Retrieved from SciFLO, Brazil.
ABSTRACT
A map of the native vegetation remaining in São Carlos County was built based on aerial images, satellite images, and field observations, and a projection of the probable original vegetation was made by checking it against soil and relief surveys. The existing vegetation is very fragmented and impoverished, consisting predominantly of cerrados (savanna vegetation of various physiognomies), semideciduous and riparian forest, and regeneration areas. Araucaria angustifolia (Bertol.) Kuntze, found in patches inside the semideciduous forest beginning at a minimum altitude of 850 m, has practically disappeared. By evaluating areas on the map for different forms of vegetation, we obtained the following results for original coverage: 27% cerrado (sparsely arboreal and short-shrub savanna, and wet meadows); 16% cerradão (arboreal savanna); 55% semideciduous and riparian forests; and 2% forest with A. angustifolia. There are now 2% cerrados; 2.5% cerradão; 1% semideciduous forest and riparian forests; 1.5% regeneration areas; and 0% forest with A. angustifolia.
This is interesting to me because I have been looking for lists of species, discussion of ecosystem structure and current conditions.
Below are some interesting bits of information from this article, published in the Brazilian Journal of Biology
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''The territory of the district is rough. There are open savannas and forests. They generally extended through the mountainous region and have been largely felled by the farmers, who have replaced them with verdant coffee plantations. In these areas the soil is, as a rule, very fertile. There are vast stretches of land whose soils are formed by the oxidation and breaking down of igneous rock – diorite (commonly known as ironstone), which has turned into the famous purple soil, of inexhaustible fertility. The open savanna is usually slightly undulating and abundantly sandy; and, specially in the southwest, by the Campo Alegre station, it is adorned with beautiful meadows, of pleasant aspect''. Regarding hydrology he mentions: ''The district is bathed by the Rivers Feijão, Lobo, Onça, Pinhal, Quebra-Canella, Mello, Monjolinho, Chibarro, Mineirinho, Corrente e Jacaré, which discharge into the Tietê; and by the Águas Turvas, dos Negros, Quilombo, da Água Vermelha, das Araras and das Cabeceiras brooks, tributaries of the Mogy-Guassú river, that also bathes the district''.
The devastation of the original areas of vegetation was a consequence of the large-scale use of soil for agriculture and pasture, beginning with the expansion of coffee planting after 1860. Until then, activity had been restricted to subsistence crops and breeding carried out by the inhabitants, useful also in supplying muleteers and travelers as they moved toward Brazil's central region (Truzzi, 2000).
In this period, semideciduous forest yielded to agriculture due to the demand for more fertile soils for coffee plantation expansion. Besides the loss of good part of the forests, even the remaining fragments were used to produce coffee seedlings and, consequently, the underwood was cleared, causing impoverishment and reduction of biodiversity in these areas, in the interior of which numerous coffee plants may still be found (Martins, 1991; Silva & Soares, 2000) The native pine [Araucaria angustifolia (Bertol.) Kuntze], which is used as the official symbol of the county, and was apparently found in patches in the semideciduous forest, has practically disappeared, due to its use for timber and its felling during land occupation. Today, only a few isolated individuals survive.
Here is the projection of the original distribution of semideciduous and riparian forest, forest containing A. angustifolia, cerrados, and cerradão. The estimated total areas of the various vegetational forms, given as percentages of the total area of São Carlos were: 27.74% cerrado, 16.14% cerradão, 54.36% semideciduous and riparian forest, and 1.76% semideciduous forest with A. angustifolia (Table 1).
This is a graphic of what remains of this flora
How does this level of change in vegetation structure compare to the Pacific Northwest. The truth is that the impacts in both places is very similar. My work seed collecting in the Williamette Valley is a struggle to find intact plant populations to sample seed sources.
To finish here is text from this article describing the main vegetation types in this county and their species diversity.
Cerrados and cerradão
In São Paulo State, savanna occurs in the form of islands or branches, mainly in a central strip from the northwest to the southeast, which includes São Carlos County (Borgonovi & Chiarini, 1965). These islands comprise the physiognomies of cerradão (arboreal savanna), cerrado, (sparsely arboreal savanna), campo cerrado (short-shrub savanna), and campo sujo (grassland sparsely shrubbed), following Coutinho's classification (1978).
Silva (1994) compared the vegetation and soil characteristics in different savanna physiognomies on Canchim Farm, São Carlos, and concluded that the dominant factor in the distribution of physiognomies was the presence of more or less sandy soils. The sandier soils, with smaller amounts of clay, are poorer in nutrients and more easily washed away by strong summer rainfalls. In richer soils, vegetation is denser and higher but as the soil becomes sandier and poorer, the arboreal and shrub vegetation becomes lower and sparser. This author found, besides the variation in physiognomy, variation in morphological characteristics such as hair density, presence of protective scales, and hardness and size of leaves.
For the São Carlos it was concluded that cerrado predominated over other physiognomic forms. We believe that campo sujo and campo cerrado occurred only in some very restricted areas, mainly in old sandy alluvial deposits.
Similarly, the wet meadow region formed where a water sheet bursts out between riparian forest and adjacent savanna formations (cerrado, campo cerrado, and cerradão), which is common in many areas of the country, is restricted in São Carlos County, when it occurs at all, to a strip of a few meters.
Much of the remaining savanna formations have a considerably more open physiognomy than the original, due to fires and pasture formation. The cerrado and campo cerrado characteristic species regenerate more easily than the cerradão when the area is abandoned. Although regeneration is facilitated by the species' ability to sprout from the subsoil, it only occurs in places where the agricultural practices do not involve digging deep into the soil. Thus, the surviving savanna does not always reflect past physiognomy.
