Nitrate deposition in terrestrial and aquatic ecosystems is increasing worldwide as a result of human activities. Between 1984 and 1996, deposition of inorganic nitrogen in Colorado’s Niwot Ridge Long Term Ecological research site doubled. Previous research suggests that small streams are the most effective sites for nitrate processing and retention; however, the role of alpine lakes has not been adequately examined. During 2006, Miller et al (unpublished) collected samples at the inlet, outlet, surface and subsurface (surface, 3m and 9m) of Green Lake 4 for nutrients, major ions, DOC, ¹⁸O and chlorophyll a and then used the ¹⁸O data to quantify lake mixing processes. Their results showed that nitrate behaved conservatively in the lake during early in the summer season when the flushing rates were high, whereas in summer during the peak of chlorophyll a, nitrate was removed in the lake ecosystem. Summertime decreases of 50% or greater were measured between the inlet and the outlet. However, there were no obvious trends with algal species distribution and the rates of nitrate uptake in the lake. To further investigate the relationship between algal populations and nitrate retention, more detailed results on the spatial and temporal variation in nitrate are being obtained during the summer of 2009 in an effort to determine if the dominance of a specific species can be correlated with increases in nitrate retention. If so, nitrate retention will be modeled as a function of dominant phytoplankton species as well as chlorophyll a. These results will aid in interpreting the paleorecord from the lake sediments and will have implications for future developments in water quality in alpine lakes in the Colorado Front Range.