Coupling Suspension Feeders to the Chesapeake Bay Eutrophication Model

A model predicting suspension-feeding bivalve biomass and its interactions with water quality has been developed and coupled with the Chesapeake Bay Eutrophication Model. This coupling included deposition of filtered particulate matter to the sediments and the recycling of inorganic nutrients back to the water column. Because individual size is a crucial determinant of bivalve filtration and respiration rates, an empirical function, was developed from data, relating computed areal biomass to size, which was then used to adjust these rates during the simulation. Biomass was strongly related to the eutrophication model's predictions of organic and total solids distributions, as well as to bottom water dissolved oxygen. The tight coupling between seasonal organic matter concentration and biomass suggested that food, or the ability of suspension feeders to ingest it given present total solids loadings, is a limiting factor baywide. Hypoxia and anoxia also reduced benthic biomass in affected locations. High site-specific temporal variability observed in the data may contain a large component of spatial patchiness, on scales below which the present estuarine eutrophication model could resolve. Further insights will be needed to incorporate the effects of patchiness, as well as other important spatial and temporal signals, such as predation and recruitment.     

Habitat influences Pacific salmon (Oncorhynchus spp.) tissue decomposition in riparian and stream ecosystems

Decomposition incorporates organic material delivered by Pacific salmon (Oncorhynchus spp.) into aquatic and terrestrial ecosystems of streams where salmon spawn. We hypothesized that salmon tissue decomposition would be faster, and macroinvertebrate abundance and biomass higher, in terrestrial compared to aquatic habitats, and this would be reflected in the nutritional quality of the tissue. Salmon tissue in coarse-mesh bags was placed in four habitats [terrestrial: riparian (RIP), gravel bars (GRA); aquatic: stream sediment surface (STR), buried in sediments (BUR)] in four southeast Alaska watersheds. After 2 (RIP, GRA) or 4 (STR, BUR) weeks of decomposition, tissue dry mass, macronutrient content, and macroinvertebrate colonizer abundance and biomass were determined. Overall, tissue decomposition was rapid (mean k = 0.088 day^?1), while nutritional quality remained high based on elemental ratios (mean C:N = 4.9; C:P = 140; N:P = 30), and differed among habitats (Linear-mixed effects model p < 0.05). Macroinvertebrate assemblages colonizing carcasses were unique to each habitat, although Diptera generally dominated. In terrestrial habitats, the dominant macroinvertebrates were Sphaeroceridae (96 % of invertebrate abundance in RIP habitat) and Calliphoridae larvae (98 % in GRA habitat). In aquatic habitats, the dominant macroinvertebrates were Chironomidae (48 % in STR habitat) and Chloroperlidae (72 % in BUR habitat). Macroinvertebrate colonizer abundance and biomass were higher in RIP (mean 286 individuals and 22 mg g^?1) than in other habitats (mean 4 individuals and 3 mg g^?1) (Friedman p < 0.05). Rapid decomposition rates and high invertebrate biomass, combined with the high nutritional quality of tissue, suggest rapid incorporation of critical salmon nutrients and energy into both aquatic and terrestrial ecosystems.     

Modelling diatom responses to climate induced fluctuations in the moisture balance in continental Antarctic lakes