In the cerrado the underwood and the interlacing branches of stunted trees, growing just above the ground, form a typical landscape: low, dense, and tortuous, hindering attempts to walk through it. From this characteristic derived the term cerrado for this vegetational physiognomy. Researchers like Coutinho (1978) extended the use of this term to more open savanna physiognomies and taller arboreal savanna, owing to the similarity of their flora. The latter, although very similar, within its different physiognomies, varies in density of each species, with sometimes more arboreal species developing and sometimes more shrubs or herbs.
Cerradão is the forest physiognomy of this vegetation. The trees can reach 20 m in height, with stem diameters exceeding 50 cm. Lianas are found everywhere while the herbaceous stratum is very poor. It occurs generally on soil of average fertility.
This savanna has a rich flora in terms of species. Many of them are valued as decorations and used in arborization of streets and public squares (Almeida et al., 1998), or cultivated for their medicinal properties (Siqueira, 1981) or fruits (Almeida, 1998).
In the regional cerradão we found predominating, in the arboreal stratum, species like Anadenanthera falcata Speg., Bowdichia virgilioides H. B. & K., Copaifera langsdorffii Desf., Dimorphandra mollis Benth.., Hymenaea courbaril L., H. stigonocarpa Hayne, Pterodon pubescens Benth., Qualea grandiflora Mart., Q. parviflora Mart.; Virola surinamensis Warb, Vochysia tucanorum Mart., Machaerium acutifolium Mart ex Benth., M. villosum Vog., Sweetia dasycarpa Benth., Miconia rubiginosa Benth,and Kielmeyera coriacea Mart. A more detailed description of the specific composition and structure of this vegetation in the county can be found in Silva (1996).
Species like Annona cacans Warm., A. coriacea Mart., A. crassiflora Mart., Syagrus flexuosa (Mart.), Ocotea pulchella Mart, Ouratea spectabilis Engl., Stryphnodendron barbadetiman (Vell) Mart., S. polyphyllum Mart., Pouteria torta Radlk, Xilopia aromatica (Lam.) Mart., Caryocar brasiliense Cambess., Myrcia lingua (O. Berg.) Mattos, and Roupala montana Aubl. are some of the short trees and bushes commonly found in the savanna of São Carlos. These species also occur in the cerradão.
In more open formations of campo cerrado we found several species of Campomanesia spp., Solanum lycocarpum A. St. Hil., Casearia sylvestris Sw., Setaria poiretiana Kunt, Bromelia antiacantha Bertol, Andira humilis Mart ex Benth., Cochlospermum regium Pilger, Didymopanax vinosum March, Aspidosperma tomentosum Mart., Hancornia speciosa Gomez, Mandevilla velutina K. Schum, Baccharis dracunculifolia D.C., B. subdentata D.C., B. trimera D.C., Calea cimosa Less, C. hispida (D.C.) Baker, Memora axillaris K. Schum., Gochnatia polymorpha Herb. Berol ex D.C., Mikania cordifolia Willd, M. micrantha H. B. & K., Vernonia apiculata Mart. ex D.C., V. brevifolia Less., V. ferruginea Less., Anemopaegna arvense (Vell.) Stelfeld ex de Souza, Arrabidaea brachyopoda Burr., Jacaranda caroba D.C., Pyrostegia ignea Presl., Tabebuia aurea Benth and Hook f. ex S. Moore, Tabebuia caraiba Bureau Mart., Zeyhera montana Mart., Ananas ananassoides (Barker) L.B. Smith, Bauhinia holophylla (Bong) Steud., Cassia spp., Kielmeyera variabilis Mart., Davilla rugosa Poir., Diospyros hispida A.D.C. Erytroxylum spp., andlianes of the genera Banisteria, Banisteriopsis, and Byrsonima. Trees and short trees of higher physiognomic formations are also, though sparsely, among these species.
In the wet meadows we observed terrestrial orchid species of the genus Habenaria; Xyris jupicai Michx., X. metallica Klotzsch ex. Seub., X. hymenachne Mart., X. savanensis Miq., X. teres Alb. Nilsson., Andropogon leuchostachyus H.B.K., several species of Miconia and Leandra, Heleocharis interstincta (Vahl) Roem. & Schult, H. mutata (L.) Roem. & Shult, Rhynchospora exaltata Kunth., R. globosa (Kunt) Roem. & Schult, Scirpus cubensis Kunth., Scleria hirtella Bach., Eriocaulon aequinoctiale Ruhl., E. modestum Kunt., E. pygmaeum Dalz., Paepalanthus blepharocnemis Mart ex Koem, P. speciosus (Bong.) Koern, Syngonanthus caulescens (Poir) Ruhland, S. fischerianus (Bong.) Ruhland, S. xeranthemoides (Bong) Ruhland, and others such as Hydrocotile bonariensis Lam., Lycopodium spp., Nymphoides indica (L.) O. Ktze. (which develop from the edge of the water bodies), Ludwigia elegans (Cambess) Hara, L. leptocarpa (Nutt.) Hara, L. longifolia (D.C.) Hara, L. multinervia (Hook & Am.) T.P. Ramamoorthy, L. suffruticosa Walt., Pontederia cordata Larranaga, and P. lanceolata Nutt.
