Richard D. Robarts

Photodegradation of DOC in a shallow prairie wetland: evidence from seasonal changes in DOC optical properties and chemical characteristics

Wetlands across the Canadian prairies are typically shallow (<1.0 m) and exhibit high dissolved organic carbon (DOC) concentrations (>10 mg l−1). Studies have shown that DOC in such shallow wetlands is not as reliable an indicator of ultraviolet radiation (UVR) attenuation as it is in clearwater. Changes in DOC character and composition as a result of sunlight exposure might provide a reasonable explanation for this observation. To test this, we investigated seasonal changes in DOC optical and chemical properties in a shallow prairie wetland over a 2-year period. Although DOC concentration increased at least two-fold from spring until fall, DOC specific absorption (at 350 nm) and fluorescence decreased by 30 and 32%, respectively, for the same period. In both years, seasonal decreases in DOC molecular weight and size (from measurements of tangential filtration and mass electrospray mass spectrometry) were reflected in concomitant increases in spectral slope. 13C NMR analysis of DOC isolated on XAD-8 resins revealed a 49% decrease in aromatic moieties when spring values were compared to those in the fall. As well, δ13C signatures of this isolated DOC became heavier seasonally. In a short term photodegradation experiment (6 days) we noted a 47% decline in DOC specific absorption coefficients at 350 nm and a 15% increase in spectral slope when water exposed to the total light spectrum was compared to that of a dark control. Taken together, all of these observations were consistent with the occurrence of seasonal DOC photodegradation in shallow prairie wetlands and underlined the importance of this process in shaping DOC character and composition in these hydrologically dynamic systems. Our data also indicates that constant mixing and shallow depths in these wetlands were factors which enhanced DOC photodegradation. Although the high DOC concentrations of prairie wetlands should theoretically offer protection for their biota, seasonal photodegradation of DOC means that these systems may not be as protected as their high DOC concentrations suggest.

Seasonal patterns of total and energy reserve lipids of dominant zooplanktonic crustaceans from a hyper-eutrophic lake

SummarySeasonal patterns of lipid reserves and lipid classes of dominant zooplankton in a hyper-eutrophic lake were examined in relation to algal food resources. Triacylglycerol was the principle lipid energy reserve in all five species examined. During the height of the yearlyAphanizomenon flos-aquae bloom, lipid levels of the principle herbivores (Daphnia pulex andLeptodiaptomus sicilis) and an omnivore (Diacyclops bicuspidatus thomasi), were at their lowest concentration, suggesting that this cyanobacterium is nutritionally inadequate. As the cyanobacterial bloom began to collapse, bacterial numbers increased rapidly. The increase in bacterial numbers coincided with a large increase in areal lipid energy reserves ofDiaphanosoma leuchtenbergianum andChydorus sphaericus. Examination of seasonal patterns in the biomass of different algal species suggested thatRhodomonas minuta andCryptomonas erosa played a key role in nutrition, lipid deposition, and reproduction ofD. pulex andL. sicilis.

Mass spectrometric determination of ergosterol in a prairie natural wetland

Fungi are the main decomposers of plant material in an aquatic system. Levels of ergosterol, a compound generally specific to the cell membranes of fungi can be used as an indirect measure of their presence and biomass. Described is a procedure utilising reversed-phase liquid chromatography with positive-ion atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI-MS-MS) for full quantification and confirmation of ergosterol in various wetland matrices. Solid and liquid samples (0.2-1 g dry weight and 10 ml) were subjected to alkaline saponification followed by serial extraction using pentane (3 x 10 ml). The procedure was applicable to quantitative analysis of wetland samples with little or no clean up. Under low energy (CID) collision induced dissociation conditions the major product-ion formed from m/z 379.4 [M + H-H2O]+ was m/z 69.4 [(CH3)2CHCH=CH]+. Selected reaction monitoring (SRM) of this transition along with the retention time were used to confirm that ergosterol was widely distributed at ppm levels (2.4 to 303 microg ash free dry mass (AFDM)) in matrices of decaying willow leaves, Scirpus stems (living and dead) and sediment collected at the water-sediment interface. Comparison between LC-APCI-MS-MS (SRM), LC-APCI-MS using selected ion monitoring (SIM) and liquid chromatography with ultraviolet absorption detection (LC-UV) indicated that SRM analysis was the most selective technique.

