Peter M. Kiffney

Establishing light as a causal mechanism structuring stream communities in response to experimental manipulation of riparian buffer width

Abstract Previous studies on the effects of logging on streams have suggested that light and water temperature were important variables structuring stream communities but, in many cases, these effects were confounded. We observed pronounced gradients in the flux of solar energy and water temperature in an earlier large-scale experiment in which we manipulated the width of riparian buffers along headwater streams. Associated with these abiotic changes were increases in periphyton biomass and primary consumer abundance. We present results from a study in streamside channels that was designed to isolate the effects of light on stream communities, while holding water temperature constant. Light treatments in the channel experiment simulated inputs of solar radiation created during the prior watershed-scale experiment. Results from the present study suggested that consumers limited periphyton biomass early in the study; however, a rainstorm midway through the experiment reduced periphyton biomass and insect consumer abundance. Following this disturbance, chlorophyll a biomass was 2 to 4 times higher in the full sunlight treatment compared to the 2 lowest light treatments. At the end of the study, primary consumer abundance, biomass, survival, and growth rate were positively related to light and periphyton resources. Therefore, we inferred biotic control of periphyton during the early part of the channel study, whereas light appeared to control periphyton at the end of the study. Results from the large-scale and channel experiments suggested that light was the primary constraint on periphyton biomass accrual. Moreover, both experiments, especially the channel study, showed that light indirectly influenced consumer performance as mediated by increased primary production.

Effects of Heavy Metals on a Macroinvertebrate Assemblage from a Rocky Mountain Stream in Experimental Microcosms

Natural assemblages of stream benthic macroinvertebrates were collected using artificial substrates from a Rocky Mountain stream and exposed for 10 d to a mixture of heavy metals (Cd, Cu, and Zn) in stream microcosms. Metal levels were 0, 1×, 5×, and 10× where × = 1.1, 12, and 110 μg/L Cd, Cu, and Zn, respectively. The 1× treatment was similar to chronic criteria values recommended by the US Environmental Protection Agency (EPA) for each metal and total metal levels measured in water at the Arkansas River, Colorado, a US EPA superfund site. Most ephemeropterans and plecopterans were sensitive to metals; however, some taxa within these groups were metal tolerant. Densities of Baetis tricaudatus (Ephemeroptera:Baetidae), Epeorus longimanus and Rhithrogena hageni (Ephemeroptera:Hepatageniidae), and Drunella grandis and D. doddsi (Ephemeroptera:Ephemerellidae) were reduced in the 1× treatment. The response of D. grandis to metals was size-dependent with small larvae being more sensitive than large ones (p = 0.02). Chironomids were generally tolerant to metals. These data show that a metal mixture was extremely toxic to stream macroinvertebrates from a Rocky Mountain stream. Our results were similar to field biomonitoring studies at the Arkansas River and Eagle River, Colorado, that examined the effects of metals on stream macroinvertebrate communities. We suggest that multispecies experiments using indigenous stream organisms be combined with field biomonitoring to rigorously define the biological effects of heavy metals on lotic systems.

Effects of Metals on Stream Macroinvertebrate Assemblages from Different Altitudes

We tested the hypothesis that macroinvertebrate assemblages from streams of different size (third- and fourth-order) and altitude (2545 and 2320 m above sea level) varied in their sensitivity to metals. We exposed macroinvertebrates collected from these sites to metals in stream microcosms and compared their responses to those measured at reference and metal-polluted sites at different altitudes. Densities of macroinvertebrate assemblages from the small, high-altitude stream were reduced more in metal-dosed mi- crocosms than those from the large, low-altitude stream. Results from the field survey were similar to experimental results, as densities of organisms from metal-polluted sites in small, high-altitude streams were lower than those of the same taxa in larger, lower-altitude streams. There are a number of factors that may contribute to the variation in metal sen- sitivity we observed, such as differences in abiotic factors or abundance of sensitive species between high- and low-altitude streams. In addition, differences in insect body size or phenology may have contributed to some of the observed variation in response. Since invertebrate assemblages from high-altitude sites were 12-85% more sensitive to metals, we suggest that metal criteria incorporate factors to allow for such differences to protect aquatic life.

