Sudeep Chandra

Bio: Sudeep Chandra is an academic researcher from University of Nevada, Reno. The author has contributed to research in topics: Water quality & Benthic zone. The author has an hindex of 23, co-authored 104 publications receiving 2335 citations. Previous affiliations of Sudeep Chandra include University of California, Davis.

Unsaturated fatty acid content in seston and tropho-dynamic coupling in lakes

Abstract: Determining the factors that control food web interactions is a key issue in ecology. The empirical relationship between nutrient loading (total phosphorus) and phytoplankton standing stock (chlorophyll a) in lakes was described about 30 years ago and is central for managing surface water quality. The efficiency with which biomass and energy are transferred through the food web and sustain the production of higher trophic levels (such as fish) declines with nutrient loading and system productivity, but the underlying mechanisms are poorly understood. Here we show that in seston (fine particles in water) during summer, specific omega3-polyunsaturated fatty acids (omega3-PUFAs), which are important for zooplankton, are significantly correlated to the trophic status of the lake. The omega3-PUFAs octadecatetraenoic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid, but not alpha-linolenic acid, decrease on a double-logarithmic scale with increasing total phosphorus. By combining the empirical relationship between EPA-to-carbon content and total phosphorus with functional models relating EPA-to-carbon content to the growth and egg production of daphnids, we predict secondary production for this key consumer. Thus, the decreasing efficiency in energy transfer with increasing lake productivity can be explained by differences in omega3-PUFA-associated food quality at the plant-animal interface.

Morphometry and Average Temperature Affect Lake Stratification Responses to Climate Change

Abstract: Climate change is affecting lake stratification with consequences for water quality and the benefits that lakes provide to society. Here we use long-term temperature data (1970–2010) from 26 lakes around the world to show that climate change has altered lake stratification globally and that the magnitudes of lake stratification changes are primarily controlled by lake morphometry (mean depth, surface area, and volume) and mean lake temperature. Deep lakes and lakes with high average temperatures have experienced the largest changes in lake stratification even though their surface temperatures tend to be warming more slowly. These results confirm that the nonlinear relationship between water density and water temperature and the strong dependence of lake stratification on lake morphometry makes lake temperature trends relatively poor predictors of lake stratification trends.

How important are terrestrial organic carbon inputs for secondary production in freshwater ecosystems

Abstract: 1. Many freshwater systems receive substantial inputs of terrestrial organic matter. Terrestrially derived dissolved organic carbon (t-DOC) inputs can modify light availability, the spatial distrib ...

Historical Food Web Structure and Restoration of Native Aquatic Communities in the Lake Tahoe (California–Nevada) Basin

Abstract: Plans for the restoration of aquatic ecosystems are increasingly focusing on the restoration and rehabilitation of self-sustaining native fish communities. Such efforts have not traditionally adopted an ecosystem-based perspective, which considers species as embedded within a broader food web context. In this study, we quantify food web changes in Lake Tahoe (California-Nevada) over the last century based on stable isotope analysis of museum-archived, preserved fish specimens collected during 4 historical periods and under present conditions. We also examine the contemporary food web of nearby Cascade Lake, which is free from most exotic species and contains a species assemblage resembling that of Lake Tahoe prior to historical species introductions. During the last century, the freshwater shrimp Mysis relicta and lake trout (Salvelinus namaycush) have been introduced and established in Lake Tahoe, and the native top predator, Lahontan cutthroat trout (Oncorhynchus clarki henshawi; hereafter LCT), has been extirpated. Isotope analysis indicates that lake trout now occupy a trophic niche similar to that of historical LCT. Fish production has shifted from benthic to pelagic, corresponding with the eutrophication of Lake Tahoe during recent decades. The current Cascade Lake food web resembles that of the historical Lake Tahoe food web. Our isotope-based food web reconstructions reveal long-term food web changes in Lake Tahoe and can serve as the basis for setting historically relevant restoration targets. Unfortunately, the presence of nonnative species, particularly Mysis and lake trout, have dramatically altered the pelagic food web structure; as such, they are barriers to native fish community restoration. Fish community restoration efforts should focus on adjacent ecosystems, such as Cascade Lake, which have a high likelihood of success because they have not been heavily affected by nonnative introductions.

