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At least 127 records · Page 7Linked to original sources

USGS2012

Low prevalence of VHSV detected in round goby collected in offshore regions of Lake Ontario

Since the first reports of mortalities due to viral hemorrhagic septicemia virus (VHSV) type IVb in the Laurentian Great Lakes basin during 2005 (Lake St. Clair, USA and Bay of Quinte, Lake Ontario, Canada), many groups have conducted surveillance efforts for the virus, primarily in nearshore areas. The round goby ( Neogobius melanostomus ) has been identified as a key species to target for surveillance, because they have a very high probability of infection at a given site. Our objective in this study was to document and quantify VHSV in round gobies in offshore waters of Lake Ontario using molecular techniques. We collected 139 round gobies from depths ranging from 55 to 150 m using bottom trawls during the early spring of 2011 and detected VHSV in 4 individuals (1/26 fish at 95 m, 2/12 fish at 105 m, and 1/24 fish at 135 m). These results expand the known depth range of VHSV in the Great Lakes. They also have implications on the management of the spread of VHSV within infected bodies of water related to the mixing of populations of fish that would remain distinct in their breeding habitats, but then have the opportunity to mix in their overwintering habitats, as well as to increase overlap of predator and prey species in overwintering habitats.

Lake Ontario↗

USGS2014

A 200 year chronology of burrowing mayflies ( Hexagenia spp.) in Saginaw Bay

After an absence of 50 years, burrowing mayflies ( Hexagenia spp.) colonized western Lake Erie which led to interest in whether this fauna can be used to measure recovery in nearshore waters throughout the Great Lakes. However, in many areas we do not know if mayflies were native/endemic and thus, whether recovery is a logical measure to assess progress of recovery. In the present study, we construct a chronologic record of relative abundance of burrowing mayflies in Saginaw Bay by the use of mayfly tusks and radionuclides in sediments (i.e., a paleoecologic record) and historic records of mayfly nymphs in the bay. These records reveal that mayflies: (1) were few before 1799, which indicates that nymphs were probably native/endemic in the bay, (2) increased between 1799 and 1807 and remained at relatively high levels between 1807 and 1965, probably in response to increased nutrient run-off from the watershed, (3) declined dramatically between 1965 and 1973, probably as a result of excessive eutrophication in the mid-1950s; and, (4) were few and highly variable between 1973 and 2001, probably as a result of low and unstable abundances of mayfly nymphs. Historic records verify that nymphs disappeared in the bay in the late-1950s to early-1960s which is in agreement with the paleoecologic record. Reoccurrence of low abundances of nymphs in the bay between 1991 and 2008 and comparison of chronologic records of nymphs in Saginaw Bay and western Lake Erie suggest that mayflies may return to Saginaw Bay in the early-21st century. Undoubtedly, watershed conservation and three decades of pollution abatement have set the stage for a recovery of burrowing mayflies in Saginaw Bay, and possibly in other areas of the Great Lakes.

Michigan↗

USGS2014

In vivo and in vitro phenotypic differences between Great Lakes VHSV genotype IVb isolates with sequence types vcG001 and vcG002

Viral hemorrhagic septicemia virus (VHSV) is an aquatic rhabdovirus first recognized in farmed rainbow trout in Denmark. In the past decade, a new genotype of this virus, IVb was discovered in the Laurentian Great Lakes basin and has caused several massive die-offs in some of the 28 species of susceptible North American freshwater fishes. Since its colonization of the Great Lakes, several closely related sequence types within genotype IVb have been reported, the two most common of which are vcG001 and vcG002. These sequence types have different spatial distributions in the Great Lakes. The aim of this study was to determine whether the genotypic differences between representative vcG001 (isolate MI03) and vcG002 (isolate 2010-030 #91) isolates correspond to phenotypic differences in terms of virulence using both in vitro and in vivo approaches. In vitro infection of epithelioma papulosum cyprini (EPC), bluegill fry (BF-2), and Chinook salmon embryo (CHSE) cells demonstrated some differences in onset and rate of growth in EPC and BF-2 cells, without any difference in the quantity of RNA produced. In vivo infection of round gobies ( Neogobius melanostomus ) via immersion exposure to different concentrations of vcG001 or vcG002 caused a significantly greater mortality in round gobies exposed to 10 2 plaque forming units ml − 1 of vcG001. These experiments suggest that there are phenotypic differences between Great Lakes isolates of VHSV genotype IVb.

