Isoscapes to address large-scale earth science challenges
No abstract available.
Eos, Transactions, American Geophysical Union↗
Geology topics
C. Kendall
Publications and source records attributed to C. Kendall.
Using Lagrangian sampling to study water quality during downstream transport in the San Luis Drain, California, USA
To investigate the mechanism for diel (24h) changes commonly observed at fixed sampling locations and how these diel changes relate to downstream transport in hypereutrophic surface waters, we studied a parcel of agricultural drainage water as it traveled for 84h in a concrete-lined channel having no additional water inputs or outputs. Algal fluorescence, dissolved oxygen, temperature, pH, conductivity, and turbidity were measured every 30min. Grab samples were collected every 2h for water quality analyses, including nutrients, suspended sediment, and chlorophyll/pheophytin. Strong diel patterns were observed for dissolved oxygen, pH, and temperature within the parcel of water. In contrast, algal pigments and nitrate did not exhibit diel patterns within the parcel of water, but did exhibit strong diel patterns for samples collected at a fixed sampling location. The diel patterns observed at fixed sampling locations for these constituents can be attributed to algal growth during the day and downstream transport (washout) of algae at night. Algal pigments showed a rapid daytime increase during the first 48h followed by a general decrease for the remainder of the study, possibly due to sedimentation and photobleaching. Algal growth (primarily diatoms) was apparent each day during the study, as measured by increasing dissolved oxygen concentrations, despite low phosphate concentrations (<0.01mgL-1).
California↗
A carbon, nitrogen, and sulfur elemental and isotopic study in dated sediment cores from the Louisiana Shelf
Three sediment cores were collected off the Mississippi River delta on the Louisiana Shelf at sites that are variably influenced by recurring, summer-time water-column hypoxia and fluvial loadings. The cores, with established chronology, were analyzed for their respective carbon, nitrogen, and sulfur elemental and isotopic composition to examine variable organic matter inputs, and to assess the sediment record for possible evidence of hypoxic events. Sediment from site MRJ03-3, which is located close to the Mississippi Canyon and generally not influenced by summer-time hypoxia, is typical of marine sediment in that it contains mostly marine algae and fine-grained material from the erosion of terrestrial C4 plants. Sediment from site MRJ03-2, located closer to the mouth of the Mississippi River and at the periphery of the hypoxic zone (annual recurrence of summer-time hypoxia >50%), is similar in composition to core MRJ03-3, but exhibits more isotopic and elemental variability down-core, suggesting that this site is more directly influenced by river discharge. Site MRJ03-5 is located in an area of recurring hypoxia (annual recurrence >75%), and is isotopically and elementally distinct from the other two cores. The carbon and nitrogen isotopic composition of this core prior to 1960 is similar to average particulate organic matter from the lower Mississippi River, and approaches the composition of C3 plants. This site likely receives a greater input of local terrestrial organic matter to the sediment. After 1960 and to the present, a gradual shift to higher values of δ 13 C and δ 15 N and lower C:N ratios suggests that algal input to these shelf sediments increased as a result of increased productivity and hypoxia. The values of C:S and δ 34 S reflect site-specific processes that may be influenced by the higher likelihood of recurring seasonal hypoxia. In particular, the temporal variations in the C:S and δ 34 S down-core are likely caused by changes in the rate of sulfate reduction, and hence the degree of hypoxia in the overlying water column. Based principally on the down-core C:N and C:S ratios and δ 13 C and δ 34 S profiles, sites MRJ03-3 and MRJ03-2 generally reflect more marine organic matter inputs, while site MRJ03-5 appears to be more influenced by terrestrial deposition.
