Evaluation of the relationship between Dissolved Organic Material (DOM), chlorophyll-a and algal species in lakes and drinking water reservoirs throughout the state of Colorado

Background/Question/Methods: Previous research suggests nonhumic DOM production can be related to chlorophyll-a concentrations.  Recent increases in DOC concentrations in surface waters have been documented in northern temperate regions.  This affect on aquatic ecosystems is not yet fully understood.  In the Green Lakes Valley of the Colorado Rocky Mountains, yearly monitoring has shown a pulse of terrestrially derived aromatic humic DOM in lakes during snowmelt, characterized by a low fluorescence index (FI) and high specific ultraviolet absorbance (SUVA). In late summer, during annual phytoplankton blooms, microbial sources contribute DOM with a high FI and low SUVA.  The aim of our study was to identify if similar activity can be found in other lakes across Colorado.  Chlorophyll-a, an indicator of algal biomass, was measured and algal species were identified using a Fluid Imaging Technologies FlowCam.  10 lakes were sampled biweekly from May through September 2010 and an additional 30 lakes were sampled during July and August.  Preliminary results show diatoms and cyanobacteria are the most abundant algal groups present. 

Results/Conclusions: DOC and chlorophyll-a levels in the 10 lakes showed a seasonal common trend.  DOC levels ranged from 2 to 8 mg/L and chlorophyll-a levels ranged from 0 to 10ug/L.  DOC levels in the 30 lakes ranged from 2 to 7mg/L and chlorophyll a levels ranged from 2 to 84ug/L.   The relationship between DOC and chlorophyll-a levels in the lakes varied, with some showing a correlation.