Riparian forest
The forests that extend along the riversides have received, through the years, denominations such as alluvial, riparian, gallery, and ciliate forest, among others. According to Ivanauskas et al. (1997) these formations have received the most varied designations owing to the variety of local characteristics, such as relief, soil, declivity, physiognomy, position in the landscape, and so on. Velozo & Goes Filho (1982) named them alluvial forests and, when alluvial soil under laid the meadows, they were called fluvial alluvial forest (Campos, 1912) or marshy forest (Lindman & Ferri, 1974; Fernandes & Bezerra, 1990). Bertoni & Martins (1987) called them meadows and Troppmair & Machado (1974), used the term condensation forest, when they occupied the valley bottom, where thick fog occurred at certain periods of the year.
As these formations border the water like eyelashes (Campos, 1912), they were also called rampart forest (Lindman & Ferri, 1974) and ciliary forest (Sampaio, 1938; Hueck, 1972; Bezerra, 1975). In the State of São Paulo, the term ciliary forest (mata ciliar) was sanctioned by Leitão Filho (1982), who defined it as broad-leaved wet forest with periodic flooding.
The ciliary forest designation has been used as a synonym for the term gallery forest (Joly, 1970; among others). However, the Ecology Glossary (Aciesp, 1987) differentiates between these terms based on forest width and the vegetational physiognomy of adjacent areas. According to this work, gallery forest is forest formations along watercourses, in regions where the interfluvial original vegetation is not forest. For regions where interfluvial original vegetation is also forest, the glossary suggests the term ciliary forest or waterside forest. The term ciliary forest, defined by Aciesp (1987), has been substituted by riparian forest (Bertoni & Martins, 1987; Catharino, 1989; Mantovani, 1989; Rodrigues, 1992), reserving the term ciliary forest, as used in the current legislation, for more generic commonly used designations (Rodrigues, 2000).
Swamp forest, also described as almost permanently flooded broadleaf wet forest (Leitão Filho, 1982), although frequently appearing associated with riparian and gallery forest, is distinct from the others, because of almost permanent presence of water in the soil. This saturated soil contributes to the selectivity of species occurring in this formation, and results from their specialized physiology adapted to hydric saturation (Ivanauskas et al., 1997).
According to Leitão-Filho (1982), swamp forest exhibits a relatively small number of very specific species, generally not deciduous, whose uppermost stratum reaches an average of 10-12 m in height.
Swamp forest is restricted to meadows or flood plains, on low, more or less flat land, found close to sources or in well-defined locations on riverbanks, by lakes, or in natural depressions. In these places there are hydromorphic soils (organic and gley; quartzose and hydromorphic sands; and plinthitic soil among others) forming a relief of low mounds and small superficial channels and presenting an irregular surface where the water flows in a definite direction.
The factors that lead to the occurrence of woods (forest physiognomy) or wet meadow (predominantly herbaceous physiognomy) on typically wet soils are still little known. However, it is believed that some of them relate to drainage, and to the presence of physical impediments in the soil and/or alteration of the original topography. In areas where water remained in the soil for long periods, to the point of almost stagnating, herbaceous vegetable formations would develop; and where the water movement was well-defined in superficial channels, forest formations would develop.
Because of its predominance on hydromorphic soils, swamp forest has a naturally restricted distribution in São Paulo State. In addition to this fragmentation, swamp-forest occupied areas have been greatly reduced in the recent past, due to programs stimulating agricultural use of the meadows and to construction of hydroelectric plants, the latter inundating a large part of these remnants. Riparian forest, besides protecting the hydrological characteristics of water bodies and the associated fauna, provides ecological corridors for biota. Such corridors can be found in São Carlos County, where the riparian forest of one hydrographic basin is continuous with the riparian forest of another, uniting two large hydrographic basins of São Paulo State drained respectively by the Mogi-Guaçu and Tietê rivers. The link is made through tributaries such as the Jacaré and Quilombo rivers (Fig. 2).
Studies of the flora and plant associations in riparian forest in the basins of the Mogi-Guaçu, Tietê, and their tributaries in São Carlos County show that the following species are common in the area, if we ignore the ecological variations from place to place: Cyclolobium vecchii A. Sampaio, Alchornea triplinervia Muell. Arg., Guarea trichilioides L., Genipa americana L., Duguetia lanceolata St. Hill., Inga vera H. B. & K., Syagrus romanzoffiana (Cham.) Glassm., Eugenia spp., Picramnia warmingiana Engl., Calophyllum brasiliense Camb., Hymenaea courbaril L., Copaifera langsdorffii Desf., Ixora gardneriana Benth., Lonchocarpus guilleminianus (Tul.) Malme, Aspidosperma peroba Saldanha da Gama, Luehea divaricata Mart, Protium heptaphyllum March, Cecropia pachystachya Trec., Talauma ovata A. St. Hill, Drymis brasiliensis Miers., Calophylum brasiliense Camb., Podocarpus sellowii Klotz. ex Endl., Inga affinis D.C., Rapanea guyanensis Aubl., Cyathea delgadii Sternb., Euterpe edulis Mart, Metrodorea nigra A. St. Hil., Croton floribundus Lund. ex Didr., Xylopia brasiliensis Spreng, and Rollinia silvatica Mart (Bertoni & Martins, 1987; Rodrigues, 1992; and collection of HUFSCar herbarium).
