Brian H. Hill

Ecoenzymatic stoichiometry of microbial organic nutrient acquisition in soil and sediment

Biota can be described in terms of elemental composition, expressed as an atomic ratio of carbon:nitrogen:phosphorus (refs 1–3). The elemental stoichiometry of microoorganisms is fundamental for understanding the production dynamics and biogeochemical cycles of ecosystems because microbial biomass is the trophic base of detrital food webs. Here we show that heterotrophic microbial communities of diverse composition from terrestrial soils and freshwater sediments share a common functional stoichiometry in relation to organic nutrient acquisition. The activities of four enzymes that catalyse the hydrolysis of assimilable products from the principal environmental sources of C, N and P show similar scaling relationships over several orders of magnitude, with a mean ratio for C:N:P activities near 1:1:1 in all habitats. We suggest that these ecoenzymatic ratios reflect the equilibria between the elemental composition of microbial biomass and detrital organic matter and the efficiencies of microbial nutrient assimilation and growth. Because ecoenzymatic activities intersect the stoichiometric and metabolic theories of ecology, they provide a functional measure of the threshold at which control of community metabolism shifts from nutrient to energy flow.

Using diatoms as indicators of ecological conditions in lotic systems: a regional assessment

Benthic diatoms and water chemistry were sampled from 49 stream sites in the Mid-Atlantic Highlands region of the United States to evaluate the use of diatoms as indicators of environmental conditions in streams across varying geographic and ecoregional areas. Diatom samples were collected from depositional and erosional habitats in a randomly selected reach in each stream site. Patterns of diatom species distributions in relation to environmental variables were determined using canonical correspondence analysis. Diatom species in both habitats were highly correlated with a pH gradient. A second gradient was correlated with variables that were commonly associated with agricultural runoff such as turbidity and total phosphorus. The relationship between diatoms and major environmental variables was quantified with regression and calibration models. The correlation between diatom-inferred and observed pH was high (r2 = 0.90). Cross-validation with jackknifing showed that pH models were reasonably robust (r2 = 0.69 for depositional habitats, r2 = 0.67 for erosional habitats). The regression and calibration models for the depositional habitats had only slightly higher predictive powers than those of erosional habitats. The relationship between diatoms and important environmental variables was robust and quantifiable, and the sensitivity of diatom assemblages to environmental conditions did not differ between erosional and depositional habitats. Therefore we concluded that diatoms can be used as quantitative indicators of environmental conditions in lotic systems.

Ecosystem services altered by human changes in the nitrogen cycle: a new perspective for US decision making

Human alteration of the nitrogen (N) cycle has produced benefits for health and well-being, but excess N has altered many ecosystems and degraded air and water quality. US regulations mandate protection of the environment in terms that directly connect to ecosystem services. Here, we review the science quantifying effects of N on key ecosystem services, and compare the costs of N-related impacts or mitigation using the metric of cost per unit of N. Damage costs to the provision of clean air, reflected by impaired human respiratory health, are well characterized and fairly high (e.g. costs of ozone and particulate damages of

Spatial patterns and ecological determinants of benthic algal assemblages in mid-atlantic streams, usa

28 per kg NO(x)-N). Damage to services associated with productivity, biodiversity, recreation and clean water are less certain and although generally lower, these costs are quite variable (<

Ecoregions and benthic diatom assemblages in Mid-Atlantic Highlands streams, USA

2.2-56 per kg N). In the current Chesapeake Bay restoration effort, for example, the collection of available damage costs clearly exceeds the projected abatement costs to reduce N loads to the Bay (

Comparison of correlations between environmental characteristics and stream diatom assemblages characterized at genus and species levels

8-15 per kg N). Explicit consideration and accounting of effects on multiple ecosystem services provides decision-makers an integrated view of N sources, damages and abatement costs to address the significant challenges associated with reducing N pollution.