Journal of Great Lakes Research↗

USGS2015

Evaluating the importance of abiotic and biotic drivers on Bythotrephes biomass in Lakes Superior and Michigan

The ability of planktivorous fishes to exert top-down control on Bythotrephes potentially has far-reaching impacts on aquatic food-webs, given previously described effects of Bythotrephes on zooplankton communities. We estimated consumption of Bythotrephes by planktivorous and benthivorous fishes, using bioenergetics and daily ration models at nearshore (18 m), intermediate (46 m), and offshore (110 m) depths along one western Lake Superior transect (April, and September-November) and two northern Lake Michigan transects (April, July, September). In Lake Superior, consumption (primarily by cisco Coregonus artedi) exceeded Bythotrephes production at all offshore sites in September-November (up to 396% of production consumed) and at the intermediate site in November (842%) with no evidence of consumption nearshore. By comparing Bythotrephes biomass following months of excessive consumption, we conservatively concluded that top-down control was evident only at the offshore site during September-October. In Lake Michigan, consumption by fishes (primarily alewife Alosa pseudoharengus) exceeded production at nearshore sites (up to 178%), but not in deeper sites (< 15%). Evidence for top-down control in the nearshore was not supported, however, as Bythotrephes never subsequently declined. Using generalized additive models, temperature, and not fish consumption, not zooplankton prey density, best explained variability in Bythotrephes biomass. The non-linear pattern revealed Bythotrephes to increase with temperature up to 16 °C, and then decline between 16 and 23 °C. We discuss how temperature likely has direct negative impacts on Bythotrephes when temperatures near 23 °C, but speculate that predation also contributes to declining biomass when temperatures exceed 16 °C.

Wisconsin and Michigan↗

USGS2016

Identifying the origin of waterbird carcasses in Lake Michigan using a neural network source tracking model

Avian botulism type E is responsible for extensive waterbird mortality on the Great Lakes, yet the actual site of toxin exposure remains unclear. Beached carcasses are often used to describe the spatial aspects of botulism mortality outbreaks, but lack specificity of offshore toxin source locations. We detail methodology for developing a neural network model used for predicting waterbird carcass motions in response to wind, wave, and current forcing, in lieu of a complex analytical relationship. This empirically trained model uses current velocity, wind velocity, significant wave height, and wave peak period in Lake Michigan simulated by the Great Lakes Coastal Forecasting System. A detailed procedure is further developed to use the model for back-tracing waterbird carcasses found on beaches in various parts of Lake Michigan, which was validated using drift data for radiomarked common loon ( Gavia immer ) carcasses deployed at a variety of locations in northern Lake Michigan during September and October of 2013. The back-tracing model was further used on 22 non-radiomarked common loon carcasses found along the shoreline of northern Lake Michigan in October and November of 2012. The model-estimated origins of those cases pointed to some common source locations offshore that coincide with concentrations of common loons observed during aerial surveys. The neural network source tracking model provides a promising approach for identifying locations of botulinum neurotoxin type E intoxication and, in turn, contributes to developing an understanding of the dynamics of toxin production and possible trophic transfer pathways.

Lake Michigan↗

USGS2020

Investigating population genetics of invasive rainbow smelt in the Great Lakes Region

Increasing our understanding of invasive species is important because of the negative impacts they can have on the economies and ecosystems of invaded regions. There is growing interest in how environmental variability (e.g. temperature) and stochastic invasion events (e.g. founder effects) affect the genetic composition of populations of invasive species. Rainbow smelt ( Osmerus mordax ) are a cold-water, planktivorous fish that spread into the Great Lakes basin in the early 1900s. We performed genetic analyses using microsatellites (N = 10) to investigate the influence stochastic invasion events have had on the genetic composition of invasive rainbow smelt populations across a broad geographic range. Genetic analyses were conducted on rainbow smelt populations (N = 30/population) from Lake Ontario, Lake Michigan, Lake Superior, and four inland lakes in Northern Wisconsin. Populations from the Great Lakes were generally less differentiated than inland populations. Additionally, we found evidence of a significant bottleneck in two inland populations and evidence for two distinct genetic strains of rainbow smelt in Lake Ontario. We also performed genetic analyses using microsatellites to determine if a thermally-induced extreme mortality event had an effect on a population of rainbow smelt and found that there was no measurable genetic effect on the population. Overall, this study provides evidence that the genetic structure and diversity of introduced populations can vary significantly, and are likely influenced by factors such as the frequency and magnitude of introductions. Also the resiliency of an invasive species can be high despite a history of bottlenecks and low genetic diversity.

