James P. Hurley

Seasonal influences on partitioning and transport of total and methylmercury in rivers from contrasting watersheds

Seven Wisconsin rivers with contrasting, relativelyhomogeneous watershed composition were selected toassess the factors controlling mercury transport.Together, these watersheds allow comparisons ofwetland, forest, urban and agricultural land-uses.Each site was sampled nine times between September1993 and September 1994 to establish seasonalsignatures and transport processes of total mercury(HgT) and methylmercury (MeHg). Our resultsclearly show that land use and land cover stronglyinfluence mercury transport processes. Under base-flowconditions, unfiltered MeHg yield varies by a factorof sixteen (12–195 mg km-2 d-1), andincreases with the fraction of wetland area in thewatershed. Elevated mercury yields during high floware particle-phase associated in agricultural sites,but filtered-phase associated in wetland sites.Methylmercury represented less than 5% of totalmercury mobilized during the spring thaw across allwatersheds. Autumn MeHg yield was generally 11–15%of HgT in wetland influenced watersheds, thougha maximum of 51% was observed. In some cases, singlehigh-flow events may dominate the annual export ofmercury from a watershed. For example, one high-flowevent on the agricultural Rattlesnake Creek had thelargest HgT and MeHg yield in the study (107 and2.32 mg km-2 d-1, respectively). The mass ofmercury transported downstream by this single eventwas an order of magnitude larger than the eight other(non-event) sampling dates combined. These resultsunderscore the importance of watershed characteristicsand seasonal events on the fate of mercury in freshwater rivers.

Pigment ratios and phytoplankton assessment in northern Wisconsin lakes

Nine lakes in northern Wisconsin were sampled from February through September 1996, and HPLC analysis of water column pigments was carried out on epilimnetic seston. Pigment distributions were evaluated throughout the water column during summer in Crystal Lake and Little Rock Lake. The purpose of our study was to investigate the use of phytopigments as markers of the main taxonomic groups of algae. As a first approach, multiple regression of marker pigments against chlorophyll a (chl a) was used to derive the best linear combination of the main xanthophylls (peridinin, fucoxanthin, alloxanthin, lutein, and zeaxanthin). A significant regression equation (r2= 0.98) was obtained for epilimnion data. The good fit indicates that the chl a:xanthophyll ratios were fairly constant in the epilimnion of the nine lakes over time. Chlorophyll a recalculated from the main xanthophylls in each sample showed good agreement with measured chl a in epilimnetic waters. A second approach used the CHEMTAX program to analyze the same data set. CHEMTAX provided estimates of chl a biomass for all algal classes and allowed distinction between diatoms and chrysophytes, and between chlorophytes and euglenophytes. These results showed a reasonably good agreement with biomass estimates from microscope counts, despite uncertainties associated with differences in sampling procedure. Changes of pigment ratios over time in the epilimnetic waters were also investigated, as well as differences between surface and deep samples of Little Rock Lake and Crystal Lake. We found evidence that changes in the ratio of photoprotective pigments to chl a occurred as a response to changes in light climate. Changes were also observed for certain light‐harvesting pigments. The comparison between multiple regression and CHEMTAX analyses for inferring chl a biomass from concentrations of marker pigments highlighted the need to take account of variations in pigment ratio, as well as the need to acquire additional data on the pigment composition of planktonic algae.

Historical Interpretation of Pigment Stratigraphy in Lake Mendota Sediments

Algal pigments are important biomakers of lake productivity and trophic interactions. Our understanding of organic matter production, sedimentation, and decomposition, phytoplankton-zooplankton interactions, and historical changes in lakes has benefited from pigment-derived information. However, several pitfalls may be encountered in interpreting pigment data. Algal pigments must be distinguished from those produced by higher plants and photosynthetic bacteria. Influences of production on pigment types and concentrations in the water column must be resolved from effects of photodegradation and chemical or biological alteration. Biases in historical sedimentary records toward pigments preferentially preserved during diagnesis must be quantified. With these complications in view, algal pigments provide important insights into lake biogeo- chemistry and paleolimnology.

Seasonal and Size-specific Distribution of Methylmercury in Seston and Zooplankton of Two Contrasting Great Lakes Embayments

Abstract The use of a large volume sieve system is described which allows quantification of mass, pigments, and methylmercury (MeHg) in five distinct size classes of suspended material: > 243 μm, 112–243 μm, 63–112 μm, 35–63 μm, and

Watershed influences on mercury transport to Lake Superior

Mercury concentrations in river waters represent the result of various geochemical and anthropogenic processes in a watershed. In rivers remote from direct point source inputs of Hg (e.g. effluent discharge, contaminated landfills), Hg sources are usually limited to chemical weathering and atmospheric deposition. Transport through the watershed may occur either by association with particulate or filtered phases. Several recent studies have shown that land use and land cover patterns exert a strong influence on Hg and methyl Hg (MeHg) release from watersheds (ST. Lours et al. 1994, HURLEY et al. 1995, BABIARZ et al. 1998). In particular, forested and wetland watersheds appear to release more total Hg (HgT) in the filtered phase relative to other land use/ land cover patterns. This is most likely due to the association of Hg with dissolved organic carbon (DOC). Secondly, and importantly from a bioaccumulation standpoint, wetland systems have been shown to be important sites for conversion of inorganic H g to MeHg (ST. Lours et al. 1994, HuRLEY et al. 1995, KRABBENHOFT et al. 1995, 1998). Microbial sulfate reduction, a process that has been shown to mediate rhe conversion of Hg to MeHg (CoMPEAU & BARTHA 1985) is important in most wetland systems (ZILLIOUX et al. 1993, GrLMOUR er al. 1998).

