Biomarker distributions in surface sediments from the Kara and Laptev Seas (Arctic Ocean)

Studies of spatial and temporal changes in modern and past sea-ice occurrence may help to understand the processes controlling the recent decrease in Arctic sea-ice cover. Here, we determined concentrations of IP25, a novel biomarker proxy for sea ice developed in recent years, phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and ß-sitosterol) in the surface sediments from the Kara and Laptev seas to estimate modern spatial (seasonal) sea-ice variability and organic-matter sources. C25-HBI dienes and trienes were determined as additional paleoenvironmental proxies in the study area. Furthermore, a combined phytoplankton-IP25 biomarker approach (PIP25 index) is used to reconstruct the modern sea-ice distribution more quantitatively. The terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries, reflecting the huge discharge by the major rivers Ob, Yenisei and Lena. Maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice-free central part of the Kara and Laptev seas. Neither IP25 nor PIP25, however, show a clear and simple correlation with satellite sea-ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea-ice diatom in the water column. Differences in the diene/IP25 and triene/IP25 ratios point to different sources of these HBIs and different environmental conditions. The diene/IP25 ratio seems to correlate positively with sea-surface temperature, while negatively with salinity distributions.

Ecosystem responses to hydrologic change and mechanisms of nitrogen sequestration in seasonally flooded tree islands of the southern Everglades

In the Florida Everglades, tree islands are conspicuous heterogeneous elements in a complex wetland landscape. I investigated the effects of increased freshwater flow in southern Everglades seasonally flooded tree islands, and characterized biogeochemical interactions among tree islands and the marsh landscape matrix, specifically examining hydrologic flows of nitrogen (N), and landscape N sequestration capacity. I utilized ecological trajectories of key ecosystem variables to differentiate effects of increased sheetflow and hydroperiod. I utilized stable isotope analyses and nutrient content of tree island ecosystem components to test the hypothesis that key processes in tree island nitrogen cycling would favor ecosystem N sequestration. I combined estimates of tree island ecosystem N standing stocks and fluxes, soil and litter N transformation rates, and hydrologic inputs of N to quantify the net sequestration of N by a seasonally flooded tree island. ^ Results show that increased freshwater flow to seasonally flooded tree islands promoted ecosystem oligotrophy, whereas reduced flows allowed some plant species to cycle P less efficiently. As oligotrophy is a defining parameter of Everglades wetlands, and likely promotes belowground production and peat development, reintroducing freshwater flow from an upstream canal had a favorable effect on ecosystem dynamics of tree islands in the study area. Important factors influencing the stable isotopic composition of nitrogen and carbon were: (1) a contribution to soil N by soil invertebrates, animal excrement, and microbes, (2) a possible NO3 source from an upstream canal and an "open" ecosystem N cycle, and (3) greater availability of phosphorus in tree islands relative to the marsh landscape, suggesting that tree island N cycling favors N sequestration. Hydrologic sources of N were dominated by surface water loads of NO3- and NH 4+, and an important soil N transformation promoting the net loss of surface water DIN was nitrate immobilization associated with soils and surficial leaf litter. The net inorganic N sequestration capacity of a seasonally flooded tree island was 50 g yr-1 m -2. Thus, tree islands likely have an important function in landscape sequestration of inorganic N, and may reduce significant anthropogenic N loads to downstream coastal systems. ^

A spatial-temporal analysis of section 404 wetland permitting in Texas and Florida: Thirteen years of impact along the coast

Over the past 200 years, an estimated 53% (about 47 million ha) of the original wetlands in the conterminous United States have been lost, mainly as a result of various human activities. Despite the importance of wetlands (particularly along the coast), and a longstanding federal policy framework meant to protect their integrity, the cumulative impact on these natural systems over large areas is poorly understood. We address this lack of research by mapping and conducting descriptive spatial analyses of federal wetland alteration permits (pursuant to section 404 of the Clean Water Act) across 85 watersheds in Florida and coastal Texas from 1991 to 2003. Results show that more than half of the permits issued in both states (60%) fell under the Nationwide permitting category. Permits issued in Texas were typically located outside of urban areas (78%) and outside 100-year floodplains (61%). More than half of permits issued in Florida were within urban areas (57%) and outside of 100-year floodplains (51%). The most affected wetlands types were estuarine in Texas (47%) and palustrine in Florida (55%). We expect that an additional outcome of this work will be an increased awareness of the cumulative depletion of wetlands and loss of ecological services in these urbanized areas, perhaps leading to increased conservation efforts.

