Characterization of turbidity in Florida's Lake Okeechobee and Caloosahatchee and St. Lucie Estuaries using MODIS-Aqua measurements

This paper describes the use of ocean color remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite to characterize turbidity in Lake Okeechobee and its primary drainage basins, the Caloosahatchee and St. Lucie estuaries from 2002 to 2010. Drainage modification and agricultural development in southern Florida transport sediments and nutrients from watershed agricultural areas to Lake Okeechobee. As a result of development around Lake Okeechobee and the estuaries that are connected to Lake Okeechobee, estuarine conditions have also been adversely impacted, resulting in salinity and nutrient fluctuations. The measurement of water turbidity in lacustrine and estuarine ecosystems allows researchers to understand important factors such as light limitation and the potential release of nutrients from re-suspended sediments. Based on a strong correlation between water turbidity and normalized water-leaving radiance at the near-infrared (NIR) band (nL_w(869)), a new satellite water turbidity algorithm has been developed for Lake Okeechobee. This study has shown important applications with satellite-measured nL_w(869) data for water quality monitoring and measurements for turbid inland lakes. MODIS-Aqua-measured water property data are derived using the shortwave infrared (SWIR)-based atmospheric correction algorithm in order to remotely obtain synoptic turbidity data in Lake Okeechobee and normalized water-leaving radiance using the red band (nL_w(645)) in the Caloosahatchee and St. Lucie estuaries. We found varied, but distinct seasonal, spatial, and event driven turbidity trends in Lake Okeechobee and the Caloosahatchee and St. Lucie estuary regions. Wind waves and hurricanes have the largest influence on turbidity trends in Lake Okeechobee, while tides, currents, wind waves, and hurricanes influence the Caloosahatchee and St. Lucie estuarine areas.     

The importance of biological oxidation of iron in the aerobic cells of the Wheal Jane pilot passive treatment system

The passive treatment system designed to treat the mine water discharge of the abandoned Wheal Jane tin mine in Cornwall consisted of a sequence of artificial wetland cells, an anaerobic cell and a final series of rock filters. Three systems were operated which differed only in the pre-treatment of the mine water before discharge to the aerobic wetland cells. The aerobic cells were designed to promote aerobic oxidation and precipitation of iron which could exceed a concentration of 100 mg/l in the raw mine water discharge. The largest investment of land area was to the artificial wetland cells and it was important to understand the processes of oxidation and precipitation of iron so that the performance of this aspect the pilot passive treatment plant (PPTP) could be managed as efficiently as possible. The generally low pH of the influent mine water and inevitable trend of decreasing pH due to hydrolysis of Fe(III) meant that distinguishing between biotic and abiotic mechanisms was fundamental for further design planning of passive treatment systems. This paper describes these observations.     

Adsorptive ozonation of 2-methylisoborneol in natural water with preventing bromate formation

This paper presents an application of our newly developed adsorptive ozonation process using a high silica zeolite adsorbent (USY) for drinking water treatment. First, the adsorption of 2-methylisoborneol (2-MIB) on USY in a river water/pure water mixture was clarified by a batch-type adsorption experiment. The results showed that 2-MIB was adsorbed on USY; however, almost all of the adsorbed 2-MIB was desorbed over time. The desorption rate was increased with the ratio of river water to pure water, indicating that compounds dissolved in the river water, such as natural organic matter (NOM), prevent the adsorption of 2-MIB on USY. Second, the ability of the river water to consume ozone was confirmed in an experiment using a USY-packed column reactor. The ozone consumption was obviously increased by the presence of USY, indicating that USY-adsorbing compounds dissolved in the river water (probably small size NOM) consumed the ozone. However, the rapid ozone consumption was occurred by 6-8 s in the retention times when 3.14-4.38 mgL(-1) of water dissolved ozone was fed, this rapid ozone consumption lasted no more than these times. This result revealed that the rapid consumption of ozone by the adsorptive compounds in our process could be avoided within a certain retention time (6-8 s; especially for the river water used in this study) when enough concentration of ozone (3.14 mgL(-1) or more; same above) was supplied. We therefore performed a trial in which 2-MIB dissolved in river water was continuously decomposed using a USY-packed column with various ozone concentrations. In the process, the adsorptive compound dissolved in the river water adsorbed and reacted with ozone in the parts of the apparatus upstream of the column, while the adsorption and decomposition of 2-MIB took place in the parts of the apparatus downstream of the column. This resulted in a sufficient 2-MIB decomposition with minimizing bromate ion formation.     

