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Using mollusks as indicators of restoration in nearshore zones of south Florida's estuaries

Current south Florida ecosystem restoration efforts are focused on restoring more natural freshwater flow through the wetlands and into the estuaries to reestablish natural salinity gradients, particularly in the nearshore zones. Indicator taxa are used to monitor and assess restoration progress and the current suite of biota used for the estuaries in south Florida (Biscayne Bay, Florida Bay, and the southwest mangrove riverine system) does not include mollusks. Mollusks make excellent indicators because they are found in all south Florida environments, are relatively stationary in postlarval stages, and, therefore, do not leave a site when conditions change. Their hard shells increase the likelihood of preservation after death, thus, making it possible to assess death assemblages. In addition to these features, many mollusks can be quickly sampled in the field and assessed in the lab, so poor visibility and tidal cycles are not an issue for monitoring surveys. Here we examine 27 years of molluscan data from 887 samples from 640 visits to 167 sites in south Florida's estuaries and present a suite of taxa that could be used as indicators for restoration of the oligohaline to mesohaline (0.5 to 17.9 psu) nearshore zones. Cyrenoida floridana , Hydrobiidae, Polymesoda caroliniana , Crassostrea virginica , and additional taxa are included with suggested sampling strategies.

Florida

Loads of nitrate, phosphorus, and total suspended solids from Indiana watersheds

Transport of excess nutrients and total suspended solids (TSS) such as sediment by freshwater systems has led to degradation of aquatic ecosystems around the world. Nutrient and TSS loads from Midwestern states to the Mississippi River are a major contributor to the Gulf of Mexico Hypoxic Zone, an area of very low dissolved oxygen concentration in the Gulf of Mexico. To better understand Indiana’s contribution of nutrients and TSS to the Mississippi River, annual loads of nitrate plus nitrite as nitrogen, total phosphorus, and TSS were calculated for nine selected watersheds in Indiana using the load estimation model, S-LOADEST. Discrete water-quality samples collected monthly by the Indiana Department of Environmental Management’s Fixed Stations Monitoring Program from 2000–2010 and concurrent discharge data from the U. S. Geological Survey streamflow gages were used to create load models. Annual nutrient and TSS loads varied across Indiana by watershed and hydrologic condition. Understanding the loads from large river sites in Indiana is important for assessing contributions of nutrients and TSS to the Mississippi River Basin and in determining the effectiveness of best management practices in the state. Additionally, evaluation of loads from smaller upstream watersheds is important to characterize improvements at the local level and to identify priorities for reduction.

