A rapid and sensitive analysis of inorganic and organic phosphorus (P) is needed to analyze water and soil extracts at submicromolar concentrations. The proposed method, based on the complexation of malachite green with phosphomolybdate under acidic conditions, was adapted to a 96-well microtiter plate format, and was tested for matrix interferences using 15 soils and some common extractants, including water, KCI, CaCl2, NaOH, and HCl. The accuracy of P determination was affected when CaCl2 and HCl concentrations were greater than 0.1 M and when NaOH concentration exceeded 0.4 M. Potassium chloride concentration up to 1 M did not interfere with P determination. The molar absorptivity was 46 841 M(-1) cm(-1) and the reagent blank absorbance was 0.071+/-0.003 (n = 10). At the 99% confidence limit, the method detection limit was calculated to be 0.006 mg P L(-1). Recovery of added inorganic P in different types of soils and extracts ranged between 95 and 112% with an average of 102%. The proposed microplate method allows P to be determined rapidly in a wide range of soil types and extracts and requires limited volume (20-200 microL). The procedure uses limited quantities (40 microL) of two stable reagents (>1 yr), and generates low amounts of hazardous waste.

No abstract

Laboratory experiments were conducted to determine the effectiveness of three floating and six emergent aquatic macrophytes in improving domestic wastewater quality, based on their capacities for O2 transport into the effluent. Oxygen transport into the rooting zone of the plants created an oxidized microenvironment, thereby stimulating C and N transformations critical to wastewater treatment. Plants were cultured in flasks containing deoxygenated primary and secondary sewage effluent for an 8-d period. Oxygen transport by the plants was measured in terms of both O2 consumed by the effluent (biological 02 demand reduction--BODs) and increased effluent dissolved 02. Two floating plants, pennywort (Hydwcotyle nmbellata L.) and waterhyacinth [Eichkornia crasslpes (Mart.) Solms], and the emergent plants pickerelweed (Pontederla cordata L.) and common arrowhead (Sagittaria latifolia L.), were superior in improving primary sewage effluent quality, by reducing BOD5 up to 88%, NH4-N up to 77%, and increasing dissolved O2 up to 6.1 mg L -I. Nitrification rates in pennywort-and water hyacinth-based water treatment systems were calculated to be in the range of 12 to 47 kg NH 4-N ha -1 d -!. Oxygen transport through plants accounted for up to 90% of the total O2 transported into the effluent. In separate batch experiments, the effectiveness of diffuse mechanical aeration (5 and 50 mL air min -t) and of biological aeration (02 transport by selected plants including pennywort, waterhyacinth, pickerelweed, and common arrowhead) on the rate of contaminant removal from deoxygenated primary sewage effluent were compared for a 26-d period. Biological and mechanical aeration effected similar BODs removal. First-order reaction rate constants for BOD~ removal were from 0.0066 to 0.0079 h -~ and from 0.0041 to 0.0051 h -1 for biological and mechanical aeration, respectively. Rate constants for NH4-N removal were from 0.0024 to 0.0107 h -~ for the plant treatments. Virtually complete BOD~ removal occurred in biological and mechanical aeration treatments within 20 d. Complete nitrification of NH4-N had occurred within 12 d after mechanical aeration was initiated, but subsequent N-loss by denitrification was inhibited. In the biological aeration treatments, negligible effluent (NO 3 + NO2)-N levels were measured, but 65 to 100% NH4-N loss occurred both by plant assimilation and by sequential nitrification-denitrification reactions.A QUATIC PLANTS rooted in anaerobic sediments and anoxic waters transport 02 through stems and leaves into their rooting zones. The mechanism ofO2 transport through aquatic plants into the rooting zone has been demonstrated by several researchers (Armstrong

No abstract

A recently constructed marsh from previously drained agricultural land currently receives nutrient-laden water from adjacent hypereutrophic Lake Apopka, located in central Florida. Lake water is allowed to cycle through the marsh, allowing settlement of participate organic matter, which forms a floe sediment layer on the native peat soil surface. The water leaving the marsh is returned to the lake after a retention time of 3 to 12 d. This study determined changes in temporal and spatial distribution of selected nutrients in the soil-water column of the marsh during the first 13 mo of operation. In situ distribution of selected chemical species (H+, NH/, soluble P, SO3~, dissolved organic C, dissolved inorganic C, CJL,, Ca, Mg, Fe, Mn, AT) were measured using soil pore water equilibrators at 3, 8, and 13 mo after marsh creation. Initial flooding of the agricultural soils resulted in high concentrations of NW (11 mg N L~') and soluble P (31 mg P L "') as a result of solubilization and anaerobic decomposition. Initially rapid soluble P flux (mean = 2.4 mg P m" 2 d" 1 ) occurred from soil to the water column, although lower flux (mean = 0.8 mg Pm" 2 d~') occurred after 10 additional months of operation. In contrast, initial flux of NHJ" into the water column was generally lower (mean = 3.4 mg N m~2 d' 1 ) than observed after 10 additional months (mean = 8.2 mg N m~' d" 1 ). Microbial degradation and nutrient regeneration from settled labile organic matter appeared to support nutrient flux to the water column. After 13 mo of flooding, 75% of the variability of NHtf-N and 65% of the variability of soluble P contained in the water and floe sediment was explained by (DIG + CHO-C mineralized from settled organic matter. Anaerobic conditions in both the floe sediment and peat soil layers (indicated by increased amounts of dissolved CHU and Fe, and by SOI' reduction) had significant effects on nutrient retention and release in the soil-water column.

