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At least 1,045 records · Page 58Linked to original sources

USGS2019

Speaking the same language: Can the Sustainable Development Goals translate the needs of inland fisheries into irrigation decisions?

Irrigated agriculture and inland fisheries both make important contributions to food security, nutrition, livelihoods, and well-being. Typically, in modern irrigation systems, these components operate independently. Some practices, commonly associated with water use and intensification of crop production, can be in direct conflict with and have adverse impacts on fisheries. Food security objectives may be compromised if fish are not considered in the design phases of irrigation systems. The 2030 Agenda for Sustainable Development provides a framework that can serve as a backdrop to help integrate both sectors in policy discussions and optimize their contributions to achieving the Sustainable Development Goals (SDGs). Inland fisheries systems do play an important role in supporting many SDG objectives, but these contributions can sometimes be at odds with irrigated agriculture. Using case studies of two globally important river catchments, the Lower Mekong and Murray-Darling Basins, we highlight the conflicts and opportunities for improved outcomes between irrigated agriculture and inland fisheries. We explore SDG 2 (Zero Hunger) as a path to advance our irrigation systems as a means to benefit both agriculture and inland fisheries, preserving biodiversity and enhancing the economic, environmental, and social benefits they both provide to people.

Marine and Freshwater Research↗

USGS2015

Origin of Atlantic Sturgeon collected off the Delaware coast during spring months

Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus was federally listed under the U.S. Endangered Species Act as five distinct population segments (DPS). Currently, at least 18 estuaries coastwide host spawning populations and the viability of these vary, requiring differing levels of protection. Subadults emigrate from their natal estuaries to marine waters where they are vulnerable to bycatch; one of the major threats to the rebuilding of populations. As a result, identifying the population origin of Atlantic Sturgeon in coastal waters is critical to development of management plans intended to minimize interactions of the most imperiled populations with damaging fisheries. We used mitochondrial DNA control region sequencing and microsatellite DNA analyses to determine the origin of 261 Atlantic Sturgeon collected off the Delaware coast during the spring months. Using individual-based assignment (IBA) testing and mixed stock analysis, we found that specimens originated from all nine of our reference populations and the five DPSs used in the listing determination. Using IBA, we found that the Hudson River population was the largest contributor (38.3%) to our coastal collection. The James (19.9%) and Delaware (13.8%) river populations, at one time thought to be extirpated or nearly so, were the next largest contributors. The three populations combined in the South Atlantic DPS contributed 21% of specimens; the Altamaha River, the largest population in the South Atlantic DPS, only contributed a single specimen to the collection. While the origin of specimens collected on the Delaware coast was most likely within rivers of the New York Bight DPS (52.1%), specimens that originated elsewhere were also well represented. Genetic analyses provide a robust tool to identify the population origin of individual sturgeon outside of their natal estuaries and to determine the quantitative contributions of individual populations to coastal aggregations that are vulnerable to bycatch and other anthropogenic threats.

Delaware↗

USGS2016

Impacts of Northern Pike on stocked Rainbow Trout in Pactola Reservoir, South Dakota

Establishment of nonnative Northern Pike Esox lucius in Pactola Reservoir, South Dakota, has prompted concern among biologists about the influence of this species on the lake’s intensively managed salmonid fisheries. Ancedotal information suggests that catch rates of Rainbow Trout Oncorhynchus mykiss have declined while mean size and abundance of Northern Pike has increased, although quantitative information on diet and growth of the Northern Pike population is lacking. To address potential interactions between Northern Pike and Rainbow Trout, we assessed size-dependent predation by Northern Pike on Rainbow Trout and determined the relative energetic contribution of stocked Rainbow Trout to Northern Pike growth using bioenergetics modeling. Stable isotopes combined with traditional diet analyses revealed that smaller Northern Pike (<600 mm TL) consumed primarily centrarchids and Rainbow Smelt Osmerus mordax , and Rainbow Trout contributed less than 10% to their annual energy consumption. In contrast, larger Northern Pike (≥600 mm TL) consumed primarily Rainbow Trout, which accounted for 56% of their annual energy consumption. Combining estimates of Northern Pike predation with production costs of catchable-size Rainbow Trout revealed that annual economic losses ranged from US$15,259 to $24,801 per year. Over its lifespan, an age-10 Northern Pike was estimated to consume ~117 Rainbow Trout worth approximately $340. Thus, Northern Pike predation substantially influences salmonid management initiatives and is likely a primary factor contributing to reduced Rainbow Trout abundance and return to anglers in Pactola Reservoir. Strategies for reducing Northern Pike predation on Rainbow Trout include increasing the size of stocked fish or altering the timing and spatial distribution of stocking events.

