Paul V. Zimba

Remote Sensing Techniques to Assess Water Quality

Remote sensing techniques can be used to monitor water quality parameters (i.e., suspended sediments (turbidity), chlorophyll, and temperature). Optical and thermal sensors on boats, aircraft, and satellites provide both spatial and temporal information needed to monitor changes in water quality parameters for developing management practices to improve water quality. Recent and planned launches of satellites with improved spectral and spatial resolution sensors should lead to greater use of remote sensing techniques to assess and monitor water quality parameters. Integration of remotely sensed data, GPS, and GIS technologies provides a valuable tool for monitoring and assessing waterways. Remotely sensed data can be used to create a permanent geographically located database to provide a baseline for future comparisons. The integrated use of remotely sensed data, GPS, and GIS will enable consultants and natural resource managers to develop management plans for a variety of natural resource management applications.

A PCR‐BASED TEST TO ASSESS THE POTENTIAL FOR MICROCYSTIN OCCURRENCE IN CHANNEL CATFISH PRODUCTION PONDS1,2

Microcystis aeruginosa is a common form of cyanobacteria (blue‐green algae) capable of forming toxic heptapeptides (microcystins) that can cause illness or death. Occasionally, blooms of cyanobacteria have caused toxic fish‐kills in catfish production ponds. We have developed a PCR test that will detect the presence of microcystin‐producing cyanobacteria. Microcystin producers are detected by the presence of the microcystin peptide synthetase B gene (an obligate enzyme in the microcystin pathway), which appears to be present only in toxin‐producing cyanobacteria. These PCR amplifications can be performed in multiplex using purified DNA from pond waters or by two‐stage amplification from native water samples. A synoptic survey of 476 channel catfish production ponds from four states in the southeastern United States revealed that 31% of the ponds have the genetic potential to produce microcystins by toxic algae.

EVALUATING THE RELATIONSHIP BETWEEN PHOTOPIGMENT SYNTHESIS AND 2-METHYLISOBORNEOL ACCUMULATION IN CYANOBACTERIA

 The relationship between photopigments and the terpene‐derived secondary metabolite, 2‐methylisoborneol (MIB), was analyzed in photoacclimated cultures of Pseudanabaena articulata Skuja throughout growth, during the diel cycle, and following chemical‐induced inhibition of the isoprenoid pathway. Accumulation of MIB coincided with the accumulation of lipophilic and phycobilin pigments during the early to mid‐exponential portion of the growth cycle with the greatest accumulation of MIB during the late‐exponential phase. Cellular release of MIB occurred as culture populations entered mid‐ to late‐logarithmic phase of growth and was greatest in irradiance‐stressed cultures. The greater correspondence of MIB accumulation with photopigments was seen in cultures transferred from a 12:12 h LD photoperiod alone and the consistent relationship between MIB and photopigment accumulation under varying irradiance suggested a photopigment‐dependent regulation for MIB synthesis. However, the consistent allocation of carbon into MIB during instances of phytofluene and tetrapyrrole biosynthetic inhibition within P. articulata and Oscillatoria perornata Skuja indicated that MIB accumulation is not limited by isopreniod‐carbon availability and does not appear to serve as an “overflow” product. Rather, MIB accumulation simply appears to reflect overall carbon accumulation resulting from increased cell metabolism.

A synoptic survey of musty/muddy odor metabolites and microcystin toxin occurrence and concentration in southeastern USA channel catfish (Ictalurus punctatus Ralfinesque) production ponds

Abstract A synoptic profile was conducted in July–August 2000 to assess the occurrence of off-flavor compounds beta -cyclocitral, 2-methylisoborneol (MIB), and geosmin, and the cyanobacterial toxin microcystin in catfish production ponds. A total of 485 ponds were sampled during a 1-week period; sample collections were weighted to reflect state area in production. Over 47% of ponds had detectable toxin concentrations, although less than 10% of ponds exceeded 1 ng/ml microcystin. MIB and/or geosmin off-flavors occurred in 25% of the samples. Beta -cyclocitral was detected in over 98% of ponds, and was strongly correlated with presence of myxoxanthin ( r =0.94) and zeaxanthin ( r =0.82), both indicative of cyanobacterial production of this compound. Off-flavor compounds (geosmin and MIB) were correlated to a lesser degree with zeaxanthin production ( r =0.78), whereas aphanizyphyl was better correlated with MIB and geosmin ( r =0.89 and 0.56, respectively), again suggesting cyanobacterial production of these compounds.

Short-Term Effect of Diuron on Catfish Pond Ecology

Abstract We examined the effects of diuron treatment on catfish pond ecology under commercial culture conditions. Nine weekly treatments of diuron (0.01 mg/L) were applied to eight 0.4-ha experimental ponds; seven ponds served as controls. Water and fish samples were collected from all ponds each week for chemical and biological analysis. Data on mechanical aeration (hours of supplemental aeration required by each pond) were supplied by the pond manager. A compound (2-methylisoborneol) that is known to cause off-flavor was significantly reduced in both water and fish fillets in diuron-treated ponds. Overall, diuron did not strongly affect water quality variables. No differences in supplemental aeration were detected between the pond groups. Diuron altered the phytoplankton composition within the ponds by reducing the biomass of filamentous blue-green algae. However, overall phytoplankton biomass was not different between treatment and control ponds; filamentous blue-green algae were replaced by diatoms. Z...