ant between the solid phase and dissolved phase (sorption), which is governed by the physical and chemical Sorption of four chlorophenols (CPs) was studied in ten wetland properties of the solute, the sorbent, and the solvent. soils with organic C contents between 1 and 44%, which were incu-Much research on organic pollutant sorption has dembated under aerobic or anaerobic conditions to simulate wetland conditions. The objectives of the study were to (i) determine the influence onstrated a strong link between the distribution ratio of aerobic and anaerobic processes on sorption, and (ii) develop sorp-(K p) and the lipophilicity of hydrophobic organic polluttion models to predict the distribution coefficient based on chemical ants, as expressed by its K ow , and the fractional amount characteristics of soils and compounds. Aerobic soils consistently had of organic C of the sorbent (f oc): lower pH than anaerobic treatments, which was a function of the amount of oxidizable constituents present in the sample. Depending K p ϭ f oc ϫ a(K ow) b [1] on the pK a of the compound relative to the pH shift, a greater fraction where a and b are empirical constants that differ deof the CP was in the neutral form in the aerobic treatments, which pending primarily on the nature of the pollutant. The was sorbed to a much greater extent than the ionic form (by about relationship has been very useful for predicting sorption 25 times). The organic C normalized distribution coefficient (K oc) was of many hydrophobic organic pollutants by a wide varistrongly related to the octanol-water distribution coefficient (K ow) and soil pH. Sorption models accurately predicted distribution coefficients ety of sorbents; on occasion, however, it has been found within a factor of 2 from the K ow and pK a of the compounds and the to be deficient for ionizable organic compounds such pH and organic C content of the sorbent. The role of sorption on CP as CPs. retention was partially negated by the formation of the nonseparable In studies on the sorption of CPs in soils and sediphase, which composed up to 8.6% of the total solid mass (depending ments, Schellenburg et al. (1984) and Lagas (1988) on the soil redox status) and had similar distribution coefficients as found that the model for hydrophobic compounds had the separable phase. This study demonstrated that microbial redox limited application because it did not account for the processes significantly influenced the soil properties and CP retention contribution of both the neutral species and the phecharacteristics, and should be considered when designing a bioremedinolate anion to overall sorption. Shimizu et al. (1992) ation plan for these compounds. derived a model that accounted for the contribution of both species to the distribution coefficient of PCP (pK a ϭ 4.74

No abstract

The use of periphyton nitrogenase activity (biological N 2 fixation) as an indicator of wetland P impact was assessed using patterns of nutrient content (C, N, P, Ca, Mg, K, Fe, and Mn) and acetylene reduction (AR) in floating cyanobacterial periphyton mat (metaphyton) communities of a P-enriched portion of the Florida Everglades, USA (Water Conservation Area-2A, WCA-2A). Spatial patterns of nutrients indicate the enrichment of floating mat periphyton N, P, Fe, and K, and the reduction of Mn and TN:TP in enriched marsh areas. In highly enriched areas, floating mat periphyton AR was approximately threefold greater than that in less enriched, interior marsh zones. Multiple regression models indicated AR dependence on P in eutrophic WCA-2A areas while the AR of more interior marsh periphyton mats was more closely related to tissue levels of Ca and Fe.Nitrogenase activity of floating mat periphyton from P-loaded mesocosms revealed a significant enhancement of N 2 fixation in samples receiving approximately 2-3 mg P m -2 of cumulative P dosing or with biomass TP content of 100-300 mg kg -1 . At P contents above the optimum, mat periphyton AR was suppressed possibly as a result of changes in species composition or increased levels of NH 4 + . After 3 years of dosing, consistently high AR occurred only at low rates of P enrichment (0.4-0.8 g P m -2 yr -1 ), and the patterns appeared to be seasonal. These findings agree with the hypothesis that P availability is a key determinant of nitrogenase activity in aquatic systems, and thus, may support the use of periphyton nitrogenase to indicate P impacts in P-limited systems. These results also demonstrate the potential existence of a P threshhold for biogeochemical alteration of periphyton mat function in the Everglades, and that cumulative loading of limiting nutrients (i.e., P), rather than instantaneous concentrations, should be considered when evaluating nutrient criteria.