South Dakota↗

USGS2010

Importance of benthic production to fish populations in Lake Mead prior to the establishment of quagga mussels

Limnologists recently have developed an interest in quantifying benthic resource contributions to higher-level consumers. Much of this research focuses on natural lakes with very little research in reservoirs. In this study, we provide a contemporary snapshot of the food web structure of Lake Mead to evaluate the contribution of benthic resources to fish consumers. In addition, we document the available food to fishes on soft sediments and changes to the invertebrate community over 2 time periods. Benthic invertebrate food availability for fishes is greater in Las Vegas Bay than Overton Arm. Las Vegas Bay is dominated by oligochaetes, whose biomass increased with depth, while Overton Arm is dominated by chironomids, whose biomass did not change with depth. Diet and isotopic measurements indicate the fish community largely relies on benthic resources regardless of basin (Las Vegas Bay >80%; Overton Arm >92%); however, the threadfin shad likely contribute more to largemouth and striped bass production in Overton Arm versus Las Vegas Bay. A 2-time period analysis, pre and post quagga mussel establishment and during lake level declines, suggests there is no change in the density of benthic invertebrates in Boulder Basin, but there were greater abundances of select taxa in this basin by season and depth than in other basins. Given the potential of alterations as a result of the expansion of quagga mussel and the reliance of the fishery on benthic resources, future investigation of basin specific, benthic processes is recommended.

Nevada↗

USGS2012

Nutrient and algal responses to winterkilled fish-derived nutrient subsidies in eutrophic lakes

Fishes inhabiting shallow, glacial lakes of the Prairie Pothole Region in the United States and Canada periodically experience hypoxia in severe winters that can lead to extensive fish mortality resulting in high biomasses of dead fish. However, the role of carcass-derived nutrient subsidies in shallow, eutrophic lakes translocated to pelagic primary producers is not well documented. This study quantified the influence of winterkill events on nutrient contributions from decaying fish carcasses of common carp ( Cyprinus carpio ) and the phytoplankton response among pre- and postwinterkill years and compared seasonal patterns of nutrient limitation and phytoplankton community composition between winterkill and nonwinterkill lakes. We found that fish carcasses contributed an estimated 2.5–4.3 kg/ha of total (Kjeldahl) nitrogen (N) and 0.3–0.5 kg/ha of total phosphorus (P) to lakes that experienced winterkill conditions. Nutrient bioassays showed that winterkill lakes were primarily N limited, congruent with the low N:P ratios produced by fish carcasses corrected for the disproportionate release of N and P (8.6). Nutrient subsidies translocated from decomposed fish to pelagic primary producers seemed to have little immediate influence on the seasonal phytoplankton community composition, but total N and subsequent chlorophyll- a increased the year following the winterkill event. Cyanobacteria density varied seasonally but was higher in winterkill lakes, presumably due to the integration of nutrients released from fish decomposition. This study provides evidence that large inputs of autochthonous fish-derived nutrients contribute to nutrient availability within winterkilled systems and increase the maximum attainable biomass of the phytoplankton community.

