In the brackish marsh CS. patens/ D. spicata ). exclosure experiments 

 demonstrated that almost 100 percent of the net primary production 

 (NPP) passes through the detritus food chain, but in the contiguous 

 fresh marsh ( H. moscheutos ) 37 percent of the NPP is utilized by the 

 grazing food chain. Underground production for S. patens/D. spicata 

 was determined by an experimental approach involving transplantation 

 of underground material and a dry weight shoot-to-root ratio of 

 1:16 was determined over a twelve-month period. An efficiency rate 

 for conversion of visible solar radiation to plant production in 1974 

 ranged from 0.11 percent for H. moscheutos in the Typha/Hibiscus zone 

 to 1.12 percent for the T. angustifolia/ H. moscheutos mixture. (A. A.) 



Keywords: productivity, saltmarsh plants, biomass, food chains, Chesapeake 

 Bay 



II-B-28 



Johnson, M. 1970. Preliminary report on species composition, chemical 

 composition, biomass, and production of marsh vegetation in the upper 

 Patuxent Estuary, Maryland. Chesapeake Biological Laboratory, Solomons, 

 Md. Ref. No. 70-130. 



In the Patuxent Estuary, extensive marshes occur over a wide range of 

 salinities and nutrient conditions. This study was concerned with the 

 primary production of the Patuxent marshes and the relationship of this 

 production to the nutrient content of the water flooding the marsh. 

 Studies showed that there were two major communities of plants in each 

 of the two marshes chosen as examples. Maloy Marsh had one cormiunity 

 with varying dominance, the mixed vegetation community, and one 

 community with Typha lati folia as the dominant plant. One community 

 in Fenno Marsh was dominated by Phragmites communis , the other by 

 Spartina alterni flora . 



By assuming that the maximum standing crop can be used to obtain 

 a good estimate of net primary production, the following production 

 figures were calculated. The Typha lati folia community produced 

 966 g dry matter m'^Yr"^; the mixed vegetation community produced 

 1246 g dry matter m"^yr"'. The Spartina alterni flora community produced 

 1207 g dry matter m"2yr"] , and the Phragmites communis community 

 1451 g dry matter m"2yr"^ . The average production of all communities 

 is 1218 g dry matter m~^yr~\ The total production of all the 

 Patuxent marshes is estimated at 23.3 x 10^ kg dry matter yr~\ of 

 which 231 X 10^ kg is nitrogen and 39 x 10-^ kg is phosphorus. 



The quantity of nutrient-rich organic matter that could potentially 

 be released to the river by the decomposition of the marsh plants is 

 large. However, it is not known how much is decomposing in the marsh 

 and how much is exported to the river. The relative contributions 



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