Fate of perchlorate-contaminated water in upflow wetlands

The potential of natural wetland systems to treat perchlorate-contaminated water was investigated in vertical upflow wetland columns planted with and without Bulrush (Scirpus sp.). In the absence of nitrate (NO3- -N <1mg/L), wetland columns were capable of removing ClO4- to levels below the detection limit (<4 microg/L) for a series of influent ClO4- (4, 8, 16, and 32 mg/L). At an influent ClO4- concentration of 32 mg/L, ClO4- breakthrough was observed with the increase in nitrate concentration. ClO4- and NO3- degradation rate constants (Kpc and KNO3- -N) were also determined using a 1-D transport model with dispersion. Kpc declined with the increase of influent ClO4- and NO3- -N concentration (6.49-0.42 day(-1) for unplanted columns, and 7.80-0.21 day(-1) for planted columns, respectively). KNO3- -N followed similar trends but was relatively higher than Kpc. Plant uptake was directly linked with ClO4- concentration in the rhizosphere, and the stem bio-concentration factor (BCF) was estimated to be 57. A mass balance indicated plant uptake accounted for 0-14.3% of initial ClO4- input. Microbial degradation played a more important role than plant uptake and transformation in ClO4- degradation in this wetland system. This study suggests that constructed wetlands may be a promising technology to treat perchlorate-contaminated waters.     

Phosphorus retention and sorption by constructed wetland soils in Southeast Ireland

It may be necessary to use constructed wetlands as a land use practice to mitigate phosphorus (P) loss from agriculture in Ireland. The objectives of this study were to determine the ability of two constructed wetland site soils to retain and sorb P. Intact soil/water column studies were used to determine P release/retention rates during a 30-day incubation period. Soil columns flooded with distilled water released P during the first 2 days; however, soluble reactive P (SRP) concentrations in overlying floodwaters decreased thereafter. Soils with overlying floodwaters spiked at 5 and 15 mg SRP L(-1) retained highest amounts of P (p < 0.05) with retention at these concentrations controlled by SRP in overlying waters. Retention rates by soils ranged between 0.3 and 60.9 mg Pm(-2) d(-1). Maximum P sorption capacity (Smax) was higher for wetland soils at Dunhill, Waterford (1464 mg P kg(-1)) in comparison to soils at Johnstown Castle, Wexford (618 mg P kg(-1)). Equilibrium P concentrations (EPC0) were low (in the microg SRP L(-1) range), indicating a high capacity of these soils to sorb P. Phosphorus sorption parameters were significantly related to ammonium oxalate extractable aluminium (Al) and iron (Fe) content of soils.     

