Refine search
Results 1-4 of 4
The use of sedimentary %C, %N, δ15N, and Pb concentrations to assess historical changes in anthropogenic influence on Portuguese estuaries
2007
Castro, P. | Valiela, I. | Freitas, H.
Vertical profiles of C, N, δ15N and Pb were measured in the Mondego and Mira estuaries as markers that conveyed notions as to the relative influence of anthropogenic influence over the past decades. Recent carbon changes in both estuaries may reflect changes in estuarine productivity, probably as a consequence of sediment reworking and erosion, and also of losses in salt marsh area and dwarf eelgrass beds. δ15N values began to diverge considerably before the %C and %N and were higher in Mondego. δ15N signatures detected N enrichment at relatively low rates, and indicated that Mondego received more enriched N than Mira. Lead concentrations differed between estuaries, with higher concentrations in Mondego. The secular increase in %N, Pb, and δ15N signatures was significantly related to human density in the watersheds of the estuaries and were sensitive indicators of anthropogenic activity. The variables C, %N, δ15N, and Pb were reliable sediment sentinels that reflected the level of anthropogenic influence in the past decades in estuarine ecosystems.
Show more [+] Less [-]Regional patterns in foliar 15N across a gradient of nitrogen deposition in the northeastern US
2007
Pardo, L.H. | McNulty, S.G. | Boggs, J.L. | Duke, S.
Recent studies have demonstrated that natural abundance 15N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, δ15N of foliage and soil also increases. We measured foliar δ15N at 11 high-elevation spruce-fir stands along an N deposition gradient in 1987-1988 and at seven paired northern hardwood and spruce-fir stands in 1999. In 1999, foliar δ15N increased from -5.2 to -0.7[per thousand] with increasing N deposition from Maine to NY. Foliar δ15N decreased between 1987-1988 and 1999, while foliar %N increased and foliar C:N decreased at most sites. Foliar δ15N was strongly correlated with N deposition, and was also positively correlated with net nitrification potential and negatively correlated with soil C:N ratio. Although the increase in foliar %N is consistent with a progression towards N saturation, other results of this study suggest that, in 1999, these stands were further from N saturation than in 1987-1988. Foliar δ15N increased with increasing N deposition from Maine to NY, but decreased between 1987-1988 and 1999
Show more [+] Less [-]Use of 15N-labelled nitrogen deposition to quantify the source of nitrogen in runoff at a coniferous-forested catchment at Gårdsjön, Sweden
2007
Kjonaas, O.J. | Wright, R.F.
To determine the source of dissolved inorganic nitrogen (N) in runoff, approx. 35 kg N enriched with the stable isotope 15N (2110[per thousand] δ15N) was added to a mature coniferous forested catchment for one whole year. The total N input was approx. 50 kg ha-1 year-1. The enrichment study was part of a long-term whole-catchment ammonium nitrate addition experiment at Gårdsjön, Sweden. The 15N concentrations in precipitation, throughfall, runoff and upper forest floor were measured prior to, during, and 3-9 years following the 15N addition. During the year of the 15N addition the δ15N level in runoff largely reflected the level in incoming N, indicating that the leached NO3- came predominantly from precipitation. Only 1.1% of the incoming N was lost during the year of the tracer addition. The cumulative loss of tracer N over a 10-year period was only 3.9% as DIN and 1.1% as DON. 15N tracer addition showed that initially the main source of NO3- in runoff was N from atmospheric deposition.
Show more [+] Less [-]Geochemical and isotopic constraints on groundwater-surface water interactions in a highly anthropized site. The Wolfen/Bitterfeld megasite (Mulde subcatchment, Germany)
2007
Petelet-Giraud, E. | Negrel, Ph | Gourcy, L. | Schmidt, C. | Schirmer, M.
The Bitterfeld/Wolfen region is a megasite with multiple contaminant sources from more than a century of industrial activity, which have a considerable impact on the environment. At present, the contaminated groundwater covers an area of about 25 km2 and poses a threat for the surrounding aquifers and the Mulde River. This study focuses on the Schachtgraben, a man-made channel in the Mulde Floodplain that collects the effluents of the industrial area. It aims to characterise the relationship between surface water (channels, rivers) and the groundwater in the shallow Quaternary aquifer. Waters are Ca-SO4 type with TDS reaching 3.8 g L-1 in the industrial area. Stable isotopes (δ18O, δ2H) show that two of the rivers are recharged mainly by groundwater that can be divided into two groups. Strontium isotopes (87Sr/86Sr) designate different geochemical end-members and enable the identification of mixing between natural and anthropogenic surface and groundwater. Modern geochemical and isotope techniques demonstrated groundwater to be the main source of surface water pollution in a hotspot of pollution in the Elbe Watershed.
Show more [+] Less [-]