Geology topics

N. Roxanna Razavi

Publications and source records attributed to N. Roxanna Razavi.

4 recordsLinked to original sources

USGS2025

Using complementary biomarkers to unravel fish lifetime exposure to hypoxia and mercury

Aquatic ecosystems are losing oxygen due to climate change. This deoxygenation can favor microbial methylation of mercury (Hg). To understand the dynamics of Hg under increasing deoxygenation, we simultaneously quantified both Hg and hypoxia (< 2 mg O2/L) lifetime chronologies in fishes. We used a novel combination of chemical biomarkers in ear stones and eye lenses. We compared these markers in two species with different life histories, benthic Round Goby (Neogobius melanostomus) and semi-demersal Yellow Perch (Perca flavescens), from two connected ecosystems with different levels of hypoxia: the Central Basin of Lake Erie and the less hypoxic but more polluted Western Basin. Overall, Central Basin Round Goby were exposed to hypoxia throughout their lifetime and exhibited significantly elevated eye lens Hg concentrations ([Hg]) compared to their Western Basin counterparts. In contrast, the Central Basin Yellow Perch were exposed to hypoxia only at their juvenile stage. Central Basin Yellow Perch exhibited significantly lower eye lens [Hg] compared to their Western Basin counterparts. Patterns revealed by eye lens [Hg] were not detectable in muscle tissue [Hg]. Findings show that exposure to hypoxia can alter fish lifetime Hg accumulation patterns, with species-specific outcomes.

central and western basins of Lake Erie↗

USGS2024

A comparison of stable isotopes and polychlorinated biphenyls 1 among genetic strains of Lake Ontario lake trout (Salvelinus namaycush)

This study quantified stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes, polychlorinated biphenyl (PCB) concentrations and growth rates among multiple genetic strains of Lake Ontario lake trout ( Salvelinus namaycush ) to evaluate the potential role of genetics in these parameters. Fish ranging in age from 1 to 31 years ( n = 72) and representing nine genetic strains including wild-recruits to hatchery fish derived from Lakes Ontario, Superior and Champlain watersheds, and individuals of unknown hatchery origin. Carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope values averaged −22.2 ‰ and 17.4 ‰, respectively, but did not differ significantly among genetic strains. ΣPCB concentrations ranged from 42 to 1820 ng/g and varied significantly among individuals including those of similar age and genetic strain. For example, Sum PCB (ΣPCB) concentrations among 7-year-old fish ( n = 16) ranged from 159 to 607 ng/g, which compares to growth rates of 3.5 – 32.9 %/yr for these same fish. Multivariate analysis of stable isotope and PCB profiles, however, provided considerable resolution among the strains. For example, fish of unknown hatchery origin ordinated most similar to Seneca Lake fish, the predominant strain stocked in Lake Ontario. Wild fish had a unique ordination with only Lake Superior Klondike strain fish overlapping into their ordination space. Lakes Champlain and Superior strain individuals had similar ordinations but did not overlap substantially with wild or Klondike strain fish. Combined, these differences agree with the ecologies described for these strains in their native ecosystems suggesting that insight can be gained from strain specific evaluations of ecological tracers and these pollutants among Great Lakes lake trout.

Lake Ontario↗

USGS2022

Tracking fish lifetime exposure to mercury using eye lenses

Mercury (Hg) uptake in fish is affected by diet, growth, and environmental factors such as primary productivity or oxygen regimes. Traditionally, fish Hg exposure is assessed using muscle tissue or whole fish, reflecting both loss and uptake processes that result in Hg bioaccumulation over entire lifetimes. Tracking changes in Hg exposure of an individual fish chronologically throughout its lifetime can provide novel insights into the processes that affect Hg bioaccumulation. Here we use eye lenses to determine Hg uptake at an annual scale for individual fish. We assess the widely distributed benthic round goby ( Neogobius melanostomus ) from the Baltic Sea, Lake Erie, and the St. Lawrence River. We aged layers of the eye lens using proportional relationships between otolith length at age and eye lens radius for each individual fish. Mercury concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry. The eye lens Hg content revealed that Hg exposure increased with age in Lake Erie and the Baltic Sea but decreased with age in the St. Lawrence River, a trend not detected using muscle tissues. This novel methodology for measuring Hg concentration over time with eye lens chronology holds promise for quantifying how global change processes like increasing hypoxia affect the exposure of fish to Hg.

Environmental Science and Technology↗

USGS2020

Mercury in fish from streams and rivers in New York State: Spatial patterns, temporal changes, and environmental drivers

Mercury (Hg) concentrations in freshwater fish across the state of New York frequently exceed guidelines considered harmful to humans and wildlife, but statewide distribution and temporal changes are not well known for the state’s streams and rivers. We analyzed existing data to describe recent spatial patterns, identify key environmental drivers, and assess temporal changes. Size classes within sportfishes and prey fishes formed ‘functional taxa’ (FT), and standardized scores were generated from 2007-2016 data for 218 sites. Muscle Hg in >1 sportfish FT exceeded human-health guidelines of 50 ng/g (sensitive populations) and 300 ng/g (general population, GP) at 93% and 56% of sites, respectively, but exceeded 1000 ng/g (a state threshold) at only 10% of sites. Whole-body Hg in >1 prey fish FT exceeded wildlife thresholds of 40 ng/g and 100 ng/g at 91% and 51% of sites, respectively. Environmental drivers of recent spatial patterns include extent of forest cover and storage, the latter an indicator of wetlands. Standardized Hg scores increased with increasing atmospheric Hg deposition and storage across rural ‘upland’ regions of New York. However, scores were not related to atmospheric deposition in more-developed ‘lowland’ regions due to the limited methylation potential of urban landscapes. Comparisons of 2010-2015 sportfish Hg concentrations with those of 1998 and 2000-2005 showed inconsistent temporal changes both among and within eight sites examined. Some recent stream and river fish Hg spatial patterns differed from those of lake-based studies, highlighting the importance of New York’s flowing waters to future Hg monitoring and risk assessment.

New York↗