Cooperative Institute for Research in Environmental Sciences

FY 2009 Accomplishments and Impacts

Examples of work in progress during 2008-2009 include assessment of the water quality of Rocky Mountain National Park (RMNP) and study of the effect of pine beetles on the chemistry of mountain streams and rivers. In addition, the Center continued its work on studies of the nitrogen cycle, with emphasis on factors controlling denitrification rates.
National Parks are managed for public accessibility, but attempt to maintain an environment that is relatively free of anthropogenic influence. The parks anticipate and successfully deal with management of foot traffic and vehicle traffic associated with public access. Some new and unanticipated problems have surfaced on the management agenda for RMNP, however. Oxides of nitrogen released into the atmosphere as a result of fossil fuel combustion along the Front Range become nitric acid through photochemical reactions that occur in the atmosphere. Nitric acid is then delivered to RMNP by atmospheric transport and removed from the atmosphere by rain. The nitric acid has two distinct and undesirable effects: acidification of weakly buffered water within the park, and enrichment of park waters with nitrate, a key plant nutrient. Park managers are frustrated by this unmanageable influence and are anxious to find out the extent to which it is changing the waters of the park.

The Center for Limnology, in collaboration with RMNP, conducted an initial water-quality mapping exercise across 185 sites during the summer of 2008. The collections, which were done in a single day, involved sampling by 70 individuals. The resulting maps are quite informative (Figure 1). Nitrate concentrations within the park are 50-100 percent higher than nitrate concentrations on the West Slope, indicating the effect of nitrate enrichment from the atmosphere and the passage of nitrate from terrestrial surfaces into water. In addition, gradients of pH and nitrate within the park probably reflect an uneven distribution of pollutant-derived nitric acid across the park. Further studies will be conducted during the summer of 2009.

Another frustrating management issue for the park has to do with fish. The park’s native fish is cutthroat trout, which occupied some, but not all of the park’s lakes and streams prior to human intervention. Where the streams have insurmountable barriers to fish, such as waterfalls, lakes above these barriers were barren of fish under natural circumstances. In the early history of the park, however, fish were introduced in many lakes where they did not formerly occur, and also in lakes where the cutthroat trout often ultimately were displaced by the non-native introduced trout. Present questions involve the desirability and feasibility of restoring the native cutthroat trout to many or all park lakes, and of maintaining or reestablishing the fishless status of some lakes. The Center for Limnology is collaborating with RMNP in the study of the latter question.

Fishless lakes have very different invertebrate communities than lakes with fish. Fish apply tremendous predation pressure on invertebrates, including crustaceans and aquatic insect larvae. As a result, the contrast between lakes with fish and lakes without fish is quite striking (Figure 2). For example, one may observe in lakes without fish large herds of mayfly larvae roaming over the sediment surface, but no such free-ranging invertebrates are observed in lakes with fish. The effects of fish may be even more pervasive than they might appear, as selective elimination of larger invertebrates may affect algal populations as well.

During 2009, the Center for Limnology will collaborate with RMNP in quantitative comparisons of lakes with and without fish. The study will encompass the community structure for aquatic foodwebs as well as some biogeochemical work that may prove to be related to the presence or absence of fish. The results will help park managers decide how intensively to manage fish populations in the park, and whether to attempt to reverse changes made in the past.

The Limnology Center also continued its work on the nitrogen cycle during 2008-2009. The focus is and has been the effect of organic matter abundance and quality on the rate of denitrification in the South Platte River, where nitrate is abundant. The denitrification process involves the conversion of nitrate to N2 gas by bacteria. This is a welcome process because it removes excess nitrate. Regulation of the process is not completely understood, but one potentially controlling factor is organic matter, which is needed by the microbes as food to support growth, even though they obtain much of their energy from the denitrification process.

In 2008-2009, the Center for Limnology used a new fluorescence method (Figure 3) for detecting specific kinds of organic matter. Studies of the South Platte River showed that a particular class of organic compounds, which could be described as labile (easily used by bacteria) is particularly abundant in the upper end of the study reach. The abundance of the labile carbon source stimulates denitrification, which explains why denitrification is higher in the upper part of the reach than the lower part of the reach. The fluorescence method shows the decay of the labile fraction of organic matter with distance downstream.

Impacts

Our research to understand the nitrogen cycle in mountain streams, the effects of disturbances, and water quality helps resource managers make better decisions and plan effective actions to steward these natural resources.