David J. Hoeinghaus

Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong

Basin-scale planning is needed to minimize impacts in mega-diverse rivers The worlds most biodiverse river basins—the Amazon, Congo, and Mekong—are experiencing an unprecedented boom in construction of hydropower dams. These projects address important energy needs, but advocates often overestimate economic benefits and underestimate far-reaching effects on biodiversity and critically important fisheries. Powerful new analytical tools and high-resolution environmental data can clarify trade-offs between engineering and environmental goals and can enable governments and funding institutions to compare alternative sites for dam building. Current site-specific assessment protocols largely ignore cumulative impacts on hydrology and ecosystem services as ever more dams are constructed within a watershed (1). To achieve true sustainability, assessments of new projects must go beyond local impacts by accounting for synergies with existing dams, as well as land cover changes and likely climatic shifts (2, 3). We call for more sophisticated and holistic hydropower planning, including validation of technologies intended to mitigate environmental impacts. Should anything less be required when tampering with the worlds great river ecosystems?

Effects of River Impoundment on Ecosystem Services of Large Tropical Rivers: Embodied Energy and Market Value of Artisanal Fisheries

Applying the ecosystem services concept to conservation initiatives or in managing ecosystem services requires understanding how environmental impacts affect the ecology of key species or functional groups providing the services. We examined effects of river impoundments, one of the leading threats to freshwater biodiversity, on an important ecosystem service provided by large tropical rivers (i.e., artisanal fisheries). The societal and economic importance of this ecosystem service in developing countries may provide leverage to advance conservation agendas where future impoundments are being considered. We assessed impoundment effects on the energetic costs of fisheries production (embodied energy) and commercial market value of the artisanal fishery of the Paraná River, Brazil, before and after formation of Itaipu Reservoir. High-value migratory species that dominated the fishery before the impoundment was built constituted a minor component of the contemporary fishery that is based heavily on reservoir-adapted introduced species. Cascading effects of river impoundment resulted in a mismatch between embodied energy and market value: energetic costs of fisheries production increased, whereas market value decreased. This was partially attributable to changes in species functional composition but also strongly linked to species identities that affected market value as a result of consumer preferences even when species were functionally similar. Similar trends are expected in other large tropical rivers following impoundment. In addition to identifying consequences of a common anthropogenic impact on an important ecosystem service, our assessment provides insight into the sustainability of fisheries production in tropical rivers and priorities for regional biodiversity conservation.

CAN STABLE ISOTOPE RATIOS PROVIDE FOR COMMUNITY-WIDE MEASURES OF TROPHIC STRUCTURE? COMMENT

Over the last few decades, the use of stable isotope ratios in ecological studies has increased greatly, most notably in the area of trophic ecology and food webs (Peterson and Fry 1987, Fry 2006). However, applications of stable isotopes in food web studies have been mostly qualitative to date, prompting the recent development of quantitative approaches to investigate different aspects of trophic ecology and food web structure using stable isotope data (e.g., Bearhop et al. 2004, Newsome et al. 2007, Schmidt et al. 2007). One such contribution (Layman et al. 2007a) proposed a series of six metrics that provide community-wide measures of trophic structure using a dual-isotope framework. However, the metrics as proposed by Layman et al. (2007a) will not accurately represent aspects of trophic structure for most ecological systems. Herein we summarize the framework and metrics proposed by Layman et al. (2007a), identify key limitations that prevent their widespread application, and discuss other directions that may facilitate the development of quantitative food web approaches using stable isotope data.

Landscape-Scale Hydrologic Characteristics Differentiate Patterns of Carbon Flow in Large-River Food Webs

Efforts to conserve, restore, or otherwise manage large rivers and the services they provide are hindered by limited understanding of the functional dynamics of these systems. This shortcoming is especially evident with regard to trophic structure and energy flow. We used natural abundances of carbon and nitrogen isotopes to examine patterns of material flow in ten large-river food webs characterized by different landscape-scale hydrologic characteristics (low-gradient river, high-gradient river, river stretches downstream of reservoirs, and reservoirs), and tested predictions from three ecosystem concepts commonly applied to large-rivers: The River Continuum Concept, The Flood Pulse Concept and the Riverine Productivity Model. Carbon derived from aquatic C3 plants and phytoplankton were the dominant energy sources supporting secondary consumers across the ten large-river food webs examined, but relative contributions differed significantly among landscape types. For low-gradient river food webs, aquatic C3 plants were the principal carbon source, contributing as much as 80% of carbon assimilated by top consumers, with phytoplankton secondarily important. The estimated relative importance of phytoplankton was greatest for food webs of reservoirs and river stretches downriver from impoundments, although aquatic C3 plants contributed similar amounts in both landscape types. Highest 99th percentile source contribution estimates for C4 plants and filamentous algae (both approximately 40%) were observed for high-gradient river food webs. Our results for low-gradient rivers supported predictions of the Flood Pulse Concept, whereas results for the three other landscape types supported the Riverine Productivity Model to varying degrees. Incorporation of landscape-scale hydrologic or geomorphic characteristics, such as river slope or floodplain width, may promote integration of fluvial ecosystem concepts. Expanding these models to include hydrologically impacted landscapes should lead to a more holistic understanding of ecosystem processes in large-river systems.

