Orientador: Hélio Grassi Filho / Coorientador: Roberto Lyra Villas Bôas / Banca: Dirceu Maximino Fernandes / Banca: Carlos Henrique dos Santos / Resumo: Contribuindo com o desenvolvimento sustentável dentro da proposta de utilizar sistemas naturais de tratamentos de baixo custo, a fim de promover uma alternativa biológica e limpa, conhecer os parâmetros físico-químicos que podem influenciar o desenvolvimento de macrófitas aquáticas flutuantes, é imprescindível conhecer a dinâmica desses vegetais no ambiente ou em meio artificial. Com isso, tendo como hipótese que a espécie de maior biomassa remove uma maior quantidade de elementos químicos, o objetivo do presente trabalho foi embasado no potencial de três espécies de macrófitas aquáticas flutuantes Eichhornia crassipes, Pistia stratiotes e Salvinia auriculata em remover os elementos químicos de água residuária. O trabalho de pesquisa foi instalado em casa de vegetação, na Fazenda Experimental Lageado, pertencente à Faculdade de Ciências Agronômicas - FCA, Campus de Botucatu/UNESP, localizada no município de Botucatu-SP, latitude 22º 51'S, longitude 48º 26'W Grw, e altitude de 740 m em casa de vegetação de polipropileno. Foram realizados dois experimentos com o delineamento experimental inteiramente casualizado, composto pelo controle (somente água residuária sem plantas) e por três espécies de plantas macrófitas aquáticas flutuantes: Eichhornia crassipes (Aguapé), Pistia stratiotes (Alface) e Salvinia auriculata (Salvínia) cultivadas em água residuária. Foram realizadas seis repetições, perfazendo-se 24 unidades experimentais, em cada experimento. No vegetal, foram realizadas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Contributing to the sustainable development within the proposal to use natural systems of low cost, in order to promote a clean and biological alternative, to know the physicochemical parameters that can influence the development of floating aquatic macrophytes is essential in the dynamics of these plants in the environment or in Artificial means. The objective of this work was based on the potential of three species of floating aquatic macrophytes Eichhornia crassipes, Pistia stratiotes and Salvinia auriculata in removing the chemical elements from Wastewater. The research work was carried out in a greenhouse at Experimental Lageado Farm, belonging to the Faculty of Agronomic Sciences - FCA, Campus Botucatu / UNESP, located in the municipality of Botucatu, Sao Paulo State, latitude 22º 51'S, longitude 48º 26'W Grw, And altitude of 740 m in a greenhouse of polypropylene. Two experiments were carried out in a completely randomized experimental design, composed of the control (only wastewater without plants) and three floating aquatic macrophyte species: Eichhornia crassipes (Aguapé), Pistia stratiotes (Lettuce) and Salvinia auriculata (Salvinia) cultivated in wastewater. Six replicates were performed, making up 24 experimental units in each experiment. In the plant, the evaluation of plant biomass potential, chemical plant analysis, efficiency of the use of chemical elements, accumulation of chemical elements, extraction of elements by plant mass, and in the effluent were carried out the chemical analysis of elements. The data were submitted to analysis of variance and Tukey test at 5% probability for the means obtained from the plant using the software SISVAR® and the Dunnett test at 5% for the means obtained from the data generated from the wastewater, Using the software Minitab® 16. The variables that showed significant interaction in the probability test f and the mean test did ... / Mestre

Orientador: Dagoberto Martins / Coorientador: Robinson Antonio Pitelli / Banca: Everlon Cid Rigobelo / Banca: Claudinei da Cruz / Banca: Gustavo Vitti Moro / Banca: Maria Renata Rocha Pereira / Resumo: As colonizações monoespecíficas ou pouco diversificadas de macrófitas e algas nos ambientes aquáticos, promovem impactos negativos ambientais, sociais e econômicos, com necessidade do uso de estratégias de manejo e, o químico tem se mostrado muito eficiente. Dentre as moléculas existente no mercado o uso do herbicida penoxsulam e dos compostos algicidas hidróxido de cobre, cloro (dicloro isocianurato de sódio di-hidratado) e peróxido de hidrogênio no controle das algas filamentosa Spirogyra e Pithophora sp. e seus efeitos para os organismos não alvos (Hyphessobrycon eques, Pomacea canaliculata, Lemna minor e Azolla caroliniana). Assim como a eficácia de produtosmencionados isolados e em mistura (penoxsulam+0,2% de hidróxido de cobre; penoxsulam+0,1% de cloro e penoxsulam+0,2% de peróxido de hidrogênio), no controle dasmacrófitas Ceratophyllum demersum, Egeria najas, Egeria densa e Hydrilla verticillatatem sido o objetivo desta pesquisa. O peróxido de hidrogênio foi o produto que promoveu a maior eficácia no controle das algas filamentosa (Spirogyra e Pithophora sp.) e médio risco ecotoxicológicopara os organismos não alvos. O hidróxido de cobre, cloro e peróxido de hidrogênio foram mais eficazes no controle do C. demersum, E. najas e E. najas, enquanto o penoxsulam isolado e em mistura (penoxsulam+0,1% de cloro) foram os promoveram maior controle da H. verticillata em condição de bioensaio. Enquanto o uso da mistura penoxsulam+0,2% de peróxido de hidrogênio em condição de mes... