Evaluating patterns of fog water deposition and isotopic composition on the California Channel Islands

Fog deposition is an important water source for endemic conifer species during the annual summer drought along the California coast (and in other coastal and montane areas). We present a new design for a passive fog collector that is useful both for characterizing fog regimes (timing and quantity of deposition) and for collecting fog water for subsequent isotopic analysis. The new collector both mimics vegetation collection efficiency and minimizes isotopic fractionation under a range of fog conditions. Low construction cost and collector durability allow widely distributed installation and greater insight into spatially heterogeneous fog patterns. We installed 21 fog collectors throughout a stand of Bishop pines (Pinus muricata D. Don) on Santa Cruz Island. In general, there was greater fog deposition with increasing elevation and decreasing frequency farther inland. Within these broad patterns, there was large spatial and temporal variability in fog deposition. Monthly samples of fog and rain waters reveal differences in stable isotope composition (δ18O and δD) large enough to serve as tracers of different water sources moving through the ecosystem.