Duration and frequency of drainage and flooding events interactively affect soil biogeochemistry and N flux in subtropical peat soils.

With the demand for restoration and future prediction of climate change effects, subtropical peatlands are expected to be subjected to hydrologic regimes with variable duration and frequency of drained and flooded conditions, but knowledge of their interactive effects on soil biogeochemistry and emission of greenhouse gases including nitrous oxide (N2O) is largely limited. The objective of this study was to investigate how the duration and frequency of drainage and flooding events interactively influence soil biogeochemical properties and denitrification and related net N2O production rates following rewetting. Surface soils are susceptible to different hydrologic regimes. Significantly higher pH, extractable organic carbon (ext. OC), ammonium (NH4+-N), denitrification enzyme activity (DEA), but lower nitrate (NO3--N), microbial biomass C and N were observed when the peat soils were under flooded conditions compared to drained conditions. Two-week and four-week drainage or flooding duration did not result in statistically significant differences in soil biogeochemical properties. A 24-week prolonged drainage led to an accumulation of NO3--N and a significantly lower pH. Soil microbial biomass and fungal:bacterial abundance likely increased with the frequency of drainage-flooding cycles. Significant differences in denitrification and net N2O production rates following reflooding were mainly found in the surface soils. Structural equation modeling indicated that hydroperiod and water-filled pore space (WFPS) prior to reflooding is likely to control denitrification and net N2O production through its regulation of NO3--N and activity of microorganisms involved in denitrification while higher drainage-flooding frequency decreases the availability of organic C and NO3--N for denitrification. Our results also suggest high NO3--N and low pH within peat soils caused by prolonged drainage likely leads to a significant N2O emission pulse following reflooding. For peat soils subjected to frequent drainage-flooding cycles, N2O emission pulses following reflooding would decrease with time, attributing to the loss of substrates for denitrification.

Soil phosphorus forms and storage in stormwater treatment areas of the Everglades: Influence of vegetation and nutrient loading.

Stormwater treatment areas (STAs) are an integral component of the Everglades restoration strategies to reduce phosphorus (P) loads from adjacent agricultural and urban areas. The overall objective of this study was to determine the forms and distribution of P in floc and soils along the flow-path of two parallel flow-ways (FWs) in STA-2 with emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV), respectively, to assess their stability and potential for long term storage. In EAV high organic matter accretion supported low bulk density and high P concentrations in floc and soil, while high mineral matter accretion in SAV resulted in high bulk density and low P concentrations. Approximately 25-30% of the total P is identified as highly reactive P (HRP) pools, 50-60% in moderately reactive P (RP) forms, and 15-20% in the non-reactive P (NRP) pool. Within HRP and RP pools, a large proportion of P in the SAV areas was inorganic while organic P was more dominant in the EAV areas. Enrichment of total P (especially in HRP and RP pools) found in the upstream areas of both FWs resulted from the P loading into FWs over time, and the surplus P conditions can potentially support flux into the water column. In EAV FW, approximately 45% of the P retained was recovered in floc and RAS and remaining was possibly retained in the above and below ground biomass and incorporated into subsurface soils. In SAV FW, all of the P retained was recovered in floc and soils suggesting P retention in plants was not significant. For STAs to continue to function effectively and meet the desired outflow TP concentrations, management strategies should be aimed to promote P limiting conditions within the system to avoid release of P from floc and soils to water column and potential downstream transport.

Influence of flow on phosphorus-dynamics and particle size in agricultural drainage ditch sediments.

Particle size is one factor affecting phosphorus (P) dynamics in soils and sediments. This study investigated how flow facilitated by hydraulic pumps and aquatic vegetation species water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes) affected particle size and P-dynamics in organic sediments in agricultural drainage ditches. Sediments with finer particle size (>0.002 mm) were hypothesized to contain greater total P (TP) and less labile P than sediments with coarser particle size. Particle size was determined using a LS 13 320 Laser Diffraction Particle Size Analyzer. Sediments were tested for pH, TP, and organic matter. Fractions of P were determined using a sequential fractionation experiment and 31P Nuclear Magnetic Resonance (NMR) Spectroscopy. Larger average particle size and lower average total P concentrations were found in the inflows of the field ditches compared to the outflows. Presence of flow and aquatic vegetation did not have a significant impact on particle size, TP, or labile P fractions. Median (p = 0.10) particle size was not significantly correlated to TP. Overall, there was an average trend of coarser particle size and lower P concentrations in the inflow compared to the outflow. The presence of inorganic limerock could have affected results due to increased P adsorption capacity and larger average particle size compared to the organic fraction of the sediment.

Studies on heavy metal accumulation in aquatic macrophytes from Sevan (Armenia) and Carambolim (India) lake systems.

Aquatic macrophytes are unchangeable biological filters and they carry out purification of the water bodies by accumulating dissolved metals and toxins in their tissue. In view of their potential to entrap several toxic heavy metals, 45 macrophytes belonging to 8 families collected from two different physiographic locations (36 from Sevan Lake, Armenia; 9 from Carambolim Lake, Old Goa, India) were studied for estimation of 14 heavy metals. The study was aimed at understanding the importance of these macrophytes in accumulation of toxic metals and controlling the heavy metal pollution and suggesting the remedial measures, if any, for the preservation and restoration of lake ecosystem. Inductively Coupled Plasma-Atomic Emission Spectrometric (ICP-AES) analyses of these aquatic macrophytes have shown the importance of aquatic macrophytes in accumulation of heavy metals and maintaining the clarity of water bodies beside their role in trophic systems. Accumulation of most of the heavy metals was higher in root system. The representative macrophytes from two different physiographic locations show similar trends and order in accumulating different metals generally. Of the 14 metals investigated, 9 (Ca, Fe, Al, Cr, Cu, Ba, Ti, Co and Pb) showed higher rates of accumulation in the root whereas 3 (Mn, Zn and Mg) showed more accumulation in stem and 1 (Ca) showed higher accumulation in the leaves. In most of the samples Cu was accumulated more in the roots (50+/-47.15 microg/g) and less in flowers (9.52+/-3.97 microg/g). Occurrence of heavy metal was much higher in macrophytes of Sevan Lake than that of the Carambolim Lake. The accumulation of 14 elements was in order of Ca>Mg>Fe>Al>Mn>Ba>Zn>Ti>Cu>Cr>Co>Ni>Pb>Cd. The present study revealed that the aquatic macrophytes play a very significant role in removing the different metals from the ambient environments. They probably play a major role in reducing the effect of high concentration of heavy metals. Therefore, the macrophyte community of the Sevan Lake area needs to be protected and restored on a priority basis. Accumulation of highly toxic metals like--Cr, Cd, Pb and Ni was lower as compared to the essential metals like Ca, Fe and Mn in all the macrophytes from both the lake systems, consequently high metal concentrations observed in both the areas may not directly reflect on the pollution level.