Geology topics

Erik Orsak

Publications and source records attributed to Erik Orsak.

7 recordsLinked to original sources

USGS2015

Novel associations between contaminant body burdens and biomarkers of reproductive condition in male Common Carp along multiple gradients of contaminant exposure in Lake Mead National Recreation Area, USA

Adult male Common Carp were sampled in 2007/08 over a full reproductive cycle at Lake Mead National Recreation Area. Sites sampled included a stream dominated by treated wastewater effluent, a lake basin receiving the streamflow, an upstream lake basin (reference), and a site below Hoover Dam. Individual body burdens for 252 contaminants were measured, and biological variables assessed included physiological [plasma vitellogenin (VTG), estradiol-17β (E2), 11-ketotestosterone (11KT)] and organ [gonadosomatic index (GSI)] endpoints. Patterns in contaminant composition and biological condition were determined by Principal Component Analysis, and their associations modeled by Principal Component Regression. Three spatially distinct but temporally stable gradients of contaminant distribution were recognized: a contaminant mixture typical of wastewaters (PBDEs, methyl triclosan, galaxolide), PCBs, and DDTs. Two spatiotemporally variable patterns of biological condition were recognized: a primary pattern consisting of reproductive condition variables (11KT, E2, GSI), and a secondary pattern including general condition traits (condition factor, hematocrit, fork length). VTG was low in all fish, indicating low estrogenic activity of water at all sites. Wastewater contaminants associated negatively with GSI, 11KT and E2; PCBs associated negatively with GSI and 11KT; and DDTs associated positively with GSI and 11KT. Regression of GSI on sex steroids revealed a novel, nonlinear association between these variables. Inclusion of sex steroids in the GSI regression on contaminants rendered wastewater contaminants nonsignificant in the model and reduced the influence of PCBs and DDTs. Thus, the influence of contaminants on GSI may have been partially driven by organismal modes-of-action that include changes in sex steroid production. The positive association of DDTs with 11KT and GSI suggests that lifetime, sub-lethal exposures to DDTs have effects on male carp opposite of those reported by studies where exposure concentrations were relatively high. Lastly, this study highlighted advantages of multivariate/multiple regression approaches for exploring associations between complex contaminant mixtures and gradients and reproductive condition in wild fishes.

General and Comparative Endocrinology↗

USGS2015

Are endocrine and reproductive biomarkers altered in contaminant-exposed wild male Largemouth Bass (Micropterus salmoides) of Lake Mead, Nevada/Arizona, USA?

Male Largemouth Bass were sampled from two locations in Lake Mead (USA), a site influenced by treated municipal wastewater effluent and urban runoff (Las Vegas Bay), and a reference site (Overton Arm). Samples were collected in summer (July '07) and spring (March '08) to assess general health, endocrine and reproductive biomarkers, and compare contaminant body burdens by analyzing 252 organic chemicals. Sperm count and motility were measured in spring. Contaminants were detected at much higher frequencies and concentrations in fish from Las Vegas Bay than Overton Arm. Those with the highest concentrations included PCBs, DDTs, PBDEs, galaxolide, and methyl triclosan. Fish from Las Vegas Bay also had higher Fulton condition factor, hepatosomatic index, and hematocrit, and lower plasma 11-ketotestosterone concentration (KT). Gonadosomatic index (GSI) and sperm motility did not differ between sites, but sperm count was lower by nearly 50% in fish from Las Vegas Bay. A positive association between KT and GSI was identified, but this association was nonlinear. On average, maximal GSI was reached at sub-maximal KT concentrations. In conclusion, the higher concentration of contaminant body burdens coupled with reduced levels of KT and sperm count in fish from Las Vegas Bay suggest that male reproductive condition was influenced by contaminant exposures. Also, the nonlinear KT-GSI association provided a framework to understand why GSI was similar between male bass from both sites despite their large difference in KT, and also suggested the existence of post-gonadal growth functions of KT at high concentrations.

Arizona, Nevada↗

USGS2013

Potential for bias in using hybrids between common carp (Cyprinus carpio) and goldfish (Carassius auratus) in endocrine studies: a first report of hybrids in Lake Mead, Nevada, U.S.A

During a 2008 study to assess endocrine and reproductive health of common carp ( Cyprinus carpio ) in Lake Mead, Nevada (U.S.A.) we identified two fish, one male and one female, as hybrids with goldfish ( Carassius auratus ) based on morphology, lateral line scale count, and lack of anterior barbels. Gross examination of the female hybrid ovaries indicated presence of vitellogenic ovarian follicles; whereas histological evaluation of the male hybrid testes showed lobule-like structures with open lumens but without germ cells, suggesting it was sterile. Because common carp/goldfish hybrids are more susceptible to gonadal tumors and may have different endocrine profiles than common carp, researchers using common carp as a model for endocrine/reproductive studies should be aware of the possible presence of hybrids.

