Diatom Diversity in Chronically versus Episodically Acidified Adirondack Streams

The relationship between algal species richness and diversity, and pH is controversial. Furthermore, it is still unknown how episodic stream acidification following atmospheric deposition affects species richness and diversity. Here we analyzed water chemistry and diatom epiphyton dynamics and showed their contrasting behavior in chronically vs. episodically acidic streams in the Adirondack region. Species richness and diversity were significantly higher in the chronically acidic brown water stream, where organic acidity was significantly higher and the ratio of inorganic to organic monomeric aluminum significantly lower. Conversely, in the episodically acidic clear water stream, the inorganic acidity and pH were significantly higher and the diatom communities were very species‐poor. This suggests that episodic acidification in the Adirondacks may be more stressful for stream biota than chronic acidity. Strong negative linear relationships between species diversity, Eunotia exigua, and dissolved organic carbon against pH were revealed after the influence of non‐linear temporal trends was partialled out using a novel way of temporal modeling. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impacts of acidification on macroinvertebrate communities in streams of the western Adirondack Mountains,New York,USA

Limited stream chemistry and macroinvertebrate data indicate that acidic deposition has adversely affected benthic macroinvertebrate assemblages in numerous headwater streams of the western Adirondack Mountains of New York. No studies, however, have quantified the effects that acidic deposition and acidification may have had on resident fish and macroinvertebrate communities in streams of the region. As part of the Western Adirondack Stream Survey, water chemistry from 200 streams was sampled five times and macroinvertebrate communities were surveyed once from a subset of 36 streams in the Oswegatchie and Black River Basins during 2003–2005 and evaluated to: (a) document the effects that chronic and episodic acidification have on macroinvertebrate communities across the region, (b) define the relations between acidification and the health of affected species assemblages, and (c) assess indicators and thresholds of biological effects. Concentrations of inorganic Al in 66% of the 200 streams periodically reached concentrations toxic to acid-tolerant biota. A new acid biological assessment profile (acidBAP) index for macroinvertebrates, derived from percent mayfly richness and percent acid-tolerant taxa, was strongly correlated (R² values range from 0.58 to 0.76) with concentrations of inorganic Al, pH, ANC, and base cation surplus (BCS). The BCS and acidBAP index helped remove confounding influences of natural organic acidity and to redefine acidification-effect thresholds and biological-impact categories. AcidBAP scores indicated that macroinvertebrate communities were moderately or severely impacted by acidification in 44–56% of 36 study streams, however, additional data from randomly selected streams is needed to accurately estimate the true percentage of streams in which macroinvertebrate communities are adversely affected in this, or other, regions. As biologically relevant measures of impacts caused by acidification, both BCS and acidBAP may be useful indicators of ecosystem effects and potential recovery at the local and regional scale.     

Meta‐Analysis of Lost Ecosystem Attributes in Urban Streams and the Effectiveness of Out‐of‐Channel Management Practices

Urban development is a leading cause of stream impairment that reduces biodiversity and negatively affects ecosystem processes and habitat. Out‐of‐stream restoration practices, such as stormwater ponds, created wetlands, and restored riparian vegetation, are increasingly implemented as management strategies to mitigate impacts. However, uncertainty exists regarding how effectively they improve downstream ecosystems because monitoring is uncommon and results are typically reported on a case‐by‐case basis. We conducted a meta‐analysis of literature and used response ratios to quantify how downstream ecosystems change in response to watershed development and to out‐of‐stream restoration. Biodiversity in unrestored urban streams was 47% less than that in reference streams, and ecological communities, habitat, and rates of nutrient cycling were negatively affected as well. Mean measures of ecosystem attributes in restored streams were significantly greater than, and 156% of, those in unrestored urban streams. Measures of biodiversity in restored streams were 132% of those in unrestored urban streams, and indices of biotic condition, community structure, and nutrient cycling significantly improved. However, ecosystem attributes and biodiversity at restored sites were significantly less than, and only 60% and 45% of, those in reference streams, respectively. Out‐of‐stream management practices improved ecological conditions in urban streams but still failed to restore reference stream conditions. Despite statistically significant improvements, assessing restoration success remains difficult due to few comparisons to reference sites or to clearly defined targets. These findings can inform future monitoring, management, and development strategies and highlight the need for preventative actions in a watershed context.     

