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At least 1,207 records · Page 67Linked to original sources
USGS1997

Stream habitat characteristics of fixed sites in the western Lake Michigan drainages, Wisconsin and Michigan, 1993-95

Habitat characteristics of 11 fixed sites in the Western Lake Michigan Drainages were examined by the U.S. Geological Survey from 1993 through 1995 as part of the ecological assessment of the National Water-Quality Assessment Program. Evaluation of habitat consisted of more than 75 measurements at three spatial levels: drainage basin, stream segment between major tributaries (length from 1 to 14 kilometers), and stream reach (approximately 150 meters). The 11 fixed sites consisted of 8 "indicator" sites with drainage basins that differ in bedrock type, surficial deposits, and land use; and 3 "integrator" sites with drainage basins that contain a mixture of bedrock type, surficial deposits, and land use. Spatial and temporal variations in habitat characteristics are described and compared. Comparisons are limited to indicator sites except for comparisons amongbasin characteristics, which include all fixed sites. Two habitat classification schemes used in Wisconsin and Michigan were used to rank the quality of habitat in indicator streams. Reach-level data were collected at two additional reaches at three of the indicator sites to assess the representativeness of the reach for overall stream conditions. Although the number of sites is small, statistical analyses indicate that spatial distribution of several characteristics can be related to land use, geology, topography, and width of the riparian zone. Land use and geology, in combination, appeared to be important factors in controlling flood magnitudes. Annual mean flow was correlated with basin shape and drainage density and low flow was correlated with permeability of soils in the basin. At the reach level, a wide variety of characteristics were observed at the eight indicator sites, with many of the characteristics significantly different between sites. Spatial differences in some reach characteristics can be attributed to the percentage of agriculture in the drainage basin, type of surficial deposits, and width of the riparian zone. Temporal variability in width, depth, and velocity can be attributed to variable flow conditions; whereas temporal variability in streambank measurements are attributed to problematic identification of the boundary between the flood plain and streambanks. Data from multiple-reach sites indicate that the primary reach adequately represented the variability found within the stream segment for depth, streambank stability index, and canopy angle. However, velocity, dominant substrate type, embeddedness, streambank height, streambank angle, and streambank vegetative stability differed among the multiple reaches at one or more of the three sites. Correlation analyses of habitat characteristics with median concentrations of four nutrients, pH, and specific conductance indicates that dissolved nitrate plus nitrite concentrations are related to percentage of agriculture in the basin and fine-grained sediment deposition in the reach. Geology and land use appear to be major influences on pH, but their influence on specific conductance, although expected, was not confirmed in this study. Habitat evaluation scores at the eight indicator sites ranged from poor to good. Scores were correlated to the percentage of agricultural or urban land in the drainage basins, width of the riparian zone, and streambank stability index. Results from this study illustrate the need for collection of habitat data at multiple scales along with water-chemistry data for determining major influences on distribution of aquatic communities. These results also indicate the importance of collecting land use, geological, and geomorphic information at the drainage-basin level to adequately describe how natural and human factors influence local aquatic habitat conditions.

