Phytoplankton Dynamics in the Very Low Salinity Region of the James River Estuary, Virginia, U.S.A.

During summer and autumn discharge from the James River estuary, Virginia, was less than 120 m3sec-1. There was a peak phytoplankton biomass in the very low salinity region (defined as the location where surface salinity measured less than 0.5$ 0/00) and this peak represented five to ten times greater biomass than adjacent waters. The peak biomass occurred independent of the tidal state and the location of nutrient inputs. It disappeared during winter and spring, and nutrient limitation was not responsible for the low phytoplankton biomass, indicating there were physical, not chemical controlling factors. The peak biomass was hypothesized to be caused by hydrodynamic trapping, the same mechanism involved in the formation of the turbidity maximum, and by increased phytoplankton residence time during periods of low river discharge. Close balance of sinking rates of dominant phytoplankton species with the net upward vertical water velocity, relatively large netplankton biomass (retained by 23 um screen), exhaustion of dissolved silicate, relatively high ratio of particulate biogenic silica to particulate organic carbon, and relatively low ratio of particulate organic carbon to chlorophyll a in the very low salinity region indicate that diatoms are selectively trapped within this zone. As river discharge increased during winter and spring, the magnitude of the turbidity maximum increased but the peak biomass disappeared as a result of decreased residence time of phytoplankton, decreased sinking rate of phytoplankton due to increased water viscosity at low temperature, and increased net-circulation which requires larger sinking rates to develope the peak biomass in the turbidity maximum zone. There were some differences between the turbidity maximum zone and the location of the peak biomass. High biomass in the very low salinity region decreased very rapidly before the 1.5 0/00, while the turbidity maximum zone encompassed a much broader area. High ratios of chlorophyll a to phaeopigments, and low ratios of particulate organic carbon to nitrogen in the very low salinity region suggest that phytoplankton within this zone grew under good physiological conditions. Mass mortality due to osmotic stress placed on freshwater phytoplankton appears to be the best explanation for the rapid loss of biomass

Bull kelp, Nereocystis luetkeana, abundance in Van Damme Bay, Mendocino County, California

Size and density data were collected for Nereocystis luetkeana sporophytes from kelp beds in Van Damme Bay, Mendocino County during May, June and July 1990. Length and weight measurements were made on individual plants from representative size groups collected from depths of 6.1 m and 12.2 m. Mean sporophyte weight was 268 g (SD 393 g), while mean stipe length was 214 cm (SD 275 cm). Densities were determined separately for those plants which had reached the surface and for all plants within the water column. Sixty-five 12.7 m2 surface quadrats yielded mean surface densities of 2.2 (SD 1.5) and 2.7 plants/m2 (SD 1.3) in June and July, respectively. Individual plants were counted within 42 1x5 m plots along benthic transect lines yielding average densities of 2.7 (SD 4.5) and 5.2 plants/m2 (SD 3.0) in May and July, respectively. Combined density and size data from July 1990 and kelp bed area estimates from fall 1988 for Van Damme Bay yielded a biomass estimate of 640 metric tons distributed over 45.7 hectares. (15pp.

Winter Barley Variety Trial

With the revival of the small grains industry in the Northeast and the strength of the localvore movement, craft breweries and distilleries have expressed an interest in local barley for malting. Malting barley must meet specific quality characteristics such as low protein content and high germination. Many farmers are also interested in barley as a high-energy concentrate source for their livestock. Depending on the variety, barley can be planted in either the spring or fall, and both two- and six-row barley can be used for malting. In 2011-2012, UVM Extension conducted a winter barley trial to evaluate the yield and quality of publicly available malting and feed barley varieties

Boom and Bust Carbon-Nitrogen Dynamics during Reforestation

Legacies of historical land use strongly shape contemporary ecosystem dynamics. In old-field secondary forests, tree growth embodies a legacy of soil changes affected by previous cultivation. Three patterns of biomass accumulation during reforestation have been hypothesized previously, including monotonic to steady state, non-monotonic with a single peak then decay to steady state, and multiple oscillations around the steady state. In this paper, the conditions leading to the emergence of these patterns is analyzed. Using observations and models, we demonstrate that divergent reforestation patterns can be explained by contrasting time-scales in ecosystem carbon-nitrogen cycles that are influenced by land use legacies. Model analyses characterize non-monotonic plant-soil trajectories as either single peaks or multiple oscillations during an initial transient phase controlled by soil carbon-nitrogen conditions at the time of planting. Oscillations in plant and soil pools appear in modeled systems with rapid tree growth and low initial soil nitrogen, which stimulate nitrogen competition between trees and decomposers and lead the forest into a state of acute nitrogen deficiency. High initial soil nitrogen dampens oscillations, but enhances the magnitude of the tree biomass peak. These model results are supported by data derived from the long-running Calhoun Long-Term Soil-Ecosystem Experiment from 1957 to 2007. Observed carbon and nitrogen pools reveal distinct tree growth and decay phases, coincident with soil nitrogen depletion and partial re-accumulation. Further, contemporary tree biomass loss decreases with the legacy soil C:N ratio. These results support the idea that non-monotonic reforestation trajectories may result from initial transients in the plant-soil system affected by initial conditions derived from soil changes associated with land-use history