Assessment of streams of the eastern United States using a periphyton index of biotic integrity

We attempted to identify spatial patterns and determinants for benthic algal assemblages in Mid‐Atlantic streams. Periphyton, water chemistry, stream physical habitat, riparian conditions, and land cover/use in watersheds were characterized at 89 randomly selected stream sites in the Mid‐Atlantic region. Cluster analysis (TWINSPAN) partitioned all sites into six groups on the basis of diatom species composition. Stepwise discriminant function analysis indicated that these diatom groups can be best separated by watershed land cover/use (percentage forest cover), water temperature, and riparian conditions (riparian agricultural activities). However, the diatom‐based stream classification did not correspond to Omernik’s ecoregional classification. Algal biomass measured as chl a can be related to nutrients in habitats where other factors do not constrain accumulation. A regression tree model indicated that chl a concentrations in the Mid‐Atlantic streams can be best predicted by conductivity, stream slope, total phosphorus, total nitrogen, and riparian canopy coverage. Our data suggest that broad spatial patterns of benthic diatom assemblages can be predicted both by coarse‐scale factors, such as land cover/use in watersheds, and by site‐specific factors, such as riparian conditions. However, algal biomass measured as chl a was less predictable using a simple regression approach. The regression tree model was effective for showing that ecological determinants of chl a were hierarchical in the Mid‐Atlantic streams.

Algae–P relationships, thresholds, and frequency distributions guide nutrient criterion development

Ecoregional differences in geology and hydrology may affect physical and chemical conditions in streams and, consequently, the species composition of algal assemblages. Stresses resulting from human disturbance, however, may constrain species membership in algal assemblages and reduce regional diversity. We expected that ecoregional differences in diatom assemblages, if they were present, would be more evident in relatively undisturbed sites than in randomly selected sites. Benthic diatom and water chemistry samples were collected from streams in 7 ecoregions of the Mid-Atlantic Highlands to evaluate correspondence between ecoregional classification and diatom assemblages. Ecoregional differences were assessed using 196 randomly selected stream sites (probability sites) and 60 sites with less disturbance by humans (reference sites). Multivariate analyses showed that significant ecoregional differences in diatom assemblages were observed only in probability sites and not in reference sites. Water chemistry was significantly different among ecoregions, both for probability sites and for reference sites. Significant differences in diatom assemblages and water chemistry were, however, evident only among ecoregions grouped by topography (i.e., montane, high plateau, and low plateau/valley). Ecoregional differences between montane regions or low plateau/valley regions were subtle. Stream sites grouped by catchments were also significantly different in water chemistry but not in diatom assemblages, both for probability sites and for reference sites. Our data suggest that diatom assemblages respond to land use, especially agricultural activities, and thus may correspond to the ecoregional classification when land use differs significantly among these ecoregions (e.g., montane vs valley ecoregions). Diatom assemblages that lack a region-specific feature may be ideal as unbiased indicators of stream water quality.

MULTIVARIATE ANALYSIS OF PERIPHYTON ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN COLORADO ROCKY MOUNTAIN STREAMS 1

1US Environmental Protection Agency, National Center for Environmental Assessment, 26 W. Martin Luther King Dr., Cincinnati, Ohio 45268 USA 2Department of Zoology, Michigan State University, East Lansing, Michigan 48824 USA 3Environmental Sciences and Resources, Portland State University, Portland, Oregon 97207 USA 4Department of Fisheries and Wildlife, Oregon State University, c/o US Environmental Protection Agency, 200 SW 35th Street, Corvallis, Oregon 97333 USA 5US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, 200 SW 35th Street, Corvallis, Oregon 97333 USA 6OAO Corporation, c/o US Environmental Protection Agency, 200 SW 35th Street, Corvallis, Oregon 97333 USA

ANALYSIS OF MACROINVERTEBRATE ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN ROCKY MOUNTAIN STREAMS

Abstract Benthic algae were collected from 272 eastern United States streams and rivers and analyzed for diatom species richness and dominance, the relative abundance of acidobiontic, eutraphentic, and motile diatoms, standing crops of chlorophyll and biomass, and alkaline phosphatase activity. These data were used to calculate a periphyton index of biotic integrity (PIBI), and values of the index were compared among reference, moderately impacted, and disturbed streams. The level of disturbance was based on stream chemistry, riparian disturbance, or a combined classification. Analyses of variance showed that PIBI was significantly higher in reference streams for all classifications. The PIBI and its metrics were correlated with many of the chemistry and habitat variables, and canonical correlation analysis revealed three significant environmental gradients which extracted 84% of the variance in the PIBI and its metrics. We used the mean 75th, 25th, and 5th percentile scores from the reference sites to set thresholds for excellent, good, fair, or poor condition. Applying these criteria to the cumulative distribution of total stream length in the region, we found that 4.3% of the stream length was in excellent condition; 20.8% in good condition; 56.4% in fair condition; and 18.5% in poor condition. The sensitivity of the PIBI and its component metrics to environmental stressors supports the use of this index for monitoring ecological conditions in streams in the eastern United States and as a tool to aid in diagnosing the causes of their impairment.