Rationale for Monitoring Discharge on the Ground

AbstractThe hydrological cycle is receiving increasing attention both as an essential natural resource for humans and ecosystems and as a critical component controlling the earth’s climate system. Better understanding of the water cycle and its interaction with changing climate will require improved monitoring of the various water fluxes and storages in hydrological processes. River discharge is a unique component reflecting an integrated hydrological signal over larger regions. Existing in situ monitoring solutions to monitor discharge are often considered too expensive and the difficulties in data sharing are viewed as insurmountable obstacles, which has led to growing interest in finding an alternative. This paper argues that in situ monitoring is far less expensive than claimed and the obstacles are not necessarily as insurmountable as often stated and a conscious effort to revitalize in situ monitoring will be needed. This paper demonstrates that there is no substitute for in situ discharge monitorin...

Spatial and temporal variability in lipid dynamics of common amphipods: assessing the potential for uptake of lipophilic contaminants

A three-tiered approach involving autoradiography, measurement of seasonal lipid patterns and deployment of in situ microcosms, was used to assess the potential of the moderately lipophilic herbicide triallate to accumulate in two amphipod species (Hyalella azteca and Gammarus lacustris) in two prairie lakes and one prairie pond. Autoradiography revealed that the storage sites for triallate in amphipod tissues were associated with lipid-rich tissues, in particular, with triacylglycerol storage sites and the nervous system. Seasonal lipid patterns (total lipid) of amphipods did not differ amongst sites within a waterbody, however, there were marked differences amongst water bodies. Female amphipods had higher lipid contents than males during the reproductive period in early summer but this difference diminished later in the summer. Bioaccumulation factors of triallate in amphipod tissues ranged from 72 to 80 times the nominal water concentrations in 7 day microcosm trials. Triacylglycerol content and triallate body burden were positively correlated (r2=0.58–0.91) for H. azteca in the two lakes in which the microcosms were deployed. However, no significant correlations were obtained between triacylglycerol content and triallate body burden for G. lacustris. Triacylglycerol contents in the amphipods were generally highest in spring and autumn, coinciding with application times for triallate.

Time for in situ renaissance

In situ monitoring of water dates to Pharaonic Egypt and remained the primary means of observation into the later part of the 20th century. Monitoring networks have declined ([ 1 ][1]–[ 4 ][2]) since the 1980s because of budgetary constraints and political instabilities. This decline paradoxically

Climatic Change and Global Warming of Inland Waters : Impacts and Mitigation for Ecosystems and Societies

The impact of climate change on the hydrosphere is explored in this book, with particular emphasis on the impacts that warming has on inland water bodies, particularly lakes. Divided into three parts, this collection of chapters draws on contributions from the World Water and Climate Network with emphasis on the physical, biogeochemical and ecological consequences of climate change. Part one comprises of regional reviews and local case studies of the impacts of changing climates with 20 chapters that are organised broadly from north to south. The section starts with an excellent overview of the impact of climate change on the pan-Arctic watersheds and hydrology and the impact of this changing hydroclimatology on the lakes and wetlands of the Arctic. Case studies include detailed assessments of the changes to lake stratification and mixing as a result of warming air temperatures in temperate zones (e.g. Eurasia, Japan, Europe, USA), as well as in sub to tropical zones (e.g. Amazon basin, African great lakes) and polar regions (Arctic and maritime Antarctic). Much of these case studies focus on the role of changing thermal conditions in lakes and the potential ecological changes in fauna, for example, the rise of cyanobacteria in tropical lakes and the decline of Daphnia in temperate lakes. Part two is comprised of two chapters that consider the impacts on societies: first, the nomadic peoples of Mongolia’s response to climate change (chapter 21), and second, planning responses to manage the effects of climate change within the 10 biggest megacities (chapter 22). Part three considers mitigation approaches and is comprised of three chapters, including hydrological modelling, radical ideas for ameliorating the effects of warming using different strategies to disperse heat in aquatic ecosystems and the potential use of electrolysis for oxygenating dead zones. Much of the emphasis of this book is given over to lakes, with considerably less content on wetlands; however, there is an excellent regional review of the wetlands of the prairie lands of North America (chapter 13). Similarly, there are only a few chapters that detail the impacts on rivers, with two chapters considering the impacts of changing climates on the Yellow and Yangtze rivers in China (chapters 4 and 5), and the challenges of using hydrological modelling coupled with global climate models (GCMs) as a management tool, and some of difficulties in downscaling GCM outputs and their lack of sensitivity to decadal and shortterm modelling scenarios (chapter 23). Local readers will find the chapter on New Zealand lakes (chapter 19) to be particularly useful as it includes a broad overview of the state of the country’s lakes and considers several local case studies. One aspect that is particularly interesting in this book is that the impacts of climate change and the rates of change vary considerably between geographic case studies, with New Zealand standing out as one of the few areas where, to date, there has been little change in the thermal strata of the lakes, unlike the examples from Europe (chapter 12) and Africa (chapter 18). The strengths of this book are chapters that examine perspectives on the impacts of climate change on regional areas, including the Arctic, African Great Lakes, North American Prairie lands, Denmark and New Zealand. These chapters provide excellent narratives on the complex interrelations between climate, hydrology and ecosystems, and evidence of changes in biological, physical and biogeochemical indicators. Many chapters suggest areas of future work, including urgent and renewed investment in monitoring, as well as innovative ideas for slowing, and even reversing the effects of bs_bs_banner