The influence of data characteristics on detecting wetland/stream surface-water connections in the Delmarva Peninsula,Maryland and Delaware

The dependence of downstream waters on upstream ecosystems necessitates an improved understanding of watershed-scale hydrological interactions including connections between wetlands and streams. An evaluation of such connections is challenging when, (1) accurate and complete datasets of wetland and stream locations are often not available and (2) natural variability in surface-water extent influences the frequency and duration of wetland/stream connectivity. The Upper Choptank River watershed on the Delmarva Peninsula in eastern Maryland and Delaware is dominated by a high density of small, forested wetlands. In this analysis, wetland/stream surface water connections were quantified using multiple wetland and stream datasets, including headwater streams and depressions mapped from a lidar-derived digital elevation model. Surface-water extent was mapped across the watershed for spring 2015 using Landsat-8, Radarsat-2 and Worldview-3 imagery. The frequency of wetland/stream connections increased as a more complete and accurate stream dataset was used and surface-water extent was included, in particular when the spatial resolution of the imagery was finer (i.e., <10 m). Depending on the datasets used, 12–60% of wetlands by count (21–93% of wetlands by area) experienced surface-water interactions with streams during spring 2015. This translated into a range of 50–94% of the watershed contributing direct surface water runoff to streamflow. This finding suggests that our interpretation of the frequency and duration of wetland/stream connections will be influenced not only by the spatial and temporal characteristics of wetlands, streams and potential flowpaths, but also by the completeness, accuracy and resolution of input datasets.     

Comparative Environmental Assessment in the Studies of Benthic Diatom,Macroinvertebrate, and Fish Communities

Community response to environmental gradients operating at hierarchical scales was assessed in studies of benthic diatoms, macroinvertebrates and fish from 44 stream sites in the New York City watershed. Hierarchical cluster analysis (TWINSPAN) of diatoms and fish partitioned the study sites into four groups, i.e., acid streams, reservoir outlets and wetland streams, large eutrophic streams, and small eutrophic streams; macroinvertebrate TWINSPAN distinguished an additional group of silty eutrophic streams. The correspondence among the three assemblage TWINSPAN groupings was moderate, ranging from 51 to 57%. The similarity across the four major group types was the highest among large eutrophic stream and acid stream assemblages, and the lowest among small eutrophic stream assemblages. Stepwise discriminant function analysis revealed that environmental factors discriminated most effectively the diatom grouping and least effectively the fish grouping. The best environmental predictors for diatom and macroinvertebrate grouping were conductance and percent surface water, while population density was most powerful in separating the fish groups. Carbaryl was the only pesticide that correlated with macroinvertebrate grouping. Partial redundancy analyses suggested a differential dependence of freshwater communities on the scale of the environmental factors to which they respond. The role of small‐scale habitat and habitatland cover/land use interaction steadily increased across the diatom, macroinvertebrate, and fish assemblages, whereas the effect of large‐scale land cover/land use declined.     

Effects of Stress from Mine Drainage on Diversity, Biomass, and Function of Primary Producers in Mountain Streams

This paper proposes a hypothesis that relates biodiversity, community biomass, and ecosystem function to a gradient of stress. According to this hypothesis, biodiversity has a low threshold of response to stress, whereas biomass and function are stable or increase under low to moderate stress and decrease only under high stress. This hypothesis was tested by examining communities of primary producers in streams under stress from mine drainage in the Rocky Mountains of Colorado, USA. Mine drainage exerts chemical stress (low pH, dissolved metals) as well as physical stress (deposition of metal oxides) on stream biota. Diversity of primary producers was usually more sensitive to stress from mine drainage than community biomass (chlorophyll a) or primary production. Diversity was negatively related to all stresses from mine drainage, but it was especially low in streams with low pH or high concentration of dissolved zinc. Biomass and production were high in streams with only chemical stress, but they were often low in streams with physical stress caused by metal oxide deposition. Stream sites with aluminum oxide deposition usually had very little algal biomass. The rate of metal oxide deposition, presence of aluminum oxides, and pH together explained 65% of the variation in biomass. The rate of net primary production was highly correlated with biomass and had a similar response to stress from mine drainage. Overall, chemical stresses (low pH, high concentration of zinc) generally led to the hypothesized trends in our model of ecosystems under stress. Physical stress (deposition of metal oxides), however, led to variable responses, and often decreased biomass and function even at low intensity, contrary to the original hypothesis. Thus, the nature of ecosystem response to stress may differ for chemical and physical stresses.     

