Since ancient times, human settlements have also found root near sources of water.
Even today the most populated places in the world are along the banks of rivers and other water sources.
This simply translates into plenty of farming along the banks.
This leads to the release of nutrients like phosphorous and nitrogen into the sources, as these farms use fertilizers for good harvests.
It was always assumed that the release of these nutrients into river streams would mean that there would be an increase in development of microorganisms and smaller animals which are the base of the food chain.
An increased number of preys would mean more predators resulting in more fish in the streams.
This however did not happen so. Researches and observations have shown that though the numbers of smaller animals or animals that are prey are still increasing, the number of predators has leveled out at one point.
Simply put though prey has increased, predators have not benefited the modification of the water chemistry to the same extent.
There are various reasons behind this phenomenon, including the simple fact that not all prey is suitable for all predators.
Scientists have come to the conclusion that increased nutrients, thanks to civilization, do not really have to mean more benefits to nature or to the food chain.
Source : Science Daily