Semideciduous forest
Semideciduous forest is known by several names according to the region and the authors. It is distributed on the inland plateaus and in peripheral depressions of the Serra do Mar and Serra Geral towards the interior of the continent (FIBGE, 1993). For some authors, such forest should be categorized as Atlantic forest (SOS Mata Atlântica), although there are floristic differences between them that depend on location (Giulietti, 1992). The forest can be increased by including swamp forest in the northeast and on the upper Uruguay River, on the border between Rio Grande do Sul and Santa Catarina States.
Torres et al. (1997) established relations among climate, soil, and arboreal flora in the São Paulo State forests, based on the possible influences of abiotic factors on the distribution of species and arboreal families. Thirteen surveys in São Paulo State were selected, representing different conditions (location at the ends of coordinates and altitudes, succession stadiums, surveying methods). By constructing phenograms the authors verified that the species studied formed two floristic blocks: hygrophilous (annual average rainfall higher than 2000 mm and no dry season) and semideciduous forest (total annual average rainfall of about 1400 mm, and variable dry season). The semideciduous forest block was divided in two groups: high altitude (average altitude higher than 750 m, average frost frequency higher than three days/year) and low altitude (below 700 m). Each of these groups was subdivided according to soil properties (texture, eutrophy, acid or alkaline dystrophy, iron content).
São Carlos County falls in the semideciduous forest block containing both floristic divisions (below 700 m and above 750 m).
Of São Paulo State, several surveys of the flora and structure of vegetation have been made, such as those of Pagano & Leitão Filho (1987), and Martins (1991). Of São Carlos there are the studies of Hora & Soares (2002) and Silva & Soares (2000) in Fazenda Canchim reserve, one of the best-preserved remnants of this forest in the county.
Remnants of semideciduous forest are, in general, very impoverished due to human interference and their reduced extent, which leads to diversity decrease. Observations in Fazenda Canchim showed that the dense soils of these forests prevent trees from rooting deeply. Roots are therefore predominantly superficial and cannot always withstand strong wind pressures on the treetops, especially those projecting above the canopy. Hence, trees fall, forming clearings. In addition, forest fragmentation makes treetops more wind vulnerable, mainly at the forest edges, and the smaller the fragment, the larger the effect of the winds is.
According to Silva & Soares (2000) the semideciduous forest shows, in general, an emerging stratum, formed by species that rise above the forest canopy; an arboreal stratum, forming a continuous canopy of about 20-30 meters; and one of smaller trees, less than 10 meters high, besides the shrub and herbaceous strata.
These authors cites as the most common species in the highest stratum Cariniana estrellensis Kunthze, Piptadenia gonoacantha Macbride, Chorisia speciosa St. Hil., Enterolobium contortisiliquum Morong.and, among species that predominate in the forest, Metrodorea nigra A. St. Hil., Pachystroma longifolium I. M. Johnston, Aspidosperma polyneuron Muell. Arg., Aspidosperma ramiflorum Muell. Arg., Savia dictyocarpa Muel. Arg., Ocotea odorifera (Vell) J. G. Rohwer, Machaerium stipitatum Vog., Holocalyx glaziovii Taub. ex. Glaziou., Cabralea cangerana Saldanha da Gama, Inga marginata H. B. & K., Actinostemon communis Pax., Actinostemon concolor Pax., Centrolobium tomentosum Guill. ex Benth. Cavassan et al. (1984) and Martins (1991) also mention, as common species in this forest, Croton salutaris Casar, Guarea trichilioides L., Acacia polyphylla Clos., Nectandra megapotamica (Spreng) Mez., Piptadenia rigida Benth., Gallezia gorazema Moq.,and Balfourodendron riedelianum Engl.
Semideciduous forest with Araucaria angustifolia
The presence of Araucaria angustifolia (Bertol.) O. Kuntze in the forest is striking. This species is shaped like a chandelier and the trees occupy within the forest structure an emerging position. When the population is sufficiently dense, the tops touch forming a continuous canopy, a configuration more common on higher plateaus in southern Brazil.
Araucaria species are typical in South American temperate and cold regions (Duarte, 1993). Their distribution in Brazil in earlier geological periods was more widespread, with only remnants remaining (Backes, 1983).
Two hypotheses are offered to explain the presence of Araucaria in São Carlos:
Paleoclimatic: occurrence a colder and drier paleoclimate in the tertiary, with Araucaria remaining in places where ecological conditions were favorable (Troppmair, 1974). Ledru et al. (1996, 1998) suggested dating the transition from a dry to a moist climate in 17,000 14 C. yr. BP and also that the presence of Araucaria, Podocarpus, and Drymys pollencan indicate high-moisture conditions in some places. In this case, the existence of A. angustifolia has a singular importance in the region of São Carlos, evidencing an ancient ecological condition.
Anthropic: indigenous populations during their migrations might have brought seeds, either planted or left behind while camping, that grew in places where favorable ecological conditions were found.
The forest with Araucaria in Southern Brazil shows a group of plant species differing little from the Atlantic formations (Jarenkow & Baptista, 1987). Thus, we believe that in the São Carlos region, Araucaria angustifolia occurred together with the semideciduous forest species, forming associations of larger or smaller density.
Wednesday, October 1, 2008
Treatment wetlands
Thinking about first design of simple biological water treatment systems and how chemicals are bound an otherwise immobilized. Next we need to look into how to monitor performance.
