ABSTRACT
Organic substances in water can be divided according to fraction of dissolved organic carbon (DOC) and particulate organic carbon (POC). DOC and POC may be used to monitor seasonal inputs of plant and soil organic matter to streams and rivers. There is data on the leaching and migration of dissolved organic matter in waters situated in agricultural areas. Organic matter dissolved in water constitutes 60 to 90% of organic substances in natural waters. Lakes contain considerable amounts of autochthonous organic matter which may range from 30% for lakes with inputs from rivers flowing through and high flushing rates, to nearly 100% for eutrophic lakes fed by ground water. Removal of organic substances from surface waters as suspended sediment also occurs. Investigations on seasonal variations of organic substances concentration are very important for aquatic ecosystems, particularly when arable fields are close to surface waters that are recharged by ground waters.
