Table 5. Hydroperiod summary, May 1985 through May 1987. 



Sites 8 



Year BIU BID TBU TBD 



1 Days 170 52 66 118 

 Events 15 5 10 18 

 Days/Event 11 10 7 7 



2 Days 231 33 66 181 

 Events 17 7 10 18 

 Days/Event 14 5 7 10 



1&2 Days 401 85 132 299 



Events 32 12 20 36 



Days/Event 13 7 7 8 



"See Table 1 for site abbreviations. 



Chabreck and Narcisse 1981) should also be questioned based upon the findings that Scirpus olneyi 

 at TBU is consistently better than in the wetter BIU marsh. Herke (1979) and Herke et al. (1987) 

 have documented decreased export and lower standing crops of important fisheries species in semi- 

 impounded marshes. Ongoing studies of aquatic vegetation in both Toms and Big Island Bayou 

 lake systems and in our new rock-weir study raise serious questions on the usefulness of semi- 

 impoundment in the long term for creation of desirable aquatic vegetation such as Ruppia maritima. 

 We have found that semi-impoundment reduces turbidity levels, allowing better aquatic vegetation 

 growth and preventing lake desiccation (Larrick and Chabreck 1976), and that lakes in semi- 

 impounded marshes have organic muck bottoms which Ruppia does not prefer. In addition, the 

 best stands of Ruppia, Eleocharis parvula, and Echinochloa crusgalli are found in lakes with normal 

 water-level cycles (low water in winter, dry in spring, wet in summer and fall). This data set is not 

 complete or statistically analyzed as yet, but the field observations are very supportive. In addition, 

 we are looking at the sedimentation rates in these marshes, and I predict that the sedimentation 

 rates (both organic and mineral) will be less in the BI than in the TB system, which further 

 encourages marsh loss. 



Upstream marshes exhibited lower total standing crops than downstream marshes in both 

 watersheds. This may be due to lower nutrient and sediment inputs upstream. In watersheds such 

 as these studied, the further upstream the marsh is, the more dependent upon rainfall it becomes. 

 If this is indeed the case, then this may broaden the "streamside effect" concept of Mendelssohn 

 et al. (1982). Mendlessohn et al. found that Spartina alterniflora was most productive and had 

 higher maximum standing crops along the edges of bayous and became less so marshward. He 

 concluded from his experimental work, including fertilizer studies, that the major reason was the 



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