Description: 34th Annual Conference of IAMSLIC held 14-18 September, 2008 at Suva, Fiji

Description: Lake Tahoe is an ultra-oligotrophic subalpine lake that is renowned for its clarity. The region experiences little cloud cover and is one of the most UV transparent lakes in the world. As such, it is an ideal environment to study the role of UV radiation in aquatic ecosystems. Long-term trends in Secchi depths showed that water transparency to visible light has decreased in recent decades, but limited data are available on the UV transparency of the lake. Here we examine how ultraviolet radiation varies relative to longer-wavelength photosynthetically active radiation (PAR, 400-700 nm, visible wavelengths) horizontally along inshore-offshore transects in the lake and vertically within the water column as well as temporally throughout 2007. UV transparency was more variable than PAR transparency horizontally across the lake and throughout the year. Seasonal patterns of Secchi transparency differed from both UV and PAR, indicating that different substances may be responsible for controlling transparency to UV, PAR, and Secchi. In surface waters, UVA (380 nm) often attenuated more slowly than PAR, a pattern visible in only exceptionally transparent waters with very low dissolved organic carbon. On many sampling dates, UV transparency decreased progressively with depth suggesting surface photobleaching, reductions in particulate matter, increasing chlorophyll a, or some combination of these increased during summer months. Combining these patterns of UV transparency with data on visible light provides a more comprehensive understanding of ecosystem structure, function, and effects of environmental change in highly transparent alpine and subalpine lakes such as Tahoe.

Description: The aim of this thesis was to examine metazoan parasite communities and viral infections of European eel, Anguilla anguilla, from fresh water, brackish and marine localities in northern Germany. The here collected data shall help to evaluate the suitability of the studied localities for potential restocking purposes regarding the presence of pathogens. In Chapter I a comparative examination of the metazoan parasite communities of the European eel was conducted including measures of parasite diversity characteristics. Special focus was given on the prevalence and intensity of infection with the invasive swim bladder nematode Anguillicoloides crassus and the gill monogenean Pseudodactylogyrus spp. In all, 29 parasite species/taxa were found in 170 eels from six different sample sites. Parasite communities of European eels clearly exhibit the habitat preferences of their hosts, salinity-dependent specificities, and a clustering into fresh-water, brackish, and marine groups. The highly pathogenic parasite species Anguillicoloides crassus and Pseudodactylogyrus spp. were found at all sampling sites in fresh water and brackish water, with high prevalence. Therefore, the common practice of catching glass eels in river estuaries for restocking solely in inland waters as management measure for stock recovery should be critically considered. To set a baseline for future trend analyses and biodiversity considerations an updated and comprehensive literature review on prevalence and distribution of parasites of the European eel in European waters was conducted (Chapter II). The resulting checklist provides evidence for 161 parasite species/taxa from 30 countries. Special consideration was given to the distribution of the swimbladder nematode Anguillicoloides crassus. A map and table of first reported records as well as a survey map indicating all published localities of A. crassus documented in the checklist are provided. In Chapter III the prevalence of virus infections in European eels from natural habitats with differing salinity regimes were evaluated. Out of the 140 examined eels, HVA was detected in two of the five investigated water bodies with an overall infection prevalence of 2%. Virus infection was only detected by direct PCR testing, whereas none of the three HVA PCR-positive eels showed any clinical sign of disease. However latent infections of HVA were found in the investigated water bodies and as proven for the first time, also in a marine habitat (Helgoland) of northern Germany. The only reliable method for the verification of viral genome in latent herpesvirus infections is by PCR examination. For the verification of even low virus copy numbers in asymptomatic carriers, a more sensitive detection method was developed (Chapter IV). This method was tested on eel samples from two freshwater localities in northern Germany, Lake Pönitz (n=16) and River Elbe (n=30). But even with this high sensitive nested-PCR, HVA positive eels were only detected in 2 eels from Lake Pönitz (Chapter IV). Hence, the rate of HVA infection seemed to be quite low among northern German eel stocks. But the source of infection is present in at least three of the seven studied localities (Chapter III & IV) and under favourable conditions for virus replication like high water temperature or stress a reactivation and further dispersal of HVA might be induced.

Description: During the SAMUM field campaign in southern Morocco in May and June 2006 density currents generated by evaporative cooling after convective precipitation were frequently observed at the Sahara side of the Atlas Mountain chain. The associated strong surface cold-air outflow during such events has been observed to lead to dust mobilization in the foothills. Here a regional model system is used to simulate a density current case on 3 June 2006 and the subsequent dust emission. The model studies are performed with different parameterization schemes for convection, and with different horizontal model grid resolutions to examine to which extent the model system can be used for reproducing dust emissions in this region. The effect of increasing the horizontal model grid resolution from 14 km to 2.8 km on the strength on the density currents and thus on dust emission is smaller than the differences due to different convection parameterization schemes in this case study. While the results in reproducing the observed density current at the Atlas Mountain varied with different convection parameterizations, the most realistic representation of the density current is obtained at 2.8 km grid resolution at which no parameterization of deep convection is needed.

Description: Jamaica Bay, NY, is a highly urbanized estuary within the boroughs of New York City conspicuously lacking published information on dissolved trace metal concentrations. The current study examines the distribution and cycling of trace metals in that embayment with data gathered during cruises in November 2004, April 2005, and June 2006. Most of the metal distributions (Fe, Zn, Co, Ag, Cu, Pb, Ni) in the water column are explained by the input of substantial volumes of treated wastewater effluent. However, several lines of evidence suggest that submarine groundwater discharge (SGD) is also an important source of dissolved Fe, Zn, Co, Ni, and isotopically distinct stable Pb ratios (206Pb, 207Pb, 208Pb) in the Bay. Conversely, the recirculated seawater component of SGD is an apparent sink for dissolved Mo. This study provides the first measurements of dissolved trace metals in the Jamaica Bay water column and subterranean estuary and provides evidence for trace metal input due to SGD.