Proceedings of the Indiana Academy of Science

Cape Romain partnership for coastal protection

This final report summarizes activities, outcomes, and lessons learned from a 3-year project titled “Climate Change Adaptation for Coastal National Wildlife Refuges” with the Cape Romain National Wildlife Refuge (NWR) and local partners in the surrounding South Carolina Lowcountry. The Lowcountry is classified as the 10-county area encompassing the coastal plain of South Carolina (this report specifically focuses on Berkeley, Charleston, and Georgetown Counties). The goals of this work, sponsored by the U.S. Geological Survey’s Southeast Climate Adaptation Science Center (SECASC), were to foster active engagement with stakeholders; to develop a comprehensive definition of adaptation problems faced by agencies, organizations, and individuals near the Cape Romain NWR that accounts for global change, local values, knowledge and perceptions; and to encourage social learning and building of effective networks and trust across South Carolina Lowcountry organizations and individuals. Although project scoping began at the scale of the Atlantic seaboard, by engaging with NWRs from Massachusetts to Florida, participating refuge personnel eventually selected the Cape Romain NWR to serve as a case study for testing our goals. The Cape Romain Partnership for Coastal Conservation was established to address global change impacts at a regional level and includes representation from Federal and State resource agencies, local conservation nongovernmental organizations, and organizations representing underserved community interests. Research topics, originating from discussions with Cape Romain Partnership for Coastal Conservation members, focused on quantifying key drivers of change including localized sea-level rise (SLR) predictions, estimates of coastal hurricane inundation as amplified by SLR, and urban growth trends and forecasts. These key drivers provided a foundation to engage stakeholders in planning exercises to begin a process of collective understanding and collaborative decision making. The goal of this process was to develop collective strategies of adaptation to enhance community and ecosystem resilience in the South Carolina Lowcountry. South Carolina’s Lowcountry is experiencing rapid environmental and social transformation because of SLR rates approaching twice the global average, chronic tidal flooding and catastrophic storm surges, erosion and loss of habitats that provide essential services to wildlife and humans, and increasing social polarization fueled by aggressive low-density urban growth and other forms of land conversion. To support characterizations of plausible future scenarios, we used available or, in some cases, developed new models to project future conditions of key environmental and social-economic drivers. Because of the imprecision of mean global SLR projections, the SECASC commissioned a climatological study to account for local conditions and multiple representative concentration pathways to project a tailored distribution of future sea levels. These projections were matched to SLR scenarios provided by existing models to anticipate the range of future coastal habitat changes in the South Carolina Lowcountry. SLR scenarios were also incorporated into existing storm-surge models, which do not account for alternate baseline sea levels, to project the local effects of future hurricanes. To evaluate the extent and effects of population growth and urban expansion, we relied on an existing urban-growth model to map the spatial distribution of land-conversion probabilities, the total area of which is predicted to increase twofold to threefold over the next 60 years. In addition to this simplified model, an econometric model is in development to account for nonlinear feedback dynamics in land value, land use, and ecosystem service production. Although not yet completed, the goals of this model are to produce more-detailed projections of growth dynamics and to allow predictions of development patterns resulting from alternate land-use planning policies and incentives. Collaborative planning for an uncertain future requires more than providing decision makers with information on future physical and ecological conditions; developing effective and consensual strategies must also integrate sociological values, multiple cultural perspectives, and an understanding of human behavior. To support broad stakeholder engagement in integrative approaches to adaptation planning, emphasis was placed on the importance of considering differences in how individuals perceive their environment and create meaning. Because cultural frameworks form the basis for perceptions and, ultimately, the behaviors of individuals and institutions, we describe a model of human behavior and how it can be used to understand the effect of cultural complexity and variation in perception on choices, behavioral change, and long-term maintenance of behaviors. We consider a model commonly used in the field of behavioral health that accommodates variation in human perception when describing stages of behavior and the dynamics of behavioral change. Tailoring communication and engagement activities to targeted stakeholders is likely to benefit from increased understanding of behavioral change processes. The complex nature of this problem limited the usefulness of a traditional decision-analytic approach, we explored alternative methods for engagement, collaborative learning and decision making. Recognizing that project partners and Lowcountry stakeholders may be at different stages of preparedness and interest level for modifying behavior as a function of global change, we facilitated a scenario-planning exercise to familiarize partners with this well-established approach for communicating the opportunities and threats arising under alternative, plausible futures. We developed narratives for four alternative South Carolina Lowcountry scenarios to be used in later strategic planning that focus on quantitative trends for three primary drivers with high impact and high uncertainty: manifestations of climate change, social-political shifts at a global level, and forces of local value and power structures. This scenario-planning exercise underscored the complex relation between the temporospatial scale of the production of ecological goods and services and the institutional scale at which they are managed. We then guided the