Widespread deoxygenation of temperate lakes

Abstract: The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity1,2, nutrient biogeochemistry3, greenhouse gas emissions4, and the quality of drinking water5. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity6,7, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production10. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world’s oceans6,7 and could threaten essential lake ecosystem services2,3,5,11. Analysis of temperate lakes finds a widespread decline in dissolved oxygen concentrations in surface and deep waters, which is associated with reduced solubility at warmer surface water temperatures and increased stratification at depth.

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Emerging threats and persistent conservation challenges for freshwater biodiversity

Abstract: In the 12 years since Dudgeon et al. (2006) reviewed major pressures on freshwater ecosystems, the biodiversity crisis in the world’s lakes, reservoirs, rivers, streams and wetlands has deepened. While lakes, reservoirs and rivers cover only 2.3% of the Earth’s surface, these ecosystems host at least 9.5% of the Earth’s described animal species. Furthermore, using the World Wide Fund for Nature’s Living Planet Index, freshwater population declines (83% between 1970 and 2014) continue to outpace contemporaneous declines in marine or terrestrial systems. The Anthropocene has brought multiple new and varied threats that disproportionately impact freshwater systems. We document 12 emerging threats to freshwater biodiversity that are either entirely new since 2006 or have since intensified: (i) changing climates; (ii) e-commerce and invasions; (iii) infectious diseases; (iv) harmful algal blooms; (v) expanding hydropower; (vi) emerging contaminants; (vii) engineered nanomaterials; (viii) microplastic pollution; (ix) light and noise; (x) freshwater salinisation; (xi) declining calcium; and (xii) cumulative stressors. Effects are evidenced for amphibians, fishes, invertebrates, microbes, plants, turtles and waterbirds, with potential for ecosystem-level changes through bottom-up and top-down processes. In our highly uncertain future, the net effects of these threats raise serious concerns for freshwater ecosystems. However, we also highlight opportunities for conservation gains as a result of novel management tools (e.g. environmental flows, environmental DNA) and specific conservation-oriented actions (e.g. dam removal, habitat protection policies,managed relocation of species) that have been met with varying levels of success.Moving forward, we advocate hybrid approaches that manage fresh waters as crucial ecosystems for human life support as well as essential hotspots of biodiversity and ecological function. Efforts to reverse global trends in freshwater degradation now depend on bridging an immense gap between the aspirations of conservation biologists and the accelerating rate of species endangerment.

Global trends in wind speed and wave height over the past 25 years

Abstract: Wind speeds over the world’s oceans have increased over the past two decades, as have wave heights. Studies of climate change typically consider measurements or predictions of temperature over extended periods of time. Climate, however, is much more than temperature. Over the oceans, changes in wind speed and the surface gravity waves generated by such winds play an important role. We used a 23-year database of calibrated and validated satellite altimeter measurements to investigate global changes in oceanic wind speed and wave height over this period. We find a general global trend of increasing values of wind speed and, to a lesser degree, wave height, over this period. The rate of increase is greater for extreme events as compared to the mean condition.

Current knowledge on non-native freshwater fish introductions

Abstract: This review provides a contemporary account of knowledge on aspects of introductions of non-native fish species and includes issues associated with introduction pathways, ecological and economic impacts, risk assessments, management options and impact of climate change. It offers guidance to reconcile the increasing demands of certain stakeholders to diversify their activities using non-native fishes with the long-term sustainability of native aquatic biodiversity. The rate at which non-native freshwater fishes have been introduced worldwide has doubled in the space of 30 years, with the principal motives being aquaculture (39%) and improvement of wild stocks (17%). Economic activity is the principal driver of human-mediated non-native fish introductions, including the globalization of fish culture, whereby the production of the African cichlid tilapia is seven times higher in Asia than in most areas of Africa, and Chile is responsible for c. 30% of the world's farmed salmon, all based on introduced species. Consequently, these economic benefits need balancing against the detrimental environmental, social and economic effects of introduced non-native fishes. There are several major ecological effects associated with non-native fish introductions, including predation, habitat degradation, increased competition for resources, hybridization and disease transmission. Consideration of these aspects in isolation, however, is rarely sufficient to adequately characterize the overall ecological effect of an introduced species. Regarding the management of introduced non-native fish, pre-introduction screening tools, such as the fish invasiveness scoring kit (FISK), can be used to ensure that species are not introduced, which may develop invasive populations. Following the introduction of non-native fish that do develop invasive populations, management responses are typified by either a remediation or a mitigation response, although these are often difficult and expensive to implement, and may have limited effectiveness.