Geo-Marine Letters↗
Characterizing the oxygen isotopic composition of phosphate sources to aquatic ecosystems
The oxygen isotopic composition of dissolved inorganic phosphate (δ 18 O p ) in many aquatic ecosystems is not in isotopic equilibrium with ambient water and, therefore, may reflect the source δ 18 O p . Identification of phosphate sources to water bodies is critical for designing best management practices for phosphate load reduction to control eutrophication. In order for δ 18 O p to be a useful tool for source tracking, the δ 18 O p of phosphate sources must be distinguishable from one another; however, the δ 18 O p of potential sources has not been well characterized. We measured the δ 18 O p of a variety of known phosphate sources, including fertilizers, semiprocessed phosphorite ore, particulate aerosols, detergents, leachates of vegetation, soil, animal feces, and wastewater treatment plant effluent. We found a considerable range of δ 18 O p values (from +8.4 to +24.9‰) for the various sources, and statistically significant differences were found between several of the source types. δ 18 O p measured in three different fresh water systems was generally not in equilibrium with ambient water. Although there is overlap in δ 18 O p values among the groups of samples, our results indicate that some sources are isotopically distinct and δ 18 O p can be used for identifying phosphate sources to aquatic systems.
Environmental Science & Technology↗
Using oxygen isotopes of phosphate to trace phosphorus sources and cycling in lake Erie
Water samples collected during three sampling trips to Lake Erie displayed oxygen isotopic values of dissolved phosphate (δ 18 O p ) that were largely out of equilibrium with ambient conditions, indicating that source signatures may be discerned. δ 18 O p values in the Lake ranged from +10‰ to +17‰, whereas the equilibrium value was expected to be around +14‰. The riverine weighted average δ 18 O p value was +11‰ and may represent one source of phosphate to the Lake. The lake δ 18 O p values indicated that there must be one or more as yet uncharacterized source(s) of phosphate with a high δ 18 O p value. Potential sources other than rivers are not yet well-characterized with respect to δ 18 O of phosphate, but we speculate that a likely source may be the release of phosphate from sediments under reducing conditions created during anoxic events in the hypolimnion of the central basin of Lake Erie. Identifying potential phosphorus sources to the Lake is vital for designing effective management plans for reducing nutrient inputs and associated eutrophication.
Environmental Science & Technology↗
Sources and transformations of nitrate from streams draining varying land uses: Evidence from dual isotope analysis
Knowledge of key sources and biogeochemical processes that affect the transport of nitrate (NO 3 - ) in streams can inform watershed management strategies for controlling downstream eutrophication. We applied dual isotope analysis of NO 3 - to determine the dominant sources and processes that affect NO 3 - concentrations in six stream/river watersheds of different land uses. Samples were collected monthly at a range of flow conditions for 15 mo during 2004-05 and analyzed for NO 3 - concentrations, ?? 15 N NO3 , and ?? 18 O NO3 . Samples from two forested watersheds indicated that NO 3 - derived from nitrification was dominant at baseflow. A watershed dominated by suburban land use had three ?? 18 O NO3 values greater than +25???, indicating a large direct contribution of atmospheric NO 3 - transported to the stream during some high flows. Two watersheds with large proportions of agricultural land use had many ?? 15 N NO3 values greater than +9???, suggesting an animal waste source consistent with regional dairy farming practices. These data showed a linear seasonal pattern with a ?? 18 O NO3 :?? 15 N NO3 of 1:2, consistent with seasonally varying denitrification that peaked in late summer to early fall with the warmest temperatures and lowest annual streamflow. The large range of ?? 15 N NO3 values (10???) indicates that NO 3 - supply was likely not limiting the rate of denitrification, consistent with ground water and/or in-stream denitrification. Mixing of two or more distinct sources may have affected the seasonal isotope patterns observed in these two agricultural streams. In a mixed land use watershed of large drainage area, none of the source and process patterns observed in the small streams were evident. These results emphasize that observations at watersheds of a few to a few hundred km 2 may be necessary to adequately quantify the relative roles of various NO 3 - transport and process patterns that contribute to streamflow in large basins. Copyright ?? 2009 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.