Relationship between biodiversity and landscape structure in the Gyungan stream basin,central Korea

The relationship between landscape structure and biodiversity was investigated in the Gyungan stream basin, central Korea, in order to prepare a biodiversity conservation plan. The study area was divided into upstream, midstream, downstream and Gonjiam stream sub‐watersheds based on the land use pattern of each sub‐watershed. The quality of the terrestrial landscape was assessed by connectivity and percentages of deciduous broad‐leaved forest and urbanized area. The quality of the terrestrial landscape was the highest in the downstream sub‐watershed followed by Gonjiam stream, midstream and upstream sub‐watersheds. The quality of the riparian landscape assessed by percentages of the number and the area that the wetland vegetation elements occupy in the whole area showed a similar trend to that of terrestrial landscape. The diversity of all taxa including fish, reptiles and amphibians, birds, mammals and wetland vegetation except benthic macroinvertebrates was the highest downstream. The diversity of benthic macroinvertebrates was the highest in the Gonjiam stream sub‐watershed. Thus, biodiversity was shown to be the highest in the downstream sub‐watershed, followed, in order, by Gonjiam stream, midstream and upstream sub‐watersheds in proportion to landscape quality. On the other hand, the quality of the aquatic environment based on the ecological score of benthic macroinvertebrate (ESB) index was the highest downstream, followed, in order, by upstream, Gonjiam stream and midstream areas. This trend is different from that of biodiversity. In order to improve landscape quality degraded by excessive land use and to increase biodiversity, we recommended a restoration plan that addresses both ecosystem and landscape.     

Beta diversity of stream diatoms at two hierarchical spatial scales: implications for biomonitoring

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春沼生态系统概述及其研究进展

小微湿地是全球最重要的淡水栖息地之一,其价值不仅在于单个小微湿地,而是由多种小微湿地构成的流域小微湿地网络,发挥着非常重要的淡水生物多样性保育功能。春沼作为自然界一种独特的临时性小微湿地类型,是流域小微湿地网络的重要组成部分,提供了多种生态服务功能。但迄今为止对于春沼生态系统,国内外相关研究较少,这类特殊而又重要的小微湿地生态系统尚未引起足够的重视。阐述了春沼的概念和形成原因,对春沼生态系统干湿交替的水文特征,以及物种组成、群落结构、生物多样性和群落动态等春沼生物群落特征进行了概述,探讨了春沼维持流域淡水生物多样性、提供物种生境、水文调节和均化洪水、净化水质和其他生态系统服务,在此基础上讨论了春沼生态系统研究存在的问题与不足,对该领域研究的未来发展方向给出了建议。     

Parallels and contrasts between intermittently freezing and drying streams: From individual adaptations to biodiversity variation

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Temporal response of stream benthic macroinvertebrate communities to the synergistic effects of anthropogenic acidification and natural drought events

1. We evaluated whether the surprisingly weak biological recovery associated with declines in acid deposition were related to drought‐induced re‐acidification of streams. We used test site analysis (TSA) to characterise temporal changes (1995–2003) in the degree and nature of impairments to stream benthic macroinvertebrate (BMI) communities influenced by acid deposition and drought. 2. The BMI communities in four historically impacted test streams were compared with communities in 30 minimally impacted reference streams. Six multivariate (e.g. ordination axes scores) and four traditional (e.g. % Diptera) summary metrics were used to describe BMI communities. Using all metrics simultaneously (i.e. Mahalanobis or generalised distance), the TSA provided a single probability that a test community was impaired. If a test community was significantly impaired, a further analysis was done to identify the metric(s) important in distinguishing the test community from reference condition. 3. Results of the TSAs indicated that the generalised distances between test communities and the reference condition were inversely related to stream water pH (n = 36). The TSAs also indicated ordination metrics based on BMI abundance were important in distinguishing significantly impaired communities from reference conditions. Temporal trends indicated that there has been short‐term recovery of these BMI communities, but that overall improvements have been hampered by acid or metal toxicity associated with drought‐induced re‐acidification of the streams. 4. Our use of a variety of summary metrics to obtain a single statistical test of significance within the context of the reference‐condition approach provided a simple and unambiguous framework for evaluating the biological condition of test sites.     

