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We assessed how diatom metrics were related to different ranges of agricultural land use. Diatom assemblage composition, nutrients, and landscape characteristics were determined at 232 sites in eight agriculturally dominated study areas of the continental United States. Two regional groups based on differences in diatom relations to human disturbance were determined. Changes in diatom species composition were related to nutrients, pH, and conductivity in the eastern study areas (due to more wetlands) and more exclusively to nutrients in the west-central study areas. Homogenization of diatom flora among streams was related to high agricultural disturbance at this transcontinental scale. Species traits were developed separately for the east and west-central study groups and calculated two ways: indicator species analysis for taxa in low and high TN or TP conditions and weighted average partial least squares models of TN and TP concentration. These diatom metrics were significantly related to many indicators of agricultural land use in watersheds, especially percent row crops. Further analysis was conducted on only the west-central region due to its larger sample size. Overall, diatom metrics using species responses to N gradients were better related to agricultural land use than were species responses to P gradients. Most nutrient-based diatom metrics changed greatly in response to low ranges of percent row crops, but only a few high N diatom metrics responded to high row crop conditions. The greater response of diatoms to changes in low agriculture conditions may be due to past diatom evolution occurring when most waters had low nutrient conditions.

Site grouping by regions or typologies, site-specific modeling and varying metrics among site groups are four approaches that account for natural variation, which can be a major source of error in ecological assessments. Using a data set from the 2007 National Lakes Assessment project of the USEPA, we compared performances of multimetric indices (MMI) of biological condition that were developed: (1) with different lake grouping methods, ecoregions or diatom typologies; (2) by varying or not varying metrics among site groups; and (3) with different statistical techniques for modeling diatom metric values expected for minimally disturbed condition for each lake. Hierarchical modeling of MMIs, i.e. grouping sites by ecoregions or typologies and then modeling natural variability in metrics among lakes within groups, substantially improved MMI performance compared to using either ecoregions or site-specific modeling alone. Compared with MMIs based on ecoregion site groups, MMI precision and sensitivity to human disturbance were better when sites were grouped by diatom typologies and assessing performance nationwide. However, when MMI performance was evaluated at site group levels, as some government agencies often do, there was little difference in MMI performance between the two site grouping methods. Low numbers of reference and highly impacted sites in some typology groups likely limited MMI performance at the group level of analysis. Varying metrics among site groups did not improve MMI performance. Random forest models for site-specific expected metric values performed better than classification and regression tree and multiple linear regression, except when numbers of reference sites were small in site groups. Then classification and regression tree models were most precise. Based on our results, we recommend hierarchical modeling in future large scale lake assessments where lakes are grouped by ecoregions or diatom typologies and site-specific metric models are used to establish expected metric values., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Regional variation in both natural environment and human disturbance can influence performance of ecological assessments. In this study we calculated 5 types of benthic diatom multimetric indices (MMIs) with 3 different approaches to account for variation in ecological assessments. We used: site groups defined by ecoregions or diatom typologies; the same or different sets of metrics among site groups; and unmodeled or modeled MMIs, where models accounted for natural variation in metrics within site groups by calculating an expected reference condition for each metric and each site. We used data from the USEPA's National Rivers and Streams Assessment to calculate the MMIs and evaluate changes in MMI performance. MMI performance was evaluated with indices of precision, bias, responsiveness, sensitivity and relevancy which were respectively measured as MMI variation among reference sites, effects of natural variables on MMIs, difference between MMIs at reference and highly disturbed sites, percent of highly disturbed sites properly classified, and relation of MMIs to human disturbance and stressors. All 5 types of MMIs showed considerable discrimination ability. Using different metrics among ecoregions sometimes reduced precision, but it consistently increased responsiveness, sensitivity, and relevancy. Site specific metric modeling reduced bias and increased responsiveness. Combined use of different metrics among site groups and site specific modeling significantly improved MMI performance irrespective of site grouping approach. Compared to ecoregion site classification, grouping sites based on diatom typologies improved precision, but did not improve overall performance of MMIs if we accounted for natural variation in metrics with site specific models. We conclude that using different metrics among ecoregions and site specific metric modeling improve MMI performance, particularly when used together. Applications of these MMI approaches in ecological assessments introduced a tradeoff with assessment consistency when metrics differed across site groups, but they justified the convenient and consistent use of ecoregions., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Diatom-based stream bioassessment is constantly being improved to meet the increasing demands of water quality management. This study examined whether percentage of live diatoms (PLD) in periphyton communities can be used as a metric of human disturbance in streams and rivers. The analyzed dataset (587 sites) was collected over the course of 3 years (2000-2002) from 12 Western US states (US EPA's Environmental Monitoring and Assessment Program). The mean PLD in Western streams and rivers was low (34.50%) and highly variable (range 2.08-97.02%). It did not differ significantly between the Mountains (MT, 36.38%) and the Xeric (XE, 35.49%) ecoregions, but it was significantly ( P < 0.05) greater than that in the Plains ecoregion (PL, 28.27%). PLD distinguished reference from impacted sites in the MT ( P < 0.05) and somewhat in the PL ( P = 0.05). However, PLD exhibited opposite patterns in the two ecoregions. It increased with human disturbance in the MT and decreased in the PL due to a potential subsidy-stress gradient of available resources. The different pattern may be largely interpreted by the quality of the reference conditions in each ecoregion. In the MT ecoregion, the selected reference sites may resemble very closely the natural state in this ecoregion. In contrast, human disturbance is much more pervasive in the low-land PL ecoregion and the 'reference sites' may reflect the best attainable conditions in this ecoregion. PLD as a metric has potential for monitoring human disturbance of streams, if reference sites represent natural conditions and differing responses among regions are included in expected effects. [ABSTRACT FROM AUTHOR]

