MiCROPHYTOBENTHIC SEDIMENT BlOMASS 



AND Production 



The shallow water environment of the Nueces Delta 

 allows a large fraction of water column phytoplankton 

 to settle to the sediment. These benthic cells mav 

 become attached to the sediment surface or remain 

 unattached to potendally re-suspended with wind 

 induced mixing. 



The absence of data during the period with the most 

 freshwater inflow (e.^s.. summer 1997 through fall 1999) 

 precluded a full assessment of the demonstradon 

 project's effects on microphytobenthic communides, 

 but some results were observed from the data available. 



Sediment Chlorophyll 



The biomass of microphytobenthic cells is often 

 estimated by chloroph\'Ll concentradons, but there is 

 no method to determine if the cells are attached and 

 growing in place or merely deposited temporarily until 

 re-suspension. Therefore, estimates of 

 microphytobenthos producdon include both types of 

 plankton. 



The sediment chlorophyll declined at all stations during 

 the course of the demonstration period (Figure 4-17), 

 but no causal mechanisms were apparent. Because two 

 stations at the Reference site (63 and 64) also exhibited 

 the decline, it is likely that the trend was not related to 

 the effects of the demonstration project. 



The ratio of chlorophyll to phaeopigments in the 

 sediment varied within a tjipical range during the 

 demonstration period (Figure 4-18). The several high 

 ratios of chlorophyll compared to phaeopigments at 

 Stations 65 and 66 (upper Rincon Bayou site) during 

 1996 indicate that chlorophyll production occurred 

 more rapidly than did pigment decomposition during 

 that period. 



The inventory of chlorophyll in the water column and 

 sediment was not closely related to saEnit}', but the 

 combined chlorophyll biomass was largest at salinit}- 

 concentrations below 60 psu (Figure 4-19). This 

 obsen-ation can partially be attributed to reciprocal 

 concentrations of high sediment and low w-ater column 

 chlorophyll (Figure 4-20). Much of the time, sediment 

 chlorophyll was high when water column chlorophyO 

 was low, but at other times, low sediment chlorophyll 

 occurred when the water column chlorophyll 

 concentration was large. 



iqg<i 



lOQA 



inn? 



Figure 4-17: Sediment chlorophyll concentrations at all water column stations (except Stations 62 and 68) for 

 each sampling date. 



4-18 



Water Column Productivity 



