Nutrient Limitation of Biofilm in Turbid Rivers

The Roles of Turbidity and Cation Induced Inhibition

Martha M. Dee

Stream Research

Extensive research has been done on nutrient processes in streams, however far less has been studied about large rivers. Current studies have used nutrient diffusing substrata (NDS) in order to measure nutrient limitation in streams. Often times aquatic environments such as streams are limited by nitrogen or phosphorus. These substances support algal colonization.  Excess nitrate due to fertilizer use, as well as ammonium are also indicators to a streams nutrient level. Different nutrient availabilities select for different biofilm compositions. The absence of nutrient limitation in a river indicates a modification that is removing this natural condition.



Assess nutrient limitation of five Western rivers to understand the processing of natural and anthropogenic nutrient inputs by these large systems.


Methods and Sites

Nutrient limitation was assed in five western rivers using NDS. The rivers that were used were the Colorado, the Green at Green River, the Green at Jensen, and the Bear all located in Utah as well as the North Platte in Wyoming. The rivers that were located relatively in the south were characterized by mountainous riparian and steep banks. The Green at Jensen displayed native vegetation and shallower banks. The rivers furthest north had the greatest measure of land devoted to agriculture. The NDS were constructed for each site to obtain the results.



The majority of the rivers were not limited by the nutrient treatments. Significant results are isolated for organic substrata, as inorganic showed minimal results. Three rivers displayed limitation by Phosphorus in GPP metabolic analyses., the Colorado, the Green, and the Bear. The other two showed a reduced response during treatment in the CR metabolic analyses.



The results illustrate how rivers are dynamic systems. While they process nutrients in similar ways as small streams, they are affected differently due to the innate size of larger systems. Because many rivers did not show limitation in one or both of the metabolic processes, an excess of nutrients in system is indicated.



Nutrient Limitation, a natural phenomenon in aquatic systems, serves to regulate biological growth. However the systems are impacted in many ways including anthropogenic inputs. Human activity has greatly affected these large systems. Nutrient limitation of large river systems must therefore be considered in management decisions in order to maintain healthy and sustainable aquatic systems.



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