Great Lakes Region↗

USGS2021

Using simulation to understand annual sea lamprey marking rates on lake trout

Sea lampreys attack fish, killing some and leaving marks on others. Great Lakes fishery managers rely on observed marking rates to assess the success of the sea lamprey control program and estimate sea lamprey-induced mortality of lake trout. Because marking rates are only observed on survivors of sea lamprey attacks, they may not provide a reliable index of actual attack or mortality rates. To investigate the effect of survivor bias, we developed a simulation model representing a single season (June–December) of sea lamprey attacks. Simulated attack rates varied with month and lake trout size; simulated pierce and lethality rates varied with month alone. Surveyed marking rates were represented by simulated survivors in October; true rates were calculated from all simulated lake trout (dead and alive) in December. Simulation results were subsetted to include only those within the range of marking rates actually observed in the Great Lakes. Type A (piercing) marking rates were a good index of the sea lamprey attack rate and the sea lamprey-induced mortality rate if annual lethality rates were relatively constant. Type B (non-piercing) marking rates were a good index of the sea lamprey attack rate and the sea lamprey-induced mortality rate if annual pierce rates were relatively constant. Due to the uncertainty surrounding the pierce and lethality rates, we recommend that sea lamprey abundance information be incorporated in existing lake trout statistical catch-at-age models via a functional response component relating sea lamprey feeding to lake trout abundance, if possible.

Journal of Great Lakes Research↗

USGS2022

Condition of resident fish communities in the Eighteenmile Creek Area of Concern, New York

The lower 3.5 km of Eighteenmile Creek, a tributary to Lake Ontario in New York, was designated as an Area of Concern (AOC) in 1985 under the Great Lakes Water Quality Agreement due to extensive contamination of bed sediments by polychlorinated biphenyls (PCBs) and other toxicants. Five beneficial use impairments (BUIs) have been identified in this AOC, including degraded fish and wildlife populations. We surveyed fish communities in the Eighteenmile Creek AOC and in a comparable section of a nearby reference stream (Oak Orchard Creek) during June 2019 to infer whether legacy contaminants are currently impairing fish communities in the AOC to an extent that they differ from the regional reference condition. Estimates of community abundance, biomass, diversity, and fish condition from each system were compared using a noninferiority testing framework. Biomass, diversity, and fish condition in the Eighteenmile Creek AOC were similar or superior to that in Oak Orchard Creek, while abundance was 20% lower in the AOC. These findings and those of a 2007 sampling effort suggest that fish communities in the Eighteenmile Creek AOC are not impaired despite recent studies indicating that PCBs are bioaccumulating in fish tissues at 1–2 orders of magnitude above background levels. Future assessments in the Eighteenmile Creek AOC might focus on the condition of benthic macroinvertebrate communities and potential toxicity of local contaminants to piscivorous wildlife in order to fully address the remaining aspects of the fish and wildlife populations beneficial use impairment.

New York↗

USGS2024

Acute toxicity of lampricides to non-target species of concern in the Lake Champlain watershed

Previous research evaluated the toxicity of the lampricide 4-nitro-3-(trifluoromethyl)phenol (TFM) and the combination of TFM with 1 % niclosamide (TFM:1%Nic) to multiple non-target species in the Laurentian Great Lakes. However, few toxicity studies have been conducted for species of concern in Lake Champlain (NY and VT). We conducted 12-hour flow-through toxicity tests with 4 species of native mussels, 6 species of fish, and 1 amphibian species. All tests included exposure of invasive larval Petromyzon marinus (sea lamprey) and were conducted with concentrations that bracketed the predicted minimum lethal concentration required to control larval sea lamprey. Mussel species’ NOEC, LOEC, LC 25 , and LC 50 values ranged from 1.33 to 2.12, 1.71–2.66, 1.75–3.05, and 2.03–4.84 times field determined LC 99.9 s for sea lamprey (×SL LC99.9 ) in TFM-only toxicity tests, and from 1.36 to 1.70, 1.68–2.03, 1.86–2.10, and 2.35–2.68 × SL LC99.9 for TFM:1%Nic toxicity tests, respectively. Fish species NOEC, LOEC, LC 25 , and LC 50 values ranged from 0.60 to 1.89, 0.73–2.13, 0.72–2.11, and 0.76–2.18 × SL LC99.9 in TFM-only toxicity tests, and from 0.64 to 2.48, 0.85–3.10, 0.74–3.05, and 0.78–3.16 × SL LC99.9 for TFM:1%Nic toxicity tests, respectively. Amphibian species NOEC, LOEC, LC 25 , and LC 50 values ranged from 0.74 to 0.75, 0.85–0.95, 0.83–0.87, and 0.85–0.91 × SL LC99.9 in TFM-only toxicity tests, and from 0.63 to 0.65, 0.80–0.88, 0.77–0.82, and 0.78–0.87 × SL LC99.9 for TFM:1%Nic toxicity tests, respectively. Generally, mussel species were tolerant, fish sensitivities were variable, and the amphibian species was sensitive to TFM and TFM:1%Nic.