Interactions among Nutrients, Periphyton, and Invertebrate and Vertebrate (Ascaphus truei) Grazers in Experimental Channels

Abstract Objectives of this study were to determine whether (1) stream algal biomass was nutrient limited, (2) stream herbivores could reduce algal biomass at different levels of productivity, and (3) a large vertebrate herbivore (Ascaphus truei) affected the abundance of insect grazers under different nutrient supply regimes. To address these objectives, we conducted a 2 × 2 factorial experiment to examine the effects of varying phosphate supply on periphyton biomass, insect grazers, and a tadpole grazer in 12 streamside experimental channels in southwestern Canada. We manipulated presence of tailed frog tadpoles (A. truei Stejneger) and varied nutrient levels using nutrient-diffusing pellets. We monitored periphyton biomass as ash-free dry mass (AFDM), insect grazer abundance, dissolved nutrients (NO3 − N and PO4 − P) in water, and tadpole growth rates over 38 days. Dissolved nitrate and phosphate concentrations were temporally variable, and there were no statistical differences among treatments, but dissolved phosphate levels were 1.7 times greater in nutrient-enriched channels (3.2 µg L−1) than in unenriched channels (1.7 µg L−1). Periphyton AFDM was significantly higher in channels with added nutrients, as was abundance of insect grazers, primarily Chironomidae and Ephemeroptera. Tadpoles in channels with nutrients had growth rates approximately four times higher than tadpoles in controls. Insect grazer abundance in channels with and without added nutrients was lower in the presence of tadpoles, and this reduction was greater in channels with nutrients. In contrast to other studies that have examined the impact of vertebrate herbivores on periphyton, tadpoles had no measurable effect on periphyton biomass. These data indicate periphyton and grazers were resource limited, as added nutrients increased periphyton biomass, as well as abundance (insect grazers) and biomass (tailed frog tadpoles) of herbivores.

Pesticides, aquatic food webs, and the conservation of Pacific salmon

Pesticides pose complex threats to the biological integrity of aquatic ecosystems. In the western US, pesticides have contaminated many surface waters that provide habitat for endangered salmon. These iconic species depend on the productivity of rivers, lakes, and estuaries to provide food for juvenile growth, a key determinant of subsequent marine survival. Despite extensive societal investments in salmon habitat restoration in recent years, the role of pesticides as a limiting factor for salmon recovery has received little attention. Pesticides can be toxic to primary producers and macroinvertebrates, thereby limiting salmon population recovery through adverse, bottom-up impacts on aquatic food webs. The integration of toxicology, environmental chemistry, population biology, community ecology, landscape ecology, conservation biology, and environmental policy is needed to better understand these indirect effects of pesticides on endangered species. We highlight key information gaps and discuss how future...

Factors Controlling Periphyton Accrual during Summer in Headwater Streams of Southwestern British Columbia, Canada

Abstract In headwater coastal streams of southwestern British Columbia, previous research suggested that light limited periphyton growth and abundance of grazing invertebrates. Logging along a reach of stream allowed us to further examine the importance of light, as well as other abiotic factors, in regulating stream periphyton and grazers. We placed unglazed ceramic tiles in three watershed, two of which served as controls. In the third watershed, we placed tiles in one reach that was newly harvested, as well as in an upstream, forested reach. Tiles were placed in streams in late June and removed weekly over a six-week period for determination of periphyton chlorophyll α and ash-free dry mass. We also measured discharge, dissolved nitrate and phosphate, and counted the number of invertebrate grazers on each removed tile weekly. Peak biomass, as chlorophyll α, was reached on day 29 with alga biomass at the logged site (19 μg m−2) seven to fourteen times higher than at the control sites. Stepwise, multiple linear regression suggested that light was the single best predictor explaining 64% of the variation in peak biomass of chlorophyll a Although periphyton biomass on tiles was much higher in the clearcut reach, so was fine sediment. Inorganic mass entrapped in the periphyton mat was two to four times higher in the clearcut stream than at other sites. Grazer abundance was not related to periphyton biomass, but was negatively related to sediment levels. Our results are consistent with the hypothesis that grazer abundance was determined by sediment levels rather than alga biomass.

The Influences of Body Size, Habitat Quality, and Competition on the Movement and Survival of Juvenile Coho Salmon during the Early Stages of Stream Recolonization

Abstract Understanding the factors influencing the success of juvenile Pacific salmon Oncorhynchus spp. in newly colonized habitats is essential to their recovery in large areas across the West Coast of the United States and Canada. We studied biotic and abiotic factors associated with survival during the early stages of colonization and population establishment of juvenile coho salmon O. kisutch in Rock Creek, a tributary of the upper Cedar River in the Lake Washington basin of Puget Sound, Washington. The stream was occupied by resident fishes (e.g., rainbow trout O. mykiss, cutthroat trout O. clarkii, speckled dace Rhinichthys osculus, and several sculpins Cottus spp.), but adult coho salmon and other anadromous fishes had been excluded by a dam from 1901 until fish ladder installation in 2003. We defined logistic regression models and used an information-theoretic approach to predict apparent survival with various combinations of individual fish condition, location competition, and local habitat quali...