Seasonal Changes in Fungal Production and Biomass on Standing Dead Scirpus lacustris Litter in a Northern Prairie Wetland

ABSTRACT Decaying macrophytes are an important source of carbon and nutrients in fungal and bacterial communities of northern prairie wetlands. Dead macrophytes do not collapse into the water column immediately after death, and decomposition by fungi and bacteria begins while the plants are standing. The seasonal variations in fungal biomass and production on Scirpus lacustris stems, both above and below water, were measured to assess which environmental factors were dominant in affecting these variations in a typical prairie wetland. Fungal biomass and production were measured from early May to November, just prior to freeze-up. Fungal decomposition began and was greatest in the spring despite low water temperatures. The fungal production, as measured by the incorporation of [1-14C]acetate into ergosterol, ranged from 1.8 to 376 μg of C g of ash-free dry mass (AFDM)−1 day−1, and the biomass, as estimated by using ergosterol, ranged from nondetectable to 5.8 mg of C g of AFDM−1. There was no significant difference in biomass or production between aerial and submerged portions of Scirpus stems. The water temperature was correlated with fungal production (r = 0.7, P < 0.005) for aerial stem pieces but not for submerged pieces. However, in laboratory experiments water temperature had a measurable effect on both biomass and production in submerged stem pieces. Changes in fungal biomass and productivity on freshly cut green Scirpus stems decaying in the water either exposed to natural solar radiation or protected from UV radiation were monitored over the summer. There was no significant difference in either fungal biomass (P = 0.76) or production (P = 0.96) between the two light treatments. The fungal biomass and rates of production were within the lower range of the values reported elsewhere, probably as a result of the colder climate and perhaps the lower lability of Scirpus stems compared to the labilities of the leaves and different macrophytes examined in other studies performed at lower latitudes.

Measurements of Cd, Cu, Pb and Zn in the lower reaches of major Eurasian arctic rivers using trace metal clean techniques

Concentrations of dissolved and particulate Cd, Cu, Pb and Zn were determined in samples collected in summer 1998 from the lower reaches of six major Eurasian arctic rivers: the Onega, Severnaya Dvina, Mezen, Pechora, Ob and Yenisey. These data comprise some of the earliest measurements of trace metals in Eurasian arctic rivers above the estuaries using recognized clean techniques. Significant (alpha = 0.05) differences were observed among mean concentrations of particulate metals in the individual rivers (F < or = 0.006), with highest levels overall observed in the Severnaya Dvina and Yenisey. No significant differences were observed among mean concentrations of dissolved metals in the individual rivers (F = 0.10-0.84). Contributions from anthropogenic sources are suggested by comparison of trace metal ratios in the samples to crustal abundances. These results establish a baseline for assessing future responses of Eurasian arctic river systems to climate-related environmental changes and shifting patterns of pollutant discharge.

EXTRACTION EFFICIENCIES AND DETERMINATION OF ERGOSTEROL IN A VARIETY OF ENVIRONMENTAL MATRICES

Fungi may be the main decomposers of plant material in an aquatic system and their presence and biomass can be measured indirectly by the detection of ergosterol, a compound generally specific to the cell membranes of fungi. Ergosterol is conveniently used as a measurement of living fungal biomass and is most often detected using high pressure liquid chromatography with a UV detector (HPLC–UV). Described in this manuscript is the general stability of ergosterol in a laboratory setting, the testing of a variety of techniques for the extraction of ergosterol and a general survey of different matrices in an aquatic environment. More importantly, data acquired from the HPLC–UV system was further confirmed with liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI/MS/MS) for the presence of ergosterol. Ergosterol was found to be quite stable over 5 days in a lab setting. Though other procedures gave overall better recoveries of ergosterol extracted, the optimum extraction method proved to be a previously established one of saponification followed by toluene extraction. This method resulted in a relatively clean sample with ergosterol recoveries of above 90%. As expected, ergosterol was widely distributed at ppm levels (2.4 to 302.9 μg ash free dry mass (AFDM)) in matrices of decaying willow leaves, Scirpus stems (living and dead) and sediment collected at the water sediment interface. In the case of water samples, the HPLC–UV system falsely indicated the presence of ergosterol thus pointing to the need for the more selective mass spectral confirmation on samples where chromatographic co-elution is a problem. Care is required when assuming the presence and levels of ergosterol are correct based only on HPLC–UV detection.