Spatiotemporal patterns in the export of dissolved organic carbon and chromophoric dissolved organic matter from a coastal, blackwater river

We examined seasonal and spatial patterns in dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) in the Chowan River watershed, North Carolina, a blackwater river which discharges into the second largest estuary in the United States, the Albemarle–Pamlico Estuarine System. From April 2008 to May 2010, DOC concentration did not significantly vary across seasons (range 7.69–30.39 mg L−1); however, CDOM molecular size and aromaticity increased throughout the spring, decreased during the summer and fall, and remained relatively low in the winter. Spectral slope ratios suggested microbial processing of CDOM in the spring and photodegradation of CDOM in the summer and fall. Spatially, DOC and CDOM concentrations were similar in the mainstem and at the mouths of two tributaries, Bennetts Creek and Wiccacon River, but were significantly higher upstream on the tributaries. DOC concentration was positively correlated with CDOM absorbance coefficients at 254 and 350 nm; however, these optical proxies explained only ~60 % of the variance. DOC and CDOM absorption loads to the Albemarle Sound ranged from 2.63 × 1010 g year−1 and 9.84 × 1010 m2 year−1, respectively, in a dry year and 7.9 × 1010 g year−1 and 2.2 × 1011 m2 year−1, respectively, in a wet year, which are comparable to non-blackwater rivers with larger watersheds. Blackwater rivers may therefore represent “hotspots” in coastal carbon chemistry, with seasonal variations in the quality and quantity of DOC and CDOM influencing estuarine food web dynamics and net ecosystem metabolism

Do zooplankton contribute to an ultraviolet clear-water phase in lakes?

Seasonal increases in the ultraviolet (UV) transparency of the surface waters of an oligotrophic lake in Pennsylvania suggest that clear-water phase (CWP) events similar to those previously observed for visible light also exist for the potentially damaging UV wavelengths. Seasonal increases in zooplankton grazers indicate that they play a role in these changes in UV that is similar to the role that zooplankton play in CWP events involving longer-wavelength visible, or photosynthetically active radiation (PAR, 400¿700 nm). The potential role of zooplankton and incident UV in generating UV CWP events was investigated with a set of in situ microcosm experiments that manipulated UV and zooplankton, and followed changes in particulate and dissolved absorbance in the UV (320 nm) and PAR wavelength ranges over an 8-d period in April. Nutrients were also manipulated independently to examine the potential role of nutrient regeneration by zooplankton grazing in altering water transparency. Photobleaching by incident solar UV led to a strong and significant decrease in dissolved UV and PAR absorbance. The presence of zooplankton grazers also significantly decreased dissolved UV absorbance but increased dissolved PAR absorbance. Neither zooplankton nor UV had any significant effects on UV or PAR absorbance by particulates. In contrast, nutrient additions significantly increased dissolved absorbance in both the UV and PAR wavelength ranges, indicating that regeneration of nutrients by zooplankton offsets decreases in UV absorbance and enhances increases in PAR absorbance due to grazing. While photobleaching by UV radiation is likely to make a consistent strong contribution to UV CWP events in lakes, the net effects of zooplankton on UV transparency in a given lake will depend upon multiple factors including zooplankton density and a balance between the edibility and extent of nutrient limitation of the phytoplankton

Phenotypic plasticity in pigmentation in Daphnia induced by UV radiation and fish kairomones.

1. Planktonic organisms are exposed to harmful ultraviolet (UV) radiation. Pigmentation offers protection but at the same time increases visibility, and therefore vulnerability, to visually orienting predators such as fish. As an adaptation against fish predation, zooplankton should be transparent, though this would leave them less protected against UV radiation. Thus both adaptations would appear to be mutually exclusive. However, phenotypic plasticity in pigmentation could allow flexible adaptation to both environmental situations. 2. We tested the hypothesis that Daphnia should be able to change their level of pigmentation in response to fish kairomone and/or UV radiation using four species of Daphnia. 3. Daphnia hyalina Leydig increased pigmentation under UV radiation and D. pulex Leydig reduced pigmentation in the fish kairomone treatment. Both species live in habitats with variable UV and fish impact. 4. Daphnia cucullata Sars and D. middendorffiana Fischer showed no reaction, probably because of their extreme adaptations: D. middendorffiana is strongly pigmented and seems to be adapted to high UV-B impact and an absence of fish in its arctic habitat. In contrast, D. cucullata has evolved in coexistence with fish. It can afford being nearly transparent because it lives in eutrophic lakes where UV-B is not relevant. 5. Our data on four species suggest that plasticity in pigmentation might be common in Daphnia adapted to environments with contrasting or variable selection pressures

Whatever happened to the third paradigm? Exploring mixed methods research designs in sport and exercise psychology

In the past, quantitative and qualitative approaches to research were portrayed as being incompatible, if not mutually exclusive. More recently, however, researchers have explored the possible complementarity of these approaches through mixed methods research (MMR) the so-called third research paradigm. The purpose of this paper is to explore the nature and implications of mixed methods designs for research in sport and exercise psychology. Having sketched the nature and origins of MMR, we highlight some advantages it offers to researchers in sport and exercise psychology. After that, we conclude by identifying some barriers to progress in using mixed methods research in this latter field.Author has checked copyrightkpw13/5/1

Computing Shapley Value in Supermodular Coalitional Games

Coalitional games allow subsets (coalitions) of players to cooperate to receive a collective payoff. This payoff is then distributed “fairly” among the members of that coalition according to some division scheme. Various solution concepts have been proposed as reasonable schemes for generating fair allocations. The Shapley value is one classic solution concept: player i’s share is precisely equal to i’s expected marginal contribution if the players join the coalition one at a time, in a uniformly random order. In this paper, we consider the class of supermodular games (sometimes called convex games), define and survey computational results on other standard solution concepts, and contrast these results with new results regarding the Shapley value. In particular, we give a fully polynomial-time randomized approximation scheme (FPRAS) to compute the Shapley value to within a (1 ± ε) factor in monotone supermodular games. We show that this result is tight in several senses: no deterministic algorithm can approximate Shapley value as well, no randomized algorithm can do better, and both monotonicity and supermodularity are required for the existence of an efficient (1 ± ε)-approximation algorithm. We also argue that, relative to supermodularity, monotonicity is a mild assumption, and we discuss how to transform supermodular games to be monotonic