The objective of this study was to measure the photo-acclimation response of stream algae inhabiting thin biofilms across a range of light treatments comparing both growth rates and net primary productivity (NPP). Algae were grown on clay tiles incubated in artificial stream channels where light levels were manipulated by layering a neutral-density shade cloth over each channel. We measured NPP and algal growth rates in the early stages of community development and compared assemblages that were either acclimated or unacclimated to a given light treatment. Algal growth rates did acclimate to light treatment, with saturation occurring at light levels that were substantially lower for the acclimated communities. Growth efficiency calculated from algal biovolume increased by a factor of 3. However, algal NPP showed a weaker photo-acclimation response, with only a 30% increase in photosynthetic efficiency. Our results indicate that diatom-dominated periphyton in thin biofilms are probably not light limited in many shaded streams with respect to growth rates, but are light limited with respect to NPP. [ABSTRACT FROM AUTHOR]

Diatom indicators of wetland condition were developed and tested by assessing human disturbance, water chemistry, and species composition of benthic, epiphytic, and planktonic diatoms from 20 wetlands sampled for 2 years. One sample from each site was randomly selected to form a development data set, while the rest were used as the test data set. Human disturbance indicated substantial differences among wetlands in hydrologic modification, impervious surface, and potential for non-point source contamination. These landscape alterations were related to increases in pH, non-nutrient ions, and nutrients and decreases in dissolved organic carbon and water color. Pre-existing diatom indicators, calculated with autecological information from lakes and aquatic habitats, correlated highly to relevant water chemistry and human disturbance scores. Weighted average models (WAM) of Cl−, conductivity, pH, and alkalinity derived with the Maine development data set correlated to relevant water chemistry and human disturbance of the test wetlands. Diatom assemblage attributes that correlated with human disturbance were selected to combine into a multimetric index of biotic condition (IBC). IBCs and WAMs from benthic and epiphytic diatoms were usually more precisely related to relevant environmental factors than planktonic diatoms. These results showed that human disturbance alkalized wetlands, enriched them with nutrients, and diatom assemblages responded to these changes. Indicator development protocols for streams can be readily adapted for use in wetlands. [ABSTRACT FROM AUTHOR]