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The monospecific or poorly diversified colonies of macrophytes and algae in aquatic environments, promote negative environmental, social and economic impacts, with the need to use management strategies, and the chemical has been very efficient. Among the molecules on the market the use of the herbicide penoxsulam and the algicide compounds copper hydroxide, chlorine (sodium dichloro isocyanurate dihydrate) and hydrogen peroxide in the control of filamentous algae Spirogyra and Pithophora sp. and its effects on non-target organisms (Hyphessobrycon eques, Pomacea canaliculata, Lemna minor and Azolla caroliniana). As well as the efficacy of the mentioned products isolated and in mixture (penoxsulam + 0.2% of copper hydroxide, penoxsulam + 0.1% of chlorine and penoxsulam + 0,2% of hydrogen peroxide), in the control of macrophytes Ceratophyllum demersum, Egeria najas, Egeria densa and Hydrilla verticillata have been the objective of this research. Hydrogen peroxide was the product that promoted the highest effectiveness in the control of filamentous algae (Spirogyra and Pithophora sp.) and medium ecotoxicological risk for non-target organisms. Copper hydroxide, chlorine and hydrogen peroxide were more effective in the control of C. demersum, E. najas and E. najas, while penoxsulam alone and in the mixture (penoxsulam + 0.1% of chlorine) were the ones that promoted greater control of H. verticillata in bioassay condition. While the use of the penoxsulam + 0.2% of hydrogen peroxide ... (Complete abstract click electronic access below) / Doutor

Made available in DSpace on 2014-06-11T19:30:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-11-18Bitstream added on 2014-06-13T19:40:36Z : No. of bitstreams: 1 leung_r_dr_rcla.pdf: 1545935 bytes, checksum: 392e9cf661ed29a1efe4f5cf02fdf7f3 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O objetivo deste trabalho foi estudar a distribuição das macrófitas aquáticas em rios da planície costeira da bacia do rio Itanhaém. A abordagem adotada foi uma combinação de estudos observacionais e experimentais. No primeiro capítulo, estudou-se a distribuição das macrófitas aquáticas em relação a variáveis ambientais da água e do sedimento em 97 km de rios em duas estações do ano (verão e inverno). A salinidade foi a principal variável ambiental responsável pela separação das macróf5tas aquáticas em duas comunidades distintas, a do estuário e a dos rios. As principais espécies que ocorreram no estuário foram Spartina alterniflora. Crinum procerum e Scirpus califhrnicus, sendo que a primeira ocorreu em trechos de maior salinidade, a segunda em trechos com salinidade intermediária e a última em trechos de menor salinidade. As espécies de água doce mais freqüentes foram Egeria densa, Eichhornia azurea, Eichhornia crassipes. Pistia stratiotes, e Salvínia molesta. Egeria densa tendeu a ocorrer em trechos com maior transparência. menor nitrogênio total e maior fração areia no sedimento. Eichhornia azurea tendeu a ocorrer em locais com alta transparência e baixas concentrações de nitrogénio total. Finja siratiotes tendeu a ocorrer em trechos de rios com maiores concentrações de nitrogênio total na água. A freqüência de ocorrência das principais espécies não diferiu entre o verão e o inverno, provavelmente devido a ausência de uma estação seca. No segundo capítulo, se estudou a ocorrência das macrófitas aquáticas em função da vegetação ciliar e da morfologia de canal em três trcchos distintos de rios. No estuário do rio ltanhaém. a ocorrência de macrófitas aquáticas emergentes foi correlacionada com o sombreamento das árvores de mangue e a declividadc da área litorânea... . / The aim of this research was to study the distribution of aquatic macrophytes in coastal piam rivers of ltanhaém basin. lhe research approach was based on observational and experimental studies. In the first chapter, the distribution of aquatic macrophyte was correlated to water and sediment environmental variables in 97 km of rivers and in two periods (summer and winter). Salinity was the most important environmental variable to separate the aquatie rnacrophytes in two distinct communities: estuarine and freshwater communities. The main species found in the estuary were Spartina alterniflora, Crinum procerum and Scirpus califohiicus. lhe first species was found in water with higher salinity, the second in water with