A laboratory study of landfill-leachate transport in soils

Continuous flow experiments were conducted using sand-packed columns to investigate the relative significance of bacterial growth, metal precipitation, and anaerobic gas formation on biologically induced clogging of soils. Natural leachate from a local municipal landfill, amended with acetic acid, was fed to two sand-packed columns operated in upflow mode. Degradation of the influent acetic acid resulted in the production of methane and carbon dioxide, and simultaneous reduction of manganese, iron, and sulphate. Subsequent increase in the influent acetic acid concentration from 1750 to 2900 mg/l, and then to 5100 mg/l, led to rapid increase in the dissolved inorganic carbon, solution pH, and soil-attached biomass concentration at the column inlet, which promoted the precipitation of Mn(2+) and Ca(2+) as carbonate, and Fe(2+) as sulphide. An influent acetic acid concentration of 1750 mg/l decreased the soil's hydraulic conductivity from an initial value of 8.8 x 10(-3)cm/s to approximately 7 x 10(-5)cm/s in the 2-6 cm section of the column. Increasing the influent acetic acid to 5100 mg/l only further decreased the hydraulic conductivity to 3.6 x 10(-5)cm/s; rather, the primary effect was to increase the length of the zone experiencing reduced hydraulic conductivity from 0-6 cm to the entire column. As bioaccumulation was limited to the 0-5 cm section of the column, and the effect of metal precipitation was negligible, the reduction on the deeper sections of the column is attributed to gas flow, which was up to 1440 ml/day. Mathematical modelling shows that biomass accumulation and gas formation were equally significant in reducing the hydraulic conductivity, while metal precipitation contributed only up to 4% of the observed reduction.     

Pesticides in fluvial wetlands catchments under intensive agricultural activities

A survey on pesticides (73 compounds) in the Bay St. Fran?ois wetland and its catchment (part of the wetlands of Lake St. Pierre area [St. Lawrence River, Québec]) was achieved in 2006. The metabolites as well as the active ingredients of pesticides (11 compounds) were detected in the wetland and its catchment. This wetland ecosystem was active in the degradation of agricultural pesticides (e.g., atrazine). The measured pesticides were individually below the criteria for aquatic species in natural water, except chlorpyrifos. Overall, the pesticides lost from agricultural field towards the streams were <1% of the quantity applied. The environmental fates of the pesticides were found to vary according to the size of the watershed. Over large catchments, half-life times were important in terms of global loss from the agricultural lands to wetlands whereas over small catchments, soil organic carbon/water distribution coefficient (Koc) was an important term for pesticides losses to water system since half-life times were not limiting factors.     

Temporal and spatial variation of phosphate distribution in the sediment of a free water surface constructed wetland

This study was aimed at determining the spatial and temporal variation of P distribution in sediment of an artificial wetland for sewage and industrial wastewater treatment, and the fraction that is potentially involved in the P exchange processes. Influent, effluent, macrophytes and sediment at the inlet, middle and outlet areas were sampled over 24 months. The P-fractionation in sediment was performed following the EDTA method. Eichhornia crassipes and Typha domingensis removed P efficiently when cover was high, but E. crassipes caused anoxic conditions. The increase in cover of T. domingensis may contribute to attain oxic conditions and to improve P removal. When macrophytes are not present or when cover is low, sediment seems to increase removal efficiency. A significant increase in the concentration of the fraction of Fe(OOH) approximately P and mainly that of CaCO(3) approximately P can be observed at the inlet. High pH, Ca(2+) and CO(3)(-)(2) concentrations in the influent suggest that P co-precipitates together with CaCO(3). Therefore, it seems that CaCO(3) approximately P represents the main precipitating mechanism. However, mineralization of organic matter maintained the sediment at a pH range lower than the high values prevailing in the influent. CO(3)(-)(2) could undergo partial dissolution and the released i-P(diss) could be readsorbed onto the Fe(OOH) approximately P fraction. Since the environment for P retention (high pH, Fe, Ca and ionic concentrations) is largely provided by the influent, the wetland may be expected to continue retaining P as far as the composition of the influent is maintained and there are available adsorption sites in the sediment.     

Phosphorus in periphyton mats provides the best metric for detecting low-level P enrichment in an oligotrophic wetland

