With the increase in human population, water resources have become more and more precious. A comprehensive study of water yield characteristics is imperative, especially in water-limited semiarid regions. The objective of this study is to examine spring flow and vegetation cover in a first-order watershed and investigate the herbaceous community structure of upland riparian zones. This study consists of two major components: (1) the effects of environmental factors and vegetation cover on spring flow at Pedernales River upland catchments, and (2) the ecological responses of vegetation to altered flow regimes that result from brush management at the upland riparian zones. The study finds that an average of 3.67% of the monthly water budget of first-order catchments in central Texas is made up of spring flow. The influence of woody plant cover on streamflow was evaluated by comparing spring sites with different percentages of woody cover three times during 2003 and 2004. Our findings indicate that changes in woody plant cover had no influence on the amounts of streamflow from these catchments, and the surface catchment area had only a minor influence. This suggests that the real spring catchment area might be different from the surface watershed boundaries that have been delineated by topography. Plant species richness and diversity gradually decreased with increasing lateral distances from the stream bank. Herbaceous richness and diversity declined with increasing Ashe juniper cover in the riparian zone. Ashe juniper canopy cover had a larger effect on the understory composition than the cover of other woody species. Herbaceous diversity and production was greater in areas with sparse tree density than in areas with no trees, but was lowest at high tree densities. The complete removal of Ashe juniper in the riparian zones is not recommended because of the potential loss of grass cover. The recommended management would be to leave a sparse cover of canopy trees to maintain understory plants.

The thermal springs along the Middle Fork of the Boise River (MFBR) within the Atlanta lobe of the Idaho batholith discharge in discrete locations that appear to be part of self-organizing flow systems. Infiltrating water flows through Basin and Range fractures to depth where it is heated and ultimately discharged at the intersection of trans-Challis oriented faults along the MFBR. Isotopic compositions of the thermal waters have a linear trend with elevation suggesting that the recharge locations are near each thermal spring and the hydrothermal system is not one large interconnected system, but rather multiple individual hydrothermal systems. Water chemically evolves along the hydrothermal flow paths dissolving feldspars and precipitating secondary minerals. PHREEQC inverse modeling of the chemical evolution based on identified minerals within the system predicts positive volume changes in the pore space within the hydrothermal flow systems can occur. Precipitation of secondary minerals is likely to occur in the cooler, subsidiary, less-efficient fractures of the hydrothermal system. Flow areas calculated using heat flow, exponential decay, and a combination of the two, show that the topographic watershed is inadequate to accommodate the water supporting the thermal springs indicating that water is being captured from outside the watershed. The positive volume changes coupled with the water capture is evidence of positive feedback loops are active within the hydrothermal system providing a mechanism for self-organization to occur in the hydrothermal systems of granite.