Capability of regulated small streams for nutrient retention in the dry season

Abstract

xl - distance from the pollution source, km; x2 - stream discharge, m3 s-1; x3 - water temperature, 0C; x4 - load from the pollution source, g d-1. With the increasing distance from the pollution source, stream load with total P decreased. Nevertheless, it remained higher than the initial level measured above the settlement in every investigated stream range. The length of investigated ranges (up to 8.6 km) was insufficient to acquire reliable relationship between the changes of stream load with total N and the distance. Receding from the pollution source, nitrogen form in the water changes from ammonia to nitrate due to nitrification processes. Streaming water is capable of self-purification from the influx of pollutants depending on various physical, chemical and biological factors. The objective of this work was the evaluation of nutrient retention factors and their dependencies in small regulated streams artificially changed b. straightening their channels. The main task was to determine the existence of significant relations between nutrient retention in the water of regulated streams and physico-chemical parameters under investigation what allow forecasting the water quality. In the dry season of 2010 - 2011 (from June to October) 5 ranges of regulated streams with a maximum distance of 8.6 km to the pollution source below the settlements of less than 2000 inhabitants were measured for evaluation of nutrient retention dependence on various factors. Streams under investigation are located in the river Nevezis basin in the Middle Lithuania which is characterized by low absolute heights (to 80 - 90 m) and urbanized landscapes intensively used for agriculture and stockbreeding. They are attributed to the same geographical zone with similarities in soil, geological conditions and hydrological regime. The discharge of investigated streams in the analyzed time period fluctuated from 0.0003 to 0.27 m3s-l with respect to their size. Different factors in the process of self - purification downstream the pollution source were measured and evaluated. After the statistical analysis was carried out, the most influential factors affecting the decrease of nutrients appeared to be water discharge, temperature and load from the pollution source. With the impact of factors evaluated, the following dependencies of stream water load with certain pollutants could be observed: total P y=153.2-59.3 xl+4811.4 x2+0.89 x4 total N y=22713.4+385498 x2-1376.6 x3+0.41 x4 here: y - stream water load with pollutants, g d-1;