To assess attributes of algal assemblages as indicators of salt marsh restoration, we chose eight pairs of salt marshes in North Carolina, USA, each pair with one restored marsh (from 1 to 28 years old) and a nearby existing salt marsh. Algae on both Spartina alterniflora and sediments (sediment algae) were collected in each marsh during spring and summer 1998 for assaying algal biomass (dry mass (DM), ash free dry mass (AFDM), chl a content, algal biovolume), algal species composition and diversity, and gross primary production. An attribute restoration ratio was calculated by dividing attribute values from each restored marsh by values from a paired reference marsh. Controlling for regional variation in reference marshes substantially increased precision in relations between attributes and the increase in age of restored marshes. The organic matter restoration ratio of sediments increased with age of restored marshes in both spring and summer. The algal biomass restoration ratios of epiphytes, calculated with algal biovolume and chl a, increased with restored marsh age in summer but not during spring. Biomass of sediment algae was not related to marsh age. The species diversity of sediment algae in summer showed an asymptotic relationship with sediment nutrient concentration. The similarity of diatom species composition between paired restored and reference sites increased with age of restored marshes during spring and summer. Primary production by epiphytic and sediment algae in summer showed site-specific changes and did not change consistently with marsh age. Algal biomass, algal diversity, and diatom species composition during summer were positively correlated with sediment nitrogen and phosphorus concentration. We concluded that other structural and functional development of restored wetlands, especially nutrient storage in sediments, regulates algal species composition and algal biomass accumulation, which can be used to evaluate salt marsh ... [ABSTRACT FROM AUTHOR]

Summary1. We wanted to determine if changes in algae in the Everglades were due to increased phosphorus (P) loading. Epiphytic algae, water chemistry, and surface sediment chemistry were characterized from 32 sloughs along a P gradient in the Everglades and changes in the algal assemblages along the P gradient were compared with those along an experimental P gradient of in situ mesocosms. The sloughs are the wettest open water habitats characterized by floating and submerged aquatic plants in the Everglades. 2. Algal species composition was much more sensitive to P concentration than algal biomass. The diatom species variance among sloughs, captured by 1st ordination axis, was more highly correlated with total P (TP) in surface sediments (r = - 0.79), than soluble reactive P (SRP) (r = - 0.08) and TP (r = - 0.48) in the water column. Algal biomass (µg chl a cm-2) was not significantly correlated with P (SRP: r = 0.22, TP: r = 0.19, sediment TP: r = 0.07) along the P gradient in the Everglades. Cluster analysis classified diatom species assemblages in 32 sloughs into three groups (TWIN I, II, III), which corresponded to three zones along the P gradient. Dominant diatom species shifted from Mastogloia smithii (40.3%), Cymbella scotica (22.3%), and Fragilaria synegrotesca (21.8%) in TWIN I to Nitzschia amphibia (22.4%) and C. microcephala (12.4%) in TWIN III. TP in surface sediments and TP in epiphyton assemblages increased 4- and 5-fold from TWIN I to TWIN III, respectively. 3. Patterns in epiphytic assemblages along the experimental P gradient in the mesocosms were very similar to those along the Everglades P gradient. Shannon diversity indices and species richness significantly increased along both P gradients. TN: TP ratio in epiphyton assemblages significantly decreased as sediment TP increased along both P gradient. Ordination analysis showed that diatom assemblages in the impacted zone (TWIN III) were ordinated closely to the assemblages from the highest P treatments in the mesocosms. The assemblages from the less impacted zone (TWIN I) were ordinated closely to the assemblages from controls in the mesocosms. 4. Concurrence between results of our survey and experiments suggest that changes in epiphytic assemblages along the P gradient in the Everglades are caused by increases in P concentrations. [ABSTRACT FROM AUTHOR]

Diatom and water chemistry data from 35 wetland sites in western Kentucky were used to assess diatoms as indicators of ecological conditions in wetlands. The wetlands were affected by different degrees of acid mine drainage and agriculture. Canonical correspondence analysis indicated that the distribution of diatoms was highly correlated with conductivity and total phosphorus (TP), two variables commonly associated with acidic mine drainage and agriculture, respectively. Diatom-based inference models were developed for use as quantitative indicators of two important environ mental variables in wetlands: conductivity and TP. Diatom-inferred conductivity and TP values were highly correlated with measured values. Cross-valuation with jackknifing procedures suggested that high apparent r[SUP2] between inferred and measured conductivity was overly optimistic and should be treated with caution. Jackknifing-derived TP inference models performed poorly in predicting TP towards the ends of low and high TP concentrations. In general, the conductivity inference models based on plankton had better predictability than those based on epiphyton. Epiphyton-based inference models can predict TP better than plankton. Therefore, diatoms in planktonic and epiphytic assemblages could provide complementary information on ecological conditions. Our data suggest that diatoms can reflect major regional environmental gradients and therefore can be used as indicators of the ecological conditions in wetlands. Quantitative inference models with known predictive power can aid the development of realistic and ecologically sound biotic indices for this region. [ABSTRACT FROM AUTHOR]

