Relations between soil management and the quality of surface- and groundwater supplies

Abstract

1. Urban and industrial waste waters, farm effluents, soil and fertilizer born nitrate and phosphate may impair the water quality in streams, groundwater bodies and lakes by oxygen deprivation and high salt contents, nitrate accumulation and eutrophication. In this paper the hygienic aspect as well as the problem of urban waste disposal were left aside, only the influence of farming upon the water quality has been discussed. 2. Farm effluents include liquid manure, manure piles runoff and silo effluents which are too concentrated and carry too high a BOD load to allow processing in treatment plants. Parts of these liquids may contaminate water courses, and enter sewage systems. Improved technology and economical help will be required to foster the safe utilization of these liquids on the land. 3. High nitrate contents in drinking water are known to have caused sometimes fatal methemoglobinemia in infants. In the Federal Republic 3.7% of the public water works supply water that contains more than 50 mg/l NO3. 4. Sources of nitrate are: urban and industrial waste waters, cesspools, farm effluents and the toplayer of cropland. Annual leaching losses of a few to 40 and more kg/ha N(NO3−) from the soil have been reported. The soil solution frequently contains nitrate concentrations in excess of the drinking water standard. 5. However, whether this will cause objectionable concentrations in drinking water supplies depends upon the share of cropland in an area and upon the local hydrological conditions. Management measures are available to partially cut nitrate leaching. 6. Phosphorus is the critical factor for eutrophication. In the watershed area of the Stockacher Aach which empties into the Lake Constance, the amount of phosphorus that originates from soils and fertilizers depends on petrographical and pedological conditions rather than upon management. Soil born phosphorus plays only a minor role in enhancing the eutrophication of the Lake. This may be different in other areas where rocks and soils do not contain limestone or where erosion is higher. 7. Nitrogen presently is not considered to be a limiting factor for the eutrophication of the Lake Constance, although the element is required for production. From a predominantly rural area most of the nitrogen input into the Lake is soil born. In 1963 it amounted to 112 t N(NO3−) from 242 km2. However there are also tributaries which carry high amounts of nitrogen that originates from urban wastes. 8. There exists no general answer as to the influence upon the quality of water supplies of farm effluents; soil born nitrate and phosphate. This rather has to be assessed according to the local conditions (share of cropland, types of soils and rocks, management, handling of farm wastes etc.) within a watershed area.