Efficiency of nutrient management in controlling eutrophication of running waters in the Middle Danube Basin

Vera Istvánovics, Márk Honti

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Nutrient emission dropped significantly during the last two decades in the Danube Basin. To assess the effect of reduced nutrient loads on the trophic status of running waters, this regional study analyzed the relationships between nutrients (P and N) and suspended chlorophyll (Chl) using long-term monitoring data in Hungary. Including the upstream catchments of trans-boundary rivers, the study covered an approximate area of 400,000 km 2, equivalent to the half of the entire Danube catchment. Decadal median Chl was unrelated to P and N concentrations in the whole data set and weakly related to total P (TP) at natural-moderately polluted (N-MP) sites, which were distinguished from highly polluted (HP) sites by using cutoff values for chloride, chemical oxygen demand and TP. At both the N-MP sites and most of the HP sites, Chl increased with channel length. This indicated that water residence time was a more important determinant of Chl than nutrients. Nutrient concentrations showed a significant downward trend in time at half of our sites. With a nearly equal frequency, a parallel trend might or might not occur in Chl. The apparent efficiency of nutrient management was expressed as the quotient of the slopes of linear trends in Chl and nutrients. At sites within 150 km from source, this efficiency was marginal. In larger rivers, efficiency improved steeply. The highest efficiency was observed in the downstream reach of the Danube (upstream length >1,300 km) where P availability might frequently limit algal growth. The results suggest that eutrophication management in rivers should be based on Chl response functions, rather than universal nutrient criteria. Four Chl response classes were identified based on the observed longitudinal P and Chl gradients.

Original languageEnglish
Pages (from-to)55-71
Number of pages17
JournalHydrobiologia
Volume686
Issue number1
DOIs
Publication statusPublished - May 2012

Keywords

  • Chlorophyll response functions
  • Nutrient management efficiency
  • River size
  • Sestonic chlorophyll
  • Water Framework Directive
  • Water residence time

ASJC Scopus subject areas

  • Aquatic Science

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