Krystyna Bialek

Pollutant fate and spatio-temporal variability in the choptank river estuary: Factors influencing water quality

Restoration of the Chesapeake Bay, the largest estuary in the United States, is a national priority. Documentation of progress of this restoration effort is needed. A study was conducted to examine water quality in the Choptank River estuary, a tributary of the Chesapeake Bay that since 1998 has been classified as impaired waters under the Federal Clean Water Act. Multiple water quality parameters (salinity, temperature, dissolved oxygen, chlorophyll a) and analyte concentrations (nutrients, herbicide and herbicide degradation products, arsenic, and copper) were measured at seven sampling stations in the Choptank River estuary. Samples were collected under base flow conditions in the basin on thirteen dates between March 2005 and April 2008. As commonly observed, results indicate that agriculture is a primary source of nitrate in the estuary and that both agriculture and wastewater treatment plants are important sources of phosphorus. Concentrations of copper in the lower estuary consistently exceeded both chronic and acute water quality criteria, possibly due to use of copper in antifouling boat paint. Concentrations of copper in the upstream watersheds were low, indicating that agriculture is not a significant source of copper loading to the estuary. Concentrations of herbicides (atrazine, simazine, and metolachlor) peaked during early-summer, indicating a rapid surface-transport delivery pathway from agricultural areas, while their degradation products (CIAT, CEAT, MESA, and MOA) appeared to be delivered via groundwater transport. Some in-river processing of CEAT occurred, whereas MESA was conservative. Observed concentrations of herbicide residues did not approach established levels of concern for aquatic organisms. Results of this study highlight the importance of continued implementation of best management practices to improve water quality in the estuary. This work provides a baseline against which to compare future changes in water quality and may be used to design future monitoring programs needed to assess restoration strategy efficacy.

Agricultural pesticides and selected degradation products in five tidal regions and the main stem of Chesapeake Bay, USA

Nutrients, sediment, and toxics from water sources and the surrounding airshed are major problems contributing to poor water quality in many regions of the Chesapeake Bay, an important estuary located in the mid-Atlantic region of the United States. During the early spring of 2000, surface water samples were collected for pesticide analysis from 18 stations spanning the Chesapeake Bay. In a separate effort from July to September of 2004, 61 stations within several tidal regions were characterized with respect to 21 pesticides and 11 of their degradation products. Three regions were located on the agricultural Delmarva Peninsula: The Chester, Nanticoke, and Pocomoke Rivers. Two regions were located on the more urban western shore: The Rhode and South Rivers and the Lower Mobjack Bay, including the Back and Poquoson Rivers. In both studies, herbicides and their degradation products were the most frequently detected chemicals. In 2000, atrazine and metolachlor were found at all 18 stations. In 2004, the highest parent herbicide concentrations were found in the upstream region of Chester River. The highest concentration for any analyte in these studies was for the ethane sulfonic acid of metolachlor (MESA) at 2,900 ng/L in the Nanticoke River. The degradation product MESA also had the greatest concentration of any analyte in the Pocomoke River (2,100 ng/L) and in the Chester River (1,200 ng/L). In the agricultural tributaries, herbicide degradation product concentrations were more strongly correlated with salinity than the parent herbicides. In the two nonagricultural watersheds on the western shore, no gradient in herbicide concentrations was observed, indicating the pesticide source to these areas was water from the Bay main stem.

Metolachlor metabolite (MESA) reveals agricultural nitrate-N fate and transport in Choptank River watershed.

Over 50% of streams in the Chesapeake Bay watershed have been rated as poor or very poor based on the index of biological integrity. The Choptank River estuary, a Bay tributary on the eastern shore, is one such waterway, where corn and soybean production in upland areas of the watershed contribute significant loads of nutrients and sediment to streams. We adopted a novel approach utilizing the relationship between the concentration of nitrate-N and the stable, water-soluble herbicide degradation product MESA {2-[2-ethyl-N-(1-methoxypropan-2-yl)-6-methylanilino]-2-oxoethanesulfonic acid} to distinguish between dilution and denitrification effects on the stream concentration of nitrate-N in agricultural subwatersheds. The ratio of mean nitrate-N concentration/(mean MESA concentration * 1000) for 15 subwatersheds was examined as a function of percent cropland on hydric soil. This inverse relationship (R(2)=0.65, p<0.001) takes into consideration not only dilution and denitrification of nitrate-N, but also the stream sampling bias of the croplands caused by extensive drainage ditch networks. MESA was also used to track nitrate-N concentrations within the estuary of the Choptank River. The relationship between nitrate-N and MESA concentrations in samples collected over three years was linear (0.95 ≤ R(2) ≤ 0.99) for all eight sampling dates except one where R(2)=0.90. This very strong correlation indicates that nitrate-N was conserved in much of the Choptank River estuary, that dilution alone is responsible for the changes in nitrate-N and MESA concentrations, and more importantly nitrate-N loads are not reduced in the estuary prior to entering the Chesapeake Bay. Thus, a critical need exists to minimize nutrient export from agricultural production fields and to identify specific conservation practices to address the hydrologic conditions within each subwatershed. In well drained areas, removal of residual N within the cropland is most critical, and practices such as cover crops which sequester the residual N should be strongly encouraged. In poorly drained areas where denitrification can occur, wetland restoration and controlled drained structures that minimize ditch flow should be used to maximize denitrification.