Detecting Sugarcane yellow leaf virus infection in asymptomatic leaves with hyperspectral remote sensing and associated leaf pigment changes

Sugarcane infected with Sugarcane yellow leaf virus (SCYLV) rarely produces visual symptoms until late in the growing season. High-resolution, hyperspectral reflectance data from SCYLV-infected and non-infected leaves of two cultivars, LCP 85-384 and Ho 95-988, were measured and analyzed on 13 July, 12 October, and 4 November 2005. All plants were asymptomatic. Infection was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Results from discriminant analysis showed that leaf reflectance was effective at predicting SCYLV infection in 73% of the cases in both cultivars using resubstitution and 63% and 62% in LCP 85-384 and Ho 95-988, respectively, using cross-validation. Predictive equations were improved when data from sampling dates were analyzed individually. SCYLV infection influenced the concentration of several leaf pigments including violaxanthin, beta-carotene, neoxanthin, and chlorophyll a. Pigment data were effective at predicting SCYLV infection in 80% of the samples in the combined data set using the derived discriminant function with resubstitution, and 71% with cross-validation. Although further research is needed to improve the accuracy of the predictive equations, the results of this study demonstrate the potential application of hyperspectral remote sensing as a rapid, field-based method of identifying SCYLV-infected sugarcane plants prior to symptom expression.

Pond age-water column trophic relationships in channel catfish Ictalurus punctatus production ponds

Abstract Long-term temporal succession changes in nutrients, phytoplankton and zooplankton have not been previously investigated in aquaculture ponds. This study analyzed relationships of pond age with nutrients, zooplankton and phytoplankton populations, and incidence of off-flavor occurrence. Nutrient levels (iron, silica, total phosphorus, and total nitrogen), phytoplankton community composition, off-flavor compounds, and zooplankton community composition were determined for 10–11 replicate commercial channel catfish Ictalurus punctatus production ponds of ages 1, 2, 3, 4, 9, 10 or 15 years postconstruction. Data were analyzed using canonical discriminant function analysis, multivariate analysis of variance (MANOVA), and multiple regression approaches. Nutrients (N and P) accumulated in ponds during the first 3 years postconstruction; however, concentrations of these nutrients leveled off after this time. The continual addition of nutrients (as feed) makes standard chlorophyll–P relationships reported from natural lakes unable to account for variation in aquaculture data. Algal composition became dominated by filamentous cyanobacteria after year 4; zooplankton composition also was dominated by larger copepods and cladocerans in older ponds. Younger ponds had lower incidence and intensity of off-flavor relative to older pond water. If ponds are drained/reworked every 3–4 years, incidence of off-flavor should decline.

Evaluation of Ferulic Acid for Controlling the Musty-Odor Cyanobacterium, Oscillatoria perornata, in Aquaculture Ponds

Abstract The cyanobacterium Oscillatoria perornata f. attenuata, a common inhabitant of channel catfish, Ictalurus punctatus, aquaculture ponds, produces the musty compound 2-methylisoborneol that causes fish to become off-flavor and unmarketable. Previous laboratory studies suggest that the natural compound trans-ferulic acid (4-hy-droxy-3-methoxycinnamic acid) is selectively toxic against O. perorna-ta. The present study was conducted to determine the effectiveness of the compound for controlling the growth of O. perornata under field conditions. The study was conducted in 12 0.1-ha earthern ponds in northwest Mississippi. Ponds contained 20,000 catfish/ha and were managed according to commercial culture practices. Half of the ponds were treated six times over a 2-month period with 5μM (0.97 mg/L) trans-ferulic acid, and the other half were untreated controls. Water samples obtained from all ponds preceding and following treatment were analyzed for phytoplankton community structure and concentrations of chlorophyll a, ferulate, and 2-methylisoborneol. Abundance of cyanobacteria, including O. perornata was not consistently affected by applications of ferulic acid. Only one of the six ferulic acid applications resulted in a decrease in abundance of O. perornata in treated ponds relative to untreated ponds (P <0.1). The ineffectiveness of trans-ferulic acid as a cyanobacterial algicide in catfish ponds appears to be caused by rapid dissipation of ferulic acid from pond waters. Use of trans-ferulic acid was neither an effective nor an economical approach to preventing musty off-flavor in pond-cultured channel catfish.

Pond Fertilization Does Not Affect Nutritional Value of Zooplankton in Channel Catfish Nursery Ponds

Abstract We determined the nutritional value of large zooplankton (500–1,000 μm) from fertilized and nonfertilized channel catfish Ictalurus punctatus nursery ponds. Proximate composition, amino acids, fatty acids, and assimilated algal pigments were statistically compared between pond groups. Analyses of vitamin and mineral composite samples of zooplankton from fertilized and nonfertilized ponds are presented. Treatment and control pond zooplankton were similar in nutritional value. Only two fatty acids (16:0 and 20:4[n-6]) were significantly different (P < 0.05) between fertilized and nonfertilized ponds, but total n-3 and n-6 highly unsaturated fatty acids were not different. The zooplankton in this study met or exceeded all nutritional requirements of channel catfish fry except that zooplankton in nonfertilized ponds appeared to contain less -than the required levels of pantothenic acid and vitamin B6. However, no statistical comparison of vitamins was made between fertilized and nonfertilized ponds. ...

Spatial and temporal variation in phytoplankton community structure in a southeastern U.S. reservoir determined by HPLC and light microscopy

Spatial and temporal variation in phytoplankton community structure within a large flood-control reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production.