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At least 1,261 records · Page 70Linked to original sources

USGS2015

Past and future warming of a deep European lake (Lake Lugano): What are the climatic drivers?

We used four decades (1972–2013) of temperature data from Lake Lugano, Switzerland and Italy, to address the hypotheses that: [i] the lake has been warming; [ii] part of the warming reflects global trends and is independent from climatic oscillations and [iii] the lake will continue to warm until the end of the 21st century. During the time spanned by our data, the surface waters of the lake (0–5 m) warmed at rates of 0.2–0.9 °C per decade, depending on season. The temperature of the deep waters (50-m bottom) displayed a rising trend in a meromictic basin of the lake and a sawtooth pattern in the other basin, which is holomictic. Long-term variation in surfacewater temperature correlated to global warming and multidecadal variation in two climatic oscillations, the Atlantic Multidecadal Oscillation (AMO) and the East Atlantic Pattern (EA).However, we did not detect an influence of the EA on the lake's temperature (as separate from the effect of global warming). Moreover, the effect of the AMO, estimated to a maximum of +1 °C, was not sufficient to explain the observed temperature increase (+2–3 °C in summer). Based on regional climate projections, we predicted that the lake will continue to warm at least until the end of the 21st century. Our results strongly suggest that the warming of Lake Lugano is tied to globalclimate change. To sustain current ecosystem conditions in Lake Lugano, we suggest that manage- ment plans that curtail eutrophication and (or) mitigation of global warming be pursued.

Lake Lugano↗

USGS2016

First direct confirmation of grass carp spawning in a Great Lakes tributary

Grass carp ( Ctenopharyngodon idella ), an invasive species of Asian carp, has been stocked for many decades in the United States for vegetation control. Adult individuals have been found in all of the Great Lakes except Lake Superior, but no self-sustaining populations have yet been identified in Great Lakes tributaries. In 2012, a commercial fisherman caught four juvenile diploid grass carp in the Sandusky River, a major tributary to Lake Erie. Otolith microchemistry and the capture location of these fish permitted the conclusion that they were most likely produced in the Sandusky River. Due to this finding, we sampled ichthyoplankton using paired bongo net tows and larval light traps during June–August of 2014 and 2015 to determine if grass carp are spawning in the Sandusky River. From the samples collected in 2015, we identified and staged eight eggs that were morphologically consistent with grass carp. Five eggs were confirmed as grass carp using quantitative Polymerase Chain Reaction for a grass carp-specific marker, while the remaining three were retained for future analysis. Our finding confirms that grass carp are naturally spawning in this Great Lakes tributary. All eggs were collected during high-flow events, either on the day of peak flow or 1–2 days following peak flow, supporting an earlier suggestion that high flow conditions favor grass carp spawning. The next principal goal is to identify the spawning and hatch location(s) for the Sandusky River. Predicting locations and conditions where grass carp spawning is most probable may aid targeted management efforts.

Lake Erie, Sandusky River↗

USGS2019

Resurgence of cisco (Coregonus artedi) population levels in Lake Michigan

In recent decades, many factors that were linked with the decline of Great Lakes cisco ( Coregonus artedi ) populations have subsided. The goal of this study was to investigate where cisco exist in Lake Michigan and evaluate evidence for recovery including when, where, and to what extent it is occurring. We evaluated datasets from several independent monitoring efforts that did and did not target cisco. We also evaluated trends in commercial and recreational catches of cisco. Across these datasets, there was strong evidence of a sustained recovery of cisco stocks that began in Lake Michigan in the mid-2000s. Fall gill net surveys and commercial fisheries provided reasonable indications of a population recovery in the northeast by 2011. Further south, Ludington Pump Storage barrier net monitoring also recorded increasing numbers of cisco starting in 2011. Recreational harvest estimates were valuable in evaluating spatial distributions but were less valuable as an early signal of abundance shifts. Measures of the recreational harvest of cisco most notably increased in 2014. The highest catch rates and harvest occurred in Grand Traverse Bay and northern Lake Michigan as evidenced by recreational, commercial, and fall netting surveys. Observations of cisco are expanding and have increased in intensity along the eastern shore of Lake Michigan south to Muskegon in both fishery dependent and independent surveys. The similarity in trends from all data sources indicate that cisco abundance has increased, and their range within the basin continues to expand.

