A modeling approach for assessing the effect of multiple alpine lakes in sequence on nutrient transport

The effects of a single lake on downstream water chemistry may be compounded by the presence of additional lakes within the watershed, augmenting or negating the effects of the first lake. Multiple, linked lakes are a common feature of many watersheds and these resemble reactors in series often studied in engineering. The effects of multiple lakes in series on nutrient transport are largely unexplored. We populated and calibrated a simple lake model to investigate the role of a sub-alpine lake (Bull Trout Lake (BTL), Rocky Mountains, USA) on the transport of the macronutrients during the summer of 2008. Further, we developed a sequential model in which four identical lakes (copies of the BTL model) were connected in series. All lakes in the sequence retarded the flux of nutrients, thus slowing their transport downstream. The first lake in the sequence dramatically altered stream water chemistry and served as a sink for C and P and a source of N, while additional lakes downstream became sources of C, N and P. Although additional downstream lakes resulted in important changes to water chemistry and nutrient transport, the nature of the changes were similar from Lakes 2 to 4 and the magnitude of the changes diminished with distance downstream. Our lake model served as an effective tool for assessing the nutrient budget of the lake and the hypothetical effect of multiple lakes in sequence in a landscape limnology framework.