Recent trends in nutrient concentrations in Estonian rivers as a response to large-scale changes in land-use intensity and life-styles

Abstract

The aim of the study was assessment of changes in nutrient concentrations in Estonian rivers as a response to improved wastewater treatment and substantial reductions in the use of fertilisers and number of livestock during the past 15-20 years. A Mann-Kendall test and flow adjusted technique to assess recent trends have been used. Statistical analysis covered time series of 53 sampling sites on 40 rivers and streams in different hydro-geographical regions and varying human pressures. The results indicate a statistically significant downward trend in nitrogen concentration in 18 sampling stations during the studied period; only very few showed an upward trend. These decreases in total nitrogen (TN) relate mainly to (i) substantial reductions in the use of fertilisers, (ii) decreased area of agricultural land, (iii) decreased point source load and (iv) increased self-purification capacity of soil-water systems. The concentration of phosphorus decreased only in 13 locations, despite of efforts to improve the efficiency of wastewater treatment. Moreover, in seven locations the concentration of phosphorus was increasing. This increase in total phosphorus (TP) probably relates to the low treatment efficiency of small wastewater treatment facilities as well as to the raised ground water table due to insufficient maintenance of drainage systems that favour transport of soil P to water bodies. Accordingly, the ratio of nitrogen and phosphorus had both decreasing and increasing trends.

Increased organic carbon concentrations in Estonian rivers in the period 1992–2007 as affected by deepening droughts

“…The largest part (38-60%) of the investigated catchments are covered by coniferous and mixed types of forests, the rest being mires (6-26%) and agricultural land (17-47%; Iital et al 2010). The main forest tree species in Estonia are pine (35%), birch (30%) and spruce (17%; Adermann 2008).…”

“…The reduction in the atmospheric deposition of nitrogen compounds can affect soil chemistry in a similar manner (Findlay 2005). In Estonia, the post-Soviet re-organisation of industry that took place in the 1990s led to a great decrease in the atmospheric deposition of SO 4 2-and nitrogen compounds (Treier et al 2004), while nitrate fluxes from agriculture dramatically decreased as well (Mander et al 1998;Iital et al 2010).…”

Weather conditions influencing phosphorus concentration in the growing period in the large shallow Lake Peipsi (Estonia/Russia)

“…These changes included lower water consumption by people and industries, improved wastewater treatment and lower intensity of agriculture (Iital et al, 2005(Iital et al, , 2010. As a result, nitrogen loading and to a lesser extent P loading from the Estonian part of the catchment to Lake Peipsi decreased in the 1990s (-39 and -13%, respectively;Nõges et al, 2007).…”

“…As a result, nitrogen loading and to a lesser extent P loading from the Estonian part of the catchment to Lake Peipsi decreased in the 1990s (-39 and -13%, respectively;Nõges et al, 2007). Despite the decline in agricultural activity in the late 1980s and early 1990s, agriculture still causes much of the diffuse pollution of inland surface waters [62% of total nitrogen (TN) and 43% of TP loading; Loigu et al, 2008; Iital et al, 2010]. Maximum nutrient inflow to Lake Peipsi occurs usually during the snowmelt in early spring (Rumyantsev et al, 2005).…”

Modelling of the Effect of Drained Peat Soils to Water Quality Using MACRO and SOILN Models

“…However, recent data analyzes of Estonian rivers show that nitrogen concentrations have increased in some rivers [1] despite the decrease of fertilizer usage [2]. An increase in nitrogen (N) concentrations has even been detected in watersheds with very low human activity [1]. Hoffmann et al [3] assumed that increases of pollution by nutrients may also be caused by wide-scale melioration.…”