The following note was to refer to the paper published in the Journal of Limnology and Oceanography, Vol.51 (1) in 2006.
This paper sums up the trends of nutrient enrichment of the U.S. rivers. Also, the authors combine the trophic status, defined in 1996 by Van Nieuwenhuyse and Jones, with the long-term data of Total Nitrogen (TN) & Total Phosphate (TP).
"The highly variable response of stream algae to nutrient enrichment has complicated efforts to develop a trophic-state classification system for streams such as that employed for lakes." and, "Published trend information has limited utility for assessing the ecological relevance of historical changes in stream nutrients; frequently, trends are reported as an absolute or percentage change in mean concentrations without any information about how the trends relate to trophic conditions. "
As a result, the major goal of this paper is to convert the chemical concentration with the biological response of the environment. In this way, the models could be used to illustrate the trends of pollution and the limit of biological overload.
This figure didn't show the current situation.
The authors sum it up, " No change occurred in the trophic-state classification at approximately 70% of the sites. As many as one-quarter to one-half of the monitoring sites, and more than 60% of the sites in predominantly agricultural and urban watersheds, were classified as eutrophic in 1994."
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The equations in the paper focus on predicting the value of single day with data that combined with seasonal and annual patterns.
Other questions arouse are, what possible reasons for why this equation cannot fit the trend in Lakes? ---> Because the ecosystem is different, we have to think are there other limiting factors? (Light!)