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Most terrestrial allochthonous organic matter enters river networks through headwater streams during high flow events. In headwaters, allochthonous inputs are substantial and variable, but become less important in streams and rivers with larger watersheds. As allochthonous dissolved organic matter (DOM) moves downstream, the proportion of less aromatic organic matter with autochthonous characteristics increases. How environmental factors converge to control this transformation of DOM at a continental scale is less certain. We hypothesized that the amount of time water has spent travelling through surface waters of inland systems (streams, rivers, lakes, and reservoirs) is correlated to DOM composition. To test this hypothesis, we used established river network scaling relationships to predict relative river network flow‐weighted travel time (FWTT) of water for 60 stream and river sites across the contiguous United States (3090 discrete samples over 10 water years). We estimated lentic contribution to travel times with upstream in‐network lake and reservoir volume. DOM composition was quantified using ultraviolet and visible absorption and fluorescence spectroscopy. A combination of FWTT and lake and reservoir volume was the best overall predictor of DOM composition among models that also incorporated discharge, specific discharge, watershed area, and upstream channel length. DOM spectral slope ratio (R2 = 0.77) and Freshness Index (R2 = 0.78) increased and specific ultraviolet absorbance at 254 nm (R2 = 0.68) and Humification Index (R2 = 0.44) decreased across sites as a function of FWTT and upstream lake volume. This indicates autochthonous‐like DOM becomes continually more dominant in waters with greater FWTT. We assert that river FWTT can be used as a metric of the continuum of DOM composition from headwaters to rivers. The nature of the changes to DOM composition detected suggest this continuum is driven by a combination of photo‐oxidation, biological processes, hydrologically varying terrestrial subsidies, and aged groundwater inputs. [ABSTRACT FROM AUTHOR]

Lakes are often defined by seasonal cycles. The seasonal timing, or phenology, of many lake processes are changing in response to human activities. However, long‐term records exist for few lakes, and extrapolating patterns observed in these lakes to entire landscapes is exceedingly difficult using the limited number of available in situ observations. Limited landscape‐level observations mean we do not know how common shifts in lake phenology are at macroscales. Here, we use a new remote sensing data set, LimnoSat‐US, to analyze U.S. summer lake color phenology between 1984 and 2020 across more than 26,000 lakes. Our results show that summer lake color seasonality can be generalized into five distinct phenology groups that follow well‐known patterns of phytoplankton succession. The frequency with which lakes transition from one phenology group to another is tied to lake and landscape level characteristics. Lakes with high inflows and low variation in their seasonal surface area are generally more stable, while lakes in areas with high interannual variations in climate and catchment population density show less stability. Our results reveal previously unexamined spatiotemporal patterns in lake seasonality and demonstrate the utility of LimnoSat‐US, which, with over 22 million remote sensing observations of lakes, creates novel opportunities to examine changing lake ecosystems at a national scale. Plain Language Summary: Lakes have seasonal cycles that result in yearly peaks in algal growth. The size and timing of these peak periods depends on the amount of nutrients available and the timing of key events such as freezing and thawing. Bluer lakes with little algae typically have one peak in the spring, while greener, high algae lakes can have multiple peaks or longer duration peaks that span the summer months. The timing and duration of these peaks manifest in changes to overall lake color. Here, we look at how these seasonal cycles changed in over 26,000 lakes across the United States between 1984 and 2020. We show that seasonal cycles are changing with distinct regional patterns. Specifically, lakes are generally moving toward stable blue states in the Pacific Northwest, while high latitude lakes in the Northeast are increasingly showing seasonal cycles associated with high algae waterbodies. Lakes at high elevations and in catchments with large year‐to‐year fluctuations in temperature and population density are most prone to changes in seasonal cycles over time. Key Points: Summer lake color phenology can be generalized into five distinct seasonal patterns of greening and blueing eventsSince the mid‐1990s, the number of lakes with color patterns corresponding to eutrophic waterbodies has been increasingWe observe these patterns using a new U.S. lake remote sensing data set that contains over 22 million lake observations [ABSTRACT FROM AUTHOR]