Nevada↗

USGS2012

Wildlife and biological resources: Chapter 5 in A synthesis of aquatic science for management of Lakes Mead and Mohave

The creation of Lakes Mead and Mohave drastically changed habitats originally found along their region of the historical Colorado River. While still continuing to provide habitat conditions that support a rich diversity of species within the water, along shorelines, and in adjacent drainage areas, the reservoirs contain organisms that are both native and non-native to the Colorado River drainage (fig. 5-1). The diversity of species within these lakes continues to change with time due to changing habitat conditions, the invasion of non-native species, and extirpations of native species. From the bottom of the food web to the top predators, all organisms within the ecosystem are interconnected in food webs or food-chain networks. As non-native invasive species continue to be introduced into the lakes, alterations to the food web, species competition, and species predation likely will continue to change the ecosystem and populations of native organisms. Following an overview of the food web, this chapter summarizes information on aquatic and aquatic-dependent wildlife at Lakes Mead and Mohave and their relationships within the food web from members of lower trophic levels to the highest: phytoplankton, invertebrates, including zooplankton, and macroinvertebrates; fishes; and birds. The following sections describe the biological diversity, limiting factors, and ecological functions of these groups in Lake Mead, and to a lesser extent, in Lake Mohave.

Circular↗

USGS2010

Importance of benthic production to fish populations in Lake Mead prior to the establishment of quagga mussels

Limnologists recently have developed an interest in quantifying benthic resource contributions to higher-level consumers. Much of this research focuses on natural lakes with very little research in reservoirs. In this study, we provide a contemporary snapshot of the food web structure of Lake Mead to evaluate the contribution of benthic resources to fish consumers. In addition, we document the available food to fishes on soft sediments and changes to the invertebrate community over 2 time periods. Benthic invertebrate food availability for fishes is greater in Las Vegas Bay than Overton Arm. Las Vegas Bay is dominated by oligochaetes, whose biomass increased with depth, while Overton Arm is dominated by chironomids, whose biomass did not change with depth. Diet and isotopic measurements indicate the fish community largely relies on benthic resources regardless of basin (Las Vegas Bay >80%; Overton Arm >92%); however, the threadfin shad likely contribute more to largemouth and striped bass production in Overton Arm versus Las Vegas Bay. A 2-time period analysis, pre and post quagga mussel establishment and during lake level declines, suggests there is no change in the density of benthic invertebrates in Boulder Basin, but there were greater abundances of select taxa in this basin by season and depth than in other basins. Given the potential of alterations as a result of the expansion of quagga mussel and the reliance of the fishery on benthic resources, future investigation of basin specific, benthic processes is recommended.

Nevada↗

USGS2007

Organic Chemical Concentrations and Reproductive Biomarkers in Common Carp (Cyprinus carpio) Collected from Two Areas in Lake Mead, Nevada, May 1999-May 2000

