Charlotte Lovengreen

A Five‐year Study of Solar Ultraviolet Radiation in Southern Chile (39° S): Potential Impact on Physiology of Coastal Marine Algae?

Abstract This study reports 5 years of (1998–2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39° S), accompanied by evaluation of the impact of ultraviolet radiation (UVR) on marine macroalgae of this site. UVR conditions showed a strong seasonal variation, which was less pronounced toward longer wavelengths. Daily maximum dose rates (clear days) averaged in winter–summer: UV-B(290–315 nm) 0.30–2.1, UV-B(290–320 nm) 0.70–3.7, UV-A(315–400 nm) 20.6–62.1, UV-A(320–400 nm) 20.2–60.5 W m−2, and photosynthetically active radiation (PAR) 969–2423 μmol m−2 s−1. The corresponding daily doses (all the days) ranged: UV-B(290–315 nm) 2.6–40.7, UV-B(290–320 nm) 6.7–78.5, UV-A(315–400 nm) 228–1539, UV-A(320–400 nm) 224–1501, and PAR 2008–13308 kJ m−2 d−1. Taking into consideration action spectra of a biological interest, the risk of UV exposure could be up to 37 times higher in summer than in winter. The photosynthetic activity (as maximum quantum yield of chlorophyll fluorescence, Fv/Fm) of the brown alga Lessonia nigrescens from the infralittoral zone was markedly more sensitive to UVR than of the green alga Enteromorpha intestinalis from the upper midlittoral, and the UV-B wave band increased markedly photoinhibition. In L. nigrescens, maximal photoinhibition (40%) took place at weighted (the action spectrum for photoinhibition of photosynthesis) UVR doses of 800 kJ m−2, irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 kJ m−2). In winter, when this alga was at its most sensitive, the weighted UV dose causing 35–40% photoinhibition was around 200 kJ m−2. In E. intestinalis, weighted doses of 800 kJ m−2 resulted in low photoinhibition (<10 %) and no clear seasonal patterns could be inferred. These results confirm that midday summer levels of UV-B and their daily doses in southern Chile are high enough to produce stress to intertidal macroalgae.

Ozone and UV Radiation over Southern South America: Climatology and Anomalies

Abstract Ozone and UV radiation were analyzed at eight stations from tropical to sub-Antarctic regions in South America. Ground UV irradiances were measured by multichannel radiometers as part of the Inter American Institute for Global Change Radiation network. The irradiance channels used for this study were centered at 305 nm (for UV-B measurements) and 340 nm (for UV-A measurements). Results were presented as daily maximum irradiances, as monthly averaged, daily integrated irradiances and as the ratio of 305 nm to 340 nm. These findings are the first to be based on a long time series of semispectral data from the southern region of South America. As expected, the UV-B channel and total column ozone varied with latitude. The pattern of the UV-A channel was more complex because of local atmospheric conditions. Total column ozone levels of <220 Dobson Units were observed at all sites. Analysis of autocorrelations showed a larger persistence of total column ozone level than irradiance. A decreasing cross-correlation coefficient between 305 and 340 nm and an increasing cross-correlation coefficient between 305 nm and ozone were observed at higher latitudes, indicating that factors such as cloud cover tend to dominate at northern sites and that ozone levels tend to dominate at southern sites. These results highlight the value of long-term monitoring of radiation with multichannel radiometers to determine climatological data and evaluate the combination of factors affecting ground UV radiation.

Environmental processes, water quality degradation, and decline of waterbird populations in the Rio Cruces wetland, Chile