Seasonal and spatial hydrological variability drives aquatic biodiversity in a flood‐pulsed,sub‐tropical wetland

1. Flood‐pulsed wetlands make vital contributions to local and global biodiversity. However, the patterns and controls of spatial and temporal variation in aquatic biodiversity in flood‐pulsed wetlands are not well understood. We analysed the relationship between variation in hydrological regime and the patterns of aquatic biodiversity in a large pristine flood‐pulsed wetland, the Okavango Delta, Botswana. 2. Surveys of water chemistry, diatoms and macroinvertebrates were conducted over the seasonal phases of the flood pulse. Hydrological variables of flood frequency and hydroperiod class were collated from 16 years of satellite images. Multivariate regression trees and generalised least squares regression were used to determine the chief controls of community composition and taxon richness. 3. Hydroperiod class, phase of the flood and conductivity explained 32% and 43% of the variation in diatom and invertebrate taxon richness, respectively. There was a negative relationship between hydroperiod class and invertebrate taxon richness on the rising, peak and receding flood, whereas at low flood there was no significant relationship. Multivariate regression tree analysis revealed hydroperiod class, phase of the flood and conductivity as the dominant forces shaping invertebrate and diatom community composition. 4. Seasonal and spatial variation in hydrological conditions are the principal drivers of variation in aquatic biodiversity in flood‐pulsed wetlands. In pristine flood‐pulsed wetlands, increased productivity caused by the arrival of the flood waters appears to override disturbance and connectivity in shaping taxon richness and community composition. Thus, these data suggest that the maintenance of a rich mosaic of habitats covering a broad range of hydroperiod is the key to preserving aquatic biodiversity and natural ecosystem function in flood‐pulsed wetlands.     

Comparing the Fish and Benthic Macroinvertebrate Diversity of Restored Urban Streams to Reference Streams

Urbanization is associated with substantial losses to stream biological diversity throughout the United States' mid‐Atlantic. Stream restoration has been used to improve stream conditions and, in part, to ameliorate these losses. However, the relationship between restoration and recovery of biological diversity is unclear. Our objective was to critically examine the efficacy of urban stream restorations with regard to biological diversity. We compared restored urban streams to urban nonrestored, nonurban, and reference (minimally degraded) streams using five measures each of fish and benthic macroinvertebrate diversity. Both multivariate and univariate statistical analyses show biological diversity of restored urban streams to be similar to nonrestored urban streams and lower than nonurban and reference streams. Restored urban sites showed no apparent increase in biological diversity through time, while diversity decreased at two of the reference streams coincident with increased urban development within their catchments. Our results indicate that restoration approaches commonly used regionally as in these urban streams are not leading to recovery of native stream biodiversity. Evidence from several sources indicates a need for dramatic changes in restoration approach, and we argue for a watershed‐scale focus including protection of the least impacted streams and adopting other land‐based actions within the watershed where possible.     

Beaver‐created successional gradients increase β‐diversity of invertebrates by turnover in stream‐wetland complexes

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Does the implementation of environmental flows improve wetland ecosystem services and biodiversity? A literature review