partners through an assessment of the relevant strengths and weaknesses of the Cape Romain Partnership for Coastal Protection, using the threats and opportunities characterized by each scenario to understand how the partnership might respond when attempting to meet conservation and societal objectives. The partnership identified key strengths including partnership experience, outreach and technical capacities, a substantial conservation land base, and high social cohesion in the South Carolina Lowcountry. Limited communication expertise, institutional inertia, and insufficient staffing and funding were recognized as important weaknesses across the partnership. By examining and scoring combinations of internal strengths and weaknesses and external threats and opportunities, the partnership developed sets of prioritized strategies to consider in the context of a given scenario. Although we had insufficient time to examine all scenarios in detail, the intent was to identify a portfolio of strategic actions to address threats and opportunities represented in multiple plausible futures. Top-ranking strategies encompassed a range of actions that focused on strengthening the conservation community and communicating the benefits of nature (that is, ecosystem services) to leveraging partnerships to expand land protection. This report also details the methods and preliminary results of several models developed or applied in support of this project. Two parcel-selection algorithms were used to evaluate anticipated habitat changes and patterns of urban growth to guide decisions on optimal conservation reserve design to protect habitat communities. One approach used a widely available planning software (MARXAN) to maximize conservation benefits near the Cape Romain NWR, whereas the other approach was a novel application of economic theory to account for uncertainty in future conditions and for the risks of unanticipated habitat loss. This latter model applies modern portfolio theory to estimate the risk of investing in any portfolio of land parcels (that is, candidate “reserves”) under climate-change uncertainty by quantifying the variation and spatial correlation of conservation benefits derived from each portfolio. We expanded the range of actions beyond simply whether or not to invest in a set of land parcels, an approach commonly used in spatial conservation planning, to also include consideration of divestment from currently protected lands. Such refinements allow for better accounting of system dynamics and can evaluate the benefits of flexible conservation tools such as rolling easements. Model results were conditional on a decision maker’s risk tolerance but highlighted general strategies of land conservation to increase future habitat representation beyond what is expected under the current protected land base. We built models that may help inform coastal planning by estimating salinity dynamics and the performance of oyster reef restoration efforts to predict the combined effects of global change and management of freshwater flows on coastal habitats and the processes that contribute to their resilience. These models can support restoration decisions by evaluating the expected benefits of site locations for shoreline protection and fisheries production. Lastly, we developed a spatially explicit economic model that predicts feedback dynamics among land value, land-use change, and effects on ecosystem service provision to explore zoning policies and incentives on urban growth and ecosystem services. We summarize these efforts with insights and considerations for the Cape Romain Partnership for Coastal Protection to continue to engage stakeholders in effective adaptation planning. First, notions of place attachment (referred to as sense of place), and the role of culture in social discourse are increasingly being used to understand the complex interactions between society and the environment and how societies respond and adapt to climate change. Sense of place was a unifying theme whenever the future of the South Carolina Lowcountry was discussed. The contribution of the South Carolina Lowcountry’s environmental wealth, rich cultural heritage, and quality of life to sense of place has important implications for how adaptation planning might best be pursued. More community-based governance of the commons (in other words, natural and cultural resources held in common), in which broad stakeholder participation and power sharing are key elements, is considered important. This devolution of governance is characterized by polycentric institutions and self-organizing social networks that promote a local culture of knowledge sharing, problem solving, and learning. These so-called bridging organizations (or individuals) often provide the leadership necessary to bring together potentially disparate Government agencies and institutions, private organizations, and individuals in a collective process of problem solving. Our observations also suggest that the conservation community in the South Carolina Lowcountry views its activities as integral to the broader governance of social-ecological systems, in which responses to the forces of global change are mediated through culture, economics, and politics. Rather than directly competing with other interests, the South Carolina Lowcountry conservation community seems to embrace an interpretation of conservation in which the fundamental objective is the quality of human life rather than environmental protection. Fundamental to the types of governance reforms described above is the notion of coproduction, in which experts and users collaborate to develop a shared body of knowledge. In this approach, scientists work with stakeholders to help frame questions, design research, and collect and analyze data. Such sustained collaborations are increasingly believed to be an effective way to produce useable (or actionable) science. The emphasis on social learning, leveraging strong social networks, coordinating and deliberating among diverse stakeholders, and applying principles of adaptive management is an essential contribution to adaptive capacity. The diverse and robust set of scientific approaches, methods to help stakeholders collaborate in effective and goal-driven planning processes, and decision tools resulting from this project hopefully will assist Cape Romain NWR and its partners prepare for climatic, ecological, and social changes over the coming decades.