The water chemistry of lake systems on the edge of the Antarctic continent responds quickly to changes in the moisture balance. This is expressed as increasing salinity and decreasing lake water level during dry periods, and the opposite during wet periods. The diatom composition of the lakes also changes with these fluctuations in salinity and lake water depth. This is important, as their siliceous remains become incorporated into lake sediments and can provide long-term records of past salinity using transfer functions. In order to develop transfer functions, diatoms and water chemistry data were inter-calibrated from five different East Antarctic oases, namely the Larsemann Hills, the Bølingen Islands, the Vestfold Hills, the Rauer Islands and the Windmill Islands. Results indicate that salinity is the most important environmental variable explaining the variance in the diatom flora in East Antarctic lakes. In oligo- saline lakes the variance is mainly explained by lake water depth. This dataset was used to construct a weighted averaging transfer function for salinity in order to infer historical changes in the moisture balance. This model has a jack-knifed r² of 0.83 and a RMSEP of 0.31. The disadvantage of this transfer function is that salinity changes in oligo-saline lakes are reconstructed inaccurately due to the edge effect and due to the low species turnover along the salinity gradient at its lower end. In order to infer changes in the moisture balance in these lakes, a second transfer function using weighted averaging partial least squares (with two components) for depth was constructed. This model has a jack-knifed r² of 0.76 and a RMSEP of 0.22. Both transfer functions can be used to infer climate driven changes in the moisture balance in lake sediment cores from oligo-, hypo-, meso- and hyper-saline lakes in East Antarctic oases between 102–75°E. The transfer function for lake water depth is promising to track trends in the moisture balance of small freshwater lakes, where changes in shallow and deep-water sediments are readily reflected in changing diatom composition.     

Recent rapid salinity rise in three East Antarctic lakes

Research in East Antarctica has shown several recent environmental changes that may be linked to human impacts on climate. In order to detect the influence and context of these changes on coastal aquatic ecosystems we examined lake sediment cores from three lakes in the Windmill Islands, East Antarctica; Beall Lake, Holl Lake and ȁ8Lake Mȁ9. Cores were sectioned at␣2.5 mm intervals. Their diatom species composition was examined to detect changes in lake salinity using a diatom-salinity transfer function, and their algal pigment content was examined to detect photoautotrophic community responses to environmental change. Results showed that Holl Lake originated in a depression exposed by Holocene recession of the continental ice sheet and that Beall Lake and Lake M originated as isolated marine basins formed by changes in relative sea level. A general late Holocene trend of declining lake salinity was evident in all three lakes, interrupted by one short-term high salinity event in Beall Lake. This is consistent with a long-term positive moisture balance. This general decline in salinity has been followed by a remarkable recent rapid increase in salinity in all three lakes in the last few decades. We speculate that this rapid increase in salinity might be linked to changes taking place in the region including feedbacks resulting from decreasing sea ice extent as recorded in the nearby Law Dome ice core, and positive feedbacks in the catchments whereby reduced snow cover has led to decreased albedo, which in turn has caused increased evaporation and sublimation. Collectively these changes have shifted the lakes across a threshold from positive to negative moisture balance. A minor, but not rapid shift in the abundance of diatom pigments relative to pigments from green algae and cyanobacteria was also detected suggesting that some changes in photoautotrophic community composition have occurred. Measurements of modern nutrient levels are also higher than would be expected in Beall Lake and Holl Lake, given the extremely low sediment accumulation rates. This may be associated with a c. 300% increase in the population of Adélie penguins in the Windmill Islands recorded since the 1950s, or may a first signs of a rapid increase in catchment development and associated lake productivity as experienced in Antarctic and Arctic lakes subject to recent rapid regional warming. The most marked feature of the records is the rapid increase in salinity in all three lakes in␣the last few decades, which has occurred in lakes both with and without resident penguin populations.Dominic A. Hodgson and Donna Roberts contributed equally to this work     

Scientific objectives for UV/visible astrophysics investigations: a summary of responsesby the community (2012)

Following several recommendations presented by the Astrophysics Decadal Survey 2010 centered around the need to define “a future ultraviolet-optical space capability”, on 2012 May 25, NASA issued a Request for Information (RFI) seeking persuasive ultraviolet (UV) and visible wavelength astrophysics science investigations. The goal was to develop a cohesive and compelling set of science objectives that motivate and support the development of the next generation of ultraviolet/visible space astrophysics missions. Responses were due on 10 August 2012 when 34 submissions were received addressing a number of potential science drivers. A UV/visible Mission RFI Workshop was held on 2012 September 20 where each of these submissions was summarized and discussed in the context of each other. We present a scientific analysis of these submissions and presentations and the pursuant measurement capability needs, which could influence ultraviolet/visible technology development plans for the rest of this decade. We also describe the process and requirements leading to the inception of this community RFI, subsequent workshop and the expected evolution of these ideas and concepts for the remainder of this decade.