Journal of Environmental Quality↗
Evaluating regional patterns in nitrate sources to watersheds in national parks of the Rocky Mountains using nitrate isotopes
In the Rocky Mountains, there is uncertainty about the source areas and emission types that contribute to nitrate (NO 3 ) deposition, which can adversely affect sensitive aquatic habitats of high-elevation watersheds. Regional patterns in NO 3 deposition sources were evaluated using NO 3 isotopes in five National Parks, including 37 lakes and 7 precipitation sites. Results indicate that lake NO 3 ranged from detection limit to 38 μeq/L, δ 18 O (NO 3 ) ranged from −5.7 to +21.3‰, and δ 15 N (NO 3 ) ranged from −6.6 to +4.6‰. δ 18 O (NO 3 ) in precipitation ranged from +71 to +78‰. δ 15 N (NO 3 ) in precipitation and lakes overlap; however, δ 15 N (NO 3 ) in precipitation is more depleted than δ 15 N (NO 3 ) in lakes, ranging from −5.5 to −2.0‰. δ 15 N (NO 3 ) values are significantly related ( p < 0.05) to wet deposition of inorganic N, sulfate, and acidity, suggesting that spatial variability of δ 15 N (NO 3 ) over the Rocky Mountains may be related to source areas of these solutes. Regional patterns show that NO 3 and δ 15 N (NO 3 ) are more enriched in lakes and precipitation from the southern Rockies and at higher elevations compared to the northern Rockies. The correspondence of high NO 3 and enriched δ 15 N (NO 3 ) in precipitation with high NO 3 and enriched δ 15 N (NO 3 ) in lakes, suggests that deposition of inorganic N in wetfall may affect the amount of NO 3 in lakes through a combination of direct and indirect processes such as enhanced nitrification.
Environmental Science & Technology↗
Influences of the unsaturated, saturated, and riparian zones on the transport of nitrate near the Merced River, California, USA
Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50-100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area. ?? Springer-Verlag 2007.
Hydrogeology Journal↗
Assessing the contribution of wetlands and subsided islands to dissolved organic matter and disinfection byproduct precursors in the Sacramento-San Joaquin River Delta: A geochemical approach
This study assesses how rivers, wetlands, island drains and open water habitats within the Sacramento-San Joaquin River Delta affect dissolved organic matter (DOM) content and composition, and disinfection byproduct (DBP) formation. Eleven sites representative of these habitats were sampled on six dates to encompass seasonal variability. Using a suite of qualitative analyses, including specific DBP formation potential, absorbance, fluorescence, lignin content and composition, C and N stable isotopic compositions, and structural groupings determined using CPMAS (cross polarization, magic angle spinning) 13C NMR, we applied a geochemical fingerprinting approach to characterize the DOM from different Delta habitats, and infer DOM and DBP precursor sources and estimate the relative contribution from different sources. Although river input was the predominant source of dissolved organic carbon (DOC), we observed that 13-49% of the DOC exported from the Delta originated from sources within the Delta, depending on season. Interaction with shallow wetlands and subsided islands significantly increased DOC and DBP precursor concentrations and affected DOM composition, while deep open water habitats had little discernable effect. Shallow wetlands contributed the greatest amounts of DOM and DBP precursors in the spring and summer, in contrast to island drains which appeared to be an important source during winter months. The DOM derived from wetlands and island drains had greater haloacetic acid precursor content relative to incoming river water, while two wetlands contributed DOM with greater propensity to form trihalomethanes. These results are pertinent to restoration of the Delta. Large scale introduction of shallow wetlands, a proposed restoration strategy, could alter existing DOC and DBP precursor concentrations, depending on their hydrologic connection to Delta channels. ?? 2008 Elsevier Ltd.
Organic Geochemistry↗
Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream
The stable isotopic composition of dissolved inorganic carbon (??13C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed ?? 13C-DIC increased between 3-5??? from the stream source to the outlet weir approximately 0??5 km downstream, concomitant with increasing pH and decreasing PCO2. An increase in ??13C-DIC of 2.4 ?? 0??1??? per log unit decrease of excess PCO2 (stream PCO2 normalized to atmospheric PCO2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO2 outgassing rather than exchange with atmospheric CO2 may be the primary cause of increased ?? 13C-DIC values downstream when PCO2 of surface freshwater exceeds twice the atmospheric CO2 concentration. Although CO2 outgassing caused a general increase in stream ??13C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in ??13C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO2 during the early spring growing season. Thus, in spite of effects from CO2 outgassing, ??13C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright ?? 2007 John Wiley & Sons, Ltd.
