Range exelosures located throughout Utah in cool desert shrub communities were analyzed tu determine, (1) the response of cryptogamic crusts tu grazing, (2) soil variables that influence the development of cryptogamic crusts and (3) the time needed fur reestablishment of cryptogamic communities after disturbance. The amount of lichen, muss and algal cuwr was found tu be considerably reduced by domestic grazing. Sites with moderate to high as opposed to light cryptognmic cuver were characterized by significantly heavier textured soils and greater salinity. Cryptognmic cwer increased from 4% to 15% during the tirst 14-18 years of exclusion from grazing, but increased only 1% during the next 20 years. Reestablishment of a cryptogsmic crust uccurs in at least 14-18 years and possibly sooner. Until recently little attention has been given the soil stabilizing role of nonvascular plants (cryptogams). Studies in the semidesert regions of Utah in the past decade have made it increasingly clear that such plants (particularly lichens, musses and algae) exert a significant impact on soil stability and rates of water infiltration (Anderson et al.

We investigated major physical-chemical characteristics and benthic algae of different alpine lotic systems comprising streams and lake outlets of rhithral and kryal origin over an annual cycle. We also evaluated the structure of the algal communities and its relation to environmental characteristics for the different stream types. Algal communities were generally dominated by diatoms, Cyanophyta, and Hydrurus foetidus (Chrysophyceae). Community structure was similar among alpine streams and lake outlets, but more algal taxa occurred in lake outlets (rhithral and kryal) than in kryal streams. Although algae were identified mainly to genera, distinct patterns in community structure were evident. A major environmental determinant of the algal community among stream types was the presence of a glacier and resulting seasonal differences in flow, temperature, and turbidity. An upstream lake was a secondary determinant in buffering seasonal fluctuations in environmental conditions thus leading to greater stability. Algal communities, consequently, were more diverse and less seasonally variable at lake outlets. The diatom genera Amphora, Denticula, Fragilaria, Gomphonema, Nitzschia, and Synedra and the blue-green algae Oscillatoria and Phormidium were characteristic. of lake outlets, whereas Chamaesiphon (blue-green) and Hydrurus foetidus were indicative of kryal sites.

A field experiment was conducted to determine the effect of disturbance frequency on diatom communities established on artificial substrates within an open canopy site and a closed canopy site of a 3rd order stream. The open canopy site (OCS) had a total of 80 diatom taxa colonizing the substrates, while the closed canopy site (CCS) had only 55 taxa. Cluster analysis revealed that the two sites had distinct diatom communities, although the most common species were similar between sites. There was no effect of disturbance frequency

The effect of nutrient regime on periphyton community development in large rivers was examined (sites ranged from oligotrophic to eutrophic). Patterns in diatom community structure were examined at a large spatial scale (ultimate), whereas at the microhabitat scale (proximate), artificial nutrient-diffusing substrata were used to examine periphyton response to amendment with nitrogen, phosphorus, and N + P. Ratios of ambient dissolved inorganic nitrogen to total phosphorus were used to make predictions of nutrient limitation (molar total inorganic nitrogen (TIN) : total phosphorus (TP)), which matched experimental results in 8 of 12 sites. Two sites with highest ambient nutrient levels (mean NO3 + NO2 and TP, 1.49 and 0.081 mg·L–1, respectively) possessed the highest diatom richness and diversity (mean richness = 42). Lowest diatom taxa richness (19) occurred in an impounded system with low TP (0.008 mg·L–1). Principal components analysis (PCA) of diatom taxa structure among sites (control treatments only) and small-scale patterns among nutrient treatments using all sites and treatments combined indicated that sites were grouped according to drainage basin (r2 = 0.79) and that there was no unified response to enrichment (r2 = 0.43). Results suggest that large spatial scale factors are more important in determining the potential benthic diatom assemblage than small-scale, proximate variables provided by the diffusers.

We investigated major physical-chemical characteristics and benthic algae of different alpine lotic systems comprising streams and lake outlets of rhithral and kryal origin over an annual cycle. We also evaluated the structure of the algal communities and its relation to environmental characteristics for the different stream types. Algal communities were generally dominated by diatoms, Cyanophyta, and Hydrurus foetidus (Chrysophyceae). Community structure was similar among alpine streams and lake outlets, but more algal taxa occurred in lake outlets (rhithral and kryal) than in kryal streams. Although algae were identified mainly to genera, distinct patterns in community structure were evident. A major environmental determinant of the algal community among stream types was the presence of a glacier and resulting seasonal differences in flow, temperature, and turbidity. An upstream lake was a secondary determinant in buffering seasonal fluctuations in environmental conditions thus leading to greater stability. Algal communities, consequently, were more diverse and less seasonally variable at lake outlets. The diatom genera Amphora, Denticula, Fragilaria, Gomphonema, Nitzschia, and Synedra and the blue-green algae Oscillatoria and Phormidium were characteristic of lake outlets, whereas Chamaesiphon (blue-green) and Hydrurus foetidus were indicative of kryal sites.