Growing concern over the ecological consequence of phosphorus (P) enrichment in freshwater wetlands has elicited considerable debate over the concentration of water column P associated with eutrophication. In the oligotrophic Everglades, the displacement of native communities by enriched ones is widespread and has occurred at sites experiencing only minimal elevations in P input. To help define regulatory criteria for P inputs to the Everglades, we constructed an experiment that mimics P input to the natural system by continuously delivering P at concentrations elevated 5, 15 and 30 microgl(-1) above ambient to 100-m long flow-through channels. We compared patterns of P accumulation in the water, periphyton, detritus and soils among the channel treatments and also along a 16 km transect from an enriched canal that inflows to the interior of the same marsh. Water column TP and SRP were unrelated to input TP concentration in both the experiment and the marsh transect. However, concentrations of TP in periphyton mats were significantly elevated at all levels of experimental enrichment and as far as 2 km downstream from water inputs into the marsh. Elevated periphyton TP was associated with significant loss of periphyton biomass. In oligotrophic wetlands, traditional measures of water column SRP and TP will substantially underestimate P loading because biotically incorporated P is displaced from the water column to benthic surfaces. Using periphyton TP as a metric of P enrichment is uncomplicated and analogous to pelagic TP assessments in lakes where most P is sequestered in phytoplankton.     

Effect of watershed parameters on mercury distribution in different environmental compartments in the Mobile Alabama River Basin, USA

Total mercury (THg) and mono-methylmercury (MeHg) levels in water, sediment, and largemouth bass (LMB) (Micropterus salmoides) were investigated at 52 sites draining contrasting land use/land cover and habitat types within the Mobile Alabama River Basin (MARB). Aqueous THg was positively associated with iron-rich suspended particles and highest in catchments impacted by agriculture. Sediment THg was positively associated with sediment organic mater and iron content, with the highest levels observed in smaller catchments influenced by wetlands, followed by those impacted by agriculture or mixed forest, agriculture, and wetlands. The lowest sediment THg levels were observed in main river channels, except for reaches impacted by coal mining. Sediment MeHg levels were a positive function of sediment THg and organic matter and aqueous nutrient levels. The highest levels occurred in agricultural catchments and those impacted by elevated sulfate levels associated with coal mining. Aqueous MeHg concentrations in main river channels were as high as those in smaller catchments impacted by agriculture or wetlands, suggesting these areas were sources to rivers. Elevated Hg levels in some LMB were observed across all types of land use and land cover, but factors such as shallow water depth, larger wetland catchment surface area, low aqueous potassium levels, and higher Chl a concentrations were associated with higher Hg burdens, particularly in the Coastal Plain province. It is suggested that the observed large variability in LMB Hg burdens is linked to fish displacement by anglers, differences in food web structure, and sediment biogeochemistry, with surficial sediment iron oxides buffering the flux of MeHg from sediments to deeper water pelagic food webs.     

Mercury and trace metal partitioning and fluxes in suburban Southwest Ohio watersheds

Many natural watersheds are increasingly affected by changes in land use associated with suburban sprawl and such alterations may influence concentrations, partitioning, and fluxes of toxic trace metals in fluvial ecosystems. We investigated the cycling of mercury (Hg), monomethylmercury, cadmium, copper, lead, nickel, and zinc in three watersheds at the urban fringe of Dayton, Ohio, over a 13-month period. Metal concentrations were related positively to discharge in each stream, with each metal having a high affinity for suspended particles and Hg also having a noticeable association with dissolved organic carbon. Although not observed for the other metals, levels of Hg in river water varied seasonally and among streams. Yields of Hg from two of the catchments were comparable to that predicted for runoff of atmospherically deposited Hg (∼25% of wet atmospheric flux), whereas the third watershed had a significantly greater annual flux associated with greater particle-specific and filtered water Hg concentrations, presumably from a point source. Fluxes of metals other than Hg were similar among each watershed and suggestive of a ubiquitous source, which could be either atmospheric deposition or weathering. Results of this study indicate that, with the exception of Hg being increased in one watershed, processes affecting metal partitioning and loadings are similar among southwest Ohio streams and comparable to other North American rivers that are equally or less impacted by urban development. Relative differences in land use, catchment area, and presence or absence of waste water treatment facilities had little or no detectable effect on most trace metal concentrations and fluxes. This suggests that suburban encroachment on agricultural and undeveloped lands has either similarly or not substantially impacted trace metal cycling in streams at the urban fringe of Dayton and, by extension, other comparable metropolitan areas.     