Michigan, Wisconsin↗
USGS2007

Toward a transport-based analysis of nutrient spiraling and uptake in streams

Nutrient addition experiments are designed to study the cycling of nutrients in stream ecosystems where hydrologic and nonhydrologic processes determine nutrient fate. Because of the importance of hydrologic processes in stream ecosystems, a conceptual model known as nutrient spiraling is frequently employed. A central part of the nutrient spiraling approach is the determination of uptake length ( S w ), the average distance traveled by dissolved nutrients in the water column before uptake. Although the nutrient spiraling concept has been an invaluable tool in stream ecology, the current practice of estimating uptake length from steady‐state nutrient data using linear regression (called here the “ S w approach”) presents a number of limitations. These limitations are identified by comparing the exponential S w equation with analytical solutions of a stream solute transport model. This comparison indicates that (1) S w is an aggregate measure of uptake that does not distinguish between main channel and storage zone processes, (2) S w is an integrated measure of numerous hydrologic and nonhydrologic processes—this process integration may lead to difficulties in interpretation when comparing estimates of S w , and (3) estimates of uptake velocity and areal uptake rate ( v f and U ) based on S w are not independent of system hydrology. Given these findings, a transport‐based approach to nutrient spiraling is presented for steady‐state and time‐series data sets. The transport‐based approach for time‐series data sets is suggested for future research on nutrient uptake as it provides a number of benefits, including the ability to (1) separately quantify main channel and storage zone uptake, (2) quantify specific hydrologic and nonhydrologic processes using various model parameters (process separation), (3) estimate uptake velocities and areal uptake rates that are independent of hydrologic effects, and (4) use shortterm, non‐plateau nutrient additions such that the effects of regeneration and mineralization are minimized. In summary, the transport‐based, time‐series approach provides a means of estimating traditional measures of nutrient uptake ( S w , v f , U ) while providing additional information on the location and magnitude of uptake (main channel versus storage zone). Application of the transport‐based approach to time‐series data from Green Creek, Antarctica, indicates that the bulk of nitrate uptake (~74% to 100%) occurred within the main channel where benthic uptake by algal mats is a likely process. Substantial uptake (~26%) also occurred in the storage zone of one reach, where uptake is attributed to the microbial community.

Limnology and Oceanography: Methods↗
USGS2016

Prey partitioning and use of insects by juvenile sockeye salmon and a potential competitor, threespine stickleback, in Afognak Lake, Alaska

Freshwater growth of juvenile sockeye salmon ( Oncorhynchus nerka ) depends upon the quality and quantity of prey and interactions with potential competitors in the foraging environment. To a large extent, knowledge about the ecology of lake-rearing juvenile sockeye salmon has emerged from studies of commercially important runs returning to deep nursery lakes, yet information from shallow nursery lakes (mean depth ≤ 10 m) is limited. We examined seasonal and ontogenetic variation in diets of juvenile sockeye salmon ( N = 219, 30–85 mm) and an abundant potential competitor, threespine stickleback ( Gasterosteus aculeatus ; N = 198, 42–67 mm), to understand their foraging ecology and potential trophic interactions in a shallow Alaska lake. This study revealed that adult insects made up 74% of all sockeye salmon diets by weight and were present in 98% of all stomachs in Afognak Lake during the summer of 2013. Diets varied temporally for all fishes, but small sockeye salmon (<60 mm) showed a distinct shift in consumption from zooplankton in early summer to adult insects in late summer. We found significant differences in diet composition between sockeye salmon and threespine stickleback and the origin of their prey indicated that they also separated their use of habitat on a fine scale; however, the two species showed overlap in size selectivity of zooplankton prey. Considering that aquatic insects can be a primary resource for juvenile sockeye salmon in Afognak Lake, we encourage the development of nursery lake carrying capacity models that include aquatic insects as a prey source for sockeye salmon.

Alaska↗
USGS2017

Predicting wading bird and aquatic faunal responses to ecosystem restoration scenarios

In large-scale conservation decisions, scenario planning identifies key uncertainties of ecosystem function linked to ecological drivers affected by management, incorporates ecological feedbacks, and scales up to answer questions robust to alternative futures. Wetland restoration planning requires an understanding of how proposed changes in surface hydrology, water storage, and landscape connectivity affect aquatic animal composition, productivity, and food-web function. In the Florida Everglades, reintroduction of historical hydrologic patterns is expected to increase productivity of all trophic levels. Highly mobile indicator species such as wading birds integrate secondary productivity from aquatic prey (small fishes and crayfish) over the landscape. To evaluate how fish, crayfish, and wading birds may respond to alternative hydrologic restoration plans, we compared predicted small fish density, crayfish density and biomass, and wading bird occurrence for existing conditions to four restoration scenarios that varied water storage and removal of levees and canals (i.e. decompartmentalization). Densities of small fish and occurrence of wading birds are predicted to increase throughout most of the Everglades under all restoration options because of increased flows and connectivity. Full decompartmentalization goes furthest toward recreating hypothesized historical patterns of fish density by draining excess water ponded by levees and hydrating areas that are currently drier than in the past. In contrast, crayfish density declined and species composition shifted under all restoration options because of lengthened hydroperiods (i.e. time of inundation). Under full decompartmentalization, the distribution of increased prey available for wading birds shifted south, closer to historical locations of nesting activity in Everglades National Park.