South Carolina

Selenium accumulation in benthic bivalves and fine sediments of San Francisco Bay, the Sacramento-San Joaquin Delta, and selected tributaries

Spatial distributions of selenium were determined in fine-grained, oxidized, surface sediments and in two benthic bivalves ( Corbicula sp., a suspension-feeding freshwater clam, and Macoma balthica , a deposit-feeding brackish-water clam) within San Francisco Bay, the San Joaquin River and three river systems unlikely to be subject to selenium inputs. Biologically available selenium enters the middle reaches of the San Joaquin River from agricultural runoff. However, selenium concentrations in sediments and Corbicula in the lower San Joaquin, upstream from San Francisco Bay, were not significantly different from concentrations in rivers with no known selenium inputs. Biologically available selenium did not appear to enter the northernmost reach of San Francisco Bay from the San Joaquin River in levels which could measurably influence bioaccumulation by Corbicula . Selenium concentrations in Corbicula were enriched in the northernmost reach of San Francisco Bay compared with the rivers, but several lines of evidence suggested that local inputs (perhaps from urban/industrial waste discharges) were the most important sources. Selenium concentrations in Macoma balthica were also elevated at one station in the northern reach of the Bay and at one station in the extreme South Bay. However, no enrichment was evident at two other stations, suggesting a lack of bay-wide contamination. No significant correlation between selenium and mercury concentrations in Corbicula tissues was observed.

California

Spatial dependence of reduced sulfur in Everglades dissolved organic matter controlled by sulfate enrichment

Sulfate inputs to the Florida Everglades stimulate sulfidic conditions in freshwater wetland sediments that affect ecological and biogeochemical processes. An unexplored implication of sulfate enrichment is alteration of the content and speciation of sulfur in dissolved organic matter (DOM), which influences the reactivity of DOM with trace metals. Here, we describe the vertical and lateral spatial dependence of sulfur chemistry in the hydrophobic organic acid fraction of DOM from unimpacted and sulfate-impacted Everglades wetlands using X-ray absorption spectroscopy and ultrahigh-resolution mass spectrometry. Spatial variation in DOM sulfur content and speciation reflects the degree of sulfate enrichment and resulting sulfide concentrations in sediment pore waters. Sulfur is incorporated into DOM predominantly as highly reduced species in sulfidic pore waters. Sulfur-enriched DOM in sediment pore waters exchanges with overlying surface waters and the sulfur likely undergoes oxidative transformations in the water column. Across all wetland sites and depths, the total sulfur content of DOM correlated with the relative abundance of highly reduced sulfur functionality. The results identify sulfate input as a primary determinant on DOM sulfur chemistry to be considered in the context of wetland restoration and sulfur and trace metal cycling.

Florida

The utility of zooarchaeological data to guide listing efforts for an imperiled mussel species (Bivalvia: Unionidae: Pleurobema riddellii)

The status of species in freshwater systems shift over time due to natural and anthropogenic causes. Determining the magnitude and cause of these shifts requires a long-term perspective. This process is complicated when there are also questions about the taxonomic validity of a species. Addressing these issues is important because both can undermine conservation and management efforts if incorrect. Pleurobema riddellii , Louisiana Pigtoe, is under review for protection under the U.S. Endangered Species Act, but its status in the Trinity River basin, where the taxon was described, remains in doubt due to questions about its taxonomy and occurrence within this basin. To address these questions, we compared shell morphometrics of P. riddellii dating to the late Holocene with modern P. riddellii , late Holocene Fusconaia sp., and modern Fusconaia sp. using multivariate analyses to test associations between the putative morphotypes. Based on these analyses, we demonstrate that P. riddellii was likely present in the Trinity during the late Holocene, which indicates questions about its taxonomic validity or presence in this basin are unfounded. Our study further highlights the role zooarchaeological studies can play in status assessments and their utility in better understanding biogeographic patterns for rare species.

Texas

Role of anaerobic ammonium oxidation (anammox) in nitrogen removal from a freshwater aquifer

