Ben N. Mcgee | Search USGS

USGS2022

Increased mercury and reduced insect diversity in linked stream-riparian food webs downstream of a historical mercury mine

Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on culturally and ecological important downstream ecosystems is not always straight-forward because of elevated natural levels of mineralization in mining-impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed (USA), we measured multiple community and chemical endpoints in downstream linked aquatic-terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was in much higher concentrations (1.3 to 11.3-fold) and isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury (MeHg) concentrations in bull trout and riparian spiders were sufficiently high (732 – 918 and 347 – 1,140 ng MeHg g -1 dw) to affect humans, birds, and piscivorous fish. Furthermore, the alpha-diversity of benthic insects was locally depressed by 12-20% within 4.3 to 5.7 km downstream of from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m -2 ) was extremely elevated downstream (10 – 1,778-fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect-mediated fluxes of total mercury were also high (~16 ng THg m -2 d -1 ). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans.

Idaho↗

USGS2019

Sand Creek characterization study for Oncorhynchus clarkii virginalis (Rio Grande Cutthroat Trout), Great Sand Dunes National Park and Preserve, Colorado

The Oncorhynchus clarkii virginalis (Rio Grande cutthroat trout, RGCT) has undergone extensive declines in distribution and population. The RGCT is the southernmost distributed subspecies of cutthroat trout. Native to the Rio Grande Basin in Colorado and New Mexico, the subspecies is also found in the headwaters of the Pecos River and Canadian River basins in New Mexico. Currently, RGCT populations represent approximately 12 percent of the historic distribution. There are many factors that have contributed to the decline of the RGCT including small population sizes; hybridization with non-native salmonids; competition with non-native salmonids; angling; and loss of habitat resulting from wildfire, stream drying, disease, increased water temperatures; and poor land management. The eastern side of Colorado’s Rio Grande Basin is also home to Great Sand Dunes National Park and Preserve and the Sand Creek watershed. This study was designed to (1) characterize current physical and biological conditions of waterbodies within the Sand Creek watershed, from headwaters to lower terminus near the dune field; (2) characterize the spatial extent of existing fisheries within the Sand Creek watershed to inform the scope of potential future reclamation efforts; and (3) evaluate key limiting factors for a future native RGCT reintroduction. Bathymetric profiles were completed for two lakes within the upper Sand Creek drainage to characterize the physical geometry of each lake and to estimate the total lake volume required for future piscicide treatment and (or) fish removal efforts. Physical and biological conditions evaluated included stream water temperature and intermittency, discharge, and the genetics and existing fish community distribution and composition within the Sand Creek watershed were key components of this study. A baseline established the geographic extent and biological constraints factored into future piscicide treatment planning and native trout reintroduction efforts. As a result of this work, the Sand Creek watershed can be broken up into several distinct categories: Lakes that are good candidates for reclamation and reintroduction of RGCT, lakes that are poor candidates for reclamation, streams that currently have fish and are good candidates for reclamation and reintroduction, streams that currently lack fish and may be good candidates for introduction of RGCT, and streams that currently lack fish and are not good candidates for introduction of RGCT. This characterization study report is intended to inform State and Federal managers of the likelihood that the Sand Creek watershed can support a sustainable population of RGCT should they be reintroduced.

Colorado↗