Lake and Reservoir Management↗

USGS2008

Book review of Avalanche Dynamics by Shiva P. Pudasaini and Kolumban Hutter. Springer: Berlin-Heidelberg, 2007. 602 pages, 225 figures, 15 tables

This highly specialized book is interesting not only because of its important subject matter but also because of its egocentric perspective. The majority of the book provides a nearly exhaustive retrospective of the authors’ many contributions to the shallow‐flow theory of granular avalanches, and it also critiques contributions by others. Indeed, some readers (including this reviewer) might be dismayed to find their own contributions critiqued inaccurately! This brief review will not attempt to correct inaccuracies, however, but will emphasize the book’s main features.

Journal of Geology↗

USGS2023

Where the past meets the present: Connecting nitrogen from watersheds to streams through groundwater flowpaths

Groundwater discharge to streams is a nonpoint source of nitrogen (N) that confounds N mitigation efforts and represents a significant portion of the annual N loading to watersheds. However, we lack an understanding of where and how much groundwater N enters streams and watersheds. Nitrogen concentrations at the end of groundwater flowpaths are the culmination of biogeochemical and physical processes from the contributing land area where groundwater recharges, within the aquifer system, and in the near-stream riparian area where groundwater discharges to streams. Our research objectives were to quantify the spatial distribution of N concentrations at groundwater discharges throughout a mixed land-use watershed and to evaluate how relationships among contributing and riparian land cover, modeled aquifer characteristics, and groundwater discharge biogeochemistry explain the spatial variation in groundwater discharge N concentrations. We accomplished this by integrating high-resolution thermal infrared surveys to locate groundwater discharge, biogeochemical sampling of groundwater, and a particle tracking model that links groundwater discharge locations to their contributing area land cover. Groundwater N loading from groundwater discharges within the watershed varied substantially between and within streambank groundwater discharge features. Groundwater nitrate concentrations were spatially heterogeneous ranging from below 0.03–11.45 mg-N/L, varying up to 20-fold within meters. When combined with the particle tracking model results and land cover metrics, we found that groundwater discharge nitrate concentrations were best predicted by a linear mixed-effect model that explained over 60% of the variation in nitrate concentrations, including aquifer chemistry (dissolved oxygen, Cl − , SO 4 2− ), riparian area forested land cover, and modeled physical aquifer characteristics (discharge, Euclidean distance). Our work highlights the significant spatial variability in groundwater discharge nitrate concentrations within mixed land-use watersheds and the need to understand groundwater N processing across the many spatiotemporal scales within groundwater cycling.

Connecticut↗

USGS2025

Spring weather influences breeding propensity, the most important productivity component for Arctic-nesting lesser snow geese

Animal reproduction is composed of several stages, which collectively determine overall productivity. Yet, it is not fully understood how different productivity components contribute to population change. To bridge this gap, we leveraged integrated population modelling and transient life-table response experiments, together with population-level data on lesser snow geese ( Anser caerulescens caerulescens ) breeding on Wrangel Island, Russia, from 1970 to 2022. We assessed contributions of breeding propensity, clutch size, nest success, egg survival, hatching success and pre-fledging survival to population change, and tested hypotheses about the effects of environmental drivers and density dependence on different components. Breeding propensity contributed the most to variation in population growth, followed by nest success. These two components were negatively affected by the timing of snow melt. We found no overall deleterious effects of climate change on productivity. Density dependence had a positive effect on multiple productivity components, likely through predator swamping. Our results show the importance of breeding propensity to the population dynamics of this long-lived animal, which is notable because this productivity component is often overlooked. Our results also demonstrate that the effects of environmental conditions and density dependence can differ among animal populations of different sizes, locations and life histories.

Wrangel Island↗

USGS2017

Defining and classifying migratory habitats as sources and sinks: The migratory pathway approach