复合电极电吸附去除水中氟离子的研究

采用复合电极对用蒸馏水加氟化钠配制成的含氟水溶液进行了动态电吸附除氟实验,研究了不同电压、流量、初始浓度对氟离子去除的影响。实验结果表明:以复合电极为电极材料,采用电吸附方法可以有效地去除水中的氟离子,复合电极对氟离子的去除与所施加的电压、流量以及初始浓度都有一定的关系。增大电压,减小进水流量,降低氟离子的初始浓度,都可提高氟的去除率。     

Phosphorus concentrations in the River Dun, the Kennet and Avon Canal and the River Kennet, southern England

Variations in phosphorus (P) concentrations in an agriculturally impacted river draining a Chalk aquifer and an associated canal in the west of the Thames Basin, southern England are examined and linked to agricultural and sewage sources and within river/canal process controls. The study area comprises the River Dun, the adjacent River Kennet and the Kennet and Avon (K&A) Canal. Large seasonal variations are observed for soluble reactive phosphorus (SRP) and dissolved silicon (Si) with low concentrations in the spring and summer times when biological activity is high. The K&A Canal shows the largest SRP and Si concentration declines. This reflects high biological activity coupled with higher temperatures and higher water residence times. The extent of SRP removal is examined in relation to organic (uptake/release with phytoplankton growth/decay) and, to a lesser extent, inorganic (SRP coprecipitation with calcite) mechanisms. Boron (B) is used as a tracer of sewage sources. Agricultural inputs of both dissolved and particulate P (PP) can be important particularly under conditions where the catchment is wet and near surface/overland flow is important: sewage treatment works effluent and septic tank discharges to groundwater also probably provide a major component of the SRP occurring within the water column. The canal, and to a lesser extent the river, acts as sink for P in sewage effluent sources due to the high biological activity especially during the spring and summer. The aquifer probably acts as a major sink for agricultural and septic tank inputs of P.     

人工湿地系统处理污染河水的填料选配

选择不同的建筑废弃物作为主填料构建了4套人工湿地的中试系统，进行了人工湿地的填料选配研究。结果表明，以等体积掺混废砖块和废陶获得的混合填料构建的人工湿地系统，在处理含高浓度和低浓度有机污染物的河水时均表现出良好的除污效果。其在进水COD和氨氮浓度分别为40～70mg／L和10～35mg／L的情况下，对COD和氨氮的平均去除率分别达40％和56％；在进水COD和氨氮浓度分别为15～30mg／L和0．3～3mg／L的情况下，COD和氨氮的平均去除率分别为25％和70％。建筑废弃物混合填料来源丰富、成本低廉，对于处理水质季节性变化很大的污染河水，人工湿地系统具有良好的适应性。     

表面流人工湿地提升河道水体感官品质研究

采用黄菖蒲表面流人工湿地处理河道水体,探究表面流湿地在三个水深(25、45、65cm)条件下对河道水感官品质提升效果的影响。结果表明,黄菖蒲湿地出水浊度由35 NTU降至5NTU以下,色度由23度降至1度以下,透明度由35 cm提升至160 cm以上,且河道进水TN和TP均得到有效削减。在水深为45 cm时,湿地出水感官品质较好,营养盐去除率较高,因此选择45 cm为表面流湿地最佳水深。在此水深条件下,对湿地进出水进行粒径分析、三维荧光分析可知,河道水体中的颗粒粒径范围较广,且颗粒粒径较大,而湿地出水中颗粒物粒径基本小于1 100 nm。原水色度较高时,原水中富里酸和类蛋白的含量较高,在湿地出水中这些物质得到了较好的削减。综合粒径分析、三维荧光分析得到,20株/m2是本研究中黄菖蒲湿地的最佳种植密度。     