intermediate salinity and the Iatter in less saline water. lhe most frequent &eshwater species were Egeria densa, Eichhornia azurea, Eichhornia crassipes, Pistia strarioles and Sal Wnia molesta. Egeria densa tended to be present in river sections with high water transparence. low total nitrogen, and high sand fraction in sediment. Eichhornia azurea tended to occur in sections with high water transparence and low total nitrogen. Pistia stratiotes tendecl to occur in river sections with high total nitrogen. lhe &equency of occurrence aquatic macrophyrtes did not significantly differed hetween sunimer and winter. due probably to the absence of a dry season. In the second chapter, we investigated the influence of riparian vegetation and stream channel morphology on aquatie rnacrophyte distribution in three streams with dstinguished landscape. In the estuary of ltanhaëm River, the occurrence of emergent rnacrophytes was correlated with mangrove shading and slope of littoral region. In Preto River... (Complete abstract, click electronic address below).

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-08-25T12:54:34Z No. of bitstreams: 1 PDF - Thainá Alves Lycarião.pdf: 852519 bytes, checksum: 636ecf5fa1e6e551257df1fb958919b3 (MD5) / Made available in DSpace on 2016-08-25T12:54:34Z (GMT). No. of bitstreams: 1 PDF - Thainá Alves Lycarião.pdf: 852519 bytes, checksum: 636ecf5fa1e6e551257df1fb958919b3 (MD5) Previous issue date: 2015-02-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Understanding the dynamics of ecosystems in semiarid regions with dry and wet extremes may help elucidate issues related to the existing pattern of interaction in these environments, and these relationships can affect the ecological interactions of organisms present in the water body. Thus, this study aimed to determine the abiotic variables that act in development of Najas arguta (Kunth) and Egeria densa (Planch), highlighting how these variables influence the relationship of the two submerged macrophytes in a reservoir in semiarid region. N arguta biomass data and E. densa were obtained in six stands, located three out of the reservoir shoreline. In each stands is selected parcels 100x50 meters, which have been measured abiotic data and collected plants through cross hooks (cor er ) 0.5m in diameter (n = 4) at depths 1m, 2m and 3m. Analysis of Variance (ANOVA) factor a + b was used to test the seasonal and spatial variation of stands and environmental variables, linear regression analysis was used to understand the dependence of N. arguta and E. densa . Generalized Linear Models (GLM) were used to select environmental variables that explain the occurrence of N. arguta , E. densa and its relationship (Najas:Egeria ). Abiotic data showed low coefficients of temporal variation (<30%) due to continued drought conditions. N. Arguta presented a variation of biomass between the months of August / 13 and April / 14, with totals of 25.67 g.m-² and 1.06 g.m-², respectively. While E. densa maintained high biomass in the entire study period. The submerged plants had different niches, showing that E. densa competition relationship with N. arguta . The predictive model for biomass of N. arguta showed that physical and chemical variables had more influence in their biomass, whereas physical, chemical and climatic variables were related more to the biomass of E. densa . The relationship Najas Egeria was influenced by conductivity, total dissolved solids and nitrite. For presenting adaptations to the conditions of the reservoir, E. densa kept his high biomass, occupying more favorable niches and suppressing the development of N. arguta . / Entender a dinâmica dos ecossistemas em regiões do semiárido que apresentam extremos de seca e cheia pode ajudar a elucidar questões relacionadas ao padrão de interação existentes nesses ambientes, bem como essas relações podem afetar nas interações ecológicas dos organismos presentes no corpo aquático. Desta forma, o presente trabalho teve como objetivo determinar as variáveis abióticas que atuam no desenvolvimento de Najas arguta (Kunth) e Egeria densa (Planch), ressaltando como estas variáveis influenciam na relação das duas macrófitas submersas em um reservatório no semiárido. Dados de biomassa de N. arguta e E. densa foram obtidos em seis bancos, localizados três em cada margem do reservatório. Em cada selecionou-se parcelas 100x50 metros, onde foram medidos dados abióticos e coletados plantas através de ganchos de 0,5m de diâmetro (n=4), nas profundidades 1m, 2m e 3m. banco Análise de Variância (ANOVA) fatorial a+b foi utilizada para testar a variação sazonal e espacial dos bancos e das variáveis ambientais, análise de regressão linear foi utilizada para entender a relação de dependência de N. arguta e E. densa . Modelos Lineares Generalizados (GLM) foram utilizados para selecionar as variáveis