Panchabi Vaithiyanathan

NUTRIENT EFFECTS ON STAND STRUCTURE, RESORPTION EFFICIENCY, AND SECONDARY COMPOUNDS IN EVERGLADES SAWGRASS

Long-term studies along a 30-yr nutrient-enrichment gradient in the northern part of the subtropical Everglades fen allowed us to assess the effects of nitrogen (N) and phosphorus (P) additions on plant community structure and chemical qualities of wetland plants. Areas in the highest P-enriched zones (>1000 mgP/kg), once dominated by open-water sloughs and surrounding monocultures of sawgrass (Cladium jamaicense, a stress-tolerant low-nutrient-status species), are now dominated by cattail (Typha domingensis, a competitive, high-nutrient-status species). Areas of moderate (750–500 mg/kg) and low (<500 mg/kg) P soil concentrations have maintained their original plant composition. Analysis of nutrient-use efficiency indicates that sawgrass is highly efficient in nutrient resorption and nutrient proficiency, but this efficiency decreases at high soil P concentrations. Both indices indicate that suboptimal concentrations of P, which limit growth and optimize retention of P within the plant, exist in the Everg...

Litter decomposition of emergent macrophytes in a floodplain marsh of the Lower Paraná River

Abstract The role of litter decomposition on organic matter accumulation and nutrient cycling was studied in a floodplain marsh of the Lower Parana River by means of in situ litterbag experiments. The effect of waterborne nutrients on decomposition rates was studied through a laboratory litterbag experiment. Litter decomposition was rather slow, remaining 40–50% of the initial mass after 2 years incubation. Similar decomposition rates were observed in laboratory and field experiments. Water fertilization did not significantly affect decomposition rates. Since organic matter production is faster than decomposition a net accumulation takes place in the upper layers of the marsh soil. N and P litter concentration increased during the decomposition experiment. Floodplain marshes represent effective sinks of nutrients through litter accumulation.

Nutrient profiles in the everglades: examination along the eutrophication gradient.

We examined the concentration profiles of nutrients in the surface water, soil and pore water along the eutrophication gradient of the Water Conservation Area-2A (WCA-2A) in the northern Everglades. Phosphorus levels in the surface waters contributed by the agricultural runoff showed an exponential decrease downstream of the inflow structures attaining background values of 7-12, 7-9 and 5-6 micrograms l-1 of TP, TDP and PO4-P, respectively, at distances of 8-10 km. The pore water PO4-P concentration in the oligotrophic areas ranged between 5 and 10 micrograms l-1. Molar ratios of dissolved inorganic N and P suggest a possible switch in nutrient limitation in the surface water from P in the oligotrophic areas to N in the eutrophic areas (DIN:DIP approximately 5). External nutrient loading has also contributed to a three- to four-fold increase in soil TP concentration and enhanced pore water PO4-P in the northern marshes. Unlike P, C and N concentration in the soils remained fairly uniform along the eutrophication gradient. 210Pb dating of soil cores suggests that the increase in soil P concentration (from < 500 to 1500 micrograms g-1) and P accumulation rate (from 0.06 to 0.46 g P m-2 per year) at the eutrophic site correlates with the installation of inflow structures in 1960-1963 through which agricultural drainage from the Hillsboro canal enters the marshes. Organic P makes up 70-90% of the total P in the soils as uptake by algae and macrophytes is the primary mechanism of P removal in these wetlands. Calcium supply from the underlying bedrock suggested from the surface and pore water chemical profiles has important consequences for P-cycling in the Everglades as Ca-bound P is the major form of inorganic P storage in the soils.

Calibration of diatoms along a nutrient gradient in Florida Everglades Water Conservation Area-2A, USA

The relationship between diatom taxa preserved in surface soils and environmental variables at 31 sites in Water Conservation Area 2A (WCA-2A) of the Florida Everglades was explored using multivariate analyses. Surface soils were collected along a phosphorus (P) gradient and analyzed for diatoms, total P, % nitrogen (N), %carbon (C), calcium (Ca), and biogenic silica (BSi). Phosphorus varied from 315-1781 μg g-1, and was not found to be correlated with the other geochemical variables. Canonical correspondence analysis (CCA) was used to examine which environmental variables correlated most closely with the distributions in diatom taxa. Canonical correspondence analysis with forward selection, constrained and partial CCA, and Monte Carlo permutation tests of significance show the most significant changes in diatom assemblages along the P gradient (p < 0.01), with additional species differences correlated with soil C, N, Ca, and BSi.Weighted-averaging (WA) regression and calibration models of diatom assemblages to P and BSi were developed. The diatom-based inference model for soil [P] had a high apparent r2 (0.86) with RMSEboot = 218 μg g-1. Indicator diatom species identified by assessing species WA optima and WA tolerance to [P], such as Nitzschia amphibia and N. palea for high [P] (~1300-1400 μ g-1) and Achnanthes minutissima var. scotica and Mastogloia smithii for low [P] (~400-600 μg g-1), may be useful as monitoring tools for eutrophication in WCA-2A as well as other areas of the Everglades. Diatom assemblages analyzed by cluster analysis were related to location within WCA-2A, and dominant taxa within clusters are discussed in relation to the geochemical variables measured as well as hydrology and pH. Diversity of diatom assemblages and a ‘Disturbance Index’ based on diatom data are discussed in relation to the historically P-limited Everglades ecosystem. Diatom assemblages should be very useful for reconstructions of [P] through time in the Florida Everglades, provided diatoms are well preserved in soil cores.