Assessing the net effect of anthropogenic disturbance on aquatic communities in wetlands: community structure relative to distance from canals

Anthropogenic alterations of natural hydrology are common in wetlands and often increase water permanence, converting ephemeral habitats into permanent ones. Since aquatic organisms segregate strongly along hydroperiod gradients, added water permanence caused by canals can dramatically change the structure of aquatic communities. We examined the impact of canals on the abundance and structure of wetland communities in South Florida, USA. We sampled fishes and macroinvertebrates from marsh transects originating at canals in the central and southern Everglades. Density of all aquatic organisms sampled increased in the immediate proximity of canals, but was accompanied by few compositional changes based on analysis of relative abundance. Large fish (>8 cm), small fish (<8 >cm) and macroinvertebrates (>5 mm) increased in density within 5 m of canals. This pattern was most pronounced in the dry season, suggesting that canals may serve as dry-down refugia. Increases in aquatic animal density closely matched gradients of phosphorus enrichment that decreased with distance from canals. Thus, the most apparent impact of canals on adjacent marsh communities was as conduits for nutrients that stimulated local productivity; any impact of their role as sources of increased sources of predators was not apparent. The effect of predation close to canals was overcompensated by increased secondary productivity and/or immigration toward areas adjacent to canals in the dry season. Alternatively, the consumptive effect of predatory fishes using canals as dry-season refuges is very small or spread over the expanse of marshes with open access to canals.

Interactions between nutrient availability and hydroperiod shape macroinvertebrate communities in Florida Everglades marshes

Hydroperiod and nutrient status are known to influence aquatic communities in wetlands, but their joint effects are not well explored. I sampled floating periphyton mat and flocculent detritus (floc) infaunal communities using 6-cm diameter cores at short- and long-hydroperiod and constantly inundated sites across a range of phosphorus (P) availability (total phosphorus in soil, floc and periphyton). Differences in community structure between periphyton and floc microhabitats were greater than any variation attributable to hydroperiod, P availability, or other spatial factors. Multivariate analyses indicated community structure of benthic-floc infauna was driven by hydroperiod, although crowding (no. g−1 AFDM) of individual taxa showed no consistent responses to hydroperiod or P availability. In contrast, community structure of periphyton mat infauna was driven by P availability, while densities of mat infauna (no. m−2) were most influenced by hydroperiod (+correlations). Crowding of mat infauna increased significantly with P availability in short-hydroperiod marshes, but was constant across the P gradient in long-hydroperiod marshes. Increased abundance of floating-periphyton mat infauna with P availability at short-hydroperiod sites may result from a release from predation by small fish. Community structure and density were not different between long-hydroperiod and constantly inundated sites. These results have implications for the use of macroinvertebrates as indicators of water quality in wetlands and suggest the substrate sampled can influence interpretation of ecological responses observed in these communities.

Ecosystem structure, nutrient dynamics, and hydrologic relationships in tree islands of the southern Everglades, Florida, USA