New York, Vermont↗

USGS2025

Prevalence and potential for biological effects of several chemicals of interest in Lake Superior tributaries

Lake Superior is typically assumed to have excellent water quality, but its tributaries have been understudied for contaminants relative to other Great Lakes. This study monitored polycyclic aromatic hydrocarbons (PAHs), alkylphenols (AP) and alkylphenol ethoxylates (APEs), bisphenols, and neonicotinoid pesticides in 18 sites on 17 United States tributaries to Lake Superior in 2022. Contaminants were analyzed from 54 surface water and 17 stream bed sediment samples. PAHs were the most prevalent contaminant class. Among 17 PAHs in 17 samples (289 instances), 71 % were positive detections. Surface water samples were not analyzed for PAHs. Next, among 4 APs and APEs analyzed, 35 % of sediment sample instances and 21 % of instances in 54 water samples were positive detections. Bisphenol analogues were detected in 2 % of sediment sample instances and 4 % of water sample instances. Bisphenol A (BPA) was not quantified due to field blank contamination, but bisphenol AF (BPAF), bisphenol E (BPE), bisphenol F (BPF), and bisphenol S (BPS) were detected in environmental samples. Neonicotinoids were detected in 0.5 % of sediment sample instances and 0.4% of water samples instances. Low detection frequencies for contaminants precluded analyses with watershed land use characteristics, but four sites (Tischer Creek, Miller Creek, Carp River and Iron River) emerged as locations with relatively elevated contaminant concentrations. Comparison of concentrations with ToxCast and other water quality guidelines suggested potential for biological effects from some samples. This study provides a baseline of low contaminant prevalence in Lake Superior tributaries while identifying a few locations that may warrant further monitoring.

Michigan, Minnesota, Wisconsin↗

USGS2025

Angler dynamics in the St. Clair-Detroit River System after decades of change

Habitat and water quality were historically degraded within the St. Clair-Detroit River System (SCDRS). Beginning in 2004, extensive habitat restoration projects were implemented remediating losses of fish spawning beds and shoreline areas. Monitoring of post-restoration activities documented recovering fish populations; however, angler response remains unknown. Extensive creel surveys were conducted pre-restoration (2002–2004), but post-restoration (2012 and later) surveys were intermittent. The goal of this project was to examine both to create a comprehensive picture of the effects of restoration on angling. We calculated catch and harvest rates and inspected answers to supplemental questions collected by state and provincial agencies. We estimated economic impact of angling with a combination of lodging and gas expenses. Post-restoration, catch rates were higher, but harvest rates were variable for Lake St. Clair and the Detroit River. The 2017 open water boat fishery on Lake St. Clair was worth ∼$26 million. Increased fishing opportunities resulting from continued habitat and population recovery are leading to increased catch rates and likely attracting anglers to the area.

Michigan, Ontario↗

USGS2025

Larger larval sea lamprey (Petromyzon marinus) have longer survival times when exposed to the lampricide 3-trifluoromethyl-4-nitrophenol

Invasive sea lamprey ( Petromyzon marinus ) in the Laurentian Great Lakes have negatively impacted ecologically and economically important fishes for nearly a century. To mitigate these effects, the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is applied annually on a rotating basis to selected Great Lakes tributaries to kill larval lamprey before they become juveniles, out-migrate to the lakes, and parasitize other fishes. It has been hypothesized that larval size (e.g., mass, length) may affect survival time in response to TFM. To test this hypothesis, we conducted an experiment with 8611 larvae across four temporal replicates, in which TFM concentrations equivalent to those used in present-day stream treatments were applied for up to 18 h. When examining the survival times of larval lamprey exposed to TFM, we found a significant, positive relationship between length, mass, toxicity, and their interactions. For every 1 mm increase in total length, a corresponding increase by 1 g of mass reduced survival time by 0.4315 min [95 % CI: 0.5283–0.2992] and vice versa (i.e., the significant interaction between length and mass revealed that as larvae increase in mass, the survival benefit to being longer decreases, and vice versa). The changes in total length and mass of larval sea lamprey stored in ethanol for 4 months was also quantified. The observation that five larvae survived well past the 12-hour time window of a typical TFM field treatment highlights the need for continuous monitoring and the development of new control strategies to ensure the continued effective management of this invasive species.