Lake and reservoir surface areas are an important proxy for freshwater availability. Advancements in machine learning (ML) techniques and increased accessibility of remote sensing data products have enabled the analysis of waterbody surface area dynamics on broad spatial scales. However, interpreting the ML results remains a challenge. While ML provides important tools for identifying patterns, the resultant models do not include mechanisms. Thus, the "black-box" nature of ML techniques often lacks ecological meaning. Using ML, we characterized temporal patterns in lake and reservoir surface area change from 1984 to 2016 for 103,930 waterbodies in the contiguous United States. We then employed knowledge-guided machine learning (KGML) to classify all waterbodies into seven ecologically interpretable groups representing distinct patterns of surface area change over time. Many waterbodies were classified as having "no change" (43%), whereas the remaining 57% of waterbodies fell into other groups representing both linear and nonlinear patterns. This analysis demonstrates the potential of KGML not only for identifying ecologically relevant patterns of change across time but also for unraveling complex processes that underpin those changes.

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Abstract: While there are many local and regional sampling efforts in lakes across the U.S., it is often difficult to compile this information into a cohesive framework to make national‐ or continental‐scale conclusions. To address this gap, the U.S. Environmental Protection Agency partners with States and Tribes to implement the National Lakes Assessment, which is a national‐scale, coordinated lake sampling program. The resulting data include colocated biological, chemical, habitat, and human use measures that are available to the scientific community. We provide a brief overview of the program, describe the data, and discuss some of the ways the results have been used. The availability of a consistent data set of this magnitude is an impressive and unique resource for the limnological community. [ABSTRACT FROM AUTHOR]

At the Large Lakes Observatory at the University of Minnesota Duluth (UMD), we are addressing issues with an outdated limnology graduate curriclum by designing a flipped-classroom, interdisciplinary limnology course sequence that incorporates partnerships with industry, meaningful field and analytical work, and integrated skills learning for our graduate students. This new curriculum is co-taught by four instructors with different research backgrounds and is meant to teach students with a wide range of undergraduate preparation without significant time spent on in-class review, or leaving anyone behind. The courses, which include lecture and practice classes each semester in the graduate students' first year, are built around a course website, , which will go public in fall of 2018. Funded by the National Science Foundation Division of Graduate Education, this pilot program will provide a new interdisciplinary curriculum applicable to graduate limnology programs and a public website with limnology modules designed to be searchable and open to the public. Here, we describe in detail our new course sequence, including curriculum, industry partnerships, and field work with the students; provide information on the challenges we faced in developing and teaching this course; and our advice for overcoming those challenges. [ABSTRACT FROM AUTHOR]

The article offers information on the aspects of limnology in the U.S. from 1930 to 1990, focusing on the works by ecologist George Evelyn Hutchinson and University of Wisconsin-Madison limnology head Arthur Davis Hasler. It offers brief profiles of Hutchinson and Hasler including their education, career in limnology, and their research in ecology topics. Other topics include their graduate students and the American Society of Limnology and Oceanography.

Lake water quality is affected by local and regional drivers, including lake physical characteristics, hydrology, landscape position, land cover, land use, geology, and climate. Here, we demonstrate the utility of hypothesis testing within the landscape limnology framework using a random forest algorithm on a national-scale, spatially explicit data set, the United States Environmental Protection Agency's 2007 National Lakes Assessment. For 1026 lakes, we tested the relative importance of water quality drivers across spatial scales, the importance of hydrologic connectivity in mediating water quality drivers, and how the importance of both spatial scale and connectivity differ across response variables for five important in-lake water quality metrics (total phosphorus, total nitrogen, dissolved organic carbon, turbidity, and conductivity). By modeling the effect of water quality predictors at different spatial scales, we found that lake-specific characteristics (e.g., depth, sediment area-tovolume ratio) were important for explaining water quality (54-60% variance explained), and that regionalization schemes were much less effective than lake specific metrics (28-39% variance explained). Basin-scale land use and land cover explained between 45-62% of variance, and forest cover and agricultural land uses were among the most important basin-scale predictors. Water quality drivers did not operate independently; in some cases, hydrologic connectivity (the presence of upstream surface water features) mediated the effect of regional-scale drivers. For example, for water quality in lakes with upstream lakes, regional classification schemes were much less effective predictors than lake-specific variables, in contrast to lakes with no upstream lakes or with no surface inflows. At the scale of the continental United States, conductivity was explained by drivers operating at larger spatial scales than for other water quality responses. The current regulatory practice of using regionalization schemes to guide water quality criteria could be improved by consideration of lake-specific characteristics, which were the most important predictors of water quality at the scale of the continental United States. The spatial extent and high quality of contextual data available for this analysis makes this work an unprecedented application of landscape limnology theory to water quality data. Further, the demonstrated importance of lake morphology over other controls on water quality is relevant to both aquatic scientists and managers. [ABSTRACT FROM AUTHOR]

