Thursday, August 7, 2008 - 3:40 PM

OOS 21-7: Lessons from LINX I and II: A network of stream experiments

Patrick J. Mulholland, Oak Ridge National Laboratory


The Lotic Inter-site Nitrogen eXperiment (LINX) consisted of two consecutive, large inter-site studies involving 15N-tracer additions to streams to determine rates and mechanisms of nitrogen cycling at the scale of entire stream reaches. These studies, referred to as LINX I and II, involved about 20 senior PI’s at different institutions. The studies were highly successful, resulting in publications in Science and Nature as well as many other peer-reviewed journal papers. Results showed that streams are important sites for uptake and retention of nitrogen in the landscape and that both autotrophic and heterotrophic processes are important in nitrogen cycling. The work also demonstrated the value of field 15N-tracer additions for studying nitrogen cycling in streams, and protocols have been shared with a number of other research groups.


This network of experimental research sites was the product of a long history of informal collaboration among stream ecologists interested in nutrient dynamics beginning at meetings in the 1980’s. A workshop held in 1995 at Coweeta Hydrologic Laboratory, organized by Donna Morrall and Judy Meyer, resulted in the LINX I proposal to NSF which included 12 sites. The NSF IRCEB competition provided the opportunity to expand the network to 72 streams for LINX II which focused on nitrate uptake and retention. In LINX II we also added a landscape component to the network by developing a model of nitrogen transport and retention in 8 large river basins across the U.S. Two different approaches were used to ensure that experiments were conducted uniformly throughout the network – a traveling post doc overseeing experiments in LINX I and a detailed set of protocols and training workshops in LINX II. The success of the LINX project is the result of several factors: a challenging and important problem, development of a technique for addressing the problem (15N-tracer additions), highly motivated senior-level researchers, central roles for students and post docs in planning and executing experiments and analyzing data (with active mentoring), and availability of funding from NSF for large projects. However, the most important factor in our success has been the willingness of participants to “leave their scientific egos at the door” in the interest of collaborating to achieve a common objective. Discussions were spirited at times, but everyone understood that success ultimately depended on agreement and consensus.