Barbara Hayford

Four decades of change: dramatic loss of zoobenthos in an oligotrophic lake exhibiting gradual eutrophication

Abstract. Native species in lakes commonly are affected by cultural eutrophication and introductions of nonnative species. The effects of these disturbances on benthic communities in large lakes have been understudied, despite the integral role that benthos play in maintaining habitat complexity and ecosystem processes. Lake Tahoe has experienced progressive eutrophication and introductions of nonnative species over the past several decades, but how its unique benthic communities have been affected is unclear. The density of Lake Tahoes benthic fauna was compared between 1960s surveys and our recent (2008–2009) survey, and the association of zoobenthos with macrophytes was examined for contemporary and historical samples. The density of benthic invertebrates and the occurrence of macrophytes in benthic samples have declined dramatically since collections made in the 1960s. Lakewide densities of benthic invertebrate taxa endemic to Lake Tahoe have declined by 80 to 100%, and the community structure of benthic invertebrate assemblages has changed considerably. Several native benthic invertebrate taxa were closely associated with deepwater macrophytes in the 1960s, but contemporary invertebrate association with macrophytes could not be evaluated reliably because of the scarcity of macrophytes in contemporary samples. Declines in native benthic invertebrate density could be related to the loss of habitat and food resources previously provided by abundant deepwater macrophyte assemblages. In addition, establishment and increases in density of nonnative species that occurred after the benthic surveys of the 1960s probably have affected native benthic invertebrate communities. The observed declines in Lake Tahoes native benthic invertebrate and macrophyte communities suggest that they are severely threatened.

Declines in diversity of crane flies (Diptera: Tipuloidea) indicate impact from grazing by livestock in the Hövsgöl region of Mongolia

Threats to biodiversity are not studied equally amongst taxa leaving some groups like insects typically understudied in conservation and management research. Crane flies (Diptera: Tipuloidea) are diverse and important members of the aquatic and terrestrial biotic communities. These semi-terrestrial larval habitat preferences place crane flies at risk of habitat degradation and loss particularly from grazing by livestock. Increased grazing by livestock in the Hövsgöl region of Mongolia has impacted both terrestrial and aquatic ecosystems. The purpose of this study is to document biodiversity of crane flies along the east shore of Lake Hövsgöl, Mongolia, and to test whether crane fly diversity differs between valleys with different grazing intensity. Ninety-six species of Tipuloidea were found in this study, nine of these new to Mongolia, with 21 new to the Hövsgöl region. Rarefaction curves indicate that predicted diversity is less for moderately and highly grazed valleys than for the lightly grazed valleys and an analysis of variance indicates that Shannon’s diversity index was significantly higher in the lightly grazed valleys. Finally, a parsimonious model based on multiple regression analysis indicates that plant biomass and relative humidity are the strongest significant predicators of variation in crane fly diversity across the grazing gradient. Since crane fly larvae are an important part of the soil and leaf litter community, impaired diversity may affect ecosystem services such as decomposition of leaf litter and bioturbation, potentially exacerbating the impact of grazing.

Survey of Chironomidae (Insecta: Diptera) from the Kuskokwim River Watershed in Western Alaska

Abstract. Rapidly declining diversity of freshwater species necessitates surveys to document and describe patterns in biodiversity. To this end, a survey of Chironomidae (Insecta: Diptera) was conducted in a remote watershed of western Alaska. Larval chironomids were collected from 16 stream sites in the Kuskokwim River watershed in 2009 and 2010. Twenty-seven chironomid taxa were identified. Orthocladiinae was the most diverse subfamily and was numerically dominant at all sites except a glacial runoff stream where Diamesinae was numerically dominant. Two rare chironomids were collected in the study: an undescribed species of Stilocladius and a species of Orthocladius (Mesorthocladius). The latter genus has only 2 described species in North America, one in Ohio and one in Minnesota. Results of a nonmetric multidimensional scaling analysis indicated that sites varied based on changes in elevation, conductivity, pH, and percent Diamesinae. Two high-elevation sites, one at the outflow of a lake and the other located along the glacial runoff stream, supported the most taxa in this study. Another lower-elevation springbrook also supported a relatively diverse assemblage of chironomids. Otherwise, diversity and richness was low at most sites. In Chironomidae, adults are often necessary for identification of many taxa to species, and so collection of adults should be a focus of future sampling of streams in western Alaska.

