket model, wherein no distinction is made be- tween bare soil evaporation and transpiration, and evapotranspiration is considered non-fractionating ( Manabe , 1969 ; Noone and Simmonds , 2002 ). Isotopic composition of the ocean surface was ﬁxed with a constant value of 0.5 for δ 18 O and 4 for δD ( Craig and Gordon , 1965 ; Hoﬀmann et al. , 1998 ). IsoCAM uses a semi-Lagrangian formulation for the water vapor and tracer transport ( Williamson and Olson , 1994 ), without the application of a mass-ﬁxer, and has been found to be suﬃciently accu- rate for conserving isotopic ratios during advection to low temperature environments ( Noone and Simmonds , 2002 ).
Understanding the hydrologic connectivity between kettle holes and shallow ground- water, particularly in reaction to the highly variable local meteorological conditions, is of paramount importance for tracing water in a hydro(geo)logically complex landscape and thus for integrated water resource management. This article is aimed at identifying the dominant hydrological processes affecting the kettle holes' water balance and their interactions with the shallow groundwater domain in the Uckermark region, located in the north-east of Germany. For this reason, based on the stableisotopesof oxygen ( δ 18 O) and hydrogen ( δ 2 H), an isotopic mass balance model was employed to compute the evaporative loss ofwater from the kettle holes from February to August 2017. Results demonstrated that shallow groundwater inflow may play the pivotal role in the processes taking part in the hydrology of the kettle holes in the Uckermark region. Based on the calculated evaporation/inflow (E/I) ratios, most of the kettle holes (86.7%) were ascertained to have a partially open, flow-through-dominated system. Moreover, we identified an inverse correlation between E/I ratios and the altitudes of the kettle holes. The same holds for electrical conductivity (EC) and the altitudes of the kettle holes. In accordance with the findings obtained from this study, a conceptual model explaining the interaction between the shallow groundwater and the kettle holes of Uckermark was developed. The model exhibited that across the highest altitudes, the recharge kettle holes are dominant, where a lower ratio of E/I and a lower EC was detected. By contrast, the lowest topographical depressions represent the discharge kettle holes, where a higher ratio of E/I and EC could be identified. The kettle holes existing in between were categorized as flow-through kettle holes through which the recharge takes place from one side and discharge from the other side.
Over land surfaces two main processes exist which include a phase transition ofwater masses: evaporation and transpi- ration. Whereas isotope fractionation occurs during an evap- oration process, it is often assumed that the transpiration is a non-fractionating process (see Gat, 1996). Many of the presently existing GCMs enhanced with isotopes do not con- sider such difference between the evaporation and transpi- ration flux but simply assume that the whole evapotranspi- ration from land surface is a non-fractionating process (see, e.g., Hoffmann et al., 1998, for a more detailed discussion of this issue). So far, only very few GCM studies, e.g., Aleinov and Schmidt (2006), have started to investigate fractionation processes over land.