wAbstract
@Previous research in agricultural catchments showed that past
inputs of nitrate continue to influence present observations and
future characteristics of nitrate concentrations in stream water
for a long period of time. This persistence manifests itself as
a gmemory effecth with a prolonged response of stream water nitrate
levels to reductions of nitrate inputs on the catchment scale.
The question we attempt to resolve is whether such a memory effect
also exists in mountainous catchments with a snowmelt-dominated
runoff regime. We analyzed long-term records (`20 years) of nitrate-nitrogen
concentrations measured in stream at three stations on the upper
Vahia‚Ì“ª‚ÉLj River (Slovakia). Applying spectral
analysis and detrended fluctuation analysis, we found a varying
degree of persistence between the three analyzed sites. With increasing
catchment area, the fluctuation scaling exponents generally increased
from 0.77 to 0.93 (fluctuation exponents above 0.5 are usually
considered as a proof of persistence while values close to 0.5
indicate gwhiteh uncorrelated noise). The nitrate-nitrogen signals
temporally scaled as a power-low function of frequently (1/f noise)
with a strong annual seasonality. This increase in persistence
might be attributable to the catchment areas upstream the sampling
sites. These results have important implications for water quality
management. In areas where reduction of nitrate in surface waters
is imposed by legislation and regulatory measures, two catchments
with different persistence properties may not respond to the same
reduction of sources of nitrogen at the same rate.
Keywords: Persistence; Memory effect; Nitrate concentrations;
Detrended fluctuation analysis; Spectral analysisx
1. Introduction
2. Materials and methods
@2.1. Study area and databases
@2.2. Analyses
3. Results
4. Discussion
5. Conclusions
Acknowledgments
References