Restoration Ecology↗
USGS2024

Reduction of large vessel traffic improves water quality and alters fish habitat-use throughout a large river

Rivers are increasingly used as superhighways for the continental-scale transportation of freight goods, but the ecological impact of large vessel traffic on river ecosystems is difficult to study. Recently, the temporary maintenance closure of lock and dam systems on the Illinois Waterway (USA) brought commercial vessel traffic to a halt along the river's length, offering a rare opportunity to study the response of the ecosystem before, during, and after an extended pause of this persistent anthropogenic disturbance. We observed improvements in main- and side-channel water quality and a redistribution of fish habitat-use during a months-long, near-complete reduction of large vessel traffic. Over 3600 water quality and 1300 fish community samples indicate that large vessel traffic reduction coincided with a 33 % reduction in turbidity as well as increased use of sampling strata near vessel navigation corridors by sound-sensitive and rheophilic fishes. Gizzard shad ( Dorosoma cepedianum ), the most abundant species in the system, also expanded their use of these ‘impact’ areas. Though inland waterway transport is an economically- and climate-friendly alternative to trucking and rail for the shipment of freight, our data suggest that intense vessel traffic may have profound physical and biological impacts across a large river. Monitoring and mitigation of ecological impacts of the ongoing expansion of inland waterway transport around the world will be critical to balancing large rivers as both useful navigation corridors and functional ecosystems.

Illinois↗
USGS2017

When perception reflects reality: Non-native grass invasion alters small mammal risk landscapes and survival

Modification of habitat structure due to invasive plants can alter the risk landscape for wildlife by, for example, changing the quality or availability of refuge habitat. Whether perceived risk corresponds with actual fitness outcomes, however, remains an important open question. We simultaneously measured how habitat changes due to a common invasive grass (cheatgrass, Bromus tectorum ) affected the perceived risk, habitat selection, and apparent survival of a small mammal, enabling us to assess how well perceived risk influenced important behaviors and reflected actual risk. We measured perceived risk by nocturnal rodents using a giving-up density foraging experiment with paired shrub (safe) and open (risky) foraging trays in cheatgrass and native habitats. We also evaluated microhabitat selection across a cheatgrass gradient as an additional assay of perceived risk and behavioral responses for deer mice ( Peromyscus maniculatus ) at two spatial scales of habitat availability. Finally, we used mark-recapture analysis to quantify deer mouse apparent survival across a cheatgrass gradient while accounting for detection probability and other habitat features. In the foraging experiment, shrubs were more important as protective cover in cheatgrass-dominated habitats, suggesting that cheatgrass increased perceived predation risk. Additionally, deer mice avoided cheatgrass and selected shrubs, and marginally avoided native grass, at two spatial scales. Deer mouse apparent survival varied with a cheatgrass–shrub interaction, corresponding with our foraging experiment results, and providing a rare example of a native plant mediating the effects of an invasive plant on wildlife. By synthesizing the results of three individual lines of evidence (foraging behavior, habitat selection, and apparent survival), we provide a rare example of linkage between behavioral responses of animals indicative of perceived predation risk and actual fitness outcomes. Moreover, our results suggest that exotic grass invasions can influence wildlife populations by altering risk landscapes and survival.