ambientais que explicam a ocorrência de N. arguta , E. densa e sua relação (Naja s:Egeria ). Os dados abióticos apresentaram baixo coeficiente de variação temporal (<30%) devido à manutenção da condição de estiagem. N. arguta apresentou variação de biomassa entre - - os meses de agosto/13 e abril/14, com valores totais de 25.67 g.m ² e 1.06 g.m ², respectivamente. Enquanto que E. densa manteve biomassa alta em todo período estudado. As macrófitas submersas apresentaram nichos diferenciados, mostrando haver uma competição de E. densa em relação N. arguta . O modelo preditivo para a biomassa de N. arguta mostrou que variáveis físicas e químicas tiveram mais influencia na sua biomassa, enquanto que variáveis físicas, químicas e climatológicas se relacionaram mais com a biomassa de E. densa . A relação de Najas:Egeria foi influenciada pela condutividade, sólidos totais dissolvidos e nitrito. Por apresentar adaptações condições do reservatório, E. densa manteve sua biomassa alta, ocupando nichos mais às favoráveis e suprimindo o desenvolvimento de N. arguta.

Orientador: Silvano Bianco / Coorientador: Robinson Antonio Pitelli / Banca: Dagoberto Martins / Banca: Silvia Patrícia Carraschi de Oliveira / Resumo: O crescimento excessivo de macrófitas e algas nos ambientes aquáticos, decorrentes das atividades urbanas e industriais, prejudicam a utilização dos corpos hídricos e os usos múltiplos da água. A aplicação de um herbicida associado a um produto algicida pode apresentar melhor eficácia no controle de macrófitas e algas. O objetivo desta pesquisa foi avaliar a eficácia do diquat, oxicloreto de cobre, hidróxido de cobre e as associações diquat + 0,1% oxicloreto de cobre e diquat + 0,1% hidróxido de cobre no controle da macrófita aquática submersa Ceratophyllum demersum L., da alga unicelular Ankistrodesmus gracilis e da alga filamentosa Pithophora kewesis e estimar a toxicidade aguda (CL50/CE50) para os organismos não alvos Hyphessobrycon eques, Pomacea canaliculata, Lemna minor e Azolla caroliniana. Para o controle de C. demersum as associações diquat + 0,1% de oxicloreto de cobre e diquat + 0,1% de hidróxido de cobre foram mais eficazes, para A. gracilis as fontes de cobre oxicloreto e hidróxido de cobre isoladas foram mais eficazes enquanto que, para P. kewesis os produtos químicos testados não foram eficazes. A macrófita aquática L. minor foi o bioindicador mais sensível aos produtos químicos testados e o peixe H. eques o menos sensível / Abstract: The excessive growth of weeds and algae in aquatic environments, arising from urban and industrial activities, hinder the multiple uses of water. The application of an herbicide associated with an algaecide product may be more effective in controlling weeds and algae. The objective of this research were to evaluate the effectiveness of diquat, copper oxychloride, copper hydroxide and the associations diquat + 0.1% copper oxychloride and diquat + 0.1% copper hydroxide in control of the submerged aquatic macrophyte Ceratophyllum demersum, unicellular algae Ankistrodesmus gracilis and the filamentous algae Pithophora kewesis and to estimate the acute toxicity (LC50/EC50) for non-target organisms Hyphessobrycon eques, Pomacea canaliculata, Lemna minor and Azolla caroliniana. For C. demersum control the associations diquat + 0.1% copper oxychloride and Diquat + 0.1% copper hydroxide were more effective.For A. gracilis control the copper oxychloride and copper hydroxide were more effective if applicated individually and none of the tested chemicals were effective on P. kewesis control. The macrophyte L. minor was the most sensitive bioindicator to the tested chemicals and the fish H. eques was the least sensitive / Mestre

In Taiwan, more than 20% of the major rivers are mildly to heavily pollute by domestic, industrial, and agricultural wastewaters due to the low hook-up rate of public underground sewerage systems in rural areas. Thus, constructed or engineered wetlands have been adopted as the major alternatives to cleanup polluted rivers. Constructed wetlands are also applied as the tertiary wastewater treatment systems to polish the secondary wastewater effluents to meet water reuse standards with lower operational costs. The studied Kaoping River Rail Bridge Constructed Wetland (KRRBCW) is the largest constructed wetland in Taiwan. It is a multi-function wetland and is used for polluted creek water purification and secondary wastewater polishment before they discharge into the Kaoping River. Although constructed wetlands are feasible for contaminated water treatment, wetland sediments are usually the sinks of organics and metals. In this study, water, sediment and macrophytes samples were collected from the major wetland basins in KRRBCW. The quarterly investigation (from 2007 to 2009) results show that more than 97% of total coliforms (TC), 55% of biochemical