Interesting basic info below
From Wikipedia,key words, treatment wetland comes a link to this article by University of Florida wastewater treatment wetlands, by William F DeBusk
Wetlands are commonly known as biological filters, providing protection for water resources such as lakes, estuaries and ground water. Although wetlands have always served this purpose, research and development of wetland treatment technology is a relatively recent phenomenon. Studies of the feasibility of using wetlands for wastewater treatment were initiated during the early 1950s in Germany. In the United States, wastewater-to-wetlands research began in the late 1960s, and increased dramatically in scope during the 1970s. As a result, the use of wetlands for water and wastewater treatment has gained considerable popularity worldwide. Currently, an estimated one thousand wetland treatment systems, both natural and constructed, are in use in North America.
The goal of wastewater treatment is the removal of contaminants from the water in order to decrease the possibility of detrimental impacts on humans and the rest of the ecosystem. The term "contaminant" is used here to refer to an undesirable constituent in the water or wastewater that may directly or indirectly affect human or environmental health. Many contaminants, including a wide variety of organic compounds and metals, are toxic to humans and other organisms. Other types of contaminants are not toxic, but nevertheless pose an indirect threat to our well-being. For example, loading of nutrients (e.g., nitrogen and phosphorus) to waterways can result in excessive growth of algae and unwanted vegetation, diminishing the recreational, economic and aesthetic values of lakes, bays and streams.
Wetlands have proved to be well-suited for treating municipal wastewater (sewage), agricultural wastewater and runoff, industrial wastewater, and stormwater runoff from urban, suburban and rural areas. Municipal wastewater originates primarily from residential and commercial sources. Wetland treatment systems for municipal wastewater vary greatly in size and scope, from single-residence backyard wetlands to regional-scale systems such as the 1200- acre (480-ha) Iron Bridge treatment wetland in central Florida. Agricultural wastewater may include runoff from crop lands and pastures, milking or washing barns and feedlots. Among the types of industrial wastewater that are amenable to treatment in wetlands are those associated with pulp and paper manufacturing, food processing, slaughtering and rendering, chemical manufacturing, petroleum refining, and landfill leachates.
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A number of physical, chemical and biological processes operate concurrently in constructed and natural wetlands to provide contaminant removal. Knowledge of the basic concepts of these processes is extremely helpful for assessing the potential applications, benefits and limitations of wetland treatment systems.
Physical Removal Processes
Wetlands are capable of providing highly efficient physical removal of contaminants associated with particulate matter in the water or waste stream. Surface water typically moves very slowly through wetlands due to the characteristic broad sheet flow and the resistance provided by rooted and floating plants. Sedimentation of suspended solids is promoted by the low flow velocity and by the fact that the flow is often laminar (not turbulent) in wetlands. Mats of floating plants in wetlands may serve, to a limited extent, as sediment traps, but their primary role in suspended solids removal is to limit resuspension of settled particulate matter.
Efficiency of suspended solids removal is proportional to the particle settling velocity and the length of the wetland. For practical purposes, sedimentation is usually considered an irreversible process, resulting in accumulation of solids and associated contaminants on the wetland soil surface. However, resuspension of sediment may result in the export of suspended solids and yield a somewhat lower removal efficiency. Some resuspension may occur during periods of high flow velocity in the wetland. More commonly, resuspension results from wind-driven turbulence, bioturbation (disturbance by animals and humans) and gas lift. Gas lift results from production of gases such as oxygen, from photosynthesis in the water, and methane and carbon dioxide, produced by microorganisms in the sediment during decomposition of organic matter. Problems with eventual buildup of sediment to detrimental levels may need to be addressed over the long term.
Biological Removal Processes
Biological removal is perhaps the most important pathway for contaminant removal in wetlands. Probably the most widely recognized biological process for contaminant removal in wetlands is plant uptake. Contaminants that are also forms of essential plant nutrients, such as nitrate, ammonium and phosphate, are readily taken up by wetland plants. However, many wetland plant species are also capable of uptake, and even significant accumulation of, certain toxic metals such as cadmium and lead. The rate of contaminant removal by plants varies widely, depending on plant growth rate and concentration of the contaminant in plant tissue. Woody plants, i.e., trees and shrubs, provide relatively long-term storage of contaminants, compared with herbaceous plants. However, contaminant uptake rate per unit area of land is often much higher for herbaceous plants, or macrophytes, such as cattail. Algae may also provide a significant amount of nutrient uptake, but are more susceptible to the toxic effects of heavy metals. Storage of nutrients in algae is relatively short-term, due to the rapid turnover (short life cycle) of algae. Bacteria and other microorganisms in the soil also provide uptake and short-term storage of nutrients, and some other contaminants.
In wetlands, as in many terrestrial ecosystems, dead plant material, known as detritus or litter, accumulates at the soil surface. Some of the nutrients, metals or other elements previously removed from the water by plant uptake are lost from the plant detritus by leaching and decomposition, and recycled back into the water and soil. Leaching of water-soluble contaminants may occur rapidly upon the death of the plant or plant tissue, while a more gradual loss of contaminants occurs during decomposition of detritus by bacteria and other organisms. Recycled contaminants may be flushed from the wetland in the surface water, or may be removed again from the water by biological uptake or other means.
In most wetlands, there is a significant accumulation of plant detritus, because the rate of decomposition is substantially decreased under the anaerobic (oxygen-depleted) conditions that generally prevail in wetland soil. If, over an extended period of time, the rate of organic matter decomposition is lower than the rate of organic matter deposition on the soil, formation of peat occurs in the wetland. In this manner, some of the contaminants originally taken up by plants can be trapped and stored as peat. Peat may accumulate to great depths in wetlands, and can provide long-term storage for contaminants. However, peat is also susceptible to decomposition if the wetland is drained or otherwise dries up. When that happens, the contaminants incorporated in the peat may be released and either recycled or flushed from the wetland.
