Geology topics

Brett M. Johnson

Publications and source records attributed to Brett M. Johnson.

6 recordsLinked to original sources

USGS2021

Using isotopic data to evaluate Esox lucius (Linnaeus, 1758) natal origins in a hydrologically complex river basin

Otolith microchemistry has emerged as a powerful technique with which to identify the natal origins of fishes, but it relies on differences in underlying geology that may occur over large spatial scales. An examination of how small a spatial scale on which this technique can be implemented, especially in water bodies that share a large proportion of their flow, would be useful for guiding aquatic invasive species control efforts. We examined trace isotopic signatures in northern pike ( Esox lucius ) otoliths to estimate their provenance between two reservoirs in the Upper Yampa River Basin, Colorado, USA. This is a challenging study area as these reservoirs are only 11-rkm apart on the same river and thus share a high proportion of their inflow. We found that three isotopes ( 86 Sr, 137 Ba, and 55 Mn) were useful in discriminating between these reservoirs, but their signatures varied annually, and the values overlapped. Strontium isotope ratios ( 87 Sr/ 86 Sr) were different between sites and relatively stable across three years, which made them an ideal marker for determining northern pike provenance. Our study demonstrates the usefulness of otolith microchemistry for natal origin determination within the same river over a relatively small spatial scale when there are geologic differences between sites, especially geologic differences underlying tributaries between sites.

Colorado↗

USGS2019

Compound effects of water clarity, inflow, wind and climate warming on mountain lake thermal regimes

Many studies have examined the effects of climate warming on lake stability, but few have addressed environmental changes concomitant with climate change, such as alterations in water clarity and lake inflow. Although air temperature rise is a predominant factor linked to lake thermal characteristics, climate-driven changes at watershed scales can substantially alter lake clarity and inflow, exacerbating the effects of future air warming on lake thermal conditions. Without accounting for potential changes in clarity and inflow, future thermal predictions could be inaccurate. We employed the General Lake Model to simulate future thermal conditions (relative thermal resistance to mixing; RTRM) of small (< 12 ha) mountain lakes of the western United States by calibrating the model to a set of lakes in the Southern Rocky Mountains, USA. We found that after air temperature, alterations in inflow had the largest effect on lake thermal conditions, changes in wind had the least effect, and larger lakes experienced more than double the increase in lake stability than smaller lakes. Generally, clear, high inflow lakes had the lowest stability now, and in the future, while the largest overall increase in thermal stability occurred in larger lakes with low inflows and high turbidity. Assuming air temperature rise alone, summer stability of mountain lakes of the western United States was predicted to increase by 15–23% at + 2 °C air temperatures, and by 39–62% at + 5 °C air temperatures. When accounting for associated changes in clarity and inflow, lake stability was predicted to increase by 208% with + 2 °C air warming and 318% with at 5 °C air warming. Thus, ignoring the multivariate effects of climate change can substantially underestimate changes to mountain lake thermal and stratification regimes. Dimictic lakes may become more strongly stratified and polymictic lakes will experience more prolonged stratification. While predicted changes to lake temperatures may not be harmful to trout species that currently inhabit mountain lakes, longer and more intense stratification could cause indirect effects, such as hypoxia, that could reduce growth and survival of these organisms.

Colorado↗

USGS2019

Estimating lake–climate responses from sparse data: An application to high elevation lakes

Although many studies demonstrate lake warming, few document trends from lakes with sparse data. Diel and seasonal variability of surface temperatures limit conventional trend analyses to datasets with frequent repeated observations. Thus, remote lakes, including many high elevation lakes, are underrepresented in trend analyses. We used a Bayesian technique to analyze sparse data that explicitly incorporated diel and seasonal variability. This approach allowed us to estimate lake warming in a region of limited knowledge: high elevation lakes (> 2100 m ASL) of the Southern Rocky Mountains, U.S.A. The analysis allowed for inclusion of lakes with few repeated measurements, and observations made before 1980 when more intensive lake monitoring began. We accumulated the largest dataset of high elevation lake temperatures analyzed to date. Data from 590 high elevation lakes in the Southern Rocky Mountains showed a 0.13°C decade −1 increase in surface temperatures and a 14% increase in seasonal degree days since 1955. This result is lower than other regional and global estimates of lake warming; however, it is similar to other high elevation lake studies. Our approach can be applied to other understudied regions, increasing our overall understanding of the effects of climate change on lakes and their temporal dynamics.