Changes in wetland ecosystems may result from the interactions of endogenous processes with exogenous factors such as environmental fluctuations and anthropogenic influences. Since mid-2004, the Río Cruces wetland, a Ramsar site located in southern Chile (40°S), exhibited a sudden increase in mortality and emigration of the largest breeding population of Black-necked swans in the Neotropics, a massive demise of the dominant macrophyte Egeria densa (the main food of swans and several aquatic birds), and a seasonal appearance of turbid waters. We compared annual variation in rainfall, river flow, and radiation over the period 2000–2005 to assess the role of environmental factors on these wetland changes. Those factors, with the exception of a decrease in river flow during 2004, did not show significant inter-annual differences. However, when comparing Landsat images, we found in the visible and near-infrared spectrum, a corresponding increase and decrease in water reflectance for 2005 with respect to 2003 and 2001, respectively. These results may reflect the appearance of turbid waters and the decrease in cover of E. densa. All temporal changes were restricted to the northern and central zones of the wetland. In addition, spatial analysis showed a gradient in turbidity across the wetland waters, which was enhanced by estuarine influence during spring-tides. Censuses of aquatic birds (1999–2005) showed that only herbivorous birds exhibited a pronounced decrease in population abundance after mid-2004, while piscivorous birds continued normal cycling, with even some positive trends in abundance during 2004–2005. Population declines in herbivorous birds may be related to the demise of E. densa and suspension of sediments during periods of reduced river flow (2004) that gave rise to the turbidity in the wetland waters. Environmental changes could be related to changes in water quality after a new pulp mill, built upstream of the wetland, initiated operations during February 2004.

The underwater light field in the Bellingshausen and Amundsen Seas (Antarctica)

The underwater light field in the Bellingshausen andAdmundsen Seas was characterised using data collectedduring the R/V Polarstern cruise ANT XI/3, from12.1.94 to 27.3.94. The euphotic zone varied from 24to 100 m depth. Spectral diffuse vertical attenuationcoefficients (Kd(λ))were determined for 12narrow wavebands as well as for photosyntheticallyavailable radiation (PAR, 400–700 nm): Kd(490)ranged from 0.03 to 0.26 m™1; Kd(550) from0.04 to 0.17 m™1; Kd(683) from 0.04 to0.17 m™1; and Kd(PAR) varied from 0.02 to0.25 m™1. Kd(λ) for wavelengths centred at412 nm, 443 nm, 465 nm, 490 nm, 510 nm, 520 nm and550 nm were significantly correlated with chlorophyllconcentration (ranging from 0.1 to 6 mg m™3). Thevertical attenuation coefficients for 340 nm and380 nm ranged from 0.10 to 0.69 m™1 and from 0.05to 0.34 m™1, respectively, and were also highlycorrelated with chlorophyll concentrations. These Kd values indicate that the 1% penetration depthmay reach maxima of 46 m and 92 m for 340 nm and380 nm, respectively. The spectral radiancereflectances (Rr(λ)) for 443 nm, 510 nm and 550 nmwere less than 0.01 sr™1. Rr(λ) for 665 nm and683 nm increased with depth up to 0.2 sr™1 because ofchlorophyll fluorescence. Using a model that predicts downwardirradiances by taking into account the attenuation bywater and absorption by chlorophyll, we show thatchlorophyll fluorescence has a significant influenceon the red downward irradiance (Ed (633, 665, 683))in deeper layers. The ability of the phytoplanktonpopulation to influence the light environment byautofluorescence and absorption processes depends onthe light conditions and on the photoacclimation ofthe cells, represented by the in vivo crosssection absorption coefficient of chlorophyll (a*). Theobtained mean chlorophyll-specific light attenuationcoefficients of phytoplankton in situ (kd) are higherthan the in vivo absorption coefficient of chlorophyll,more than to be excepted from the scattering. a*(λ), m2 mg chl™1, decreased due topackaging effect with increasing chlorophyllconcentrations.

Ultraviolet solar radiation at Valdivia, Chile (39.8°S)

Daily and annual cycles of solar ultraviolet radiation were characterised at Valdivia, Chile (39.8°S), using data collected with a multichannel radiometer between January 1995 and March 1999. First, the instruments measurements at 305 and 340 nm were analysed. In a second step, erythemal dose rates and daily doses were calculated from the measured data and their daily and seasonal variation was evaluated. In January, hourly mean irradiance at noon reaches 7.4 and 64 μW cm−2 nm−1 for 305 and 340 nm, respectively; corresponding values for July are 0.3 and 20 μW cm−2 nm−1. Erythemal daily doses vary from 300 to 6000 J m−2 between July and January. Episodes with high radiation are classified in duration and accumulated dose. A single event with very low total ozone and corresponding high UV levels is presented. Images from the Total Ozone Mapping Spectrometer (TOMS) are used to show its evolution. Variations in total ozone, measured from space, and cloud changes, inferred from observed UV-A radiation, explain 77% of the daily changes in UV-B.

