ABSTRACT:

Freshwater habitats comprise some of the most altered ecosystems on Earth, primarily due to anthropogenic disturbances in hydrology and nutrient cycling. Many freshwater systems in North America are limited by nitrogen and phosphorus, and their addition from anthropogenic sources (from agricultural and residential runoff or atmospheric deposition from air pollution) can cause eutrophication. Changes in abiotic and biotic factors due to eutrophication often result in reduced water quality and ecosystem services such as water filtration. Projected shifts in regional precipitation and temperature as a component of global climate change will further alter the functioning of freshwater ecosystems. Alterations in precipitation, coupled with shifts in land-use, are projected to increase sediment loading in freshwater systems. Sediment loading in freshwater ecosystems can result in changes to community structure, biomass, and primary productivity. In addition, sedimentation can reduce net photosynthesis rates by smothering periphyton, the photosynthetic protists that exist in the biofilm that forms on surfaces. Sediment can be cleared in freshwater systems through several routes, including consumption of sediments by animals and bioturbation (biological activity that influences sediment transport, deposition, and accrual). Larval amphibians (primarily tadpoles) may play an important role in sediment accrual and nutrient recycling rates through both sediment consumption and bioturbation. Bioturbation by larval amphibians, as any other behavior, may be affected by environmental stressors. Nitrogen, in the form of nitrate or nitrite, may influence tadpole activity rate. Although we have an understanding of the effects of nutrient and sediment loading on aquatic systems, we do not understand how organisms such as larval amphibians might mediate the effects of these two stressors on primary producers in aquatic systems. Bioturbation and grazing by amphibians could affect growth of primary producers in three ways: 1) tadpoles could increase the amount of nitrogen suspended in the water column; 2) tadpoles can clear sediment from surfaces, thereby increasing light available for periphyton photosynthesis; 3) tadpole grazing on primary producers (phytoplankton and periphyton) could reduce biomass of these primary producers. Sedimentation and nutrient loading are issues negatively affecting Utah’s water quality.
Our work focuses on two areas of the southern region where nitrogen inputs and sedimentation are important regional stressors. We will first sample natural sedimentation rates and nitrogen levels in ponds at the Canyonlands Research Center (near Moab, UT) and sites in and near Cedar City, UT, and then experimentally manipulate nitrate addition, macrophyte presence, sedimentation, and tadpole presence to test the effects of nitrogen and sedimentation on tadpole behavior and primary production. Our work will begin to identify potential community linkages in consumers and primary producers in the presence of two abiotic stressors. Understanding the connections among species and how those connections influence the response of functional groups in the community (i.e. primary producers) is increasingly important in the face of local and global environmental changes.