Summer Distribution and Growth of Juvenile Coho Salmon during Colonization of Newly Accessible Habitat

Abstract Pacific salmon Oncorhynchus spp. are capable of exploiting vacant habitat, but most research has focused on straying and colonization by adults. However, dispersal of juveniles of stream-rearing species, such as coho salmon O. kisutch, may also be an important component of colonization. Installation of fish passage structures on the Cedar River, Washington, and subsequent adult migration into the newly accessible habitat provided a rare opportunity to investigate colonization as coho salmon regained access to 33 km of habitat from which they had been excluded for more than a century. In this study, we describe the spatial distribution and growth patterns of the first two generations of juvenile coho salmon produced in the new habitat. Snorkel surveys in the Cedar River revealed patchy distributions of juvenile coho salmon that largely matched the distribution of adults spawning the previous fall, and higher densities occurred in lower reaches (i.e., those not far upstream from the dam). However, ...

Linking resource availability and habitat structure to stream organisms: an experimental and observational assessment

An experiment and a mark-recapture field study of juvenile coho salmon (Oncorhynchus kisutch) were conducted to identify controls of key energy flow chains in river food webs. In the small-scale experiment, we investigated the individual and interactive effects of physical habitat structure (PHS) as small wood and resource availability (tissue of adult Chinook salmon, O. tshawytscha) on nutrients, algae, invertebrates, and fish predators including juvenile coho. In the field, we quantified the effects of natural variation in prey availability (invertebrate drift biomass), PHS (wood), and local fish density on summer growth of juvenile coho across multiple stream reaches. Adding salmon tissue to experimental channels resulted in strong bottom-up effects on select invertebrates including increased population biomass of chironomids and baetids, the numerically dominant invertebrates, and faster growth of juvenile coho. We link the enhanced growth of coho to chironomid productivity: for instance, adult chiron...

The influence of metal exposure history and ultraviolet-B radiation on benthic communities in Colorado Rocky Mountain streams

Abstract Interest in understanding the influence of ultraviolet-B (UVB; 280–320 nm) radiation in aquatic ecosystems has increased since the early 1990s. Pollution from historic mining operations coupled with physicochemical characteristics of Rocky Mountain streams that increase exposure of benthic communities to UVB provided an opportunity to examine how UVB interacted with heavy metal contamination to structure stream communities. We integrated a series of UVB addition experiments done in stream microcosms with a large-scale UVB shading experiment to test the hypothesis that effects of UVB were greater on benthic communities from metal-polluted streams than from reference streams. Microcosm experiments involved short-term exposure (7–10 d) of natural benthic macroinvertebrate communities collected from reference and metal-contaminated sites to lamp-generated UVB. In all cases, abundance decreased in UVB-treated streams compared to controls. Moreover, effects of UVB addition were significantly greater on communities from metal-polluted sites than from reference sites. The field experiment involved shading portions of the streambed from UVB for 60 d at 12 streams along a Zn gradient. Median Zn concentration at these sites ranged between 5 and 530 μg/L, and mean UVB reaching the streambed varied from 6.5 to 29.0 J/cm2. Results of the field experiment indicated that removal of UVB significantly increased total macroinvertebrate abundance and abundance of grazers, mayflies, caddisflies, Orthocladiinae midges, and the mayfly Baetis bicaudatus compared to controls. Grazer abundance was significantly greater in UVB removal treatments compared to controls, but UVB removal had no effect on algal biomass. As with the microcosm experiments, the effects of UVB removal on benthic communities were generally greater at metal-polluted sites than at reference sites. We speculate that the energetic cost of regulating metals might inhibit the ability of some organisms to repair efficiently DNA damaged by UVB exposure. Our results demonstrate that benthic communities in Colorado Rocky Mountain streams are negatively influenced by UVB radiation and that communities subjected to long-term metal exposure are more sensitive to UVB than are reference communities. As a consequence, the effects of increased UVB radiation reaching the earths surface might be more severe than previously considered in systems receiving multiple stressors.