Rapid determination of free tryptophan in plant samples by gas chromatography-selected ion monitoring mass spectrometry

Abstract An isotope dilution assay for plant tryptophan is described. The method consists of solid-phate extraction techniques, the one-step formation of the N-acetyl methyl ester derivative, followed by purification by C 18 high-performance liquid chromatography and analysis by gas chromatography-selected ion monitoring mass spectrometry. The method can be used effectively to measure free tryptophan in plant samples as small as 10 mg fresh weight.

Development of Genetic and Analytical Systems for Studies of Auxin Metabolism

Early investigations of auxin conjugates concerned the general “release” of auxin in vivo or in situ [e.g., 8]. More recent studies have examined either IAA released by hydrolysis of extracts of plant tissue, or have studied specific conjugates formed by the covalent attachment of IAA to other molecules. Conjugated forms of IAA can be classified by size, type of covalent linkage, or the molecule to which the IAA is attached. Low molecular weight conjugates include esters such as IAA-glucose and IAA-myo-inositol and amides such as IAA-aspartate and IAA-glutamate. The higher molecular weight conjugates include esters where the IAA is linked to the carbohydrate portion of a glycoprotein [17], or is linked to a glucan [18]. Higher molecular weight amide conjugates are also known, where IAA is linked directly to a peptide or protein [3]. These higher molecular weight conjugates have been difficult to study due to the lack of suitable methods for macromolecular separations and structure determination. Improvements in available methods for studies of macromolecules now make it practical to examine these types of compounds in more detail and begin to ask questions as to their role in the hormonal relationships within the plant.

Role of Riparian Areas in Atmospheric Pesticide Deposition and Its Potential Effect on Water Quality

Riparian buffers are known to mitigate hydrologic losses of nutrients and other contaminants as they exit agricultural fields. The vegetation of riparian buffers can also trap atmospheric contaminants, and these pollutants can subsequently be delivered via rain to the riparian buffer floor. These processes, however, are poorly understood especially for pesticide residues. Therefore, we conducted a four-year study examining stemflow and throughfall to a riparian buffer which was adjacent a cultured Zea mays field treated with atrazine and metolachlor. Stemflow is rain contacting the tree canopy traveling down smaller to larger branches and down the tree trunk, whereas throughfall is rain that may or may not contact leaves and branches and reaches the earth. Stemflow concentrations of the herbicides were larger than throughfall concentrations and accounted for 5-15% of the atrazine and 6-66% of the metolachlor depositional fluxes under the canopy. Larger depositional fluxes were measured when leaves were more fully emerged and temperatures and humidity were elevated. Rain collected outside the riparian buffer on the field side and on the back side revealed the trees trapped the herbicide residues. Herbicide loading to the riparian buffer stream was found to be linked to tree canopy deposition and subsequent washoff during rain events. These results indicate that in agricultural areas canopy washoff can be an important source of pesticides to surface waters.

Stable isotope techniques for the analysis of indole auxin metabolism in normal and mutant plants

Techniques for the analysis of indole-3-acetic acid (IAA) using stable isotope dilution are now well established. This basic technology, designed for the measurement of levels of phytohormone, can be extended to study the metabolic relationship of IAA to other indolic compounds and thus provide a more complete picture of hormone metabolism. We have developed methods for the analysis of the biosynthesis of IAA in plants and have applied these techniques to study IAA metabolism in normal and mutant plants as well as during embryogenesis, seed germination and root formation. The approaches we have recently used in our laboratory are: 1) To expand our analytical techniques to encompass additional indolic compounds and precursors. 2) To use D2O as a totally invasive label which can be incorporated into very early precursors in the aromatic biosynthetic pathway. Such experiments are able to answer the question “Is IAA being made de novo in this plant tissue?” 3) To use stable isotope labelled precursors to measure pool sizes and turnover of compounds important for the biosynthesis of tryptophan (Trp) and IAA, resulting in a quantitative approach to understanding carbon flow in these pathways. 4) To use stable isotope labelled compounds to track the interconversion of indolic compounds. 5) To develop techniques for the production and selection of mutant plants well suited for measurement of auxin metabolism in situ. In this paper we will discuss the methodology we use to study several plant systems which have been chosen to illustrate how to answer specific questions with regard to auxin metabolism. The plant systems we will discuss include carrot embryogenic cultures, seed germination in Phaseolus, precursor studies using normal and mutant Lemna and measurement of IAA and IBA levels in carrot transformed with Agrobacterium rhizo genes.