Moshe Agami

Phosphorus dynamics in selected wetlands and streams of the lake Okeechobee Basin

Lake Okeechobee is becoming increasingly eutrophic, presumably due to P loading from numerous dairy operations in the Lakes northern drainage basin. Phosphorus released from this basin is transported through canals, streams, and wetlands before its discharge into the lake. This paper summarizes the results of several studies on P dynamics in wetlands and stream sediments in the Lake Okeechobee Basin with primary focus on P interaction with soil/sediment-water column and vegetation. Stream sediments and wetland soils in the basin were characterized for labile and non-labile pools of P. The labile inorganic P (Pi) pool (KCl-extractable) accounted for 0.1 to 2.3% and 0.1 to 0.7% of the total P in sediments and wetland soils, respectively. The NaOH extractable Pi, representing the P associated with Fe and Al oxyhydroxides, was the dominant Pi in both stream sediments and wetland soils (accounting for up to 71 and 43% total P, respectively). The NaOH-Po (humic and fulvic acid associated organic P) is considered resistant to biological breakdown and accounted for 6 to 56% of total P. Stream sediments showed higher buffer intensity for P sorption than wetlands. Phosphate sorption capacity (Smax) and buffer intensity (Kd-adsorption coefficient) were highly correlated with oxalate extractable [Fe + Al] and total organic carbon (TOC) suggesting P sorption is associated with amorphous and weakly crystalline forms of Fe and Al, and/or complexed with organic matter. Phosphorus assimilation in vegetation was found to be short-term and dependent upon plant species, P loading, and wetland hydrology. Decomposition of detrital tissue resulted in rapid release of P into the water column. Phosphorus release was rapid during decomposition of floating macrophytes, as compared to herbaceous vegetation. Phosphorus retention coefficients were positively correlated with oxalate extractable Fe and Al content of soils and sediments. The average EPCw (threshold P concentration in the water column where P retention = P release) for stream sediments was 0.10 mg p l−1 and 0.42 mg P l−1 for wetland soils. The stability of the P retained was regulated by the physico-chemical properties of the soils and sediments.

Influence of nitrogen supply rates on growth and nutrient storage by water hyacinth (Eichhornia crassipes) plants

Abstract The effect of nitrogen (N) levels of the culture medium (0.5–50.5 mg N l−1 or 38–3820 mg N m−2 day−1) on net productivity and nutrient (N, phosphorus (P) and potassium (K)) storage by water hyacinth (Eichhornia crassipes (Mart.) Solms) plants was investigated using outdoor tanks. Net productivity increased with N supply rate of up to 5.5 mg N l−1 (or 416 mg N m−2 day−1); higher concentrations did not significantly increase the yield. The net productivity increased until plant tissue N content reached 16 mg N g−1 dry weight, but additional increase in tissue N content did not improve yield. However, N storage in the plant tissue increased in response to N supply rate with maximum N storage (80 g N m−2) measured in plants cultured at 50.5 mg N l−1. Plant density affected N storage in the tissue; when water hyacinths were cultured in N-limited water, plant tissue-N decreased by 75% within 4 weeks of growth. The storage of P and K in the plant tissue was increased up to 5.5 mg N l−1 and 2.5 mg N l−1 in the culture medium, respectively.

Influence of phosphorus on growth and nutrient storage by water hyacinth (Eichhornia crassipes (Mart.) Solms) plants

Abstract The net productivity and nutrient (phosphorus (P), nitrogen (N), and potassium (K) uptake and storage by water hyacinth ( Eichhornia crassipes (Mart.) Solms) were evaluated at P concentrations of 0.06, 0.26, 0.56, 1.06, 2.56 and 10.06 mg P l −1 in the culture medium, using 1000-l outdoor tanks with a surface area of 1.7 m 2 . Biomass yield increased with an increase of P up to 1.06 mg P l −1 , but higher concentrations did not increase biomass yield. Phosphorus storage by water hyacinth increased and decreased in response to P concentrations in the water. Maximum net productivity was measured at a plant tissue P content of 4.3 mg P g −1 . Further increase in tissue P did not increase productivity. Plant density affected P storage in the tissue. When water hyacinth plants were cultured at a low P concentration (0.06 mg P l −1 ), plant tissue P decreased by 50% within the first week of growth. Nitrogen and K storage in plant tissue increased with P supply of up to 2.56 and 1.06 mg P l −1 in the culture medium, respectively.

The role of fish in distribution and germination of seeds of the submerged macrophytes Najas marina L. and Ruppia maritima L.

SummaryThe effects of three species of fish (tilapia, grass carp and common carp) on the seeds of Najas marina L. and of Ruppia maritima L. were investigated. Practically all the seeds that were injested by the common carp were digested. The two other fish were less affective: they digested seeds with soft seed-coats but excreted a good portion of the hard ones. Germination of the excreted seeds was improved. Seeds have been retained in the digestion tracts of the fish for up to 65 h. It is thus suggested that tilapias and grass-carps play a role in the distribution and the improvement of reproduction of Najas and Ruppia.