Anaerobic ammonium oxidation (anammox) couples the oxidation of ammonium with the reduction of nitrite, producing N 2 . The presence and activity of anammox bacteria in groundwater were investigated at multiple locations in an aquifer variably affected by a large, wastewater-derived contaminant plume. Anammox bacteria were detected at all locations tested using 16S rRNA gene sequencing and quantification of hydrazine oxidoreductase ( hzo ) gene transcripts. Anammox and denitrification activities were quantified by in situ 15 NO 2 – tracer tests along anoxic flow paths in areas of varying ammonium, nitrate, and organic carbon abundances. Rates of denitrification and anammox were determined by quantifying changes in 28 N 2 , 29 N 2 , 30 N 2 , 15 NO 3 – , 15 NO 2 – , and 15 NH 4 + with groundwater travel time. Anammox was present and active in all areas tested, including where ammonium and dissolved organic carbon concentrations were low, but decreased in proportion to denitrification when acetate was added to increase available electron supply. Anammox contributed 39–90% of potential N 2 production in this aquifer, with rates on the order of 10 nmol N 2 –N L –1 day –1 . Although rates of both anammox and denitrification during the tracer tests were low, they were sufficient to reduce inorganic nitrogen concentrations substantially during the overall groundwater residence times in the aquifer. These results demonstrate that anammox activity in groundwater can rival that of denitrification and may need to be considered when assessing nitrogen mass transport and permanent loss of fixed nitrogen in aquifers.

Environmental Science & Technology

Physiological and endocrine changes in Atlantic salmon smolts during hatchery rearing, downstream migration and ocean entry

Billions of hatchery salmon smolts are released annually in an attempt to mitigate anthropogenic impacts on freshwater habitats, often with limited success. Mortality of wild and hatchery fish is high during downstream and early ocean migration. To understand changes that occur during migration, we examined physiological and endocrine changes in Atlantic salmon (Salmo salar) smolts during hatchery rearing, downstream migration, and early ocean entry in two successive years. Gill Na + /K + -ATPase activity increased in the hatchery during spring, increased further after river release, and was slightly lower after recapture in the ocean. Plasma growth hormone levels increased in the hatchery, were higher in the river, and increased further in the ocean. Plasma IGF-I remained relatively constant in the hatchery, increased in the river, then decreased in the ocean. Plasma thyroid hormones were variable in the hatchery, but increased in both river- and ocean-captured smolts. Naturally reared fish had lower condition factor, gill NKA activity, and plasma thyroxine than hatchery fish in the river but were similar in the ocean. This novel data set provides a vital first step in understanding the role and norms of endocrine function in smolts and the metrics of successful marine entry.

Maine

Estuarine submerged aquatic vegetation habitat provides organic carbon storage across a shifting landscape

Submerged aquatic vegetation (SAV) thrives across the estuarine salinity gradient providing valuable ecosystem services. Within the saline portion of estuaries, seagrass areas are frequently cited as hotspots for their role in capturing and retaining organic carbon (C org ). Non-seagrass SAV, located in the fresh to brackish estuarine areas, may also retain significant soil C org , yet their role remains unquantified. Given rapidly occurring landscape and salinity changes due to human and natural disturbances, landscape level carbon pool estimates from estuarine SAV habitat blue carbon estimates are needed. We assessed C org stocks in SAV habitat soils from estuarine freshwater to saline habitats (interior deltaic) to saline barrier islands (Chandeleur Island) within the Mississippi River Delta Plain (MRDP), Louisiana, USA. SAV habitats contain C org stocks equivalent to those reported for other estuarine vegetation types (seagrass, salt marsh, mangrove). Interior deltaic SAV C org stocks (231.6 ± 19.5 Mg C org ha −1 ) were similar across the salinity gradient, and significantly higher than at barrier island sites (56.6 ± 10.4 Mg C org ha −1 ). Within the MRDP, shallow water SAV habitat covers up to an estimated 28,000 ha, indicating that soil C org storage is potentially 6.4 ± 0.1 Tg representing an unaccounted C org pool. Extrapolated across Louisiana, and the Gulf of Mexico, this represents a major unaccounted pool of soil C org . As marshes continue to erode, the ability of coastal SAV habitat to offset some of the lost carbon sequestration may be valuable. Our estimates of C org sequestration rates indicated that conversion of eroding marsh to potential SAV habitat may help to offset the reduction of C org sequestration rates. Across Louisiana, we estimated SAV to offset this loss by as much as 79,000 Mg C yr −1 between the 1960s and 2000s.

