Water depth on the marsh flood during 

 these peak-tide events varied accord- 

 ing to land elevation and time of day 

 but usually averaged between 6 and 

 10.5 cm. 



The obvious results of this 

 study were (1) that nutrient concen- 

 trations present in flood and ebb 

 tides were similar (Table 1) and fol- 

 lowed one another very closely on a 

 temporal basis (Figure 4 and 5) and 

 (2) that based on the eight-month 

 study period there was a net import 

 of nutrients into the Nueces deltaic 

 marsh (Table 2). Although a net im- 

 port of C, N, and P was documented, 

 periods where nutrients (C, N, and P) 

 were exported from the system were 

 also observed. 



Total organic carbon (TOC) and 

 particulate organic carbon (POC) con- 

 centrations reflected the low marsh 

 flooding event that occurred during 

 May (Table 1). During this event, 

 TOC and POC concentrations reached 

 their maximum levels of 12.6 and 6.8 

 g/m , respectively, on the ebb tide. 

 Flood tide values were 10.5 and 5.5 

 g/m respectively. 



Transport rates of TOC and POC 

 were highest during April and May be- 

 cause it was during these months that 

 flood and ebb tide flows were at 

 their highest recorded levels (Table 

 2) . During these high spring tides 

 mean transport rates of 70 kg/hr of 

 TOC and 32 kg/hr of POC into the 

 marsh were observed. Net transport 

 derived from these dates represented 

 43 percent and 55 percent respective- 

 ly of the TOC and POC import that oc- 

 curred in the eight-month study pe- 

 riod. Most of the TOC and POC ex- 

 ported from the marsh occurred dur- 

 ing February when the difference in 

 tidal inflows and outflows were 

 greatest. Transport rates observed 

 during this period were 34 and 20 



kg/hr for TOC and POC respectively. 

 This amounted to 53 percent and 31 

 percent respectively of the net TOC 

 and POC export. Transport of POC, 

 whether during export or import, was 

 generally 40 to 50 percent of the TOC 

 transport. 



Inorganic carbon concentration 

 tended to vary between tides and 

 months during the study period (Table 

 1). Transport rates varied as a 

 function of tidal flows with 40 per- 

 cent of the transport occurring in 

 April. During this month, a mean of 

 435 kg/hr of IC was being imported to 

 the marsh. The period of largest ex- 

 port was during February when an 

 average of 136 kg/hr was transported 

 to the bay representing 51 percent of 

 the export of IC. 



Like carbon, total and ortho- 

 phosphorus were imported into the 

 marsh during the course of the 

 study. It is interesting to note 

 that both forms were imported in 

 similar amounts. Net transport rates 

 of 11.97 and 9.43 kg/hr for total and 

 ortho-phosphorus respectively were 

 observed. Examination of the data 

 also revealed that most of the trans- 

 port occurred during mid and late 

 spring when tides (flood and ebb) 

 were at their maximum. 



Throughout the study period am- 

 monia and organic nitrogen were the 

 most actively transported nitrogen 

 forms. Organic nitrogen and ammonia 

 were imported into the marsh at rates 

 of 19.7 and 1.5 kg/hr respectively 

 (Table 2). Although ammonia and or- 

 ganic nitrogen were exported during 

 most of the fall and winter months, 

 this export only represented 26 per- 

 cent and 21 percent respectively of 

 the net flux for these two para- 

 meters. In comparison, export rates 

 of nitrate and nitrite nitrogen, 

 during the same period, represented 



478 



