Source identification of nitrate by means of isotopic tracers in the Baltic Sea catchments

Abstract

Abstract. Nitrate input to a river is largely controlled by land use in its catchment. We compared the information carried by the isotopic signatures of nitrate in 12 Baltic rivers, in relation to the vegetation cover, land use, and fertilization of agricultural land of their catchments. We found isotope values in nitrate ranging from −2 to 14‰ for δ 15 N and 8 to 25‰ for δ 18 O. The annual variability of riverine nitrate isotope signatures is presented in detail for one Nordic, the Kemijoki, and two southern rivers, the Vistula and Oder. Nordic rivers with relatively pristine vegetation in their catchments show not only low δ 15 N values and high δ 18 O-NO − 3 but also lower annual variability than rivers draining densely populated land. Seasonal signals were found in all the rivers. We used load weighted nitrate isotope data and data from the three major N sources (farmland/sewage, atmospheric deposition and from runoff of pristine soils) to theoretically estimate the shares of nitrate from these sources. The results of an isotope mixing model (IMM-1) agree reasonably well with the same estimates for agricultural land derived from a Global Land Cover (GLC) data base, with a deviation varying from −16% to +26%. The comparison with an emission model (EM) reveals relatively good agreements for intensively used catchments (−18 to +18% deviation). Rather unsatisfactory agreement was found between the IMM-1 and GLC calculations for pristine catchments (−36 to +50% deviation). Advantages and limitations of the tested model are discussed.

Nitrite consumption and associated isotope changes during a river flood event

“…Afterwards, the C / N ratio decreases, probably because water masses from tributaries and upstream regions contribute to the pool, as it has been observed during a previous flood event in the Elbe River (Baborowski et al, 2004). At the same time, assimilation by phytoplankton is low, probably due to high turbidity, short residence times, dilution of active cells, and decreased light availability (Deutsch et al, 2009;Voss et al, 2006). After 14 June, dropping discharge allows for a recovery of phytoplankton, which is also visible in rising oxygen concentration.…”

Effects of seabird nesting colonies on algae and aquatic invertebrates in coastal waters

“…The low salinity enables only a few marine and freshwater species to occur in the Baltic Sea. Eutrophication is one of the major environmental problems in the Baltic Sea, especially in coastal regions, and the main nitrogen sources are rivers and atmospheric deposition (Elmgren 2001, Voss et al 2006. The yearly nitrogen deposition in the central Baltic Sea was estimated to be 617 mg N m -2 yr -1 and composed of 10% organic N and approximately equal amounts of ammonium and nitrate, with an average δ 15 N = 2.0 ‰ (Rolff et al 2008).…”

Diagenetic control of nitrogen isotope ratios in Holocene sapropels and recent sediments from the Eastern Mediterranean Sea

“…5) follow the same linear relationship between OM preservation and nitrogen isotope composition as was found for recent samples from Ierapetra Deep (MC 284, MC 285, MID 01-03) and the paleo record from Eratosthenes Seamount (M51-3 #569). But even if the trend is highly linear, some influence of different nitrate sources/utilization may be present: extremely 15 N depleted OM in cores from the deep basins may have been contributed mainly by nitrogen fixing cyanobacteria, whereas locations closer to land may have been more influenced by terrestrial/riverine OM inputs that are somewhat less depleted in 15 N (0 to 4‰; Mayer et al, 2002;Voss et al, 2006). Possibly due to the dominant atmospheric source today, recent Eastern Mediterranean surface sediments display a more or less homogeneous pattern in δ 15 N without pronounced gradients from open marine to nearshore environments or from north to south (see Fig.…”