Two plots of each flow treatment were constructed (Fig. 1). The plots, thus represent replication at the 

 treatment level. Two control plots, 1 m x 1 m area, were delineated by PVC comer poles. Two weir plots 

 (increased flow) were constructed of 1 m x 0.5 m, 3/4" (1.9 cm) plywood attached to 1.5 m PVC poles (Figs. 1 

 and 2). Net plots (decreased flow) were 2 m long and 1 m wide and made of 2.5 cm mesh attached to 1 .5 m 

 PVC poles (Fig. 2a). All PVC poles extended 1 m into the sediment. The open faces of the weirs and the long 

 sides of the net faced southeast, the direction of predominant tidal and wind driven flow (Montagna et al. 

 1998). All experimental sampling areas were 1 m x 1 m squares within the central region of each structure 

 (Fig. 2a). 



Structures were biult within a 0.25 km^ region (Fig. 2b). Furthest downstream were a weir plot and a net plot. 

 Fxirthest upstream were a control plot and a net plot. In between were a weir plot and a control plot. Plots 

 were staggered to Umit possible structure interactions and were all roughly the same water depth. Structure 

 interactions are unlikely because Rincon Bayou is generally a low-inflow, microtidal environment. 



Frequency of disturbance was varied. Four distiubance frequency treatment levels (i.e., undisturbed, biweekly, 

 monthly, and bimonthly) were nested within each flow treatment plot (Fig. 1). Disturbance was imitated by 

 emplacement of defaunated sediment in trays. Undisturbed sediment was the control for the disturbance 

 frequency treatment. Bi-weekly disturbance was the most frequent disturbance investigated and trays remained 

 in the field for 2 weeks. Monthly disturbance was the moderate frequency level and trays remained in the field 

 for 4 weeks. Bimonthly disturbance was the least frequent disturbance investigated and trays remained in the 

 field for 8 weeks. Short-term frequencies of disturbance were used to determine effects on development of 

 early succession communities. 



Disturbance ttays were constructed from 6.5-cm diameter acrylic tubes, 3 cm high, and fused to 7 cm x 7 cm 

 square bottoms. Trays were filled with sediment collected from station C and defaunated using a microwave. 

 Approximately 500 ml of sediment were microwaved for 1 5 minutes to bring sediment temperatures to roughly 

 100 °C. Microscopic investigation of subsampled sediment yielded no live animals following defaunation. 

 Trays were filled with well-mixed defaunated sediment in the field, and placed at predetermined random 

 positions within the experimental area of each flow plot. Flagged rods were used for treatment identification 

 and to avoid tray loss. Only one tray was turned over and lost during the study. 



The disturbance frequency experiment was replicated two different ways: by initial placement date (23 April and 

 04 June), and by ending sampling date (20 June and 01 August) (Fig. 3). This required eight sampling dates over 

 a 14- week period (Fig. 3). On each sampling date, three replicate tray samples and three undisturbed samples 

 (the top 3 cm of a 6.5-cm diameter core) were taken in each disturbance frequency level (Fig. 1). 



Measurements 



Hydrographic data (e.g., salinity, temperature, dissolved oxygen) were collected from each flow treatment plot 

 on each field date using a Hydrolab 4000 Sonde. Three turbidity samples were collected from each flow 

 treatment plot and analyzed using a HACH model 2100A turbidimeter. Rainfall, tidal stage, and flow volumes 

 were collected from a gage placed at the mouth of Rincon Bayou where it connects to the Nueces River 

 (unpubUshed data collected by the United States Geological Survey at Station 08211503, Rincon Bayou Channel 

 near Calallen, Texas). 



Flow velocity was measured twice for each flow treatment plot and level to determine the effect of the 

 structures. How velocity was measured only twice because flooding prevented equipment deployment and 

 retrieval on most dates. Flow was measured on 07 May and 17 July 1997 using a UNIDATA Starflow 

 Ultrasonic Doppler flow meter. Velocity, depth, and temperature were recorded every two minutes for 6 to 

 24 minutes per flow plot per date while sediment samples were being taken from the adjacent flow plot. 



Macro fauna were extracted from sediment using a 0.5-mm sieve, identified to the lowest taxonomic level 

 practicable, and counted. Lecithotrophic larvae were assumed to be Streblospio benedicti . which are more 

 common at Rincon Bayou than the alternative Polydora comuta (Montagna and Ritter unpublished data). 

 Biomass was determined for each taxonomic group by drying samples for 24 hours in a 55 °C oven and 

 weighing to the nearest 0.01 mg. Abundance and biomass were converted to a per meter basis and (natural 

 logarithm) transformed for statistical analysis as follows: In (n m"^-l-l) and In (g m'^+1) respectively. Hill's 

 diversity (Nl), and Peliou's evenness (El) were calculated to summarize community structure characteristics. 



Appendix F ♦ F-3 