Wyoming↗
USGS1993

Effect of organic loading on nitrification and denitrification in a marine sediment microcosm

The effects of organic additions on nitrification and denitrification were examined in sediment microcosms. The organic material, heat killed yeast, had a C/N ratio of 7.5 and was added to sieved, homogenized sediments. Four treatments were compared: no addition (control, 30 g dry weight (dw) m-2 mixed throughout the 10 cm sediment column (30 M), 100 g dw m-2 mixed throughout sediments (100M), and 100 g dw m-2 mixed into top 1 cm (100S). After the microcosms had been established for 7-11 days, depth of O2 penetration, sediment-water fluxes and nitrification rates were measured. Nitrification rates were measured using three different techniques: N-serve and acetylene inhibition in intact cores, and nitrification potentials in slurries. Increased organic additions decreased O2 penetration from 2.7 to 0.2 mm while increasing both O2 consumption, from 30 to 70 mmol O2 m-2 d-1, and NO3- flux into sediments. Nitrification rates in intact cores were similar for the two methods. Highest rates occurred in the 30 M treatment, while the lowest rate was measured in the 100S treatment. Total denitrification rates (estimated from nitrification and nitrate fluxes) increased with increased organic addition, because of the high concentrations of NO3- (40 ??M) in the overlying water. The ratio of nitrification: denitrification was used as an indication of the importance of nitrification as the NO3- supply for denitrification. This ratio decreased from 1.55 to 0.05 with increased organic addition.

FEMS Microbiology Ecology↗
USGS2021

Fire frequency impacts soil properties and processes in sagebrush steppe ecosystems of the Columbia Basin

Increased fire frequency in semi-arid ecosystems can alter biochemical soil properties and soil processes that underpin ecosystem structure and functioning, thus threatening native plant communities and the species that rely on them. However, there is much uncertainty about the magnitude of change as soils are exposed to more fires, because soil recovery and changes in fire severity following a first fire mediate the impact of successive fires on soil properties. With this study we aim to evaluate how increased fire frequency affects soil biochemical properties (i.e. soil pH, soil organic matter (SOM), soil organic carbon (SOC), soil structure and mineral N) and processes (i.e. microbial and enzymatic activity) in a sagebrush-steppe ecosystem located in the Columbia Plateau Ecoregion, Washington, USA. During 2016, we collected soils from once (2012), twice (2003 and 2012), and thrice (2003, 2007, and 2012) burned areas, enabling us to test the hypothesis that increasing fire frequency will exacerbate the impact of fire on soil properties and processes. Our study yielded three main results: (1) fire reduced the total soil C concentration and soil C in aggregates relative to unburned soil, but only when soil was exposed to fire once (i.e. the most recent fire), (2) compared to the unburned soils, SOM contents, enzyme activity and microbial CO 2 respiration were suppressed in the once and thrice burned soils, but not in the twice burned soils, and (3) fire increased NO 3 − -N contents across the once and twice burned sites, and reduced enzyme activity associated with N cycling in the thrice burned sites. Taken together, our findings suggest that a one-time fire in this shrub dominated semi-arid ecosystem significantly changes soil biochemical attributes and microbially driven processes. With sufficient time between fires, these structural and functional properties can partially recover, and this may persist even after a second fire, but recovery is limited when a third fire creates an additional disturbance at a shorter time interval. Furthermore, while soil C pools and microbial decomposition processes were able to recover with sufficient time, greater soil resource availability prevailed in soil across all fire frequencies, indicating that fire is likely to promote invasion and reduce ecosystem stability, even when other soil properties recover.