Quantifying lake biogeochemical processing at broad spatial scales requires that we scale processes along with physical metrics. Past work has primarily scaled lentic processes using estimates of lake surface area. However, many processes important to lakes, such as material, energy and biological fluxes and biogeochemical cycling, scale with lake perimeter., We estimate the total lake perimeter for the contiguous United States (U.S.) and examine the sensitivity of this estimate to measurement resolution. At the original mapping resolution, lakes in the contiguous U.S. have a total perimeter of over 1.8 million km., The change in measured perimeter versus measurement resolution for the contiguous U.S. had a log-log slope (also known as the fractal dimension) of −0.21, generally less than previously reported estimates. With changing observation resolution, total measured perimeter was most sensitive to the inclusion or exclusion of small lakes, not shoreline complexity., The total aquatic-terrestrial interface in lakes is less than one-tenth that of streams and rivers, which collectively account for over 21 million km of shoreline in the contiguous U.S. This study further describes the distribution of lake perimeter and proposes a technique that can contribute to understanding continental-scale processes. [ABSTRACT FROM AUTHOR]

Abstract: Between 1997 and 2002, 16 cases of acute childhood leukemia were diagnosed in children who either lived in Churchill County, Nevada at the time of diagnosis or had lived in the county before their diagnosis. The cases were characterized as a cluster of like illnesses and the probability of having such a cluster occur by chance was estimated to be very small (approximately one in 2.33×108). This suggested that the cluster could be linked to one or more physical, limnological, chemical, or biological agents. This review discusses the setting in which the cluster took place, the epidemiological investigations carried out by the Nevada Bureau of Health Protection Services, the National Center for Environmental Health Centers for Disease Control and Prevention and the Agency for Toxic Substances and Disease Registry, and subsequent investigations supported by a special allocation of federal funds through the US Environmental Protection Agency’s Region IX office in San Francisco, CA. This review is meant as background for the papers in this special issue that report results from multi- and interdisciplinary research into environmental and biological factors potentially related to the Churchill County leukemia cluster. [Copyright &y& Elsevier]

Abstract: Branched and isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs) are abundant in lake sediments and have potential use for determining past changes in climate and limnology. However, emerging evidence suggests that both classes of GDGTs can be associated with both allochthonous soil organic matter and in situ production, potentially complicating interpretation of these compounds in lacustrine sedimentary environments. Here, we investigate the “dual source” issue surrounding lacustrine GDGTs – with an emphasis on the branched GDGTs – by studying both core and intact polar GDGTs within a pond and its watershed in Warwick, RI. Significant differences in both absolute concentrations of branched GDGTs and the percent of branched GDGTs present as IPLs between the soils and shallow lake sediments suggests in situ production of these compounds within the lake environment. Principal components analysis of GDGT lipid concentrations and environmental parameters in Sand Pond sediments and soils highlights two prominent trends in the data, one related to the absolute concentrations of “type I” branched GDGTs (brGDGT-I, Ib, Ic) and the majority of the isoprenoidal GDGTs, and another related to the concentration of the more methylated “type III” branched GDGTs (brGDGT-III, IIIb, IIIc) and isoprenoidal GDGT-0. The latter trend exhibits a subsurface maximum in the sediment column, potentially indicating in situ production of more highly methylated branched GDGTs and GDGT-0 within the lacustrine sediment column. Trends in the distributions of branched GDGTs (as reflected by the MBT and CBT indices) imply mixing of two distinct sources of branched GDGTs (soil-derived and in situ), or alternatively, two or more different microbial producers. Both possibilities present a challenge to the application of brGDGT-based paleoenvironmental proxies in lakes. This study highlights the importance of determining the sources of GDGTs to the lacustrine environment prior to paleoenvironmental application. [Copyright &y& Elsevier]