Spatiotemporal variation in fish assemblage structure in tropical floodplain creeks

Biotic assemblages of aquatic floodplain systems have great potential to randomly reshuffle during annual flood periods, and have been described both as stochastically and deterministically assembled. However, only a limited number of studies have been conducted in relatively few habitat types. To evaluate large-bodied fish assemblage structure of floodplain creeks, we used experimental gill nets to sample fishes at sites spaced at even intervals within three creeks in consecutive dry seasons. A total of 60 species were collected, 41 of which were collected both years. The most frequently collected species were piscivores and algivores/detritivores. Multivariate analysis suggested non-random patterns of assemblage structure in both years. Correspondence analysis (CA) of the species abundance-by-site matrix for 2001 suggests species assemblages were most similar among sites within the same creek regardless of depth or longitudinal position. Discriminant function analysis (DFA) correctly predicted 100% of samples based on creek identity, and species ordination scores revealed creek-specific species subsets. In 2002, CA and DFA did not distinguish creeks based on species assemblages. Instead, we observed a significant positive relationship between assemblage composition and site depth and position along the creek longitudinal gradient. Assemblages were most similar among sites of comparable depth and longitudinal position, regardless of creek identity. Predators occurred almost exclusively at mouth and mid-reach sites. Flood duration prior to our 2002 sampling period was prolonged due to abnormally heavy rainfall in November and December 2001 (typically the falling-water period), and may account for the observed inter-annual variation in fish assemblage structure.

Loss of Rare Fish Species from Tropical Floodplain Food Webs Affects Community Structure and Ecosystem Multifunctionality in a Mesocosm Experiment

Experiments with realistic scenarios of species loss from multitrophic ecosystems may improve insight into how biodiversity affects ecosystem functioning. Using 1000 L mesocoms, we examined effects of nonrandom species loss on community structure and ecosystem functioning of experimental food webs based on multitrophic tropical floodplain lagoon ecosystems. Realistic biodiversity scenarios were developed based on long-term field surveys, and experimental assemblages replicated sequential loss of rare species which occurred across all trophic levels of these complex food webs. Response variables represented multiple components of ecosystem functioning, including nutrient cycling, primary and secondary production, organic matter accumulation and whole ecosystem metabolism. Species richness significantly affected ecosystem function, even after statistically controlling for potentially confounding factors such as total biomass and direct trophic interactions. Overall, loss of rare species was generally associated with lower nutrient concentrations, phytoplankton and zooplankton densities, and whole ecosystem metabolism when compared with more diverse assemblages. This pattern was also observed for overall ecosystem multifunctionality, a combined metric representing the ability of an ecosystem to simultaneously maintain multiple functions. One key exception was attributed to time-dependent effects of intraguild predation, which initially increased values for most ecosystem response variables, but resulted in decreases over time likely due to reduced nutrient remineralization by surviving predators. At the same time, loss of species did not result in strong trophic cascades, possibly a result of compensation and complexity of these multitrophic ecosystems along with a dominance of bottom-up effects. Our results indicate that although rare species may comprise minor components of communities, their loss can have profound ecosystem consequences across multiple trophic levels due to a combination of direct and indirect effects in diverse multitrophic ecosystems.

Preliminary examination of food web structure of Nicola Lake (Taim Hydrological System, south Brazil) using dual C and N stable isotope analyses

Taim Ecological Reserve is located within the Taim Hydrological System and was created to protect a heterogeneous and productive landscape harboring exceptional biological diversity in southern Brazil. Using stable isotope ratio analyses of carbon (d13C) and nitrogen (d15N), we provide a preliminary description of the food web structure, including estimates of production sources supporting fish populations and vertical trophic structure, within a representative lake of this system. A total of 21 organisms (5 macrophytes, 3 mollusks and 13 adult fishes) representing 16 species were collected for isotope analysis. Fishes had d13C values ranging from -24.30o/oo to -28.31o/oo , showing concordance with the range of values observed for macrophytes (-25.49 to -27.10o/oo), and suggesting that these plants could be a major carbon source supporting these fishes. d13C signatures of Corbicula (-30.81o/oo) and Pomacea (-24.26o/oo) indirectly suggest that phytoplankton and benthic algae could be alternative carbon sources for some consumers. Nitrogen isotope ratios indicated approximately three consumer trophic levels. The pearl cichlid Geophagus brasiliensis was a primary consumer. Two catfishes (Trachelyopterus lucenai and Loricariichthys anus) were secondary consumers. Two congeneric pike cichclids (Crenicichla lepidota and C. punctata), a catfish (Pimelodus maculatus) and the characids Astyanax fasciatus and Oligosarcus robustus were tertiary consumers. Further studies including additional primary producers and consumers and greater sample numbers should be conducted to provide a more complete and detailed description of food web structure and dynamics within the reserve.