Tree islands are an important structural component of many graminoid-dominated wetlands because they increase ecological complexity in the landscape. Tree island area has been drastically reduced with hydrologic modifications within the Everglades ecosystem, yet still little is known about the ecosystem ecology of Everglades tree islands. As part of an ongoing study to investigate the effects of hydrologic restoration on short hydroperiod marshes of the southern Everglades, we report an ecosystem characterization of seasonally flooded tree islands relative to locations described by variation in freshwater flow (i.e. locally enhanced freshwater flow by levee removal). We quantified: (1) forest structure, litterfall production, nutrient utilization, soil dynamics, and hydrologic properties of six tree islands and (2) soil and surface water physico-chemical properties of adjacent marshes. Tree islands efficiently utilized both phosphorus and nitrogen, but indices of nutrient-use efficiency indicated stronger P than N limitation. Tree islands were distinct in structure and biogeochemical properties from the surrounding marsh, maintaining higher organically bound P and N, but lower inorganic N. Annual variation resulting in increased hydroperiod and lower wet season water levels not only increased nitrogen use by tree species and decreased N:P values of the dominant plant species (Chrysobalanus icaco), but also increased soil pH and decreased soil temperature. When compared with other forested wetlands, these Everglades tree islands were among the most nutrient efficient, likely a function of nutrient immobilization in soils and the calcium carbonate bedrock. Tree islands of our study area are defined by: (1) unique biogeochemical properties when compared with adjacent short hydroperiod marshes and other forested wetlands and (2) an intricate relationship with marsh hydrology. As such, they may play an important and disproportionate role in nutrient and carbon cycling in Everglades wetlands. With the loss of tree islands that has occurred with the degradation of the Everglades system, these landscape processes may have been altered. With this baseline dataset, we have established a long-term ecosystem-scale experiment to follow the ecosystem trajectory of seasonally flooded tree islands in response to hydrologic restoration of the southern Everglades.

Response of diatom assemblages to 130 years of environmental change in Florida Bay (USA)

Coastal ecosystems around the world are constantly changing in response to interacting shifts in climate and land and water use by expanding human populations. The development of agricultural and urban areas in South Florida significantly modified its hydrologic regime and influenced rates of environmental change in wetlands and adjacent estuaries. This study describes changes in diatom species composition through time from four sediment cores collected across Florida Bay, for the purposes of detecting periods of major shifts in assemblage structure and identifying major drivers of those changes. We examined the magnitude of diatom assemblage change in consecutive 2-cm samples of the 210Pb-dated cores, producing a record of the past ~130 years. Average assemblage dissimilarity among successive core samples was ~30%, while larger inter-sample and persistent differences suggest perturbations or directional shifts. The earliest significant compositional changes occurred in the late 1800s at Russell Bank, Bob Allen Bank and Ninemile Bank in the central and southwestern Bay, and in the early 1900s at Trout Cove in the northeast. These changes coincided with the initial westward redirection of water from Lake Okeechobee between 1881 and 1894, construction of several canals between 1910 and 1915, and building the Florida Overseas Railroad between 1906 and 1916. Later significant assemblage restructurings occurred in the northeastern and central Bay in the late 1950s, early 1960s and early 1970s, and in the southwestern Bay in the 1980s. These changes coincide with climate cycles driving increased hurricane frequency in the 1960s, followed by a prolonged dry period in the 1970s to late 1980s that exacerbated the effects of drainage operations in the Everglades interior. Changes in the diatom assemblage structure at Trout Cove and Ninemile Bank in the 1980s correspond to documented eutrophication and a large seagrass die-off. A gradual decrease in the abundance of freshwater to brackish water taxa in the cores over ~130 years implies that freshwater deliveries to Florida Bay were much greater prior to major developments on the mainland. Salinity, which was quantitatively reconstructed at these sites, had the greatest effect on diatom communities in Florida Bay, but other factors—often short-lived, natural and anthropogenic in nature—also played important roles in that process. Studying the changes in subfossil diatom communities over time revealed important environmental information that would have been undetected if reconstructing only one water quality variable.

Cultural perceptions of space and place in the South Florida *environment

Public opinion polls in the United States reveal that a great majority of Americans are aware and show concern about ecological issues and the need to preserve natural areas. In South Florida, natural resources have been subjected to enormous strain as the pressure to accommodate a growing population has led to rapid development. Suburbs have been built on areas that were once natural wetlands and farmlands, and the impact today shows a landscape where natural places have all but disappeared. This dissertation examines the intersection between the perceptions that individuals living in the South Florida region have with respect to the natural environment and local ecological problems with where their relationship to nature takes place. ^ The research is based upon both quantitative and qualitative data. The principal methodology used in this research is the ethnographic method, which employed the data gathering techniques of in-depth interviewing and participant observation. The objective of the qualitative portion of the study was to determine how people perceive and relate to their immediate environment. The quantitative portion of the study employed telephone survey data from the FIU/Florida Poll 2000. Data collected through this survey provided the basis to statistically test responses to the research questions. ^ The findings show that people in South Florida have a general idea of the relationship between the human population and the environment but very little knowledge of how they individually affect each other. The experience of private places and public spaces in everyday life permits people to compartmentalize cultural values and understandings of the natural world in separate cognitive schemas. The appreciation of the natural world has almost no connection to their personal sense of obligation to preserve the environment. That obligation is only felt in their home space even though the South Florida environment overall struggles desperately with water shortages, land encroachment, and a rapidly expanding human population whose activities continuously aggravate an already delicate natural balance. ^