The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, National Park Service, Bureau of Reclamation, and Nevada Department of Wildlife, collected and assessed data to determine the general health and reproductive status of common carp (Cyprinus carpio) at two study areas in Lake Mead, Nevada, during May 1999-May 2000. These data will form the basis of interpretations and provide a comparison for continuing studies on the health of the ecosystem in Lake Mead. One study area, Las Vegas Bay, is in the western part of Lake Mead. Las Vegas Bay receives inflows from Las Vegas Wash, which is predominantly tertiary-treated wastewater effluent, and to a lesser extent stormwater runoff from Las Vegas, Henderson, and other nearby communities, and from ground water underlying Las Vegas Valley. The other study area, Overton Arm, is in the northern extent of Lake Mead. Overton Arm receives inflow from the Virgin and Muddy Rivers, which historically are not influenced by wastewater effluent. Both sexes of common carp were collected bimonthly for 12 months using boat-mounted electrofishing gear (a direct electric current is used to temporarily immobilize fish for capture) to determine their health and reproductive status and any relation between these factors and environmental contaminants. This report presents fish tissue chemistry, organic chemical compound concentrations, and biomarker data for 83 male common carp collected from Las Vegas Bay, similar organic chemistry results for 15 male common carp, and similar biomarker measures for 80 male common carp collected from Overton Arm. Tissue chemistry results also are presented for 16 female common carp and biomarker measures for 79 female common carp collected from Las Vegas Bay, and tissue chemistry results for 15 female common carp and biomarker measures for 81 female common carp collected from Overton Arm. Thirty-three organic chemical compounds plus total concentrations for four groups of compounds (chlordanes, polychlorinated biphenyls [PCBs], brominated diphenyl ethers [BDEs], and triclosans) were analyzed from extracts of whole-body tissue using gas chromatography/mass spectrometry in male common carp from Las Vegas Bay during May 1999 through May 2000. All 33 compounds were detected in at least one sample of whole-body tissue from male common carp collected in Las Vegas Bay. In Overton Arm, 37 organic compounds plus total concentrations of three groups of compounds (PCBs, BDEs, and triclosans) were analyzed in male common carp where 20 (54 percent) of the compounds were detected. Sixteen of the 33 compounds detected in male common carp from Las Vegas Bay and 10 compounds detected in males from Overton Arm have the potential to disrupt the endocrine system in fish in Lake Mead. During May and June 1999, the mean concentration of all organic compounds detected in male common carp was 670 micrograms per kilogram from Las Vegas Bay and 109 micrograms per kilogram from Overton Arm. Twenty-seven organic compounds plus total PCBs were analyzed from extracts of whole-body tissue in female common carp collected in Las Vegas Bay and Overton Arm during May 1999. Twenty-four (86 percent) of these compounds were detected in at least one sample of whole-body tissue from female common carp collected from Las Vegas Bay while 10 (36 percent) chemical compounds were detected in female common carp from Overton Arm during that same period. Median concentrations of all chemical compounds were higher in female common carp from Las Vegas Bay compared to those collected from Overton Arm except Dacthal (DCPA), which was similar between sites. Biomarker measures obtained for male and female common carp include gonadosomatic index (percentage of gonad weight to total body weight), plasma vitellogenin (a phospholipid protein normally produced by female common carp and other oviparous fish), and condition factor [body weight/(fork length)3]. Biomarker measures for male c

Data Series↗

USGS2006

Investigations of the Effects of Synthetic Chemicals on the Endocrine System of Common Carp in Lake Mead, Nevada and Arizona

Introduction: Lake Mead is the largest reservoir by volume in the United States and was created by the construction of the 221-meter high Hoover Dam in 1935 at Black Canyon on the lower Colorado River between Nevada and Arizona (fig. 1). Inflows of water into the lake include three rivers, Colorado, Virgin, and Muddy; as well as Las Vegas Wash, which is now perennial because of discharges from municipal wastewater treatment plants (Covay and Leiker, 1998) and urban stormwater runoff. As the population within the Las Vegas Valley began to increase in the 1940s, the treated effluent volume also has increased and in 1993 it constituted about 96 percent of the annual discharge of Las Vegas Wash (Bevans and others, 1996). The mean flow of Las Vegas Wash into Las Vegas Bay from 1992 to 1998 was about 490,000 m3/d (Preissler and others, 1999) and in 2001 increased to 606,000 m3/d (U.S. Bureau of Reclamation, 2001). The nutrient concentration in most areas of the lake is low, but wastewater discharged into Las Vegas Bay has caused an increased level of nutrients and primary productivity (aquatic plant and algal production) in this area of the lake (LaBounty and Horn, 1997). A byproduct of this increase in productivity has been the establishment of an important recreational fishery in Las Vegas Bay. However, concentrations of chlorophyll a (a measure of algal biomass) have also increased (LaBounty and Horn, 1997). In the spring of 2001, parts of Lake Mead experienced massive algal blooms. In addition to nutrient loading by wastewater, the presence of numerous synthetic chemicals in water, bottom sediments, and in fish tissue also has been reported (Bevans and others, 1996). Synthetic chemicals discharging into Las Vegas Bay and Lake Mead (fig. 1) originate from several sources that include surplus residential-irrigation water runoff, stormwater runoff, subsurface inflow, and tertiary treated sewage effluent discharging from three sewage-treatment plants. Chemicals detected in Las Vegas Wash and Bay environments include polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (including DDT and DDE), and 'emerging contaminants' such as fragrances/musks, flame retardants, triclosan and its breakdown products, personal care products, and pharmaceuticals (Bevans and others, 1996; Boyd and Furlong, 2002; Leiker and others, in press). Many of these compounds are able to interact with the endocrine system of animals and potentially cause reproductive impacts. The National Park Service (NPS) manages Lake Mead National Recreation Area (LMNRA) with about 8 million yearly visitors including 500,000 anglers drawn to its world-class recreational fishery. The U.S. Fish and Wildlife Service (FWS) provides management for the federally designated, endangered razorback sucker (Xyrauchen texanus) and for more than 180 species of migratory birds that utilize LMNRA surface waters. These multiple uses of surface water in the area demonstrate their vital importance to the LMNRA as well as the need to maintain the quality of water at levels that are adequate for these uses.

Fact Sheet↗