Hydrological Processes↗
Factors controlling nitrogen release from two forested catchments with contrasting hydrochemical responses
Quantifying biogeochemical cycles of nitrogen (N) and the associated fluxes to surface waters remains challenging, given the need to deal with spatial and temporal variability and to characterize complex and heterogeneous landscapes. We focused our study on catchments S14 and S15 located in the Adirondack Mountains of New York, USA, which have similar topographic and hydrologic characteristics but contrasting stream nitrate ($\hbox{NO}_{3}^{-}$) concentrations. We characterized the mechanisms by which $\hbox{NO}_{3}^{-}$ reaches the streams during hydrological events in these catchments, aiming to reconcile our field data with our conceptual model of factors that regulate nutrient exports from forested catchments. Combined hydrometric, chemical and isotopic (δ$\hbox{NO}_{3}^{-}$) data showed that the relative contributions of both soil and ground water sources were similar between the two catchments. Temporal patterns of stream chemistry were markedly different between S14 and S15, however, because the water sources in the two catchments have different solute concentrations. During late summer/fall, the largest source of $\hbox{NO}_{3}^{-}$ in S14 was till groundwater, whereas shallow soil was the largest $\hbox{NO}_{3}^{-}$ source in S15. $\hbox{NO}_{3}^{-}$ concentrations in surface water decreased in S14, whereas they increased in S15 because an increasing proportion of stream flow was derived from shallow soil sources. During snowmelt, the largest sources of $\hbox{NO}_{3}^{-}$were in the near‐surface soil in both catchments. Concentrations of $\hbox{NO}_{3}^{-}$ increased as stream discharge increased and usually peaked before peak discharge, when shallow soil water sources made the largest contribution to stream discharge. The timing of peaks in stream $\hbox{NO}_{3}^{-}$concentrations was affected by antecedent moisture conditions. By elucidating the factors that affect sources and transport of N, including differences in the soil nutrient cycling and hydrological characteristics of S14 and S15, this study contributes to the overall conceptualization of $\hbox{NO}_{3}^{-}$ release from temperate forested catchments.
Hydrological Processes↗
Comment on “Two New Carbonate Stable Isotope Standards”
Friedman et al (1) propose that NBS 19 calcium carbonate substitute for PDB. This is in apparent conflict with the recommendation of the September 1976 consultants’ meeting convened by the International Atomic Energy Agency on stable isotope standards. Furthermore, Friedman et al suggest ɛ‐values be adopted for NBS 19 that do not take into account the ɛ‐values of NBS 20 (Solenhofen limestone). We believe that adoption of these proposals may lead to confusion in the stable isotope literature and to lack of correspondence between historic and future isotopic results. In sharp contrast to the results of Friedman et al (1), we find NBS 20 to be a satisfactory reference material if it is handled properly. Copyright © 1982, Wiley Blackwell. All rights reserved
Geostandards Newsletter↗
Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California
[1] A seasonal analysis assesing variations in the oxygen isotopic composition of dissolved inorganic phosphate (DIP) was conducted in the San Francisco Bay estuarine system, California. Isotopic fractionation of oxygen in DIP (exchange of oxygen between phosphate and environmental water) at surface water temperatures occurs only as a result of enzyme‐mediated, biological reactions. Accordingly, if phospate demand is low relative to input and phosphate is not heavily cycled in the ecosystem, the oxygen isotopic composition of DIP (δ 18 O p ) will reflect the isotopic composition of the source of phosphate to the system. Such is the case for the North San Francisco Bay, an anthropogenically impacted estuary with high surface water phosphate concentrations. Variability in the δ 18 O p in the bay is primarily controlled by mixing of water masses with different δ 18 O p signatures. The δ 18 O p values range from 11.4‰ at the Sacramento River to 20.1‰ at the Golden Gate. Deviations from the two‐component mixing model for the North Bay reflect additional, local sources of phosphate to the estuary that vary seasonally. Most notably, deviations from the mixing model occur at the confluence of a major river into the bay during periods of high river discharge and near wastewater treatment outlets. These data suggest that δ 18 O p can be an effective tool for identifying P point sources and understanding phosphate dynamics in estuarine systems.