San Francisco Coastal System grain size and geochemical data for sand provenance study

Over 150 million cubic meter of sand-sized sediment has disappeared from the central region of the San Francisco Bay Coastal System during the last half century. This enormous loss may reflect numerous anthropogenic influences, such as watershed damming, bay-fill development, aggregate mining, and dredging. The reduction in Bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches, wetlands, and submarine environments. A unique, multi-faceted provenance study was performed to definitively establish the primary sources, sinks, and transport pathways of beach sized-sand in the region, thereby identifying the activities and processes that directly limit supply to the outer coast. This integrative program is based on comprehensive surficial sediment sampling of the San Francisco Bay Coastal System, including the seabed, Bay floor, area beaches, adjacent rock units, and major drainages. Analyses of sample morphometrics and biological composition (e.g., Foraminifera) were then integrated with a suite of tracers including 87Sr/86Sr and 143Nd/144Nd isotopes, rare earth elements, semi-quantitative X-ray diffraction mineralogy, and heavy minerals, and with process-based numerical modeling, in situ current measurements, and bedform asymmetry to robustly determine the provenance of beach-sized sand in the region.

DISSOLVED AND GASEOUS FLUXES OF CARBON AND NITROGEN FROM URBAN WATERSHEDS OF THE CHESAPEAKE BAY

Carbon and nitrogen loading to streams and rivers contributes to eutrophication as well as greenhouse gas (GHG) production in streams, rivers and estuaries. My dissertation consists of three research chapters, which examine interactions and potential trade-offs between water quality and greenhouse gas production in urban streams of the Chesapeake Bay watershed. My first research project focused on drivers of carbon export and quality in an urbanized river. I found that watershed carbon sources (soils and leaves) contributed more than in-stream production to overall carbon export, but that periods of high in-stream productivity were important over seasonal and daily timescales. My second research chapter examined the influence of urban storm-water and sanitary infrastructure on dissolved and gaseous carbon and nitrogen concentrations in headwater streams. Gases (CO2, CH4, and N2O) were consistently super-saturated throughout the course of a year. N2O concentrations in streams draining septic systems were within the high range of previously published values. Total dissolved nitrogen concentration was positively correlated with CO2 and N2O and negatively correlated with CH4. My third research chapter examined a long-term (15-year) record of GHG emissions from soils in rural forests, urban forest, and urban lawns in Baltimore, MD. CO2, CH4, and N2O emissions showed positive correlations with temperature at each site. Lawns were a net source of CH4 + N2O, whereas forests were net sinks. Gross CO2 fluxes were also highest in lawns, in part due to elevated growing-season temperatures. While land cover influences GHG emissions from soils, the overall role of land cover on this flux is very small (< 0.5%) compared with gases released from anthropogenic sources, according to a recent GHG budget of the Baltimore metropolitan area, where this study took place.