Colorado↗

USGS2012

Origins of invasive piscivores determined from the strontium isotope ratio ( 87 Sr/ 86 Sr) of otoliths

We examined strontium isotope ratios ( 87 Sr/ 86 Sr) in fish otoliths to determine the origins of invasive piscivores in the Upper Colorado River Basin (UCRB, western USA). We examined 87 Sr/ 86 Sr from fishes in different reservoirs, as well as the temporal stability and interspecies variability of 87 Sr/ 86 Sr of fishes within reservoirs, determined if 87 Sr/ 86 Sr would be useful for "fingerprinting" reservoirs where invasive piscivores may have been escaping into riverine habitat of endangered fishes in the UCRB, and looked for evidence that such movement was occurring. Our results showed that in most cases 87 Sr/ 86 Sr was unique among reservoirs, overlapped among species in a given reservoir, and was temporally stable across years. We identified the likely reservoir of origin of river-caught fish in some cases, and we were also able to determine the year of possible escapement. The approach allowed us to precisely describe the 87 Sr/ 86 Sr fingerprint of reservoir fishes, trace likely origins of immigrant river fish, and exclude potential sources, enabling managers to focus control efforts more efficiently. Our results demonstrate the potential utility of 87 Sr/ 86 Sr as a site-specific and temporally stable marker for reservoir fish and its promise for tracking fish movements of invasive fishes in river-reservoir systems.

Upper Colorado River Basin↗

USGS2004

Cumulative effects of nutrients and pH on the plankton of two mountain lakes

We conducted enclosure experiments to examine the cumulative effects of nutrient enrichment and acidification on the plankton of two mountain lakes with differing nutrient conditions. The low-nitrate lake responded to N, N plus acid, and N plus acid plus P additions, showing four- to seven-fold increases in chlorophyll a , increased photosynthetic rate, compositional shifts toward large chlorophytes, and decreased zooplankton biomass. The high-nitrate lake responded minimally to either N or P alone but responded strongly to combined additions of N plus acid plus P, showing eightfold increases in chlorophyll a , increased cell density and photosynthetic rates, and compositional shifts toward chlorophytes and the dinoflagellate Gymnodinium . In both study lakes, changes in chlorophyll a were linked to addition of limiting nutrients regardless of pH, whereas shifts in phytoplankton species composition were apparently affected by both nutrient conditions and acidity. The most striking changes in species composition and biomass occurred in combined N plus acid plus P treatments, indicating that continued nutrient enrichment may interact with acidification to produce marked changes in the plankton of mountain lakes.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2004

Nitrogen regulation of algal biomass, productivity, and composition in shallow mountain lakes, Snowy Range, Wyoming, USA

We investigated the effects of increased nitrate (NO 3 ), alone and in combination with phosphorus (P), on phytoplankton, epilithon, and epipelon in shallow lakes of the Snowy Range, Wyoming, using two enclosure experiments during early and late summer. Phytoplankton responded strongly to N and N + P, but not to P, with increased cell density, chlorophyll a , and photosynthesis and shifts in composition from chrysophytes to cyanophytes, chlorophytes, and diatoms. Zooplankton density and biomass were unaltered despite the additional phytoplankton stock, probably as the result of poor food quality. In the late summer, algae on tiles responded to N and N + P additions with greater chlorophyll a and increases in cyanophyte and chlorophyte density. Algae on sediment dominated whole-enclosure algal biomass but were spatially variable and responded insignificantly to nutrients. Consequently, N controlled productivity and community composition of phytoplankton and algae on hard substrates but had less impact on ecosystem algal biomass because of the large pool of nutrient-sufficient sediment algae. Phytoplankton were more photosynthetically efficient than the benthos, however, such that primary productivity did shift more toward the water column.

Canadian Journal of Fisheries and Aquatic Sciences↗