Michigan↗

USGS2026

Lake trout colonization of artificial reefs: Who’s interested, and how long does it take?

Restoring self-sustaining lake trout ( Salvelinus namaycush ) populations has been a major management objective for decades across the species’ native range. Reproduction has been observed but recruitment has been limited in many areas of the Laurentian Great Lakes. Reef restoration and construction have been proposed to increase recruitment, leading to the construction of experimental spawning reefs in Thunder Bay, Lake Huron, during 2009–2010. Research shortly after reef construction demonstrated lake trout quickly colonized those reefs during spawning. We revisited this site after 10 years to evaluate lake trout encounter rate and residency on each reef over time and relative to an adjacent historical, anthropogenic reef complex using fine-scale acoustic telemetry. Encounter frequency increased at most experimental reefs since reef construction, but changes in residency were dependent on lake trout origin (hatchery or wild). Hatchery-produced fish increased their residency on the experimental reefs and spent more time on these reefs collectively than the historical reef; wild lake trout continued to primarily use the historical reef. We expected younger wild fish to have increased residency on the experimental reefs assuming these individuals could have originated from those reefs and were therefore more likely to return to them; however, residency on experimental reefs remained low (< 50%) for these fish. These results indicate that reef construction provided additional habitat used by spawning lake trout, but wild individuals continue to prefer older habitat including naive wild fish born after reef construction.

Michigan↗

USGS2026

Re-examining the growing degree day minimum for grass carp spawning initiation in Lake Erie: Have we missed the mark?

Understanding the timing of life history processes of invasive fish species, such as adult aggregations during spawning, allows natural resource managers to optimize targeted population control efforts. Temperature-based estimates of the timing of spawning initiation for grass carp ( Ctenopharyngodon idella ) exist from its native range, but have not previously been developed for grass carp reproduction in its invaded range in the Laurentian Great Lakes of North America. We accounted for differences among methods across studies and calculated cumulative growing degree days (GDD) for the dates of grass carp egg capture in Lake Erie tributaries (Sandusky, Maumee, and Huron rivers) during 2015–2024 and compared these values to the existing GDD base 15°C requirement estimate from the native range (633 GDD–15°C). The earliest egg detection in Lake Erie (Sandusky River) was 19 GDD–15°C or 361 GDD–5°C (latest egg detection was 2285 GDD–5°C from the Sandusky River), indicating that spawning was initiated up to 25 days earlier than would be predicted by the native range GDD. Moreover, spawning in Lake Erie tributaries occurred earlier than predicted for 58% of spawning events examined based on the native range GDD. The GDD values for spawning initiation in Lake Erie tributaries can be used to refine the timing of control efforts targeting pre-spawn and spawning adult fish, inform the timing of egg sampling, and provide linkages to existing early life stage models to infer the length of the growing season available for age-0 fish to reassess tributary suitability.

Ohio↗

USGS2007

Effect of compost age and composition on the atrazine removal from solution

Compost samples from two composting facilities, the Urbana (Illinois) Landscape Recycling Center (ULRC) and Illinois State University (ISU), were selected to examine the effect of compost age on atrazine removal from solution. The ULRC samples were made from yard waste without an additional nitrogen source. The ISU samples were made from yard waste or sawdust with the addition of manure. The 6-month-old ULRC compost had the greater capacity to remove atrazine from solution, which we attributed to its greater organic carbon content. The addition of nitrate into ULRC compost could influence the extent of atrazine removal, but did not have a significant impact on atrazine removal when applied to ISU compost, probably because manure was added to the yard waste to produce the compost. For both ULRC and ISU samples, the presence of sodium azide inhibited atrazine removal, suggesting that microbial activity contributed to the atrazine removal. Metabolic analysis demonstrated that hydroxyatrazine was the major identified metabolite that accumulated in solution before significant ring mineralization could occur. When compared with the ISU compost, the ULRC compost sample had a greater capacity to remove atrazine from solution during the 120 days of study because of the larger humic acid content. The experimental results suggested that less-mature compost may be better suited for environmental applications such as removing atrazine from tile-drainage waters. ?? 2006 Elsevier B.V. All rights reserved.