Probabilistic approach of water residence time and connectivity using Markov Chains with application to tidal embayments

Markov Chain analysis was recently proposed to assess the time scales and preferential pathways into biological or physical networks by computing residence time, first passage time, rates of transfer between nodes and number of passages in a node. We propose to adapt an algorithm already published for simple systems to physical systems described with a high resolution hydrodynamic model. The method is applied to bays and estuaries on the Eastern Coast of Canada for their interest in shellfish aquaculture. Current velocities have been computed by using a 2 dimensional grid of elements and circulation patterns were summarized by averaging Eulerian flows between adjacent elements. Flows and volumes allow computing probabilities of transition between elements and to assess the average time needed by virtual particles to move from one element to another, the rate of transfer between two elements, and the average residence time of each system. We also combined transfer rates and times to assess the main pathways of virtual particles released in farmed areas and the potential influence of farmed areas on other areas. We suggest that Markov chain is complementary to other sets of ecological indicators proposed to analyse the interactions between farmed areas - e.g. depletion index, carrying capacity assessment. Markov Chain has several advantages with respect to the estimation of connectivity between pair of sites. It makes possible to estimate transfer rates and times at once in a very quick and efficient way, without the need to perform long term simulations of particle or tracer concentration.

Water quality trading: credit stacking and ancillary benefits

Ecosystems can provide many services. Wetlands, for example, can help mitigate water pollution from point sources as well as non-point sources, serve as habitat for wildlife, sequester carbon and serve as a place for recreation. Studies have found that these services can have substantial value to society. The sale of ecosystem credits has been found to be a possible way to finance construction investments in wetlands and easements to farmers to take their land out of production. At the same time, selling one ecosystem service credit may not always be enough to justify the investment. Traditionally market participants have only been allowed to sell a single credit from one piece of land, but recently there have been discussions about the possibility of selling more than one credit from a piece of land because it potentially could lead to more efficient ecosystem service provision. Selling multiple credits is sometimes referred to as credit stacking. This paper is an empirical study of the potential for credit stacking applied to the services provided by wetlands in the Upper Mississippi River Basin, specifically nitrogen, phosphorus and wildlife credits. In the setting of our study where costs are discrete rather than continuous we found that wetlands are a cost-effective way to reduce the nitrogen loads from wastewater treatment plants and that stacking nitrogen, phosphorus and wildlife credits may improve social welfare while leading to a higher level of ecosystem services. However, for credit stacking to be welfare improving we found that there needs to be a substantial demand for the credit that covers the majority of the investment in wetlands, while the credit aggregator has a choice between what ecosystem projects to undertake. If the credit that covers the majority of investment is sold first and is the sole basis of the investment decision and the objective is to improve welfare, a sequential implementation of ecosystem credits is not recommended; it would not lead to an increase in the total amount of ecosystem services provided though it would increase profit for the credit producer.

Sea otter predation and the distribution of bivalve prey in the Elkhorn Slough National Estuarine Research Reserve

The California sea otter population is gradually expanding in size and geographic range and is consequently invading new feeding grounds, including bays and estuaries that are home to extensive populations of bivalve prey. One such area is the Elkhorn Slough, where otters have apparently established a spring and summer communal feeding and resting area. In anticipation of future otter foraging in the slough, an extensive baseline database on bivalve densities, size distributions, biomasses, and burrow depths has been established for three potential bivalve prey species, Saxidomus nuttalli, Tresus nutallii, and Zirphaea pilsbryi. In 1986, the Elkhorn Slough otters were foraging predominately at two areas immediately east and west of the Highway 1 bridge (Skipper's and the PG&E Outfall). Extensive subtidal populations of Saxidomus nuttalli and Tresus nuttallii occur in these areas. Shell records collected at these study areas indicated that sea otters were foraging selectively on Saxidomus over Tresus. The reason for this apparent preference was not clear. At the Skipper's study site, 51% of the shell record was composed of Saxidomus, yet this species accounted for only 16% of the in situ biomass, and only 39% of the available clams. Tresus represented 49% of the shell record at Skipper's, yet this species accounted for 84% of the in situ biomass and 61% of the available clams. There was no difference in mean burrow depth between the two species at this site so availability does not explain the disparity in consumption. At the PG&E Outfall, Saxidomus represents 66% of the in situ biomass and 81% of the available clams, while Tresus accounts for 34% of the in situ biomass and 19% of the available clams. Saxidomus accounts for 96% of the shell record at this site vs. 4% for Tresus, again indicating that the otters were preying on Saxidomus out of proportion to their density or biomass. High densities and biomasses of a third species, Zirphaea pilsbryi, occur in areas where sea otters were observed to be foraging, yet no cast-off Zirphaea shells were found. Although it is possible this species was not represented in the shell record because the otters were simply chewing up the shells, it is more likely this species is avoided by sea otters. There were relatively few sea otters in the Elkhorn Slough in 1986 compared to the previous two years. This, coupled with high bivalve densities, precluded any quantitative comparison of bivalve densities before and after the 1986 sea otter occupation. Qualitative observations made during the course of this study, and quantitative observations from previous studies indicate that, after 3 years, sea otters are not yet significantly affecting bivalve densities in the Elkhorn Slough.

