Academic journal article Estonian Journal of Ecology

Nitrogen and Phosphorus in Estonian Rivers Discharging into Lake Peipsi: Estimation of Loads and Seasonal and Spatial Distribution of concentrations/Lammastik Ja Fosfor Peipsisse Suubuvates Eesti-Poolsetes Jogedes: Ajalis-Ruumiline Varieeruvus

Academic journal article Estonian Journal of Ecology

Nitrogen and Phosphorus in Estonian Rivers Discharging into Lake Peipsi: Estimation of Loads and Seasonal and Spatial Distribution of concentrations/Lammastik Ja Fosfor Peipsisse Suubuvates Eesti-Poolsetes Jogedes: Ajalis-Ruumiline Varieeruvus

Article excerpt

INTRODUCTION

Intensification of human activities has led to widespread nutrient enrichment of surface waters causing a range of environmental, social, and economic problems encompassed under the term of eutrophication (Carpenter et al., 1998; Smith et al., 1999). The most common effects of eutrophication are enhanced vegetation growth and the imbalance of the aquatic ecosystems (Smith et al., 1999). However, the degradation of water resources by eutrophication has also more far-reaching effects such as fishing and boating recreation use losses, reduced biodiversity and conservation and amenity values, human health threat through the production of toxic cyanobacterial blooms (Carpenter et al., 1998; Smith et al., 1999; Moss et al., 2005; Dodds et al., 2009). Rivers are particularly vulnerable due to their proximity to population centres and sensitivity to land use changes (Withers & Jarvie, 2008). Nutrient concentrations in rivers are of great importance to the ecology of the river itself, but riverine transport of nutrients is also relevant to any further receiving medium (Salvia-Castellvi et al., 2005).

Eutrophication is the most serious environmental problem in many shallow lakes in lowland areas (Moss et al., 2005), including Lake Peipsi. The limno- logical time-series data since the 1950s indicate deterioration of lake water quality and adverse changes in the whole ecosystem of Lake Peipsi. Eutrophication has led to an undesirable growth of algae, massive blooms of cyanobacteria accompanied by oxygen depletion during the night and fish kills, low water transparency, and siltation of the lake bottom (Kangur & Mols, 2008). Riverine transport is the most important pathway for input of nutrients from both point and nonpoint sources to Lake Peipsi (Loigu & Leisk, 1996; Blinova, 2001). Reduction of nutrient input into lakes should focus especially on decreasing the inputs by rivers, and requires knowledge of the sources and their contribution to the transport by the rivers (Behrendt & Opitz, 2000). Regional differences in weather and the hydrological regime in catchments together with local variations in nutrient emissions from various point and diffuse sources have a great impact on the accuracy of estimating the riverine loads (Kronvang et al., 2007).

The relative importance of the different nutrient sources varies greatly between different catchments depending on anthropogenic pressures and discharge (Raike et al., 2003; Stalnacke et al., 2004; Kronvang et al., 2005; Oenema et al., 2005; Withers & Jarvie, 2008). Therefore, qualitative and quantitative determinations of nutrients (i.e. concentrations and loads) are required to characterize and predict system responses. Although considerable research has been devoted to estimations of external nutrient loads to Lake Peipsi (Blinova, 2001; Stalnacke et al., 2002; Mourad et al., 2006; Loigu et al., 2008), much less attention has been paid to systematic evaluation of the seasonal and spatial distribution of nutrient dynamics in the catchment area of the lake. However, detailed knowledge of seasonal dynamics of nutrients in rivers is useful for the management and control of nutrient loadings to Lake Peipsi. In the present study we focused on nitrogen and phosphorus because enhanced availability of these nutrients is a worldwide cause for eutrophication of rivers, lakes, estuaries, and coastal oceans (Carpenter et al., 1998).

We aimed in our study at determining both the riverine nutrient loading to Lake Peipsi sensu stricto (s.s.) and the seasonal and spatial distribution of nitrogen and phosphorus in the rivers. The specific objectives of the study were (1) to estimate Estonian riverine loads of nutrients to Lake Peipsi s.s. and to compare nutrient export coefficients among basins; (2) to examine the seasonal dynamics of nutrients in the rivers discharging into the lake and the effect of seasonality, water temperature, and discharge on the dynamics of nutrients. …

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