45 percent and 20 percent respective- 

 ly of their net flux. It is apparent 

 then that, (1) the winter export of 

 all nitrogen parameters is over- 

 shadowed by the larger imports ob- 

 served during the spring, and (2) 

 nitrate and nitrite nitrogen are ex- 

 ported in nearly the same percentages 

 as ammonia and organic nitrogen. As 

 was the case with carbon and phos- 

 phorus transport rates, fluxes were 

 greatest during the periods of high 

 flood and ebb tides (i.e., during 

 April and May) . 



year. The reason for this is that 

 the Nueces River must reach a flow 

 rate in excess of 3000 cfs in order 

 to top its bank and flood the marsh. 

 Apparently with such infrequent 

 flooding, it would then appear that 

 most of the annual nutrient transport 

 occurring in the marsh system would 

 depend mostly on tidal inundation. 

 Obviously, during wet years when 

 flooding occurs more frequently and 

 is of longer duration, the importance 

 of nutrient flux on tidal flows will 

 tend to be lower relative to total 

 nutrient flux. 



DISCUSSION 



Our data indicate that the Nue- 

 ces Deltaic marsh served as a 

 nutrient sink during our eight-month 

 study period. The fact that we found 

 the Nueces marsh serving as a nu- 

 trient sink agrees with a seasonal 

 study performed by Espey, Huston, and 

 Associates (1977). Other investiga- 

 tors (Ho et al. 1970; Pomeroy et al. 

 1972; and Valiela et al. 1973) have 

 also suggested that tidal marshes 

 may act as nutrient sinks. However, 

 most investigations have determined 

 that brackish marshes tend to export 

 C, N, and P on an almost continuous 

 basis (Armstrong and Gordon 1977; 

 Dawson and Armstrong 1975; Armstrong 

 and Hinson 1977; and Heinle and Fle- 

 mer 1976). Thus, the Nueces marsh 

 offers an interesting contrast to the 

 normally encountered brackish marsh 

 system, at least with respect to nu- 

 trient transport. 



The Nueces marsh is unlike most 

 river-impacted tidal and brackish 

 marshes in that it is totally inun- 

 dated only on rare occasions. His- 

 torical data compiled by the Texas 

 Water Development Board (1958-1979) 

 indicate that Nueces River spills oc- 

 cur on an average of only 22 days a 



From the data in Table 1, quan- 

 tified nutrient flux in the Nueces 

 marsh appears slight relative to 

 other studies (de la Cruz 1965, Teal 

 1962) , even though there is a defi- 

 nite import phenomenon occurring. 

 Carbon transport data in our study 

 is positive — that is, we found car- 

 bon to be imported. Teal (1962), on 

 the other hand, suggest that as much 

 as 45 percent of the net production 

 of a Spartina sp . marsh is available 

 for export (as detritus). De la Cruz 

 (1965) described similar occurrences 

 when he measured suspended and float- 

 ing particulate organic matter in a 

 Georgia marsh and found that 19 to 29 

 percent of the annual net production 

 may be exported to the estuary. 



The fact that the importation of 

 particulate organic carbon (which 

 amounted to 66 percent of the TOC) 

 was so high, is not so unusual be- 

 cause most of the import occurred 

 during the spring when low detrital 

 production and increasing planktonic 

 populations are observed. Thus, the 

 higher TOC and POC concentration on 

 flood tides would be expected. Chan- 

 ley (1957) has also suggested that 

 low export of TOC and POC, especially 

 in the higher elevation marshes, 

 could possibly be due to the utili- 

 zation of detritus in the production 

 of peat or peat-related material. 



484 