The Beasley Lake watershed (BLW), established for the Mississippi Delta Management Systems Evaluation Area project, represents the US Mississippi Delta region in the national Conservation Effects Assessment Project. The 915-ha (2,260-ac) BLW drains into an oxbow lake that has been monitored since 1995 when row crops were grown on 79% of the area, and the remaining area included a 25-ha (62-ac) lake and a 135-ha (330-ac) riparian forest. Currently, row crops account for 66.5% of the area with 12.4% enrolled in the Conservation Reserve Program. Cotton (Gossypium hirsutum L.) acreage has decreased from 63.3% to 8.9%. Historical and current research in BLW focuses on monitoring lake limnology, evaluating conservation practice effects on edge-of-field runoff, quantifying changes associated with the Conservation Reserve Program, and modeling watershed responses. Applying combinations of conservation practices can significantly reduce nonpoint source pollution. For example, converting row crops to reduced tillage and transgenic herbicide-resistant crops in BLW reduced suspended sediment (70% reduction), total phosphorus (41% reduction), and pesticide concentrations in lake water. Corresponding increases in Secchi visibility (97%) and chlorophyll a (a primary productivity indicator) likely contributed to improved fish productivity (e.g., fish weight increase comparing 1998 and 2004: Micropterus salinoides 87%, Lepomis macrochirus, 65%) during this period. Additional studies should quantify effects of individual practices and improve modeling tools for making better management decisions. The utilization of the Annualized Agricultural Non-Point Source (AnnAGNPS) model and the Riparian Ecosystem Management Model (REMM) together provides additional information on the effectiveness of conservation practices within the watershed by combining technology that assesses riparian buffer effectiveness in filtering nutrients at the field scale with the watershed water quality transport capabilities of the AnnAGNPS model. [ABSTRACT FROM AUTHOR]

A eutrophication model developed to generate primary-production estimates in Lake Michigan can simulate 17 state variables, including three plankton classes and several nutrients. The model, known as the Lake Michigan Eutrophication model (LM3-Eutro), has a high-resolution computational grid that enables good spatial description of spring temperature and phytoplankton concentrations, which have significant gradients in the lakes. The grid also allows the model to predict concentrations in nearshore areas and other regions of interest. The model provided more accurate estimates of algal light limitation based on three-hour intervals compared to daily averages that are used in most eutrophication models, especially during sunny summer days when algal photo-inhibition often occurs. Model output was compared to field data using statistical parameters such as squares of the correlation coefficients to determine the best model fit. The calibrated model output fit the field data reasonably well for nutrients and phytoplankton, which provided confidence in the framework, governing equations, and coefficients used. [ABSTRACT FROM AUTHOR]

The relationships between diatom assemblages and important limnological variables were investigated in 494 lakes from northeastern North America (Pennsylvania, USA, to Nova Scotia, Canada). The limnological variable most significantly related to diatom assemblages was lake water pH, although dissolved organic carbon and nutrients were also important. Based on these strong relationships, highly significant diatom-based inference models were developed to reconstruct key limnological variables based on diatom assemblages using weighted averaging (WA), maximum likelihood (ML), and modern analogs technique (MAT). The performances of the pH-inference models were high, similar, and significant (WA: r2boot = 0.89, root mean squared error of prediction (RMSEP) = 0.43; ML: r2boot = 0.89, RMSEP = 0.45; MAT: r2boot = 0.89, RMSEP = 0.46). In addition, distribution of sites along a pH gradient did not have the anticipated bias, especially with respect to the WA model, although an evenly distributed study set did result in slightly less noise. While some regionally specific information may be lost by utilizing a large number of lakes from a wide geographic area, the broad limnological gradients allow a more realistic, accurate, and complete description of the ecological characteristics of diatom species. In addition to providing new autecological data on diatoms for northeastern North America, these inference models can now be used to infer accurately and precisely lake water pH and associated variables for limnologists and lake managers. [ABSTRACT FROM AUTHOR]