Pore water N and P concentration in a floodplain marsh of the Lower Paraná River

Inorganic nitrogen and soluble reactive phosphate (o-P) concentrations were measured in the water of a marsh and in its interstitial water at two sites, and in the river water of a floodplain marsh of the Lower Paraná River. These values were compared with the N and P concentration in sediments and macrophyte biomass in order to assess nutrient availability, fate and storage capacity. High variability was found in the interstitital water using a 1 cm resolution device. Nitrate was never detected in the pore water. Depth averaged NH4+ concentrations in the upper 30 cm layer often ranged from N = 1.5 to 1.8 mg l-1, but showed a pronounced minimum (0.5–0.7 mg l-1), close to (March 95), or relatively soon after (May 94) the end of the macrophyte growing season. Soluble phosphate showed a large variation between P = 0.1–1.1 mg l-1 without any discernible seasonal pattern. NH4+ depletion in the pore water concentration and low N/P ratios (3.7 by weight) within the macrophyte biomass at the end of the growing period suggest that available N limits plant growth. NH4+ and o-P concentrations were 35 and 7 times higher, respectively, in the pore water than in the overlying marsh, suggesting a permanent flux of nutrients from the sediments. o-P accumulate in the marsh leading to higher concentrations than in the incoming river. NH4+ did not accumulate in the marsh, and no significant differences were observed between the river and the marsh water, while the NO3- contributed by the river water was depleted within the marsh, caused probably by coupled nitrification-denitrification at the sediment–water interface. Although an order of magnitude smaller, the pore water pool can supply enough nutrients to build up the macrophyte biomass pool, but only if a fast turnover is attained. The Paraná floodplain marsh retains a large amount of nutrients being stored mainly in the sediment compartment.

An Ecological Basis for Establishment of a Phosphorus Threshold for the Everglades Ecosystem

Numerous studies have shown that the Everglades fen is a phosphorus-limited ecosystem (Steward and Ornes 1975a,b; Craft and Richardson 1993a; Koch and Reddy 1992; Richardson et al. 1999; Richardson and Qian 1999; Noe et al. 2001). From this it can be hypothesized that increases in phosphorus concentrations in the water column and the soils of the Everglades above the ecosystem’s P assimilative capacity (Chap. 23) will result in significant imbalances in the structure and function of the Everglades ecosystem (Richardson and Qian 1999). In the following chapter we provide information on our experimental results and general organism and ecosystem responses to P additions, as well as provide a statistical basis for determining a P threshold as it relates to ecological imbalance. However, before assessing the experimental P-dosing results, it is necessary to establish quantifiable metrics or indices of trophic level response to P concentrations as well as to determine a priori a scale of acceptable P effects. Various ideas have been proposed to aid in the development of a phosphorus threshold for the Everglades. They range from simply using the background concentration of P found in the water column or soils in the most areas of the Everglades to utilizing technology-based criteria founded on best available P removal technology. It has also been argued that the P standard could be based on the geometric mean or median P concentration found in the water column of a reference or least disturbed area of the Everglades that displays the native balance of plant and animals (SFWMD 2001, 2002, 2003, 2005, 2006). This concept is attractive in that it is based on the recently popular use of a reference area as the standard conditions for comparing wetland functions (Brinson et al. 1995; US EPA 1997b). The selection of the reference area itself is the key to this entire approach since it dictates the baseline environmental conditions that are used for each wetland type by region. This approach requires the selection of numerous reference areas and measurements over time to capture the high natural variation with the system (Brinson et al. 1995). However, this method has not been fully tested or calibrated, especially as it relates to water quality standards in wetlands. Also, the use of interior reference systems alone also does not account for the natural nutrient and hydrologic gradients that exist in wetland from the edge inward (Keddy 2000).

Macrophyte Slough Community Response to Experimental Phosphorus Enrichment and Periphyton Removal

Natural plant communities generally respond to fertilization with increases in growth rates for many species, but differential plant responses to excess nutrients more often result in species composition change. Some species are better adapted to take advantage of increased availability of nutrient resources and grow faster than others when supplied with abundant nutrients (Tilman 1990; Tilman et al. 1997). In many cases these might be termed “r” adapted species or “weedy” species. Shifts in species abundance in enriched communities often occur as a result of competition for light or space as plant cover increases due to fertilization. Fast growing plants that eventually tend to dominate the fertilized community are generally those species that can dominate sites by suppressing species not able to take advantage of fertilization through greatly increasing their growth, cover, or overall competitiveness. In many wetland macrophyte communities, a different pattern of response to eutrophication appears to have been developed. Macrophyte declines in response to eutrophication have been reported at various sites worldwide (Moss 1976; Phillips 1978; Ostendorp 1989; Vymazal 1995). Eutrophication of a body of water results in dense phytoplankton growth, reduced water clarity because of light adsorption by phytoplankton (shading), and increased concentrations of dissolved organic compounds produced by phytoplankton (Sand-Jensen and Borum 1991). These factors inhibit the growth of most submerged plants. It is likely that dense phytoplankton growth also inhibits growth of rooted submerged macrophytes by generating high pH, thus hampering inorganic carbon uptake and making submerged plants more dependent on the light-driven utilization of HCO 3 − of for photosynthesis (Maberly and Spence 1983). It has also been shown that shallow lakes that are macrophyte-dominated systems can usually withstand some level of nutrient additions without a shift in major species; however, when a critical level is reached, the stable state of the systems shifts from the clear water, macrophyte-dominated state to a turbid state devoid of macrophytes and dominated by phytoplankton (Scheffer et al. 1993). Turbidity shading does not appear to account for the decline in Phragmites density in Europe, since Phragmites tends to have most of its leaf area