Impact of climatic ¯uctuations and land use change on runoff and nutrient losses in rural landscapes U È lo Mander a,* , Ain Kull a , Va Èino Tamm b , Valdo Kuusemets a , Riho Karjus a a Institute of Geography, University of Tartu, 46 Vanemuise St., EE-2400 Tartu, Estonia b Institute of Rural Engineering, Estonian Agricultural University, 5 Fr.R. Kreutzwaldi St., EE-2400 Tartu, Estonia Abstract Results on the in¯uence of land use and climatic changes on nutrient losses in the Porijo Ägi river catchment, south Estonia, are presented. The main tendency in land use changes is a signi®cant increase in abandoned lands (from 1.7% in 1987 to 12.5% in 1994), and a decrease in arable lands (from 41.8 to 22.5%). Signi®cant climatic ¯uctuations were observed from 1951±1994. Warmer winters (increase from 7.9 to 5.88C from 1950±1994) and a change in the precipitation pattern have in¯uenced the mean annual water discharge. This results in more intensive material ¯ow during colder seasons and decreased water runoff in summer. Changes in water discharge and land use are also re¯ected in the mean annual runoff of total inorganic nitrogen (TIN) and total-P which decreased from 15.6 to 2.7 kg N ha 1 yr 1 (83%) and 0.32 to 0.21 kg P ha 1 yr 1 (34%), respectively during this period. However, nutrient losses from the forest subcatchment (upper course) did not change signi®cantly. In contrast, the mean annual runoff of water, organic matter (after biological oxygen demand: BOD 5 ), TIN, total-P and SO 4 from cultivated subcatchments showed a signi®cant decrease. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Climatic ¯uctuations; Land use change; Catchment; Potential and actual evapotranspiration; Nutrient losses 1. Introduction Nutrient cycling in rural catchments has been well documented (Hill, 1978; Miller, 1979; Houston and Brooker, 1981; Meyer et al., 1981; White et al., 1981; Pilgrim et al., 1982; Cameron and Wild, 1984; Yarbro et al., 1984; Grobler and Silberbauer, 1985; Webb and Walling, 1985: Schreiber and Neumaier, 1987; Auers- wald et al., 1988; Fleischer and Hamrin, 1988; Kelly, 1988; Lowrance and Leonard, 1988; Whigham et al., 1988; Kronvang et al., 1993). However, few investiga- tions have analyzed long-term trends of nutrient cycling (see Jordan et al., 1986; Andersen, 1994). Land use changes and climatic ¯uctuations play an essential role in material cycling and energy ¯ow in the long-term. Most earlier studies dealt with the in¯uences of land use on nutrient budgets, whereas climatic change analysis is a relatively new approach (Panagoulia, 1991; Arnell, 1992). Since changing land use has a major in¯uence on global climatic processes (Unsworth and Wolfe, 1995), and nutrient runoff is directly related to climate, these factors should be analyzed in combination. Previous analyses of the impacts of different human activities on nutrient losses from rural catchments include: general land use intensi®cation (White et al., 1981), fertilization (Miller, 1979), afforestation (Bormann and Likens, 1979), and stream channeliza- tion (Yarbro et al., 1984; Krug, 1993). However, less Landscape and Urban Planning 41 (1998) 229±238 *Corresponding author. Tel.: +37 27 375819; fax: +37 27 375825; e-mail: mander@math.ut.ee 0169-2046/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0169-2046(98)00061-9