Sediment magnetic properties of a short core from Sharkey Lake, MN, record the effects of Euroamerican settlement and climate change over the last 150 yr. The onset of European-style farming led to increased erosion, reflected in high values of concentration-dependent parameters such as magnetic susceptibility (κ), Isothermal Remanent Magnetization (IRM), and Anhysteretic Remanent Magnetization (ARM). These high values are only partially due to increased supply of terrigenous material to the lake, and recent sediment contains an additional component of authigenic fine (single-domain) magnetite, most likely magnetosomes from magnetotactic bacteria. High organic productivity in the lake during the 1920s to 1940s drought increased this authigenic component resulting in highly magnetic fine-grained sediment. A comparison with older Holocene sediment from the same lake shows that, over time, most of the fine magnetic signal is lost after deposition, leading to decreases in magnetization and a bimodal grain size distribution of ultrafine, superparamagnetic grains and coarser multidomain particles, evident from measurements of ARM/IRM ratios, hysteresis measurements, and low-temperature analyses. The effects of dissolution and the superposition of climate and land-use signals complicate the use of recent sediments as modern analogs for sediment magnetic analyses. [Copyright &y& Elsevier]

Presents a study which compared phytoplankton and periphyton productivity along a eutrophication gradient in Greenland, U.S. and Danish lakes. Background of studies on eutrophication; Methods used; Results; Discussion.

Reports on a long-term study in January 1997 to investigate various aspects of the physics, chemistry and biology of the Salton Sea in California. Description of the mixing, thermal and dissolved oxygen regimes along with climatic data for the period 1997 to 1999; Effects of the physical and chemical behavior of the system on the plankton, benthos, fish and aquatic birds of the Sea.

Analyzes the limnological factors controlling the growth of the brine shrimp Artemia franciscana and cyst production over 12 months in 1994 and 1995 in the Great Salt Lake of Utah. Dependence of inter-brood intervals on temperature and on food level; Limited production of ovoviviparous eggs during the summer; Control of Artemia densities by algal production in the lake.

Evaluates the feasibility of using hypolimnetic oxygenation in Walker Lake, Nevada. Use of experimental chambers to examine if maintenance of an oxygenated sediment-water interface would inhibit accumulation of ammonia and sulfide in water overlaying sediments; Monitoring of ammonia profiles in 1998 to compare the accumulation rate of ammonia with experimental results.

Examines the effects of dessication on the limnology of Walker Lake in western Nevada. Extinction of two zooplankton species; Decrease in the lake's volume and increase in salinity as a result of anthropogenic dessication between 1882 and 1996; Factors that have caused trout populations to be stressed out.

Examines the long-term solutions to accelerated eutrophication on the Eastern Shore of Maryland, and the view that they must provide mechanisms for redistributing nutrients flowing into concentrated animal-producing regions. Initial strategy; Questions which have been raised by Pfiesteria outbreaks; Phosphorus transport in agricultural drainage and on the Eastern Shore.

Focuses on the study of the limnological conditions in Mono Lake, California. Level of temperature; Absence of holomixis during winter; Availability of nitrogen.

Focuses on the study of limnology by various scientists in the U.S. Awareness on the physical, chemical, biological, and metereological conditions in various lakes; Origin of the lake basins; Causes of water contamination.

Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high-N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world's lakes, even in lakes far from direct human disturbance. [ABSTRACT FROM AUTHOR]

The article focuses on the research works in limnology and its role in preserving freshwater biology in the U.S. It describes that experimental limnology includes study on fundamental concepts of aquatic environment and communities, and various factors that influence its environmental biology. It states that earlier research works in limnology used small lakes as experimental models and presents the results of a study on Cather Lake and Lake Peter in Wisconsin. It mentions about the studies that aimed at population dynamics in the lakes and its effects on the ecology. Several other topics focused in experimental limnology include effects of ion transport, plankton migration, and aggregation of fishes.

Remote sensing of ice phenology for small lakes is hindered by a lack of satellite observations with both high temporal and spatial resolutions. By merging multi-source satellite data over individual lakes, we present a new algorithm that successfully estimates ice freeze and thaw timing for lakes with surface areas as small as 0.13 km2 and obtains consistent results across a range of lake sizes. We have developed an approach for classifying ice pixels based on the red reflectance band of Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, with a threshold calibrated against ice fraction from Landsat Fmask over each lake. Using a filter derived from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) surface air temperature product, we removed outliers in the time series of lake ice fraction. The time series of lake ice fraction was then applied to identify lake ice breakup and freezeup dates. Validation results from over 296 lakes in Maine indicate that the satellite-based lake ice timing detection algorithm perform well, with mean absolute error (MAE) of 5.54 days for breakup dates and 7.31 days for freezeup dates. This algorithm can be applied to lakes worldwide, including the nearly two million lakes with surface area between 0.1 and 1 km2. [ABSTRACT FROM AUTHOR]