The importance of immigration, growth, and competition for nutrients and light in benthic diatiom succession was studied in experimental channels in a low-nutrient stream. Diatom accumulation was greater in channels enriched with nitrate and phosphate (NP) than in control channels, reaching about 5 × 10[sup6] And 2 × 10[sup6] Cells · cm[sup2] respectively, after 30 d. Shading during late stages of community development reduced algal standing crop. Synedra ulna (Nitz,) Her. And Achnanthes minutissima kütz were codominant during early stages of community development in both habitats, but succession of an a. minutissima-dominated community was much faster in NP-enriched than in control conditions. Species dominating early stages tended to immigrate quickly whereas species that increased in relative abundance during community development had either fast growth rates of fast immigration and average growth rates. Decreases in growth rates indicated resource supply became limiting during community development in control and enriched channels. Density-dependent competition was indicated because nutrient concentrations in the water column and light did not decrease during the 30-d study. Species autecologies were defined by effects of nutrient enrichment, shading, and community development on species growth rates. Differing autecologies of early and late succession species indicated that competition for nutrients was more important than competition for light. Species autecologies also indicated ecological strategies. The species most stimulated by nutrient enrichment were least able to maintain growth rates as algal abundances on substrata increased. In addition, these species that best sustained their growth rates during succession tended to have the highest immigration rates, indication that drift and immigration may have been an important mechanism of persistence for some populations when resources become limiting within thick benthic mats. [ABSTRACT FROM AUTHOR]

Short-term (3 day) diatom colonization of clean ceromic tiles and tiles conditioned with a thin, nonolgal biofilm was examined in fast- and slow-current outdoor experimental stream channels to assess effects of organic conditioning and current regime on diatom colonization. Colonization rates onto unconditioned tiles were 10 times lower in fast current than in slow. Substratum conditioning reduced the effects of current because organic conditioning reduced the effect of current because organic conditioning of tiles significantly enhanced colonization in fast current, but not in slow current. Two diatom taxa (Nitzschia acicularis W. Sm. and Synedra radians Kütz.) colonized unconditioned tiles more rapidly than conditioned tiles in slow current, suggesting the existence of negative interactions between these diatoms and bacteria and/or organics in conditioning films. [ABSTRACT FROM AUTHOR]

Community structure of benthic diatoms in two sandy streams was studied for two summers to assess differences in abundances and species composition among habitats and between years and streams. The greatest difference in abundances (cells·cm[sup2]) were lower abundances on rocks than on sand, whether the sand was clean or covered with flocculent organic material. Relatively little variation in abundance occurred between years and streams. Species composition of diatom communities varied more among habitats and between stream than from year to year. Species composition was most unique in floc-covered sond than communities in clean and floc-coverred sand, rock, plant, and plankton were compared. Diatom species composition in these sandy streams was most similar on sand and rocks. [ABSTRACT FROM AUTHOR]

We studied the hypothesis that diatom immigration abilities are related to their fitness for colonizing stream substrates. Diatom abundances on artificial substrates exposed for 24 h (the measure of immigration rate) and abundances of stream plankton were determined in six habitats. Diatom immigration varied among habitats from 50-2500 cells cm[SUP-2] d[SUP-1], Immigration rats decreased 10-fold with increases incurrent form 10 to 30 cm[SUP-1] but changed little during a 40-d summer period. Immigration abilities of diatom taxa were characterized as ratios of either their abundances or relative abundances in immigration assemblages versus in the plankton. Immigration abilities varied over 100-fold among different species. Immigration of some species could be characterized as slower that others in different streams; however variation in immigration abilities of other species among streams in dicated that environment also affected immigration. Diurnal variation in abundance and species composition of the immigration pool (stream plankton) can be important in assessing immigration abilities. Immigration ability may affect benthic diatom fitness. Monoraphid diatoms had a lower probability of immigrating from the plankton than araphid diatoms. [ABSTRACT FROM AUTHOR]

The study analyzes the impact of conditions associated with depth upon benthic algal communities in Lake Michigan. Diatom abundance was greater at 9.1 and 14.6 m depths than 6.5, 22.6 and 27.4 m. Shallow (6.5 m), middepth (9.1 and 14.6 m) and deep (22.6 and 27.4 m) zones were distinguishable on the basis of community composition, structure and abundance. Dominance of benthic species, high diversity and low abundance in shallow communities probably resulted from substantial substrate disturbance by wave action in this productive zone. Dominance of benthic species, high diversity and high abundance characterized mid-depth communities where less wave disturbance enabled algal accumulation. Preponderance of living planktonic taxa, low diversity and low abundance delineated deep communities where planktonic algae accumulated and low light levels reduced growth of benthic species. [ABSTRACT FROM AUTHOR]