Although microorganisms may provide a measurable amount of contaminant uptake and storage, it is their metabolic processes that play the most significant role in removal of organic compounds. Microbial decomposers, primarily soil bacteria, utilize the carbon (C) in organic matter as a source of energy, converting it to carbon dioxide (CO2) or methane (CH4) gases. This provides an important biological mechanism for removal of a wide variety of organic compounds, including those found in municipal wastewater, food processing wastewater, pesticides and petroleum products. The efficiency and rate of organic C degradation by microorganisms is highly variable for different types of organic compounds.
Microbial metabolism also affords removal of inorganic nitrogen, i.e., nitrate and ammonium, in wetlands. Specialized bacteria (Pseudomonas spp.) metabolically transform nitrate into nitrogen gas (N2), a process known as denitrification. The N2 is subsequently lost to the atmosphere, thus denitrification represents a means for permanent removal, rather than storage, of nitrogen by the wetland. Removal of ammonium in wetlands can occur as a result of the sequential processes of nitrification and denitrification. Nitrification, the microbial (Nitrosomonas and Nitrobacter spp.) transformation of ammonium to nitrate, takes place in aerobic (oxygen-rich) regions of the soil and surface water. The newly-formed nitrate can then undergo denitrification when it diffuses into the deeper, anaerobic regions of the soil. The coupled processes of nitrification and denitrification are universally important in the cycling and bioavailability of nitrogen in wetland and upland soils.
Chemical Removal Processes
In addition to physical and biological processes, a wide range of chemical processes are involved in the removal of contaminants in wetlands. The most important chemical removal process in wetland soils is sorption, which results in short-term retention or long-term immobilization of several classes of contaminants. Sorption is a broadly defined term for the transfer of ions (molecules with positive or negative charges) from the solution phase (water) to the solid phase (soil). Sorption actually describes a group of processes, which includes adsorption and precipitation reactions.
Adsorption refers to the attachment of ions to soil particles, by either cation exchange or chemisorption. Cation exchange involves the physical attachment of cations (positively charged ions) to the surfaces of clay and organic matter particles in the soil. This a much weaker attachment than chemical bonding, therefore the cations are not permanently immobilized in the soil. Many constituents of wastewater and runoff exist as cations, including ammonium (NH4+) and most trace metals, such as copper (Cu2+). The capacity of soils for retention of cations, expressed as cation exchange capacity (CEC), generally increases with increasing clay and organic matter content. Chemisorption represents a stronger and more permanent form of bonding than cation exchange. A number of metals and organic compounds can be immobilized in the soil via chemisorption with clays, iron (Fe) and aluminum (Al) oxides, and organic matter. Phosphate can also bind with clays and Fe and Al oxides through chemisorption.
Phosphate can also precipitate with iron and aluminum oxides to form new mineral compounds (Fe- and Al-phosphates), which are potentially very stable in the soil, affording long- term storage of phosphorus. In the Everglades, and other wetlands that contain high concentrations of calcium (Ca), phosphate can precipitate to form Ca-phosphate minerals, which are also stable over a long period of time. Another important precipitation reaction that occurs in wetland soils is the formation of metal sulfides. Such compounds are highly insoluble and represent an effective means for immobilizing many toxic metals in wetlands.
Volatilization, which involves diffusion of a dissolved compound from the water into the atmosphere, is another potential means of contaminant removal in wetlands. Ammonia (NH3) volatilization can result in significant removal of nitrogen, if the pH of the water is high (greater than about 8.5). However, at a pH lower than about 8.5, ammonia nitrogen exists almost exclusively in the ionized form (ammonium, NH4+), which is not volatile. Many types of organic compounds are volatile, and are readily lost to the atmosphere from wetlands and other surface waters. Although volatilization can effectively remove certain contaminants from the water, it may prove to be undesirable in some instances, due to the potential for polluting the air with the same contaminants.
Conclusions
A wide range of physical, chemical and biological processes contribute to removal of contaminants from water in wetlands. These processes include sedimentation, plant uptake, chemical adsorption and precipitation, and volatilization. Removal of contaminants may be accomplished through storage in the wetland soil and vegetation, or through losses to the atmosphere.
An understanding of the basic physical, chemical and biological processes controlling contaminant removal in wetlands will substantially increase the probability of success of treatment wetland applications. Furthermore, a working knowledge of biogeochemical cycling, the movement and transformation of nutrients, metals and organic compounds among the biotic (living) and abiotic (non-living) components of the ecosystem, can provide valuable insight into overall wetland function and structure. This level of understanding is useful for evaluating the contaminant-removal performance of constructed wetlands and for assessing the functional integrity of human-impacted, restored and mitigation wetlands. More detailed discussions of wetland biogeochemistry and contaminant removal in treatment wetlands can be found in the references listed below.
References
Kadlec, R.H., and R.L. Knight. 1996. Treatment wetlands. Lewis Publishers, Boca Raton, FL.
Mitsch, W.J., and J.G. Gosselink. 1993. Wetlands. Van Nostrand Reinhold, New York.
Reddy, K. R., and E. M. D'Angelo. 1994. Soil processes regulating water quality in wetlands. p. 309-324. In Mitsch, W. J. (ed.) Global wetlands: old world and new. Elsevier Science, Amsterdam.
