No abstract

Landscape patterns, consisting of alternating densely vegetated bands and sparsely vegetated interbands, occur in semi-arid and arid regions of Africa, Asia, Australia and North America. The structure of vegetation patterns has been well documented, but a wide array of underlying environmental factors and ecological processes have been suggested, with no consensus regarding the genesis and persistence of these patterns. The purpose of this study was to assess ecohydrological interactions within this banded pattern by quantifying reallocation of rainfall and soil sediments. Even subtle redistribution impacted plant biomass production and species composition. Although runoff losses from interbands accounted for only 4% total rainfall, reallocation supported tree species and bunchgrasses that would not be sustained if precipitation were evenly distributed. Additionally, a rainfall threshold was identified. When storm totals exceeded 16 mm, even the densely vegetated bands were unable to capture all the rainfall and run-on from the upslope sodgrass interbands; a portion of the runoff from interbands flowed through the vegetated bands and continued downslope into the next interband.

Ecohydrological connectivity is a system level property that results from the linkages in the networks of water transport through ecosystems, by which feedbacks and other emergent system behaviours may be generated. We created a system dynamics model that represents primary ecohydrological networks to examine how connectivity between ecosystem components impacts ecosystem processes. Here, we focused on the savanna ecosystems, although the analyses may be expanded to other ecosystem types in the future. To create the model, a set of differential equations representing ecohydrological processes was programmed into the dynamic solver Vensim. Stocks of water storage (e.g. atmospheric and soil moisture) were linked by flows [e.g. precipitation and evapotranspiration (ET)] that were in turn dynamically controlled by the amount of water stored. Precipitation was forced stochastically, and soil moisture and potential ET controlled actual ET. The model produced extended, probabilistic time series of stocks and flows, including precipitation, soil moisture, runoff, transpiration, and groundwater recharge. It was used to describe the behaviour of several previously studied savanna ecosystems in North America and Africa. The model successfully reproduced seasonal patterns of soil moisture dynamics and ET at the California site. It also demonstrated more complex, system level behaviours, such as multiyear persistence of drought and synergistic or antagonistic responses to disconnection of system components. Future improvements to the model will focus on capturing other important aspects of long-term system behaviour, such as changes in physiology or phenology, and spatial heterogeneity, such as the patchwork nature of savannas. Figure 6. Comparison of (a) volumetric water content and (b) ET results from initial testing to data from the Arizona riparian shrubland. In this test case, the model was driven by the actual precipitation data, rather than a random time series, to demonstrate its validity. The model was calibrated using the ] Measured ET [mm d -1 ]

Satellite thermal imagery is combined with automated chemical analysis of surface waters off central California to detect and better understand a 'nutrient upwelling' entering the California Current system. While thermal surface water features have been mapped successfully from satellites for a number of years, the relationship of satellite thermal imagery to nutrients, such as nitrates and phosphates, has not been established. As a result of such efforts, satellite remote sensors may help to explain the relationship between chemical mesoscale and pelagic ecosystems of the ocean.