Beneficial and detrimental interactive effects of dissolved organic matter and ultraviolet radiation on Zooplankton in a transparent lake

While changes in dissolved organic matter (DOM) concentrations are expected to affect zooplankton species through attenuation of potentially damaging ultraviolet (UV) radiation, generation of potentially beneficial or harmful photoproducts, pH alteration, and microbial food web stimulation, the combined effects of such changes on zooplankton community structure have not been studied previously. Our purpose was to determine how an increase in allochthonous DOM and associated changes in pH in an initially transparent lake may affect zooplankton community structure, and how exposure to solar UV may alter these DOM and pH effects. We ran microcosm experiments manipulating UV, DOM, and pH near the surface of Lake Giles in northeastern Pennsylvania. We found that when DOM was added in the presence of ambient UV, Daphnia and copepod UV-mortality was reduced by approximately three and two times compared to UV exposure without extra DOM. When DOM was added in the absence of UV, adult Daphnia and copepods were reduced compared to no DOM addition in the absence of UV. Daphnia and cyclopoid egg production and rotifer abundance were generally higher in the presence of DOM, regardless of UV treatment. The lower abundance yet high egg production in the presence of DOM and absence of UV may be explained by higher abundance of egg-bearing adults compared to non-egg-bearers. We conclude that allochthonous DOM benefits some zooplankton in a high-UV environment, but may be detrimental under low-UV conditions. Overall, Daphnia abundance and egg production were higher than that of calanoid copepods in the DOM additions, indicating that in some lakes an increase in allochthonous DOM may lead to a zooplankton community shift favoring Daphnia over calanoid copepods.     

Altered microbial community structure and organic matter composition under elevated CO2 and N fertilization in the duke forest

The dynamics and fate of terrestrial organic matter (OM) under elevated atmospheric CO₂ and nitrogen (N) fertilization are important aspects of long‐term carbon sequestration. Despite numerous studies, questions still remain as to whether the chemical composition of OM may alter with these environmental changes. In this study, we employed molecular‐level methods to investigate the composition and degradation of various OM components in the forest floor (O horizon) and mineral soil (0–15 cm) from the Duke forest free air CO₂ enrichment (FACE) experiment. We measured microbial responses to elevated CO₂ and N fertilization in the mineral soil using phospholipid fatty acid (PLFA) profiles. Increased fresh carbon inputs into the forest floor under elevated CO₂ were observed at the molecular‐level by two degradation parameters of plant‐derived steroids and cutin‐derived compounds. The ratios of fungal to bacterial PLFAs and Gram‐negative to Gram‐positive bacterial PLFAs decreased in the mineral soil with N fertilization, indicating an altered soil microbial community composition. Moreover, the acid to aldehyde ratios of lignin‐derived phenols increased with N fertilization, suggesting enhanced lignin degradation in the mineral soil. ¹H nuclear magnetic resonance (NMR) spectra of soil humic substances revealed an enrichment of leaf‐derived alkyl structures with both elevated CO₂ and N fertilization. We suggest that microbial decomposition of SOM constituents such as lignin and hydrolysable lipids was promoted under both elevated CO₂ and N fertilization, which led to the enrichment of plant‐derived recalcitrant structures (such as alkyl carbon) in the soil.     

Impact of solar radiation in disinfecting drinking water contaminated with Giardia duodenalis and Entamoeba histolytica/dispar at a point-of-use water treatment

Aims:  To determine the impact of natural sunlight in disinfecting water contaminated with cysts of Giardia duodenalis and Entamoeba histolytica/dispar using plastic containers.
Methods and Results:  Known quantities of Giardia duodenalis and Entamoeba histolytica/dispar cysts in sterile water were exposed to the sun. Containers were made of polyethylene terephthalate, eight painted black on one side, one not painted and another cut open at the top and the last was a high density polypropylene container. Viability testing was performed using vital and fluorescent dyes. The same assays were conducted under cloudy conditions. Thermal control tests were also performed using heat without ultra violet light from the sun. Results show that 99·9% of parasites was inactivated when water temperatures reached 56°C after sunlight exposure.
Conclusion:  Both solar radiation and heat produced by the sun have a synergistic effect in killing cysts of Giardia duodenalis and Entamoeba histolytica/dispar when temperatures rise above 50°C, with complete death at 56°C, using painted 2-l PET containers.
Significance and Impact of the Study:  Solar disinfection system using PET containers painted black on one side can be used to disinfect water against Giardia duodenalis and Entamoeba histolytica/dispar using natural sunlight.     

