The spread of farming from western Asia to Europe had profound long-term social and ecological impacts, but identification of the specific nature of Neolithic land management practices and the ...dietary contribution of early crops has been problematic. Here, we present previously undescribed stable isotope determinations of charred cereals and pulses from 13 Neolithic sites across Europe (dating ca . 5900–2400 cal B.C.), which show that early farmers used livestock manure and water management to enhance crop yields. Intensive manuring inextricably linked plant cultivation and animal herding and contributed to the remarkable resilience of these combined practices across diverse climatic zones. Critically, our findings suggest that commonly applied paleodietary interpretations of human and herbivore δ ¹⁵N values have systematically underestimated the contribution of crop-derived protein to early farmer diets.
Eutrophication is a globally significant challenge facing aquatic ecosystems, associated with human induced enrichment of these ecosystems with nitrogen (N) and phosphorus (P). However, the limited ...availability of inherent labels for P and N has constrained understanding of the triggers for eutrophication in natural ecosystems and appropriate targeting of management responses. This paper proposes and evaluates a new multi-stable isotope framework that offers inherent labels to track biogeochemical reactions governing both P and N in natural ecosystems. The framework couples highly novel analysis of the oxygen isotope composition of phosphate (δ18OPO4) with dual isotope analysis of oxygen and N within nitrate (δ15NNO3, δ18ONO3) and with stable N isotope analysis in ammonium (δ15NNH4). The River Beult in England is used as an exemplar system for initial evaluation of this framework. Our data demonstrate the potential to use stable isotope labels to track the input and downstream fate of nutrients from point sources, on the basis of isotopic differentiation for both P and N between river water and waste water treatment work effluent (mean difference = +1.7‰ for δ18OPO4; +15.5‰ for δ15NNH4 (under high flow); +7.3‰ for δ18ONO3 and +4.4‰ for δ15NNO3). Stable isotope data reveal nutrient inputs to the river upstream of the waste water treatment works that are consistent with partially denitrified sewage or livestock sources of nitrate (δ15NNO3 range = +11.5 to +13.1‰) and with agricultural sources of phosphate (δ18OPO4 range = +16.6 to +19.0‰). The importance of abiotic and metabolic processes for the in-river fate of N and P are also explored through the stable isotope framework. Microbial uptake of ammonium to meet metabolic demand for N is suggested by substantial enrichment of δ15NNH4 (by 10.2‰ over a 100 m reach) under summer low flow conditions. Whilst the concentration of both nitrate and phosphate decreased substantially along the same reach, the stable isotope composition of these ions did not vary significantly, indicating that concentration changes are likely driven by abiotic processes of dilution or sorption. The in-river stable isotope composition and the concentration of P and N were also largely constant downstream of the waste water treatment works, indicating that effluent-derived nutrients were not strongly coupled to metabolism along this in-river transect. Combined with in-situ and laboratory hydrochemical data, we believe that a multi-stable isotope framework represents a powerful approach for understanding and managing eutrophication in natural aquatic ecosystems.
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•First combined application of nitrogen and phosphate oxygen isotopes.•Isotopic differentiation for both P and N between river and effluent water.•Partially denitrified agricultural sources of nitrate identified.•Isotopes showed effluent-derived nutrients not strongly coupled to metabolism.•Powerful new approach for understanding and responding to eutrophication.
The need to reduce both point and diffuse phosphorus pollution to aquatic ecosystems is widely recognised and in order to achieve this, identification of the different pollutant sources is essential. ...Recently, a stable isotope approach using oxygen isotopes within phosphate (δ18OPO4) has been used in phosphorus source tracing studies. This approach was applied in a one-off survey in September 2013 to the River Taw catchment in south-west England where elevated levels of phosphate have been reported. River water δ18OPO4 along the main channel varied little, ranging from +17.1 to +18.8‰. This was no >0.3‰ different to that of the isotopic equilibrium with water (Eδ18OPO4). The δ18OPO4 in the tributaries was more variable (+17.1 to +18.8‰), but only deviated from Eδ18OPO4 by between 0.4 and 0.9‰. Several potential phosphate sources within the catchment were sampled and most had a narrow range of δ18OPO4 values similar to that of river Eδ18OPO4. Discharge from two waste water treatment plants had different and distinct δ18OPO4 from one another ranging between +16.4 and +19.6‰ and similar values to that of a dairy factory final effluent (+16.5 to +17.8‰), mains tap water (+17.8 to +18.4‰), and that of the phosphate extracted from river channel bed sediment (+16.7 to +17.6‰). Inorganic fertilizers had a wide range of values (+13.3 to +25.9‰) while stored animal wastes were consistently lower (+12.0 to +15.0‰) than most other sources and Eδ18OPO4. The distinct signals from the waste water treatment plants were lost within the river over a short distance suggesting that rapid microbial cycling of phosphate was occurring, because microbial cycling shifts the isotopic signal towards Eδ18OPO4. This study has added to the global inventory of phosphate source δ18OPO4 values, but also demonstrated the limitations of this approach to identifying phosphate sources, especially at times when microbial cycling is high.
