Responses of sawgrass and spikerush to variation in hydrologic drivers and salinity in Southern Everglades marshes

Abstract

Aboveground net primary production (ANPP) by the dominant macrophyte and plant community composition are related to the changing hydrologic environment and to salinity in the southern Everglades, FL, USA. We present a new non-destructive ANPP technique that is applicable to any continuously growing herbaceous system. Data from 16 sites, collected from 1998 to 2004, were used to investigate how hydrology and salinity controlled sawgrass (Cladium jamaicense Crantz.) ANPP. Sawgrass live biomass showed little seasonal variation and annual means ranged from 89 to 639 gdw m )2 . Mortality rates were 20-35% of live biomass per 2 month sampling interval, for biomass turnover rates of 1.3-2.5 per year. Production by C. jamaicense was manifest primarily as biomass turnover, not as biomass accumulation. Rates typically ranged from 300 to 750 gdw m )2 year )1 , but exceeded 1000 gdw m )2 year )1 at one site and were as high as 750 gdw m )2 year )1 at estuarine ecotone sites. Production was negatively related to mean annual water depth, hydroperiod, and to a variable combining the two (depth-days). As water depths and hydroperiods increased in our southern Everglades study area, sawgrass ANPP declined. Because a primary restoration goal is to increase water depths and hydroperiods for some regions of the Everglades, we investigated how the plant community responded to this decline in sawgrass ANPP. Spikerush (Eleocharis sp.) was the next most prominent component of this community at our sites, and 39% of the variability in sawgrass ANPP was explained by a negative relationship with mean annual water depth, hydroperiod, and Eleocharis sp. density the following year. Sawgrass ANPP at estuarine ecotone sites responded negatively to salinity, and rates of production were slow to recover after high salinity years. Our results suggest that ecologists, managers, and the public should not necessarily interpret a decline in sawgrass that may result from hydrologic restoration as a negative phenomenon.

Seasonal differences in the CO2 exchange of a short-hydroperiod Florida Everglades marsh

“…Wet seasons in most temperate wetlands coincide with the growing season, thus periods of maximum CO 2 uptake (Roulet et al, 2007;Bonneville et al, 2008;. In the Everglades, aboveground NPP in the dominant macrophyte, Cladium, is relatively aseasonal (Table 3, Childers et al, 2006) and only minor changes in LAI were found between seasons ( Fig. 7), so it is unlikely that seasonal variation in CO 2 exchange is related to vegetative growth cycles.…”

“…Aboveground NPP has been found to reach >10,000 g C m -2 yr -1 in some Everglades marl (calcium carbonate soil) marshes, though rates of 1000-2000 g C m -2 yr -1 are more common (Ewe et al, 2006). Hydroperiod is of central importance in determining productivity in the Everglades and is the product of both active water management and climate (Busch et al, 1998;Childers et al, 2006).…”

“…These changes have had many ecological consequences, including alterations in nutrient concentration and distribution, plant community composition, aboveground net primary production, and periphyton dynamics (Newman et al, 1996;Ross et al, 2000;Armentano et al, 2006;Childers et al, 2006;Iwaniec et al, 2006). In an effort to reverse these alterations, significant Everglades restoration activities began in the 1970s (Lodge, 2005), and now fall under the Comprehensive Everglades Restoration Plan (CERP).…”

Quantitative Comparison of Plant Community Hydrology Using Large-Extent, Long-Term Data

“…Although mean water depth is often used to describe plant species or community hydrology (Wood and Tanner 1990;Ross et al 2003;Childers et al 2006), the mean water depth variable in our study performed relatively poorly in predicting vegetation class, even when calculated as the mean of wet events only. Thus, although mean water depth provides a description of one aspect of community hydrology, it is not the most suitable hydrologic indicator for plant community distribution.…”

“…Although hydroperiods have been defined in various ways (Ross et al 2003;Childers et al 2006;Givnish et al 2008;Zweig and Kitchens 2008;Todd et al 2010;LoGalbo et al 2013), they are usually calculated as annual means. In our study, use of environmentally-defined hydroperiods (the hydrologic interval) enlarged the hydrological description by allowing the length of the wet or dry event to extend over several years when appropriate.…”