Journal of Geophysical Research G: Biogeosciences↗
Nitrogen sources and cycling in the San Francisco Bay estuary: A nitrate dual isotopic composition approach
We used the dual isotopic composition of nitrate (δ 15 N and δ 18 O) within the estuarine system of San Francisco (SF) Bay, California, to explore the utility of this approach for tracing sources and cycling of nitrate (NO 2 − ). Surface water samples from 49 sites within the estuary were sampled during July–August 2004. Spatial variability in the isotopic composition suggests that there are multiple sources of nitrate to the bay ecosystem including seawater, several rivers and creeks, and sewage effluent. The spatial distribution of nitrate from these sources is heavily modulated by the hydrodynamics of the estuary. Mixing along the estuarine salinity gradient is the main control on the spatial variations in isotopic composition of nitrate within the northern arm of SF Bay. However, the nitrate isotopic composition in the southern arm of SF Bay exhibited a combination of source mixing and phytoplankton drawdown due mostly to the long residence time during the summer study period. Very low δ 18 O NO3 values (as low as −5.0%) at the Sacramento–San Joaquin River delta region give rise to a wide range of δ 18 ONO3 values in the SF Bay system. The range in δ 18 O NO3 values is more than twice that of δ 15 N NO3 , suggesting that δ 18 O NO3 is an even more sensitive tool for tracing nitrate sources and cycling than δ 15 N NO3 .
Limnology and Oceanography↗
Geographical patterns of human diet derived from stable-isotope analysis of fingernails
Carbon and nitrogen isotope ratios of human fingernails were measured in 490 individuals in the western US and 273 individuals in southeastern Brazil living in urban areas, and 53 individuals living in a moderately isolated area in the central Amazon region of Brazil and consuming mostly locally grown foods. In addition, we measured the carbon and nitrogen isotope ratios of common food items to assess the extent to which these isotopic signatures remain distinct for people eating both omnivorous and vegetarian diets and living in different parts of the world, and the extent to which dietary information can be interpreted from these analyses. Fingernail ??13C values (mean ?? standard deviation) were -15.4 ?? 1.0 and -18.8 ?? 0.8??? and ??15N values were 10.4 ?? 0.7 and 9.4 ?? 0.6??? for southeastern Brazil and western US populations, respectively. Despite opportunities for a "global supermarket" effect to swamp out carbon and nitrogen isotope ratios in these two urbanized regions of the world, differences in the fingernail isotope ratios between southeastern Brazil and western US populations persisted, and appeared to be more associated with regional agricultural and animal production practices. Omnivores and vegetarians from Brazil and the US were isotopically distinct, both within and between regions. In a comparison of fingernails of individuals from an urban city and isolated communities in the Amazonian region, the urban region was similar to southeastern Brazil, whereas individuals from isolated nonurban communities showed distinctive isotopic values consistent with their diets and with the isotopic values of local foods. Although there is a tendency for a "global supermarket" diet, carbon and nitrogen isotopes of human fingernails hold dietary information directly related to both food sources and dietary practices in a region. ?? 2006 Wiley-Liss, Inc.
American Journal of Physical Anthropology↗
Solute sources in stream water during consecutive fall storms in a northern hardwood forest watershed: A combined hydrological, chemical and isotopic approach
Understanding the effects of climate change including precipitation patterns has important implications for evaluating the biogeochemical responses of watersheds. We focused on four storms in late summer and early fall that occurred after an exceptionally dry period in 2002. We analyzed not only the influence of these storms on episodic chemistry and the role of different water sources in affecting surface water chemistry, but also the relative contributions of these storms to annual biogeochemical mass balances. The study site was a well studied 135-ha watershed in the Adirondack Park of New York State (USA). Our analyses integrated measurements on hydrology, solute chemistry and the isotopic composition of NO 3 − (δ 15 N and δ 18 O) and SO 4 2− (δ 34 S and δ 18 O) to evaluate how these storms affected surface water chemistry. Precipitation amounts varied among the storms (Storm 1: Sept. 14–18, 18.5 mm; Storm 2: Sept. 21–24, 33 mm; Storm 3: Sept. 27–29, 42.9 mm; Storm 4: Oct. 16–21, 67.6 mm). Among the four storms, there was an increase in water yields from 2 to 14%. These water yields were much less than in studies of storms in previous years at this same watershed when antecedent moisture conditions were higher. In the current study, early storms resulted in relatively small changes in water chemistry. With progressive storms the changes in water chemistry became more marked with particularly major changes in C b (sum of base cations), Si, NO 3 − , and SO 4 2− , DOC and pH. Analyses of the relationships between Si, DOC, discharge and water table height clearly indicated that there was a decrease in ground water contributions (i.e., lower Si concentrations and higher DOC concentrations) as the watershed wetness increased with storm succession. The marked changes in chemistry were also reflected in changes in the isotopic composition of SO 4 2− and NO 3 − . There was a strong inverse relationship between SO 4 2− concentrations and δ 34 S values suggesting the importance of S biogeochemical redox processes in contributing to SO 4 2− export. The isotopic composition of NO 3 − in stream water indicated that this N had been microbially processed. Linkages between SO 4 2− and DOC concentrations suggest that wetlands were major sources of these solutes to drainage waters while the chemical and isotopic response of NO 3 − suggested that upland sources were more important. Although these late summer and fall storms did not play a major role in the overall annual mass balances of solutes for this watershed, these events had distinctive chemistry including depressed pH and therefore have important consequences to watershed processes such as episodic acidification, and the linkage of these processes to climate change.
