San Marcos River Observing System

The San Marcos River Observing System represents efforts by the River Systems Institute and Department of Biology at Texas State University to develop and maintain a high spatial and temporal resolution characterization and monitoring program within the Upper San Marcos River watershed (Texas), a spring-fed river system with substantial conservation concerns.  A distributed rainfall-runoff model has been calibrated that incorporates historical (1987), present (2006), and future conditions (2025 and 2050) in terms of land use, land cover, and full build-out scenarios based on hourly climate data from 1970 to 2009.  In addition, the upper 9 kilometers of the San Marcos River has been intensively characterized in terms of the physical, chemical, and biological components of the ecosystem.  Spatial characterization is based on available LIDAR, 0.10 meter resolution multispectral imagery, 3-dimensional channel topography mapping with an average of 3,000 underwater topography points per 100 meters of stream, subsurface sediment characterization using ground penetrating radar, aquatic vegetation mapping at 1 meter resolution, complete riparian community delineation in terms of species composition, and densitometer readings under leaf and leaf-off conditions.  Aquatic vegetation mapping integrates results from 1989 to the 2010.  Continuous water quality monitoring and periodic sampling is maintained at eight locations, and storm event driven sediment and nutrient loading monitoring is maintained at six locations. Tributary sites document pulses of nutrients and sediment during storm events, while sites at spring openings in the headwaters document subtle changes related to large storm events and seasonal to multi-year changes in hydrologic conditions. Community level aquatic biota monitoring is conducted on a seasonal basis and builds on over 8 years of seasonal monitoring at five locations.  Topographic data have been integrated with hydraulic calibration data at multiple flow rates to calibrate 2-dimensional hydrodynamic models of the entire river system at 0.25 meter resolution.   A 10 meter longitudinal water temperature model at an hourly time step has been calibrated and, in conjunction with the hydrodynamic models, has been used to develop predictive habitat models for two key sentinel endangered species; fountain darter (Etheostoma fonticola), and Texas wild rice (Zizania texana).  The intent of the observing system is to collect and maintain a high temporal and spatial data set covering biological and physiochemical attributes that will permit testing and evaluation of sampling strategies, data analysis, and modeling techniques in riverine systems, and to document long-term changes within system.