Competition for space between Eichhornia crassipes (Mart.) Solms and Pistia stratiotes L. cultured in nutrient-enriched water

Abstract The interrelationships between two free-floating aquatic macrophytes, Eichhornia crassipes (Mart.) Solms and Pistia stratiotes L, were investigated using a reciprocal replacement series for the intermixed combinations. The carrying capacity for each species was investigated in monoculture. The plants were cultured in outdoor tanks in Gainesville, Florida, where nutrient-enriched water was replenished at weekly intervals. E. crassipes showed dominance over P. stratiotes when the species were grown together. Interaction between the two species for growth space became apparent within the first month of the experimental period. The luxuriant growth and high plasticity of E. crassipes plants enabled them to grow above the P. stratiotes plants, thus shading and stressing them. Higher concentrations of nitrogen (N) (by about two-fold) were accumulated in the shoots of E. crassipes than in its roots, whereas N accumulation in the roots and shoots of P. stratiotes was similar. The N content of E. crassipes shoots increased throughout the experimental period ∼ six-fold, while the N content of roots increased two-fold. Phosphorus accumulation was equally distributed between the roots and shoots of both species.

Bioactive Chemicals and Biological-Biochemical Activities and Their Functions in Rhizospheres of Wetland Plants

Wetland soils provide anoxia-tolerant plants with access to ample light, water, and nutrients. Intense competition, involving chemical strategies, ensues among the plants. The roots of wetland plants are prime targets for root-eating pests, and the wetland rhizosphere is an ideal environment for many other organisms and communities because it provides water, oxygen, organic food, and physical protection. Consequently, the rhizosphere of wetland plants is densely populated by many specialized organisms, which considerably influence its biogeochemical functioning. The roots protect themselves against pests and control their rhizosphere organisms by bioactive chemicals, which often also have medicinal properties. Anaerobic metabolites, alkaloids, phenolics, terpenoids, and steroids are bioactive chemicals abundant in roots and rhizospheres in wetlands. Bioactivities include allelopathy, growth regulation, extraorganismal enzymatic activities, metal manipulation by phytosiderophores and phytochelatines, various pest-control effects, and poisoning. Complex biological-biochemical interactions among roots, rhizosphere organisms, and the rhizosphere solution determine the overall biogeochemical processes in the wetland rhizosphere and in the vegetated wetlands. To comprehend how wetlands really function, it is necessary to understand these interactions. Such understanding requires further research.

Constructed wetlands for river reclamation: Experimental design, start-up and preliminary results

Abstract The use of constructed wetlands for the treatment of secondary effluents, to allow for safe river discharge, was the subject of a research project carried out at the Alexander River basin in Israel. Four pilot-scale units, each about 100 m2, were built: two were designed for subsurface flow with gravel as the medium and two units were designed for free water surface with local soil as the medium. Secondary treated effluent from the Netanya sewage treatment plant was used as the influent. To support the field study and broaden the understanding of the processes involved, two smaller concrete units, 10 m2 each, were built at the Technion site. Results from the first 6 months of the constructed wetlands operation at the Alexander River site and the Technion site showed that the removal of BOD and SS was very efficient under all the conditions studied: retention time of 4–15 days (hydraulic loading of 20–80 m3/0.1 hectare/day) and BOD loading of 1–5.5 kg BOD/0.1 hectare/day. BOD and SS concentrations in treated liquids were always lower than 20 mg/l and most of the time lower than 10 mg/l. However, the removal efficiency of the nitrogen and phosphorous compounds varied within a very wide range; from 95% to as low as zero removal.

Influence of potassium supply on growth and nutrient storage by water hyacinth

The net productivity and nutrient storage of potassium (K), nitrogen (N), and phosphorus (P) by water hyacinth (Eichhornia crassipes [Mart.] Solms) were evaluated at several K concentrations in the culture medium (between 2 and 52 mg K liter−1) using 1000-liter outdoor tanks for a period of about 4 months. Maximum plant biomass (3·1 kg (dw) m−2) was reached at culture medium K concentrations of 12–52 mg K liter−1. Potassium storage in water hyacinth tissue steadily increased at K supplies of up to 52 mg K liter−1 with a maximum tissue K content of 72 mg K g−1. Maximum N and P storage in the plant biomass was reached at K concentrations of 12 and 22 mg K liter−1, respectively; further increases in K concentration did not increase either N or P storage.

Germination of Najas marina L.

Abstract Germination of Najas marina L. was investigated under field and controlled conditions. In the absence of pre-treatment, germination was very low (∼ 11%), but rose to 62% after the seed coats were cracked. Optimum germination occurred in a temperature range of 20–25°C. Dark conditions also increased germination, whereas light of different intensities had no effect. Seeds retain viability for over 4 years, even when stored dry. The ecological implications of such behaviour are discussed.

Relationship between water pollution and the flora of two coastal rivers of Israel

Abstract Changes in the vegetation of two coastal rivers in Israel were studied in relation to increasing pollution. Pollution levels were defined mainly in terms of ammonium content, presence of detergents and dissolved oxygen concentration at various depths and at various times of the day. It was found that species diversity was greatest in the clean-water sections of the rivers and decreased considerably with increasing pollution. No floating-leaved or submerged species were found in the polluted sections; these and some other species were exclusive to the clean-water sections. On the other hand, none of the hygrophyte species was exclusive to polluted sections. The distribution of several plant species across the rivers and the river banks was noted and it appears that although tolerant species can grow partly submerged in clean water, they avoid direct contact with polluted water.