Understanding and conserving migratory species requires a method for characterizing the seasonal flow of animals among habitats. Source-sink theory describes the metapopulation dynamics of species by classifying habitats as population sources (i.e. net contributors) or sinks (i.e. net substractors). Migratory species may have non-breeding habitats important to the species (e.g. overwintering or stopover habitats) that traditional source-sink theory would classify as sinks because these habitats produce no individuals. Conversely, existing migratory network models can evaluate the relative contribution of non-breeding nodes, but these models make an equilibrium assumption that is difficult to meet when examining real migratory populations. We extend a pathway-based metric allowing breeding habitats, non-breeding habitats and migratory pathways connecting these habitats to be classified as sources or sinks. Rather than being based on whether place- or season-specific births exceed deaths, our approach quantifies the total demographic contribution from a node or migratory pathway over a flexibly defined yet limited time period across an organism's life cycle. As such, it provides a snapshot of a migratory system and therefore does not require assumptions associated with equilibrium dynamics. We first develop a generalizable mathematical notation and then demonstrate how the metric may be used with two case studies: the common loon ( Gavia immer ) and Yellowstone cutthroat trout ( Oncorhynchus clarkii bouvieri ). These examples highlight how stressors can impact stopover and wintering habitats (loons) and habitat management targeting migratory pathways can improve population status (trout). Synthesis and applications . Each of the two case studies presented describes how effects at one location are felt by populations in another through the seasonal flow of individuals. The contribution metric we present should be helpful in allocating regulatory and management attention to times and locations most critical to migratory species persistence.

Journal of Applied Ecology↗

USGS2017

Examining fluvial fish range loss with SDMs

Fluvial fishes face increased imperilment from anthropogenic activities, but the specific factors contributing most to range declines are often poorly understood. For example, the range of the fluvial‐specialist shoal bass ( Micropterus cataractae ) continues to decrease, yet how perceived threats have contributed to range loss is largely unknown. We used species distribution models to determine which factors contributed most to shoal bass range loss. We estimated a potential distribution based on natural abiotic factors and a series of currently occupied distributions that incorporated variables characterizing land cover, non‐native species, and river fragmentation intensity (no fragmentation, dams only, and dams and large impoundments). We allowed interspecific relationships between non‐native congeners and shoal bass to vary across fragmentation intensities. Results from the potential distribution model estimated shoal bass presence throughout much of their native basin, whereas models of currently occupied distribution showed that range loss increased as fragmentation intensified. Response curves from models of currently occupied distribution indicated a potential interaction between fragmentation intensity and the relationship between shoal bass and non‐native congeners, wherein non‐natives may be favored at the highest fragmentation intensity. Response curves also suggested that >100 km of interconnected, free‐flowing stream fragments were necessary to support shoal bass presence. Model evaluation, including an independent validation, suggested that models had favorable predictive and discriminative abilities. Similar approaches that use readily available, diverse, geospatial data sets may deliver insights into the biology and conservation needs of other fluvial species facing similar threats.

Conservation Biology↗

USGS2017

The nexus of fun and nutrition: Recreational fishing is also about food

Recreational fishing is a popular activity in aquatic ecosystems around the globe using a variety of gears including rod and line and to a lesser extent handlines, spears, bow and arrow, traps and nets. Similar to the propensity to engage in voluntary catch-and-release, the propensity to harvest fishes strongly varies among cultures, locations, species and fisheries. There is a misconception that because recreational fishing happens during non-work (i.e. leisure) time, the nutritional motivation is negligible; therefore, the role of recreational fishing in supporting nutrition (and thus food security) at regional, national or global scales is underappreciated. We consider the factors that influence whether fish will be harvested or released by examining the motives that underlie recreational fishing. Next, we provide an overview of the magnitude and role of recreational fishing harvest in supporting nutrition using regional case-studies. Then, we address issues such as contaminants and parasites that constrain the ability of fish harvested by recreational fishers to be consumed. Although recreational fishing is foremost a leisure activity, the harvest of fish for personal consumption by recreational fishers has contributed and will continue to contribute to human nutrition by providing an accessible, affordable and generally highly sustainable food source, notwithstanding concerns about food safety and possibly overfishing. Attempts to better quantify the role of fish harvested by recreational fishers and the relative contribution to overall food security and personal nutrition will provide resource managers and policymakers the information needed to guide management activities and policy development.