Washington↗
USGS2025

Breaking down Palila decline: Assessing the role of drought and vegetation health in the population loss of an endangered Hawaiian honeycreeper

The Palila ( Loxioides bailleui ), the last member of the once speciose finch-billed Hawaiian honeycreeper clade (Drepanidinae) in the main Hawaiian Islands, faces critical conservation challenges as an endangered species. Understanding the drivers of its decline is essential for effective management. We used additive decomposition models to examine temporal trends in climatic variables (temperature, precipitation, drought) and Normalized Difference Vegetation Index (NDVI), a vegetation health metric hypothesized to be associated with long-term trends in Palila abundance at landscape (250 m) scales on the Island of Hawai'i. A breakpoint analysis identified 2005–2009 as critical years of Palila decline. Vegetation health metrics at the 250 m scale lined up well both spatially and temporally with trends in Palila declines, with a significant browning from January 2004 to January 2014. Given the strong correlation between vegetation health and drought metrics at the landscape scale (r = 0.75, p < 0.001), NDVI changes appeared driven by drought. To enable the future projection of habitat quality in this area, we explored a stepwise linear regression to explain the variation in MODIS NDVI in recent years. We found that 87 % of the variability in NDVI can be explained by wet season precipitation and vapor pressure deficit from the previous dry season. The model is largely driven by a strong positive correlation between wet season precipitation and NDVI (r = 0.72, adjusted p < 0.001). Areas that maintained a low likelihood of NDVI decline throughout the time series and experienced increases in predicted Palila count represent potential drought microrefugia for the species. This higher elevation microrefugia is likely resilient against decreases in wet season precipitation through supplemental water retention from fog drip. While NDVI rebounded after 2014, Palila have not recovered. Our analysis highlights the importance of trend decomposition for monitoring endangered species with limited rebound potential due to small population dynamics and indicate continued warm, dry conditions may prevent Palila recovery without intervention.

Hawaii↗
USGS2008

Effects of disturbance on germination and seedling establishment in a coastal prairie grassland: A test of the competitive release hypothesis

1. We evaluated the responses of native grassland sods to a variety of types of disturbance in order to assess hypotheses about the competitive effects of established vegetation on seed germination and seedling establishment. In particular, we consider whether germination is more responsive to the magnitude and duration of vegetation removal (competitive release) or to individual disturbance types (specific effects). 2. Field-collected sods of coastal tallgrass prairie were subjected to no manipulation, cutting with clippings left, cutting with clippings removed (hayed), burning, and complete destruction of established vegetation under greenhouse conditions. The emergence and fate of seedlings, as well as light penetration through the canopy, were followed for a period of 4.5 months. 3. Total seedling emergence increased from cut to control, hayed, burned and plants-removed treatments. Several periods of increased seedling emergence suggested responses to both light penetration and seasonal change. 4. Species richness was lowest in cut sods and highest in sods that had plants removed or were burned. Rarefaction analysis showed that these differences were largely those expected from differences in seedling number, except for the cut treatment, which produced fewer species per seedling than other treatments. 5. Indicator species analysis and ordination methods revealed that seedling community composition overlapped strongly across all treatments, although the area of ordination space did increase with increasing numbers of seedlings. 6. Overall, most of the effects of disturbance could be explained by cumulative light penetration to the soil surface, an indicator of total competitive release, although a few specific effects could be found (particularly for the cutting treatment). Thus, these results generally support the competitive release hypothesis.

Journal of Ecology↗
USGS1997

The influence of seine capture efficiency on fish abundance estimates in the upper Mississippi River

The effects of season, presence of vegetation, and time of day on seine capture efficiency for fish were evaluated using test enclosures in the upper Mississippi River. Overall capture efficiency of the seine haul was 49% (53% during the day and 43% at night). During daytime tests, the efficiency ranged from 39% to 74% but did not differ statistically between sites or among dates. At night, the efficiency was higher at the vegetated than at the nonvegetated site (55% vs 32%) and declined through time from 56% in May to 28% in October. Although susceptibility to capture differed among taxa, we could not predict either total catch efficiency or efficiency within a given taxon for a given sample. Adjustment of catch data with various estimates of efficiency reduced the mean absolute error for all sampling dates from 51% to 24%, but the error of the adjusted data still ranged from -58% to +54% on any given sampling date. These results indicate that it is difficult to make accurate adjustment of catch data to compensate for gear bias in studies of seasonal habitat use.

