Small-Scale Analyses 



Incli\'idual species percent cover and LAI readings 

 taken at each sampling point were analyzed on a small- 

 scale basis by the means of a GIS. Each sampling 

 point was given geographic coordinates (Universal 

 Transverse Mercator; Zone 14) based on differential 

 Global Positioning System (GPS) points taken in the 

 field at the four comers of the transects. Percent cover 

 and LAI data acquired in the field were assigned to the 

 corresponding geographic location at each sampUng 

 point then incorporated from tabular format in 

 Microsoft Excel to ArcView GIS software. The 

 Inverse Distance Weighting function in Arc View's 

 Spatial Analyst extension was used to interpolate grids 

 for the area within the transect using the data points 

 taken in the field as reference numbers. The method 

 assumes that each point has a local influence that 

 diminishes with distance so that points closer to the 

 cell containing the field measurement have greater 

 values than those farther away. A grid cell size of 

 0.25 m (the same size as the quadrat) was used, 

 providing a means of small-scale analyses. 



Maps of percent cover and LAI for each transect were 

 analyzed to determine changes in species cover and 

 bare area before and after hydrographic events at each 

 station. For percent cover, vegetation maps for each 

 sampling date were created by querying the data to find 

 areas in the transect where cover for each individual 

 species were greater than 50%. This allowed all species 

 to be mapped together on the transect. Maps from the 

 sampling date prior to an event were then compared to 

 maps for the three sampling dates following the event. 

 The conversion of the point data into interpolated 

 surfaces allowed for mathematical manipulations and 

 analyses in a spatially coherent, three-dimensional 

 manner, which naturally represented the data. 



BlOMASS 



Four replicate samples of monospecific stands oi Batis 

 maritima, Borrichia Jrutescens, Monanthocloe litioralis and 

 Distkhlis spkata growing near the transect were sampled 

 bi-annuaUy (winter and spring) using a PVC corer 

 (10 cm diameter, 30 cm length). The corer was placed 



around the vegetation and above-ground plant material 

 clipped. The corer was then dri\'en into the ground for 

 collection of below-ground material. Plant material 

 was sequentially sieved using a 1 cm sieve foUowed by 

 a 1 miHtmeter (mm) sieve, sorted into above- and 

 below-ground portions and dried at 60° C to a 

 constant weight. Samples were weighed to the nearest 

 0.1 gram (g), and biomass was converted to an area 

 basis. Root to shoot (RjS ratios) ratios were calculated 

 from biomass measurements. 



RESULTS 



Vegetation and physio-chemical parameters [i.e., 

 salinity and nitrogen levels) were examined based on 

 changes observed within and between the stations 

 before and after periods with significant freshwater 

 inflow or precipitation (Table 6-1). In general, 

 vegetation from three different sampling periods 

 exhibited measurable responses to these hydrographic 

 influences: July 1997, October 1998 and September 

 1999. The major hydrographic events (Chapter .3) 

 preceding each of these sampling dates include Event 

 16 (June 21 through July 3, 1997), Event 17 Quly 4 

 through 26, 1997), Event 25 (October 16 through 29, 

 1998), Event 35 (August 19 through September 3, 

 1999) and Event 36 (September 4 through 20, 1999) 

 (Table 6-1). Where any sampling period was preceded 

 by more than one identified hydrographic event {e.g., 

 July 1997 and September 1999), it was assumed that 

 any measurable change observed in the vegetation 

 could be due to a combination of those events. 

 Therefore, for the purposes of this vegetation analysis, 

 the events preceding each sampling period during 

 which a response was observed were collectively 

 referred to as the composite hydrographic events of 

 July 1997, October 1998 and September 1999. During 

 each of these periods, the Rincon Overflow Channel 

 was activated and Station II was subjected to the 

 influence of project diversions. 



Because salt marsh vegetation also often responds to 

 direct precipitation, total monthly precipitation was 

 reported separately to allow precipitation-mediated 



6-6 



Vegetation Communities 



