This occurs when nutrients introduced from a river 

 stimulate primary production (Deegan et al. 1986; 

 Nixon et al. 1986). The primary' production can be 

 deposited, but it may also be advected and deposited 

 further downstream, potentially increasing benthic 

 productivity away from the river inflow source. This 

 assumes that fresh water and low salinity do not have a 

 negative effect. Salinity stress on physiology (Finney 

 1979) and hypoxia (Ritter and Montagna 1999) could 

 reduce benthic populations. The net effect of 

 freshwater inflow on biological processes {i.e., 

 enhanced productivity, recruitment gains and losses ■via 

 low-saHnity intolerance) is therefore a function of the 

 interaction between physical processes {i.e., 

 sedimentation, re-suspension, advection and seawater 

 dilution) and chemical processes {i.e., nutrient 

 enrichment and cycling). 



If freshwater inflow enhances benthic producti^'ity, 

 then increased abundance and biomass should be 

 found if inflow were re-introduced into Rincon Bayou 

 and the upper Nueces marsh. Benthic infauna are 

 useful indicator species in studies of long-term effects, 

 because they are relatively immobile and long-Uved 

 compared to plankton of similar size. The larger 

 macrofauna (organisms greater than 0.5 millimeters 

 (mm) in length) and smaller meiofauna (between 0.5 

 and 0.063 mm in length) have different ecological roles 

 in marine ecosystems (CouU and Bell 1979; Coull and 

 Palmer 1984). Therefore, macrofauna and meiofauna 

 could respond to freshwater inflow at different spatial 

 and temporal scales. Macrofauna, with planktonic 

 larval dispersal, indicate effects over larger spatial scales 

 and longer temporal scales. Meiofauna, with direct 

 benthic development and generation times as short as 

 one month, indicate effects over smaller spatial scales 

 and shorter temporal scales. Even where meiofauna 

 share ecological properties with macrofauna, the 

 meiofaunal processes operate on much smaller spatial 

 and temporal scales (Bell 1980). 



OBJECTIVES 



1) To assess the effect of the demonstration project 

 on benthic infauna biomass, abundance and 

 diversit}'; 



2) To assess the response of different trophic levels 

 by examining meiofauna and macrofauna; and 



3) To assess the utilization of marsh habitats by 

 infaunal species. 



METHODS AND APPROACH 

 Study Design 



Increased opportunity for freshwater inflow into the 

 study area was accomplished by lowering the Nueces 

 River bank leading to Rincon Bayou (Nueces Overflow 

 Channel) just east of where U.S. Highway 37 crosses 

 the Nueces River (Chapter 1). A Before vs. After/ 

 Control vs. Impact (BACI) experimental design (Green 

 1 979) was used to determine effects of the 

 demonstration project on benthos. Samples were 

 taken both before and after the Nueces Overflow 

 Charmel was opened. During each sampling period, 

 "control" and experimental impact sites were sampled 

 (Figure 5-1). An experimental control did not really 

 exist, because the system could not be sampled "with" 

 and "without" an overflow charmel at the same time. 

 In addition, there is large natural variability in 

 hydrographic and organismal responses in this 

 ecosystem. Therefore, a reference site was chosen that 

 reflected changes caused by natural variability but not 

 the overflow channel. The site, which was largely 

 unaffected by the demonstration project, was 

 considered a reference site to the sites affected by the 

 project. The BACI design allowed establishment of 

 two kinds of reference points to distinguish variability 

 caused by the project from natural variability. 



A second component of the experimental design was 

 to replicate at the treatment level to avoid "pseudo- 

 replication." Pseudo- replication occurs when 

 treatments are confounded with replicates (Hurlbert 

 1984). For example, if each site were represented by 



5-2 



Benthic Communities 