Louisiana

Ecosystem-engineered infections: Beaver-modified wetlands are associated with conflicting drivers of amphibian pathogen prevalence

Beavers are ecosystem engineers and keystone species that protect freshwater resources and increase biodiversity. Beaver reintroductions are promoted for amphibian conservation, yet their impact on Batrachochytrium dendrobatidis (Bd), a pathogen linked with amphibian population declines worldwide, remains unclear. We investigated the abiotic and biotic drivers of Bd prevalence in Columbia spotted frogs ( Rana luteiventris ) and western toads ( Anaxyrus boreas ) in 20 beaver-modified and 23 non-beaver wetlands in Glacier National Park, USA. We found that beavers increased wetland hydroperiod, which was associated with higher Bd prevalence. However, beavers also reduced wetland canopy cover, which was associated with lower Bd prevalence. Our models also predicted higher Bd prevalence associated with higher adult density of both species of amphibians, although species’ densities were similar in beaver-modified and non-beaver wetlands. These results suggest that beavers have a cumulatively negligible net effect on Bd prevalence owing to their effects on both hydroperiod and canopy cover, which is encouraging for amphibian conservation. Our findings also suggest that decreasing canopy cover may be a potential management option to reduce Bd prevalence. In addition, these findings indicate that beaver-mimicking restoration projects may harm amphibian populations if they increase wetland hydroperiods without reducing canopy cover.

Montana

Impacts of acute and chronic suspended solids exposure on juvenile freshwater mussels

Construction activities may affect adjacent water systems by introducing increased levels of suspended solids into the water body and may subsequently affect the survival and growth of freshwater mussels. We tested three sediment types from sites in Missouri, including Spring River sediment (SRS), Osage River bank clay soil (ORC), and quarried limestone from Columbia (LMT). We prepared series of suspensions of each sediment with total suspended solids concentrations ranging from 0 to 5000 mg/L. Juveniles from three mussel species, Fatmucket ( Lampsilis siliquoidea ), Arkansas Brokenray ( Lampsilis reeveiana ), and Washboard ( Megalonaias nervosa ) were exposed to these suspensions in both acute (96-h) and chronic (28-d) tests. No clear impact on survival was observed from the acute or chronic exposures, but chronic test showed that juvenile mussels' growth was strongly affected. Interestingly, growth was enhanced at lower levels of SRS and ORC (≤500 mg/L, p < 0.05), and the juvenile mussels exposed to 500 mg/L SRS exhibited approximately 60 % more dry weight than those reared in the control. LMT did not enhance growth. Growth was slowed by high concentrations (>1000 mg/L) of all three sediments, implying that high suspended solids levels could reduce survival in the long term. Our findings may help to inform regulations and guidelines for construction activities to minimize adverse effects on juvenile mussels.

Science of the Total Environment

Research in thermal biology: Burning questions for coldwater stream fishes

With the increasing appreciation of global warming impacts on ecological systems, in addition to the myriad of land management effects on water quality, the number of literature citations dealing with the effects of water temperature on freshwater fish has escalated in the past decade. Given the many biological scales at which water temperature effects have been studied, and the growing need to integrate knowledge from multiple disciplines of thermal biology to fully protect beneficial uses, we held that a survey of the most promising recent developments and an expression of some of the remaining unanswered questions with significant management implications would best be approached collectively by a diverse research community. We have identified five specific topic areas of renewed research where new techniques and critical thought could benefit coldwater stream fishes (particularly salmonids): molecular, organism, population/species, community and ecosystem, and policy issues in water quality. Our hope is that information gained through examination of recent research fronts linking knowledge at various scales will prove useful in managing water quality at a basin level to protect fish populations and whole ecosystems. Standards of the past were based largely on incipient lethal and optimum growth rate temperatures for fish species, while future standards should consider all integrated thermal impacts to the organism and ecosystem. ?? Taylor and Francis Group, LLC.

