The concentrations of phytoplankton pigments in suspended and settling particles were measured in Trout Lake, Wisconsin, U.S.A., during the 1993 ice-free season. A decrease in water column concentrations of chlorophyll a coincident with an increase in pheophorbide and pheophytin concentrations occurred during a "clear-water" phase in June. The lack of a corresponding decrease in carotenoid pigment concentrations indicated that carotenoid pigments were degraded to a lesser extent than chlorophyll a during this period of heavy grazing pressure. Chlorophyll a, pheophorbide, and pheophytin showed temporal trends in fluxes to sediment traps that were similar for all pigments but did not correspond to trends in water column pigment concentration. Fucoxanthin concentrations and microscopic examination indicated that the sedimentation of large, dense diatoms increased the sedimentation rate of chlorophyll during the clear-water phase. In addition, ungrazed diatoms apparently were the main source of pheophorbide in trap material during the clear-water phase, indicating that pheophorbide should not be used as a surrogate for fecal pellet sedimentation in lakes influenced by the sedimentation of large diatoms.

4994. A 6-yr record of nutrient element sedimentation and recycling in three north temperate lakes. Can. j. Fish. Aquat. Sci. 51: 2457-2466. Sedimentation of C, N, and P from the water column was assessed during the ice-free seasons of 1986-91 in three northern Wisconsin lakes. Seasonal trends in mass sedimentation were different among lakes but consistent from year to year within each lake. High rates of nutrient sedimentation were associated with spring and fall blooms of large siliceous algae. Nutrient recycling, calculated as the difference between uptake during photosynthesis and loss to sedimentation, showed seasonal trends that were related to sedimentation. Recycling within the water column was the most important source of nutrients to primary producers, accounting for 85-90% of P demand during the summer stratified period.La sedimentation du C, du N et du P dans la colonne d'eau a 6te evalu6e durant la saison sans glace dans trois lacs du nord dee Wisconsin de 4986 2 1991. Les tendances saisonnikres de la sedimentation etaient differentes dans chacun lac, mais elles etaient constantes d'une annee 2 I'autre dans chacun des lacs. Les taux eleves de skdimentation des nutriments ktaient lies a I'efflorescence printani&re et automnale des grandes algues siliceuses. Le recyclage des nutriments, calcule comme la difference entre la captation effectuee pendant la photssynthibse et la perte due A la sedimentation, a montr4 des tendances saisonnieres qui etaient likes 2 la sedimentation. Le recyclage dans la colonne d'eau constituait la plus impartante source de nutriments poker les producteurs primaires et comptait pour 85-98% de la demande en P durant la pkriode de stratification estivale.

Aulacoseira ambigua abundance and filament length were measured weekly during spring and autumn bloom periods in Trout Lake, Wisconsin, USA. In addition, several chemical and biological variables thought to influence A. ambigua growth were assessed. Results of the field-based observations were complimented with controlled laboratory experiments to evaluate the effects of phosphorus availability on A. ambigua growth. Relative to the autumn bloom period, A. ambigua colonies were generally larger and more abundant in spring prior to the termination of the bloom in June. Chlorophyll-a concentrations indicated that other phytoplankton were also more abundant during the spring bloom. Batch culture experiments indicated that increased phosphorus availability during the spring bloom contributed to the seasonal increase in A. ambigua filament length and abundance. Increase in A. ambigua filament length in response to increased phosphorus availability is discussed as a mechanism that may increase nutrient removal through sedimentation and subsequently decrease the efficiency of nutrient regeneration in higher productivity lakes.

To evaluate the effect of particle size and composition on seasonal changes in the sedimentation rate, suspended and sedimenting particles were collected from Trout Lake, Wisconsin, USA during the 2002 ice-free season. Particles were characterized with regard to particulate biogenic silicon (PBSi) concentration and distribution between four size classes. The concentration of particulate chlorophyll and chlorophyll degradation products was also measured in water column particles and sediment trap material collected during the first half of the sampling period. The highest rates of mass sedimentation during the stratified period were measured in spring and early summer. Seasonal increases in sedimentation are related to the presence of large colonial diatoms in the water column as indicated by elevated PBSi concentrations. The majority of particulate matter in the water column was found in the smallest (<20 lm) size fraction while most of the mass of sediment trap material was in larger size fractions (>20 lm). Smaller cells appear to carry out most of the photosynthesis in Trout Lake but larger cells are responsible for seasonal trends in sedimentation. These results may explain how pelagic photosynthesis and sedimentation rates can be quantitatively decoupled across a range of trophic conditions but appear correlated when based on mid-summer measurements.

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The abundance of Aulacoseira granulata (Ehrenburg) Simonsen and Gloeocystis planctonica (West & G.S.West) Lemmermann was assessed during the summers of 2005 and 2010 in the eutrophic Fox River, Wisconsin, USA. In both years, a mid-summer bloom of G. planctonica was followed by the rapid growth of A. granulata. Laboratory experiments in which A. granulata was grown in cell-free filtrate of a G. planctonica culture revealed that the growth of A. granulata was stimulated in the G. planctonica-treated medium relative to controls. This effect was detected when dormant A. granulata cells were used as the source culture for the experiment but not when actively growing cells were used. Dormant A. granulata also grew more rapidly in river water collected after the 2010 G. planctonica bloom relative to river water collected before the bloom. These results suggest that the summer bloom of A. granulata in the river was stimulated by G. planctonica. This relationship can be described as stimulated rejuvenation, an interaction where the transition of an algal resting stage into active growth is triggered by exposure to another species.

The formation of seleniferous ephemeral pools that result from shal. low water table rise through seleniferous soils was studied in laboratory columns of soils from Kesterson Reservoir, Merced County, California. Variables included in the column experiments included the depth interval of the soils, the rate of shallow water table rise and temperature. The columns were packed with either surface (0-0.15 m) soils (with and without the original salt crust), or subsurface soils (0.15-0.30 m) sampled from the southwest corner of Pond 1, Kesterson Reservoir. Controlled inputs of nonseleniferous, saline water through the bottoms of the columns provided water table rise rates of 3, 10 and 30 mm d-lo The soil columns were maintained at either room temperature (~-25°C) or 5°C. The amount of Se transported from the soils into the overlying ponding waters was proportional to the water. extractable soil Se content, and was positively correlated with the rate of water table rise. The 5°C experiments resulted in greater Se trans. fers into the ponding waters in the columns subjected to 10 and 30 mm d -t rates of water table rise (relative to comparable room tempernture columns), while the reverse effect was observed with 3 mm d -1 columns.