Describe possible relationship between urban population density and urban runoff

As described below.

Explanation:

There exists a relationship with the amount of agricultural runoff and the population density of the region and the large agricultural lands have a population of just rural people most of the runoff comes from the crops in the form of pesticides and insecticides.  these are dangerous chemicals and harmful substances that indirectly impact the soil fertility and water quality of the nearby streams and river systems. The urban runoff has several criticisms as it is untreated and wastewater that enters the river and destroys their BOD levels by nitrification and contamination. The urban population has more air pollution than the surface runoff and the urban areas don't have large bodies of water like lakes or seas but the rivers are highly polluted by the effluent emitted by the untreated industrial waters. Both this runoff affects human health which can be seen in urban flooding and problems of drainage systems in cities.

Answer decreased soil salinity;