Reviews in Fisheries Science

River discharge controls phytoplankton dynamics in the northern San Francisco Bay estuary

Phytoplankton dynamics in the upper reach of the northern San Francisco Bay estuary are usually characterized by low biomass dominated by microflagellates or freshwater diatoms in winter, and high biomass dominated by neritic diatoms in summer. During two successive years of very low river discharge (the drought of 1976-77), the summer diatom bloom was absent. This is consistent with the hypothesis that formation of the diatom population maximum is a consequence of the same physical mechanisms that create local maxima of suspended sediments in partially-mixed estuaries: density-selective retention of particles within an estuarine circulation cell. Because the estuary is turbid, calculated phytoplankton growth rates are small in the central deep channel but are relatively large in lateral shallow embayments where light limination is less severe. When river discharge falls within a critical range (100–350 m 3 s −1 ) that positions the suspended particulate maximum adjacent to the productive shallow bays, the population of neritic diatoms increases. However, during periods of high discharge (winter) or during periods of very low discharge (drought), the suspended particulate maximum is less well-defined and is uncoupled (positioned downstream or upstream) from the shallow bays of the upper estuary, and the population of neritic diatoms declines. Hence, the biomass and community composition of phytoplankton in this estuary are controlled by river discharge.

California

Patterns and processes of wetland loss in coastal Louisiana are complex: A reply to Turner 2001. Estimating the indirect effects of hydrologic change on wetland loss: If the Earth is curved, then how would we know it?

The coastal wetlands of Louisiana comprise a vast expanse of marine to freshwater wetland plant communities interspersed w-ith shallow bays and bayous. These wetlands were built by processes associated with the present-day Mississippi and Atchatfalaya River deltas and older distributaries occupied by the river over the past 7,000 }rears. The high rates of wetland loss identified in this system during the 20th century have serious consequences for living resources (Boesch et al. 1994) and coastal residents, and they affect our ability to maintain navigation and flood control. The restoration and management response to this problem must be grounded in a sound understanding of the causative factors. The system has been highly altered by river levees, roads and railway embankments, impoundments, and canals of many dimensions dredged for a variety of purposes. These changes have been imposed on a landscape that is essentially the result of a delicate natural balance between wetland building processes and compaction, subsidence, and sea-level rise. Many now recognize that coastal wetlands can cope with relatively high rates of subsidence and sea-level rise, as long as the processes that ensure wetland sustainability through vertical accumulation of substrate remain unimpaired (Boesch et al. 2000). The challenge facing both the scientific community and coastal resource managers in Louisiana is to look to the future. We must use our understanding of the problem and how it evolved to develop a multi-use ecosystem management plan, and some efforts have been made by state and federal agencies towards this goal (LCWCRTF & WCRA 1998). The present discussions (Turner 1997, 2001; Day et al. 2000; Gosselink 2001) demonstrate the complexity of the issues faced in Louisiana. While such discourse is common in the scientific community where varied approaches and interpretations are a sign of vitality, it is helpful to be clear about the state of knowledge and what levels of uncertainty exist. We seek to clarify some of the issues that have been raised in the discussion, recognizing that our best-available science cannot yet resolve many of them as completely as all would like.

Louisiana

Impact of thermoelectric power plant operations and water use reporting methods on thermoelectric power plant water use

Thermoelectric power generation accounts for over 41% of total U.S. freshwater withdrawals, making understanding the determinants of power plants’ water withdrawals (WW) and consumption (WC) critical for reducing the sector’s reliance on increasingly scarce water resources. However, reported data inconsistencies and incomplete analysis of potential determinants of thermoelectric water use hinder such understanding. We address these challenges by introducing a novel data filtering method and a more complete assessment of water use determinants. First, we applied a power-cooling ratio as an operations-based data filter that removed operationally implausible records while retaining more original data, outperforming previous statistical filtering methods. Second, we found that different water use reporting methods (WURMs) provided statistically significantly different WW and WC values, revealing the importance of this previously unrecognized feature in reported water use records. Third, our data-driven approach showed that traditionally emphasized features─such as cooling technology and gross generation─are of primary importance but can be surpassed by other, often overlooked, features when modeling WW or WC individually. The plant configuration, cooling technology, and gross generation were the most important features of WW, whereas WURM, cooling technology, and reporting month were the most important for WC. These findings can improve thermoelectric power plant management, water use reporting accuracy, and water use modeling.