Interesting basic info below
From Wikipedia,key words, treatment wetland comes a link to this article by University of Florida wastewater treatment wetlands, by William F DeBusk
Wetlands are commonly known as biological filters, providing protection for water resources such as lakes, estuaries and ground water. Although wetlands have always served this purpose, research and development of wetland treatment technology is a relatively recent phenomenon. Studies of the feasibility of using wetlands for wastewater treatment were initiated during the early 1950s in Germany. In the United States, wastewater-to-wetlands research began in the late 1960s, and increased dramatically in scope during the 1970s. As a result, the use of wetlands for water and wastewater treatment has gained considerable popularity worldwide. Currently, an estimated one thousand wetland treatment systems, both natural and constructed, are in use in North America.
The goal of wastewater treatment is the removal of contaminants from the water in order to decrease the possibility of detrimental impacts on humans and the rest of the ecosystem. The term "contaminant" is used here to refer to an undesirable constituent in the water or wastewater that may directly or indirectly affect human or environmental health. Many contaminants, including a wide variety of organic compounds and metals, are toxic to humans and other organisms. Other types of contaminants are not toxic, but nevertheless pose an indirect threat to our well-being. For example, loading of nutrients (e.g., nitrogen and phosphorus) to waterways can result in excessive growth of algae and unwanted vegetation, diminishing the recreational, economic and aesthetic values of lakes, bays and streams.
Wetlands have proved to be well-suited for treating municipal wastewater (sewage), agricultural wastewater and runoff, industrial wastewater, and stormwater runoff from urban, suburban and rural areas. Municipal wastewater originates primarily from residential and commercial sources. Wetland treatment systems for municipal wastewater vary greatly in size and scope, from single-residence backyard wetlands to regional-scale systems such as the 1200- acre (480-ha) Iron Bridge treatment wetland in central Florida. Agricultural wastewater may include runoff from crop lands and pastures, milking or washing barns and feedlots. Among the types of industrial wastewater that are amenable to treatment in wetlands are those associated with pulp and paper manufacturing, food processing, slaughtering and rendering, chemical manufacturing, petroleum refining, and landfill leachates.
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A number of physical, chemical and biological processes operate concurrently in constructed and natural wetlands to provide contaminant removal. Knowledge of the basic concepts of these processes is extremely helpful for assessing the potential applications, benefits and limitations of wetland treatment systems.
Physical Removal Processes
Wetlands are capable of providing highly efficient physical removal of contaminants associated with particulate matter in the water or waste stream. Surface water typically moves very slowly through wetlands due to the characteristic broad sheet flow and the resistance provided by rooted and floating plants. Sedimentation of suspended solids is promoted by the low flow velocity and by the fact that the flow is often laminar (not turbulent) in wetlands. Mats of floating plants in wetlands may serve, to a limited extent, as sediment traps, but their primary role in suspended solids removal is to limit resuspension of settled particulate matter.
Efficiency of suspended solids removal is proportional to the particle settling velocity and the length of the wetland. For practical purposes, sedimentation is usually considered an irreversible process, resulting in accumulation of solids and associated contaminants on the wetland soil surface. However, resuspension of sediment may result in the export of suspended solids and yield a somewhat lower removal efficiency. Some resuspension may occur during periods of high flow velocity in the wetland. More commonly, resuspension results from wind-driven turbulence, bioturbation (disturbance by animals and humans) and gas lift. Gas lift results from production of gases such as oxygen, from photosynthesis in the water, and methane and carbon dioxide, produced by microorganisms in the sediment during decomposition of organic matter. Problems with eventual buildup of sediment to detrimental levels may need to be addressed over the long term.
Biological Removal Processes
Biological removal is perhaps the most important pathway for contaminant removal in wetlands. Probably the most widely recognized biological process for contaminant removal in wetlands is plant uptake. Contaminants that are also forms of essential plant nutrients, such as nitrate, ammonium and phosphate, are readily taken up by wetland plants. However, many wetland plant species are also capable of uptake, and even significant accumulation of, certain toxic metals such as cadmium and lead. The rate of contaminant removal by plants varies widely, depending on plant growth rate and concentration of the contaminant in plant tissue. Woody plants, i.e., trees and shrubs, provide relatively long-term storage of contaminants, compared with herbaceous plants. However, contaminant uptake rate per unit area of land is often much higher for herbaceous plants, or macrophytes, such as cattail. Algae may also provide a significant amount of nutrient uptake, but are more susceptible to the toxic effects of heavy metals. Storage of nutrients in algae is relatively short-term, due to the rapid turnover (short life cycle) of algae. Bacteria and other microorganisms in the soil also provide uptake and short-term storage of nutrients, and some other contaminants.
In wetlands, as in many terrestrial ecosystems, dead plant material, known as detritus or litter, accumulates at the soil surface. Some of the nutrients, metals or other elements previously removed from the water by plant uptake are lost from the plant detritus by leaching and decomposition, and recycled back into the water and soil. Leaching of water-soluble contaminants may occur rapidly upon the death of the plant or plant tissue, while a more gradual loss of contaminants occurs during decomposition of detritus by bacteria and other organisms. Recycled contaminants may be flushed from the wetland in the surface water, or may be removed again from the water by biological uptake or other means.
In most wetlands, there is a significant accumulation of plant detritus, because the rate of decomposition is substantially decreased under the anaerobic (oxygen-depleted) conditions that generally prevail in wetland soil. If, over an extended period of time, the rate of organic matter decomposition is lower than the rate of organic matter deposition on the soil, formation of peat occurs in the wetland. In this manner, some of the contaminants originally taken up by plants can be trapped and stored as peat. Peat may accumulate to great depths in wetlands, and can provide long-term storage for contaminants. However, peat is also susceptible to decomposition if the wetland is drained or otherwise dries up. When that happens, the contaminants incorporated in the peat may be released and either recycled or flushed from the wetland.