oxygen demand (BOD), and 30% of nutrients [e.g., total nitrogen (TN), total phosphorus (TP)] were removed via the constructed wetland system. However, results from the sediment analyses show that wetland sediments contained high concentrations of metals (e.g., Cu, Fe, Zn, Cr, and Mn), organic contents (sediment oxygen demand = 1.7 to 7.6 g O2/m2-d), and nutrients (up to 18.7 g/kg of TN and 1.22 g/kg of TP). Thus, sediments should be excavated periodically to prevent the release the pollutants into the wetland system and causing the deterioration of wetland water quality. Results of polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), and nucleotide sequence analysis reveal that an increase in microbial diversities in the wetland systems was observed. Results from the DGGE analysis indicate that all sediment samples contained significant amounts of microbial ribospecies, which might contribute to the carbon degradation and nitrogen removal. Gradually disappearing of E. coli was also observed along the flow courses through the natural attenuation mechanisms. The factor analysis of SPSS 12.0 shows that 17 water-quality items of the study site could obtain four to six principal components, including nitrate factor, phosphorus factor, eutrophication factor, organic factor, and environmental background factor, the major influencing components are nutrition factor and eutrophication factor. The ponds of the study site were classified into two or three clusters depend on in-and-out flow location. This study attempted to establish a forecasting model of wetland pollutants concentration through the time series (ARIMA), results show that the outcome of the B7 pond was better than others. Results indicate that the ARIMA model can be used to simulate the trend of treatment efficiency using the wetland system. Experience and results obtained from this study would provide solutions for water quality control. Thus, the wetland system has a significant effect on water quality improvement and is capable of removing most of the pollutants from the local drainage system before they are discharged into the downgradient water body. Other accomplishments of this constructed wetland system include the following: providing more green areas along the riversides, offering more water assessable eco-ponds and eco-gardens for public, and rORPabilitating the natural ecosystem. The Kaoping River Rail Bridge Constructed Wetland has become one of the most successful multi-function constructed wetlands in Taiwan. The experience obtained from this study will be helpful in designing similar natural treatment systems for river water quality improvement and wastewater treatment.

Abstract Constructed wetlands can be treated as a imulated natural treatment system,which use solar adiation as the source of energy. By analogy with some removalmechanisms in natural wetlands, constructed wetlands are able to transform and remove pollutants from the wastewater. Other features provided by the constructed wetland include wildlife support, hydrologic odification, erosion protection, and open space and aesthetics. It has been applied for domestic wastewater purification for decades. The goal of this study was to evaluate the ffectiveness of using constructed wetlands on industrial wastewater treatment. In this study, grit chamber and furnace waste from steel-making were used as the media for plant growth. Two -tank (dimension for each tank: 4L ¡Ñ1W ¡Ñ1H) system was designed and constructed to simulate the constructed wetland. Reed and cattail were planted in the first and second tanks, respectively. In the system, media in the first and second tanks were filled to a height of 0.4 m (furnace waste from steel-making) and 0.1 m (waste grit), respectively. The depth of water was maintained at 0.3 m. The hydraulic retention time was approximately 5 days. The following parameters were analyzed during the operational period: nutrients, chemical oxygen demand (COD), suspended solids (SS), and biochemical oxygen demand (BOD). The calculated removal rates (g/m2/day) in the first tank were¡GCOD 5.92¡Ó0.64¡BBOD 3.48¡Ó0.95¡BSS (suspended solids) 3.42¡Ó1.44¡BTKN (total kjedal nitrogen, TKN) 0.94¡Ó0.26¡BTP (total phosphorus) 1.33¡Ó0.2¡CThe removal rates (g/ m2/day) in the second tank were: COD 5.17¡Ó0.62¡BBOD 3.21¡Ó0.92¡B SS 2.92¡Ó1.29¡BTKN 0.59¡Ó0.21¡BTP 0.66¡Ó0.15. Results from this study indicate that the media and plants in both tanks created a biofiltration system for microbial growth and pollutant removal. Sorption and biodegradation were the two major pollutant removal mechanisms in the system. During the operational period, the average removal efficiencies (%) in the first tank were: COD 55~62, BOD 73~90, SS 66~84, TKN 36~66, TP 28~39. The average removal efficiencies (%) in the first tank were: COD 49~54, BOD 73~83, SS 45~69,TKN 15~43, TP 9~24.

