University of California Water Resources Center

We investigated the roles of three tall emergent macrophytes (Scirpus acutus, S. californicus and Typha domingensisi in carbon cycling at a local wetland constructed for wastewater treatment and at an adjacent stream fed freshwater marsh. Combined above ground standing biomass ranged from 1125 g/m2 in freshwater to 3192 g/m2 in wastewater. Scirpus acutus (SA) densities ranged from 86 plants/m- in freshwater to 206 plants/m2 in wastewater. A combination of T. doming ens is and T. latifolia (TS) densities ranged from zero plants/m2 in wastewater and freshwater to 19 plants/m2 in wastewater. Growth rates of SA were highest for plants between 50 to 100 em and the average maximum rate was 6 cm/day. For TS the highest rates were recorded for plants between 0 and 50 ern and the average maximum rate was 4.5 ern/day. Growth for both SA and TS slows at heights between 2.5 and 3 m. Both SA and TS are subjected to grazing, TS more so than SA and there is no difference if they are in freshwater or wastewater. Carbon to nitrogen ratios vary throughout the year with the fall ratios indicating much higher carbon in the above ground biomass. Decomposition rates of above ground material in the water column vary within the wastewater treatment system with material closer to the inflow of wastewater having slower rates than those furthest from the inflow. Decomposition of below ground biomass, buried at -15 cm, is much faster for TS than for SA.

A mesocosm study investigating biomass and nutrient allocations indicates that the ratio of above ground biomass to below ground biomass changes with nutrient availability. In low nutrient situations the ratio for SA and T domingensis (TD) ranged from 0.3 to 0.4 (over 70% of the biomass below ground). In high nutrient situations SA had a ratio of 1.2 and TD had a ratio of 0.7.

A water level competition experiment indicates that SA establishes quicker than TD or S. californicus (SC). However, after one year SA gives way to SC in deeper water (50- 80 em) and maintains dominance in shallower water (10-40 em). TD was the slowest starter and had the lowest percent cover of all three species after one year (24%).