Heat flux through a geothermally heated fluidized bed at the bottom of a lake

Heat fluxes and the underground inflow through a natural fluidized bed within the main sub-basin of Lake Banyoles are studied and parameterized. In the upper part of this fluidized bed, at a depth of about 30 m, the vertical gradients of particle concentration and temperature are very sharply located within an interface a few centimeters thick. Within this interface (lutocline), the depths where the temperature and the concentration gradients are maximum match exactly. On the other hand, the lutocline determines a flat, horizontal surface dividing the water column into a hot, turbid medium at the bottom and clear, colder, bulk water above. Through this interface the flow regime also varies from being laminar just below it, to turbulent due to convective processes developing above it. More precisely, in studied main sub-basin a buoyant plume develops above the lutocline, as a result of the heat flux, and affects the lake's water quality due to particles dragged along by it. In this paper it is proposed to determine the temperature at the depth of maximum gradient within the interface by means of measured temperature profiles, and consider the stationary heat transport equation in the laminar region below it, in order to obtain the water velocity and the heat flux. Heat flux parameterization is given based on a large number of thermal high-resolution profiles, covering six campaigns in different years and seasons. Furthermore, and in consideration of the fact that high-resolution thermal profiles are not always available, some alternative parameterizations for the heat flux are presented based only on the temperature of the fluidized bed and that of the lower hypolimnion.     

Modelling of the long term fate of pesticide residues in agricultural soils and their surface exchange with the atmosphere: Part I. Model description and evaluation

Sources of pesticides in the atmosphere can be releases of new material through current use, or emission/reemission from soil residues resulting from historical use. It is the latter aspect, soil residues, that is the focus of this study. This paper describes the application of a simple coupled atmosphere-soil pesticide exchange model that can assist in the interpretation of soil residue and air concentration measurements, and in the projection of short period field measurements to larger spatial scales and longer time periods. Only dry gaseous exchange (emission and deposition) between bare agricultural lands and the atmosphere is modelled. Wet deposition and particle associated deposition of pesticide are not included. Model results are compared with published co-located air and soil pesticide concentration measurements made on agricultural lands in the southern U.S. that have soil residues of lindane and the following six highly persistent pesticides: cis-, trans-chlordane, p,p'-DDE, dieldrin, trans-nonachlor and toxaphene. The study results show: (i) that measured air concentrations of toxaphene and p,p'-DDE above agricultural soils in the southern U.S. can be attributed to emissions due to local soil residues of these pesticides rather than to the regional background air concentrations; (ii) that both soil emissions and background air concentrations of dieldrin contribute significantly to the measured air concentrations; (iii) that measured air concentrations of cis- and trans-chlordane as well as trans-nonachlor and lindane are mainly due to the regional background with little contribution from local soil residues. An analysis of modelled summer day and night average soil-air exchange fluxes shows that toxaphene and p,p'-DDE soil residues are strong sources of emission to the atmosphere during both the day and night while the chlordanes, trans-nonachlor, lindane and dieldrin are deposited from the atmosphere to the soil during the night hours and emitted to the atmosphere during the day time. This result illustrates the model's capability to simulate the processes that lead to the 'grasshopper' effect whereby persistent pesticides in soils can be transported in the atmosphere by successive periods of emission and deposition to terrestrial surfaces. In the second part to this paper, the model is used to study the trends of pesticide residues and air concentrations over a twenty year period.     

A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Diagnostic and sensitivity analyses

A deterministic mass balance model for nutrient and phytoplankton dynamics was previously developed and calibrated to a comprehensive set of field data for Lake Okeechobee. In the present study, diagnostic and sensitivity analyses were conducted with the calibrated model to better understand factors controlling phytoplankton and load-response dynamics in the lake. Phytoplankton growth rate limitation due to underwater light attenuation appears to be substantially greater than growth rate limitation due to non-optimal phosphorus concentrations. Phytoplankton biomass appears strongly controlled by the supply rate of dissolved available phosphorus to the water column. The dynamics of total phosphorus and chlorophyll a concentrations in the lake are strongly influenced by sediment-water phosphorus fluxes. There is a wide range of uncertainty in responses of total phosphorus and cholorophyll a concentrations to changes in tributary phosphorus loadings. Much of this uncertainty is due to a lack of quantitative understanding of sediment responses to changes in tributary loadings. Other important factors are inter-annual variability in hydrometeorological conditions and the potential influence of wind-induced resuspension of particulate phosphorus. Responses of total phosphorus and chlorophyll a concentrations for a given change in tributary loading depend not only on the magnitide of the loading change, but also on the time frame after the loading change due to a lag in sediment response. Load-response predictions for Lake Okeechobee must take into account changes in available phosphorus loadings to the water column, and must be premised on assumptions for changes in internal phosphorus loadings from the sediments. Results from this preliminary modeling analysis are provisional in that they do not include potential nitrogen limitation, potential interactions between phosphorus and nitrogen, or phytoplankton responses to potential nitrogen fixation.     