Michigan↗

USGS2019

Age truncation of alewife in Lake Michigan

Empirical evidence has shown increased variability in harvest and recruitment of exploited fish populations, which can result directly from exploitation or indirectly from interactions between external drivers and the internal dynamics of age-structured populations. We investigated whether predation in a freshwater system could affect a prey fish population, in the same way fishing affects targeted populations. Using fishery-independent trawl survey data and a suite of quantitative indicators, we evaluated changes in the alewife population in Lake Michigan. Our results provide evidence for a reduction in the mean spawner age, a reduction in the diversity of age classes and the distribution of biomass across them, and increased variability in the proportion of first time spawners in the spawning stock. We used wavelet analysis and estimates of lifetime egg production to demonstrate how the alewife population displays behaviors of instability as the overall biomass declines. Our results provide evidence that predation pressure can influence prey fish populations in a similar manner to fishing on harvested populations, and that conservation of a broad reproducing age structure is likely to be important for buffering against adverse environmental fluctuations and for sustainable management of fish populations.

Lake Michigan↗

USGS2021

Lake sturgeon (Acipenser fulvescens) annual adult survival estimated from acoustic telemetry

Survival of adult fishes is critical to the conservation and management of wild populations, particularly for long-lived, slow to reproduce species. Most sturgeon species are of conservation concern, but their long lifespans and large ranges have made estimation of adult survival rates challenging. In this study, acoustic telemetry was used to track 205 lake sturgeon ( Acipenser fulvescens ) tagged in the St. Clair and Detroit rivers of the Laurentian Great Lakes over seven years (2012–2019). The objective of this study was to determine if annual survival was related to sex, size, tagging location (river), or year post-tagging using Cormack-Jolly-Seber (CJS) models. Annual survival was high among all seven years (range of point estimates: 95–99%) and did not differ based on sex, tagging year, size at time of tagging, or tagging location. Lake sturgeon detection probability on acoustic receivers was high each year (range of point estimates: 82–99%) and increased as the number of receivers in the system increased. High survival rates of lake sturgeon were consistent with levels thought required for lake sturgeon to be self-sustaining in the St. Clair – Detroit river system. Our application of acoustic telemetry detections as input to CJS models demonstrated the usefulness of this approach and should be considered for population assessment studies throughout the Great Lakes and beyond.

Michigan↗

USGS2022

Microbial source tracking and evaluation of best management practices for restoring degraded beaches of Lake Michigan

Attempts to mitigate shoreline microbial contamination require a thorough understanding of pollutant sources, which often requires multiple years of data collection (e.g., point/nonpoint) and the interacting factors that influence water quality. Because restoration efforts can alter shoreline or beach morphology, revisiting source inputs is often necessary. Microbial source tracking (MST) using source-specific molecular markers, genomic community analyses, and physical modeling was used to identify contamination sources along three Lake Michigan beaches of the Laurentian Great Lakes with historically high fecal indicator bacteria (FIB, E. coli ) concentrations. Genetic markers for human (Bacteroides HF183) and mixed gull species ( Catellicoccus marimammalium ) fecal sources were tested from water and sediment. Gene sequencing (16S rRNA) was used to identify similarities in bacterial communities in nearshore water, river inputs, sand, sediment, and groundwater. Synoptic surveys of water exchange were conducted to determine nearshore-offshore interactions of FIB. In addition to these MST studies, best management practices to mitigate FIB, including gull deterrence, slope grading, wetland establishment, and shoreline plantings, were reviewed for their effectiveness at reducing FIB concentrations over time. Using multiple tools for MST helped identify primary and secondary sources of FIB (gulls, stormwater inputs) and the physical processes that exacerbate FIB concentrations (onshore currents, limited circulation). Management actions were successful in the short-term at reducing FIB, but scope of success was temporally limited, with FIB concentrations often rebounding. Results highlight the usefulness of MST to inform best management practices and the need for a sustained adaptive approach that adjusts for changes in the coastal system.