Although microorganisms may provide a measurable amount of contaminant uptake and storage, it is their metabolic processes that play the most significant role in removal of organic compounds. Microbial decomposers, primarily soil bacteria, utilize the carbon (C) in organic matter as a source of energy, converting it to carbon dioxide (CO2) or methane (CH4) gases. This provides an important biological mechanism for removal of a wide variety of organic compounds, including those found in municipal wastewater, food processing wastewater, pesticides and petroleum products. The efficiency and rate of organic C degradation by microorganisms is highly variable for different types of organic compounds.
Microbial metabolism also affords removal of inorganic nitrogen, i.e., nitrate and ammonium, in wetlands. Specialized bacteria (Pseudomonas spp.) metabolically transform nitrate into nitrogen gas (N2), a process known as denitrification. The N2 is subsequently lost to the atmosphere, thus denitrification represents a means for permanent removal, rather than storage, of nitrogen by the wetland. Removal of ammonium in wetlands can occur as a result of the sequential processes of nitrification and denitrification. Nitrification, the microbial (Nitrosomonas and Nitrobacter spp.) transformation of ammonium to nitrate, takes place in aerobic (oxygen-rich) regions of the soil and surface water. The newly-formed nitrate can then undergo denitrification when it diffuses into the deeper, anaerobic regions of the soil. The coupled processes of nitrification and denitrification are universally important in the cycling and bioavailability of nitrogen in wetland and upland soils.
Chemical Removal Processes
In addition to physical and biological processes, a wide range of chemical processes are involved in the removal of contaminants in wetlands. The most important chemical removal process in wetland soils is sorption, which results in short-term retention or long-term immobilization of several classes of contaminants. Sorption is a broadly defined term for the transfer of ions (molecules with positive or negative charges) from the solution phase (water) to the solid phase (soil). Sorption actually describes a group of processes, which includes adsorption and precipitation reactions.
Adsorption refers to the attachment of ions to soil particles, by either cation exchange or chemisorption. Cation exchange involves the physical attachment of cations (positively charged ions) to the surfaces of clay and organic matter particles in the soil. This a much weaker attachment than chemical bonding, therefore the cations are not permanently immobilized in the soil. Many constituents of wastewater and runoff exist as cations, including ammonium (NH4+) and most trace metals, such as copper (Cu2+). The capacity of soils for retention of cations, expressed as cation exchange capacity (CEC), generally increases with increasing clay and organic matter content. Chemisorption represents a stronger and more permanent form of bonding than cation exchange. A number of metals and organic compounds can be immobilized in the soil via chemisorption with clays, iron (Fe) and aluminum (Al) oxides, and organic matter. Phosphate can also bind with clays and Fe and Al oxides through chemisorption.
Phosphate can also precipitate with iron and aluminum oxides to form new mineral compounds (Fe- and Al-phosphates), which are potentially very stable in the soil, affording long- term storage of phosphorus. In the Everglades, and other wetlands that contain high concentrations of calcium (Ca), phosphate can precipitate to form Ca-phosphate minerals, which are also stable over a long period of time. Another important precipitation reaction that occurs in wetland soils is the formation of metal sulfides. Such compounds are highly insoluble and represent an effective means for immobilizing many toxic metals in wetlands.
Volatilization, which involves diffusion of a dissolved compound from the water into the atmosphere, is another potential means of contaminant removal in wetlands. Ammonia (NH3) volatilization can result in significant removal of nitrogen, if the pH of the water is high (greater than about 8.5). However, at a pH lower than about 8.5, ammonia nitrogen exists almost exclusively in the ionized form (ammonium, NH4+), which is not volatile. Many types of organic compounds are volatile, and are readily lost to the atmosphere from wetlands and other surface waters. Although volatilization can effectively remove certain contaminants from the water, it may prove to be undesirable in some instances, due to the potential for polluting the air with the same contaminants.
Conclusions
A wide range of physical, chemical and biological processes contribute to removal of contaminants from water in wetlands. These processes include sedimentation, plant uptake, chemical adsorption and precipitation, and volatilization. Removal of contaminants may be accomplished through storage in the wetland soil and vegetation, or through losses to the atmosphere.
An understanding of the basic physical, chemical and biological processes controlling contaminant removal in wetlands will substantially increase the probability of success of treatment wetland applications. Furthermore, a working knowledge of biogeochemical cycling, the movement and transformation of nutrients, metals and organic compounds among the biotic (living) and abiotic (non-living) components of the ecosystem, can provide valuable insight into overall wetland function and structure. This level of understanding is useful for evaluating the contaminant-removal performance of constructed wetlands and for assessing the functional integrity of human-impacted, restored and mitigation wetlands. More detailed discussions of wetland biogeochemistry and contaminant removal in treatment wetlands can be found in the references listed below.
References
Kadlec, R.H., and R.L. Knight. 1996. Treatment wetlands. Lewis Publishers, Boca Raton, FL.
Mitsch, W.J., and J.G. Gosselink. 1993. Wetlands. Van Nostrand Reinhold, New York.
Reddy, K. R., and E. M. D'Angelo. 1994. Soil processes regulating water quality in wetlands. p. 309-324. In Mitsch, W. J. (ed.) Global wetlands: old world and new. Elsevier Science, Amsterdam.
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