Estuary hydrogeomorphology affects carbon sources supporting aquatic consumers within and among ecological guilds

The relative importance of carbon sources supporting aquatic food webs within and among estuaries may be influenced by factors that affect relative availability of autotrophic carbon sources, as well as movement of individuals among marine, estuarine and freshwater zones. We used stable isotopes of carbon and nitrogen to examine (1) the relative importance of carbon sources supporting estuarine consumers among estuaries with different hydrogeomorphic characteristics, (2) stable isotope signatures of consumer ecological guilds defined by dependence on estuarine habitats and residence time, and (3) if patterns in stable isotope signatures of ecological guilds repeat across estuaries with distinct hydrogeomorphological features. At the assemblage level, consumer carbon isotope signatures reflected the consumption of locally abundant primary production sources and differed across estuary types (choked lagoon, coastal river). Consumer ecological guilds differed in δ13C within sites, and the same trend repeated across sites but with differing magnitudes. This variation is attributed to movement and residence patterns in addition to differences in the relative abundances of autotrophic sources across sites. Although within-estuary variation in consumer resource use is to be expected, estuarine food webs may be broadly classified according to landscape-scale hydrogeomorphic factors that allow an initial prediction of the relative importance of carbon sources to secondary production. Predictions may be refined at the species level using knowledge of habitat use and residence time. Such predictions are useful as a starting point for poorly studied regions such as ours in southern Brazil, as well as for global-scale analyses of patterns in estuarine food webs.

Compositional change in fish assemblages along the Andean piedmont - Llanos floodplain gradient of the río Portuguesa, Venezuela

Llanos corresponde a uma area extensa de savanas e planicies de inundacao situadas no centro e no oeste da Venezuela, abrangendo um gradiente de elevacao desde o rio Orinoco ate a regiao montanhosa na base da cordilheira dos Andes. O rio Portuguesa e um dos principais rios desta regiao, ate recentemente livre de maiores impactos antropogenicos, mantendo relevantes migracoes sazonais de peixes. Apesar disto, poucos estudos sobre ecologia de peixes tem sido conduzidos neste ambiente. O presente estudo analisa colecoes de museus amostradas em 28 locais ao longo do gradiente longitudinal do rio Portuguesa, avaliando a similaridade na composicao das especies desde a regiao montanhosa na base da cordilheira dos Andes ate as terras baixas da planicie de inundacao do Llanos. As amostras padronizadas utilizadas nesta analise continham mais de 133 especies, representando 6 ordens e 27 familias, dominadas por caraciformes (61 especies) e siluriformes (52 especies). A ordenacao das amostras atraves da analise de correspondencia com remocao do efeito do arco (DCA) revelou um padrao continuo de mudanca na composicao, com taxa de adicao de especies superior a de perda no sentido base da cordilheira ao baixo Llanos. Com base na DCA, as amostras dos tres segmentos com distintas altitudes apresentaram diferencas significativas na composicao das especies de peixes. Assembeias do trecho superior contiveram unicamente especies de loricarideos, pimelodideos de pequeno porte e tricomicterideos, alem de caraciformes de pequeno porte nao observados nos segmentos inferiores. O trecho inferior apresentou especies de ciclideos, bagres de grande porte e caracideos nao coletados nas outras duas regioes. Amostras do trecho intermediario revelaram uma composicao transicional de especies. A alteracao longitudinal na composicao de especies reflete, provavelmente, diferencas nas caracteristicas ambientais, como: velocidade da agua, composicao do substrato e regime de disturbio. Os achados desta analise de ampla-escala podem contribuir como ponto de partida para futuros estudos de ecologia de peixes nesta regiao.

Fracking vs Faucets: Balancing Energy Needs and Water Sustainability at Urban Frontiers

ewly accessible shale deposits have dramatically increasedglobal gas reserves and are touted as a bridge to a cleanenergy future. For example, in the U.S., where shale gas isprojected to comprise 49% of national natural gas productionby 2035, proponents argue that shale gas production canprovide energy independence, create employment, andstimulate regional economies.