Biogeochemistry↗
Oxygen isotopes of phosphatic compounds - Application for marine particulate matter, sediments and soils
The phosphate oxygen isotopic composition in naturally occurring particulate phosphatic compounds (δ 18 O p ) can be used as a tracer for phosphate sources and to evaluate the cycling of phosphorus (P) in the environment. However, phosphatic compounds must be converted to silver phosphate prior to isotopic analysis, a process that involves digestion of particulate matter in acid. This digestion will hydrolyze some of the phosphatic compounds such that oxygen from the acid solution will be incorporated into the sample as these phosphatic compounds are converted to orthophosphate (PO 4 3− ). To determine the extent of incorporation of reagent oxygen into the sample, we digested various phosphatic compounds in both acid amended with H 2 18 O (spiked) and unspiked acid and then converted the samples to silver phosphate for δ 18 O p analysis. Our results indicate that there is no isotopic fractionation associated with acid digestion at 50 °C. Furthermore, we found that reagent oxygen incorporation is a function of the oxygen to phosphorus ratio (O:P) of the digested compound whereby the percentage of reagent oxygen incorporated into the sample is the same as that which is required to convert all of the P-compounds into orthophosphate. Based on these results, we developed a correction for reagent oxygen incorporation using simple mass balance, a procedure that allows for the determination of the δ 18 O p of samples containing a mixture of phosphatic compounds. We analyzed a variety of environmental samples for δ 18 O p to demonstrate the utility of this approach for understanding sources and cycling of P.
Marine Chemistry↗
Using stable isotopes of water and strontium to investigate the hydrology of a natural and a constructed wetland
Wetlands cannot exist without water, but wetland hydrology is difficult to characterize. As a result, compensatory wetland mitigation often only assumes the proper hydrology has been created. In this study, water sources and mass transfer processes in a natural and constructed wetland complex were investigated using isotopes of water and strontium. Water isotope profiles in the saturated zone revealed that the natural wetland and one site in the constructed wetland were primarily fed by ground water; profiles in another constructed wetland site showed recent rain was the predominant source of water in the root zone. Water isotopes in the capillary fringe indicated that the residence time for rain is less in the natural wetland than in the constructed wetland, thus transpiration (an important water sink) was greater in the natural wetland. Strontium isotopes showed a systematic difference between the natural and constructed wetlands that we attribute to the presence or absence of peat. In the peat‐rich natural wetland, δ 87 Sr in the pore water increased along the flowline due to preferential weathering of minerals containing radiogenic Sr in response to elevated Fe concentrations in the water. In the constructed wetland, where peat thickness was thin and Fe concentrations in water were negligible, δ 87 Sr did not increase along the flowline. The source of the peat (on‐site or off‐site derived) applied in the constructed wetland controlled the δ 87 Sr at the top of the profile, but the effects were restricted by strong cation exchange in the underlying fluvial sediments. Based on the results of this study, neither constructed wetland site duplicated the water source and weathering environment of the adjoining natural wetland. Moreover, stable isotopes were shown to be effective tools for investigating wetlands and gaining insight not easily obtained using non‐isotopic techniques. These tools have potential widespread application to wetlands that have distinct isotopic endmember sources.
Ground Water↗