Illinois, Wisconsin↗

USGS2022

Evaluation of post-stocking dispersal and mortality of juvenile lake trout Salvelinus namaycush in Lake Ontario using acoustic telemetry

Wild reproduction by stocked lake trout Salvelinus namaycush in Lake Ontario has yet to produce a self-sustaining population, requiring a reliance on stocking. Once released, age-1 juvenile lake trout are not typically surveyed until age-2, creating a gap in knowledge of fine-scale post-release behaviors. A method to track fine-scale movements and estimate mortality of juvenile lake trout could complement standard survey methods and benefit management decisions regarding stocking locations. We used acoustic telemetry to estimate post-stocking mortality and observe fine-scale spatial and temporal movements of 38 hatchery-reared, age-1 lake trout from an offshore stocking site in the eastern basin of Lake Ontario from 2017 to 2018. Cumulative post-stocking mortality was estimated at 5.3%, 10.5%, and 26.3% after one week, one month and one year, respectively. The majority of lake trout (68.4%) emigrated from the stocking location within two months and entered deep water (∼50 m) once warm-water incursions at the stocking site exceeded lake trout thermal preferences (15 °C). Lake trout made large movements (i.e., median 1.9 km, maximum 12.4 km straight-line distance) within the first hour post-release and had an average swimming speed of 1.64 km‧hr −1 over the first day. There was no statistically significant relationship between total distance traveled and time of day, although distance traveled tended to be greater during crepuscular and dark periods compared to daylight. Our results provide a conservative estimate of post-release mortality and reveal behaviors of hatchery-reared juvenile lake trout that may be helpful when selecting stocking locations beneficial to restoration program goals.

Lake Ontario↗

USGS2023

Initial insights on the thermal ecology of lake whitefish in northwestern Lake Michigan

Lake whitefish Coregonus clupeaformis are a native coldwater species supporting important recreational and commercial fisheries in the Laurentian Great Lakes. Climate-related changes in water temperature may have important implications for the future sustainability of these fisheries. However, projecting future habitat availability is difficult because limited information is available on lake whitefish thermal ecology in the region. In this study, archival temperature loggers were implanted into 400 lake whitefish from northwestern Lake Michigan, including Green Bay, during October–November 2017. Loggers recorded temperature for 11 months at 4-hr intervals. Thirteen recovered temperature loggers were used in analyses. In winter (1 December–31 March), temperatures occupied by lake whitefish ranged from 0 to 8.0 °C, while in spring (1 April–31 May) temperatures ranged from 0 to 20.0 °C. In summer (1 June–15 September) and fall (16 September–7 November), lake whitefish occupied temperatures of 4–21.5 and 4–21.0 °C, respectively. Average temperatures in summer (10.8 °C) were within the previously proposed optimal temperature range (10–14 °C) and broad thermal niche (7–17 °C); however, 58% of observations were outside the optimal temperature range and 11% of observations were outside the broad thermal niche. Our results suggest that lake whitefish from northwestern Lake Michigan inhabit temperatures both above and below previously reported expected temperature ranges. This study provides initial insights on lake whitefish thermal ecology in Lake Michigan and can be used as a baseline for future work aimed at determining how lake whitefish habitat availability may change in the future.

Wisconsin↗

USGS2024

Controls on in-stream nitrogen loss in western Lake Erie tributaries

Management efforts to reduce cyanobacterial harmful algal blooms (cHABs) in the Great Lakes have focused on decreasing tributary inputs of phosphorus (P). Recent research has indicated that reduction of both P and nitrogen (N) can lessen cHABs severity. Microbially mediated N cycling in streambed sediment may reduce N riverine loads, yet little is known about in-stream N processing rates in the Maumee River Basin, a major source of nutrients to Lake Erie. During summer of 2019 and 2021, we sampled streambed sediment to measure potential nitrification and denitrification rates using the acetylene block method at 78 sites throughout the Maumee River network. We used structural equation models to identify indirect and direct drivers of denitrification. Precipitation was greater in 2019, resulting in a 67 % increase in mean discharge, 41 % of farm fields to be fallow, and a 50 % reduction in fertilizer use. During summer field surveys, median stream-water nitrate concentrations were not different between 2019 and 2021. Median denitrification rates were 13.3 mg N/m2/h and 31.2 mg N/m2/h, respectively, indicating high potential to remove N. Nitrate concentrations and nitrification rates were strong direct drivers of denitrification, especially in 2019 when coupled nitrification–denitrification sustained denitrification. Nitrate concentrations varied with land use. Notably, nitrate concentrations increased with the area of fallow land, which may indicate the presence of a legacy N source. These findings indicate that promoting streambed denitrification could reduce N loads to Lake Erie, but legacy N currently stored in the system may mask N reduction efforts.