Multichannel radiometer calibration: a new approach.

The error in irradiance measured with Sun-calibrated multichannel radiometers may be large when the solar zenith angle (SZA) increases. This could be particularly detrimental in radiometers installed at mid and high latitudes, where SZAs at noon are larger than 50 degrees during part of the year. When a multiregressive methodology, including the total ozone column and SZA, was applied in the calculation of the calibration constant, an important improvement was observed. By combining two different equations, an improvement was obtained at almost all the SZAs in the calibration. An independent test that compared the irradiance of a multichannel instrument and a spectroradiometer installed in Ushuaia, Argentina, was used to confirm the results.

The role of phytoplankton in determining the underwater light climate in Lake Constance

At all seasons, the underwater light field of meso-eutrophic large (480 km2) deep (mean: 100 m) Lake Constance was studied in conjunction with the assessments of vertical distributions of phytoplankton chlorophyll concentrations. Vertical profiles of scalar, downwelling and upwelling fluxes of photosynthetically available radiation, as well as fluxes of spectral irradiance between 400 and 700 nm wavelength were measured.The overall transparency of the water for PAR is highly dependent on chlorophyll concentration. However, the spectral composition of underwater light is narrowing with water depth regardless of phytoplankton biomass.Green light is transmitted best, even at extremely low chlorophyll concentrations. This is explained by the selective absorption of blue light by dissolved organic substances and red light by the water molecules. Nevertheless, significant correlations were found between vertical attenuation coefficients of downwelling spectral irradiance and chlorophyll concentrations at all wavelengths. The slopes of the regression lines were used as estimates of chlorophyll-specific spectral vertical light attenuation coefficients (Kc(λ)).The proportions of total upwelling relative to total downwelling irradiance (reflectance) increased with water depth, even when phytoplankton were homogeneously distributed over the water column. Under such conditions, reflectance of monochromatic light remained constant. Lower reflectance of PAR in shallow water is explained by smaller bandwidths of upwelling relative to downwelling light near the water surface. In deeper water, by contrast, the spectra of both upwelling and downwelling irradiance are narrowed to the most penetrating components in the green spectral range. Reflectance of PAR was significantly correlated with chlorophyll concentration and varied from ∼ 1% and ∼1-% at low and high phytoplankton biomass, respectively. Over the spectrum, reflectance exhibited a maximum in the green range. Moreover, in deeper layers, a red maximum was observed which is attributed to natural fluorescence by phytoplankton chlorophyll.

Calibration improvement of the IAI Network for the measurement of UVR: multichannel instruments

The IAI Network for the measurement of ultraviolet radiation in Chile, Argentina and Puerto Rico is composed of ten multi-channel radiometers (GUV 511, Bisopherical Instruments Inc.), which are periodically sun calibrated with a traveling reference GUV (RGUV). The RGUV is calibrated under solar light against a SUV100 spectroradiometer. This calibration is then transferred to each instrument in the network through the RGUV. A previous multi-regression model proved to be suitable to derive narrowband irradiance from broadband irradiance, ozone column and solar zenith angles (SZA). A recent modification of the existing multi-regression model improved the multi-channel instrument sun calibration against spectroradiometers. In this approach, the narrowband irradiance is the SUV spectral irradiance and the broadband is the multi-channel GUV irradiance. We included the azimuth angle as a parameter into the multi-regression equation and we applied a non-linear function, instead of a single coefficient, to correct for SZA. In this paper, the new multi-regression approach is applied to both steps of a GUV calibration: SUV - RGUV and RGUV - GUV and the results are compared with traditional calibration methods. Important improvements are observed in the calibration, in particular for SZA larger than 50°.