Fish and Fisheries↗

USGS2008

Habitat, topographical, and geographical components structuring shrubsteppe bird communities

Landscapes available to birds to select for breeding locations are arrayed along multiple dimensions. Identifying the primary gradients structuring shrubsteppe bird communities in the western United States is important because widespread habitat loss and alteration are shifting the environmental template on which these birds depend. We integrated field habitat surveys, GIS coverages, and bird counts from 61 Breeding Bird Survey routes located in shrubsteppe habitats across a >800 000 km2 region to determine the gradients of habitat, topography, and geography underlying bird communities. A small set of habitat features dominated the primary environmental gradients in a canonical ordination; the 13 species in the shrubsteppe bird community were closely packed along the first two axes. Using hierarchical variance partitioning, we identified habitat as the most important pure (31% explained variation) or shared component. Topography (9%) and geography (4%) were minor components but each shared a larger contribution with habitat (habitat-topography 21%; habitat-geography 22%) in explaining the organization of the bird community. In a second tier partition of habitat structure, pure composition (% land cover) was more important (45%) than configuration (patch size and edge) (7%); the two components shared 27% of the explained variation in the bird community axes. Local (9%), community (14%), and landscape (10%) levels contributed equally. Adjacent organizational levels had a larger shared contribution (local-community 26%; community-landscape 27%) than more separated local-landscape levels (21%). Extensive conversion of shrubsteppe habitats to agriculture, exotic annual grasslands, or pinyon (Pinus spp.)-juniper (Juniperus spp.) woodlands is occurring along the primary axes of habitat structure. Because the shrubsteppe bird community was organized along short gradients dominated by habitat features, relatively small shifts in their available environment will exert a strong influence on these bird populations in the absence of buffering by alternative gradients. ?? 2008 The Authors.

Ecography↗

USGS2007

Cautions and suggestions for geochemical sampling in fractured rock

Collecting water samples for geochemical analyses in open bedrock boreholes or in discrete intervals of boreholes intersected by multiple fractures is likely to yield ambiguous results for ground water chemistry because of the variability in the transmissivity, storativity, and hydraulic head of fractures intersecting the borehole. Interpreting chemical analyses of water samples collected in bedrock boreholes requires an understanding of the hydraulic conditions in the borehole under the ambient flow regime in the aquifer as well as during sampling. Pumping in open boreholes, regardless of the pumping rate and the location of the pump intake, first draws water from the borehole and then from fractures intersecting the borehole. The time at which the volumetric rate of water entering the borehole from fractures is approximately equal to the pumping rate can be identified by monitoring the logarithm of drawdown in the borehole as a function of the logarithm of time. Mixing of water entering the borehole from fractures with water in the borehole must be considered in estimating the time at which the pump discharge is representative of aquifer water. In boreholes intersected by multiple fractures, after the contribution from the borehole volume has diminished, the contribution of fractures to the pump discharge will be weighted according to their transmissivity, regardless of the location of the pump intake. This results in a flux‐averaged concentration in the pump discharge that is biased by the chemical signature of those fractures with the highest transmissivity. Under conditions where the hydraulic head of fractures varies over the length of the borehole, open boreholes will be subject to ambient flow in the water column in the borehole. In some instances, the magnitude of the ambient flow may be similar to the designated pumping rate for collecting water samples for geochemical analyses. Under such conditions, the contributions to the pump discharge from individual fractures will be a function not only of the transmissivity of the fractures, but also of the distribution of hydraulic head in fractures intersecting the borehole. To reduce or eliminate the deleterious effects of conducting geochemical sampling in open boreholes, a straddle‐packer apparatus that isolates a single fracture or a series of closely spaced fractures is recommended. It is also recommended that open boreholes be permanently outfitted with borehole packers or borehole liners in instances where maintaining the hydraulic and chemical stratification in the aquifer is of importance. In a field example, a comparison of results from sampling in an open borehole and in discrete intervals of the same borehole showed dramatic differences in the concentrations of chemical constituents in the water samples, even though chemical field parameters stabilized prior to both open borehole and discrete interval sampling.

