Tempe Town Lake Water Quality
Constructed in 1997, the Tempe Town Lake is a small man-made reservoir that transforms a section of the typically-dry Salt River bed into a 224-acre lake in the heart of Tempe, Arizona. To accommodate the river when it flows, the lake features hydraulically-operated steel gates that allow water to pass through the system unimpeded. The lake has been a remarkable success as a community amenity and as a driver of economic growth in the area around the lake. The lake provides an ideal model system for the many artificial lakes constructed in arid-land cities owing to management decisions, such as draining, that affect their operation and ecology. At the same time, dramatic shifts in hydrology and chemistry when the lake is transformed to a flowing river and back into a lake during and after floods, provide opportunities to study the system’s dynamic evolution to new limnological steady states. The CAP LTER has been measuring water quality (temperature, pH, conductivity, and dissolved oxygen), dissolved organic carbon (DOC), DOC quality (via 3D-fluorescence), and total nitrogen in the lake since 2005. In addition, the CAP LTER regularly harvests relevant meteorological and hydrologic flow data to augment water-quality data. Analyses suggest variable impacts of extreme events, climate variability, and management decisions. Complex seasonal and inter-annual patterns in dissolved organic carbon (DOC) quantity and quality suggest that carbon cycling in the lake responds both to meteorological/climatological events and to anthropogenic activity. Time-series analysis is revealing that water flow into the lake and rainfall have a positive effect on DOC concentration and composition. Finally, seasonal patterns in dissolved oxygen concentration from 2005–2015 revealed supersaturation more than 70% of the time, suggesting that the lake is autotrophic and, thus, is a sink for atmospheric carbon dioxide.