most of the monitoong period. However, several 

 observations of blooms of other phytoplankton were 

 noted immediately after freshwater inflow events. 

 These blooms were typically comprised of single celled 

 blue-green algae (not of the filamentous cyanobacteria 

 of algal mats) normally present in fresh water or very 

 low saUnity environments. These blooms were also 

 short-lived, persisting no more than a few days. The 

 presence of these blooms did not occur in the study 

 area prior to the demonstration project except xmder 

 natural freshening events that occurred every several 

 years. The more firequent presence of these blooms in 

 the upper and central Rincon Bayou were an indication 

 that the water column ecosystem was showing a more 

 typical response to freshwater inflow. 



An additional indication of improved conditions for 

 phytoplankton growth during and after freshwater 

 inflow events was shown by an increase in the 

 N;P ratio (dissolved inorganic nitrogen to phosphate 

 ratio), which would provide a relative increase of 

 nitrogen needed for plant growth. These increases 

 following inflow events indicate that relatively smaller 

 amounts of denitrification probably occurred during 

 and following the inflow events. 



Benthic Communities 



Benthos consists of two main types of infauna, which 

 have different ecological roles in marine ecosystems 

 and respond to inflow at different spatial and temporal 

 scales. These are the larger macrofauna (organisms 

 greater than 0.5 mm in length) and smaller meio fauna 

 (between 0.063 and 0.05 mm in length). Macrofauna 

 have planktonic larval dispersal and indicate effects of 

 the demonstration project over larger spatial scales and 

 longer temporal scales. Meiofauna have direct benthic 

 development and generation times as short as one 

 month, thus indicate effects over smaller spatial scales 

 and shorter temporal scales. 



Diverted fresh water lowered salinity concentrations 

 which triggered bursts of benthic iavertebrate 

 productivity as indicated by increases in density and 

 biomass. Salinity levels between 20 and 45 ppt 

 appeared to correspond with high macrofauna biomass 



(> 2 g/m^. Macrofaunal abundance also increased 

 with increasing biomass. Meiofaunal biomass and 

 abundance increased when salinity values were between 

 10 and 40 ppt, with the greatest numbers being seen in 

 the salinity range of 1 8 to 22 ppt. Biodiversity 

 increased several months (3 to 6) following inflow 

 events, indicating more species were able to utilize the 

 marsh habitat. The macrofauna and meiofauna 

 responded to inflow with similar patterns, indicating 

 both trophic levels of benthos were responding 

 positively to inflow events. Most importantiy, the 

 lowest biomass and abundance values occurred during 

 times when there were no flow events. Additionally, 

 strong seasonal increases of biomass occurred during 

 the spring, when salinity concentrations were lowest. 

 In contrast, during summer when salinity values were 

 highest, density and biomass were always lowest. 



Vegetation Communities 



The most significant changes in the emergent 

 vegetation also coincided with changing salinity regimes 

 caused by flow through the demonstration features or 

 by direct precipitation. During sampling periods with 

 no hydrographic events, soil salinity levels were as high 

 as 80 to 90 ppt, and water column salinity was upwards 

 of 40 to 60 ppt. Following a large hydrographic event, 

 surface and soil salinity concentrations were reduced, 

 with the degree and duration of salinity suppression 

 being a function of the timing and duration of the 

 hydrographic event. Major hydrographic events 

 lowered open water salinity values by over 40 ppt at 

 some stations, and smaller, precipitation-mediated 

 events exhibited smaller decreases. 



Hydrographic events that alleviated soil salinity levels 

 during the late faU/early winter allowed the successfiil 

 germination and establishment of Salicomia higelovii 

 during the spring and summer, independent of whether 

 or not the seasons were wet or dry in regards to 

 precipitation. Because this plant species is an annual 

 succulent that reproduces primarily by seeds, successfiil 

 establishment seemed to occur only if soil salinity 

 concentrations were reduced at the appropriate time of 

 year to a level that covdd alleviate osmoticaUy induced 

 seed dormancy. 



7-6 V Synthesis and Conclusions 