Seasonality in coastal macrobenthic biomass and its implications for estimating secondary production using empirical models

Macrobenthic secondary production is widely used to assess the trophic capacity, health, and functioning of marine and freshwater ecosystems. Annual production estimates are often calculated using empirical models and based on data collected during a single period of the year. Yet, many ecosystems show seasonal variations. Although ignoring seasonality may lead to biased and inaccurate estimates of annual secondary production, it has never been tested at the community level. Using time series of macrobenthic data collected seasonally at three temperate marine coastal soft-bottom sites, we assessed seasonal variations in biomass of macrobenthic invertebrates at both population and community levels. We then investigated how these seasonal variations affect the accuracy of annual benthic production when assessed using an empirical model and data from a single sampling event. Significant and consistent seasonal variations in biomass at the three study sites were highlighted. Macrobenthic biomass was significantly lower in late winter and higher in summer/early fall for 18 of the 30 populations analyzed and for all three communities studied. Seasonality led to inaccurate and often biased estimates of annual secondary production at the community level when based on data from a single sampling event. Bias varied by site and sampling period, but reached similar to 50% if biomass was sampled at its annual minimum or maximum. Since monthly sampling is rarely possible, we suggest that ecologists account for uncertainty in annual production estimates caused by seasonality.Agência financiadora EDF French Ministry of Higher Education, Research and Innovation French Ministry for the Ecological and Inclusive Transition through the Marine Strategy Framework Directive Agreement French Biodiversity Agency (Agence francaise pour la biodiversite) as part of the CAPANOUR projectinfo:eu-repo/semantics/publishedVersio

Seasonal Biomass and Carbohydrate Allocation Patterns in Southern Minnesota Curlyleaf Pondweed Populations

Four southern Minnesota populations of curlyleaf pondweed ( Potamogeton crispus L.) were sampled monthly from January 2001 to November 2002 to determine seasonal phenological, biomass, and carbohydrate allocation patterns. Low periods of carbohydrate storage in the seasonal phenological cycle indicate potentially vulnerable periods in the plant’s life cycle and may be the ideal time to initiate management and control efforts

Evaluation of spatial, radiometric and spectral Thematic Mapper performance for coastal studies

On 31 March 1983, the University of Delaware's Center for Remote Sensing initiated a study to evaluate the spatial, radiometric and spectral performance of the LANDSAT Thematic Mapper for coastal and estuarine studies. The investigation was supported by Contract NAS5-27580 from the NASA Goddard Space Flight Center. The research was divided into three major subprojects: (1) a comparison of LANDSAT TM to MSS imagery for detecting submerged aquatic vegetation in Chesapeake Bay; (2) remote sensing of submerged aquatic vegetation - a radiative transfer approach; and (3) remote sensing of coastal wetland biomass using Thematic Mapper wavebands

Controls on ecosystem respiration of carbon dioxide across a boreal wetland gradient in Interior Alaska

Thesis (M.S.) University of Alaska Fairbanks, 2012Permafrost and organic soil layers are common to most wetlands in interior Alaska, where wetlands have functioned as important long-term soil carbon sinks. Boreal wetlands are diverse in both vegetation and nutrient cycling, ranging from nutrient-poor bogs to nutrient- and vascular-rich fens. The goals of my study were to quantify growing season ecosystem respiration (ER) along a gradient of vegetation and permafrost in a boreal wetland complex, and to evaluate the main abiotic and biotic variables that regulate CO₂ release from boreal soils. Highest ER and root respiration were observed at a sedge/forb community and lowest ER and root respiration were observed at a neighboring rich fen community, even though the two fens had similar estimates of root biomass and vascular green area. Root respiration also contributed approximately 40% to ER at both fens. These results support the conclusion that high soil moisture and low redox potential may be limiting both heterotrophic and autotrophic respiration at the rich fen. This study suggests that interactions among soil environmental variables are important drivers of ER. Also, vegetation and its response to soil environment determines contributions from aboveground (leaves and shoots) and belowground (roots and moss) components, which vary among wetland gradient communities.Introduction -- Introduction to boreal wetlands -- Ecosystem respiration and its role in peatland function -- Brief rationale for this study -- Goals, objectives, and hypotheses -- Methods -- Description of study site and the gradient design -- Atmospheric and soil environmental variables -- Ecosystem respiration fluxes -- Root respiration fluxes and aboveground vegetation measurements -- Results -- Soil environmental variables along the gradient -- Ecosystem respiration -- Contributions of root respiration to ER -- Discussion -- Patterns of ecosystem respiration along the wetland gradient -- The role of roots in ecosystem respiration of CO₂ -- Study limitations and ideas for future research -- Conclusions