Environmental flow releases are a tool for wetland restoration, but there has been no systematic evaluation of their success. We systematically assessed 102 published studies from a wide range of wetland ecosystems across the globe to determine whether releasing environmental flows could maintain or promote biodiversity and increase ecosystem services, and which strategies were most effective. We found that environmental flow releases remarkably increased regulating services (sediment regulation and water purification) and supporting services (primary production and habitat maintenance), and maintained biodiversity and provisioning services. Biodiversity responses were positive only in river wetlands, and were negative in coastal, lake, and marsh wetlands; the overall delivery of ecosystem services responded positively in all ecosystem types except artificial wetlands. The effects were positive for ecosystem services under all environmental flow regimes, and seasonal minimum flow releases could maintain biodiversity and improve ecosystem services. We also found that long‐term environmental flow releases (years to decades) maintained biodiversity. Values of a change‐in‐flow parameter (D) ranging from 0 to 10% improved both biodiversity and ecosystem services. In summary, long‐term implementation, a high‐flow regime, and D ranging from 0 to 10% for the environmental flows promoted biodiversity and improved ecosystem services around the world, particularly in river wetlands. Regional‐level conclusions might be applicable to guide the implementation of environmental flow releases, but small sample sizes reduce their reliability. We also found that the effect sizes of environmental flow release projects for biodiversity and ecosystem services were significantly and positively correlated in rivers, but not in other wetlands.     

Context‐dependent resistance of freshwater invertebrate communities to drying

More freshwater ecosystems are drying in response to global change thereby posing serious threat to freshwater biota and functions. The production of desiccation‐resistant forms is an important adaptation that helps maintain biodiversity in temporary freshwaters by buffering communities from drying, but its potential to mitigate the negative effects of drying in freshwater ecosystems could vary greatly across regions and ecosystem types. We explored this context dependency by quantifying the potential contribution of desiccation‐resistance forms to invertebrate community recovery across levels of regional drying prevalence (defined as the occurrence of drying events in freshwaters in a given region) and ecosystem types (lentic, lotic) in temporary neotropical freshwaters. We first predicted that regional drying prevalence influences the selection of species with desiccation‐resistant forms from the regional species pools and thus increases the ability of communities to recover from drying. Second, we predicted lentic freshwaters harbor higher proportions of species with desiccation‐resistant forms compared to lotic, in response to contrasted hydrologic connectivity. To test these predictions, we used natural experiments to quantify the contribution of desiccation‐resistant forms to benthic invertebrate community recovery in nine intermittent streams and six geographically isolated temporary wetlands from three Bolivian regions differing in drying prevalence. The contribution of desiccation‐resistant forms to community recovery was highest where regional drying prevalence was high, suggesting the species pool was adapted to regional disturbance regimes. The contribution of desiccation‐resistant forms to community recovery was lower in streams than in wetlands, emphasizing the importance of hydrologic connectivity and associated recolonization processes from in‐stream refuges to recovery in lotic systems. In all regions, the majority of functional traits were present in desiccation‐resistant taxa indicating this adaptation may help maintain ecosystem functions by buffering communities from the loss of functional traits. Accounting for regional context and hydrologic connectivity in community recovery processes following drying can help refine predictions of freshwater biodiversity response to global change.     

Aquatic macroinvertebrate community responses to wetland mitigation in the Greater Yellowstone Ecosystem

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Are landscape-based wetland condition indices reflected by invertebrate and diatom communities?

Assessments of wetland condition are generally based on measures of variables related to plants or large animals (birds, fish), and catchment or landscape features. This approach ignores the considerable biodiversity and functional values of small aquatic organisms. The aim of this study was to assess the correspondence between landscape-based indices of wetland condition and the community composition of both aquatic invertebrates and diatoms across a broad range of wetlands in the West Coast region of New Zealand. Aquatic invertebrates and diatoms were sampled from 29 lowland wetlands subject to varying degrees of catchment modification. Wetland condition was assessed independently using two methods: a field-based method to give the Wetland Condition Index, and a GIS-based method that gave an Index of Ecological Integrity. Strong relationships existed between community composition and pH, so we partitioned the community data into groups according to wetland pH. We found only weak relationships between wetland condition scores and invertebrate and diatom communities within each pH group. In most cases, data describing the nutrient status of the water had the strongest influence on invertebrate and diatom communities. Lack of strong associations between measured wetland condition indices and either diatom or invertebrate community composition suggests that neither index was dominated by variables directly influencing the aquatic component of wetland biota. The challenges now are to identify the critical variables, and to develop complementary wetland scoring systems that better reflect the status of small aquatic organisms.     