Biogeochemical Cycling in a Headwater Stream and Riparian Zone

Several teams of researchers at multiple universities are currently measuring annual and seasonal fluxes of carbon dioxide and other greenhouses gases (nitrous oxide and methane) in riparian wetlands and upland forests in the Tenderfoot Creek Experimental Forest (TCEF), a subalpine watershed in the Little Belt Mountains, Montana. In the current thesis, the author characterized the geochemistry and stable carbon isotope composition of shallow groundwater, soil water, and stream water in upper Stringer Creek, near sites that are being investigated for gas chemistry and microbial studies. It was hypothesized that if methanogenesis were a dominant process in the riparian wetlands of upper Stringer Creek, then this should impart a characteristic signal in the measured stable isotopic composition of dissolved inorganic carbon in shallow groundwater. For the most part, the major solute composition of shallow groundwater in upper Stringer Creek was similar to that of the stream. However, several wells completed in wetland soil had highly elevated concentrations of Fe2+ and Mn2+ which were absent in the well-oxygenated surface water. Use of sediment pore-water samplers (peepers) demonstrated a rapid increase in Fe2+ and Mn2+ with depth, most feasibly explained by microbial reduction of Fe- and Mn-oxide minerals. In general, the pH of shallow groundwater was lower than that of the stream. Since concentrations of CO2 in the groundwater samples were consistently greater than atmospheric pCO2, exchange of CO2 gas across the stream/air interface occurred in one direction, from stream to air. Evasion of CO2 partly explains the higher pH values in the stream. Microbial processes involving breakdown of organic carbon, including aerobic respiration, anaerobic respiration, and methanogenesis, explain the occurrence of excess CO2 in the groundwater. In general, the isotopic composition of total dissolved inorganic carbon (DIC) decreased with increasing DIC concentration, consistent with aerobic and/or anaerobic respiration being the dominant metabolic process in shallow groundwater. However, a minority of wells contained high DIC concentrations that were anomalously heavy in u13C, and these same wells had elevated concentrations of dissolved methane. It is concluded that the wells with isotopically-heavier DIC have likely been influenced by acetoclastic methanogenesis. Results from shallow groundwater wells and one of the peeper samplers suggest a possible link between methanogenesis and bacterial iron reduction.

¬FISH DISTRIBUTIONS IN LAKE ONTARIO’S EASTERN BASIN AND THE UPPER ST. LAWRENCE RIVER: AN ANALYSIS USING GIS AND OCCUPANCY MODELLING TECHNIQUES

Predictive models of species distributions are important tools for fisheries management. Unfortunately, these predictive models can be difficult to perform on large waterbodies where fish are difficult to detect and exhaustive sampling is not possible. In recent years the development of Geographic Information Systems (GIS) and new occupancy modelling techniques has improved our ability to predict distributions across landscapes as well as account for imperfect detection. I surveyed the nearshore fish community at 105 sites between Kingston, Ontario and Rockport, Ontario with the objective of modelling geographic and environmental characteristics associated with littoral fish distributions. Occupancy modelling was performed on Round Goby, Yellow perch, and Lepomis spp. Modelling with geographic and environmental covariates revealed the effect of shoreline exposure on nearshore habitat characteristics and the occupancy of Round Goby. Yellow Perch, and Lepomis spp. occupancy was most strongly associated negatively with distance to a wetland. These results are consistent with past research on large lake systems indicate the importance of wetlands and shoreline exposure in determining the fish community of the littoral zone. By examining 3 species with varying rates of occupancy and detection, this study was also able to demonstrate the variable utility of occupancy modelling.