Journal of Freshwater Ecology↗
USGS2018

Effects of sea lamprey substrate modification and carcass nutrients on macroinvertebrate assemblages in a small Atlantic coastal stream

Aquatic macroinvertebrates respond to patch dynamics arising from interactions of physical and chemical disturbances across space and time. Anadromous fish, such as sea lamprey, Petromyzon marinus , migrate from the ocean and alter physical and chemical properties of recipient spawning streams. Sea lamprey disturb stream benthos physically through nest construction and spawning, and enrich food webs through nutrient deposition from decomposing carcasses. Sea lamprey spawning nests support greater macroinvertebrate abundance than adjacent reference areas, but concurrent effects of stream bed modification and nutrient supplementation have not been examined sequentially. We added carcasses and cleared substrate experimentally to mimic the physical disturbance and nutrient enrichment associated with lamprey spawning, and characterized effects on macroinvertebrate assemblage structure. We found that areas receiving cleared substrate and carcass nutrients were colonized largely by Simuliidae compared to upstream and downstream control areas that were colonized largely by Hydropsychidae, Philopotamidae, and Chironomidae. Environmental factors such as stream flow likely shape assemblages by physically constraining macroinvertebrate establishment and feeding. Our results indicate potential changes in macroinvertebrate assemblages from the physical and chemical changes to streams brought by spawning populations of sea lamprey.

Maine↗
USGS2020

Successful restoration of Metrosideros polymorpha (ʻōhiʻa) is possible in forest sites with active Rapid ‘Ōhiʻa Death infections

Rapid ʻŌhiʻa Death (ROD), caused by the fungal pathogen Ceratocystis , is killing large numbers of ʻōhiʻa trees ( Metrosideros polymorpha ) in Hawaiʻi. ʻŌhiʻa are a dominant tree in Hawaiian forests, have a range that goes from arid to wet forest climates, and are important for endangered species habitat and ecosystem function. To test whether actively planting ʻōhiʻa seedlings is a viable restoration strategy in areas with high ROD mortality, we planted ʻōhiʻa in a ROD‐affected forest and crossed this with weeding and fencing treatments to compare ROD mortality to other stressors. We also tested for viable Ceratocystis spores in soils around planting areas. We found that seedlings were more likely to die in unweeded and unfenced treatments than controls. Although viable Ceratocystis spores were found in soil, none of the 41 dead seedlings tested positive for Ceratocystis . This indicates that competition from exotic plants and exotic feral ungulate damage are more likely to kill seedlings than ROD within the first year after planting.

Hawaii↗
USGS1996

Episodic acidification of small streams in the northeastern United States: Ionic controls of episodes

As part of the Episodic Response Project (ERP), we intensively monitored discharge and stream chemistry of 13 streams located in the Northern Appalachian region of Pennsylvania and in the Catskill and Adirondack Mountains of New York from fall 1988 to spring 1990. The ERP clearly documented the occurrence of acidic episodes with minimum episodic pH ≤ 5 and inorganic monomeric Al (Al im ) concentrations > 150 μg/L in at least two study streams in each region. Several streams consistently experienced episodes with maximum Al im concentrations >350 μg/L. Acid neutralizing capacity (ANC) depressions resulted from complex interactions of multiple ions. Base cation decreases often made the most important contributions to ANC depressions during episodes. Organic acid pulses were also important contributors to ANC depressions in the Adirondack streams, and to a lesser extent, in the Catskill and Pennsylvania streams. Nitrate concentrations were low in the Pennsylvania streams, whereas the Catskill and Adirondack study streams had high NO 3 - concentrations and large episodic pulses (≤ 54 μ eq/L). Most of the Pennsylvania study streams also frequently experienced episodic pulses of SO 4 2- (≤ 78 μ eq/L), whereas the Adirondack and Catskill streams did not. High baseline concentrations of SO 4 2- (all three study areas) and NO 3 - (Adirondacks and Catskills) reduced episodic minimum ANC, even when these ions did not change during episodes. The ion changes that controlled the most severe episodes (lowest minimum episodic ANC) differed from the ion changes most important to smaller, more frequent episodes. Pulses of NO 3 - (Catskills and Adirondacks), SO 4 2- (Pennsylvania), or organic acids became more important during major episodes. Overall, the behavior of streamwater SO 4 2- and NO 3 - is an indicator that acidic deposition has contributed to the severity of episodes in the study streams.