The impacts of a watershed CaCO3 treatment on stream and wetland biogeochemistry in the Adirondack Mountains

Temporal and longitudinal variations in the chemistry of two tributary streams of Woods Lake in the Adirondack Mountains of New York were monitored before and after a watershed CaCO₃ application. One subcatchment of the lake had a large beaver pond and wetland at its headwaters, while the second was free-flowing. Treatment of both subcatchments with CaCO₃ resulted in an immediate increase in acid neutralizing capacity (ANC) associated with Ca²⁺ release. The extent and duration of the response to the treatment were greater in the wetland-impacted stream. Aluminum was retained and complexed with organic solutes generated within the beaver-pond. In the free-flowing stream, NO ₃ ^– concentration increased significantly after the manipulation; this pattern was not evident in the wetland-impacted stream. Net retention of SOkinf4/sup2– was evident in the beaver pond prior to and following treatment, and this response was enhanced after the watershed liming. Comparisons of beaver pond inlet/outlet concentrations, mass balance calculations, and in-pond profiles of chemical parameters revealed patterns of retention of SO ₄ ^2– , NO ₃ ^– and Al, and release of Fe²⁺, dissolved organic carbon (DOC) and NH ₄ ⁺ in the wetland during the summer before CaCO₃ treatment. Post-treatment releases of Ca²⁺ from the near-sediment zone in the beaver pond corresponded to anoxic periods in mid- to late-summer and under ice in winter. These findings demonstrate the importance of increased microbial processing of organic matter, along with high partial pressure Of CO₂ (Pco₂) in facilitating the dissolution of the applied CaCO₃. Dissolved silica (H₄SiO₄) was retained in the wetland during the summer prior to treatment but was released after the manipulation. This phenomenon may reflect the dissolution of diatom frustules or silicate minerals in the wetland at higher pH and DOC concentrations. Within two years of the CaCO₃ treatment 60% of the CaCO₃ applied to the beaver pond and surrounding wetland was dissolved and transported from the pond, in contrast to only 2.2% of the CaCO₃ applied to the upland subcatchment draining into the wetland. These results, coupled with high quantities of exchangeable Ca²⁺ found in sediments and onSphagnums mosses in the pond, demonstrate the importance of hydrologic source areas and wetlands in facilitating the dissolution of added CaCO₃ and in regulating the production of chemical species important in ANC generation.     

Forest sources and pathways of organic matter transport to a blackwater stream: a hydrologic approach

Quantitative information regarding landscape sources and pathways of organic matter transport to streams is important for assessing impacts of terrestrial processes on aquatic ecosystems. We quantified organic C, a measure of organic matter, flowing from a blackwater stream draining a 12.6 km² watershed on the upper Atlantic Coastal Plain in South Carolina, and utilized a hydrologic approach to partition this outflow between its various pathways from upland and wetland forest sources. Results of this study indicate that 28.9 tonnes C yr^–1 were exported in stream flow, which was estimated to be 0.5% of the annual C input from forest detritus to the watershed. Upland forest, which covers 94% of the watershed area, contributed only 2.0 tonnes C yr^–1 to stream flow, which amounted to 0.04% of detritus annually produced by the upland forest. Organic matter was transported from uplands to the stream almost entirely through groundwater. Apparently, upland soils are too sandy to support overland flow, and the sloping topography insufficiently extensive or steep enough to drive important quantities of interflow. Riparian wetland forest, which covers only 6% of the watershed area, contributed 26.9 tonnes C yr^–1 to stream flow, amounting to about 10.2% of detritus annually produced by the wetland forest. Dissolved organic C leached from wetland soil accounted for 63% of all organic C entering the stream, and was transported chiefly in baseflow. These results indicate that upland detritus sources are effectively decoupled from the stream despite the sandy soils and quantitatively confirm that even small riparian wetland areas can have a dominant effect on the overall organic matter budget of a blackwater stream. In view of the recognized importance of dissolved organic matter in facilitating transport of other substances (e.g., cation nutrients, metals, and insoluble organic compounds), our results suggest that the potential for movement of these substances through wetland soils to streams in this region is high.