Geology topics

John R. Stevenson

Publications and source records attributed to John R. Stevenson.

4 recordsLinked to original sources

USGS2022

Dammed water quality — Longitudinal stream responses below beaver ponds in the Umpqua River Basin, Oregon

Beaver-related restoration (BRR) has gained popularity as a means of improving stream ecosystems, but the effects are not fully understood. Studies of dissolved oxygen (DO) and water temperature, key water quality metrics for salmonids, have demonstrated improved conditions in some cases, but warming and decreased DO have been more commonly reported in meta-analyses. These results point to the contingencies that can influence outcomes from BRR. We examined water quality related to beaver ponds in a diverse coastal watershed (Umpqua River Basin, OR, USA). We monitored water temperature 0–400 m above and below beaver ponds and at pond surfaces and bottoms across seven study sites from June through September of 2019. DO was also recorded at two sites at pond surfaces and pond bottoms. Downstream monthly mean daily maximum temperatures were warmer than upstream reference locations by up to 1.9°C at beaver dam outlets but this heating signal attenuated with downstream distance. Downstream warming was greatest in June and July and best predicted by pond bottom temperatures. DO at pond surfaces and bottoms were hypoxic (≤5 mg/L) for more than half of the 32-day monitoring period. Water temperatures increased for short distances below monitored beaver ponds and observed oxygen conditions within ponds were largely unsuitable for salmonid fishes. These findings contrast with some commonly stated expectations of BRR, and we recommend that managers consider these expectations prior to implementation. In some cases, project goals may override water quality concerns but in streams where temperature or DO restoration are objectives, managers may consider using BRR techniques with caution.

Oregon↗

USGS2020

What to do when invaders are out of control?

Biological invasions threaten species and ecosystems worldwide. Impacts from invasions are especially prevalent in freshwaters, where managers have struggled to contain the problem. Conventional approaches to managing invaders focus on prevention and control. In practice, these measures have proven to be variably effective. Control or eradication of established invaders is particularly difficult and, even if ecologically feasible, it may not be socially desirable. Here we propose a new alternative to managing invasive species: managing impact modifiers (MIM). The MIM approach focuses on managing impacts, rather than controlling the invader directly. We reviewed the literature for the world's worst invasive fishes in freshwaters to show there is strong evidence to support the potential for MIM as an effective means of managing impacts of invasions. This included evidence pointing to characteristics of the environment or species themselves that modify impacts of invasions. Detail of three case studies reinforces the potential for MIM as a viable option. Although MIM appears promising, effective application could involve significant investment in an information gathering phase to identify impact modifiers and the means to manage them. Accordingly, MIM is best incorporated into management plans that include a strong learning or adaptive component. Ultimately, MIM may be one of the only viable alternatives for managing invasive species that are truly out of control.

WIREs Water↗

USGS2012

Design and performance of radio telemetry systems for assessing juvenile fish passage at three hydroelectric dams

Studies of the effects of hydroelectric dams on fish populations are common (Williams 2008). Dams block passage of migratory and resident fish, alter habitats from free-flowing to lacustrine, and can alter water temperatures both upstream and downstream. At some dams, structures or operations are modified to reduce their effects on fish populations. In these cases, it is recommended that a series of studies be conducted before and after the alterations to help assess the effectiveness of the actions. We will describe three studies at hydroelectric dams on the Columbia and Snake rivers in the Pacific Northwest of the United States prompted by a need to reduce their effects on fishes, primarily salmonids, listed under the Endangered Species Act (ESA 1973). Hydroelectric development on the Columbia and Snake rivers occurred chiefly between the early 1930s and the late 1970s. Fish originating in the upper portions of the Columbia and Snake rivers must pass as many as eight dams on these rivers during their seaward migration and again on their trip back to their natal waters. Small changes in passage survival at each dam can be important, due to the multiplicative effects of the series of dams. For example, if downstream passage survival at each of eight dams and reservoirs was 90% and it was increased by only 3% per dam, the numbers of fish surviving through the entire hydro system would increase from 43% to 56%. Thus, precisely measuring small changes in passage survival are important to the overall program. This has been achieved by designing efficient telemetry systems and releasing large numbers of tagged fish.

Book chapter↗

USGS2012

Optimization of radio telemetry receiving systems

The performance of radio telemetry receiving systems can be affected by numerous factors, thus it is important for researchers to understand these factors when designing a radio telemetry study. One approach that has been used to describe these factors is the radio system equation which defines six variables that affect radio receiving systems (Sisak and Lotimer 1998; Section 5.1). This equation is: P r = P t – L w – L awi –L air + G r – L rtl where P r is the received power level, P t is the transmitted power level, L w is the signal loss in water, L awi is the loss at the air-water interface, L air is the loss in air, G r is the gain of the receive antenna, and L rtl is the loss of the receive transmission line (Figure 1). Three of these variables (L w , L air , and L awi ) are affected by factors that researchers have little control over (i.e., distance traveled by a given radio signal, water conductivity and temperature, angle of refraction of the signal as it exits the water). However, P t , G r , and L rtl can be influenced by the user and planning for the effects of each is an essential first step towards designing a radio receiving system that operates at the highest level possible. The first of these factors P t , is addressed while choosing which transmitter to purchase, a topic which was covered in a previous Section. Much of the information that we present will focus on maximizing the strength of the signal that is received by the radio receiver which is affected by G r and L rtl . Additionally, we will cover techniques to minimize the effects of ambient (or background) noise which is also an important aspect of radio receiving systems. Ambient noise is important because low signal-to-noise ratios will result in signals that cannot be detected by the receiving system. In other words, tagged fish within range of the receiving system are not detected because ambient noise levels exceed the received signal at the receiver.

Book chapter↗