Journal of Hazardous Materials↗

USGS2007

The feasibility of applying immature yard-waste compost to remove nitrate from agricultural drainage effluents: A preliminary assessment

Nitrate is a major agricultural pollutant found in drainage waters. Immature yard-waste compost was selected as a filter media to study its feasibility for removing nitrate from drainage water. Different operation parameters were tested to examine the denitrification efficiency, including the amounts of compost packed in columns, the flow rate, and the compost storage periods. The experimental results suggested that hydraulic retention time was the major factor to determine the extent of nitrate removal, although the amount of compost packed could also contribute to the nitrate removal efficiency. The effluent nitrate concentration increased as the flow rate decreased, and the compost column reduced nitrate concentrations from 20 mg/L to less than 5 mg/L within 1.5 h. The solution pH increased at the onset of experiment because of denitrification, but stabilized at a pH of about 7.8, suggesting that the compost had a buffering capacity to maintain a suitable pH for denitrification. Storing compost under air-dried conditions may diminish the extent nitrate removed initially, but the effects were not apparent after longer applications. It appeared that immature yard-waste compost may be a suitable material to remove nitrate from tile drainage water because of its relatively large organic carbon content, high microbial activity, and buffering capacity. ?? 2006 Elsevier B.V. All rights reserved.

Journal of Hazardous Materials↗

USGS2021

Months-long spike in aqueous Arsenic following domestic well installation and disinfection: Short- and long-term drinking water quality implications

Exposure to high concentration geogenic arsenic via groundwater is a worldwide health concern. Well installation introduces oxic drilling fluids and hypochlorite (a strong oxidant) for disinfection, thus inducing geochemical disequilibrium. Well installation causes changes in geochemistry lasting 12 + months, as illustrated in a recent study of 250 new domestic wells in Minnesota, north-central United States. One study well had extremely high initial arsenic (1550 µg/L) that substantially decreased after 15 months (5.2 µg/L). The drilling and development of the study well were typical and ordinary; nothing observable indicated the very high initial arsenic concentration. We hypothesized that oxidation of arsenic-containing sulfides (which lowers pH) combined with low pH dissolution of arsenic-bearing Fe (oxyhydr)oxides caused the very high arsenic concentration. Geochemical equilibrium considerations and modeling supported our hypothesis. Groundwater equilibrium redox conditions are poised at the Fe(III) (s) /Fe(II) (aq) stability boundary, indicating arsenic-bearing Fe (oxyhydr)oxide mineral sensitivity to pH and redox changes. Changing groundwater geochemistry can have negative implications for home water treatment (e.g., reduced arsenic removal efficiency, iron fouling), which can lead to ongoing but unrecognized hazard of arsenic exposure from domestic well water. Our results may inform arsenic mobilization processes and geochemical sensitivity in similarly complex aquifers in Southeast Asia and elsewhere.

Minnesota↗

USGS2004

Overland flow generation in two lithologically distinct rainforest catchments

Streams on uniformly rainforest-covered, but lithologically very diverse Barro Colorado Island in central Panama?? show remarkable differences in their runoff response to rainfall. This lithological diversity is reflected in equally diverse soilscapes, and our objective was to test the hypothesis that contrasting runoff responses derive from soilscape features that control the generation of overland flow. We determined the soil saturated hydraulic conductivity (Ks) of two neighboring, but hydrologically contrasting catchments (Lutz Creek with a flashy and Conrad Trail with a delayed response to rainfall), and quantified the spatial and temporal frequency of overland flow occurrence. The median Ks values at a depth of 12.5 cm are large enough to rule out Hortonian overland flow, but a marked decrease in K s in Lutz Creek catchment at 30 cm suggests the formation of a perched water table and the generation saturation overland flow; the decrease in Ks in the Conrad Trail catchment is more gradual, and a perched water table is expected to form only at depths below 50 cm. In Lutz Creek, overland flow was generated frequently in time and space and regardless of topographic position, including near the interfluve, with very low thresholds of storm magnitude, duration, intensity and antecedent wetness, whereas in Conrad Trail, overland flow was generated much less frequently and then only locally. We conclude that soilscape features and microtopography are important controls of overland flow generation in these catchments. Our results contribute to the growing evidence that overland flow and forests are not a priori a contradiction in terms. ?? 2004 Elsevier B.V. All rights reserved.

Journal of Hydrology↗