In this literature review the characteristics of two free-floating macrophytes, water hyacinth   (Eichhornia crassipes) and duckweed (Lemna sp.), and two microalgae, Chlorella and Scenedesmus, have been examined regarding their suitability as efficient nutrient removers in the treatment of wastewater with high levels of nutrients and suspended solids from a biogas plant in Loudden. The needs required for the plants to be able to grow in wastewater and the amounts of biomass they can produce have also been studied. The results show that Chlorella is capable of a very high uptake of nutrients in photobioreactors with high nutrient loadings. With an ammonia uptake maximum value at 10900mg/m2/d Chlorella outshines the other organisms in this study. The test organism that performed the closest to Chlorella in terms of nitrogen uptake was water hyacinth with an uptake about 1602mg/m2/d. One factor affecting nutrient uptake in a positive way is the growth rate. Free-floating macrophytes produce more biomass than algae do, and water hyacinth have been shown to be the most productive. It is important to conduct a regular harvest of the plants if a high production should be maintained. High quantity of biomass per unit area can inhibit the growth, and algae are more sensitive to this than the macrophytes often suffering from self-shading when the density is too high. The high level of nutrients in the wastewater prevents growth and dilution is required to achieve any growth at all. Therefore, conventional treatment methods might prove to be a better option.

The phytotoxicities of monensin, the 10:2 saturated fluorotelomer carboxylic acid (10:2 FTCA), and atrazine to freshwater macrophytes were investigated in three microcosm-based assessments. Both responses of plants grown as individuals in “cone-tainers” and those grown in mixed and monocultures were examined to permit comparison of the toxicological sensitivities of macrophytes under each planting design, and investigation of whether interactions between neighbours may modify plant response to an environmental contaminant. Exposures of monensin and the 10:2 FTCA at environmentally relevant concentrations were found to produce few significant effects in the higher aquatic plants across all growth conditions, thus direct comparisons of effective concentrations were not conducted. Significant differences between relative growth rates (RGR) of plant grown in assemblages versus individually indirectly indicate that over longer exposure durations toxicity may be underestimated using the individual “cone-tainer” method. RGRs and sensitivities of plants to atrazine were found to be in the same range across planting methods, demonstrating that responses of aquatic plants in the individual-test system reflected those observed in model populations and two-species communities. A lack of observed relations between plants in the mixed and monoculture tests, however, meant that the potential for modification of toxicity through plant interactions was not investigated.

This experiment manipulated water levels in boreal marshes within the Saskatchewan River Delta, a 9500 km2 region in northern Canada. Water levels in three wetland cells were lowered in a partial drawdown by a mean of 0.32 m. Water clarity, nutrient concentrations, and periphyton nutrient limitation were measured over the summer preceding and the summer following manipulation. The water levels of three adjacent control wetlands were not manipulated. Lowering wetland water levels reduced the wind velocity necessary to resuspend bottom sediments, which led to increases in turbidity, dissolved organic carbon, and concentrations of organic and inorganic nitrogen and phosphorus. Prior to drawdown, wetland periphyton communities were limited by nitrogen or co-limited by nitrogen and phosphorus. The input of nutrients from the sediment resulted in a shift from nutrient deficiency to nutrient sufficiency. Periphyton and phytoplankton production increased in response to the nutrient input. Increased turbidity, nutrient concentrations, and algal production were correlated with depth, rather than being inherent to the drawdown condition. Other water level manipulation studies have found that a reflood after a period of total drawdown caused a pulse of nutrients leaching from decomposing litter. This work suggests that these changes may not require complete drying out of sediments, or the input of large amounts of litter from drowned annual mudflat species, but rather can occur when depths are shallow enough that sediments are more frequently resuspended by wind. These findings have implications for future management of these marshes for waterfowl and muskrat production.