Ecological Applications↗
USGS2016

Impacts of the Deepwater Horizon oil spill on deep-sea coral-associated sediment communities

Cold-water corals support distinct populations of infauna within surrounding sediments that provide vital ecosystem functions and services in the deep sea. Yet due to their sedentary existence, infauna are vulnerable to perturbation and contaminant exposure because they are unable to escape disturbance events. While multiple deep-sea coral habitats were injured by the 2010 Deepwater Horizon (DWH) oil spill, the extent of adverse effects on coral-associated sediment communities is unknown. In 2011, sediments were collected adjacent to several coral habitats located 6 to 183 km from the wellhead in order to quantify the extent of impact of the DWH spill on infaunal communities. Higher variance in macrofaunal abundance and diversity, and different community structure (higher multivariate dispersion) were associated with elevated hydrocarbon concentrations and contaminants at sites closest to the wellhead (MC294, MC297, and MC344), consistent with impacts from the spill. In contrast, variance in meiofaunal diversity was not significantly related to distance from the wellhead and no other community metric (e.g. density or multivariate dispersion) was correlated with contaminants or hydrocarbon concentrations. Concentrations of polycyclic aromatic hydrocarbons (PAH) provided the best statistical explanation for observed macrofaunal community structure, while depth and presence of fine-grained mud best explained meiofaunal community patterns. Impacts associated with contaminants from the DWH spill resulted in a patchwork pattern of infaunal community composition, diversity, and abundance, highlighting the role of variability as an indicator of disturbance. These data represent a useful baseline for tracking post-spill recovery of these deep-sea communities.

Marine Ecology Progress Series↗
USGS2017

Using high-throughput DNA sequencing, genetic fingerprinting, and quantitative PCR as tools for monitoring bloom-forming and toxigenic cyanobacteria in Upper Klamath Lake, Oregon, 2013 and 2014

Monitoring the community structure and metabolic activities of cyanobacterial blooms in Upper Klamath Lake, Oregon, is critical to lake management because these blooms degrade water quality and produce toxic microcystins that are harmful to humans, domestic animals, and wildlife. Genetic tools, such as DNA fingerprinting by terminal restriction fragment length polymorphism (T-RFLP) analysis, high-throughput DNA sequencing (HTS), and real-time, quantitative polymerase chain reaction (qPCR), provide more sensitive and rapid assessments of bloom ecology than traditional techniques. The objectives of this study were (1) to characterize the microbial community at one site in Upper Klamath Lake and determine changes in the cyanobacterial community through time using T-RFLP and HTS in comparison with traditional light microscopy; (2) to determine relative abundances and changes in abundance over time of toxigenic Microcystis using qPCR; and (3) to determine relative abundances and changes in abundance over time of Aphanizomenon , Microcystis , and total cyanobacteria using qPCR. T-RFLP analysis of total cyanobacteria showed a dominance of only one or two distinct genotypes in samples from 2013, but results of HTS in 2013 and 2014 showed more variations in the bloom cycle that fit with the previous understanding of bloom dynamics in Upper Klamath Lake and indicated that potentially toxigenic Microcystis was more prevalent in 2014 than in years prior. The qPCR-estimated copy numbers of all target genes were higher in 2014 than in 2013, when microcystin concentrations also were higher. Total Microcystis density was shown with qPCR to be a better predictor of late-season increases in microcystin concentrations than the relative proportions of potentially toxigenic cells. In addition, qPCR targeting Aphanizomenon at one site in Upper Klamath Lake indicated a moderate bloom of this species (corresponding to chlorophyll a concentrations between approximately 75 and 200 micrograms per liter) from mid-June to mid-August, 2014. After August 18, the Aphanizomenon bloom was overtaken by Microcystis late in the season as microcystin concentrations peaked. Overall, results of this study showed how DNA-based, genetic methods may provide rapid and sensitive diagnoses for the presence of toxigenic cyanobacteria and that they are useful for general monitoring or ecological studies and identification of cyanobacterial community members in complex aquatic habitats. These same methods can also be used to simultaneously address spatial (horizontal and vertical) and temporal variation and under different conditions. Additionally, with some modifications, the same techniques can be applied to different sample types, including water, sediment, and tissue.