Evaluations of phytoplankton communities using varied techniques: a multi-media comparison of lakes in northern Wisconsin USA

The quantity and compositJOn of a lakes phytoplankton community are key considerations for many limnological assessments (e.g. REYNOLDS 1997). Unfortunately, obraining detailed information on the quantity of the members of rhe phytoplankton community is a daunting task that requires considerable expertise, and which can be quite expensive. In addirion to direct microscopic counts of phyroplankton species, researchers have developed several alternative methods for evaluating the producer community. Most typically, the overall quantity of pigments associated with production has been routinely assessed as tora! chlorophyll for more than the Jast 40 years (WETZEL & LIKENS 1991). More recendy, techniques using High Performance Liquid Chromatography have attempted to identiry the quantities of a variety of pigments that can serve as indicators of specific algal groups (MILLIE et al. 1993). Similarly, electronic instruments have been developed that can enumerate the abundances of particles in different size caregories (SHELDON et al. 1973). The availabiliry of these varied, and potentially automated, methods has raised the potential that information on phytoplankton communities may be more readily available. The use of such information, however, requires careful comparisons of these different methods. Here we report an initial comparison of these four different techniques for evaluating phyroplankton using samples rhat were collected during summer 1996 from seven lakes in northern Wisconsin, USA. These dara are being made available for more derailed comparisons. Our study sites have been evaluated since 1981 as primary study lakes of rhe North Temperate Lakes, Long-Term Ecological Research (NTL-LTER) Program (MAGNUSON et al. 1997). They have been assessed for a wide variety of limnological features (e.g. KRATZ et al. 1986) but their phytoplankton

Pigments and phytoplankton composition in LTER lakes (Wisconsin, USA)

Nine lakes of northern Wisconsin were sampled from February through September 1996, and HPLC analysis of water column pigments was carried out on epilimnion seston. Two lakes, Crystal Lake and Little Rock Lake, were studied throughout the water column, at least during the summer period. The purpose of the study was to investigate the use of key carotenoid pigments as markers of the main taxonomic groups of algae. Multiple stepwise regression was used to derive the best linear combination of the specific xanthophylls to recalculate chlorophyll a biomass (according to GIESKES & KRMY 1983). A highly significant regression equation (R = 0.98) has been obrained through processing the epilimnion data for the ser of nine lakes, and a particular equation was determined for Crystal lake data (R = 0.95). The good fit shows that the ratio of chlorophyll a to main specific xanthophylls was fairly constant in the nine lakes, and varied little with time and depth. Biomass expressed as chlorophyll equivalems has been calculated for each taxonomic group, using the chlorophyll a l xanthophyll ratios (Chlalxan) derived from the regressions. Those Chlalxan ratios were 3.54 for peridinin (marker for autotrophic dinoflagellates), 1.37 for fucoxanthin (marker for Chrysophytes and diatoms), 6.2 for alloxanthin (specific to Cryptophyres), 8.65 for lurein (specific to Chlorophytes). The chlorophyll a l zeaxamhin ratio (indicative of Cyanobacreria) was not significant, and echinenone (another Cyanobacteria pigment) was observed only in a few samples. Chlorophyll a biomass was recalculared by summing up the contributions of the main taxonomic groups: the good agreement with measured chlorophyll a, even in deep samples, demonstrates litde effect of photoacclimation. Only for deep samples of Litde Rock Lake were discrepancies sometimes observed. Alternatively, the CHEMTAX procedure (MACKEY et al. 1996), which allows biomass estimates from several markers per algal class, was applied to the LTER pigment data ser. This program uses a factor analysis and a steepest descent algorithm to find the best fit to the data based on a pigment ratio matrix for the classes to be determined. The result is the contribution of the algal classes to total phytoplankton biomass, expressed as chlorophyll a. Afi:er a few runs, a pigment ratio matrix was determined for the various algal classes identified (from microscope examinations) in the nine lakes, essentially based on the regression analysis and on literature data on pigment composition of freshwater algae in pure culture. The data ser was split into shallow and deep samples, to allow for possible photoacclimation, as well as into samples with low (<20% of total phorbins) and high (>20% of total phorbins) phaeopigment content. The data from two bog lakes were finally processed separately, as their algal assemblage probably contained high proportions of the Raphidophyceae Gonyostomum semen, of which litde is known about the pigment composition. The final results of the CHEMTAX runs yielded estimates of biomass of Chrysophytes, Chlorophytes, Cryptophytes, diatoms, autotrophic dinoflagellates, Cyanobacteria (two categories, with and without echinenone) and Euglenophytes. These results were compared with the biovolume estimates from microscope counts of epilimnion samples at two dates: despite uncertainties about the accuracy of biovolume estimates, the biomass estimates from CHEMTAX seem consistent for most of the data set. To conclude, the pigment ratios obtained in the LTER lakes were then compared with pure cultures and field data: as a whole, little variation was observed in these ratios, which indicated that assessment o f biomass o f different taxonomic groups from their pigments can be done with a good reliability in marine and freshwater environments. The use of CHEMTAX in fresh waters seems particularly promising, even though some validation has still to be done. To improve the use of such programs, the acquisition of new data about pigment ratios in freshwater algae from different environments is still 0368-077010010027-0930

Mercury methylation in periphyton of the Florida Everglades

0.50 ©2000 E. Schweizerbansche Verlagsbuchhandlung, D-70176 Sturrgarr ].-P. Descy et al., Pigments and phytoplankton composition in LTER lakes 931