Agricultural Lakes in Finland: Current Water Quality and Trends

Abstract

Agriculture is the largest source of nutrients into surface waters in Finland, and yet relatively little is known about the actual impact of the agricultural load on the state of lakes. We analysed the water quality data of 20 Finnish agricultural lakes and found that they had higher levels of nutrients, chlorophyll a and turbidity than did the other types of lakes (e.g. those receiving point-source load) in the national monitoring network (the Finnish Eurowaternet). Currently, six of the agricultural lakes can be classified as eutrophic and 14 as hypertrophic. Trend analysis (based on Kendall's tau-b) indicated that during 1976-2002 the water quality of the lakes either remained constant or showed signs of increasing eutrophication and elevated turbidity. Decreasing nutrient concentrations were found only in one intensively restored lake. In none of the lakes had the chlorophyll a concentration decreased. The results of the trend analysis are compatible with the recent finding that, despite vigorous efforts, the nutrient load from agriculture has not declined in Finland. Recovery of the most eutrophied agricultural lakes would call for a drastic reduction in the external nutrient load, possibly supplemented with in-lake restoration.

Quantifying Relationships Among Phosphorus, Agriculture, and Lake Depth at an Inter-Regional Scale

“…As several studies provided more information on the type of agriculture, we know that at least a few regions were dominated by pastureland (namely Galbraith and Burns 2007; Chen and others 2008; Prairie and Parkes unpublished), whereas others were predominantly cropland (namely Arbuckle and Downing 2001;Vander Zanden and others 2005;Ekholm and Mitikka 2006). Given this variability in agricultural land-use practices and in the data ranges represented across studies, we, not surprisingly, found a broad spectrum of correlation coefficients (r = 0.15-0.86) when the TP-% Agr relationship was assessed with linear correlation for each study individually (Table 1).…”

“…The mixed-effects estimates are often referred to as shrinkage estimates as they 'shrink' the individual OLS estimates toward the common population estimate, providing robustness to individual outlying behavior (Pinheiro and Bates 2004). The shrinkage toward the common term is particularly noticeable in the Finnish dataset (Figure 2; Ekholm and Mitikka 2006).…”

Distribution pattern of an expanding Osprey (Pandion haliaetus) population in a changing environment

“…A possible reason is the different quality of water bodies in different landscapes. Lakes in agricultural landscapes tend to be more eutrophic, as intensive agriculture is usually the primary source of nutrients in surface waters (Mehner et al 2005;Ekholm and Mitikka 2006;Schindler et al 2006). The higher productivity in eutrophic lakes has been related to the population increase of several waterfowl species (Suter 1995;Fernandez et al 2005).…”

Influence of EU policy on agricultural nutrient losses and the state of receiving surface waters in Finland

“…The 20 lakes studied are listed in Table 2 and have been described in detail by Ekholm and Mitikka (2006). Their size ranged from 0.4 to 155 km 2 and their maximum depth from 1.7 to 68 m. The majority did not undergo thermal stratification in summer.…”

“…Recent assessments of agricultural impacts on aquatic systems showed no clear reduction in either nutrient loading or eutrophication (Mitikka and Ekholm 2003, Räike et al 2003, Ekholm and Mitikka 2006. This may partly be explained by the lag period between the measures taken and the desired outcome due to the large nutrient reserves accumulated in the soil (Stålnacke et al 2003.…”