1. We tested the degree to which a lake's landscape position constrains the expression of limnological features and imposes a characteristic spatial pattern in a glacial lake district, the Northern Highland Lake District in north-central Wisconsin. 2. We defined lake order as a metric to analyze the effect of landscape position on limnological features. Lake order, analogous to stream order, is based solely on geographical information and is simple to measure. 3. We examined the strength of the relationship between lake order and a set of 25 variables, which included measures of lake morphometry, water optical properties, major ions, nutrients, biology, and human settlement patterns. 4. Lake order explained a significant fraction of the variance of 21 of the 25 variables tested with ANOVA. The fraction of variance explained varied from 12% (maximum depth) to 56% (calcium concentration). The variables most strongly related to lake order were: measures of lake size and shape, concentrations of major ions (except sulfate) and silica, biological variables (chlorophyll concentration, crayfish abundance, and fish species richness), and human-use variables (density of cottages and resorts). Lake depth, water optical properties, and nutrient concentrations (other than silica) were poorly associated with lake order. 5. Potential explanations for a relationship with lake order differed among variables. In some cases, we could hypothesize a direct link. For example, major ion concentration is a function of groundwater input, which is directly related to lake order. We see these as a direct influence of the geomorphic template left by the retreat of the glacier that led to the formation of this lake district. 6. In other cases, a set of indirect links was hypothesized. For example, the effect of lake order on lake size, water chemistry, and lake connectivity may ultimately explain the relation between lake order and fish species richness. We interpret these relationships as the result of constraints imposed by the geomorphic template on lake development over the last 12 000 years. 7. By identifying relationships between lake characteristics and a measure of landscape position, and by identifying geomorphologic constraints on lake features and lake evolution, our analysis explains an important aspect of the spatial organization of a lake district. [ABSTRACT FROM AUTHOR]

We studied the annual distributions of dissolved oxygen, temperature, and four aquatic vertebrates in two relatively young ponds (Road Pond and Strip Mine Pond) formed by strip mining operations in Alabama.On the basis of the limnological data, Road Pond was classified as warm polymictic and Strip Mine Pond as warm monomictic. In Strip Mine Pond, the summertime distribution of fish (bluegills, Lepomis macrochirus) was clearly related to oxygen availability, with fish avoiding severely hypoxic or anoxic water found at depths >2 m. However, bullfrog tadpoles commonly occurred in water at depths =/> 2 m, where the PO2 was at or below their critical O2 tension. Tadpoles occurring at these depths switched from facultative air-breathing to obligate air-breathing and may have been using these depths as a refugium. In Road Pond, fishes (fathead minnows, Pimephales promelas, and golden shiners, Notemigonus crysoleucas) congregated duringsummertime in shallower waters. Bullfrog (Rana catesbeiana) tadpolespreferred the deeper portions of Road Pond. The contrasting distributions of tadpoles in the two ponds are potentially explainable on thebasis of predation pressure. [ABSTRACT FROM AUTHOR]

We analyzed inter-annual patterns in first-year abundance of 11 fishspecies in Oneida Lake, New York, USA, using trawl data collected from 1961 to 1997. We found two major recruitment patterns among the 11species. One group (yellow perch, walleye, logperch and tessellated darter) decreased in abundance after the mid-1980s. These species arespring or early summer spawners with benthic juveniles. In the second group, most species increased during the early to mid 1980s (smallmouth bass, trout-perch, white bass, gizzard shad and freshwater drum), while two recruited episodically (white perch and pumpkinseed). These species spawned later than the first group and juvenile habitat use was variable. We investigated three specific mechanisms which couldexplain these patterns (1) competition with young-of-year (YOY) yellow perch, the dominant fish species in the lake, (2) buffering of predation by walleye by YOY yellow perch, and (3) correlation with watertemperature and productivity (indexed through total phosphorus levels, TP). Buffering from predation by walleye was likely important for the species in the first group, as indicated by positive correlationsbetween inter-annual abundance patterns of the four species. Even though species in the second group tended to increase as YOY yellow perch declined, we found little support for the competition hypothesis. Growth and abundance of these species were not significantly correlated with abundance of YOY yellow perch. Temperature was positively correlated with growth of 10 of the 11 species. Decreasing TP levels andassociated changes in the lake could be causing a shift in the fish community, but the mechanism is not decreased food production. Pelagic zooplankton abundance, a direct link from nutrients to YOY fish production, has not declined since 1975. [ABSTRACT FROM AUTHOR]