Indiana, Michigan, Ohio↗

USGS2024

Capturing potential: Leveraging grass carp behavior Ctenopharyngodon idella for enhanced removal

Effective management of invasive species benefits from a comprehensive understanding of the species’ behavior and interactions with the invaded system. We investigated temporal dynamics of telemetry detections and the potential utility of a traitor approach for informing response efforts to the invasive grass carp ( Ctenopharyngodon idella ) population in the Sandusky River, a major tributary to Lake Erie. Telemetered grass carp exhibited heightened activity at night and early morning, suggesting that capture and removal be more effective during these time periods. Analysis of catch per unit effort (CPUE) across different removal methods, trammel nets, electrofishing, and hoop nets. suggested that incorporating the traitor approach could improve capture. Low catchability values (<0.026), based on the number of telemetered grass carp present in the river on a weekly basis and the number of those telemetered fish captured, suggest the species is difficult to capture. Optimizing response effort efficiency is important and refining catchability estimates will lessen errors in population models and improve interpretation of low CPUE data. Results from generalized additive models suggest capture could be improved using telemetry data, night removals, and by attempting exploratory removal efforts in fall and winter months. By incorporating telemetry data and acknowledging the complexities of grass carp behavior and ecology, we found that a multifaceted and data-driven approach to invasive species control could be beneficial, ultimately promoting conservation and sustainability in dynamic ecosystems like Lake Erie.

Ohio↗

USGS2025

Beach nourishment response and recent morphological evolution of Minnesota Point, Lake Superior

Beach nourishments are a popular nature-based alternative to armoring for shoreline erosion mitigation, but nourishments have been criticized due to their environmental impacts and uncertain sustainability. Monitoring is often nonexistent or insufficient to constrain nourishment longevity and inform the renourishment interval required to maintain shoreline protection. This study uses a combination of topobathymetric surveys, high-resolution satellite-derived shorelines, and coastal engineering analyses to investigate the recent evolution of Minnesota Point and the fate of three beach nourishments constructed adjacent to littoral barriers. We use semi-empirical formulations for sediment compatibility, wave runup, and longshore sediment transport to inform the observed nourishment behavior. Minnesota Point experienced widespread foredune retreat averaging 7±2.8 m from 2009–2019 and 130,000 (70,000–140,000) m 3 of sediment was eroded during this interval. The 2019 nourishment at the Superior Entry was rapidly eroded by strong storms, losing >80% of the added beach width by the following spring. The 2020 and 2021 nourishments at the Duluth Entry retained >80% of the nourishment material at the time of the last topobathymetric survey in the fall of 2022, and satellite-derived shorelines indicate that the beach remained 10 m wider than pre-nourishment conditions at the end of 2023. Modeled longshore transport rates over the period 2009–2022 averaged 11,400 m 3 yr −1 northwestward at the Superior Entry, nearly 3x greater than the 4000 m 3 yr −1 southeastward transport modeled at the Duluth Entry. These observations show that differences in shoreline orientation, littoral sediment supply, and grain size compatibility can lead to contrasting beach nourishment longevities, and this study provides additional measurements of Minnesota Point’s long-term morphological change which can help inform coastal resiliency efforts.