Oregon↗
USGS2016

Feeding ecology of the walleye (Percidae, Sander vitreus), a resurgent piscivore in Lake Huron (Laurentian Great Lakes) after shifts in the prey community

Recovering populations of piscivores can challenge understanding of ecosystem function due to impacts on prey and to potentially altered food webs supporting their production. Stocks of walleye (Percidae, Sander vitreus ), an apex predator in the Laurentian Great Lakes, crashed in the mid‐1900s. Management efforts led to recovery by 2009, but recovery coincided with environmental and fish community changes that also had implications for the feeding ecology of walleye. To evaluate potential changes in feeding ecology for this apex predator, we assessed diets in the main basin of Lake Huron and in Saginaw Bay, a large embayment of Lake Huron, during 2009–2011. Walleye switched their diets differently in the main basin and Saginaw Bay, with non‐native round goby (Gobiidae, Neogobius melanostomus ) and rainbow smelt (Osmeridae, Osmerus mordax ) more prevalent in diets in the main basin, and invertebrates, yellow perch (Percidae, Perca flavescens ) and gizzard shad (Clupeidae, Dorosoma cepedianum ) more prevalent in diets in the bay. Feeding strategy plots indicated that there was a high degree of individual specialisation by walleye in the bay and the main basin. Bioenergetic simulations indicated that walleye in Saginaw Bay need to consume 10%–18% more food than a walleye that spends part or all of the year in the main basin, respectively, in order to achieve the same growth rate. The differences in diets between the bay and main basin highlight the flexibility of this apex predator in the face of environmental changes, but changes in diet can alter energy pathways supporting piscivore production.

Ecology of Freshwater Fish↗
USGS2007

Quantifying the extent of river fragmentation by hydropower dams in the Sarapiquí River Basin, Costa Rica

Costa Rica has recently experienced a rapid proliferation of dams for hydropower on rivers draining its northern Caribbean slope. In the Sarapiquí River Basin, eight hydropower plants were built between 1990 and 1999 and more projects are either under construction or proposed. The majority of these dams are small (<15 m tall) and operate as water diversion projects. While the potential environmental effects of individual projects are evaluated prior to dam construction, there is a need for consideration of the basin-scale ecological consequences of hydropower development. This study was a first attempt to quantify the extent of river fragmentation by dams in the Sarapiquí River Basin. Using simple spatial analyses, the length of river upstream from dams and the length of de-watered reaches downstream from dams was measured. Results indicated that there are currently 306.8 km of river (9.4% of the network) upstream from eight existing dams in the Sarapiquí River Basin and 30.6 km of rivers (0.9% of the network) with significantly reduced flow downstream from dams. Rivers upstream from dams primarily drain two life zones: Premontane Rain Forest (107.9 km) and Lower Montane Rain Forest (168.2 km). Simple spatial analyses can be used as a predictive or planning tool for considering the effects of future dams in a basin-scale context. In the Sarapiquí River Basin, we recommend that future dam projects be constructed on already dammed rivers to minimize additional river fragmentation and to protect remaining riverine connectivity.

Aquatic Conservation: Marine and Freshwater Ecosys↗