Environmental Science & Technology

Plastic debris in 29 Great Lakes tributaries: Relations to watershed attributes and hydrology

Plastic debris is a growing contaminant of concern in freshwater environments, yet sources, transport, and fate remain unclear. This study characterized the quantity and morphology of floating micro- and macroplastics in 29 Great Lakes tributaries in six states under different land covers, wastewater effluent contributions, population densities, and hydrologic conditions. Tributaries were sampled three or four times each using a 333 μm mesh neuston net. Plastic particles were sorted by size, counted, and categorized as fibers/lines, pellets/beads, foams, films, and fragments. Plastics were found in all 107 samples, with a maximum concentration of 32 particles/m 3 and a median of 1.9 particles/m 3 . Ninety-eight percent of sampled plastic particles were less than 4.75 mm in diameter and therefore considered microplastics. Fragments, films, foams, and pellets/beads were positively correlated with urban-related watershed attributes and were found at greater concentrations during runoff-event conditions. Fibers, the most frequently detected particle type, were not associated with urban-related watershed attributes, wastewater effluent contribution, or hydrologic condition. Results from this study add to the body of information currently available on microplastics in different environmental compartments, including unique contributions to quantify their occurrence and variability in rivers with a wide variety of different land-use characteristics while highlighting differences between surface samples from rivers compared with lakes.

Environmental Science & Technology

Microbiological reduction of Sb(V) in anoxic freshwater sediments

Microbiological reduction of millimolar concentrations of Sb(V) to Sb(III) was observed in anoxic sediments from two freshwater settings: (1) a Sb- and As-contaminated mine site (Stibnite Mine) in central Idaho and 2) an uncontaminated suburban lake (Searsville Lake) in the San Francisco Bay Area. Rates of Sb(V) reduction in anoxic sediment microcosms and enrichment cultures were enhanced by amendment with lactate or acetate as electron donors but not by H2, and no reduction occurred in sterilized controls. Addition of 2- 14 C-acetate to Stibnite Mine microcosms resulted in the production of 14 CO 2 coupled to Sb(V) reduction, suggesting that this process proceeds by a dissimilatory respiratory pathway in those sediments. Antimony(V) reduction in Searsville Lake sediments was not coupled to acetate mineralization and may be associated with Sb-resistance. The microcosms and enrichment cultures also reduced sulfate, and the precipitation of insoluble Sb(III)-sulfide complexes was a major sink for reduced Sb. The reduction of Sb(V) by Stibnite Mine sediments was inhibited by As(V), suggesting that As(V) is a preferred electron acceptor for the indigenous community. These findings indicate a novel pathway for anaerobic microbiological respiration and suggest that communities capable of reducing high concentrations of Sb(V) commonly occur naturally in the environment.

Environmental Science & Technology

Comparative behavioral ecotoxicology of Inland Silverside larvae exposed to pyrethroids across a salinity gradient

Pyrethroids, a class of commonly used insecticides, are frequently detected in aquatic environments, including estuaries. The influence that salinity has on organism physiology and the partitioning of hydrophobic chemicals, such as pyrethroids, has driven interest in how toxicity changes in saltwater compared to freshwater. Early life exposures in fish to pyrethroids cause toxicity at environmentally relevant concentrations, which can alter behavior. Behavior is a highly sensitive endpoint that influences overall organism fitness and can be used to detect toxicity of environmentally relevant concentrations of aquatic pollutants. Inland Silversides ( Menidia beryllina ), a commonly used euryhaline model fish species, were exposed from 5 days post fertilization (~1-day pre-hatch) for 96 h to six pyrethroids: bifenthrin, cyfluthrin, cyhalothrin, cypermethrin, esfenvalerate and permethrin. Exposures were conducted at three salinities relevant to brackish, estuarine habitat (0.5, 2, and 6 PSU) and across 3 concentrations, either 0.1, 1, 10, and/or 100 ng/L, plus a control. After exposure, Inland Silversides underwent a behavioral assay in which larval fish were subjected to a dark and light cycle stimuli to determine behavioral toxicity. Assessment of total distanced moved and thigmotaxis (wall hugging), used to measure hyper/hypoactivity and anxiety like behavior, respectively, demonstrate that even at the lowest concentration of 0.1 ng/L pyrethroids can induce behavioral changes at all salinities. We found that toxicity decreased as salinity increased for all pyrethroids except permethrin. Additionally, we found evidence to suggest that the relationship between log K OW and thigmotaxis is altered between the lower and highest salinities.

Science of the Total Environment