Minnesota, Wisconsin↗

USGS2025

Detroit River becoming a crucible for boundary organization experimentation

The Detroit River has a long history of human use and abuse, resulting in public outcry over water pollution and resource degradation. This public outcry helped catalyze the enactment of many laws and the Canada-U.S. Great Lakes Water Quality Agreement which led to enhanced research, monitoring, and water pollution control. As pollution from industries and municipal wastewater treatment plants came under control and progress was made in management of single species, the focus shifted to a more comprehensive ecosystem approach that accounted for all the sources of pollution and targeted restoring ecosystem health with resilience. Over time, the Detroit River became a “proving ground” or crucible for experimenting with boundary organizations to overcome geographical, political, institutional, and disciplinary boundaries and strengthen science-policy-management linkages for ecosystem-based management. This study identified 15 boundary organizations functioning in the Detroit River watershed and evaluated two case studies – St. Clair-Detroit River System Initiative and State of the Strait Conferences. Key lessons learned from this study include: 1) establishing boundary organizations, promoting cooperative learning, and building capacity for boundary-spanning are essential for use of an ecosystem approach; 2) boundary spanning requires specific skills, experience, and improved linkages between research and practice; 3) the 15 boundary organizations provide a unique opportunity to collaborate in a community of practice to share knowledge, foster cooperative learning, enhance problem-solving, build trust, and demonstrate leadership; and 4) continued actionable science, investment in capacity building, and cooperative learning are essential to meet long-term goals of sustainability.

Detroit River↗

USGS2025

Application of a data-limited stock assessment model to understand the historical population of cisco in Lake Erie

Historically, cisco (Coregonus artedi) supported one of the largest commercial fisheries in Lake Erie with over 25 million kilograms landed in a single year during the fisheries’ peak in 1912. Like many other coregonines in the Laurentian Great Lakes, the Lake Erie cisco population eventually collapsed and is now considered extirpated. Management interest in restoring coregonine abundance and diversity across the Great Lakes motivated the development of a multi-agency, science-based framework aimed at restoring or enhancing populations. As part of that framework, we applied a data-limited model (depletion-based stock reduction analysis) to a reconstructed catch series to estimate historical levels of abundance of cisco in Lake Erie. Estimated historical carrying capacity was 171 million kilograms (66.5 kg/ha) and estimated annual exploitation was as high as 70 %. Model projections suggested the population should have rebuilt following a fishery collapse in 1925; however, the fishery remained depressed and cisco disappeared from Lake Erie despite the end of targeted exploitation in 1965. Other factors, such as habitat degradation and invasive species, are believed to have played a part in impeding recovery of cisco. The results of this study could be used in setting potential restoration targets for Lake Erie cisco given current conditions. The likelihood of achieving recovery targets based on historical population size will be dependent on the suitability of current conditions for sustaining the population.

Lake Erie↗

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↗

USGS2004

A methodology to asess relations between climatic variability and variations in hydrologic time series in the southwestern United States

A new method for frequency analysis of hydrologic time series was developed to facilitate the estimation and reconstruction of individual or groups of frequencies from hydrologic time-series and facilitate the comparison of these isolated time-series components across data types, between different hydrologic settings within a watershed, between watersheds, and across frequencies. While climate-related variations in inflow to and outflow from aquifers have often been neglected, the development and management of ground-water and surface-water resources has required the inclusion of the assessment of the effects of climatic variability on the supply and demand and sustainability of use. The regional assessment of climatic variability of surface-water and ground-water flow throughout the southwestern United States required this new systematic method of hydrologic time-series analysis. To demonstrate the application of this new method, six hydrologic time-series from the Mojave River Basin, California were analyzed. The results indicate that climatic variability exists in all the data types and are partially coincident with known climate cycles such as the Pacific Decadal Oscillation and the El Nino-Southern Oscillation. The time-series also indicate lagged correlations between tree-ring indices, streamflow, stream base flow, and ground-water levels. These correlations and reconstructed time-series can be used to better understand the relation of hydrologic response to climatic forcings and to facilitate the simulation of streamflow and ground-water recharge for a more realistic approach to water-resource management. Published by Elsevier B.V.

