nutrients than did control plants. In 

 plots given the high level of sewage 

 fertilization, the amount of roots was 

 less than in the lower fertilization 

 level plots or in the control plots. 



In plots fertilized with urea, the 

 root mass was about the same as that of 

 control roots. In the high marsh, there 

 were also fewer live roots in the high 

 enrichment level than in the control. 

 However, the amount of rhizomes and the 

 amount of dead matter differed very lit- 

 tle between the fertilized and unfertil- 

 ized plots. Sewage fertilization appar- 

 ently does not stimulate belowground 

 growth, and may, in fact, decrease root 

 growth in salt marshes. Valiela et al. 

 (1976) found a seasonal root production 

 pattern with an increase of root growth 

 in the spring, followed by a decline in 

 live root biomass. 



Sewage enrichment can effect pro- 

 cesses in the marsh other than plant 

 growth. Addition of sewage fertilizer 

 to a Massachusetts salt marsh decreased 

 rates of nitrogen fixation in the marsh 

 after the amount of ammonia in the sedi- 

 ment interstitial water increased (Van 

 Raalte et al. 1974). An increase in 

 denitrification was observed in the en- 

 riched plots that was significantly 

 higher than that of the unfertilized 

 plots (Valiela et al, in press). The 

 authors did not quantify this to deter- 

 mine exactly how much of the added ni- 

 trogen was lost through reduction to 

 gas. Consequently, they surmised that 

 the marsh could effectively remove the 

 nitrogen in sewage. Sewage nitrogen de- 

 pressed the natural rate of nitrogen 

 fixation, and the marshes used nitrogen 

 in the sewage rather than nitrogen that 

 would have been available through nitro- 

 gen fixation. At the same time, in- 

 creased rates of denitrification in the 

 marsh could remove more of the nitrogen 

 in the sewage. 



The rate of benthic algal produc- 

 tion, which might be expected to be stim- 

 ulated, actually decreased in Massachu- 

 setts (Estrada et al. 1974; Van Raalte 

 et al. 1976). This decrease is a good 

 example of an indirect effect of sewage 

 enrichment. The rate of benthic algal 

 production decreased in the fertilized 

 plots because the increased standing 

 plant biomass shaded the algae to the 



extent that the algae were light-limit- 

 ed. In our marsh, Bob Christian and 

 Keith Bancroft studied the effect of 

 sludge fertilization on microbial popu- 

 lations and activity. They measured 

 adenosine tri -phosphate (ATP) in the 

 sediment and found no differences in ATP 

 (as a measure of microbial biomass) in 

 the experimental plots compared to the 

 control plots. Bancroft also analyzed 

 the "energy charge" of the macrobial 

 population as a measure of microbial 

 activity, i.e., whether they are simply 

 resting spores with a low energy charge 

 or cells growing exponentially with a 

 high energy charge. No difference in 

 the energy charges was found between the 

 sludge fertilized plots and the control. 

 Apparently, the microbial populations in 

 a mature marsh soil are very resistant 

 to change in their immediate enrichment. 

 Valiela et al. (in press) presented 

 a summary of the natural budgets of 

 three different heavy metals (lead, 

 zinc, and cadmium) in a marsh and com- 

 pared the same budgets with a forcing 

 function of the added metals in a sludge 

 fertilizer applied to a marsh. About 

 90% of the added lead was retained in 

 the marsh sediments, a small amount was 

 lost, and some was accumulated in the 

 marsh plants. More of the zinc (16.7%) 

 was lost from the marsh, and Valiela 

 et al. (in press) theorized that the 

 zinc was exported from the marsh on 

 sediment particles or as dissolved inor- 

 ganic compounds. The remainder of the 

 added zinc was accumulated in marsh sed- 

 iments and plants. About half of the 

 cadmium was lost by unknown mechanisms, 

 and half was accumulated in sediments 

 and marsh plants. 



Is salt marsh disposal a good way 

 to get rid of sewage? I agree with 

 Pomeroy et al. (1969) that we should 

 probably regard sewage as a resource 

 rather than as a waste product. If we 

 need to get rid of sewage, in some re- 

 spects the salt marsh is a good tertiary 

 treatment facility. Marsh plants and 

 benthic algae have high rates of produc- 

 tion and can assimilate some nutrients. 

 The clay soils in Georgia estuaries can 

 accumulate a lot of phosphate. The 

 marsh is a fairly stable community and 

 appears to be quite resilient, at least 

 to enrichment stresses. The accreting 



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