Spatial and seasonal variations in delta18O and deltaD values in the River Sava in Slovenia.

Stable isotope measurements of oxygen and hydrogen (delta18O and deltaD) in stream waters and precipitation were used to investigate hydrological pathways and residence times in the River Sava catchment in Slovenia. delta18O and deltaD values of precipitation exhibited strong seasonal variations. Precipitation is of mixed Atlantic–Mediterranean origin which is also reflected in the isotopic composition of River Sava surface waters. The isotopic content of the river water is dependent on temperature, elevation of the recharge area and amount of precipitation. Spatially, rivers water is 16O-enriched in the high mountain areas due to higher amount of precipitation, lower temperature and higher elevation of the recharge area, while in the lower part of the River Sava catchments the delta18O values are higher. It is also observed that the River Sava responds quickly to precipitation which is reflected in its delta18O and deltaD values and the low residence time estimated in the river. Using an exponential flow model it was calculated that mean stream water residence times varied between 0.4 and 2.1 years. The shortest residence time determined at Savica is connected mainly to the higher amount of precipitation in the upper Sava watershed and the mountains carbonate karst terrain characterized by a higher runoff. The mean residence time in the main stream water of the River Sava was estimated to be 1.32 years and is in a good agreement with the residence time determined using 3H measurements. These data extend our knowledge in understanding the hydrological cycle of the River Sava, the interactions between precipitation, surface water and groundwater and, at the same time, demonstrate the utility of isotope tracers in determining catchments characteristics

Isotopic composition of precipitation in relation to air circulation patterns in the Mediterranean basin

International Workshop , UNESCO, Pari

The influence of water quality and sediment geochemistry on the horizontal and vertical distribution of phosphorus and nitrogen in sediments of a large, shallow lake

Distinct horizontal water column concentration gradients of nutrients and chlorophyll a (Chl a) occur within large, shallow, eutrophic Lake Taihu, China. Concentrations are high in the north, where some of the major polluted tributaries enter the lake, and relatively low in the south, where macrophytes generally are abundant. It is not clear, however, whether these water column concentration gradients are similarly reflected in spatial heterogeneity of nutrient concentrations within the bottom sediments. The main objective of this study was therefore to test if horizontal and vertical variations in the phosphorus and nitrogen content in bottom sediments of Lake Taihu are significantly related to (1) horizontal variations in overlying water column nutrient concentrations and (2) other sediment geochemical constituents. We measured the concentration of total phosphorus (TP) and total nitrogen (TN) in surficial sediments (0–2 cm) and TP, TN and Chl a concentrations in water column samples, collected from 32 sites in 2005. In 2006 sediment, TP, TN, carbon, iron and manganese concentrations were measured vertically at 2 cm intervals, extending to a depth of approximately 20 cm, at an additional eight sites. Linear correlation analysis revealed that surficial sediment TP concentrations across the 32 stations were related significantly, though weakly, to annual mean water column concentrations of TP, TN as well as Chl a. Correlations of surficial sediment TN with water column variables were, however, not significant (P[0.05).Amongst the geochemical variables tested, the vertical variability of sediment TP concentrations was most strongly related to sediment manganese and carbon concentrations. A multiple stepwise linear regression revealed that the combination of sediment manganese and carbon concentrations explained 91% of the horizontal variability in sediment TP concentrations and 65% of the vertical variability