Journal of Hydrology↗

USGS2008

Temporal downscaling of decadal sediment load estimates to a daily interval for use in hindcast simulations

In this study we used hydrologic proxies to develop a daily sediment load time-series, which agrees with decadal sediment load estimates, when integrated. Hindcast simulations of bathymetric change in estuaries require daily sediment loads from major tributary rivers, to capture the episodic delivery of sediment during multi-day freshwater flow pulses. Two independent decadal sediment load estimates are available for the Sacramento/San Joaquin River Delta, California prior to 1959, but they must be downscaled to a daily interval for use in hindcast models. Daily flow and sediment load data to the Delta are available after 1930 and 1959, respectively, but bathymetric change simulations for San Francisco Bay prior to this require a method to generate daily sediment load estimates into the Delta. We used two historical proxies, monthly rainfall and unimpaired flow magnitudes, to generate monthly unimpaired flows to the Sacramento/San Joaquin Delta for the 1851-1929 period. This step generated the shape of the monthly hydrograph. These historical monthly flows were compared to unimpaired monthly flows from the modern era (1967-1987), and a least-squares metric selected a modern water year analogue for each historical water year. The daily hydrograph for the modern analogue was then assigned to the historical year and scaled to match the flow volume estimated by dendrochronology methods, providing the correct total flow for the year. We applied a sediment rating curve to this time-series of daily flows, to generate daily sediment loads for 1851-1958. The rating curve was calibrated with the two independent decadal sediment load estimates, over two distinct periods. This novel technique retained the timing and magnitude of freshwater flows and sediment loads, without damping variability or net sediment loads to San Francisco Bay. The time-series represents the hydraulic mining period with sustained periods of increased sediment loads, and a dramatic decrease after 1910, corresponding to a reduction in available mining debris. The analogue selection procedure also permits exploration of the morphological hydrograph concept, where a limited set of hydrographs is used to simulate the same bathymetric change as the actual set of hydrographs. The final daily sediment load time-series and morphological hydrograph concept will be applied as landward boundary conditions for hindcasting simulations of bathymetric change in San Francisco Bay.

California↗

USGS2009

Defining restoration targets for water depth and salinity in wind-dominated Spartina patens (Ait.) Muhl. coastal marshes

Coastal wetlands provide valued ecosystem functions but the sustainability of those functions often is threatened by artificial hydrologic conditions. It is widely recognized that increased flooding and salinity can stress emergent plants, but there are few measurements to guide restoration, management, and mitigation. Marsh flooding can be estimated over large areas with few data where winds have little effect on water levels, but quantifying flooding requires hourly measurements over long time periods where tides are wind-dominated such as the northern Gulf of Mexico. Estimating salinity of flood water requires direct daily measurements because coastal marshes are characterized by dynamic salinity gradients. We analyzed 399,772 hourly observations of water depth and 521,561 hourly observations of water salinity from 14 sites in Louisiana coastal marshes dominated by Spartina patens (Ait.) Muhl. Unlike predicted water levels, observed water levels varied monthly and annually. We attributed those observed variations to variations in river runoff and winds. In stable marshes with slow wetland loss rates, we found that marsh elevation averaged 1 cm above mean high water, 15 cm above mean water, and 32 cm above mean low water levels. Water salinity averaged 3.7 ppt during April, May, and June, and 5.4 ppt during July, August, and September. The daily, seasonal, and annual variation in water levels and salinity that were evident would support the contention that such variation be retained when designing and operating coastal wetland management and restoration projects. Our findings might be of interest to scientists, engineers, and managers involved in restoration, management, and restoration in other regions where S. patens or similar species are common but local data are unavailable.

Journal of Hydrology↗

USGS2010

Consumptive use and resulting leach-field water budget of a mountain residence

Consumptive use of water in a dispersed rural community has important implications for maximum housing density and its effects on sustainability of groundwater withdrawals. Recent rapid growth in Colorado, USA has stressed groundwater supplies in some areas, thereby increasing scrutiny of approximate methods developed there more than 30 years ago to estimate consumptive use that are still used today. A foothills residence was studied during a 2-year period to estimate direct and indirect water losses. Direct losses are those from evaporation inside the home, plus any outdoor use. Indirect loss is evapotranspiration ( ET ) from the residential leach-field in excess of ET from the immediately surrounding terrain. Direct losses were 18.7% of water supply to the home, substantially larger than estimated historically in Colorado. A new approach was developed to estimate indirect loss, using chamber methods together with the Penman–Monteith model. Indirect loss was only 0.9% of water supply, but this value probably was anomalously low due to a recurring leach-field malfunction. Resulting drainage beneath the leach-field was 80.4% of water supply. Guidelines are given to apply the same methodology at other sites and combine results with a survey of leach-fields in an area to obtain more realistic average values of ET losses.

Colorado↗