Spatial heterogeneity in macroinvertebrate density from Lake Hövsgöl, Mongolia

Lake Hovsgol is a large, ancient, asymmetrical grabenlake located in north central Mongolia. The lake is longalong its north/south axis and the west shore of the lake islined by steep mountains with little human activity; where-as the east shore of the lake is lined by shallow hills char-acterized by pastoral land use. Lake Hovsgol is a pristinelake with high concentrations of dissolved oxygen, lowconcentrations of nutrients, and deep blue color(Kozhova

High Gamma Diversity and Low Beta Diversity of Non-Biting Midges (Diptera: Chironomidae) in Streams of the Gorkhi Terelj National Park, Outer Mongolia

ABSTRACT. The purpose of this study was to document gamma diversity of Chironomidae in Outer Mongolia by documenting alpha and beta diversity of chironomids from streams sites within Gorkhi Terelj National Park and in the surrounding area. Pupal exuviae of Chironomidae were collected from streams using standardized, semi-quantitative sampling methods so that patterns in community structure could be compared to patterns in the study sites. Gamma diversity for the twelve sites in this study was 98 species, including 26 new records for Mongolia; alpha diversity of Chironomidae ranged from 3 to 37 species. Beta diversity ranged from 0–0.44 and mean beta diversity was 0.17. Species diversity did not correlate to distance between sites. The Chao 1 species estimator estimated 126 species of Chironomidae from the streams in Gorkhi Terelj National Park. Ad hoc analysis comparing chironomid communities from Gorkhi Terelj National Park and Lake Hovsgol area stream and lake sites increased the estimated number of species to 144. Dominant species were used in a double dendrogram analysis which yielded three distinct communities of chironomids which corresponded to three clusters of study sites that differed by habitat type, water quality, and physical characteristics. This study produced data for use in conservation of streams in Gorkhi Terelj National Park.

Macroscale drivers influencing the structural and functional organization of stream macroinvertebrate metacommunities: potential role of hydrological connectivity

We assessed the potential influence of hydrological connectivity among subdrainages on the structural and functional organization of stream macroinvertebrate metacommunities in 2 adjacent, large Asian watersheds (~1.4 million km2). To examine the structural organization of metacommunities, we used multisite β-diversity partitioning and applied the Elements of Metacommunity Structure (EMS) framework to resolve aspects of taxon associations and metacommunity assembly. We also decomposed functional β diversity into nestedness and turnover to assess functional organization of metacommunities among watersheds of contrasting connectivity. To describe changes in functional composition, we used a multidimensional functional trait analysis to calculate the 3 primary components of functional diversity. The nestedness component of β diversity had a higher contribution in the watershed displaying isolated subdrainages, and apparent lack of hydrological connectivity had a significant effect on the ecological fitting of macroinvertebrate metacommunities, generating a discrete composition of communities. Partitioning of functional β diversity suggested no difference among watersheds in metacommunity functional organization and a high level of functional redundancy among communities of subdrainages independent of hydrological isolation. These results show that hydrological connectivity is potentially an important driver structuring stream macroinvertebrate metacommunities at a macroecological scale. Patterns of metacommunity structure were expressed better using taxonomic than functional-trait diversity. In spite of a perceived functional redundancy, a wider functional space was observed in the absence of hydrological connectivity, a result suggesting discrete but partially overlapping functional entities associated with hydrological isolation in these watersheds.

Patterns in Benthic Biodiversity Link Lake Trophic Status to Structure and Potential Function of Three Large, Deep Lakes

Relative to their scarcity, large, deep lakes support a large proportion of the world’s freshwater species. This biodiversity is threatened by human development and is in need of conservation. Direct comparison of biodiversity is the basis of biological monitoring for conservation but is difficult to conduct between large, insular ecosystems. The objective of our study was to conduct such a comparison of benthic biodiversity between three of the world’s largest lakes: Lake Tahoe, USA; Lake Hövsgöl, Mongolia; and Crater Lake, USA. We examined biodiversity of common benthic organism, the non-biting midges (Chironomidae) and determined lake trophic status using chironomid-based lake typology, tested whether community structure was similar between the three lakes despite geographic distance; and tested whether chironomid diversity would show significant variation within and between lakes. Typology analysis indicated that Lake Hövsgöl was ultra-oligotrophic, Crater Lake was oligotrophic, and Lake Tahoe was borderline oligotrophic/mesotrophic. These results were similar to traditional pelagic measures of lake trophic status for Lake Hövsgöl and Crater Lake but differed for Lake Tahoe, which has been designated as ultra-oligotrophic by traditional pelagic measures such as transparency found in the literature. Analysis of similarity showed that Lake Tahoe and Lake Hövsgöl chironomid communities were more similar to each other than either was to Crater Lake communities. Diversity varied between the three lakes and spatially within each lake. This research shows that chironomid communities from these large lakes were sensitive to trophic conditions. Chironomid communities were similar between the deep environments of Lake Hövsgöl and Lake Tahoe, indicating that chironomid communities from these lakes may be useful in comparing trophic state changes in large lakes. Spatial variation in Lake Tahoe’s diversity is indicative of differential response of chironomid communities to nutrient enrichment which may be an indication of changes in trophic state within and across habitats.