Ecological risk assessment and risk management call for 'state-of-the-science' methods and sound scientific assessments of ecosystem health and stressor effects. In this paper recent developments of periphyton indicators of biotic integrity and ecosystem stressors of streamsand wetlands are related in a framework of ecological metrics that can be used to quantify risk assessment and risk management options. Many periphyton metrics have been employed in past assessments of water quality and a periphyton indices of biotic integrity has been applied by the state of Kentucky. In addition, the sensitivity of species composition of periphytic diatom assemblages has been shown to respond predictably to ecological stressors so that specific pH, conductivity, and total phosphorus in wetlands and streams can be inferred withweighted average indices. Inference of nutrient conditions by diatomindicators of total phosphorus is shown to have sufficient precisionto be a valuable complement to one-time measurement of highly variable total phosphorus in streams Quantitative indices of sustainabilityand restorability of ecosystem integrity are proposed, respectively,as the changes in ecological conditions that can occur without significant change in ecological integrity or changes that are necessary to restore ecological integrity. [ABSTRACT FROM AUTHOR]

• Benthic algae assessments in the EU and US share common goals based in policy. • Diatoms are primary indicators in both EU and US. • Assessment sampling, analysis, and ecological health endpoints are similar. • Considerable variation in approach among states in both EU and US. • Harmonizing taxonomy and endpoints plus new technologies will strengthen programs. Freshwaters face multiple environmental problems including eutrophication, acidification, salinization, and climate-change, all of which can lead to impairment of ecosystem structure and function. Furthermore, these stressors often act in combination. Benthic algal-based assessments to quantify impairment are used in both the EU and US. In this review, we use case studies, experience, and the literature to compare concepts, approaches, and methods between the EU and US to offer an updated picture of benthic algal-based assessments. Both the US and EU are composed of numerous constituent states having considerable flexibility to adopt individual methods. The goal of this work is to synthesize the various approaches that are used across the EU and US. Specifically, we compare and contrast benthic algal assessment performed in response to core legislation – the Water Framework Directive in the EU and the Clean Water Act in the US, with a particular focus on the steps taken to ensure consistency at different stages of the process. This includes consideration of approaches to sampling design and field methods, taxonomic resolution and laboratory harmonization, metric selection and choice of algal groups, assessment of stressors and stressor/response relationships. A number of commonalities emerged during this process, particularly the focus on diatoms over other algal groups. However, there are also a number of key differences, including more widespread use of multimetric indices in the US compared with the EU. Finally, we consider emerging opportunities, including the potential for using metagenomic approaches for bioassessment in the future. [ABSTRACT FROM AUTHOR]

Eutrophication and recovery of Muskegon Lake resulted from a complex set of interacting factors according to diatom-inferred total phosphorus (TP), geochemical proxies, detailed modeling of land use land cover change in the watershed, and accounts of past point source management and non-native species invasions. Benthic and planktonic diatoms responded to phosphorus environments differently in this lake that receives 95% of its input from one river and has only a 23 days average retention time. Planktonic diatoms reflected river conditions more than benthic diatoms, and benthos reflected lake conditions more than plankton. Inferred TP from planktonic diatoms indicated the Muskegon River was relatively nutrient rich compared to inferred TP for Muskegon Lake based on benthic diatoms before Europeans settled the watershed. Early European settlement and logging caused no changes in phosphorus condition in the Muskegon River, but modest increases in phosphorus were indicated in Muskegon Lake during the middle and late thirds of the 19th century. Extensive watershed-scale agricultural activity in the early 20th century apparently had little effect on trophic status of the lake, perhaps because it preceded high fertilizer use on farms. During the industrial and population boom in the watershed during the early half of the 20th century, river conditions changed little, but eutrophication of Muskegon Lake increased greatly. Reduction in river phosphorus by dams occurred during the first half of the 20th century. Phosphorus reduction in the lake was indicated after advanced wastewater treatment for Muskegon Township was implemented in 1973. Current diatom inferred phosphorus concentration in the lake is the same as before European settlement, however many attributes of the lake still differ because other stressors persist. [ABSTRACT FROM AUTHOR]