Accumulation rates of organic matter associated with different successional stages from open water to carr forest in former turbaries

This paper investigates the rates of peat accumulation associated with different phases in the succession from open water to carr forest in shallow ponds created by peat dredging in The Netherlands. Four phases had been recognized in a previous study of aerial photographs for the period 1937–1990, i.e. open water (Aq), reed swamp (SA), brownmoss quaking fen (BM) and carr forest (CF). Peat accumulation rates were estimated by relating the amounts of organic matter stored to the data on the successional history for 21 different sites.The organic matter accumulation rates were highest in the SA phase (1.12 kg m^-2 y^-1 on a dry weight basis), intermediate in the BM and CF phases (0.49 and 0.58 kg m^-2 y^-1), and lowest in the Aq phase (0.26 kg m^-2 y^-1). These values are high in comparison with values determined for fen ecosystems with stratigraphic methods in combination with radiocarbon dating. The accumulation rates were inversely related to the average duration of the successional phases, suggesting that peat accumulation is a major driving force behind the succession.     

Variation of chromophoric dissolved organic matter and possible attenuation depth of ultraviolet radiation in Yunnan Plateau lakes

The increase of ultraviolet radiation (UVR, 280–400 nm) caused by stratospheric ozone depletion has profound effects on aquatic ecosystems. High-altitude lakes in the Yunnan Plateau are exposed to high intensities of UVR and contain low concentrations of chromophoric dissolved organic matter (CDOM). Thirty-eight lakes in the Yunnan Plateau with elevations from 1291 to 3809 m above sea level were investigated to study CDOM concentrations and possible effects of UVR on the lake ecosystem. The attenuation of UVR in the Yunnan Plateau lakes was calculated from the absorption coefficient of CDOM based on an empirical relationship from lakes in the Alps and Pyrenees mountains. Absorption coefficients [α(λ)] at 320 nm [α(320)] ranged from 0.52 to 14.05 m⁻¹ (mean ± standard deviation, 4.40 ± 3.85 m⁻¹) and at 380 nm [α(380)] from 0.05 to 4.51 m⁻¹ (1.40 ± 1.30 m⁻¹). The exponential slope coefficient for the relationship of wavelength to α(λ) ranged from 16.2 to 41.4 μm⁻¹ (21.74 ± 4.93 μm⁻¹) over the 280–400 nm interval. Normalized fluorescence emission (NFLU) at 450 nm from an excitation wavelength of 355 nm, F _n(355), averaged 7.93 ± 3.22 NFLU. A significant positive relationship was found between α(355) and F _n(355). The estimated diffuse attenuation coefficients of UV-B (320 nm) and UV-A (380 nm) ranged from 0.55 to 15.77 m⁻¹ and from 0.24 to 6.73 m⁻¹; the corresponding 1% attenuation depths ranged from 0.29 to 8.44 m and from 0.68 to 19.12 m. Twenty-five of 38 lakes had 1% UV-B attenuation depths of 1.5 m or more. The median 1% attenuation depth was 28.8% of the sampling depth for UV-B radiation and 60% for UV-A. In addition to CDOM, chlorophyll α (Chla) and total suspended matter (TSM) also may contribute to attenuation of UVR.     

Rapid organic matter mineralization coupled to iron cycling in intertidal mud flats of the Han River estuary,Yellow Sea

Organic matter oxidation represents a transfer of elements to inorganic nutrients that support biological productivity and food web processes. Therefore, quantification of the controls of organic matter mineralization is crucial to understanding the carbon cycle and biogeochemical dynamics in coastal marine environments. We investigated the rates and pathways of anaerobic carbon (C) oxidation in an unvegetated mud flat (UMF) and a vegetated mud flat (VMF) of the Ganghwa intertidal zone of the macro-tidal Han River estuary, Yellow Sea. Analyses of geochemical constituents revealed relatively oxidized conditions and high reactive Fe(III) concentrations (40–100 μmol cm⁻³) in the sediments. A pronounced depth stratification in Fe(III) was observed at the VMF site likely due to the lower number of infaunal burrows along with dense root formation by the macrophytes, Suaeda japonica. Depth-integrated rates of anaerobic C mineralization as well as sulfate- and Fe(III) reduction at the VMF were consistently higher than those at the UMF, likely driven by the dense vegetation that supplied organic C substrates and electron acceptors to the rhizosphere. Sediment inventories revealed that solid Fe(III) was up to 17 times more abundant than pore water sulfate, and direct rate measurements showed that microbial Fe(III) reduction comprised an equal or larger percentage of C oxidation (36–66 %) in comparison to sulfate reduction (36–40 %) at both sites studied. Time-course experiments indicated that sulfate reduction rates were likely underestimated, especially in the VMF rhizosphere, due to the reoxidation of reduced S in the presence of high Fe(III). The high rates of C mineralization suggest that the Ganghwa intertidal mud flats are a significant sink against the external loading of organic compounds, and organic matter mineralization is enhanced by chemical exchange regulated by extreme tidal flushing and macro-microorganisms interactions.