- 1 - PILOT MONITORING OF TILE DRAINAGE AND SMALL STREAM WATER QUALITY IN THE SKUTE REGION Milan melík 1 , František Doležal 2 , and Zbynk Kulhavý 3 Research Institute for Soil and Water Conservation, Prague, Czech Republic 1 Research Base Skute, 2 Prague-Zbraslav, 3 Research Station Pardubice 1. Abstract Water in the streams of several small watersheds (few km 2 ) in the Skute region (East Bohemia), prevailingly under the agricultural land use, was investigated as to its quality. The sampling started in 1985 and continued, with some breaks, up to this day. The analyses made comprised pH and the concentrations of nitrate, nitrite, phosphate and ammonia, and later, starting from 2001, also the electrical conductivity and the concentrations of sulfate and chloride. The quality of tile drainage water has also been monitored since 2001. The results are presented as chronological graphs, seasonal variation graphs and the probability-of- exceedance graphs. Two partial periods (1989-1993 and 2001-2003) were selected to demonstrate long-term trends. In general, the concentrations of pollutants (especially nitrate and ammonia ions) decreased between 1989-1993 and 2001-2003 due to the reduction of intensity of agriculture, but the concentrations of nitrite increased. The tile drainage water is significantly more polluted with nitrate and more acid than the stream water but in other aspects the former is cleaner than the latter. The Kotelský potok, a watershed without human settlements and with a high density of tile drainage systems, differs from the other sites and its stream water quality resembles that of the tile drainage water. Some watersheds reveal anomalously high sulfate and chloride concentrations and electrical conductivities or abnormally high phosphate concentrations. Water pollution shows a distinct seasonal periodicity, with the maximum nitrate concentrations occurring in late winter and early spring and the maximum phosphate concentrations appearing in late summer and early autumn. The conductivity is not a suitable indicator of nitrate pollution. More frequent sampling (such as once per week) would be necessary for the detection of short-term variations and seasonal trends. The paper provides background data for identification of underlying mechanisms of runoff and water quality formation, for improvement of future monitoring and for the appropriate remediation measures. 2. Introduction The quality of water in streams and tile drainage strongly varies in both space and time and its monitoring is expensive and difficult to generalize. No systematic monitoring of tile drainage water quality has up to now been carried out in the Czech Republic, even though as much as about one quarter of total agricultural lands in the country had been tile drained (the term „tile drainage“ used in this paper also includes plastic pipes drainage systems). No less difficult is the selection of water quality indicators for this purpose. Moreover, it is becoming obvious that a plain monitoring is not enough; one has to investigate the mechanisms of water quality formation, which are intimately associated with the mechanisms of runoff formation. Several research teams in the Research Institute for Soil and Water Conservation (RISWC) in Prague, Czech Republic, are currently working on the problem. This paper provides basic description