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•Can sources of aquatic PO4 be traced using its stable oxygen isotope ratio?•Various PO4 sources within a catchment were analysed for their δ18OPO4.•River δ18OPO4 indicated that rapid microbial cycling of PO4 was occurring.•This method appears inappropriate in systems where PO4 cycling is rapid.
In a large study on early crop water management, stable carbon isotope discrimination was determined for 275 charred grain samples from nine archaeological sites, dating primarily to the Neolithic ...and Bronze Age, from the Eastern Mediterranean and Western Asia. This has revealed that wheat (Triticum spp.) was regularly grown in wetter conditions than barley (Hordeum sp.), indicating systematic preferential treatment of wheat that may reflect a cultural preference for wheat over barley. Isotopic analysis of pulse crops (Lens culinaris, Pisum sativum and Vicia ervilia) indicates cultivation in highly varied water conditions at some sites, possibly as a result of opportunistic watering practices. The results have also provided evidence for local land-use and changing agricultural practices.
1. Carbon and nitrogen isotope ratios in consumer tissues are known to correlate with diet isotope composition, and nitrogen isotope ratios are observed to increase with increasing trophic level. 2. ...We analysed nitrogen and hydrogen isotope ratios of collagen from 19 species of British fish, birds and mammals to investigate how δD also correlated with trophic level and with feeding environment (terrestrial or aquatic). 3. A strong relationship between trophic level and δD was discovered for both terrestrial and aquatic consumers. 4. The correlation between trophic level and δ15was apparent for terrestrial consumers, but less so for aquatic consumers. 5. No differentiation was found between δD of aquatic and terrestrial consumers at the same trophic level. 6. This observation should provide an additional tool in the study of current and ancient animal and human food web ecology.
Various studies over the last 15 years have attempted to describe the processes of N retention, saturation and NO₃⁻ leaching in semi-natural ecosystems based on stable isotope studies. Forest ...ecologists and terrestrial biogeochemists have used ¹⁵N labelled NO₃⁻ and NH₄⁺ tracers to determine the fate of atmospheric deposition inputs of N to terrestrial ecosystems, with NO₃⁻ leaching to surface waters being a key output flux. Separate studies by aquatic ecologists have used similar isotope tracer methods to determine the fate and impacts of inorganic N species, leached from terrestrial ecosystems, on aquatic ecosystems, usually without reference to comparable terrestrial studies. A third group of isotopic studies has employed natural abundances of ¹⁵N and ¹⁸O in precipitation and surface water NO₃⁻ to determine the relative contributions of atmospheric and microbial sources. These three sets of results often appear to conflict with one another. Here we attempt to synthesize and reconcile the results of these differing approaches to identifying both the source and the fate of inorganic N in natural or semi-natural ecosystems, and identify future research priorities. We conclude that the results of different studies conform to a consistent conceptual model comprising: (1) rapid microbial turnover of atmospherically deposited NO₃⁻ at multiple biologically active locations within both terrestrial and aquatic ecosystems; (2) maximum retention and accumulation of N in carbon-rich ecosystems and (3) maximum leaching of NO₃⁻, most of which has been microbially cycled, from carbon-poor ecosystems exposed to elevated atmospheric N inputs.
► Examines sources of nitrate in some of Europe’s highest nitrate groundwaters. ► Measures, rather than assumes isotope composition of potential sources. ► Indicates soil nitrification as the most ...likely source. ► Examines implications for a country with a long history of cultivation.
