Biological and Physical Assessment of Streams in Northern California: Evaluating the Effects of Global Change and Human Disturbance

Human disturbance at global and local scales is profoundly impacting stream ecosystems in California. For example, climate change, which is considered a form of human disturbance in this dissertation, is causing notable increases in air temperature and decreases in precipitation in some regions of the state. These changes are outside the range of natural variability and are expected to intensify. Furthermore, these changes affect stream-water temperatures, stream-flow levels, and aquatic biota. Human disturbance at the local scale in California includes, but is not limited to, urbanization, the development and use of land for timber extraction and agriculture, and manipulation of habitats for recreation or for the preservation of endangered species. I examined the impacts of global change and human disturbance on stream ecosystems in Northern California at a variety of sites and using a variety of biological and physical techniques. The sites were located in five California counties, including Lake, Marin, Napa, Siskiyou, and Sonoma. Monitoring and analytical techniques for benthic macroinvertebrates used both standard and novel approaches and metrics of biological assessment. Physical techniques included surveys of channel widths and longitudinal profiles, bankfull-channel estimates, flow measurements, pebble counts, fine-sediment measurements, and large-wood inventories, which were analyzed using a variety of geomorphological and hydrological approaches. I found that: 1) the common metrics used in biological assessment will have continued applicability for biological assessment programs in Northern California and that a new metric for detecting climate-change effects could be developed; 2) stream-crossing reconstruction was causing increased patchiness of benthic-macroinvertebrate communities in the short term; 3) vineyard water-withdrawals were having an effect on stream communities that occurred after a threshold level of vineyard coverage and extent was reached; and 4) the addition of engineered, large-wood structures to streams for physical-habitat restoration increased pool frequency and caused changes in the benthic community, although the resulting levels of large wood in the channels were still lower than levels typically found in other regions of the northwestern United States