Groundwater Monitoring & Remediation↗

USGS2007

Application of GPS and GIS to map channel features in Walnut Creek, Iowa

A 12-km reach of Walnut Creek was mapped at the Neal Smith National Wildlife Refuge in Jasper County, Iowa to identify and prioritize areas of the stream channel in need of further investigation or restoration. Channel features, including streambank conditions, bottom sediment materials and thickness, channel cross-sections, debris dams, tile lines, tributary creeks, and cattle access points, were located to one-meter accuracy with global positioning system (GPS) equipment and described while traversing the stream. The GPS data were exported into a Geographic Information System (GIS) format, and field descriptions were added to create a series of coverages. Channel features were coupled with existing land cover data for analysis. Left and right streambank erosion rates varied from slight in many areas to severe at outside meander bends, debris dams or cattle access points. Erosion estimates from this study suggest that stream banks contribute about 50 percent of the annual suspended sediment load in the channel. Substrate materials varied from bare or thinly mantled pre-Illinoian till to thick silty muck (> 0.3 m) behind some debris dams and cattle access points. Occurrences of sand and gravel areas were generally restricted to cattle access areas and bridge crossings. A total of 81 debris dams were identified in the stream channel, ranging from fallen trees and beaver dams to several large debris dams. Numerous tile lines (52 total) and tributary creeks (45 total) were mapped as contributing flow to the main channel. Cross-sections measured at 34 locations indicated Walnut Creek averages 10.64 m wide and 2.77 m deep, with the width and depth increasing downstream. Channelization and tile discharge in row crop land use areas have contributed to increased bed degradation and channel widening throughout the watershed. The results of this study indicate the effectiveness of a one-time detailed mapping program to characterize stream system variability and identify spatial relationships among many stream characteristics. Stream survey data are being used to model watershed conditions, identify water sampling points and evaluate and select appropriate channel rehabilitation measures.

Iowa↗

USGS2005

Drought effects on water quality in the South Platte River Basin, Colorado

Twenty-three stream sites representing a range of forested, agricultural, and urban land uses were sampled in the South Platte River Basin of Colorado from July through September 2002 to characterize water quality during drought conditions. With a few exceptions, dissolved ammonia, Kjeldahl nitrogen, total phosphorus, and dissolved orthophosphate concentrations were similar to seasonal historical levels in all land use areas during the drought. At some agricultural sites, decreased dilution of irrigation return flow may have contributed to higher concentrations of some nutrient species, increased primary productivity, and higher dissolved oxygen concentrations. At some urban sites, decreased dilution of base flow and wastewater treatment plant effluent may have contributed to higher dissolved nitrite-plus-nitrate concentrations, increased primary productivity, and higher dissolved oxygen concentrations. Total pesticide concentrations in urban and agricultural areas were not consistently higher or lower during the drought. At most forested sites, decreased dilution of ground water-derived calcium bicarbonate type base flow likely led to elevated pH and specific-conductance values. Water temperatures at many of the forested sites also were higher, contributing to lower dissolved oxygen concentrations during the drought.

Journal of the American Water Resources Associatio↗

USGS2009

Estimating nitrogen loading to ground water and assessing vulnerability to nitrate contamination in a large karstic springs Basin, Florida

A nitrogen (N) mass-balance budget was developed to assess the sources of N affecting increasing ground-water nitrate concentrations in the 960-km 2 karstic Ichetucknee Springs basin. This budget included direct measurements of N species in rainfall, ground water, and spring waters, along with estimates of N loading from fertilizers, septic tanks, animal wastes, and the land application of treated municipal wastewater and residual solids. Based on a range of N leaching estimates, N loads to ground water ranged from 262,000 to 1.3 million kg/year; and were similar to N export from the basin in spring waters (266,000 kg/year) when 80-90% N losses were assumed. Fertilizers applied to cropland, lawns, and pine stands contributed about 51% of the estimated total annual N load to ground water in the basin. Other sources contributed the following percentages of total N load to ground water: animal wastes, 27%; septic tanks, 12%; atmospheric deposition, 8%; and the land application of treated wastewater and biosolids, 2%. Due to below normal rainfall (97.3 cm) during the 12-month rainfall collection period, N inputs from rainfall likely were about 30% lower than estimates for normal annual rainfall (136 cm). Low N-isotope values for six spring waters (??15N-NO3 = 3.3 to 6.3???) and elevated potassium concentrations in ground water and spring waters were consistent with the large N contribution from fertilizers. Given ground-water residence times on the order of decades for spring waters, possible sinks for excess N inputs to the basin include N storage in the unsaturated zone and parts of the aquifer with relatively sluggish ground-water movement and denitrification. A geographical-based model of spatial loading from fertilizers indicated that areas most vulnerable to nitrate contamination were located in closed depressions containing sinkholes and other dissolution features in the southern half of the basin. ?? 2009 American Water Resources Association.