Levels of nitrate in Malta’s groundwater are high. Median concentrations in the main sea-level aquifers of Malta and Gozo are 14 and 10
mg NO
3–N L
−1, respectively, and even higher in the younger groundwaters of the perched aquifers on Malta (37
mg NO
3–N L
−1). The wide variations in groundwater nitrate concentration are not due to denitrification, as
15N/
14N and
18O/
16O analyses of 47 samples from the three aquifer types found clear evidence for this process in only one sample. 90% of the groundwater nitrate samples had δ
18O values in the range +3.1 to +6.1‰, which correspond exactly to those expected for nitrate formed by microbial processes in the presence of Maltese surficial waters (δ
18O of H
2O typically −5.3 to −4.3‰). The δ
15N values of these groundwater nitrate samples, +7.7 to +11.7‰, were compared with those of a wide variety of potential nitrate sources in Malta (fertilizers, sewage, manure and soils). The closest correspondence was found for the organic N in cultivated soils (+6.0 to +11.2‰). These relatively high δ
15N values for soils may reflect greater fluxes of N from soils with a low C/N ratio and a long history of cultivation. While the isotope data support soil nitrification as the source for nitrate in the groundwaters, they do not rule out direct leaching of manure-derived nitrate as a source.
In order to investigate the effect of glaciation on mineral weathering, the stream water chemistry and the bacterial community composition were analysed in two catchments containing nominally ...identical sedimentary formations but which differed in the extent of glaciation. The stream waters were analysed for major ions, δ34S, δ18OSO4 and δ18OH2O and associated stream sediments were analysed by 16S rRNA gene tagged sequencing.
Sulphate comprised 72–86% and 35–45% of the summer anion budget (in meq) in the unglaciated and glaciated catchments respectively. This indicates that sulfuric acid generated from pyrite weathering is a significant weathering agent in both catchments. Based on the relative proportions of cations, sulphate and bicarbonate, the stream water chemistry of the unglaciated catchment was found to be consistent with a sulphide oxidation coupled to silicate dissolution weathering process whereas in the glaciated catchment both carbonates and silicates weathered via both sulfuric and carbonic acids.
Stable isotope measurements of sulphate, together with inferences of metabolic processes catalysed by resident microbial communities, revealed that the pyrite oxidation reaction differed between the two catchments. No δ34S fractionation relative to pyrite was observed in the unglaciated catchment and this was interpreted to reflect pyrite oxidation under oxic conditions. In contrast, δ34S and δ18OSO4 values were positively correlated in the glaciated catchment and were positively offset from pyrite. This was interpreted to reflect pyrite oxidation under anoxic conditions with loss of S intermediates.
This study suggests that glaciation may alter stream water chemistry and the mechanism of pyrite oxidation through an interplay of biological, physical and chemical factors.
•Comparison of weathering processes in a glaciated and an unglaciated catchment•Combination of major elements, δ34S, δ18O-SO4, δ18O–H2O and 16S rRNA•Mechanism of pyrite oxidation differed between the two catchments.•No evidence for sulphate reduction
•Multi technique approach to understand C, N and P within catchment processes.•Changes in nutrient stoichiometry/bioavailability under contrasting flow conditions.•N and O isotopes show dominance of ...waste water (WW) inputs during baseflow.•Fluorescence DOM indices characterise WW inputs to rivers.•Grid-to-Grid distributed model used to assess spatial variations in nutrient flux.
This study employed complementary geochemical techniques and distributed hydrological modelling to investigate multiple sources of catchment macronutrients and characterise their changes in contrasting storm and baseflow conditions. This approach was demonstrated for the Beult catchment in the county of Kent (England), a designated Site of Special Scientific Interest (SSSI) indentified as failing to meet water quality standards for key nutrients under the Water Framework Directive. Significant changes in nutrient stoichiometry and bioavailability are observed for surface waters under contrasting flow regimes. Soluble reactive phosphorus (SRP) concentrations are approximately twice as high during baseflow compared to high flow, while the inverse is true for particulate, colloidal and dissolved hydrolysable phosphorus, dissolved organic carbon and nitrate. Nitrogen (N):phosphorus (P) ratios are lower during baseflow for most surface waters impacted by diffuse sources of pollution. Fluorescence indices of dissolved organic matter (DOM) show that waste water inputs may be locally important sources of more complex low molecular weight DOM, particularly during baseflow. Nitrate N and O isotope signatures, combined with other dissolved chemical tracers, confirm the dominance of wastewater N inputs at sites downsteam of sewerage treatment works during baseflow, with a shift towards the soil N pool in surface waters across the catchment during high flow. Distributed hydrological modelling using the Grid-to-Grid model reveal areas with the greatest runoff also export higher N and P concentrations, and hence deliver a greater flux of macronutrients, while forested areas with low nutrient concentrations reduce runoff and nutrient fluxes. During periods of high runoff, nested sampling indicates that nutrient fluxes scale with catchment area. This combined approach enables a more thorough assessment of the macronutrient sources and dynamics, better informing management options in nutrient impacted catchments.
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