Changes in agricultural landscape pattern and its spatial relationship with forestland in the State of Selangor, peninsular Malaysia

In Malaysia, the development of two major agricultural crops, i.e. oil palm and rubber, is one of the primary causes of forest loss. However, understanding of this relationship has not been quantified, which is vital to improve the planning and management of the agricultural land uses. To understand the relationship, this study addresses their dynamic change, patchiness and spatial relationship with forestland in the State of Selangor, Malaysia as a case study. Data development and analysis were based on three land-use maps of 1966, 1981 and 1995 where forest and, wetland forest and marshland land use categories were referred to as forestland. Two defined natural landscapes; forest and wetland landscapes were used as a basic unit of analysis to determine the patchiness of the agricultural lands at the expense of large tract of forestland. During the periods studied, oil palm area increased whereas rubber area reduced. The development of oil palm had caused loss much of forestland, particularly wetland forest and marshland. Its expansion at the expense of large tract of wetland forest and marshland earnestly occurred between 1966 and 1981 but slowed down between 1981 and 1995. By using the landscape type approach this study recommended a way to determine the patchiness of the agricultural lands at the expense of large tract of forestland. With these findings, we conclude that it is important to understanding the relationship quantitatively in order to describe the implications for land development of the agricultural crops.     

Atrazine mineralization potential in two wetlands

The fate of atrazine in agricultural soils has been studied extensively but attenuation in wetland systems has received relatively little attention. The purpose of this study was to evaluate the mineralization of atrazine in two wetlands in central Ohio. One was a constructed wetland, which is fed by Olentangy River water from an agricultural catchment area. The other was a natural fen (Cedar Bog) in proximity to atrazine-treated cornfields. Atrazine mineralization potential was measured by 14CO2 evolution from [U-ring-14C]-atrazine in biometers. The constructed wetland showed 70-80% mineralization of atrazine within 1 month. Samples of wetland water that were pre-concentrated 200-fold by centrifugation also mineralized 60-80% of the added atrazine. A high extent of atrazine mineralization (75-81% mineralized) was also associated with concentrated water samples from the Olentangy River that were collected upstream and downstream of the wetland. The highest levels of mineralization were localized to the top 5 cm zone of the wetland sediment, and the activity close to the outflow at the Olentangy wetland was approximately equal to that near the inflow. PCR amplification of DNA extracted from the wetland sediment samples showed no positive signals for the atzA gene (atrazine chlorohydrolase), while Southern blots of the amplified DNA showed positive bands in five of the six Olentangy wetland sediment samples. Amplification with the trzD (cyanuric acid amidohydrolase) primers showed a positive PCR signal for all Olentangy wetland sediment samples. There was little mineralization of atrazine in any of the Cedar Bog samples. DNA extracted from Cedar Bog samples did not yield PCR products, and the corresponding Southern hybridization signals were absent. The data show that sediment microbial communities in the Olentangy wetland mineralize atrazine. The level of activity may be related to the seasonality of atrazine runoff entering the wetland. Comparable activity was not observed in the Cedar Bog, perhaps because it does not directly receive agricultural runoff. Qualitatively, the detection of the genes was associated with measurable mineralization activity which was consistent with the differences between the two study sites.