Journal of the American Water Resources Associatio↗

USGS2011

Nutrient inputs to the Laurentian Great Lakes by source and watershed estimated using SPARROW watershed models

Nutrient input to the Laurentian Great Lakes continues to cause problems with eutrophication. To reduce the extent and severity of these problems, target nutrient loads were established and Total Maximum Daily Loads are being developed for many tributaries. Without detailed loading information it is difficult to determine if the targets are being met and how to prioritize rehabilitation efforts. To help address these issues, SPAtially Referenced Regressions On Watershed attributes (SPARROW) models were developed for estimating loads and sources of phosphorus (P) and nitrogen (N) from the United States (U.S.) portion of the Great Lakes, Upper Mississippi, Ohio, and Red River Basins. Results indicated that recent U.S. loadings to Lakes Michigan and Ontario are similar to those in the 1980s, whereas loadings to Lakes Superior, Huron, and Erie decreased. Highest loads were from tributaries with the largest watersheds, whereas highest yields were from areas with intense agriculture and large point sources of nutrients. Tributaries were ranked based on their relative loads and yields to each lake. Input from agricultural areas was a significant source of nutrients, contributing ∼33-44% of the P and ∼33-58% of the N, except for areas around Superior with little agriculture. Point sources were also significant, contributing ∼14-44% of the P and 13-34% of the N. Watersheds around Lake Erie contributed nutrients at the highest rate (similar to intensively farmed areas in the Midwest) because they have the largest nutrient inputs and highest delivery ratio.

Laurentian Great Lakes↗

USGS2015

Legacy effects of no-analogue disturbances alter plant community diversity and composition in semi-arid sagebrush steppe

Questions (i) What role does the type of managed disturbance play in structuring sagebrush steppe plant communities? (ii) How does the composition of post-disturbance plant communities change with time since disturbance? (iii) Does plant community diversity change over time following managed disturbance? Location Field study within the sagebrush steppe ecosystem. Rich County, Utah, USA. Methods We developed a chronosequence spanning up to 50 yrs post-treatment to study sagebrush steppe vegetation dynamics. Direct ordination was used to examine plant community composition by managed disturbance type and time since disturbance, and factorial analysis of covariance was used to examine diversity dynamics following disturbance. Indicator species values were calculated in order to identify characteristic species for each disturbance type. Results Plant communities experienced a shift toward distinct community composition for each of the three managed disturbance types, and gave no indication of returning to untreated community composition or diversity. Small post-disturbance increases in the number of non-native grass species were observed in the treatments relative to reference, with native forb species making the largest contribution to altered composition. On fire- and chemically-treated sites the proportional native forb species richness increased over time since disturbance, while the proportional contribution of non-native forbs to total species richness decreased. For all three treatment types, native grasses contributed less on average to total richness than on reference sites, while non-native grasses made up a higher proportion of total richness. Conclusions Common shrubland management techniques have legacy effects on the composition and diversity of sagebrush steppe plant communities, and no-analogue disturbances, such as chemical or mechanical treatments, have more pronounced legacy effects than treatments similar to natural disturbance regimes (fire). This study informs a broader understanding of how management actions affect natural systems by highlighting the importance of long-term management legacies as drivers of plant community structure and function.

Utah↗