Experiments were performed to determine the range and optima of environmental conditions under which indigenous species of Alaskan Porphyra can grow. Growth of the conchocelis phase of Porphyra abbottae, P.torta and P. pseudolinearis was measured, when cultured in enriched media, under long days (16 h light) and varying conditions of irradiance (20, 40, 80 and 160 Mumol photons m-2 s-1),temperature (7, 11, 15 and 19 deg. C) and salinity (5, 10, 20, 30 and 40). Optimal growth (7.6% increase in volume day-1) ofP. abbottae occurred at 11 deg. C, 80 Mumol photons m-2 s-1 and 30. Porphyra torta grew best (6.5% day-1) at 15 deg. C, 80 Mumol photons m-2 s-1 and 30. Porphyra pseudolinearis generally had higher growth rates than the other two species with optimal growth (8.8% day-1) occurring at 7 deg. C, 160 Mumol photons m-2 s-1 and 30. For all three species salinity between 20 and 40 had little effect on growth, but there was virtually no growth at salinity of 10 and below. Irradiances between 20 and 160 Mumol photons m-2 s-1 generally had little effect on growth rates. However, growth of P. abbottae increased with irradiance at 7 deg. C but was inhibited at irradiances over 40 Mumol photons m-2 s-1 at 15 deg. C and higher. Porphyra torta also showed growth inhibition at 15 deg. C and higher irradiances. Porphyra pseudolinearis appeared to be the most robust species with respect to tolerance to extremes of salinity and irradiance. [ABSTRACT FROM AUTHOR]

Attached algae were examined from eight sites in Central Colorado streams (five sites on St. Vrain Creek and three on the Snake River) between June and November, 1995. The sites ranged in elevation from 1600 m to 3500 m a.s.l.(plains zone to alpine zone). Seasonal variation in algal communities were qualified in forms of species composition and abundance (cell counts and biovolumes). The Ochiai coefficient of similarity was used to estimate degree of similarity between communities at different times, on different streams, and at different locations on the same stream. The composition of communities across streamsfor alpine and foothills zones was very close, but montane communities differed greatly across streams (similarity < 0.1). Temporal variability of attached algae was almost absent in the alpine zone, but was high in other zones. The composition of the alpine community in August developed downstream with a temporal shift: October in the montane and foothills zones, November in the plains zone. [ABSTRACT FROM AUTHOR]

A seasonal study of two spring-fed stream systems in south-central Texas was undertaken over a 15-month period from June 1996 to September 1997. Relative abundance of the epilithic diatom flora, percent cover of macroalgae, and several physical and chemical conditions were monitored in one 20-m stretch in each of the streams at approximately two-month intervals. Six additional spring-fed stream segments were sampled in May 1996 for macroalgae and measured for the same conditions, in order to determine how representative the macroalgal floras of the study sites were of south-central and western Texas. Conditions in the two stream segments were relatively constant over the 15 months, except for maximum depth; this finding is similar those reported for other spring-fed systems worldwide. Sixty-eight diatom taxa and nine macroalgae taxa were identified from the San Marcos River, which compares to 46 diatom taxa and six macroalgae taxa from the Comal River. Several diatom and macroalgae species were significantly correlatedto stream conditions (e.g. Dichotomosiphon tuberosus and Hildenbrandia angolensis with daylength, and Amphora pediculus with maximum depth). Twenty-one macroalgal taxa were identified from the six additional spring-fed steam segments. Conditions in these streams were very similar to those measured in the San Marcos River and Comal River, except that they had a higher average pH ([?x] = 8.1 versus [?x] = 7.6). The epilithic diatom flora of the San Marcos River and the Comal River contains many of the diatom and some macroalgal taxa commonly reported from springs globally. [ABSTRACT FROM AUTHOR]